Thanks to everyone for their input.  I all plugged up over it.

Steve
Mass Design

----- Original Message -----
From: "Dwight Mattix" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, January 29, 2003 13:26
Subject: Re: [TN] Completely Plugging Vias.


> At 08:09 AM 1/28/2003 -0800, Macko, Joe @ IEC wrote:
> >Dwight,
> >
> >Great feedback.  Many of our new designs are locating vias in the solder
> >pads due to space limitations which are causing solder problems as you
would
> >expect.
> >
> >I read the PETERS tech data sheet for PP 2795-SD plugging paste.  Sounds
> >like it is formulated for plugging buried vias and does not address blind
or
> >through vias.  What has been your experience plugging blind vias in
solder
> >pads?
> >
>
> Works well as look as the fill is complete or nearly complete so that
> chemistry entrappment isn't a problem. Otherwise you can get problems with
> the final surface finish (e.g. ENIG) from process solutions being
entrapped
> and then leaching out to interfere with solderability (at worst) or stain
> (at best) the final surface finish.
>
> dw
>
>
> >joe
> >
> >-----Original Message-----
> >From: Dwight Mattix [mailto:[log in to unmask]]
> >Sent: Monday, January 27, 2003 1:58 PM
> >To: [log in to unmask]
> >Subject: Re: [TN] Completely Plugging Vias.
> >
> >
> >At 09:47 AM 1/27/2003 -0800, Jindra, Larry wrote:
> >
> >
> >
> >Dwight, et al-
> >
> >We're looking at plating over conductive filled via-in-pad for 1mm pitch
> >BGAs (small vias, thick boards).  How much trouble are we going to get
into?
> >
> >
> >
> >Keep the CTE match in mind.  It's the main issue...
> >Conductive pastes typically have a CTE around 75 ppm.
> >Non-conductive pastes are on the order of 25ppm and therefore more
closely
> >matched to the FR4/Cu combination.
> >
> >In general, it depends on how good a job your supplier does of filling
> >without entrapment of bubbles and curing the paste (gotta get the
volatiles
> >out).  Most of the conductive pastes we've encountered are ~3% volatiles
and
> >something like peanut butter in consistency so it's a nice trick getting
the
> >toothpaste back in the tube without entrapped bubbles. It can be done but
> >very ew North American fabs have the tools and a repeatable procedure for
> >via fill (high end Asian shops have via fill nailed).   You should be
> >alright if the paste is in individual holes with individual annular
rings.
> >Even better if the fill is not plated over. Plating over the fill
provides a
> >surface for the fill to act on in the Z axis.
> >
> >Most of the problems we've had have been when filling tight clusters of
> >gnd/thermal vias located all in the same pad or piece of foil; then
plated
> >over to make a planar, pretty finished surface.
> >
> >The surface plating acts like a head over a gang of expanding "pistons."
All
> >the Z axis force of the vias acting together sometimes lifts that pad
> >(usually a gnd slug under some high temp IC).  It's not it's an everyday
> >occurrence but frequent enough that it's not our preferred solution.
> >
> >The only real advantage I see to the conductive fill is that plating
> >adhesion has been better that for the non-conductive fills.  As a result
> >conductive fill has pretty much been relegated to the province of ATE DUT
> >cards that need a perfect planar (filled via) surface for their delicate
> >probes (IC test sockets).  Even so our suppliers are getting to the point
> >where plating adhesion over non-conductive fill is getting good enough
that
> >we'll probably get away from conductive fill all together.
> >
> >cheers,
> >Dwight
> >
> >
> >
> >
> >
> >
> >
> >Larry Jindra
> >Mfg Engr Group Lead
> >[log in to unmask]
> >
> >
> >-----Original Message-----
> >
> >From: Dwight Mattix [ mailto:[log in to unmask]
> ><mailto:[log in to unmask]> ]
> >
> >Sent: Friday, January 24, 2003 2:01 PM
> >
> >To: [log in to unmask]
> >
> >Subject: Re: [TN] Completely Plugging Vias.
> >
> >
> >
> >Consider using a 100% solids via fill material.  There's several good
ones
> >available.  Peters and Taiyo (HBI-200DB4/TA20DB4) probably have the best
and
> >MacuVia should be fine for this requirement as well.    Stay away from
the
> >conductive fills if possible (CB100 et al).
> >
> >dw
> >
> >
> >
> >At 09:54 AM 1/24/2003 -0500, you wrote:
> >
> >
> >
> >
> >
> >Greeting mighty TechNetters.
> >
> >
> >
> >Here's a common question, I think, but not common enough that I found it
in
> >a search.
> >
> >
> >
> >Scenario-Small PWB fab shop.  Customer wants vias (no larger than .016
inch)
> >plugged to prevent light, vacuum, you name it, from escaping through.
Must
> >be plugged from at least one side, and tented on the other.  We build it
on
> >an 16x18 panel, probably .063 finished thickness with 1/1 outers.  LPI
and
> >SMOBC ink are applied manually at this time. (squeegee, squeegee, bake
[or
> >tack])  We have not come up with a reliable process.  New equipment is
> >probably not an option yet, unless its like a bigger squeegee. (ha ha).
> >
> >
> >
> >Any assistance is appreciated.
> >
> >
> >
> >Steve MacDonald
> >
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