Conductive fill

[jzsori]

Tom (or anyone)- do you have any experience with conductive fill on vias. We have experienced some problems with vias opening after the board was assembled and out in the field. Conductive fill was suggested as a possible solution to more reliable vias. The board is large (12X14) with approx 6000 vias. Via size is (sorry for inch base) 25 mil pad with 10 mil finished hole.

[Tom]

John,

There are a couple of ways to plug vias. One is LPI soldermask, but it is not conductive. Another method is Silver Epoxy by Dupont and it is conductive. Another method is "Via Overplate" where all other holes are temporarily masked and the via holes are plated closed. This is also conductive because the Overplate is copper. The manufacturer can create templates for these processes by using the drill data coordinates.

In my opinion, the better of the two conductive methods is Silver Epoxy. Silver is one of the least expensive exotic conductive metals and is soft enough that it doesn't become brittle and crack. Ask your manufacturer what process they use for via plugging because new techniques for solving this problem are quickly evolving. Also ask what you need to provide to the manufacturer to make their job easier.