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Solderability of Gold plating pads without Nickel barrier

2007

We are using bare pcbs with Gold plating without nickel barrier, the solderability of the same is very poor a compared to other plating like ENIG & HASL etc..
We would like to know the solution for getting better solderability with shiny appearance.
E.g., what type of solder, cleaning solvent, soldering temperaure, etc.

Saina M S
Sr. Engineer - Cochin, Kearala, India

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Hello, Saina. It sounds like you already know exactly what is wrong (I would concur with you), but you have committed to not fixing it :-)

So please tell us why you don't want to EN plate. Thanks!

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2007

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2007

In the early days of printed circuits, the standard thickness of gold on connectors was 5 microns. This was the minimum thickness to ensure that there was no porosity in the gold, and hence that copper corrosion products did not appear on the surface. It was also sufficient to prevent diffusion of copper into the gold.
When the cost of gold increased, thicknesses were reduced and an underplate of nickel was introduced to overcome these problems.
When gold is soldered with tin/lead solder, some of the gold dissolves into the solder and forms intermetallic compounds (AuSn6 if my memory is right. The problem is that although the surface solders readily, the resulting joint is weak as the intermetallic compounds form accicular crystals which are brittle and make the joint look dull. Below (I believe) about 5% gold/solder ratio, the effect is minor and this is usually the case with thin gold over nickel.
Cleaning and fluxing will not help. I agree with Ted. Nickel is cheap and effective.
If nickel is not an option, please come back.

Geoff Smith
Hampshire, England