Metal Etching -- looking for the right terminology

jsw

Thanks for the link. That's exactly the process I was looking for, and if they don't have enough search terms then I'm just not looking hard enough!

Hi Tim,

The usual process is as you described and called variously photo etching, photo-chemical machining, photo-chemical milling, chemical machining. There are a bunch of places that do this if you search with those terms. Tolerances depend on the metal thickness and can be as small as a couple of microns. The price per square inch is pretty low, but the tooling charges can be several thousand. The usual materials are stainless and berylium copper, but they can do others as well.

There is another company called Metrigraphics

that does electroforming (electrochemical deposition on a mandrel). They get very nice edge surface finish and edge roughness and can do very small apertures repeatably. I think the tooling and per part cost is more though.

If you are looking just for small pinholes or slits, National Aperture has them off the shelf

This stuff isn't that hard to do yourself, even, if you have a way to make the master films. I make solder paste stencils this way. I use .003" brass shim stock, and laminate dry film photoresist to both sides. I make mirror-image films with a photoplotter and align them to each other. I then slip the sensitized brass between the films and expose both sides to UV from the filtered black light bulbs. Develop the photoresist in sodium carbonate and then etch with ferric chloride in a double-sided spray etcher. I've gotten down to .010" apertures or thereabouts.

positional accuracy of the apertures can be quite high, easily to .001", maybe better. SIZE accuracy depends on how well-controlled their process is. Mine isn't so great, I get a lot of undercutting where the etchant gets between the resist layers and opens up the apertures, even with short etch times. But, I guess a professional vendor of such work can hold tighter tolerances.

There are outfits that will make "solder stencils" for $50 each, up to maybe a foot square. If you can get them the artwork in Gerber file format they do it pretty much by the process I described above, or by laser-cutting the apertures. This is done for the printed circuit assembly industry, you should get a million hits googling for "solder stencil".

Jon

I recall seeing a kit for photo-etching model parts in I think it was the Micromark catalog.

--This sounds fascinating. I'd looove to see a photo essay of you doing this. Got any links??

Hmmm, well, not really. I do have some stuff on my web pages showing some of the gear. Here's a poor picture of the laser photoplotter.

I put litho film on the drum, it records the image in a raster fashion, building up the image at .6 inches/minute. Develop with usual photo chemistry.

I snagged a Kepro dry film laminator on eBay years ago. It is made for laminating the resist to PC boards, but if you put a shim of several sheets of heavy paper under the brass shim stock, it laminates perfectly to thin shim stock, too. You put the resist on both sides, and then expose with mirror-image photo masters. The resist is developed and then put in a Kepro spray etching machine that I got just before it hit the dumpster at work.

I used to use this gear to make PC boards, but they make these so cheap in China now that I rarely make my own. (I have scraps left over from so many projects that I can usually find a board that can be re-purposed for new experimental projects.)

I built the photoplotter myself. The machine wasn't too hard to make, once diode lasers came out. The software was a lot harder to do.

I've got some pics and story about getting the Philips pick and place machine in my basement. That was an ORDEAL!

Jon

some other hobby uses and techniques for photochemical electro etching, that are less tech intensive [i.e. less expensive].

A nice little project you have there. Do you get much trouble with temperature stability. I ask as my local photo plotter mentioned that they keep the plotter in a temperature controlled room and also that the film itself is quite sensitive to temperature changes. IIRC their photo plotter was 2000DPI for normal use but could go higher and the sheets were about 2ft x 2ft.