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

Joe Smetana

Alcatel-Lucent

Asia Meeting 5/18/2011

The issue(s)The issue(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 or 8 layers, thickness .093

• 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 preferred or 4-point bend?– Will need to include some amount of strain gage measurements– Both Single Bend to Break and Repeated Load to Break

• On the same boards ALSO perform Cold Ball Pull testing for a correlation to actual pad cratering.

– Intel will support this

• Other Possibilities– AE (Acoustic Emission) Testing – identifies actual onset of pad cratering (Anurag Bansal – Cisco)

• Challenges – need to understand test equipment/test and evaluation– Charpy Impact testing – Doug Sober taking lead on how to get this done. Bob Nevis (Microtek) will

support testing.• Suggested by Shengyi• Could correlate extent of impact damage to pad cratering propensity• Promising idea since may track with fracture toughness/pad cratering

– If it does – can readily also test this at higher temperatures (200C)

• Key question – how to design to QUANTIFY results

What this Project will ProvideWhat this Project will Provide

• Rank order of materials to Pad Cratering in mechanical bend testing– At selected strain rate

• 3000-3500 uε/sec (sweet spot)– At single bend to break– At repeated load to break

• 60-70%? (TBD) lowest single bend to break load

• Correlation or lack thereof of HPP testing to mechanical bend to break testing– Currently no support for this

• Correlation of AE to Electrical open?• Correlation of AE and/or Electrical open to

Charpy Impact test?

Bend to Break TestingBend to Break Testing

• Meadville to support Bend to Break testing– Need to better define this

– 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.

Simplified Bend to Break TestSimplified Bend to Break Test

This will not necessarily catch the first break point, but should correlate to it and should properly rank order the materials.

Key IssuesKey Issues• Define the test component

– 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

• 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/Design the Test Board (ALU/Meadville)• Define the required sample size

– 10? Single Bend to Break– 20? Repeated Bend to Break

Proposed ComponentProposed Component

Rough Proposed StackupRough Proposed Stackup

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

Prepreg L4 1 ounce Cu Plane

Laminate L5 1/ 2 ounce Cu

L6 1/ 2 ounce Cu

L1 1/ 2 ounce Cu

L2 1/ 2 ounce Cu

Laminate L3 1 ounce Cu Plane

Design RoughDesign Rough

Header for

event detector attach

BGA at 45 degrees to allow for either spherical or 4 point bend

Need the following specifics defined:• Minimum distance from component to board edges?•What type of header or board connector is needed the event detector?•Edge contacts?

BGA pattern duplicated on bottom side using either VIP or SMD pads for comparison

Considerations for Pad Cratering TestConsiderations for Pad Cratering Test

• 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, – Enlarged pads at corners– Microvia in Pad vs. No Microvia in pad (including Dogbone

Microvia vs Dogbone Through Via),– Conformal Microvia vs Filled Micro via Note - With a single

design can only do 1 of the options

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– ITEQ IT-180i– Panasonic R2125– Grace GA-170LE

• 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-872L or SLK – EMC EM-828 – MGC FL-700 – Panasonic Megtron 6 – Nelco Mercurywave 9350

• Cap Materials (over what material?)– Zeta– Shengyi S1160F – Hitachi KS-6600 – Hitachi CUTE

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/cooldown as material properties above Tg will be very different from those at room temperature.

• If Charpy Impact correlates to pad cratering – can 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– Board design related issues (slide 10)

• Meadville

– Can we do AE? (Cisco)• Impact on test location (Cisco or Meadville)

– Can we do Charpy Impact• Yes probably – who will do it?

• How to quantify the result (design input?)

– 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

Project MilestonesProject Milestones

• Define the full extent of the Project - Team• Define the test vehicle - Team

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

• Design the Test Vehicle - ALU• Determine materials to test - Team• 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• Procure components – Sun +?• Assemble Test vehicles – Celestica/Flextronics?• Bend to break testing- Meadville

– Include AE testing? (Cisco?)

• Hot Pin Pull testing (assuming we include this)• Charpy Impact?• Data analysis and reporting