Completely closed via holes can only be guaranteed by using Via Filling.
We can produce 2 types of Via Filling:
- Via Filling with Resin
- Via Filling with soldermask.
Via Filling with Resin
The vias to be filled are filled with a special hole plugging resin, TAIYO THP-100 DX1 thermally curable permanent hole filling material, 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 pressing.
Overview of the extra processes:
- Drilling of only the vias that need filling
- 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 plugging with resin
- Baking: 150°C for 1.5 hours
- Brushing
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After these steps the normal PCB production process starts or continues: drilling of the other PTH holes, and the normal outer layer production processes.
Using the IPC-4761 via protection type classification, this Via Filling type with Resin process ALWAYS results in a “Type VII – Filled and Capped” via.
Note: This Via Filling with Resin type is suitable for Via-in-Pad application.
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Via Filling with Soldermask
The vias to be filled are filled using soldermask ink as hole-filler substance. This Via Filling technology uses a drilled ALU sheet to push normal soldermask ink in the via holes to the filled. This is a screen-printing process. This is a step before the normal soldermask process.
Important:
- The filling is always done from the top side of the board
- Vias filled with soldermask always get a reverse soldermask pad added with size via-toolsize+0.10mm.
In other words, this Via Filling type will always be covered with soldermask on top and bottom.
Using the IPC-4761 via protection type classification, this Via Filling type with Soldermask process ALWAYS results in a “Type VIb – Filled and Covered” via.
Note: This Via Filling with Soldermask type is NOT suitable for Via-in-Pad application.
Technical specifications
| Via Filling with Resin | Via Filling with Soldermask | ||
| ToolSize / EndSize (mm) | Min | 0.20 / 0.10 | 0.20 / 0.10 |
| Max | 0.60 / 0.50 | 0.60 / 0.50 | |
| Material Thickness (mm) | Min | 1.00 | 0.50 |
| Max | 2.40 | 3.20 | |
| Outer StartCopper Thickness (µm) | Min | 18 | NA |
| Max | NA | NA | |
| UL certification | No | Yes | |
| IPC-4761 via protection type | VII – Filled and Capped | VIb – Filled and Covered | |
| Via-in-Pad application | Yes | No |
- ONLY PTH holes can have Via Filling (PTH hole = hole with copper pad on TOP and BOT side).
- ONLY through hole vias can have Via Filling, so Blind vias can NOT have Via Filling.
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.
Below is a short video explaining the Via Filling process.
Eurocircuits Insight Technology – Via Hole Filling with resin from Eurocircuits on Vimeo.
