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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