Soldering to copper foil inductors

[martinw]

Dear all,

OK, it doesn't have anything to do with CNC, but I still plead for help from you wise people out there.

I have some AlphaCore copper foil air-core inductors. Loudspeaker crossover stuff.

Simple question... what is the best way to make a really good electrical connection to the copper foil?

Best wishes,
Martin

[Geof]

You title your thread:

"Soldering to copper foil inductors"

Then in the introductory post ask:

"Simple question... what is the best way to make a really good electrical connection to the copper foil?"

Which, of course, is the question to which you have already provided the answer.

Which prompts an even simplerer question...Why?

[martinw]

Dear Geof,

Sorry, I didn't make the question clear. The copper foil of the inductors has a cross-section that is about 0.1mm by about 32mm. The foil is folded twice, so it comprises of three layers which together have a cross-section of about 0.3mm by 10mm. The length of this tail emerging from the body of the inductor is about 100mm. I want to solder equipment wire and resistors to the tail but thought that the thermal mass of this amount of copper might make it difficult. I was thinking of cutting the foil so the soldered section had a csa of 0.1 by 10mm. Yes I could experiment, but I'd rather get it right first time because the more I bend the foil, the greater the risk of it stress hardening and cracking. They are audio grade inductors for loudspeaker crossovers and cost a fair bit of money.
I was wondering if anybody else had gone down this road before. My soldering iron is 48 watts and has temperature control.



Best wishes

Martin

[Geof]

Is there a problem with getting the whole mass of foil up near soldering temperatures?

Or is that okay and the only problem getting a heat source with sufficient power to heat that mass?

On a larger scale than you are dealing with I have thermally isolated the bulk of the material by clamping it to a copper bar which was either immersed in water or wrapped in water soaked cloth. This means that on the opposite side of the copper bar location your material is not going to be hotter than 100 C. However, you have to pour a lot of heat into the side you want at solder melting temperature.

Also on a larger scale in order to get a lot of heat into something without a localised heat source, such as a flame, impinging on a thin material I have clamped on a copper bar and then heated the bar. Taking care to avoid soldering the bar to the workpiece. This was essentially creating a big high power soldering iron.

If a lot of heat everywhere is no problem why not use the heating surface on the top of your cooking source as a high power heat source? You could even set the temperature just below solder melt, hold the foil in contact somehow so you heat the bulk and then use your small soldering iron to heat the work are the extra little bit for your soldering.

If a lot of heat everywhere is a problem you will have to figure out some way to thermally isolate the work area, and heat it strongly which will be a bit more involved.

[martinw]

Dear Geof,

Many thanks for the advice. The case of the inductor is plastic and I think the insulation between the turns of foil is polythene, so I'm a bit concerned about heat conduction along the "tail" and into the body of the inductor. I like the idea of a metal "thermal dam". A couple of small aluminium flats clamped to the foil top and bottom should work. I'm still waiting for my exotic equipment wire to turn up. When it does, I'll suck it and see.

Thanks.

Best wishes

Martin

[Geof]

Originally Posted by martinw Dear Geof, ...I like the idea of a metal "thermal dam".... Thanks. Best wishes Martin

If you are drawing the water analogy it is more of a "thermal flood channel" .

The real water version of which, various locations over there were in dire need of a few weeks ago.

EDIT: And on a small scale that is what I am currently working on down the side of our property to stop rain water draining from next door which has been built up about a metre higher.