Ah Dave, so glad you asked that question. Started doing work with plastic BGA's in the beautiful summer of 95. Did some of the first IBM ceramic types about a year earlier. Had much fun with both. At Amdahl, and another not mentionable company, had the best of everything except tools to place BGA's. This did not stop us from doing some serious, at the time, soldering experiments using both home made table top diffused IR cookers and the newest model, at the time, convection IR ovens. Solder paste was a bit different then and we developed some for internal use as required. My first thoughts were using micro vias, of a type I developed in the early 80,s, in Kapton as a compliant layer on top of the rigid MLB substrate. Used paste first but didn't like the voiding found using transmissive x-ray equipment. Attributed most of it to outgassing from the vias. This, as most know, wasn't the only contributing factor. Reliability issues arose so I did some HALT/HAST testing to determine cycles to failure. Mostly turned out to be no big deal but created an internal specification limiting acceptable voiding to 20% maximum. Did other work without solder paste. Instead, used flux paste and determined, that with eutectic balls, no apparent voiding. Liked the idea for no particularly good reason. Re visited the HALT/HAST testing and found no significant difference between soldering with or without solder paste. This meant finding the difference in solder volume was not a factor either. However, coplanarity raised its ugly head occassionaly so I went back to solder paste as a preferred process to overcome the issue. Later, with ceramic device types becoming available, I went back to flux only and most in the unmentionable company liked the results. The big problem, of course, you can't use flux only in production for obvious reasons. I believe Phil Zarrow had some comments and similar thoughts on this issue as well. However, during rework operations, I never used solder paste when the option is available. One advantage here is seldom ever do shorting problems occur with no added solder paste and, again, even with less solder volume in the joints, no negative reliability issues are apparent. Some other companies I've worked with (HP, Celestica, and others) also have found this to be true. One example at HP concerned their inability to effect good solder joints, on some perimeter BGA's (super BGA's) on a particularl high density MLB. I introduced my idea, though they had been kicking it around for a time, both in production and rework operations. Problems were solved and no reliability issues or field return problems were encountered. There's so much more, but as Phil Z said they ain't no big deal. Having said that all, I'm now getting involved in some aerospace applications, again, requiring COTS parts as plastic BGA's. The wheel just keeps on turning as what goes around - yada yada. Who's willing to share their high rel plastic stories? Anything new and exciting but for coplanarity, moisture sensitivity, or? Earl Moon --------------------------------------------------------------------------------- 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 ---------------------------------------------------------------------------------