Castellation PCB is a processing technology in PCB manufacturing.
What’s castellation PCB? When daughter circuit board need to be welded on mother circuit board,The electrically connected is not good if use round hole welded daughter circuit board to mother circuit board , because the hole size is large and cold welding questions.So there is castellation hole, castellation hole of the printed circuit board edge has the same hole conduction function, but also can make use castellation holes welded and fixed, the surface pad of mother circuit board can be directly welded with castellation hole.
Traditional castellation hole process:
Drilling—> Chemical copper—>Panel plating—>Image transfer—>Pattern plating—>Striping film—>Etching—>Solder mask printing—>Surface finishing—>Castellation hole and outline milling
The castellation hole is formed after round hole drilling, and the phenomenon is easy occur that the copper residue and copper skin twist in the castellation hole, which affects the function of the castellation hole, and leads to the decrease of the performance and yield of the product.
In order to avoid the above-mentioned defects, the following castellation hole process steps shall be carried out:
- Drilling in the substrate plate edge, drilling plate side hole.
- Plating through hole to form a layer of copper on the hole wall of the plate edge hole.
- Outer layer image—>exposing—>developing—> second copper plating—>Tin plating(make the hole wall covered by an anti-corrosion tin layer).
- The castellation holes milling
- Remove the anti plating film.
- Etching the substrate to remove the exposed copper on the outer surface of the substrate.
- Peeling tin of the substrate, remove the tin of castellation holes, expose the copper of castellation holes.
After twice copper plating and tin plating on the substrate, castellation holes perfect avoided copper residue and copper skin twist phenomenon and completely connected with copper as the adhesion force is large.
After castellation hole forming is finished, the film is then etched, and no copper surface oxidation occurs, so as to effectively avoid the occurrence of residual copper or even short circuit. This kind of difficult technology improved the conformance rate of the printed circuit board for small batch urgent PCB.