Hi Graham, You wrote: >We are looking at an application using a ceramic BGA (429 balls, 1.27 mm >pitch), in a high reliability, harsh environment application (in a vehicle). >I have two questions: >1) on FR4, say an 8 layer board, will I need an underfill for this application? I am assuming that this BGA is about 1-inch-square; such a large ceramic component on FR-4 will give you inadequate fatigue life even in relatively benign environments, e.g. telecommunications. In automotive applications it is likely that not even solder columns are adequate. You can verify this with your design details with the analysis recommended in IPC-D-279. >2) the IC's manufacturer is using balls made of 46% Sn, 46% Pb, 8% Bi. > Why this alloy, and are there any precautions I should know building with >this? This alloy makes little sense in this application; commonly, high-melt alloys, such as 10/90 Sn/Pb, are used so that a maximum solder joint height is maintained--I do ot know what the Liquidus of this alloy is (it is likely h igher than eutectic Sn/Pb but much lower than 10/90 Sn/Pb). Werner Engelmaier Engelmaier Associates, L.C. Electronic Packaging, Interconnection and Reliability Consulting 7 Jasmine Run Ormond Beach, FL 32174 USA Phone: 904-437-8747, Fax: 904-437-8737 E-mail: [log in to unmask], Website: www.engelmaier.com ############################################################## TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c ############################################################## To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TECHNET <your full name> To unsubscribe: SIGNOFF TECHNET ############################################################## Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information. If you need assistance - contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ##############################################################