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From: | |
Reply To: | TechNet E-Mail Forum. |
Date: | Wed, 28 Jan 1998 17:04:02 +0200 |
Content-Type: | text/plain |
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Hi All,
The pads of PBGA`s that we use are defined by solder mask on our
multilayer FR4 pcb`s
The diameter of stensil aperture is bigger than the pad diameter , so we
are actually printing
( no-clean ) paste on the soldermask.
Is this OK, or should it be avoided ? I presume that the adhesion between
stensil
aperture-paste is bigger than the other one between soldermask and paste,
resulting
to increased risk to solder balls, which could be fatal under PBGA ( pitch
.05" )
Stencil width is 0.15 mm ( 6 Mils ), laser cut
Stensil diameter .56 mm ( 0.22" )
Pad diameter 0.72 mm ( 0.28" ) max
Solder Mask diameter 0.52 mm ( 0.20" )
Any opinions?
Brs, Johannes
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