GENUS P.C.B PLANT

Genus is one of the fastest emerging PCB industry in India, manufacturing single sided, double sided, RF, metal clad and multilayer PCBs.

Cu clad laminates of 1 square metre are purchased.We have 2 main processes - one is remove excess Cu and other is to deposit Cu on the places where more thickness of Cu is desired.

1. ShearingShearing of the Cu laminate as per the required size.

Stalking of the sheared Cu laminates is done.

Now the stalked laminate is sent for drilling.

2.CNC DrillingDrilling refers to making holes of different diameter in the PCB using spindle according to the design sent by the customer. Data related to it is fed through a software in the drilling machine.

Parameters involved are - tool life, spindle speed, feed, no. of holes per sec, total no of holes on the panel. This is one of the most expensive process. Operator must ensure that there is no missing hole, all holes are according to the software, drill bit is properly grinned, burrs are removed using deburring machine.

3. CleaningIt is basically a mild etching process in which Cu layer of few micron is removed so that surface of the panel is smooth.

4. PTH (Plating through holes)

Electroless deposition of Cu through the holes as holes are composed of epoxy initially. After Cu deposition, panel is dipped in acid dip and anti-tarnish solution to prevent against oxidation. It is of two types - horizontal and vertical. Horizontal PTH is for carbon deposition and vertical PTH is for Cu deposition.

5. PIT (Photo Image Transfer)

Cu laminate after PTH is sent to the yellow room where initially Dry green film which is photosensitive is coated over the Cu laminate. After this, pattern printing is done with a help of the pattern sent by the customer which is made to expose to UV light. Pattern is designed such that UV light only passes through the unwanted area and this area when exposed to UV light becomes hard and becomes resistant to Cu and Sn plating. The panel is then passed through a developing process, which removes all the dry film from the soft area.Yellow room must be made according to CLASS 10,000

6. PlatingFirst Cu is plated on soft area according to the thickness required by the customer. This soft area was the one which was not exposed to UV.

After Cu is plated, Sn is coated over it where Cu laminate is made anode and electrolysis takes place.

Cu & Sn does not gets coated over the hard area.

7. SES (Stripping Etching Stripping)

First the green dry film is stripped out and then Cu is etched out from the hard area since Sn prevents removal of Cu from the soft area.

After this Sn is also stripped out, as a result of which Cu remains only on the soft area.

8. BrushingIt involves Cu laminate being rinsed with chemicals in order to prepare the surface for PISM (Photo Imaginable Solder Mass).

9. PISMAfter brushing, Cu laminate is taken to PISM room where it is coated with an ink film and then it is made to expose to UV light such that only the area where Solder is to be deposited(if HAL) is not exposed to the UV.

After exposure, the panel is developed to wash away the unexposed solder mask. The mask is then cured.PISM room must be made according to CLASS 100,000

10. HAL(Hot Air Levelling)

It involves coating of solder over the unexposed area(area where components are to be mounted).

Instead of solder some other material may also be deposited according to the demand of the customer. These are :-• ENIG is used for gold• Lead free HAL• Silver• Tin• OSP

11. Legend PrintingThis process refers to printing markings for the components to be mounted later in SMT by rubbing the ink over the Cu laminate through the pattern and then it is made to hardened by passing it through heat or UV exposure.

12. Carbon Printing (optional)

It is preferred where the component to be mounted on PCB needs to pressed repeatedly. Eg: Enter button etc.

13. V Cut GroovingGrooves are made on the Cu laminate to enable easy separation of PCBs from the panel. Eg: If the panel consist of 8 PCBs so each PCB has to be separated after SMT as all the PCBs are to be used separately.

14. RoutingThe routing process is a milling process in which a routing bit is used to cut the profile of the desired board contour. The panels are “pinned and stacked” as previously done during the “Drill” process. The usual stack is 1 to 4 panels.(This process is part of the design)

15. Bare Board TestingThe purpose of an electrical test is to check the electrical integrity of the circuit, i.e to make sure that the circuits are complete and carry the correct currents. Using a test fixture, which consists of a series of pins, every circuit is tested. The pins are aligned with the features. Current is passed between one test point and a test point on the same track. If a signal is detected the circuit is okay.

16. Peel maskingThis process involves coating peelable (blue in colour) over the holes which is to be mounted with the components manually after passing it through SMT machine.

Peelable as the name suggest can be easily removed when needed.

17. FQC (Final Quality Control)

AQL - Accepted Quality limit

Shearing CNC Drilling PTH

PITPlatingSES

PISM HAL Carbon Printing

Legend Printing Routing

In case 4 layers PCB :-

Cu plate of 0.8mm is taken. On top and bottom of the Cu plate, 2 layers of Prepreg are placed(each of 0.17mm). Finally two Cu layers each of 0.035 mm are placed on top and bottom. This is compressed to obtain 4 layer PCB.

Major Defects in PCB1. Extra Short - when two paths or pads gets joined as a result of

which circuit gets short.

2. Track Out - when a path gets break down as a result of which circuit becomes open.

3. Handling Scratch - when scratches get developed on PCB during circulation of PCB from one process to other or may be due to carelessness of the operators.

4. LP Shift - LP gets shifted as a result of which markings get misaligned.

5. More X Out - X out refers to PCBs which are damaged beyond being able to be worked upon.

6. V Cut Shift

7. Dry Film Hang - It occurs when dry film fails to get stripped out during SES

LP Shift is caused due to improper alignment of the printing pattern over the Cu laminate.

Shorting and Track Cut are caused due to presence of dust, germ, dry film on the PCB.

Dry Film Hang occurs due to improper developing during PIT.

Causes

Track Cut Extra Short

Main IssueTo minimise wastage of Cu laminate during Shearing and at the end when required panel is separated from the Cu laminate.