It is the fact that it's always the 2nd last ball on the top outside row that I find interesting. Is there no damage to the adjacent corner ball, as this is often the first one to go in CTE differences/creep fatigue situations? Thinking aloud for possible causes: Is the substrate material used for the failing boards different from the other products on which the BGA is used? Is it of a substantially different thickness? Is the board reaching high temperature in use, or is it subjected to wide temperature varience? Is this product subjected to greater levels of vibration and/or flexing in the field than other products? Is there a feature on or in the board that is acting as a very good heatsink just under or close to the failing pin? If everything else is heating up and this ball isn't, it's relative lack of expansion might pull the joint apart at its weakest point. Is there an inherent weakness in the BGA design or manufacture at this particular ball position? Is there anything different about the attachment point of this ball in comparison with the others if this device? Have you microsectioned any of the failed boards? Is the form of the solder joint significantly different from the others - shape, size, cleanliness, grain structure, etc? Have you tried doing a peel test on a sample board that hasn't failed? Do you suffer from Poltergeists? Any combination of the above? I can't give you a definitive answer as to what causes the problem, but do you use any underfill material with your BGA's? If not, you could try using a urethane or epoxy underfill to support the solder joints - enough, maybe, to hold the thing together. There are thermally conductive types of which there are types that flow under the component and others that don't flow under the component. I suggest you use a type that flows under the component. Although it makes it more difficult to remove the BGA again later, its thermal conduction properties may serve to even out any differences in joint expansion and preserve the weak one. Hope something here inspires some better ideas for you. Regards Pete Duncan Asst Principal Engineer ST Aerospace Rudolph Yu <ylt@EARTHLIN To: [log in to unmask] K.NET> cc: Sent by: Subject: [TN] BGA crack- major headache TechNet <[log in to unmask] ORG> 03/29/01 12:48 AM Please respond to "TechNet E-Mail Forum."; Please respond to Rudolph Yu Here are the facts: PBGA-272 balls FR4 with HASL finishes 8 layers The failure point always happens at the same I/O which is the 2nd last ball of the top outmost row of the package. It is not located near the edge of the board or any breakaway point. Failure mode Micro fracture found near the intermetallic layer between the BGA package and the solder ball attached to it. Around 0.001% of the products we built failed in the field because of this. None of these were caught during the ICT or Functional test. The same ASIC is also used on several other Products and have never seen an issue like this. Somehow this failure mode with this ASIC only occurs in one particular product /design. The ASIC / fab lot-related , ICT pin interference, stress by the breakaway tab, and stencil cleanliness assumptions had already ruled out after a controlled lot was built few weeks back. All boards passed the tests. But now some boards started failing in the field. Why the crack always happen to one single location(ball) with the same product we built?? We have run out all the possibilities that we can think of. I hope all the experts in TechNet can share their opinions on this. Customer kept asking for the root cause analysis. Right now we just cannot came up with a reasonable one. Thanks Rudolph Yu --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 --------------------------------------------------------------------------------- --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------