Via Hole Filling – new advanced PCB technology options in our calculator

Updated 03 July 2020 – Via Filling with Soldermask discontinued due to Via Filling with Resin providing a overall better solution.

Completely closed via holes can only be guaranteed by using Via Filling.

We offer 2 solutions:

• Via Filling with soldermask (Discontinued July 2020)
• Via Filling with Resin

Via Filling with soldermask we provide already for many years. Via Filling with resin is NEW.

Last year we invested in the ITC THP 30 Hole Filling machine which allows us to fill holes with resin.  Now we can fill the vias with non-conductive material, the resin, and then cap them with copper to provide a solid conductive platform for the solder pad.

The biggest advantage of this process is that it offers designers the possibility of vias in pads without compromising the solder quality. We have seen more and more requirements for this solution as board designs become denser because of fine pitch components, thus prohibiting the use of common fan-out options, and of course the general miniaturisation of electronics in general.

Erwin Haertl, the president of ITC, wrote a nice article to motivate the value of the investment in Hole Filling technology and the use of his machine. You can find the story here or click on the image showing the ITC THP 30.

The resin product we use is TAIYO THP-100 DX1. It is described as a Thermally Cured Gap Filling Dielectric. Among other valuable properties, the low shrinkage is important for us.  The filling quality after final baking results in a proper underlay for planar capping. The resin can also be found under this UL-file.

Filling via’s with resin may have an advantage during the assembly process too, as it allows soldering on SMD pads located on top or very near to via holes filled with that technology. The cross section shows the result.

Via Filling with Resin

The vias to be filled are filled with a special hole plugging resin, TAIYO THP-100 DX1 a thermally curable permanent hole filling material, applied using a dedicated machine, ITC THP 30. The extra production steps needed for Resin Via Filling are performed before the 2-layer PCB production process. In case of making multi layers, this is after the pressing stage.

Overview of the extra processes:

• Drilling of only the vias that need plugging
• Cleaning: plasma and brushing
• Black Hole
• Apply dry resist
• Imaging of ONLY the via holes
• Via hole galvanization (PTH)
• Strip dry resist
• Brushing if needed
• Baking: 150°C for 1 hour
• Via Filling with resin
• Baking: 150°C for 1.5 hours
• Brushing

After these steps the normal PCB production process continues: drilling of the other PTH holes, and the normal outer layer production processes.

• ONLY PTH holes can have Via Filling (PTH hole = hole with copper pad on TOP and BOT side).
• ONLY through holes (top to bottom) can have Via Filling. Blind and Buried vias may be filled as a result of the prepress flow during the Bonding process.

Important parameters are resin content, aspect ratio of the hole and the thickness of the core involved.  A complete filling can’t be guaranteed.

Avoid naming confusion between Via Filling and Via Plugging

The IPC-4761 via protection type classification, clearly defines the difference between

Filling  and Plugging  .

In our manufacturing processes we only use Via Filling as it has considerable advantages over Via Plugging.

See our PCB Design Guidelines – Via Filling page for more detailed information.

Where can you find this new Via Filling option?

In the PCB calculator of STANDARD pool, under advanced options, you can find the technical options: Via Filling.

Default of the option is set to “No”. You may now change the selection to “Resin” for resin filled vias covered with copper.

How to make clear in your board data which holes need to be filled?

In your CAD software, in your job, you create an extra layer “Via Filling”. In this layer you include all holes that need to be filled. One layer is enough.

In PCB Visualizer you can check the result of your design actions and eventually change the functionality of some holes with the drill editor should you spot some anomalies.