Modern Printed Circuits: Advanced Assembly

MARCH ‘14

Kevin RyanPresident of

Advanced Assembly

Isola’s New PCB Substrate

Circuit Design:4 Tips from the Experts

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Modern Printed Circuits CONTENTS

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FIRST-TIME-RIGHT CIRCUIT BOARD DESIGN:4 Tips From the ExpertsWritten by: Aaron Schellenberg

At Nuvation we’re known for our impressive track record of first-time-right designs and our ability to dramatically accelerate development schedules. Just recently we completed a High-density Interconnect (HDI) PCB design based on a Xilinx Virtex-7 FPGA with numerous 933MHz DDR3 memory buses, multiple PCI Express Gen 3 endpoints, and FDR Infiniband (56Gbit) off-board links, all on a (slightly modified) PCI Express card form factor. We delivered the board to the client on budget, 100% functional, and with no ‘blue wires’.

Aaron Schellenberg is a Senior Hardware Engineer at Nuvation Engineering, an engineering design services firm specializing in new product development.

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"We are very fortunate to have the equipment necessary to produce the high quality our customers expect."

customer desperately needed it to ship the next day. Three of our machine operators voluntarily worked over night to get the order out early the next morning.

The last thing I’d like to mention about our culture, which is really important, is that the people enjoy working here and have fun. While we are very serious about what we do, we don’t take ourselves too seriously, and that leads to a good environment. We do the typical summer picnics and just recently had a big year-end bash with dinner, dancing, playing sports and video games. We take our work dead serious, but I think it is important to laugh with each other for a little bit and have fun.

What excites you the most about the future of Advanced Assembly?It is still about the continuous improvement aspect. Not only do we want to meet the customers’ needs and expectations, we actually want to blow them out of the water. That may not necessarily occur one hundred percent of the time now, but that’s what we want in the future, and that’s what we work for. To be in a company this size, literally having a hundred other people you are growing with, it’s just a great feeling.

Customers and buyers who are relatively new to the printed circuit board (PCB) industry may be confused as to how a particular project is priced by the fabricator. In this article series, we’ll begin to demystify the factors used by fabricators to calculate price, empowering you to better plan and price your next PCB project.

KEY COST DRIVING FACTORSWhen Quoting Printed Circuit Boards[Part 1] By Peter Brissette, Bay Area Circuits

The cost-driving factors in the manufacturing industry as a whole

all have some similarities, including the need for a facility, equipment overhead, and labor and raw material costs. In addition to these basic requirements, manufacturing a printed circuit board also utilizes chemical processes and waste water treatment systems, which require special (and expensive) approvals, permits, and zoning. Although every manufacturing industry has raw material costs, the raw materials used in the printed circuit board fabrication process can be very expensive (examples include copper, gold, lead, nickel, silver, fiberglass, epoxy resin, and a variety of chemicals).

Manufacturing overhead aside, when a fabricator sets out to calculate the cost of a printed circuit board, there are both primary (board size, quantity, layer count, lead time, etc.) and secondary (tooling, finish type, drill type, lamination process, etc.) cost considerations. In this article, we’ll tackle the primary cost considerations.

BOARD SIZE The size of the PCB is the first cost factor. Often referred to as the “real estate” of the board, the larger the board the more real estate required to manufacture it. One complicating factor is, depending on the dimensions, you may have a board that takes up less real estate but is actually higher in cost. The reason for this relates to the overall size of the panel used to manufacture the PCB. One dimension may fit the production panel better than the other. An example of this would be two parts with the exact same total square inches per board. The first is 2” x 6” and the second is 3” x 4”. On a standard production panel we can fit more of the 3” x 4” sized PCB on the panel and therefore the per-board cost would be lower.

QUANTITY Quantity is important because many manufacturers will have a minimum cost for an order. For instance, you may only need 10 pieces but the minimum order cost would include 20 pieces. As the quantity increases, the per-board cost will go down until you reach the minimum manufacturing cost.

One benefit we provide our customers is by giving a higher quantity discount but delivering smaller quantities over time. For example, you could order at the 500-piece price and have 100 pieces delivered each month at the lower price.

“Often referred to as the “real estate” of the board, the larger the board the more real estate required to manufacture it.”

FEATURED ARTICLEA Look at Isola’s Breakthrough PCB Laminate

TECH ARTICLEFirst-time-right Circuit Design:4 Tips from the Experts

COVER INTERVIEWKevin Ryan President of Advanced Assembly

TECH ARTICLEKey Cost Factors When Quoting PCBs

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Modern Printed Circuits

ISOLA’S BREAKTHROUGH LAMINATEOFFERS LOW INSERTION LOSS FOR HIGH-SPEED DIGITAL DESIGNS

The need for laminate materials that can enable higher data rates is a distinct technology trend in the electronics industry. Electronics Manufacturing Services (EMS) providers, contract manufacturers, PCB fabrication houses, and Original Equipment Manufacturers (OEMs) alike have sought the most suitable, yet cost-effective PCB material possible to adequately deal with those rapidly growing high-speed applications.

Up to now, Polytetrafluoroethylene (PTFE), or better known by the generic name Teflon, has been the material used for ultra high-speed PCBs. But in some circles, it is not regarded as the ideal material for multilayer PCBs due to its high costs, high coefficient of thermal expansion (CTE) and processing difficulties at the fabricators. Therefore, the use is relegated to low layer count and/or hybrid designs.

To address this issue, Isola Group S.à r.l. of Chandler, AZ has come to market with its Tachyon™ brand of PCB laminates and prepregs aimed at resolving the cost, performance, and processing issues PTFE-based materials pose. They are targeted at high-layer count backplanes for the 100 Gbps market with channel data rates in excess of 25 Gbps. Currently in an alpha test stage, the product is said to produce very low dielectric constant (Dk) and insertion loss, as well as a low dissipation factor (Df) of 0.0021. Tachyon has a very comprehensive offering of laminates and prepregs. See table # 1 and # 2 for the laminate and prepreg offerings along with the dieclectric constants (Dks) and dissipation factors (Dfs).

“The absence of the fiberglass allows PTFE based laminates to have very good electrical properties.”

THE PROBLEM:

Most PTFE-based laminates are film based and are not structurally reinforced with woven fiberglass. The absence of the fiberglass allows PTFE based laminates to have very good electrical properties.

However, there’s a consequence to this. The PTFE suppliers use ceramic fillers to reduce the CTE and to make the PTFE substrates more process friendly. Ceramic filled PTFE-based substrates still possess a relatively high coefficient of thermal expansion or CTE values in the X, Y and Z axes. See table #3 for a comparison of CTEs, Dks and DFs on Tachyon, ceramic filled PTFE and FR4 laminates.

As a result, there are dimensional stability issues with excessive and inconsistent movement that affect registration in the X/Y direction. The excessive movement in the Z axis (thickness direction) also has an adverse effect on plated through-hole (PTH) reliability. A majority of OEMs are moving toward even greater board layers and demanding higher reliability for their sub-assemblies. That means CTE is of special interest

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ISOLA’S BREAKTHROUGH LAMINATEOFFERS LOW INSERTION LOSS FOR HIGH-SPEED DIGITAL DESIGNS

The need for laminate materials that can enable higher data rates is a distinct technology trend in the electronics industry. Electronics Manufacturing Services (EMS) providers, contract manufacturers, PCB fabrication houses, and Original Equipment Manufacturers (OEMs) alike have sought the most suitable, yet cost-effective PCB material possible to adequately deal with those rapidly growing high-speed applications.

Up to now, Polytetrafluoroethylene (PTFE), or better known by the generic name Teflon, has been the material used for ultra high-speed PCBs. But in some circles, it is not regarded as the ideal material for multilayer PCBs due to its high costs, high coefficient of thermal expansion (CTE) and processing difficulties at the fabricators. Therefore, the use is relegated to low layer count and/or hybrid designs.

To address this issue, Isola Group S.à r.l. of Chandler, AZ has come to market with its Tachyon™ brand of PCB laminates and prepregs aimed at resolving the cost, performance, and processing issues PTFE-based materials pose. They are targeted at high-layer count backplanes for the 100 Gbps market with channel data rates in excess of 25 Gbps. Currently in an alpha test stage, the product is said to produce very low dielectric constant (Dk) and insertion loss, as well as a low dissipation factor (Df) of 0.0021. Tachyon has a very comprehensive offering of laminates and prepregs. See table # 1 and # 2 for the laminate and prepreg offerings along with the dieclectric constants (Dks) and dissipation factors (Dfs).

“The absence of the fiberglass allows PTFE based laminates to have very good electrical properties.”

THE PROBLEM:

Most PTFE-based laminates are film based and are not structurally reinforced with woven fiberglass. The absence of the fiberglass allows PTFE based laminates to have very good electrical properties.

However, there’s a consequence to this. The PTFE suppliers use ceramic fillers to reduce the CTE and to make the PTFE substrates more process friendly. Ceramic filled PTFE-based substrates still possess a relatively high coefficient of thermal expansion or CTE values in the X, Y and Z axes. See table #3 for a comparison of CTEs, Dks and DFs on Tachyon, ceramic filled PTFE and FR4 laminates.

As a result, there are dimensional stability issues with excessive and inconsistent movement that affect registration in the X/Y direction. The excessive movement in the Z axis (thickness direction) also has an adverse effect on plated through-hole (PTH) reliability. A majority of OEMs are moving toward even greater board layers and demanding higher reliability for their sub-assemblies. That means CTE is of special interest

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in their multilayer designs that require better registration because of smaller pitches and pad sizes and that rely on plated through-holes to create connections between the different PCB layers.

As another downside, PTFEs filled with ceramic fillers are more difficult to drill. Those materials are abrasive to drill bits. Instead of achieving a thousand hits from one run on drills bits, the fab house may only get 500. Drill bits are one of the most expensive items at fab houses. Finally, PTFE material is expensive with a high cost of ownership. For example, OEMs want to save cost when running a hybrid process. This means saving cost by putting high-cost material where needed—for instance, in a PTFE core—and then use a low cost prepreg. This arrangement works since some low-cost prepregs cure at 60 minutes at 360oF. But if that process is performed vice versa, using the PTFE as the prepreg, then it may have to be cured at 400oF to 500oF. The result is the other part of the hybrid is burned up. Fred Hickman, Senior Director of High-Speed Digital Products for Isola Group S.à r.l., told EEWeb that, “At this point in time, there are no suitable solutions for resolving the 100 gigabit per second (Gbps) needs when using standard PCB practices. I would say that PTFE and some of these other products are not considered standard.”

LOW DK AND REDUCED INSERTION LOSS:

“Compared to PTFE, our new product is about 30 to 40 percent lower cost, which is a significant amount,” Hickman told EEWeb. “It’s also worth mentioning that Tachyon uses current equipment and processes to produce a product that’s viable for 100 Gbps applications.”

Isola selects the right raw material upfront, allowing the lowest loss and most consistent Dk. This is achieved with spread glass, low profile coppers, and resins with properties that help get them to those end points. That formula yields a Dk of 3.02, which according to Hickman is lower than most other high-speed products on the market. “That lower Dk allows the fabricator to run wider lines,” Hickman said. “The wider the lines, the less loss you are going to lose as well. Also, spread glass has the benefit of mitigating

skew. For instance, if you have two traces running side by side, the ideal result is to have the signals from one end arrive to the other end at the same time. But if the trace travels through the resin more than the glass, it will get there faster because resin has a lower Dk.”

The Dks and Dfs are two major parameters affecting PCB circuits’ performance and must be consistent across a wide temperature range. The Dk of 3.02 and Df of 0.0021 Hickman cites for this new product is said to be stable between -40°C and +140°C all the way up to 40 GHz. See graphs # 1 & # 2 for the temperature coefficient of the Dk and Df of Tachyon from -40 - 140˚C. For comparative purposes, high performance PCB material currently available on the market demonstrates a Dk ranging from 4.2 to 3.48 up to 10GHz. Dk provides the fabricator a measure in two ways. First, it is a measure of the effect insulating material has on a conductor’s surrounding capacitance. Second, Dk is a measure showing how much an electromagnetic wave slows down as it moves through insulating material. In the world of physics, when the relative Dk parameter is high, a signal travels slower on a wire. In most instances, lower Dks get the fabricator’s nod

Hickman noted that Tachyon uses the same cycle used to laminate the more conventional and widely used FR4 PCB material as well as the same cycle to desmear FR4. These can translate into significant processing savings. He explained that desmear is when “the fabricator’s drill gets overly heated during via formation and leaves residues on the pads.” The objective of desmearing is to remove those residues. This can be a very serious issue on PTFE built boards since plasma or a sodium etch is required to remove smear due to the high melting temperature of the PTFE. See table# 4 for a comparison of key processing parameters of Tachyon to other material options. As for low insertion loss, which is measured in decibels per inch (dB/inch), graph # 3 demonstrates these levels for the new Isola products based on the IPC standard/Intel’s low loss specification of 0.48 dB/inch at 4 GHz. Hickman explained that with a 3.5-mil trace width—well below the 0.4 standard—insertion

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in their multilayer designs that require better registration because of smaller pitches and pad sizes and that rely on plated through-holes to create connections between the different PCB layers.

As another downside, PTFEs filled with ceramic fillers are more difficult to drill. Those materials are abrasive to drill bits. Instead of achieving a thousand hits from one run on drills bits, the fab house may only get 500. Drill bits are one of the most expensive items at fab houses. Finally, PTFE material is expensive with a high cost of ownership. For example, OEMs want to save cost when running a hybrid process. This means saving cost by putting high-cost material where needed—for instance, in a PTFE core—and then use a low cost prepreg. This arrangement works since some low-cost prepregs cure at 60 minutes at 360oF. But if that process is performed vice versa, using the PTFE as the prepreg, then it may have to be cured at 400oF to 500oF. The result is the other part of the hybrid is burned up. Fred Hickman, Senior Director of High-Speed Digital Products for Isola Group S.à r.l., told EEWeb that, “At this point in time, there are no suitable solutions for resolving the 100 gigabit per second (Gbps) needs when using standard PCB practices. I would say that PTFE and some of these other products are not considered standard.”

LOW DK AND REDUCED INSERTION LOSS:

“Compared to PTFE, our new product is about 30 to 40 percent lower cost, which is a significant amount,” Hickman told EEWeb. “It’s also worth mentioning that Tachyon uses current equipment and processes to produce a product that’s viable for 100 Gbps applications.”

Isola selects the right raw material upfront, allowing the lowest loss and most consistent Dk. This is achieved with spread glass, low profile coppers, and resins with properties that help get them to those end points. That formula yields a Dk of 3.02, which according to Hickman is lower than most other high-speed products on the market. “That lower Dk allows the fabricator to run wider lines,” Hickman said. “The wider the lines, the less loss you are going to lose as well. Also, spread glass has the benefit of mitigating

skew. For instance, if you have two traces running side by side, the ideal result is to have the signals from one end arrive to the other end at the same time. But if the trace travels through the resin more than the glass, it will get there faster because resin has a lower Dk.”

The Dks and Dfs are two major parameters affecting PCB circuits’ performance and must be consistent across a wide temperature range. The Dk of 3.02 and Df of 0.0021 Hickman cites for this new product is said to be stable between -40°C and +140°C all the way up to 40 GHz. See graphs # 1 & # 2 for the temperature coefficient of the Dk and Df of Tachyon from -40 - 140˚C. For comparative purposes, high performance PCB material currently available on the market demonstrates a Dk ranging from 4.2 to 3.48 up to 10GHz. Dk provides the fabricator a measure in two ways. First, it is a measure of the effect insulating material has on a conductor’s surrounding capacitance. Second, Dk is a measure showing how much an electromagnetic wave slows down as it moves through insulating material. In the world of physics, when the relative Dk parameter is high, a signal travels slower on a wire. In most instances, lower Dks get the fabricator’s nod

Hickman noted that Tachyon uses the same cycle used to laminate the more conventional and widely used FR4 PCB material as well as the same cycle to desmear FR4. These can translate into significant processing savings. He explained that desmear is when “the fabricator’s drill gets overly heated during via formation and leaves residues on the pads.” The objective of desmearing is to remove those residues. This can be a very serious issue on PTFE built boards since plasma or a sodium etch is required to remove smear due to the high melting temperature of the PTFE. See table# 4 for a comparison of key processing parameters of Tachyon to other material options. As for low insertion loss, which is measured in decibels per inch (dB/inch), graph # 3 demonstrates these levels for the new Isola products based on the IPC standard/Intel’s low loss specification of 0.48 dB/inch at 4 GHz. Hickman explained that with a 3.5-mil trace width—well below the 0.4 standard—insertion

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loss is 0.40 at 4 GHz. He added that the 3.5 mil line is thinner than those currently used by PCB designers. However, with a thicker trace width of 5 mils, insertion loss is at 0.32 dB/inch at 4 GHz, 0.48 dB/inch at 8 GHz and 0.62 dB/inch at 12.5 GHz. With a 7-mil trace width, insertion loss is 0.28 dB/inch at 4 GHz. “The product gets more lossy as the frequency gets higher,” Hickman said. Isola has also used a 16 layer TV designed by Lee Ritchey of Speeding Edge to run compare insertlion loss, skew, extracted Dk and Df on a number of materials. The results on Tachyon clearly show that it is an enablber for 100GE applications (See graph # 4).Tachyon only has 0.795 db/in insertion loss on an 8” line. Megtron 6, the current non PTFE product has an insertion loss of 1.016 dB/in. at the same frequency which is 37% higher. “For fabricators using PTFE or hydrocarbon ceramic-filled or products, I’d recommend replacing them products with low loss like Tachyon or Astra MT laminates, which are suited for RF/microwave and HSD PCB designs,” he explained. Astra MT features a Dk of 3.0 that is stable between -40°C and +140°C at up to 20 GHz. It also provides fabricators with a lower dissipation factor (Df) of 0.0017, making it a cost-effective alternative to PTFE and other commercial microwave laminate materials.

FITTED WITH VLP2:

Very low profile copper with a 2μm surface roughness (VLP2) copper foil is a standard feature of the Tachyon product. In the past, fabricators called for copper roughness as a way to assure delamination did not occur during PCB assembly. To avoid delamination, copper surfaces are made sufficiently rough to make sure there is good adhesion between the resin in the prepreg and the copper associated with PCB planes and traces.

More recently, however, copper roughness has received even more attention because the roughness of copper on a trace and its adjacent plane can have a direct effect on overall signal path loss at high frequencies. Two places where copper roughness can affect this loss is during the manufacturing of the copper foils used to create the laminate and during PCB fabrication when inner layers are prepared for lamination.

Experts say the best way to manage and avoid this signal path loss is to maintain close coordination among material vendor, fabricator, and PCB design and assembly house. In particular, a stack-up drawing and comprehensive fabrication notes are critical for specifying the method the fabricator prepares inner PCB layers to minimize or avoid signal path loss.

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loss is 0.40 at 4 GHz. He added that the 3.5 mil line is thinner than those currently used by PCB designers. However, with a thicker trace width of 5 mils, insertion loss is at 0.32 dB/inch at 4 GHz, 0.48 dB/inch at 8 GHz and 0.62 dB/inch at 12.5 GHz. With a 7-mil trace width, insertion loss is 0.28 dB/inch at 4 GHz. “The product gets more lossy as the frequency gets higher,” Hickman said. Isola has also used a 16 layer TV designed by Lee Ritchey of Speeding Edge to run compare insertlion loss, skew, extracted Dk and Df on a number of materials. The results on Tachyon clearly show that it is an enablber for 100GE applications (See graph # 4).Tachyon only has 0.795 db/in insertion loss on an 8” line. Megtron 6, the current non PTFE product has an insertion loss of 1.016 dB/in. at the same frequency which is 37% higher. “For fabricators using PTFE or hydrocarbon ceramic-filled or products, I’d recommend replacing them products with low loss like Tachyon or Astra MT laminates, which are suited for RF/microwave and HSD PCB designs,” he explained. Astra MT features a Dk of 3.0 that is stable between -40°C and +140°C at up to 20 GHz. It also provides fabricators with a lower dissipation factor (Df) of 0.0017, making it a cost-effective alternative to PTFE and other commercial microwave laminate materials.

FITTED WITH VLP2:

Very low profile copper with a 2μm surface roughness (VLP2) copper foil is a standard feature of the Tachyon product. In the past, fabricators called for copper roughness as a way to assure delamination did not occur during PCB assembly. To avoid delamination, copper surfaces are made sufficiently rough to make sure there is good adhesion between the resin in the prepreg and the copper associated with PCB planes and traces.

More recently, however, copper roughness has received even more attention because the roughness of copper on a trace and its adjacent plane can have a direct effect on overall signal path loss at high frequencies. Two places where copper roughness can affect this loss is during the manufacturing of the copper foils used to create the laminate and during PCB fabrication when inner layers are prepared for lamination.

Experts say the best way to manage and avoid this signal path loss is to maintain close coordination among material vendor, fabricator, and PCB design and assembly house. In particular, a stack-up drawing and comprehensive fabrication notes are critical for specifying the method the fabricator prepares inner PCB layers to minimize or avoid signal path loss.

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GOING FORWARD:

Isola is now sampling its Tachyon product with multiple OEMs testing it out. The Tachyon laminate materials are available in laminate and prepreg forms in typical thickness and standard panel sizes. According to Isola, they provide a complete material solution for high-speed digital designs. To date, the product has been used to build a 24” x 36”, 36-layer backplane and a 16” x 18” 28-layer board, both 0.300” (7.6 mm) thick. The latter was built using a hybrid design using Isola’s 370 HR laminates

and prepregs in the centermost dielectrics. It has also been sampled on a # of SI and thermal TVs that allow the OEMs to compare how it performs relative to other materials tested.

According to Hickman, the closest competitor—while it’s able to meet the 40 Gbps range—cannot comply with subsequent 100 Gbps market needs. “As you go up to higher data rates, there are higher risks for data loss, as well. Some ceramic filled PTFE products can work, but then again, those are more expensive solutions.”

“Experts say the best way to manage and avoid this signal path loss is to maintain close coordination among material vendor, fabricator, and PCB design and assembly house.”

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A thorough space study should be adequate for a seasoned board designer to make a judgment call regarding the technical requirements of the PCB. Outputs from the space study may include:

An approximate placement of the major components and routing channels

The estimated layer count requirements for power and signal routing

A preliminary PCB stackup

The general layer assignments for the various buses and signal classes

The estimated trace lengths and worst-case layer transitions for any critical high-speed signals

A board-level power distribution and grounding strategy.

An estimate as to whether any advanced PCB fabrication technologies may be required, such as microvias, blind/buried vias, narrow traces, etc.

An approximate representation of where the component power dissipation occurs on the PCB

The space study is not just a simple mechanical drawing based on component package sizes; it is a preliminary layout exercise done in CAD software (such as Altium Designer, Cadence Allegro, or Mentor Expedition), in which all design aspects of the board are considered simultaneously. The emphasis here is that it must be done early in the design phase – often before schematic capture has started – in order to limit design iteration cycles.

PERFORM PRE-LAYOUT SIGNAL INTEGRITY ANALYSIS

The results of the space study will provide crucial input for getting started on pre-layout Signal Integrity (SI) analysis. One does not need to wait until the board routing is complete in order to perform SI analysis. With a preliminary stackup, layer assignments, and estimated trace lengths in hand, it is a good time to run pre-layout simulations using a 3D field solver to validate the selected components and the topologies of the high-speed signals. This is particularly important for routing to an FPGA with tight trace length or length matching

START WITH A SPACE STUDY

During the PCB space study, the engineer maps out how the critical components will fit into the available board area. Critical components include FPGAs or processors, power supplies, ICs, and anything with significant size or height. This is done early on in the design phase so that risks can be identified as soon as possible. Potential problems could lead to component substitutions, PCB form factor modifications, or even fundamental changes to the hardware architecture. The space study is not a final component placement, of course; it’s a tool to help identify potential layout issues before the design gets too far underway. Clearly, it is best to make any necessary design changes sooner rather than later.

requirements. Layout constraints can then be generated for routing the board based on the SI simulation results. This will help avoid numerous design iterations, as the post-layout SI simulations on the physical design should then only lead to minor design tweaks and refinements. By doing the space study early on in the development, the pre-layout SI analysis can take place in parallel with the detailed schematic work, which allows us to minimize the development schedule.

Board outline for a PCIe card

Sample PCB stackup

Noise and frequency measurements

THINK ABOUT LAYER COUNT

Often one of the most constraining design requirements in an HDI board is the overall PCB thickness. For example, consider the situation where we are designing a PCI Express Add-in card that needs to fit into a 1.57mm edge connector. This limits the layer count to at most 16 layers in many situations – and often less, depending on signal impedance requirements. Furthermore, HDI PCB designs tend to feature power-guzzling FPGAs and processors that require 1oz and 2oz copper planes to distribute the power around the board. These heavier copper weights will increase your plane thickness and make it even harder to stay within your desired board size. By considering your layer usage up front in your space study and assigning groups of signals to the layers in your stackup early on, you can help prevent a situation later in the design cycle where you are going to increasingly more exotic PCB fabrication techniques just to get your design to fit.

CONSIDER THERMAL MANAGEMENT

The space study, along with power dissipation estimates for the major components on your board, can provide the necessary input to perform a preliminary thermal analysis of your design using thermal modeling software. A mechanical engineer can work in parallel with the hardware engineer to ensure that there is adequate airflow across all areas of the board, with no blockage from components or board features. Appropriate heat sink sizing, forced airflow rates, and local component-level fan requirements can be determined early on so that an allowance can be made for these in the design, and you avoid the risk of your FPGA or main processors overheating. It is important to have a good idea as to how the board will behave thermally in its intended environment prior to starting the detailed layout.

In the field of electronic design there is no substitute for experience. Veteran design engineers will be able to assess the complexity of the design early on in the development phase and have an intuitive feel for how cleanly the board will route. As a junior engineer you can get a jumpstart on the learning process by familiarizing yourself with Design for Manufacturability guidelines and consulting an expert wherever you can.

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When it comes to HDI PCBs, particularly those with complex FPGA designs, every board is different. If you have a fixed PCB form factor (size, shape, and especially board thickness) there are many things you need to consider. Here are some techniques we use to avoid potential design iterations and costly PCB respins.

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A thorough space study should be adequate for a seasoned board designer to make a judgment call regarding the technical requirements of the PCB. Outputs from the space study may include:

An approximate placement of the major components and routing channels

The estimated layer count requirements for power and signal routing

A preliminary PCB stackup

The general layer assignments for the various buses and signal classes

The estimated trace lengths and worst-case layer transitions for any critical high-speed signals

A board-level power distribution and grounding strategy.

An estimate as to whether any advanced PCB fabrication technologies may be required, such as microvias, blind/buried vias, narrow traces, etc.

An approximate representation of where the component power dissipation occurs on the PCB

The space study is not just a simple mechanical drawing based on component package sizes; it is a preliminary layout exercise done in CAD software (such as Altium Designer, Cadence Allegro, or Mentor Expedition), in which all design aspects of the board are considered simultaneously. The emphasis here is that it must be done early in the design phase – often before schematic capture has started – in order to limit design iteration cycles.

PERFORM PRE-LAYOUT SIGNAL INTEGRITY ANALYSIS

The results of the space study will provide crucial input for getting started on pre-layout Signal Integrity (SI) analysis. One does not need to wait until the board routing is complete in order to perform SI analysis. With a preliminary stackup, layer assignments, and estimated trace lengths in hand, it is a good time to run pre-layout simulations using a 3D field solver to validate the selected components and the topologies of the high-speed signals. This is particularly important for routing to an FPGA with tight trace length or length matching

START WITH A SPACE STUDY

During the PCB space study, the engineer maps out how the critical components will fit into the available board area. Critical components include FPGAs or processors, power supplies, ICs, and anything with significant size or height. This is done early on in the design phase so that risks can be identified as soon as possible. Potential problems could lead to component substitutions, PCB form factor modifications, or even fundamental changes to the hardware architecture. The space study is not a final component placement, of course; it’s a tool to help identify potential layout issues before the design gets too far underway. Clearly, it is best to make any necessary design changes sooner rather than later.

requirements. Layout constraints can then be generated for routing the board based on the SI simulation results. This will help avoid numerous design iterations, as the post-layout SI simulations on the physical design should then only lead to minor design tweaks and refinements. By doing the space study early on in the development, the pre-layout SI analysis can take place in parallel with the detailed schematic work, which allows us to minimize the development schedule.

Board outline for a PCIe card

Sample PCB stackup

Noise and frequency measurements

THINK ABOUT LAYER COUNT

Often one of the most constraining design requirements in an HDI board is the overall PCB thickness. For example, consider the situation where we are designing a PCI Express Add-in card that needs to fit into a 1.57mm edge connector. This limits the layer count to at most 16 layers in many situations – and often less, depending on signal impedance requirements. Furthermore, HDI PCB designs tend to feature power-guzzling FPGAs and processors that require 1oz and 2oz copper planes to distribute the power around the board. These heavier copper weights will increase your plane thickness and make it even harder to stay within your desired board size. By considering your layer usage up front in your space study and assigning groups of signals to the layers in your stackup early on, you can help prevent a situation later in the design cycle where you are going to increasingly more exotic PCB fabrication techniques just to get your design to fit.

CONSIDER THERMAL MANAGEMENT

The space study, along with power dissipation estimates for the major components on your board, can provide the necessary input to perform a preliminary thermal analysis of your design using thermal modeling software. A mechanical engineer can work in parallel with the hardware engineer to ensure that there is adequate airflow across all areas of the board, with no blockage from components or board features. Appropriate heat sink sizing, forced airflow rates, and local component-level fan requirements can be determined early on so that an allowance can be made for these in the design, and you avoid the risk of your FPGA or main processors overheating. It is important to have a good idea as to how the board will behave thermally in its intended environment prior to starting the detailed layout.

In the field of electronic design there is no substitute for experience. Veteran design engineers will be able to assess the complexity of the design early on in the development phase and have an intuitive feel for how cleanly the board will route. As a junior engineer you can get a jumpstart on the learning process by familiarizing yourself with Design for Manufacturability guidelines and consulting an expert wherever you can.

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When it comes to HDI PCBs, particularly those with complex FPGA designs, every board is different. If you have a fixed PCB form factor (size, shape, and especially board thickness) there are many things you need to consider. Here are some techniques we use to avoid potential design iterations and costly PCB respins.

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INTERVIEW WITH KEVIN RYAN - PRESIDENT OF ADVANCED ASSEMBLY

Advanced Assembly is a PCB assembly house that specializes in low-volume, SMT assembly services. By using a proprietary software, Advanced Assembly is able to set-up its prototyping machines in minutes rather than days. The result is easy, fast, and high-quality prototyping that allows the engineer to focus on other aspects of the design.

EEWeb spoke with Kevin Ryan, President of Advanced Assembly, about the company’s focus on servicing the engineer, its proprietary prototyping software, and some of the biggest challenges facing the industry.

COVER INTERVIEW

19


INTERVIEW WITH KEVIN RYAN - PRESIDENT OF ADVANCED ASSEMBLY

Advanced Assembly is a PCB assembly house that specializes in low-volume, SMT assembly services. By using a proprietary software, Advanced Assembly is able to set-up its prototyping machines in minutes rather than days. The result is easy, fast, and high-quality prototyping that allows the engineer to focus on other aspects of the design.

EEWeb spoke with Kevin Ryan, President of Advanced Assembly, about the company’s focus on servicing the engineer, its proprietary prototyping software, and some of the biggest challenges facing the industry.

20


"At our core, we specialize in servicing engineers. The company was founded on the fact that design engineers get frustrated when they try to get their prototypes and low-volume orders assembled."

Can you tell us about the PCB Assembly services that you offer, specifically in your company?At Advanced Assembly, we do things faster. Other companies may boast about it, but we actually do it. We assemble high-quality boards at very low volumes in five days or less. We do this, in part, by using a proprietary software that allows us to program and set-up our machines in minutes rather than the days it typically takes many of our competitors. In this way, we’ve made it possible to deliver machine-placed SMT assembly services for just one or two boards at a time.

At our core, we specialize in servicing engineers. The company was founded on the fact that design engineers get frustrated when they try to get their prototypes and low-volume orders assembled.

How are your services unique in the marketplace given that there are a lot of PCB Assembly houses out there?We have evolved so much since our company was founded. Today, we can literally take a customer’s assembly projects from cradle to grave. We can assemble their prototypes and then move up from there. What is unique about our company is that we focus on assembly. We are not a shop that builds fabrication boards with assembly as an add-on service—we say what we do and do what we say.

The other thing that makes us unique in the marketplace is that 40% of our employees are in upfront services. Whether they are in the engineering staff, purchasing group, or client services, they are all there to set customers up for success. We really recognize that our customers—who are engineers mostly—put so much trust in us. Our customers come to us and they literally hand over the success of their projects to us.

What advice can you give hardware designers about PCB assembly?I am shocked at how many engineers tell me they are the ones in the lab building their boards, and how frustrated they get because they are not set up to do it right. What I always tell engineers is to focus on what you do best. Using our proprietary software, a design engineer sends us a design, and we put it through our design for assembly check; that’s not DFM, but DFA. Eighty percent of the jobs that have come to us have flaws in the design that could put the assembly process on hold. Our software engineering group finds these flaws, works with the customer to resolve them, and then we move the design forward. Right upfront, we’re adding value to the customer.

Another hassle we eliminate for customers is purchasing kits. Did you know it takes an average of 15 hours to find and order parts for a typical pcb assembly order? With our turnkey business, we order the parts and boards in addition to

handling the assembly. Our extensive partnerships with leading part and board suppliers allow us to select the right vendor for each order. This saves engineers a lot of time and delivers the best results. Again, I’d say let us do what we do best - we are experts at pcb assembly—so you have time to do what you do best.

How do you ensure the quality in your company operations, making sure that engineers trust you to do the job right?It’s all about continuous improvement. Globally, at Advanced Assembly, it starts with a serious commitment to quality at all levels and across all departments. It’s just an accepted fact here that quality has to be paramount. Our entire company, and specifically our cross functional quality team, is responsible for maintaining our high quality standards. The quality team meets weekly to discuss trends and opportunities for improvement. From its recommendations, QA initiatives are created and executed. Often the initiatives involve better training, process adjustments and bringing in equipment or technology that we do not currently have.

It’s also about scalable processes. When you grow a company from a couple of employees to around a hundred now, the processes have to scale. As you get larger, you really do have to hone in on scalable, repeatable processes, and that’s what our quality group does.

COVER INTERVIEW

21

"At our core, we specialize in servicing engineers. The company was founded on the fact that design engineers get frustrated when they try to get their prototypes and low-volume orders assembled."

Can you tell us about the PCB Assembly services that you offer, specifically in your company?At Advanced Assembly, we do things faster. Other companies may boast about it, but we actually do it. We assemble high-quality boards at very low volumes in five days or less. We do this, in part, by using a proprietary software that allows us to program and set-up our machines in minutes rather than the days it typically takes many of our competitors. In this way, we’ve made it possible to deliver machine-placed SMT assembly services for just one or two boards at a time.

At our core, we specialize in servicing engineers. The company was founded on the fact that design engineers get frustrated when they try to get their prototypes and low-volume orders assembled.

How are your services unique in the marketplace given that there are a lot of PCB Assembly houses out there?We have evolved so much since our company was founded. Today, we can literally take a customer’s assembly projects from cradle to grave. We can assemble their prototypes and then move up from there. What is unique about our company is that we focus on assembly. We are not a shop that builds fabrication boards with assembly as an add-on service—we say what we do and do what we say.

The other thing that makes us unique in the marketplace is that 40% of our employees are in upfront services. Whether they are in the engineering staff, purchasing group, or client services, they are all there to set customers up for success. We really recognize that our customers—who are engineers mostly—put so much trust in us. Our customers come to us and they literally hand over the success of their projects to us.

What advice can you give hardware designers about PCB assembly?I am shocked at how many engineers tell me they are the ones in the lab building their boards, and how frustrated they get because they are not set up to do it right. What I always tell engineers is to focus on what you do best. Using our proprietary software, a design engineer sends us a design, and we put it through our design for assembly check; that’s not DFM, but DFA. Eighty percent of the jobs that have come to us have flaws in the design that could put the assembly process on hold. Our software engineering group finds these flaws, works with the customer to resolve them, and then we move the design forward. Right upfront, we’re adding value to the customer.

Another hassle we eliminate for customers is purchasing kits. Did you know it takes an average of 15 hours to find and order parts for a typical pcb assembly order? With our turnkey business, we order the parts and boards in addition to

handling the assembly. Our extensive partnerships with leading part and board suppliers allow us to select the right vendor for each order. This saves engineers a lot of time and delivers the best results. Again, I’d say let us do what we do best - we are experts at pcb assembly—so you have time to do what you do best.

How do you ensure the quality in your company operations, making sure that engineers trust you to do the job right?It’s all about continuous improvement. Globally, at Advanced Assembly, it starts with a serious commitment to quality at all levels and across all departments. It’s just an accepted fact here that quality has to be paramount. Our entire company, and specifically our cross functional quality team, is responsible for maintaining our high quality standards. The quality team meets weekly to discuss trends and opportunities for improvement. From its recommendations, QA initiatives are created and executed. Often the initiatives involve better training, process adjustments and bringing in equipment or technology that we do not currently have.

It’s also about scalable processes. When you grow a company from a couple of employees to around a hundred now, the processes have to scale. As you get larger, you really do have to hone in on scalable, repeatable processes, and that’s what our quality group does.

22


“Our extensive partnerships with leading part and board suppliers allow us to select the right vendor for each order. This saves engineers a lot of time and delivers the best results.”

The other challenge I see is constantly honing our processes to make them more and more efficient. As we break through each of these steps in growth, it’s a constant challenge to push back and reevaluate our processes. With our commitment to ISO 9001, whether it is in the management review or in the auditing itself, every year we have a positive outcome. Every single year, it gives us the chance to go back and make sure we are challenging ourselves in operations. That sounds like a resource drain, but it actually provides a great deal of benefit to the company.

What’s the culture like in your company?For most of my career, I’ve considered myself a “techie.” I grew up professionally in cultures that empower employees to do the right thing even when sometimes it might be a little risky. Advanced Assembly’s culture is very similar. The company values its employees and our employees value our customers. We recognize and respect the trust that our customers give us and spend every day trying to do the right thing for them. As an example, one day we had a job with an issue that needed to be fix, but the

How does Advanced Assembly stay ahead of its competitors?We invest in people, we invest in processes, and we invest in equipment. We are very fortunate to have the equipment necessary to produce the high quality our customers expect. Over the past few years, we have acquired very high tech, state-of-the-art washers and vapor reflow machinery. The technology for vapor reflow really speaks to niche—it allows the introduction of gallium in the vacuum chamber, which heats the boards very evenly. For boards with disparate size parts this is a tremendous benefit, and the solder outcome is just amazing.

Where do you see the most opportunity for innovation in PCB assembly, given the way the technology is changing?The first one I see is continued miniaturization. The other one is paste application. There are some new technologies out there that could revolutionize paste application. I’ve seen some amazing things being done with programmable paste printers and wouldn’t be surprised if we added this capability in the very near future.

Another trend I see is continued automation in general. Using automation to drive out set-up time and deliver pcb assembly even faster is always a consideration for us. There is some machinery that at first looks good and helpful, but later on you

realize it takes hours just to set up for a job. That’s not a smart investment for us. The last opportunity I’d like to mention is service. This company got its start because of frustrated engineers. While our service isn’t where I’d like it to be yet, I believe it’s the best in the industry and getting better every year.

What are the biggest challenges that you face in your company?Our biggest challenge is scaling to handle forecasted growth without losing what makes our company so special. Since inception, this company has experienced double and triple digit growth year over year, all while improving our on-time delivery and quality. This year we expect to see another 20 to 25 percent growth, but we’ve got to manage it in a controlled fashion. If we don’t deliver on quality or on-time delivery because we’re trying to be all things to all people, then we are going to fail.

We really are focused on staying true to what we do; quick-turn, pcb assembly. Nobody likes to say “no” to a customer. It’s very tempting to try and do it all. We get a lot of folks who will come talk to us because they are very pleased with our service and then they’ll ask us to do something just a little bit outside of our niche. I’m confident that if we stay true to ourselves as a company, our customers will benefit.

COVER INTERVIEW

23

“Our extensive partnerships with leading part and board suppliers allow us to select the right vendor for each order. This saves engineers a lot of time and delivers the best results.”

The other challenge I see is constantly honing our processes to make them more and more efficient. As we break through each of these steps in growth, it’s a constant challenge to push back and reevaluate our processes. With our commitment to ISO 9001, whether it is in the management review or in the auditing itself, every year we have a positive outcome. Every single year, it gives us the chance to go back and make sure we are challenging ourselves in operations. That sounds like a resource drain, but it actually provides a great deal of benefit to the company.

What’s the culture like in your company?For most of my career, I’ve considered myself a “techie.” I grew up professionally in cultures that empower employees to do the right thing even when sometimes it might be a little risky. Advanced Assembly’s culture is very similar. The company values its employees and our employees value our customers. We recognize and respect the trust that our customers give us and spend every day trying to do the right thing for them. As an example, one day we had a job with an issue that needed to be fix, but the

How does Advanced Assembly stay ahead of its competitors?We invest in people, we invest in processes, and we invest in equipment. We are very fortunate to have the equipment necessary to produce the high quality our customers expect. Over the past few years, we have acquired very high tech, state-of-the-art washers and vapor reflow machinery. The technology for vapor reflow really speaks to niche—it allows the introduction of gallium in the vacuum chamber, which heats the boards very evenly. For boards with disparate size parts this is a tremendous benefit, and the solder outcome is just amazing.

Where do you see the most opportunity for innovation in PCB assembly, given the way the technology is changing?The first one I see is continued miniaturization. The other one is paste application. There are some new technologies out there that could revolutionize paste application. I’ve seen some amazing things being done with programmable paste printers and wouldn’t be surprised if we added this capability in the very near future.

Another trend I see is continued automation in general. Using automation to drive out set-up time and deliver pcb assembly even faster is always a consideration for us. There is some machinery that at first looks good and helpful, but later on you

realize it takes hours just to set up for a job. That’s not a smart investment for us. The last opportunity I’d like to mention is service. This company got its start because of frustrated engineers. While our service isn’t where I’d like it to be yet, I believe it’s the best in the industry and getting better every year.

What are the biggest challenges that you face in your company?Our biggest challenge is scaling to handle forecasted growth without losing what makes our company so special. Since inception, this company has experienced double and triple digit growth year over year, all while improving our on-time delivery and quality. This year we expect to see another 20 to 25 percent growth, but we’ve got to manage it in a controlled fashion. If we don’t deliver on quality or on-time delivery because we’re trying to be all things to all people, then we are going to fail.

We really are focused on staying true to what we do; quick-turn, pcb assembly. Nobody likes to say “no” to a customer. It’s very tempting to try and do it all. We get a lot of folks who will come talk to us because they are very pleased with our service and then they’ll ask us to do something just a little bit outside of our niche. I’m confident that if we stay true to ourselves as a company, our customers will benefit.

24






SMT Assembly for Engineers







http://bit.ly/1gH38fc

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TECH ARTICLE

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One benefit we provide our customers is by giving a higher quantity discount but delivering smaller quantities over time.

Single- or double-sided PCBs are roughly the same cost to manufacture. However, multi-layer PCBs create additional costs in materials and the manufacturing process.

LEAD TIME Time is money. The faster you need your order the more it will cost. There are real costs associated with manufacturing a PCB faster and making some jobs a higher priority than others. Depending on the turn time, the increased costs can be between 30% and 200% or more. LAYER COUNT The number of layers is a significant cost-driving factor. Single- or double-sided PCBs are roughly the same cost to manufacture. However, multi-layer PCBs create additional costs in materials and the manufacturing process. To go from a 2-layer PCB to a 4-layer PCB can typically double the price or more. Once you move from double-sided to multi-layer, the price increase related to adding more layers is not as pronounced. For example, the cost to go from 4 layers to 6 layers might only be about a 50% increase instead of doubling in cost.

DRILL SIZE AND COUNT Another factor is the smallest hole size to be drilled and the total number of drilled holes. When the hole size gets under 0.015”, the cost can increase 5% to 10%. A large number of holes can increase the cost by that same percentage as well. The manufacturing process has to be adjusted with smaller hole sizes and large hole counts. The number of panels that can be drilled at one time decreases.

MATERIAL TYPE AND THICKNESS There are many material types that can be used to manufacture a PCB. The most common of which is called FR4. That is simply fiberglass and material woven together with an epoxy resin that includes fire-resistant properties. Other material types that could be selected include higher temperature FR4, polyamide, Rogers, flex, etc. These other material types can significantly increase the cost of the PCB. The most common thickness is 0.062”. Other thicknesses could increase the cost by 5% to 10% depending on if you use a standard thickness type or request a custom thickness.

TRACE/SPACE Many of the designs needed today require components that are very small. This drives the spacing between copper features on a PCB to be smaller and smaller. If at all possible, you want to leave as much space as you can in your board to keep the costs down. You could see a 5% to 10% increase in costs for trace/space that goes below 0.006”. These are the primary variables a fabricator will consider when preparing a price quotation for a customer but there are many more. Understanding the considerations and calculations behind a quoted price will hopefully help you design smarter, more cost-effective printed circuit boards.

In the next article, we’ll wrap up by diving deeper into some of the secondary cost-determining factors.

One benefit we provide our customers is by giving a higher quantity discount but delivering smaller quantities over time.

Single- or double-sided PCBs are roughly the same cost to manufacture. However, multi-layer PCBs create additional costs in materials and the manufacturing process.

LEAD TIME Time is money. The faster you need your order the more it will cost. There are real costs associated with manufacturing a PCB faster and making some jobs a higher priority than others. Depending on the turn time, the increased costs can be between 30% and 200% or more. LAYER COUNT The number of layers is a significant cost-driving factor. Single- or double-sided PCBs are roughly the same cost to manufacture. However, multi-layer PCBs create additional costs in materials and the manufacturing process. To go from a 2-layer PCB to a 4-layer PCB can typically double the price or more. Once you move from double-sided to multi-layer, the price increase related to adding more layers is not as pronounced. For example, the cost to go from 4 layers to 6 layers might only be about a 50% increase instead of doubling in cost.

DRILL SIZE AND COUNT Another factor is the smallest hole size to be drilled and the total number of drilled holes. When the hole size gets under 0.015”, the cost can increase 5% to 10%. A large number of holes can increase the cost by that same percentage as well. The manufacturing process has to be adjusted with smaller hole sizes and large hole counts. The number of panels that can be drilled at one time decreases.

MATERIAL TYPE AND THICKNESS There are many material types that can be used to manufacture a PCB. The most common of which is called FR4. That is simply fiberglass and material woven together with an epoxy resin that includes fire-resistant properties. Other material types that could be selected include higher temperature FR4, polyamide, Rogers, flex, etc. These other material types can significantly increase the cost of the PCB. The most common thickness is 0.062”. Other thicknesses could increase the cost by 5% to 10% depending on if you use a standard thickness type or request a custom thickness.

TRACE/SPACE Many of the designs needed today require components that are very small. This drives the spacing between copper features on a PCB to be smaller and smaller. If at all possible, you want to leave as much space as you can in your board to keep the costs down. You could see a 5% to 10% increase in costs for trace/space that goes below 0.006”. These are the primary variables a fabricator will consider when preparing a price quotation for a customer but there are many more. Understanding the considerations and calculations behind a quoted price will hopefully help you design smarter, more cost-effective printed circuit boards.

In the next article, we’ll wrap up by diving deeper into some of the secondary cost-determining factors.

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