PCB Via Hole Process _ X-Parts Way

What is a via hole in a PCB?

A via hole is a PTH (Plated Through Hole) in a Printed Circuit Board which enables electrical interconnections between different layers of the PCB. Different from a pad hole for THT (Through Hole Technology Mounting), a via hole is not designed for mounting a component, it plays a crucial role of creating electrical connections and allowing the PCB designer to route traces and connect Electronic Components in a more space-saving manner. And it also helps with heat dissipation.

Since via holes are very important for PCBs, this article is going to talk more about Via Hole Process.

– What are the main via hole processes of PCBs?
– Benefits and drawbacks analysis on each type of via hole.
– How to define the via hole properties in your PCB Design?
– Key Takeaways & Summary

What are the main via hole processes of PCBs?

Via hole processes can be classified into these four types:

1. Via Opening
2. Via Tenting
3. Via Plugging
4. Via Filling (Conductive or Non-Conductive)

Benefits and Drawbacks Analysis on Each Type of Via Hole

Via Opening

Via Opening also means Via Soldermask Opening, it refers that the copper annular ring and barrel of a via hole is left exposed without soldermask covering.

The exposed via holes are conductive and solderable which can meet the specific requirements of the PCB designer or owner, such as test point measurements or special electronic components soldering or enhance heat dissipation.

Besides of the special intentions on making via holes opening, we usually don’t recommend it. Because the exposed via holes may create paths for solder paste seeping inside them, which will eventually cause short circuits. And there will also be chances for dusts and other contaminants getting into the holes. As time goes by, the exposed copper will corrode slowly. As a result, the electronic device will fail more quickly.

So please be cautious to choose via hole opening in your PCB design.

Tips:
If you need to make all or partial of the via holes as soldermask opening, please double confirm that you converted your Gerber Files correctly. Better to mention your requirements with your manufacturer prior to fabrication.

Via Opening Vs Via Tenting_X-Parts Way

Via Tenting

Via Tenting means covering the via holes with a soldermask layer, also called as LPI (Liquid Photo Imageable) ink. Via Tenting can usually cover the annular copper rings of the via holes completely, but it’s not able to ensure the inner barrels of via holes can be completely covered.

Via Tenting can be applied on single side or both sides of a PCB. It depends on different purposes and situations.

Benefits

– No extra cost involved.
– Protecting the via from the entry of solder paste, dusts and any other contaminants.
– It’s the simplest process for via protection.

Drawbacks

– Tenting is suggested to apply on small vias with a finished hole diameter of less than 0.3MM.
– Tenting is not able to perfectly avoid solder paste and other particles seeping inside of the holes.

Tips:
Please double confirm that you converted your Gerber Files correctly. We will do PCB Fabrication as per your Gerber Files unless special requirements provided.

Via Opening Vs Via Tenting Comparison_X-Parts Way

Via Plugging

Via Plugging usually means the via holes be plugged with LPI (Liquid Photo Imageable) ink.

Via Plugging is a supplement of Via Tenting, referring to cover and plug the via holes with solder resist ink completely.

Benefits

– Cost-effective compared to Via Filling (Conductive or Non-Conductive) process.
– Better performance on protecting vias from being contaminated or corroded by other particles (e.g. excessive solder paste, chemical contaminants and dusts etc.) than Via Tenting only.
– Simpler process compared to Via Filling process.

Drawbacks

– Plugging is suggested to apply on small vias with a finished hole diameter of less than 0.5MM.
– Not suitable for Via In Pad process.

Tips:
If you need to plug all or partial of the via holes with soldermask ink, please indicate it in your PCB Specifications during RFQ (Require For Quote) stage.

Via Plugging_X-Parts Way

Via Filling (Conductive or Non-Conductive)

Via Filling is a technique in which the PCB via hole is filled with a conductive (usually use copper) or non-conductive (usually use resin or epoxy) material.

Normally, any types of vias (e.g. through holes, microvias, blind vias and buries vias) can be filled according to different design purposes and manufacturing processes.

You need to consider the suitable type of Via Filling during design as it will impact PCB performance, costs and production lead time.

Via In Pad_X-Parts Way 1

A. Conductive Via Filling

Filled the via holes with conductive materials like copper or silver epoxy. It’s a good option for a PCB which carries with stronger signal transformation and higher current capacity. This PCB has via holes with soldermask opening on single side and / or has Via In Pad with soldermask opening on both sides.

Benefits

– Enhance electrical signal transformation and thermal conductivity.
– Help with heat dissipation.
– Improve the mechanical strength of vias and pads.
– Protecting the vias from contamination or corrosion.
– Avoid solder-wick issue.

Drawbacks

– More expensive than other via hole processes.
– Higher manufacturing complexity.
– Longer production lead time.

B. Non-Conductive Via Filling

Filled the via holes with non-conductive materials, mainly refers to resin or epoxy paste. The filled vias will also be planarized and metalized on their surfaces to achieve good solderability. It is usually used to provide structural support to a PCB with Via In Pad (with soldermask opening on both sides) and / or through holes with single side soldermask opening.

Benefits

– Protecting the vias from contamination or corrosion.
– Improve the mechanical strength and structural support to active pads (Via In Pad).
– Less expensive than conductive via filling.
– Lower manufacturing complexity.

Drawbacks

– It doesn’t improve electrical nor thermal conductivity.

Tips:
To fill or not to fill, to fill with conductive materials or non-conductive materials will quite depend on your design purposes, working conditions of your devices and budget.

Please always clearly mention the filling type (conductive or non-conductive); please pay attention that the CTE (Coefficient of Thermal Expansion) values of filling materials and dielectric materials should be equivalent to avoid stress fracture due to expansion; please specify plating thickness and Via-In-Pad specifications if any.

How to define the via hole properties in your PCB Design?

If you share PCB design files with your manufacturer, you can specify via hole process in PCB production specifications, because the via hole process can be modified. But if you are going to share Gerber Files, please make sure you convert your Gerber Files correctly, otherwise the via hole process might be mishandled.

Here we take Altium Designer as an example to explain how to set via properties in your design.

There are pre-placement settings and post-placement settings options for you to define via hole properties in your design.

Via Tenting Manual Setting_Altium Designer_1

Fig.1 Pre-Placement Settings

Rule – select to have the solder mask expansion for the via follow the defined value in the applicable Solder Mask Expansion design rule.

Via Tenting Manual Setting_Altium Designer_2

Fig.2 Post-Placement Settings

Manual – select to override the applicable design rule and specify the solder mask expansion value for the via.

If you don’t choose “Tented”, it means the via holes should be made as soldermask opening; on the contrary, the via holes should be made as tented.

Partial and full tenting of vias can be achieved by defining an appropriate value for Solder Mask Expansion.

By setting the expansion value to a suitable value in your Altium Designer, you can achieve the following:

To partially tent a via–covering the land area only, set the Expansion to a negative value that will close the mask right up to the via hole.

To completely tent a via–covering the land and hole, set the Expansion to a negative value equal to or greater than the via radius.

To tent all vias on a single layer, set the appropriate Expansion value and ensure that the scope (Full Query) of a Solder Mask Expansion rule targets all vias on the required layer.

To completely tent all vias in a design, in which varying via sizes are defined, set the Expansion to a negative value equal to or greater than the largest via radius. When tenting an individual via, options are available to follow the expansion defined in the applicable design rule or to override the rule and apply a specified expansion directly to the individual via in question.

Key Takeaways For Your Reference

PCB Via Hole Process Summary-X-Parts Way

We just talked about the main types and classifications of the via hole processes on Printed Circuit Boards. Covering vias can protect via holes from being contaminated and corroded in an easy and economic method. Filling vias can improve the electrical conductivity, mechanical strength and thermal dissipation of the PCBs. It’s best to choose the most suitable one based on your design, budget and via properties required.

It’s very important to find a capable manufacturer who has the capabilities and good experience on manufacturing circuit boards with different via types. Check more about PCB Design, PCB Fabrication and PCB Assembly with X-Parts Way.