1st off for the forum folk, I don't like the fact that the new system only let's you see the posting your replying too, I'd rather be able to see the thread.....
Anyhoo, why this alloy?, it's because it's the device manufacturers preferred and the customer has all the life testing data for it and non for std tin/lead ot tin/lead/silver.
Dave, like the idea's, similar to our train of thought, the problems with these are: 1. can't use hi melt as this crosses soem patent with IBM which would add to the cost.... we have get to component vendor to add copper stand off's for future buildss and reduce the heat spreader thickness to reduce the overall component weight. 2. shimming the corners, yep work's great when your doing rework but not when your doing an sizable SMT run...lot's of smudged paste...it's similar for the stainless stuff plus as is the PCB designers want there are lot's of 0603's arranged nicely around the 4 sides to limit any space you use to have to play with Glass spheres may be an idea, I actually have some of various sizes for some work we were doing calibrating xray equipment.... I liked the repair arrows idea, not that we have many of them around....the downside is that again we'd nbeed to put these in the middle of the BGA rather than the corners which mean's leaving them in, the arrows are paper and the adhesive is some what hydroscopic so where there's humidity issues for some countries these wouldn't go well.
it's looking like some glue dot's in the middle of the decice, we're gonna run some trials to figure out how much glue you need to sdeispence to get a cured glue dot of X height, on the fun of it all.....
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