Small to Medium Batch PCB Fab & PCBA Service

Drill / Through Plating

The PCB Drilling process is a very important process to drill holes on the copper clad PC Board. These holes are mainly used to provide Electrical connection and/or fixing and positioning of various components.

Holes are divided into mainly these types based on their function / usage :

  1. Pad holes (these are generally used for component placement and fixation),
  2. Via holes (these are used to establish electrical connection between traces on multiple layers.
  3. Guidance, Fixation, Screw Holes

drill holes

Pad Holes: These are copper pads with a hole in their (usually) center. The hole size or diameter is slightly bigger than the leg of the part that has to pass through them, and the size of the copper pad surrounding the hole is bigger than the hole diameter. These holes and their pads are generally defined as part of the component in a footprint library (in the CAD design software for PCB). Thus these are for Through-Hole (THT) components that will require wave soldering.

Pad holes can also have electrical conductivity between different layers, by process of Electroplating and metalization (PTH).

Via Holes: Vias are basically similar to Pads, but smaller in diameter, and their sole purpose is to provide electrical connection between traces on different layers. Since they do not need to have a component leg pas through them for fixation, they can be and usually are much smaller than a Pad hole. Vias are almost always metalized to provide electrical connection to other layers.

There are few types of Vias :

  1. Through Via : this via is a standard via, that goes through the top surface of the PCB to the bottom surface of the PCB, passing any and all layers In the middle.
  2. Blind Vias : This type of Via goes from any of the Top or Bottom surface of PCB to any of the inner layers, BUT not the other outer layer. So for example, Blind vias extend from top surface to any of the inner layers -OR-  from the Bottom surface of the PCB to any of the inner layers.
  3. Burried Via : These vias only connect inner layers of a PCB to themselves. And since they are inside the top surface and bottom surface of eh PCB, they can not be seen from the outside, hence their name Burried Vias.

Guidance / Fixation / Screw Holes : These holes are used for Guiding pin insertion (during manufacturing), OR for Fixation of some pins for particular parts, OR for SCREWs on a PCB to fix it to an enclosure.

These holes generally do not have Electrical connections and thus are Non-Electroplated through holes (NPTH).

PCB Board Drilling Process

The drilling process varies slightly for Double side boards and Multi-layer boards.

Double-side PCB drilling process
Multi-Layer PCB Drilling Process

PCB Board Common Drilling Issues and Solutions

  • It is important to give us a Drill table, also called a Hole Schedule In the manufacturing industry. This table lists all the different types of holes on the PCB, their drill diameter, and whether they are Electroplated through holes (PTH) -OR-  Non electroplated through holes (NPTH).

  • In case of Multi-layer board, especially where Blind and/or buried vias are used, sometimes holes on different layers will overlap, one on top of the other. It is a recommended best practice to not have them overlap.
  • As per our process, we suggest using the following guidelines for Holes :
  1. Hole diameter tolerance : PTH = ±076mm, NPTH = ±0.05mm
  2. Through-hole copper thickness: minimum 18um, average 20um.
  3. Solder mask thickness: 10 ~ 50 um, minimum 5um on trace corner,
  4. Bow and Twist:≤75%,
  • Vias have generally Three covering options :

Usually, Vias are Open, Tented or Plugged. Open Vias are normally visible (if on the surface of PCB). Tented vias are those that have a Cover ink on them. This ensures that their copper pads are not exposed to avoid any shorts. Plugged vias are those that have their holes filled with Plugging resin.

  1. Cover Ink (for tenting vias),
  2. Insert Resin (for Plugging vias),
  3. Via hole with Window opening.

If there is no special requirement, we generally produce with cover ink. For holes that are used under BGAs for fanout, we generally plug them as well, using Insert Resin process.

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