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Re: BGA Assembly



John,
thanks!

>What I can tell you is that there should be no need for any
>form of limiting feet, etc. The surface tension of solder
>balls on BGAs is sufficient to provide self centreing during
>reflow.

Are you sure this would be the case also with the holes I have
under each ball? I suspect it would be OK, but this was (is)
my first board with BGAs and on top of this there is no room
for errors... so I put the feet just to make sure I would not
end up with a flat block of solder :-).

>Your problem (below) sounds very much like a lack of flux.

No, there was plenty of it. And the BGAs did not float in it
because it did run through the holes. They did not solder well
also the second time because the feet I had put were a bit too high
(because of remnants of the glue, I suppose).

I am pretty sure I'll solder the second board free of problems, yet
I need the first one working as well.

I suppose I'll go on with the feet for another while, because I noticed
that through those holes, which have a pad for a decoupling capacitor
at the opposite board side, more solder from the ball had flown just
wetting the metal area; and having all the solder of such a ball
run through the hole and destroy the connection (quite
unlikely, I guess) is a mess I don't even want to think of :-).

Please advise (or speculate) on the above. I will be also very
grateful if you have some other advice on that topic.

Dimiter

-----------------------------------------------------------------------
Dimiter Popoff
Transgalactic Instruments, Gourko Str. 25 b, 1000 Sofia, Bulgaria
http://transgalactic.freeyellow.com
Email: tgi@bulnet.bg, tgi_earth@yahoo.com
Phone: 00359/2/9923340, 00359/2/9805997, Fax: 00359/2/9540384