Surface Finishes

Surface Finishes

There are many options for circuit board surface finishes, each varying in price, availability, shelf life, reliability and assembly processing.

 

While each finish has its own benefits, in most cases the process, product or environment will dictate the surface finish that is best-suited for the application. It is recommended that the end-user, designer or assembler work closely with their PCB supplier to select the best finish for the specific product design. Canadian Circuits’ extensive experience in lead-free manufacturing of printed circuit boards has been instrumental in successfully converting countless projects from solder to a lead- free alternative.

HASL (Hot Air Solder Levelled)

Solder deposited on SMD features and in PTH pads and holes. Typical solder thickness is 0.1-1.0 mils on surface features. Solder thickness varies by board geometry, aspect ratio, and hole size and is therefore considered unfavourable in higher technology SMD applications. The solder coating consists of 63%-37% eutectic SnPb.

solder finish board

ENIG (Electroless Nickel, Immersion Gold)

Electroless nickel-immersion gold deposited on solderable features. Typically 100-200μ of nickel is deposited and 2-8μ of gold. Applied after the solder mask process. Full ENIG coverage under solder mask is manufacturable, but not desirable due to reduced mask adhesion and increased cost.

gold solder finish board

Immersion Silver

Silver deposited on solderable features. Typically 5-25μ of silver is deposited, with a nominal thickness of 15μ. Immersion silver is applied after solder mask.

Combination Finishes

Typically a global solderable finish after a selective hard/soft gold finish has been applied. The preferred solderable finish in combination applications is OSP. Other solderable finishes are possible, but involve more process steps, which may increase the risk and associated costs.

Soft Gold (Wire Bondable)

Electrolytic gold deposited to the customer’s specified thickness (typically 30-50μ). Gold deposit has a purity >99.9%, a hardness of 50-90 Knoop. Soft gold is typically applied to selective features, but can be employed as a solderable coating.

ENEPIG
(Electroless Nickel Electroless Palladium Immersion Gold)

In ENEPIG, electroless palladium is deposited onto the nickel phosphorus layer and is then finished with immersion gold. This method allows for increased package and interconnection density.

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