| Has anyone had experience with placing BGA on gold plated boards. I thought I read a while ago there was a problem with embrittlment causing cracked joints. If anyone has experience with this your feedback would be great. | Mike
Mike, We and industry has put a stop to this phenomonon. Yes, gold is available as an alternative to HASL and OSP but in a new form as "flash" plated. Actually, it is not electroplated in the old sense where large amounts were depositied on solder surface areas. Now gold, and other metals, are electrolessly deposited in small amounts (thicknesses) so as not to negatively impact soldering, solderability, or solder joint acceptance or long term reliability. The problem used to be, as with gold traditionally, that, as in your wave solder pot, gold would "contaminate" the solder, and resulting joints, in large enough amounts to do the damage. Now, gold, and other metals, are depositied in thickness ranging from 3 to 7 milllionths of an inch - thus rendering a flat, solderable surface without the deleterious affects it once had. The problem is the relative newness of the technology (hence your question and that of many others). Therefore, there are but a few, but growing by demand, number of suppliers that know how to manage the processes. Part of the problem with flash is the netative interaction between processes associated with these very good finishes with solder masks. Again, this is a function of effective process management, or not. Another issues involves applying approximately 100 millionths of nickel to the copper surface to prevent copper leaching into and contaminating the gold. There are two ways to apply the "new" metal finishes. One is to place solder mask over an all gold board. The other is to use the immersion processes to "selectively plate" only the termination areas found after stripping the LPI solder mask away from those areas. Key suppliers now consist of the "top shops" like Hadco, Praegetzer, Multek, Collins, and a host of smaller shops jumping in as demand increases. These surface finishes are an excellent alternative most of us have been seeking. Hope this helps, Earl Moon (Guys, I just happened to see this one and had to respond as it's a big part of my new job).
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