Via Filling

Introduction

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

Types of Via Filling

We offer 2 solutions:

  • With Resin.
  • With Soldermask.

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

IMPORTANT

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

Filling with Soldermask

The Via holes are filled using Soldermask ink.

The filling technique uses a drilled ALU sheet to push normal Soldermask ink in the via holes that are to be filled.

This is a similar to a screen printing process and is performed before the Soldermask is applied to the boards.

Via filled with SoldermaskVia filled with Soldermask

IMPORTANT
  • The filling is always done from the top side of the PCB.
  • Vias Holes with Soldermask will always have a reverse Soldermask pad added with a size of via size-toolsize+0.10mm.

Via Hole filled using Soldermask will always be covered with Soldermask on top and bottom of the PCB.

Using the IPC-4761 via protection type classification,  Via Holes filled type with Soldermask will ALWAYS results in a “Type VIb – Filled and Covered” Via Holes.

Via Holes filled with Soldermask are NOT suitable for Via-in-Pad application.

Technical Specifications

Filling with Resin
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 Start Copper 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 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.

A complete filling cannot be guaranteed.

Avoid Confusion

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

Filling

Via Filling

Plugging

  Via Plugging Via Plugging

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