Soldering fixture test: stainless steel mesh + silicone foam

Categories
Contrivances Mucking About With Things The Diary of Lupin Pooter
The setup I tried: a length of white silicone foam, a roughly square piece of stainless steel mesh, and binder clips to keep the mesh pressed against the foam.
Here’s the setup I tried: a cut-off length of white silicone foam (with a 15mm x 20mm rectangular cross-section), a roughly square piece of stainless steel mesh, and binder clips securing the mesh against the foam.

On occasion, one needs or wants to solder wires to a small and irregularly-shaped component. Last month, I tried the lowest-effort technique that had sprung to mind: short lengths of high-temperature adhesive tape, placed sticky-side-up. In that experiment (Success: eliminated as non-optimal one way of soldering wires onto tiny, irregularly-shaped components), I was able to get the leads soldered onto the bottom of a tiny switch. The ultimate failure of those solder joins was due to the slimness of the pads and their weak attachment to the rest of the switch, but the tape-only method was still a pain. The switch and the wires moved around a bit, especially when I pressed the tip of my soldering iron against them.

Afterwards, it occurred to me to try placing fiddly little components on a surface that had some give and using a piece of comparatively-more-rigid mesh to hold the component and wire(s) firmly in place by pressing them against the squishy surface below. Each would have to be made of a material that tolerates high temperatures instead of melting, catching fire, or degassing significant amounts of hazardous chemicals. I settled on silicone foam for the substrate and, because stainless steel is known to be difficult to solder, stainless steel for the mesh. I bought some of both and waited for the stuff to arrive. Spoiler: fiberglass rather than stainless steel mesh would probably have been a wiser choice.

About a month ago, I gave it a shot and the photos have been sitting on my disk, waiting for me to do the write-up.

This is a microscope photo of the grade of mesh I used for this experiment: grade-10 mesh with 2.3mm-square holes.
I’d gotten one-meter-square lengths of 304 stainless steel mesh in six different grades of fineness, ranging from “10” (0.37mm-thick wire and a hole size of 2.3mm square) down to “400” (0.034mm-thick wire and 0.03-mm-square holes). This time, I used a small swatch of the largest type of mesh I’d bought: billed as “10 mesh”, 0.37mm-thick wire with 2.3mm-square holes.

Meter-square pieces of metal fabric are a bit unwieldy, so I used tin snips to shear off a narrow strip of each sheet and wrapped the rest back up and stowed them all away. The finer grades of mesh are very floppy and fabric-like and present a low puncture risk. Scissoring away at the coarser grades of mesh without inadvertently poking a sharp end of wire deep into my skin was a fun challenge. Before I was finished, I’d managed to stick one of my fingers deeply enough to draw a decent amount of blood, prompting me to dig out a pair of leather-palm gloves and wear them for the remainder of the exercise.

From a narrow meter-long strip of the coarsest mesh, I snipped off a smaller, square piece. Then, using duckbill vice grips, I folded over all four edges. the wire ends on the edges weren’t perfectly flat, so I taped over the edges and stapled through the doubled-over mesh to hold the fiberglass-reinforced Teflon tape. In the image of that swatch above, the voids seem to be larger than the specified 2.3mm, in one dimension, but the wire “threads” that comprise the mesh aren’t tacked to one another at cross-over points, so flexing/pulling while I was cutting or afterwards (during the folding and taping) may or may not explain the discrepancy.

Not wanting to waste another little oddly-shaped miniature component (and also interested in seeing how well the silicone foam would fare when it got hot), I elected to use lengths of solid-core wire instead.

Before-, during-, and post-soldering pictures of the joined wires and the mesh.
Clockwise from top left: one pair of wires twisted together (with the copper showing through the tinning here and there), the same region marinating in a little puddle of liquid flux, the finished solder join, and a concretion of cooked flux sticking to the mesh at the crossover that had been directly above.

In short, it worked. The solder flowed around the mesh and the copper wires didn’t get welded to the stainless steel wire. The flux didn’t eat away at the foam and the foam tolerated the heat. As I said near the outset, however, fiberglass mesh would likely have yielded a better result. The reason why may have been obvious to you from the moment you read that I’d decided to use stainless steel: the mesh seemed to (yeah no duh) conduct away much of the heat that I was trying to apply to the wire ends, making the process harder than it should have been. I’ve gotten some fiberglass mesh fabric and may redo this experiment later. Alternately, I could give the stainless fabric another go, but first snip away small areas of the mesh to expose only the regions where soldering would need to be done. That would be extra work, however, and would mean hand-crafting a new bit of mesh for any given soldering job.