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Subject:	Re: MiniBGA pad conflicts
From:	"Stephen R. Gregory" <[log in to unmask]>
Reply To:	TechNet E-Mail Forum.
Date:	Wed, 2 Feb 2000 13:55:44 EST
Content-Type:	text/plain
Parts/Attachments:	text/plain (45 lines)

In a message dated 02/02/2000 12:35:26 PM Central Standard Time,
[log in to unmask] writes:

<< I'm a little confused.  J-STD-013 recommends 22 mil pads for 1.00mm pitch
 BGAs, but the guideline for IPC7527 suggests 15 mil round pads with a square
 paste opening.  Is anyone out there having good luck with one or the other?
 Why the large disparity?

 Thanks-

 > Larry Jindra
 > TRW/Avionics Systems Division
 > mailto:[log in to unmask]   ph (858) 592-3424   fax (858) 592-3606 >>

Hi Larry!

I just finished building a prototype board yesterday that had a 256-ball
microBGA that had .020" pads, and I had my stencil apertures made into .020"
squares my stencil was 4-mils thick, and I had all the other larger apertures
left at 1-to-1 (I usually get a 20% reduction) to make-up for the loss of
volume that the 4-mil stencil is giving me. Worked great! The square aperture
will release the paste easier than a round pad that small, and it'll give ya'
a little bit of "slop factor" for placement too...as long as the balls are in
the paste, the part will self-center during reflow. I will say that the
fillets on some of my larger ceramic chip caps (1812's) were a tad bit shy
with the 4-mil stencil (least my inspectors didn't like them) but everything
else looked okay. Maybe next time I'll go up a mil to a 5-mil stencil and
make em' look better...

-Steve Gregory-

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