Pad Crater ProjectPad Crater Project““Definition StageDefinition Stage””

Thilo Sack

Celestica

Update for Member Meeting

9/21/2011

The The issue(sissue(s))

• Pad Cratering defects are a significant challenge

with Pb-free PCB materials and/or Pb-free solders,

particularly associated with large BGA devices

• Pad Pull or Ball shear testing has not shown to

consistently represent the actual propensity for pad

cratering of a material and in some cases can give

misleading and/or opposite results from what

actually occurs in real assemblies

• A way is needed to rank order materials that is

directly related to actual pad cratering

Project OverviewProject Overview

• Create a relatively simple test vehicle with a single large BGA assembled in the middle– 6 layers, 0.093” thick

• Fabricate the bare boards from multiple different materials– Include a significant variety of materials, filled and unfilled

– Include materials that have also done “well” in HDPUG Pb-free materials projects

– Don’t test materials that have done poorly in HDPUG Pb-free materials projects

– Other materials as suggested by members

• Perform bend to break testing to rank order the materials– Design TV to virtually ensure trace breaks simultaneous with

laminate (Electrical break)

– Spherical bend testing

– Will need to include some amount of strain gage measurements (CLS to support a limited subset)

– Both Single Bend to Break and Repeated Load to Break

Project Overview (contProject Overview (cont’’d)d)

• On the same boards ALSO perform Cold Ball Pull testing for

a correlation to actual pad cratering

– Intel will support this

• On the same boards – ALSO perform Charpy Impact testing

(May or may not track with fracture toughness/pad

cratering).

– Bob Nevis (Microtek) and Shengyi have both offered to

support this testing.

– Need to understand how to quantify these results

What this Project will ProvideWhat this Project will Provide

• Rank order of materials (based on

electrical failure) in

– Single bend to break

– Repeated bend to break

– Cold Ball Pull (CBP Testing)

– Charpy Impact & Surface Impact Testing

– Limited strain data

• Correlation of the results (if possible)

between tests

Bend to Break TestingBend to Break Testing

• Meadville to support Bend to Break testing

– Spherical bend to be used

– 3000-3500 uε/sec is the sweet spot to

minimize scatter in the results ...

• 1000 and lower introduces a different failure mode,

6000-7000 exhibits twice the scatter in the results ...

this is typical of behavior seen in a brittle material.

Spherical Bend Fixture

Key IssuesKey Issues

• Define the materials to be tested

– Compare filled vs. unfilled, FR4 – brominated and HF,

Selected High speed materials

– Look at “cap” technologies – such as Zeta

– Select “good” materials (HDPUG Pb-free Materials 1

and 2)

• Material suppliers need to supply the materials at no cost

– First Draft/Proposed Material List follows

• Define the required sample size

– 10? Single Bend to Break

– 20? Repeated Bend to Break

ComponentComponent

• Practical Components A-PBGA680-1.0mm-35mm-DC-LF-305

• PBGA 680 35x35mm Perimeter+ BGA, 1mm pitch

• 689 x 689 mil die size

• Quote of 1000 for $10,700.00

Test Vehicle DesignTest Vehicle Design

Topside of

board

shown.

Bottom side

of board is

identical

with a

footprint

change

Rough Proposed Rough Proposed StackupStackup –– To be refined To be refined

to specify exact glass stylesto specify exact glass styles

6 layer board - rough stackup

Prepreg - 106 or 2113 (Hi vs. Low Resin)- Cap for those specific constructions

Prepreg - 106 or 2113 (Hi vs. Low Resin)- Cap for those specific constructions

.093" over laminate

PrepregL4 1 ounce Cu Plane

LaminateL5 1/2 ounce Cu

L6 1/4 ounce Cu

L1 1/4 ounce Cu

L2 1/2 ounce Cu

LaminateL3 1 ounce Cu Plane

Test Vehicle (continued)Test Vehicle (continued)

Top - NSMDBottom – NSMD

except for corners as shown are SMD

• “Bend to break” of Cu trace feature• 3 mil traces off the corner pads

CBP Standard Coupon

16 mil

18 mil

15 mil

17 mil

14 mil

0.125” tooling holes1.75” apart

10 x 10 pad arrays on 1 mm centers

14 mil pad with 24 mil soldermask clearance

15 mil pad with 25 mil soldermask clearance

16 mil pad with 26 mil soldermask clearance 17 mil pad with 27 mil soldermask clearance

18 mil pad with 28 mil soldermask clearance

Charpy Impact Test

Surface Impact Test

Surface Impact Test (cont’d)

Proposed Panelization

16 mil

18 mil

15 mil

17 mil

14 mil

Surface Impact

Coupon

Cold Bump Pull

Coupon

CharpyImpact Test

Coupon

Charpy and Surface Impact Test Coupons will be free of all copper in the inner layers.

Repeated Bend to Break

• What was the correct limits ??

– current proposal for 2 levels 60% and 80% of

“single bend to break value” ??

• Select a small subset of materials (ie.

370HR and a higher modulus) material to

perform initial larger range of “repeated

bend to break” values to better establish

practical limits

Considerations for Pad Considerations for Pad CrateringCratering TestTest

• Materials

– Filled vs Unfilled Hi Tg Phenolic Resin

– Halogen Free

– Dicy

– Mid Tg

– High Speed

– Cap Layers

• Resin Content/Glass style effect on outer layers

– 106 vs. 2116 between L1-2 and N-N-1

• Pad Size

– Normal vs. enlarged solder mask defined pads,

PreliminaryPreliminary Material List (part 1) Material List (part 1)

• High Tg Filled Phenolic FR4s– Isola 370HR– EMC EM-827– Panasonic R1755V – Shenzen Pacific (PIC) FL-170 (Possibly replace with Hitachi MCL-E-75G)– ITEQ IT-180i– Panasonic R2125– Grace GA-170LE– Shengyi S1190

• High Tg Non-filled Phenolic FR4s– Isola 370 Turbo– Shengyi S1170– TUC TU-722

• High Tg Halogen Free FR4s– Grace GA-HF-17– ITEQ IT-170GRA – EMC EM-370(D) or EMC-370 (one but not both)– Panasonic R1577 (Megtron 2) – Shengyi S1165– Ventec VT-447– TUC TU-862HF– Hitachi MCL-HE-679G

PreliminaryPreliminary Material List (part 2) Material List (part 2)

• Mid-Tg FR4s

– ITEQ IT-158

– EMC EM-825

– Isola 254 - This a dicy FR4 -OK in low layer count Pb-free

• High Speed Materials

– Isola FR-408HR

– Panasonic Megtron 4

– TUC TU-872LK or SLK

– EMC EM-828

– MGC FL-700

– Panasonic Megtron 6

• Cap Materials (over Isola 370HR)

– Zeta

– Shengyi S1160F

– Hitachi KS-6600

– Hitachi CUTE

Proposed Process Flow

Impact Tests

DMA Test

Bend TestMonotonic or

Spherical Bend(Meadville)

Ship to Assembler

Precondition Bake 4hrs 120C

& Cool

PCB Fabrication

Precondition Bake 8hs 120C

& Cool

Procure Components

Ship to Assembler

Mark Lot Codes & SN

on PCBs

Kit PCBs, Components & Materials

Assemble & Test

Ship to Test Lab

Divide & Kit Test

Specimens

Precondition Bake 4hrs 120C

& Cool

DMA

Cold Bump Pull(Intel)

Charpy & Surface Impact

(Shengyi)

Modulus 25-200CGlass Transition

Variables at Fail

Document Post Impact Conditions

What this Project WILL NOT DO What this Project WILL NOT DO

(as currently planned)(as currently planned)

• It will not provide data that necessarily correlates to

pad cratering occurring by thermo-mechanical

stresses – such in reflow/cool-down as material

properties above Tg will be very different from those

at room temperature.

• If Charpy Impact correlates to pad cratering – can

possibly repeat on hot boards comparatively easily

(Phase 2 – using same boards built as same time in

this project?)

Where are we on this Project?Where are we on this Project?

• Need to resolve– Materials list/sample sizes

• Current funding for 500 parts only

• Either we increase the funding to get 1000 parts or decrease either

– Samples size per material

– Number of materials/options

• Need to finalize

– Stackup

– Material stackup options

– Material supplier commitments (to provide materials)

– Fabricators to build

Project MilestonesProject Milestones

• Define the full extent of the Project - Team

• Define the test vehicle – Team - complete– Component

– Board (layers, thickness, size, etc.)

• Design the Test Vehicle – ALU - complete

• Determine materials to test – Team – in progress

• Determine the required sample sizes - Team

• Material suppliers provide materials at no cost in return for rank ordering (coded)

• Fabricators to build the test vehicle – TBD - Multiple

• Procure components – Oracle +?

• Assemble Test vehicles – Celestica/Flextronics?

• Limited strain gauge testing - Celestica

• Bend testing- Meadville

• Cold Ball Pull testing – Intel

• Charpy & Surface Impact testing - Shengyi

• Data analysis and reporting