What is metallized castellated hole PCB

With the rapid development of electronic products, miniaturization of high-density and multi-function has become the development direction. Components on printed circuit boards are increasing geometrically while board sizes are shrinking, often requiring small carrier boards.

What is metallized castellated holePCB

The definition of metallized castellated hole is that the first hole is drilled and then drilled, and the shape process is completed. Finally, half of the metallized hole (groove) is reserved. Simply put, half of the metallized hole on the edge of the board is cut. In the PCB industry, it is also called a stamp hole. It can directly weld the edge of the hole to the main edge, which can save connectors and space. It usually appears in signal circuits.

If the round hole of the small carrier board is soldered to the mother circuit board with solder, due to the large size of the round hole, there is a problem of virtual soldering, which makes the child and mother printed circuit boards unable to be electrically connected well, so a metallized semi-conductive circuit board appears. Orifice PCB. Metallized half-hole board PCB features: the individual is relatively small, and there is a whole row of metallized half-holes on the side of the unit. soldered together.

Castellated hole PCB process

1. Process the half-side hole with double V-shaped cutting tool.

2. The second drill adds guide holes on the side of the hole, removes the copper skin in advance, reduces burrs, and uses groove cutters instead of drills to optimize the speed and drop speed.

3. Immerse copper to electroplate the substrate, so that a layer of copper is electroplated on the hole wall of the round hole on the edge of the board.

4. Production of the outer layer circuit After lamination, exposure, and development of the substrate in sequence, the substrate is subjected to secondary copper plating and tin plating, so that the copper layer on the hole wall of the round hole on the edge of the board is thickened and the copper layer is covered with covered by a tin layer for corrosion resistance;

5. Half-hole forming Cut the round hole on the edge of the board in half to form a half-hole;

6. In the step of removing the film, the anti-electroplating film pressed during the film pressing process is removed;

7. Etching The substrate is etched, and the exposed copper on the outer layer of the substrate is removed by etching;

8. Tin stripping The substrate is stripped of tin, so that the tin on the half-hole wall can be removed, and the copper layer on the half-hole wall is exposed.

9.After forming, use red tape to stick the unit boards together, and remove the burrs through the alkaline etching line

10. After secondary copper plating and tin plating on the substrate, the round hole on the edge of the board is cut in half to form a Castellated hole, because the copper layer on the hole wall is covered with a tin layer, and the copper layer on the hole wall is completely intact with the copper on the outer layer of the substrate Connection, involving strong bonding force, can effectively prevent the copper layer on the hole wall from being pulled off or copper warping when cutting;

11. After the castellated hole is formed, the film is removed and then etched, so that the copper surface will not be oxidized, effectively avoiding the occurrence of residual copper or even short circuit, and improving the yield rate of the metallized semi-hole PCB circuit board.

Difficulties in metallized Castellated hole PCB processing:

1. Metallized Castellated hole PCB has blackened copper skin on the hole wall, burrs, and misalignment after forming, which has always been a difficult problem in the forming process of various PCB factories.

2. Especially the entire row of half-holes that look like postage stamp holes, the hole diameter is about 0.6mm, the hole wall spacing is 0.45mm, and the outer pattern spacing is 2mm. Because the spacing is very small, it is very easy to cause a short circuit due to the copper skin.

3. The general metallized half-hole board PCB molding processing methods include CNC milling machine gong board, mechanical punch punching, VCUT cutting and other methods. When these processing methods remove unnecessary part of the hole copper, it will inevitably lead to Copper wires and burrs remain on the cross-section of the remaining PTH holes, and in severe cases, the copper skin on the entire hole wall is lifted and peeled off.

On the other hand, when the metallized castellated hole is formed, due to the influence of PCB expansion and contraction, drilling hole position accuracy, and forming accuracy, the left and right sides of the same unit have large deviations in the size of the remaining castellated hole during the forming process. Come to great trouble.