No...Sometimes solder will spread all over the pad with OSP...sometimes
not!  That's the peril of OSP.  If your customer wants better solder
spread, then they must either use an easier solder spreading surface
finish like ENIG, or use an easier spreading solder paste, like an
aggressive water soluble flux.

Something you can do as the fabricator to "help" the wetting is evaluate
different OSP formulations since not all OSP formulations are created
equal.  And/Or replace your pumice scrub with a micro-etch.  My
observations have been that the micro-etch generally provides easier
wetting compared to the pumice scrub, including when using ENIG as the
final finish.  Be advised the difference in spread is MINOR.

However, none of the suggested changes will ever guarantee the solder
will always cover the complete pad, but a solder colored surface finish
such as immersion silver generally fools the eye into thinking the whole
pad is soldered.  (ENIG accomplishes this by dissolving the gold and
exposing the nickel several tens of microns beyond the boundary of the
solder.)

Ryan Grant

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Baski Devre
Sent: Wednesday, April 06, 2005 7:59 AM
To: [log in to unmask]
Subject: [TN] incomplete wetting

Dear All

We have been shipping OSP covered PCBs to our customers.There is a
component
having 72 pads at 4 sides   dimensions of pads are 480X1500 microns the
distance between the pads are 500 microns. These pads are subjected to
cream
solder in customers production. As known that appertures on the stencils
are
produces smaller than the pads dimensions to release solder paste on the
pads. By considering these solder can not spread all over the pad during
soldering at customer side so pads have incomplete wetting apperance
because
appertures dimensions are smaller than pad dimensions. We have dispute
with
our customer about this issue. They want all the pad pitch to be
soldered.
So I want to learn about your comment on these incomplete wetting. Is it
always possible to solder all the pad in the customer side.



Yusuf GOMEC
Product Quality Engineer


BASKI DEVRE SAN. ve TIC. LTD. STI.
Ceyhan Sk. No:10 81490 Pendik-Istanbul-Turkey
Tel:0090 216 3901036(4 Line)/4836560(4 Line)
Fax:0090 216 3544941/4913269
Gsm:0090 533 6579897/7480014
Internet: www.baskidevre.com.tr

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