The vias are the holes in your printed circuit board that allow signals to transmit from one side of the board to the other or from one layer of the board to another. They are typically copper plated to allow conductivity through the via. Some PCB fabricators feel that these holes should be covered rather than left exposed. If the hole is closed entirely, this is called a filled via or mask plugged via, depending upon the method you use to close the hole. If the annual ring is merely covered over with solder mask, this is called tenting the via.
Why is tending via important to PCB manufacturing？
Tenting vias of a printed circuit board is a common practice to protect printed circuit boards. It is often preferred over mask plugging or epoxy filling because of cost. The most cost-effective form of via tenting is LPI, or liquid photoimageable solder mask tenting. If you’re very concerned about the tenting coming loose and exposing the annular ring, you may choose to use a somewhat more expensive resin filling.
The main goal of via tenting is to leave fewer exposed conductive pads on the surface of your printed circuit board. This should, in turn, mean fewer shorts brought about during solder bridging during assembly. Another benefit is a reduction of paste migration from SMT pads, which can occur when vias are drilled on standard BGA “dog-bone” patterns or when the vias are on the edges of SMT pads. Tenting will also help ensure that the via is less likely to be damaged by exposure to the elements.
Tenting is usually more effective with smaller vias (diameter of 12 mil or less), so if you have larger vias that you need to protect, you may want to consider some kind of fill to close the via instead. Filling your vias will not usually significantly affect conductivity as electrical travel through the copper plating is unimpeded.