Beagle Esc 4

5/12/2018 Beagle Esc 4 - slidepdf.com

http://slidepdf.com/reader/full/beagle-esc-4 1/84

Hardware Lessons Learned from

Building Beagle

Gerald ColeyESC-401



Topics Covered What¶s in a name?

Specification

Schematic

PCB Layout Assembly

Testing

Support

Implementing Lessons Learned Questions and discussion



The Name:

Where did we get the nameBeagleBoard?



How did we arrive at BeagleBoard?

Every project needs a name

Named for my dog. ± Just ³temporary´

± We will fix it later

± Well, It Stuck

A Beagle is: ± Like Tux, non threatening

± Curious

± Loyal ± Fun

± And gives back as much as it receives

Lesson Learned«If you name it, it will stick!



So, we need an acronym

Bring your own peripherals

Entry-level

ARM Cortex-A8

Graphics & DSP

Linux and open source

Environment for SW innovators



The Specification: A buffet

or just meat and potatoes?



The Goals

Get OMAP3530 into people¶s hands

Low Cost <$150 ± Under the spousal radar

± Reach as many people as we can

Small Size ± Keeps the cost down

± ³Cool´ Factor

Internally focused

± Cortex-A8 + NEON ± DSP

± 3D Graphics

± Accelerators



First Pass Features

OMAP3530 Processor 3.5´ LCD

± VGA/QVGA ± Touch screen

S-Video Keypad 2 Serial Ports

SD/MMC Ethernet Camera 128MB DDR 128MB NAND USB

± Host ± OTG

USB/DC Power Stereo In/Out Battery w/Charger Full Expansion Bus

COST: $1500

Size: 5´ x 8´

Something has to go!!



Bring Your Own

Not everyone needs everything

Everything is needed

Bring your Own ± User adds only what they need

± They don¶t have to pay for what they alreadyhave

± Allows for maximum exposure to HW

More than just one component supplier



Final Pass Features OMAP3530

3.5´ LCD.-VGA/QVGA

± Touch screen USB Touch Screen

DVI-D VGA, SVGA, XGA

S-Video

Keypad ± 1 button USB Keyboard & Mouse

2 Serial Ports ± 1 Port USB & Expansion

SD/MMC 6 in 1 Slot

Ethernet ± USB Dongle & WiFI

Camera ± USB Camera

128MB DDR

128MB NAND

USB Host OTG

USB/DC Power Stereo In/Out

Battery w/Charger ± USB Battery Adapter

Size 5´ x 8´ 3´ x 3´

Full Expansion Bus ± Standard buses

Standard on BeagleBring your own

Just meat and potatoes,

but still room for dessert!!

COST: $149



The Schematic



Play It Safe Leverage everything we can

± Used OMAP35xx EVM as base

Maintain compatibility with other platforms

± Common hookup

± Subset used the same

Keep the component count low

Use what is proven to work Leave off what is not needed



Leveraged Advantages

OMAP35xx Processor Symbol/Design verified

TWL4030/TPS65950 Symbol/Design verified

± Removed a lot of features here SD/MMC Verified

DVI-D verified

UART Verified Lowered the overall risk



PCB Layout



Rules We Used

PCB

Design

PCB

FAB

PCB

ASSEMBLYMemory

Vendors

TI

Failure to include the fab and assembly team members can prove costly since choices

made early in the design will adversely impact the final cost of the assembled board



The Challenges

OMAP35xx Package

± .4mm Pitch

± Routing

TPS65950(TWL4030)

± .4mm pitch PMIC

POP Implications

Limited area for connectors

± Location driven and not layout driven



OMAP3530 Package



What Exactly Is POP?

OMAP

Memory



PMIC TPS65950 (TWL4030)



Fixed Location of Connectors

Routing complicated by locations

± Connector not always on the best side

± We tried to make this as easy as possible Not the best locations for routing

± The DVI-D was the longest route

We need to keep the layer count down ± Our goal was to stick with 6 layers



Recommended Trace and Via Connections

viaBGA

Don¶t gang BGA

pads with ground

plane

Trace should never

be larger than pad

Good

Better

Best

Poor

Better

Watch for solder traps



Blind and Buried ViasDefinitions and Terminology

Through hole via has access to both external layers

Buried via provides connection within inner layers

Blind via does not pass through the entire board



Via-in-PadPlaces the via directly in the BGA pad

Greatly improves board routing

Has special requirements for manufacturability

Given a 10mil BGA pad

Use a 4mil microvia

Laser drilled

Via must be filled or capped to minimize void formation

Via-fill Material

Check with board fabricator for their preferences

Fill material can be conductive or non-conductive

Via fill material¶s particle size must be <1mil for complete penetration

You must validate your board fabricator¶s capability to reliably build with this

class of technology



.4mm Pitch

No routing between pads

Use top layer routing on outside pads

Use vias-in-pad wherever needed



Soldermask

Exposed pad should be the same size asthe pad on the mounted device

Need to make the pad larger to addstability

Calls for soldermask defined pads



Surface FinishThe PCB surface finish provides a coating over the outer layer copper

that prevents oxidation and provides an electrically conductivesurface.

Organic Solderability Preservative (OSP) Thin layer of organic material toprevent copper oxidation. It is removed by the assembly flux. Does nottolerate multiple heat cycles.

Immersion Tin (ImSn) Thin layer of tin directly on top of the copper surface.Produces an extremely flat surface for mounting of surface mountcomponents. Downside is the possible formation of Tin whiskers.

Immersion Silver (ImAg) Thin layer of silver directly on top of the copper surface. Produces a very flat surface. Compatible with no-clean assemblyprocesses. Maintains high solderability after multiple heat cycles. Downsideis that the plating will tarnish over time.

Electroless Nickel Immersion Gold (ENIG) Commonly used finish that isnice and flat for fine-pitch devices. Not easily reworked and more expensive. Hot-air solder leveling (HASL) Immersing the PCB in solder. It is

inexpensive and widely available, but it is not flat and therefore does notwork well with fine-pitch devices



Final BeagleBoard Design

OMAP3 Triton-2

TFP410



OMAP3530 BGA Footprint

Pad Type Solder Mask Defined

Pad Pitch A 400um

Pad Opening B 254um (10mils)

Pad Dia C 280um (11mils)

Mask Web D 150um



Via-In-Pad Topology Stacked Microvia-In-Pad Pad 11mils copper (10mil SMD)

Top-Layer2 stacked with Layer2-Layer-3 Top-Layer2 Laser Drill 6mil (0.152mm) Solder-mask defined pads Non-conductive epoxy via plugs, plated over and planarized

Top Signal

Lyr2-GND

Lyr3-SIG

Lyr4-SIG

Lyr5-PWR

Bottom Signal

OMAP3

Top Soldermask

Bottom Soldermask

Blind/Stacked1-3

Blind1-2

BeagleBoard does not use buried vias



Top

Lyr2-GND

Lyr3-SIG

Lyr4-SIG

Lyr5-PWR

Bottom

T

hru-hole via from top to bottom 18mil radius pad 8 mil drilled hole Plugged, plated and planarized

Must be levelNo dimples

Standard Vias

Not To Scale



Top Layer-Signal(Area under OM AP3 Chip)

Via 1-6

V-I-P

BGA

PAD

3mil trace

10mil trace



Bottom Layer

Bypass Capacitor Locations

Capacitor Spec

Type: Ceramic X7R

Size: 402Value: 0.1uF

Bypass Capacitor Location andSolder Pads

Via 1-6

Component

Pad

Min trace width 3 mils



PCB Fabrication Concerns

High Board cost

± Because they can charge more

± Unknown = $$$$$

± Does not necessarily mean the production $$will be high

Unfamiliar with fine pitch

Soldermask registration critical



Board Assembly:

Putting it all together



POP Assembly Concerns

POP was the number one concern

Nitrogen and air were the two options

What should we do? ± Picked the one that was the most applicable

to as many assembly houses aspossible«.Air

POP soldering in air ± Air #1

± Air #2



Mounting .4mm Parts

No real concerns

Equipment can handle it

Warping of the processor due to POP wasa possibility

± Saw no reason to be concerned

T

here could be an issue with shorts if soldermask not correct

We were comfortable



Solderpaste Equipment



Pick and Place Machine

My DATA (MY9)

D-014-1486 F30



Reflow Oven

Heller EXL



X-Ray Machine

Glenbrook TechnologiesRTX-113



POP Mounting Configurations

Method A ± POP onto OMAP3 first reflow ± Back side Second reflow ± Top side third w/POP+OMAP3530 reflow

Method B ± Mount back side reflow ± Mount top side with OMAP3530 reflow ± Mount Memory w/ Pick & Place reflow

Method C ± Mount backside reflow ± Mount topside with OMAP3530 and POP reflow



Method A ProcessTopGEL

HandMount

Paste SMT Reflow

OMAP3 OMAP3

POP

PasteReflow

Bottom side of board Top side of board

Mount w/SMT

Hand Assembly



Method B Process

Paste SMT Reflow


ApplyGel

Reflow

Paste SMT Reflow

SMT

POP Memory

Hand Assembly



Method C Process

Paste SMT Reflow


Paste

SMT

Reflow

POP Memory POP Memory

Dipping Arm isused to applypaste

Hand Assembly



POP Mounting Analysis

Method A ± No real issues seen ± We abandoned it when we ran into issues ± Issues were not related to this process

Method B ± Final method adopted ± Have had excellent results

Method C

± Dipping Arm«POP Memory dipped into GEL ± Have a lot of high volume customers doing this ± Did not try as we had no dipping arm



Panelization

Method A ± 4 boards per panel

± Used it on the first runs

± Had concerns about warping across thescoring that could cause solder shorts

± Nothing ever proven that this was an issue

Method B ± One board per panel

± Method chosen



Other Parameters

Stencil thickness

± .4mils

Solder Paste ± AMTECH LF -4300 Lead Free

± Chemistry Sn96.5/Ag3.0/Cu.5

Tacky paste flux (memory)

± Amtech Tacky Solder Flux



Reflow Profile Diagram

Time

50

100

150

200

250

Preheatingstage

Reflow

Peak

T e m p e r a t u r e -

D e g r e e s C

Cooldown



Board Profile Settings

BOT TOP POP

# Zones In Oven 18 18 18

Pre-Heat Temp. 145 OC 170 OC 150 OC

Pre-Heat Dwell 98 sec 95 sec 100 sec

Reflow 118 sec 115 sec 120 sec

Duration Peak 18 sec 15 sec 20 sec

Peak Reflow Temp. 245 OC 260 OC 250 OC

Cool Down 8 OC/sec 8 OC/sec 8 OC/sec

Speed 52cm/s 55cm/s 50cm/s



Issues on 1st Run

Solder Shorts under the processor ± Always a power rail

10% Yields

Could it be related to«.? ± POP Package

± Profile

± PCB ± Parts

± Solder



Solder Shorts



2nd Run

What is the easiest thing to change?

± Adjusted the temperature profile

Same results 90% Fail

Shorts under processor



3rd Run

Shotgun approach

Changed PCB Vendor

Went to single board penalization

Changed POP method from A to B

Kept the original profile

Results ± 96% Yields

± No Shorts



Analysis of 2nd Run

What was the issue? Gut said PCB soldermask

± Contacted first supplier ± No issue w/soldermask per supplier

Ordered more board and ran again with all other methods from Run 3 ± Same problem; 90% fail

Ordered shotguns and raided first supplier ± They admitted that they opened the soldermask ± Had them run another batch w/o changing soldermask

Result ± 96% yields ± No shorts



Good/Bad SoldermaskGOOD BAD



Other Issues Along the Way

SMT PCB audio connectors can rip off

± Only happened on two boards

± Pads detached from the board

± Added clear epoxy to connectors

± Adding vias to pads to add strength (Rev B6)

SMT USB connectors can rip off

± Only happened on one board

± Adding vias to pads to add strength (Rev B6)



Final Analysis

Soldermask is the key issue

± PCB suppliers do their own thing

± Make sure that the thing they do is your thing!

All three POP methods should work Panalization should not be an issue, but not

confirmed

± It will be an issue if the soldermask is bad

Beagle profile is a good place to start

± Will need to be adjusted based on equipment used



Board Testing Process



Inspection Points

PCB ± Visual inspection

Solder Paste ± Bottom side application

± Top side application Shorts ± After re-flow

AOI ± After final assembly

Manual inspection ± Final inspection



Assembly Inspection Points

Paste SMT Reflow


ApplyGel

Reflow

Paste SMT Reflow

SMT

POP Memory

Hand Assembly

PastePCB Paste Shorts

Shorts Visual AOI



PCB Check

Check soldermask ± Overlap (Soldermask defined pads)

± Soldermask over vias

Check finish ± Discoloring of finish

Dimples in via in pads ± Must be smooth

Check Pads ± Look for dimples in the vias in pad areas



Solderpaste Inspection

Check paste for smooth applicationCheck for missing paste (not sticking to PCB)



Shorts Test

Implemented when we had solder shorts

Easy check for main issues we have seen

Check across the caps using a ohmmeter ± Run as a spot check

± Can be done at 100%



AOI Machine

Testronics 505 Machine Vision

-Works off of a known good board-Check for part orientation-Check for missing parts



Final Inspection

Bad soldering

Contamination

Misaligned Parts

Wrong parts



Functional Test

Tests all interfaces onthe boardProgram NAND with

XLoader and UBootTested pre and postburn-in



Burn-In72 Hour Burn InRoom temperatureRunning UBoot



Final Results

96%+ yield

Kept single board penalization

Kept assembly POP process Kept Profile

Now have three suppliers of PCB

± DDI (Dynamic Details, Inc) ± MEI

± Streamline



REV A...Each Revision Only 50 units built

Rev A...Initial Version Rev A1«Normalized LED brightness levels

Rev A2...Changed resistor loading options for S-Video

Rev A3«Lowered pull-up values for the I2C busses

Rev A4...Lowered value of USB cap due to turn on issues ± Too much current drain

Rev A5...Incorrect inductor value on TPS65950 switchers

± Typo in BOM

Issues to be fixed:

± DC Voltage jack

± 1K pull-up on wait line

± Plated through hole issues

± Remove 4 test points

± User0 and User1 LEDS shorted



REV B ...Each Revision

Rev B1«Initial Release ± Fixed outstanding Rev A issues

Rev B2«USB Host not working reliably ± Removed from BOM and assembly ± Questions around the layout

Rev B3«Added a few caps back in from B2 Rev B4...Some USB HUBS not connecting on OTG Port

± Noise level too high«Added a capacitor onto USB power rail

Rev B5...Serial Port disconnects after a while ± Removed a capacitor on the 32KHZ Clock

Rev B6«PCB spin to change package of U9 and U11 Issues To be Fixed:

± USB Host



Big Issue Emerges REV B

Failures of the serial port and EDID

Traced to a bad package on TXS0102

± Delamination issue

60% Failure rate

Started 72 burn in process to weed out

Still have 1% making it out Only solution is to move to a different

package



1st Rev C Proto

Attempted to fix USB Host

± Significant improvement

± Still not 100%

This version became the board for Rev B6

± Replaced U9 and U11 package

± Changed Revision to B1



2nd Rev C

PCB In FAB

Moved USB Host to port 2 ± Aligned with other platforms

± Success on Port2

Added native LCD access ± Lot of demand for this feature

± Ability to interface to different displays withsmall paddle boards (LVDS, TTL, etc.)

± Kept current expansion header



Support Process



Key Issues from Users

Serial Port Issues

± Confusion over cables

± Serial port failures

OTG to host connectors

± Need ³special´ cable

± Brought on by lack of USB Host port

Connecting another video output

± LCD



The Returns



RMA By Subsystem

Audio««««..0 DVI-D««««..2 Serial Port««..19

Memory«.««..0 S-Video«.««..0 SD/MMC«««.0 USB OTG««...0

User Issue««..9 PMIC«««««3 Nothing Found...1

34 Total««..1.7%

Serial Port«..1.0%



The Serial Ports

60% of returns for this reason

Issue with a small number of boards dueto part problem

This issue masks other real issues

± Wrong IDC Cable

± Wrong SERIAL Cable

± Wrong terminal setup

± Well, it works on that other board?



Implementing the LessonsLearned:

What¶s Next?



Changes Being Made

Documentation

± Troubleshooting Section for Serial Port

± Pictures

± Step by Step process

Diagnostic SW

New Translator Package

± PCB Change REV B6

LCD Interface (Rev C)



Design Material Available

Schematics ± PDF Version http://www.beagleboard.org/uploads/BBSRM_B5.pdf

± OrCAD Version http://www.beagleboard.org/uploads/BEAGLE_ORCAD_B4.zip

BOM ± Excel http://www.beagleboard.org/uploads/Beagle_BOM_B4.xls

PCB Files ± PCB Gerber Files http://www.beagleboard.org/uploads/Beagle_Allegro_B.zip

± PCB Allegro Files http://www.beagleboard.org/uploads/Beagle_Gerbers_B.zip

Viewers ± PDF ± OrCAD ± Gerber

± Allegro

PCB Design Guideline http://focus.ti.com/dsp/docs/dspsupporttechdocsc.tsp?sectionId=3&tabId=409&familyId=1526&abstractName=spraav1

System Reference Manual http://www.beagleboard.org/uploads/BBSRM_B5.pdf

± Rev B6 on its way

http://beagleboard.org/hardware/design



Can you do OMAP3?

Take the BeagleBoard and build it

± Verifies if the PCB Fabricator can do it

± Verifies if the Assembly house can build it

± All material needed is provided

All needed SW is available

± Diagnostics

± Kernels

± Distributions



Thanks To:

Contract Manufacturer CircuitCo www.circuitco.com

PCB Fabricators

Marcel Electronics mei4pcbs.com

Dynamic Details www.ddiglobal.com

Streamline www.streamlinecircuits.com

PCB Layout

ION Design www.iondesign.com Keith Gutierrez , Texas Instruments



Questions and Discussion

Documents

Beagle Esc 4