PCB Design Guidelines-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.

Filling with Resin
The Via Holes are filled with a special plugging resin.
The 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.
Overview 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.