Achieve via protection with the surface finish (HASL in this case). Leave
the barrel of the vias open (relieved of soldermask.)
thanks,
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Bush, Jeffrey D. (US
SSA)
Sent: Wednesday, June 17, 2009 9:36 AM
To: [log in to unmask]
Subject: Re: [TN] SolderMask Question
If you do a LPI via plug prior to the final LPI coat, the thickness will
be more uniform and provide DWV. The DF via feature cap is a legacy
attempt to insulate vias that I recall testing at AT&T MMV in the 80's.
You can also try a post LPI coat via cap with LPI, which does insulate
but also creates a higher profile. We have also used a thicker LPI
coating which has better uniformity, lower cost and provides good
coverage. Much is process/equipment dependent.
Jeffrey Bush
Sr. Principle Product Assurance Engineer
Space Systems and Electronics - Performance Excellence
BAE SYSTEMS
P.O. Box 868, MER24-116A
Nashua, NH 03061-0868
Facility: 144 DW Highway
Merrimack, NH 03054
Office +1 603.885.8137
Mobile +1 603.318.8056
Fax +1 603.885.5258
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Vargas, Stephen M
Sent: Wednesday, June 17, 2009 12:22 PM
To: [log in to unmask]
Subject: [TN] SolderMask Question
All:
We have a Class III PCB, that we are building using leaded technology
(non-RoHS), HASL finish, where my customer is specifying double masking
over vias for "via protection". Dry film is initially being placed over
the vias only, then the board is covered by LPI. Our problem is that it
creates problems with the solder stencil not properly gasketing to the
PCB during screen-printing resulting in solder defects. We are seeing
raised solder mask as high as .003". Is this (double masking)
commonplace? Are there more "manufacturing friendly" options for optimum
via protection? I've asked about possibly using dry film mask only (no
LPI on top), but was told that the mask feature sizes are too small for
dry film. Any insight would be appreciated.
Regards,
Steve Vargas
Polaris Contract Mfg Inc
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