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Soft soldering to aluminium

 

We are trying to soft solder a small multi lead aluminium component (7075 aluminium alloy) to a printed circuit board (PCB), each lead has a solder area of about 1 mm square. It would be nice to use the same solder paste and reflow techniques that we are using for the surface mount electronic components that are also on the PCB.

Does anyone know how to treat the aluminium so that we can solder to it? It was suggested zinc then copper plating may work, is this worth trying?

We're mainly electronic engineers so this is a bit outside our stomping ground, any help would be well appreciated.

Peter Vincent
aeronautical and maritime research - Melbourne, Victoria, Australia

Hello Peter, we silver plate all aluminium components that need soldering in our products. This involves a nickel under coat to seal the aluminium and then silver finish coat. We do this mainly because it makes the aluminium more electrically conductive and the silver oxide is also conductive. I have also heard of some special flux that allows you to solder aluminium. I think I also seen a reference to it on Finishing.com Regards

Darren Wass
Brisbane Australia

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I would say that if you cross-sectioned and etched your solder joint, you would find that you actually soldered onto the nickel layer, which is probably what you want to do. The nickel plating has molecular adhesion to the aluminum, so problems with the aluminum oxide layer formed in air is eliminated.

Peter is probably referring to zincate and then copper plating, which would work; the nickel undercoat also requires some kind of zincate or stannate pretreatment in order to get perfect adhesion to the aluminum.

The zincate or stannate step lays down a layer of metal onto the aluminum, preventing the oxide from reforming, then the nickel or copper bonds to either it or to the aluminum, some zinc or tin usually is removed during the plating, being dissolved into the plating bath solution, but in any case, adhesion to the aluminum or the preplate is of a high order, if done using proper plating methods..

  
Tom Pullizzi
Falls Township, Pennsylvania