Hi Jack,
I just asked a similar question of our board vendor and this is the reply I
got.
"My sources tell me the material now common for via filling is a high solids
solder mask material slightly modified. The main difference in this material
and regular solder mask is the solids content and viscosity. These are
adjusted to better allow the mask to fill the holes to a greater depth than
standard mask. The material is also not tinted as solder mask sometimes is.
You will notice that most via filling material is transparent."
Susy
Susy Webb, CID
Sr PCB Designer
Carlo Gavazzi Computer Systens
281-875-1500 x33
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]]On Behalf Of Jack
C. Olson
Sent: Thursday, December 13, 2001 8:29 AM
To: [log in to unmask]
Subject: [DC] Plugged Vias
I need a quick verification here, hope someone can help...
I have always been under the impression that when a
drawing specifies "plugged vias", it means the holes
are filled (or at least partially filled) with an epoxy, the
epoxy is cured, and then the vias tented with solder-
mask. In the batch of boards we just recieved, I'm pretty
sure they just used the LPI soldermask to fill the holes,
and the fabrication vendor says "well, soldermask is
epoxy, so what's the difference". I'm not sure LPI glopped
into the holes is cured properly, and in my application the
board is maintaining a pressure seal, no air is supposed
to escape "through" the board, which is why I asked them
to plug the holes in the first place.
Can anyone enlighten me on this point? Is soldermask the
same epoxy as the epoxy used to fill holes? Or has it
always just been soldermask in the holes and I just didn't
know it?
thanks in advance,
Jack
p.s. If plugging really is a separate step, would it help to
supply a separate artwor that just has vias exposed so
they know what to plug? just curious, not a-retentive : )
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