A via is a plated-through hole in a PCB that you can use to route a trace from your board’s surface layer to the inner and other layers. It is essential to realize that you can drill PCB vias mechanically, and you can plate them to create electrical connections.
Vias are vital in multi-layered boards, which are challenging to design and produce. They create routes for the sufficient flow of electrical and thermal current between the board’s different layers. In brief, vias are basically “channels” that vary in size and type.
Types of Vias
First of all, let’s look at the different types of vias that are used in the fabrication of a printed circuit board:
- Thru-hole: This is the standard via that is used on PCBs to provide a conductive path for signals going from one layer to another. These vias are mechanically drilled all the way through the board and can get down to 0.006 inches in size.
- Blind: A via that starts on an external layer but only goes partway through the board is known as a blind via.
- Buried: This via is similar to a blind via, but it will span only internal layers without any connection to the external layers of the board.
- Microvia: These vias are drilled with a laser instead of a mechanical drill which allows them to be smaller than 0.006 inches. A microvia only spans 2 layers, and its smaller size makes it a better fit for high-density PCB designs. Microvias can be stacked on top of each other, stacked on a buried via, or staggered depending on the needs of the design.
Vias are often enhanced later in the fabrication process in order to increase their thermal conductivity or to improve their assembly yields. These enhancements are known as tenting, plugging, or filling. Vias that aren’t enhanced like this can wick solder down into them, especially if they are being used in a pad. Tenting a via with solder mask is one option as long as the via isn’t used in a pad, but it also allows pressure to build up in the barrel of the via. This can potentially outgas during the soldering process and either break solder joints or spray solder causing shorts to nearby circuits. Plugging the vias with non-conductive materials is a better solution while filling the vias with conductive materials will give the best thermal performance although it is also the most expensive choice.
How to make PCB via?
Vias are plated along with the rest of the circuit board during its regular fabrication process. Micro-vias are different in that they are laser drilled and depending on which layers they are on, the process will vary. There are also different processes for blind and buried vias as well. But for standard thru-hole vias, the process can be summarized like this:
Vias are plated along with the rest of the circuit board during its regular fabrication process. Microvias are different in that they are laser drilled and depending on which layers they are on, the process will vary. There are also different processes for blind and buried vias as well. But for standard thru-hole vias, the process can be summarized like this:
Once the different board layers have been composited together, all of the thru-holes are drilled. This includes component pin holes, non-plated holes, and vias. The holes are cleaned of debris from the drilling operation. This can range from burrs on the edge of the holes, to resin residue inside the holes. A combination of abrasive mechanical and chemical processes is used for this.