PCB Surface Finish

Introduction

To prevent oxidation and to preserve the solderability a surface finish is applied to the exposed copper pads on a PCB which are not covered by the solder mask.

The most commonly used surface finishes are electroless nickel immersion gold (ENIG) or hot air solder leveling (HASL).

ENIG

The ENIG surface finish is made up of a 4–7 µm thick nickel layers covered by a thin gold layer between 0.05 µm — 0.1 µm.

While the use of gold and the more complex manufacturing process results in higher cost, ENIG shines with a smooth surface, making it suitable for fine pitched components and BGAs.

HASL

HASL is one of the most cost-effective surface finishes. The panel will be dipped into a solder bath and the excess solder will be blown away with air. After the process, the pads will be covered by a tin layer with a thickness between 1 µm and 40 µm. This uneven surface is one of the disadvantages of HASL.

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