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Pad Crater Project “Definition Stage”. Joe Smetana Alcatel-Lucent Asia Meeting 5/18/2011. 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
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Pad Crater Project“Definition Stage” Joe Smetana Alcatel-Lucent Asia Meeting 5/18/2011
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 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 (AnuragBansal – 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 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 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 Test This will not necessarily catch the first break point, but should correlate to it and should properly rank order the materials.
Key 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
Design Rough • 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? Header for event detector attach BGA at 45 degrees to allow for either spherical or 4 point bend BGA pattern duplicated on bottom side using either VIP or SMD pads for comparison
Considerations 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 vsDogbone Through Via), • Conformal Microvia vs Filled Micro via Note - With a single design can only do 1 of the options
Preliminary 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) orEMC-370 (one but not both) • Panasonic R1577 (Megtron 2) • Shengyi S1165 • Ventec VT-447 • TUC TU-862HF • Hitachi MCL-HE-679G
Preliminary 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 (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? • 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 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