Via Filling


Via Filling is the process where the barrel of the Via Hole is filled with resin and is the only way to guaranteed the Via Holes are sealed.


To make it very clear for the manufacturer to correctly prepare the production data, it is recommended to define these Via Holes that need filling in a separate drill file.

Best to name this dril file: “Filled Vias”. Supply it in Gerber X3, X2plus, X2, X1 or in drill format.

Filling with Resin

The Via Holes are filled with a special plugging resin.

We use the  TAIYO THP-100 DX1 thermally curable permanent hole filling material.

This resin is applied using a dedicated machine the ITC THP 30.

There are additional process required for resin filling and these must be performed before the normal PCB production can begin.

In case of making multi layers the inner layers are produced and bonded together before the filling process.

Cross Section of Filled ViaOverview of the extra process steps:

  • 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 plugging with resin.
  • Baking: 150°C for 1.5 hours.
  • Brushing.

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, Via Holes filled with Resin will always results in a “Type VII – Filled and Capped” Via Holes as shown below.

Via Filled and Capped


The type Resin we use is suitable for Via-in-Pad application.

Technical Specifications

Filling with Resin
TOOLSIZE / ENDSIZE (mm)Min0.20 / 0.10
Max0.60 / 0.50
Material Thickness (mm)Min1.00
Outer Start Copper Thickness (µm)Min12
UL CertificationNo
IPC-4761 Via Protection typeVII – Filled and Capped
Via-in-Pad ApplicationYes
  • ONLY PTH holes can be filled (PTH hole = hole with copper pad on TOP and BOT side).
  • ONLY through hole vias can be filled, so Blind Via Holes can NOT be filled.

Important parameters are resin content, aspect ratio of the hole and the thickness of the core involved.

In compliance with the IPC-A-600 and IPC-6012 class 2, holes that require Via Filling must have a minimum of 60% of the hole volume filled.

Avoid Confusion

The IPC-4761 via protection type classification, clearly defines the difference between Filling and Plugging.


Via Filling


  Via Plugging Via Plugging

In our manufacturing processes we only use Filling as it has considerably more advantages than Plugging.

Page Update History

17/03/2020 – Changed – Minimum Start Copper for Via Filling with resin.

03/07/2020 – Via Filling with Soldermask discontinued July 2020

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