Bob, Do I understand that you want to use an underfill style material to help heat flow away from BGA's which are running hot during operation? Should be ok (in theory) there are a wide range of underfill materials available, and the usuall suppliers should be able to help you with data sheets and samples (Emmerson and Cummins, Alpha, Dexter, Loctite etc) The thing to be aware of is that these "traditional" underfills are designed to be used with flip chips, and in small volumes, you are proposing underfilling three BGA per board, and that could be potentially expensive, so expensive it may be prohibative Loctite were working on an underfill specifically for CBGA, and that mey help, or be more cost effective. I suppose the other potential advantage could be an improved reliability, the epoxy should be sharing the strains with the solder balls, similar to flip chip designs, and this could give an improved lifetime. On the downside, if the BGA is running real hot, then the underfill will need a high Tg to minimise thermal mismatch during service, and stop an accelerated failure of the balls. In order to get this, you may need a pretty high cure schedule, which could exceed the Tg of your FR4, and give problems elsewhere. I guess the way round that would be spec a high Tg board (160C+) but that will cost!! In terms of processing, I would assume its much the same as a flip chip, attach the part, possible clean depending on which flux technology is being used, and underfill. (this will take longer than a flip chip, and a multi pass dispense may be needed to ensure 100% coverage under the BGA) Scanning Accoustic Microscopy, or possibly Xray could be used to check the underfill flow. One major point to consider is the need for rework. I know we shouldnt mention it, but we all need to rework something, some time for some reason, and if its gunked up with epoxy, "you is gunna have a problem" there are reworkable underfills available, but they can need a two stage cure, with rework being carried out before the final cure, again suppliers should be able to help with that aspect. All in all, if there is a real need to underfill a BGA try it out, but beware, the potential cost is high, in terms of additional process routes, equipment and also material cost. If you want to talk more, contact me anyway you can. Roger [log in to unmask] tel +44 1462 831125 fax +44 1462 831336 ______________________________ Reply Separator _________________________________ Subject: [TN] Underfill, BGA??? Author: "TechNet E-Mail Forum." <[log in to unmask]> at #email Date: 01/07/99 14:12 Hi all.. Have a question relating to cooling a HOT 225-ball BGA. I tried to look in the archieves, but my search technique must be lacking or I am using the wrong "words". Can I use an "underfill" to help cool a hot BGA or is that the wrong term? I am considering using a thermally conductive, electrically insulating material under the part (3parts/assy), but have no hands-on experience with "what material, how do I apply it and what are the related war stories". Any help out there in TechNet land???? Thanks in advance, have a great day and a super/safe 4th holiday!!!!!!!!! Regards, Bob Vanech Bob Mango Computers Norwalk, Ct. (203) 857-4008 x 108