Mike,

Stay with 2 mil off for 20mil stencil apertures.  Our 20 mil stencil
apertures have 3mil off for gold plated boards and we use 5 mil
stencil for all boards that have 20 mil QFP's.  We still have more
than enough solder for QFP pins.  If you change to 1 to 1,
definitely it causes more solder bridges and solder balls.  Just
one note, all reflowed solder joints have dull or gray-looking
appearance.  That's normal.  Gold diffuses into melting solder
causing dull or gray-looking solder joints.

regards
matthew
NII-Norsat International Inc.


>>> "McMonagle, Michael R." <[log in to unmask]>
August 21, 1998  2:17 pm >>>
Folks,
        We are converting an assembly from HASL to gold that has
large
quantities of 20mil devices. With HASL boards, we used a rule of
thumb
of 2mil off of aperture width on these parts, 1mil on each side.
Based
on the lack of pre-existing solder, should we go 1:1 on the gold
board
stencil apertures? One of our engineers is recommending this,
but I am
concerned about the possibility of bridging on 14mil wide pads.
Our
stencils are 6mil laser cut/electropolish. Any insights would be
appreciated....

Mike McMonagle
PCA Process Engineering Supervisor
K*Tec Electronics
1111 Gillingham Lane
Sugar Land, TX  77478
(281) 243-5639 Phone
(281) 243-5539 Fax
[log in to unmask]

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