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 difficulties in fully utilizing the advantages of these
processes. In this article, PCBasic will explain these concepts in detail,
helping you accurately and clearly specify your design requirements when
submitting PCB files for 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
Tenting
vias is one of the most popular and mature processes 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 main purpose of tenting
vias is insulation, so it is essential to ensure that the solder mask fully
covers the pad and is thick enough. This prevents solder from adhering to the
vias during surface-mount or through-hole component installation.
Note:
If
your design file is in PADS or Protel format, please carefully check whether
the through-holes for components are categorized as vias when requesting
tenting vias from PCBasic. If they are, the component through-holes will be
covered with solder mask, making them impossible to solder.
Plugged
Vias 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, resulting in a defect known as false copper exposure. Poor via
plugging can also negatively affect the appearance and quality of the PCB.
Vias
Not Covered
Vias
not covered, also known as vias with solder mask opening, is the opposite of
tenting vias—neither the via holes nor the pads are covered with solder mask.
This
process increases the heat dissipation area, which is beneficial for thermal
management. Therefore, if your PCB 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, this
process is also necessary.
However,
vias with solder mask opening have a potential risk of solder bridging and
short circuits, so design and manufacturing should be handled carefully.
