Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


BGA/Fine pitch footprints


Loz

#27444

BGA/Fine pitch footprints | 2 March, 2004

Hi all, we have recently seen a design that consists off a QFP100, pitch at 25". Also in the centre of this footprint is a FBGA165 footprint, pad size .4mm @ 1mm pitch. We have been informed that we will fit the QFP. I want to remove the BGA pads from the stencil as they are not required. However one of my colleagues, suggest that they remain in situe, and we place the QFP100 over the top, leaving the paste in place. If left in place I can see all sorts of problems occuring, hence my reasoning to remove them. Any advice appreciated.

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RDR

#27445

BGA/Fine pitch footprints | 2 March, 2004

I have done this before, We print with a 5-6mil stencil and have had no problems with any underneath solder. If you are still nervous instead of removing from stencil use some 3 mil kapton tape or equivelant and tape off the BGA pads. This way they are still there if you need them. This shouldn't promote bridging on a 25 mil pitch device.

Russ

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#27495

BGA/Fine pitch footprints | 4 March, 2004

Print paste in the holes you don't plan to use and let it dry. That way you don't affect your paste volume in other apertures.

The bad news: When you don't want paste to dry and close your apertures, it will do it. When you want paste to dry and close your aperatures, it will crack and fall-out.

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