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고주파 기술

Why do PCB plated-through drillings require a copper pad?
2019-09-02
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Author:ipcb      Share

The PCB dimension of the drillings specified by the designer represent the final dimension from a manufacturers point of view. Due to the through-plating, the PCB surface finish and the copper build-up in particular, the drilling diameter has to be carried out larger to eventually reach the desired size. Plated-through drillings without an annular ring provide significantly less stability to the final PCB product.

The PCB drill-hole allowances for the fabrication of printed circuit board(PCB) may vary among manufacturers. In the PCB outer layers, an allowance of 0.3 mm for drill pads (plus the final diameter) by default is considered as sufficient. For a low-cost PCB mass production even larger allowances may be required.


Examples for drill allowances in the fabrication of printed circuit board(PCB):
Surface finish chemical gold:drill allowance +0.10 mm to +0.20 mm
Surface finish chemical tin:drill allowance +0.10 mm to +0.20 mm
Surface finish HAL (non-leaded):drill allowance +0.15 mm to +0.25 mm


If an allowance of 0.15 mm is applied, the annular rings width is 0.075 mm only (standard width: 0.3 mm plus the diameter of the PCB drill-hole).

Desired size: 0.3 mm final diameter / 0.6 mm pad = 0.15 mm annular ring

Fabricated size: 0.45 mm drilling diameter / 0.6 mm pad = 0.075 mm annular ring