Pad Crater Project Definition Stage Joe Smetana Alcatel-Lucent For Member Meeting 2/9/2011 San Jose, CA
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. Spherical bend testing preferred or 4-point bend? Other 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 HPP testing for a correlation to actual pad cratering. How valuable is it? No support for this so far
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
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
Proposed Component
Rough Proposed Stackup 6 layer board - rough stackup L1 1/2 ounce Cu.093" over laminate Prepreg - 106 or 2113 (Hi vs. Low Resin)- Cap for those specific constructions L2 1/2 ounce Cu Laminate L3 1 ounce Cu Plane Prepreg L4 1 ounce Cu Plane Laminate L5 1/2 ounce Cu Prepreg - 106 or 2113 (Hi vs. Low Resin)- Cap for those specific constructions L6 1/2 ounce Cu
Design 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? 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 vs Dogbone 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) or EMC-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 someone has an idea of how to test this speak up! It is a critical issue.
Where are we on this Project? We have held a few preliminary meetings and some off-line discussions with key players Everything is currently draft and subject to change Delayed active pursuit of this project while we finished the Pb-free materials project Ready for regular meetings to resolve open issues and move forward
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 Hot Pin Pull testing (assuming we include this) Data analysis and reporting