The process Brian alludes to in his last paragraph below was patented 7-8 years ago by a Japanese company - I think Hitachi, but am not sure now - they used perfectly flat Au surfaces and claimed greater reliability than conventional joining methods. The question really is: are they using it...., but if not why not? Mike Fenner ----- Original Message ----- From: Brian Ellis <[log in to unmask]> To: <[log in to unmask]> Sent: 04 January 2000 08:38 Subject: Re: [TN] Harsh Environments? Paul A 0,5 mm space below the 50 mm BGA is easy-peasy, lemon squeezy, given the right equipment, materials and sufficient time for the process. It's when the space gets down to less than 0,1 mm that I start worrying, such as LCCCs with a mass of flux residues underneath, for them to slowly exude onto the solder joints. I agree with you that "no-clean" is fine under the right conditions. But I challenge you to achieve long-term reliability in Anil's exterior climate (or in Darwin, nearer home for you) with an 800 or so pin-out micro-BGA on an HDIS circuit with a "no-clean" flux and voltage gradients well into the hundreds of V/mm. I have had personal experience of portable equipment (semi-professional digital video camera costing several thousand USD) failing during a one-off occasion in Indonesia because of the inconsiderate use of "no-clean" flux - and I was not pleased as I had travelled 200 km from Jakarta especially to film the event. Apparently, I was not alone, as this manufacturer is now cleaning his top-end equipment, although he is still using "no-clean" on his consumer camcorders (which, being smaller, with tighter boards, probably require cleaning, but that's another story!). For micro-BGA circuits and similar, I forecast that the days of soldering are approaching the end, partially because of this and especially because of lead-free soldering being imposed. I don't think conductive adhesives are the answer, either, especially anisotropic ones. The crystal ball I have interfaced into my computer tells me that we are going to see an upsurge of shrinking insulating epoxies which will pull the BGA into electrical contact and underfill it, at the same time: a very cheap and reliable method of interconnection with long-term reliability thrown in, provided the substrate and the component are perfectly clean at the outset. Brian Paul Klasek wrote: > Agree, Anil definitely speaks from experience, having here one fellow ex > TATA in Bombay, > the horror stories (perfect antistatic environment as the condensations runs > from tables) are real . > ........ ############################################################## 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 Gayatri Sardeshpande at [log in to unmask] or 847-509-9700 ext.5365 ##############################################################