Michael,

I don't think that the IPC task group has yet released a specification on
filled vias; the draft is in process.

We do not find any advantage for conductive fill for this application; the
non-conductive fills will cap and plate over as well as the conductives;
be a whole lot less expensive; and, since they are not as "thick", will
fill small, high aspect ratio holes "better" (better being less voiding).
Conductive is usually specified as less than 6:1 aspect ratio fill
capable, while non-conductives are 10 to 14:1 (depends on which brand and
who you ask).

We only specify 60% fill in our acceptance spec without going into
particulars about the largest size of any void and so forth.
We also specify that filled vias have the same plating thickness as
non-filled vias.

You will need to call out the filled vias as a separate hole size on your
chart and give them a separate D-code in the database so that they can be
extracted and worked on independent of all the other non-filled vias. We
have a simple note which says "See holes in hole schedule to be filled
with a (then we have 2 check boxes) conductive (or) non-conductive
material {the designer checks off the appropriate one}. Finished pad
planarity to be within +000/-.002" on outer layers. Filled holes to be
plated consistent with the surrounding surface finish."

We do not specify any particular brand or brands (maybe we should, but we
haven't tested them all).

I would also appreciate anyone else's feedback on our approach.

Valerie






Michael Bonek <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
07/26/2004 11:59 AM
Please respond to "TechNet E-Mail Forum."; Please respond to Michael Bonek


        To:     [log in to unmask]
        cc:
        Subject:        [TN] conductive via fill drill drawing note


We want to fill our via's in smd land with conductive material so the land
will be flat and no PPT will fall into the hole. I cannot find an IPC
specification that calls out a conductive via fill for a drill drawing
note. I know not to be too specific on the type of material to be used and
that I do want it planerized and followed with subsequent plating finish.
Is anybody aware of an IPC drill drawing specification or would like to
share how they specify this process on there drill drawing?

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