Screaming Circuits: How to Fill a Via


How to Fill a Via

We here at Screaming Circuits keep telling people to fill and plate over vias in BGA pads. The same goes for small passives too, like 0402s and 0201s. As I closed in this post, best option is to fill and plate over. Bigger parts can use some of the solder mask techniques, but BGAs and tiny passives really do require filled and plated vias.

The question of the day, however, is: "Just how do I get those vias filled?" Here again is another place where our old Gerber file format falls a little short.

Filled vias 

Copper filled via on the left and conductive epoxy filled on the right.

There are quite a number of different methods for filling vias: Copper plugs, copper plate, surface material (i.e.  HASL), conductive epoxy, non-conductive epoxy. Maybe others. But, the Gerbers don't have a method for specifying this.

So here's what you do. 1) You need to contact your fab house to determine what techniques they have available and what they recommend for your fab project. 2) You have to create a set of fab drawings or special instructions that point out which vias need to be filled and with what material.

Duane Benson
Maybe raspberry jelly filling?

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Comments

Many thanks to Duane for his efforts over all of these years to educate us. After all, we all started out as Greenhorns.

"2) You have to create a set of fab drawings or special instructions that point out which vias need to be filled and with what material."

Any layout person worth their salt knows this. If you are encountering situations where via-in-pad is not specified to be filled, then you are dealing with a greenhorn that is not being trained properly.

Thanks. Perhaps a series of posts could be done regarding fab drawings - the good, the bad and the ugly.

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