Via Tenting, Plugging, and Filling

There are many reasons a printed circuit board designer might want to have a via tented, plugged or filled. First, let's start with defining these terms since they can be frequently misused and misunderstood.

Via Tenting
This is the easiest and least costly process—actually there is no added cost for this process. Simply remove the mask clearances from the vias you wish to have tented. Tenting a via simply means to cover the annular ring and via hole with solder mask. No special steps are taken to ensure the hole opening remains closed. Tenting a via will sometimes result in the hole remaining covered but it isn't guaranteed. Smaller diameter vias (12mil diameter or less) have the best chance of remaining closed. The main purpose for tenting shouldn't be to close the opening of a hole but rather, cover the annular ring to prevent exposure to the elements and reduce accidental shorting or contact with the circuit.

Mask (LPI) Plugged Vias (Non-Conductive Fill)
With a mask plugged via, (a.k.a. Mask Filled or Non-Conductive Filled via), specific measures are taken to ensure the via is plugged and sealed with mask and the annular ring is covered. A common application for this is on a BGA design where vias are commonly found in very close proximity to the BGA’s SMD pads. The concern is during assembly, solder will wick away from the intended pad and flow down the via creating poor or non-existent solder joints.

Via In Pad (Active Pad)
This process is becoming more and more common as BGA packages are becoming tighter. Rather than using the standard “dog bone” land pattern to transfer signal from the BGA footprint to a via that passes signal to other layers, vias can be drilled directly into the BGA footprint pads. This allows much simpler routing by soldering directly over the via. Make sure this process is called out in your fab notes.