Aluminium soldering

[nsv]

I'm new to Eng Tips, so I am not sure which forum to ask - hopefully you can help or redirect me.

Soldering of aluminium is critical and diffiult compared to copper because of the very inert layer of aluminium oxide that immediately forms when the metal is exposed to air.

In our production we have a proces in which a polyurethane insulated 0,12mm (approx. 0,005" or AWG 36) Alu-wire is soldered to a pre-tinned copper braid. We use the heat of the melted tin to strip off the insulation, then dip it in a very agressive flux and lastly back to the tin bath for soldering.
Unfortunately it is not very efficient, and often we have failures because the PU-insulation is still there when the actual soldering takes place. Also we are worried that the agressive flux wil cause corrosion in the long run.

Ultrasound could be a solution to remove insulation and alu-oxide, but how will it affect the thin wire?
Anyone has a tip as how to strip such a wire other than the heat of the melted tin?

NSV

 

[MikeHalloran]

I've been disapponted by ultrasound, twice. Shame on me. I suggest you proceed cautiously, and don't believe _anything_ an ultrasound salesperson says.

;---

Maybe gentle abrasion or an air blast to remove the insulation's decomposition products after the first dip?

Are the first and second tin dip steps in the same tin bath?

;---

How about insulation displacement connectors with protective grease, like the telco jellybeans?



Mike Halloran
Pembroke Pines, FL, USA

 

[nsv]

Thanks for your reply, Mike - in what way were you disappointed with ultrasound?

Even the gentlest abrasion is death to a 0.005" wire and I'm concerned about the ultrasound ripping it apart.

We use the same tin bath to strip and solder. Perhaps this is a wrong solution - better to have a hot bath for stripping and a standard for soldering?

NSV

 

[MikeHalloran]

I followed the ultrasound guys' directions for part design, exactly, and the parts still didn't bond consistently.

I, personally, can't strip a 30AWG wire without breaking it. Thermal is all that makes sense for stripping anything smaller.

Molten tin is plenty hot to strip PU, which melts in boiling water. But separate baths would reduce the possibility of PU decomposition products interfering with the soldering operation.

How about buying bare wire and varnishing the part you need insulated?



Mike Halloran
Pembroke Pines, FL, USA