Hello,

Just wondering what current practices are working with respect to through
hole vias under BGA devices.
We have a PWA that has BGAs and is also wave soldered, so we are concerned
about the possibility of solder balls under the device.
Currently I am using solder mask encroachment (not tenting) with LPI mask
on all vias. Via holes are 0.012".
Also, am I worrying too much about the wave solder travelling up this size
hole?

I've seen suggestions of;

1) 100% plugging using multiple screening passes from the component side.
(looks like a good idea)
2) 'tenting' with LPI from the component side - (no cleaning problems under
the BGA, but voids on wave side.)
3) 'tenting' with LPI from the wave side - (void problem under BGA)
4) dry film solder mask with top and bottom tenting - (most shops use LPI,
film too thick etc.)

Of course, another solution is to use blind microvias for the BGAs, then
there are no through holes under the BGA, but we are a bit worried about
the increased cost.

Any comments or suggestions would be welcome.

thanks,

Phil.





Phil Dutton C.I.D.
Senior CAD Technician
IPC Certified Interconnect Designer
Vision Abell Pty Ltd
Second Avenue, Technology Park,
Mawson Lakes.  SOUTH AUSTRALIA  5095
===============================================================
Phone :         (08) 8300 4400 (reception)
Fax :           (08) 8349 7420
email:          [log in to unmask]
Internet Page:  http://www.vsl.com.au
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