Soldering many 1.5mm silver disks to 41 swg enamelled copper wire

Dear all

I need to prepare 1500 sets that would consist of:
a. a silver disk 1.5mm in diameter, 0.7mm thin, and
b. 41 swg enamelled copper wire, several inches long
More or less like on the picture below:


The set is supposed to work as a touch sensor glued to plastic foil. The connection should to be powerful enough to resist light but steady stimulation for several hours.

Now, I have the following questions:
1. would you recommend soldering or electrically conductive adhesive?
2. if soldering
2.1. what equipment would you recommend? e.g. electric iron or gas torch?
2.2. what procedure? e.g. heat the wire tip to burn the enamel, dip it in flux, touch against the disk, melt tin wire on both
I must add I've only soldered a couple of wires in my life. But I'm ready to learn it and spend several days on the project.
3. if adhesive
3.1. what kind?
3.2. would it be elastic enough and not crumble under pressure?

Kind regards,
Greg

99% silver epoxy may do the job if you can have a jig to hold it together.
Strain relief is not included unless you add a tail to the wire interface.

Ultrasonic is the preferred method.
Soldering may be impossible for a newbie.

horek said:

a silver disk

Click to expand...

This adds up to a lot of silver. Is it really silver, or plated metal? Only a few metals easily take solder.

Did you try a solder connection?

If it does not work, then conductive epoxy is a good choice. I used it to connect thin wires to photovoltaic cells. (Soldering was unsuccessful.)

I found that the wires easily broke at the connection. It took just a few bends back and forth. So I glued an insulated section of the wire to the PV cell. This acted as strain relief. The same possibility may be important for success of your project.

I also had the silvery liquid conductive pen. It is good for very thin wires. You must find a way to keep the wire held against the surface while the liquid dries.

Such a small disc ought to be easy to solder even with a
low power iron. The trick would be to keep it where it is
supposed to be. I think a small jig to hold multiple discs
and the wire, flat against them would be time well spent.
Using a paste type solder might be easier than wire solder.
And of course if you had an oven capable of the temperature,
paste solder, jig-pan and flat-laid wire could become a
batch process. A PCB assembly reflow oven, for example.

If you have a long piece of angle material (ali or plastic) then a strip of "Blue Tack" along the flat side would be a good holder for your discs and if you run a strip of "Blue Tack" along the top edge this could hold the wire in place while your conductive epoxy cures.
Frank

the type of metal is important and special fluxes will help (not plumbing type-acidic) Future-Active and others may carry small jars of flux paste for electronic-type to reduce surface better than resin core alone.

Ideal soldering time is 3 seconds with pre-tinned wire. Avoid kinks in wire shape exiting disk, but a folded wire is ok. With magnet wire, excess heat can burn off plastic coating without stripping, otherwise there is chemical dip to strip enamel. A soldering gun may be useful here to apply heat, burn off enamel solder and turn off heat while holding down wire., applying solder to tip to envelope wire to burn off enamel then adhere to metal vs normal soldering of applying heat to surface and drawing solder towards surface, since the enamel must be removed first.

If metal is not conducive to soldering, a liquid tin fluid can be used to soak discs as a better surface for soldering.

Hi,

SunnySkyguy said:

99% silver epoxy may do the job if you can have a jig to hold it together

Click to expand...

I went through some of these
https://www.tedpella.com/adhesive_html/adhesive-comparison.htm
and on searched
https://www.amazon.com/s/ref=nb_sb_...6310091,k:Silver+Epoxy+Adhesive+conductive+99
and none seems to be 99%. Is that what you meant? \

SunnySkyguy said:

Strain relief is not included unless you add a tail to the wire interface.

Click to expand...

That really worried me - the fact that I have no strain relief on the wire at the point of contact with the epoxy/tin. Which will make this place particularly prone to breaking. You seem to have an idea how to do it but I don't quite understand what you mean by adding a tail to the wire interface...

- - - Updated - - -

Hi,

BradtheRad said:

This adds up to a lot of silver. Is it really silver, or plated metal? Only a few metals easily take solder.

Click to expand...

real silver, because of anti-bacterial effect and durability

BradtheRad said:

Did you try a solder connection?

Click to expand...

No. I'm gathering knowhow before I decide to buy the materials and try to do it on my own. If I could afford to buy them, I think that's what they would be - soldered rather than glued. The original I'm trying to imitate is below (the wire is broken at the connection though). I don't know what technique was used to solder it.

BradtheRad said:

I found that the wires easily broke at the connection. It took just a few bends back and forth. So I glued an insulated section of the wire to the PV cell. This acted as strain relief. The same possibility may be important for success of your project.

Click to expand...

Excellent idea. I just wonder if I will be able to remove insulation from the tip e.g. 0.75mm of the wire so that the next 0.75mm retains the insulation that can be glued to the disk 1.5mm in diameter.

Thank you!

I would guess the wire was spot welded, with such fine wire it wouldn't take much current.

I would say soldering is out of the question, 1.5mm is very tiny (less than 1/16 inch) and the wire diameter is only the width of a hair. I would be worried about removing the insulation and the cohesive effect of the liquid solder. Even with a fine soldering tip the disc will tend to stick to it unless it can be held down somehow.

Are the discs single or supplied in a 'snap off' strip?

Brian.

betwixt said:

I would guess the wire was spot welded, with such fine wire it wouldn't take much current.

Click to expand...

So maybe just put the wire between two discs and have them ?

But how to make sure the discs don't get welded to the cathode/anode? Any thoughts about the current and how to make the electrodes?

betwixt said:

Even with a fine soldering tip the disc will tend to stick to it unless it can be held down somehow.

Click to expand...

double sided sticking tape?

betwixt said:

Are the discs single or supplied in a 'snap off' strip?

Click to expand...

I'll use a punch and a sheet of silver 0.7mm

horek said:

Hi,


I went through some of these
https://www.tedpella.com/adhesive_html/adhesive-comparison.htm
and on searched
https://www.amazon.com/s/ref=nb_sb_...6310091,k:Silver+Epoxy+Adhesive+conductive+99
and none seems to be 99%. Is that what you meant? \


That really worried me - the fact that I have no strain relief on the wire at the point of contact with the epoxy/tin. Which will make this place particularly prone to breaking. You seem to have an idea how to do it but I don't quite understand what you mean by adding a tail to the wire interface...



Thank you!

Click to expand...

There are tons of conductive adhesives ranging in price and current capacity from mA to Amps Epoxy room temp, high temp cure, instant adhesives etc
https://www.girr.org/girr/tips/tips5/adhesive_tips.html#conductive one source, not best.

Strain relief should be >=3x diameter reducing to 1x over with 1cm length.
This can be same epoxy using a dental pick applicator.
Durability depends on vibration, and number of flexes. Copper is very brittle unless annealed. Even braid is brittle. ( I've worn out many mic wires, headset wires using AWG48x7 braid. Can you define expected stress levels?

What is applied current? __uA? frequency? or DC. keep in mind inductance, may want to use Litz wire if pulsed.