Hi Jack -
Via fill material can be one of the epoxy solder mask materials, however,
there are a number of much more efficient via fill compounds available,
generally with a higher solids content. I have generally used a drawing
note which allows the board fab house to use whichever compound their
processes are set up for, provided that it yields me a void free via fill
which is non-nutrient and can later be overcoated with solder mask (prior
to final finish, ie., tin/lead, "white tin",or whatever. Most of the major
circuit board chemistry/material suppliers have their own proprietary via
fill compounds. Their application and process requirements vary
sufficiently that it is best to allow the board supplier to utilize what he
is set up for.
There are also a number of metal filled via fill compounds, which offer
higher thermal conductivity. In general, the raw materials are more
expensive and the application somewhat more difficult. I have not
personally found these compounds to be justified in most applications,
unless the design is really marginal, thermally. The only method I have
found to justify their use is physical specimen testing.
Above all - avoid tented vias or solder filled vias. Both of these
approaches tend to change as a result of the assembly soldering processes,
giving an unpredictable end result.
Regards - Kelly
> [Original Message]
> From: Jack C. Olson <[log in to unmask]>
> To: <[log in to unmask]>
> Date: 12/13/01 8:29:28 AM
> 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 : )
>
>
----------------------------------------------------------------------------
-----
> DesignerCouncil Mail List provided as a free service by IPC using
LISTSERV 1.8d
> To unsubscribe, send a message to [log in to unmask] with following text in
> the BODY (NOT the subject field): SIGNOFF DesignerCouncil.
> To set a vacation stop for delivery of DesignerCouncil send: SET
DesignerCouncil NOMAIL
> Search previous postings at: www.ipc.org > On-Line Resources & Databases
> E-mail Archives
> Please visit IPC web site (http://www.ipc.org/html/forum.htm) for
additional
> information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700
ext.5315
>
----------------------------------------------------------------------------
-----
--- Kelly M. Schriver
--- [log in to unmask]
--- EarthLink: It's your Internet.
---------------------------------------------------------------------------------
DesignerCouncil Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF DesignerCouncil.
To set a vacation stop for delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------
|
