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Date: | Wed, 27 Jan 2010 11:51:28 -0500 |
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I had a similar problem in a previous position building space rated product. The standard home plate design for no clean paste did not work. I had to modify it to take in account how much the solder paste squeezed out under the chip parts after SMT placement. In the case of the machine I was working with it was 5 mils. I move the apex of the home plate off the heel by 5 mils and it eliminated the small solder balls (similar to mid-chip solder balls) that would extrude under a low profile part and not coalesce back into the solder fillet.
Tom
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Rob Strecker
Sent: Wednesday, January 27, 2010 11:13 AM
To: [log in to unmask]
Subject: [TN] Solder Ball Under Chip Cap
We recently received a call from one of our customers that their boards are failing Hi-Pot test. They sent us a picture of a solder ball under one of the chip caps (package 1825). Apparently it's present on all 50 boards we built and always in the same place. We are using leaded paste for this build and the stencil we received was from the previous manufacture who could not fix the problem and went to hand soldering the part (info we got after the fact). I have inspected the stencil and it looks fine. The apertures are a 1:1, so the only thing I can think of is getting a reduction of some kind on the stencil. I will send the picture to Steve to get it posted.
Thanks,
Rob Strecker
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