In PCB design, the differences between tenting vias, plugged vias with solder mask, and vias not covered often cause confusion. Many designers easily mix them up, leading to an inability to fully leverage the advantages of these processes. In this article, we will discuss these concepts in detail, helping you to accurately and clearly specify your design requirements when submitting PCB files for final manufacturing.

What is a Via?

A via is a small hole in a printed circuit board (PCB) used to connect electrical traces between different layers. By establishing electrical connections between the layers of the board, vias enable signals to transmit between them. Since vias are not used for mounting component leads, their hole and pad diameters are typically smaller.

Tenting Vias

Undoubtedly, tenting vias is the most popular and mature process in PCB manufacturing. The "ink" in tenting vias refers to solder mask ink, and tenting vias means covering the via pad with this solder mask ink. The purpose of tenting vias is insulation, so it is essential to ensure that the ink fully covers the pad and is thick enough. This way, during the subsequent processes of surface mount and through-hole component installation, the solder will not adhere to the vias.

Note: If your file is in PADS or Protel format, be sure to carefully check whether the through-holes for components are categorized as vias when requesting tenting vias from the factory. If they are, the component through-holes will be covered with solder mask, making them impossible to solder.

Plugged Vas with Solder Mask

Plugged vias with solder mask involve using an aluminum sheet to fill the vias with solder mask ink during PCB production, followed by applying solder mask to the entire board. This ensures that all vias are completely opaque. The purpose of this process is to block the vias to prevent solder balls from getting trapped inside. Solder balls can melt at high temperatures and flow onto the pads, causing short circuits, especially under BGAs (Ball Grid Arrays).

If the vias are not properly filled with solder mask ink, the edges of the holes may appear red, leading to a defect known as "false copper exposure." Additionally, poorly executed via plugging can negatively affect the board's appearance.

Vias Not Covered

Vias not covered, also known as vias with solder mask opening, is a process opposite to tenting vias—neither the via holes nor the pads are covered with solder mask.

Vias with solder mask opening increase the heat dissipation area, which is beneficial for thermal management. Therefore, if your board has high thermal requirements, you can choose vias with solder mask opening. Additionally, if you need to use a multimeter to perform measurements on the vias, vias with solder mask opening are necessary. However, there is a risk with vias with solder mask opening, as they can easily lead to solder bridging and short circuits.