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Organic flux reaction on Type II yellow zinc plate

2006

I recently came across a problem I need a bit of advice on.
I have Monitoring and Diagnostics equipment made for the passenger rail industry.
The spec. requires that all CRS parts be plated with yellow zinc plating type II.

On part holds a front panel and an important circuit board together via a large electrical connector. The connector is mechanically attached, then a "non-corrosive" water soluble organic flux is applied before soldering the connector to the board. The board is then washed in de-ionized H2O.

The flux reacts with the plating so that it appears that the metal substrate is exposed in those spots where it touches, but the surface remains smooth.

The question: Is yellow chromate non-resistant to organic acids? Or, is the zinc plating oxidizing?

Thank you and regards,

Ben Blady
Passenger Rail Controls Systems - Arlington Heights, Illinois, USA

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Dear Ben Blady,

Nope, zinc plating will not resist any organic flux even the "non" corrosive type. What you see is the probably the zinc dissolving away certainly not oxidising. You may want to touch up paint over the soldered portion with an aluminium rich paint.

Best regards

Khozem Vahaanwala
Saify Ind

Bengaluru, Karnataka, India

2006