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Hardware Lessons Learned from Building Beagle Gerald Coley ESC-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 name BeagleBoard?

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topics covered
Topics Covered
  • What’s in a name?
  • Specification
  • Schematic
  • PCB Layout
  • Assembly
  • Testing
  • Support
  • Implementing Lessons Learned
  • Questions and discussion
how did we arrive at beagleboard
How did we arrive at BeagleBoard?
  • Every project needs a name
  • Named for my dog.
    • Just “temporary”
    • 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
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 goals
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
    • “Cool” Factor
  • Internally focused
    • Cortex-A8 + NEON
    • DSP
    • 3D Graphics
    • Accelerators
first pass features
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
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 already have
    • Allows for maximum exposure to HW
      • More than just one component supplier
final pass features
Final Pass Features

Standard on Beagle

Bring your own

  • 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 

COST: $149

Just meat and potatoes, but still room for dessert!!

play it safe
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
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
rules we used
Rules We Used

PCB

Design

PCB

FAB

PCB

ASSEMBLY

TI

Memory

Vendors

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
The Challenges
  • OMAP35xx Package
    • .4mm Pitch
    • Routing
  • TPS65950(TWL4030)
    • .4mm pitch PMIC
  • POP Implications
  • Limited area for connectors
    • Location driven and not layout driven
fixed location of connectors
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

via

BGA

Good

Trace should never

be larger than pad

Better

Don’t gang BGA

pads with ground

plane

Best

Recommended Trace and Via Connections

Poor

Better

Watch for solder traps

blind and buried vias
Blind and Buried Vias
  • Definitions 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 pad
Via-in-Pad
  • Places 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
.4mm Pitch
  • No routing between pads
  • Use top layer routing on outside pads
  • Use vias-in-pad wherever needed
soldermask
Soldermask
  • Exposed pad should be the same size as the pad on the mounted device
  • Need to make the pad larger to add stability
  • Calls for soldermask defined pads
surface finish
Surface Finish

The PCB surface finish provides a coating over the outer layer copper that prevents oxidation and provides an electrically conductive surface.

  • Organic Solderability Preservative (OSP) Thin layer of organic material to prevent copper oxidation. It is removed by the assembly flux. Does not tolerate 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 mount components. 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 assembly processes. Maintains high solderability after multiple heat cycles. Downside is that the plating will tarnish over time.
  • Electroless Nickel Immersion Gold (ENIG) Commonly used finish that is nice 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 not work well with fine-pitch devices
slide28

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

slide29

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

BeagleBoard does not use buried vias

OMAP3

Top Soldermask

Top Signal

Blind

1-2

Blind/Stacked

1-3

Lyr2-GND

Lyr3-SIG

Lyr4-SIG

Lyr5-PWR

Bottom Signal

Bottom Soldermask

slide30

Standard Vias

  • Thru-hole via from top to bottom
  • 18mil radius pad
  • 8 mil drilled hole
  • Plugged, plated and planarized
    • Must be level
    • No dimples

Top

Lyr2-GND

Lyr3-SIG

Lyr4-SIG

Lyr5-PWR

Bottom

Not To Scale

slide31

Top Layer-Signal

(Area under OMAP3 Chip)

Via 1-6

V-I-P

BGA

PAD

3mil trace

10mil trace

slide32

Bypass Capacitor

Location and

Solder Pads

Via 1-6

Component

Pad

  • Min trace width 3 mils

Bottom Layer

Bypass Capacitor Locations

Capacitor Spec

Type: Ceramic X7R

Size: 402

Value: 0.1uF

pcb fabrication concerns
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
pop assembly concerns
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 as possible….Air
  • POP soldering in air
    • Air #1
    • Air #2
mounting 4mm parts
Mounting .4mm Parts
  • No real concerns
  • Equipment can handle it
  • Warping of the processor due to POP was a possibility
    • Saw no reason to be concerned
  • There could be an issue with shorts if soldermask not correct
  • We were comfortable
pick and place machine
Pick and Place Machine

My DATA (MY9)

D-014-1486 F30

reflow oven
Reflow Oven

Heller EXL

x ray machine
X-Ray Machine

Glenbrook Technologies RTX-113

pop mounting configurations
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 process
Method A Process

Hand Mount

TopGEL

POP

Mount w/SMT

OMAP3

OMAP3

Paste

SMT

Reflow

Reflow

Paste

Top side of board

Bottom side of board

Hand Assembly

method b process
Method B Process

Paste

Paste

SMT

Reflow

SMT

Reflow

Top side of board

Bottom side of board

ApplyGel

POP Memory

SMT

Reflow

Hand Assembly

method c process
Method C Process

Dipping Arm is used to apply paste

POP Memory

POP Memory

Paste

Paste

SMT

Reflow

Reflow

SMT

Top side of board

Bottom side of board

Hand Assembly

pop mounting analysis
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
Panelization
  • Method A
    • 4 boards per panel
    • Used it on the first runs
    • Had concerns about warping across the scoring that could cause solder shorts
    • Nothing ever proven that this was an issue
  • Method B
    • One board per panel
    • Method chosen
other parameters
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

Peak

250

200

Temperature - Degrees C

150

100

50

Preheating stage

Cooldown

Reflow

Reflow Profile Diagram

Time

issues on 1 st run
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
2 nd run
2nd Run
  • What is the easiest thing to change?
    • Adjusted the temperature profile
  • Same results
  • 90% Fail
  • Shorts under processor
3 rd run
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 2 nd run
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
other issues along the way
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
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
inspection points
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
Assembly Inspection Points

PCB

Paste

Paste

Paste

Shorts

Paste

SMT

Reflow

SMT

Reflow

Top side of board

Bottom side of board

ApplyGel

POP Memory

Visual

Shorts

AOI

SMT

Reflow

Hand Assembly

pcb check
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
Solderpaste Inspection
  • Check paste for smooth application
  • Check for missing paste (not sticking to PCB)
shorts test
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
AOI Machine

Testronics 505 Machine Vision

-Works off of a known good board

-Check for part orientation

-Check for missing parts

final inspection
Final Inspection
  • Bad soldering
  • Contamination
  • Misaligned Parts
  • Wrong parts
functional test
Functional Test
  • Tests all interfaces on the board
  • Program NAND with XLoader and UBoot
  • Tested pre and post burn-in
burn in
Burn-In
  • 72 Hour Burn In
  • Room temperature
  • Running UBoot
final results
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
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 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
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
1 st rev c proto
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
2 nd rev c
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 with small paddle boards (LVDS, TTL, etc.)
    • Kept current expansion header
key issues from users
Key Issues from Users
  • Serial Port Issues
    • Confusion over cables
    • Serial port failures
  • OTG to host connectors
    • Need “special” cable
    • Brought on by lack of USB Host port
  • Connecting another video output
    • LCD
rma by subsystem
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
The Serial Ports
  • 60% of returns for this reason
  • Issue with a small number of boards due to part problem
  • This issue masks other real issues
    • Wrong IDC Cable
    • Wrong SERIAL Cable
    • Wrong terminal setup
    • Well, it works on that other board?
changes being made
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
Design Material Available

http://beagleboard.org/hardware/design

  • Schematics
    • PDF Versionhttp://www.beagleboard.org/uploads/BBSRM_B5.pdf
    • OrCAD Versionhttp://www.beagleboard.org/uploads/BEAGLE_ORCAD_B4.zip
  • BOM
    • Excelhttp://www.beagleboard.org/uploads/Beagle_BOM_B4.xls
  • PCB Files
    • PCB Gerber Fileshttp://www.beagleboard.org/uploads/Beagle_Allegro_B.zip
    • PCB Allegro Fileshttp://www.beagleboard.org/uploads/Beagle_Gerbers_B.zip
  • Viewers
    • PDF
    • OrCAD
    • Gerber
    • Allegro
  • PCB Design Guidelinehttp://focus.ti.com/dsp/docs/dspsupporttechdocsc.tsp?sectionId=3&tabId=409&familyId=1526&abstractName=spraav1
  • System Reference Manualhttp://www.beagleboard.org/uploads/BBSRM_B5.pdf
    • Rev B6 on its way
can you do omap3
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
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