We have an application where we are soldering a PCB onto aluminium pins which have been embedded in plastic. The pins are about 10mm long and 3 mm diameter with a shoulder that takes the diameter down to 0.9mm where the pcb would be soldered.
Questions:
1) Do i have to treat the Al before soldering - some say that i should electroplate it with silver, which sounds expensive for a consumer product.
2) Is there lead-free solder for this?
3) Can we use normal solder mask on the board? or do we need also need some special solder on the solder mask on the PCB?
4) Will the heat not just dissipate into the pin and melt the plastic before we can get the solder wetting the aluminium?
Thanks, Vahid.
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C
Chris Carlen
Why do it this way? I mean, couldn't you simply use a spacer and a screw which can go into the plastic? Or can you get the pins threaded on the reduced shank so a nut can fasten the PCB? Otherwise, soldering to the aluminum will present many problems...
I haven't heard of doing this, as I have soldered aluminum directly. If you could afford the cost of added treatments to the pins, why not just design them to be a normal threaded standoff, or spacer?
Yes. What works to solder Al at low temps is Sn91Zn9 alloy. I got mine from indium.com which is alloy #201. It requires a flux (Indium's flux #3) which is rather nasty, containing organic fluorides and other glop. This is the bad part. You don't dare breath the fumes like you can get away with when using rosins. You must also clean away the flux residues very thoroughly. The good news is that it is actually not terribly difficult to make very good flowing solder joints with this solder/flux combo. The alloy melts at 199C which is slightly under typical SAC305 lead-free.
Repeat, if you can deal with the cost of the exotic soldering operation, why not just use ordinary mechanical methods?
Don't know if there is any issue with PB mixing with the Sn91Zn9. I soldered aluminum wire to pads on a PCB, which I think were just plain tin.
Yes, which is another reason why ordinary mechanical means are probably wiser.
Good day!
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Christopher R. Carlen
Principal Laser&Electronics Technologist
Sandia National Laboratories CA USA
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C
colin
probably
how about a spring clip, pushes over the pin and wont come off, looks a bit like a bent washer with pointy bits on the inside wich slide easily one way but dig in when going the other way
Colin =^.^=
C
Clifford Heath
They don't work for making reliable electrical contact to aluminium if they're subject to even the slightest vibration. They gradually into the Al until they're not tight, then you get oxide and no contact.
C
Clifford Heath
eat
sorry for the unintended deletion.
C
colin
the aluminium is going into plastic, so I cant see why there is a need for electrical contact, if there is the OP didnt mention it.
mechanicaly, aluminium probably isnt the most suitable material for this.
Colin =^.^=
I
ian field
AFAIK you can tin the pin with alusol and then ordinary solder will take.
J
James Beck
Gotta' watch which alusol you mean. Around here alusol is a machining lubricant for aluminum. If you want the flux look for "Finex Alusol" or search for aluminum soldering flux.
Jim
I
ian field
I didn't know there was another product with the same name, but if I did I would have figured that the context made it obvious which one.
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