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Tin plating surface "discoloration"

I created a pcb board and tinned it using some product(now discontinued I think) from MG chemicals.

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The method was after etching I removed the resist using 1:1 NaOH(Maybe too strong or waste but doens't matter). I then rinsed the boards using water and dried them off. Poured the tin solution over them. They "tinned" up almost immediately.

The color in the pictures look much worse than it is. In the proper light and angl ethey look really nice with almost a constant tin color.

But I'm curious as to what I could do in the future to improve the look and prevent that discoloration. I guess it's some type of precipitant from the solution... maybe because the board had water moisture. Note that the copper did not oxidate because I kept them in the NaOH solution while I was preparing to Tin them(and the time lapse was only a few mins). It's possible I needed to sand the copper slightly but After removing the photoresist I can't imagine it would have been oxidized at all.

I have noticed this on other boards I did previous too. Not sure if a slight sanding/polishing would do any good but I don't want to remove the tin.

Anyone know whats going on?

Reply to
Jon Slaughter
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BTW, it really looks like some crude on the surface.

Reply to
Jon Slaughter

Horrible stuff. It makes the board unsolderable.

Bare copper solders nicely if you rub it with a Scotchbrite pad first.

John

Reply to
John Larkin

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I'm tempted to take a hunk of sheet metal, bend the edges up, weld the corners and melt a big slab of solder over my propane torch. Drizzle on some flux, board face down, wipe it off with a cotton (or linen or wool) towel, and finish with hot air gun for that HAL look.

So far I've been doing it by hand with the soldering iron, which is tedious, but I don't mind.

Tim

Reply to
Tim Williams

The recommended app method is a 2 to 5 Minute agitated soak, to develop coating thicknesses of 0.3 to 0.5 microns at room temperature. The deposition rate and thickness increases with temperature (x4 @ the

60C limit).

An alcaline prewash is supposed to handle serious surface contamination. As the solution is highly acidic, an ion-controlled post-wash is recommended - distilled water for dilution/rehydration.

I've used it once or twice, but was never happy with the resulting cosmetic appearance. The discoloration can be polished off, but then so can the thinner surface coatings. I'm as clued out as you are.

Fluoroboric Acid 9-11% /wt Stannous Fluoroborate 9-11% /wt Thiourea 4-6% /wt

The 'liquid tin' 421 product isn't discontinued by MG.

RL

Reply to
legg

Well, the one I got said it was discontinued... I think. Brought it several months ago. I did try to polish with #5 white diamond and it started to show copper. I moved to #6 red rouge and it worked some but was slow. I ended up adding some scratches from somewhere. In any case I painted the board so it's not going to show up anyways.

Reply to
Jon Slaughter

Well, I've done that and it gives higher current capacity but tends to look very nasty. I thought about trying to immerse the boards into solder like you mentioned but haven't got around to trying. (don't have that much solder anyways)

I don't think one needs a large amoutn though. Just enough to run the surface of the board through.

Reply to
Jon Slaughter

If you wanted you could make a "Roller Tinning" machine quite easily.

I made one a good few years back for a small producer of pcb's. It was just two rollers, one steel and one wood mounted one above the other like a mangle. The steel roller dipped into a trough of molten solder heated by a gas burner. The roller was turned with a cranked handle attached to the spindle.

I later attached a foot switch and motor with a gear chain to make operation easier.

You passed the board between the rollers. The top one applying light pressure and the bottom one transferring solder to the pcb. It made an excellent job of tinning pcb's.

--
Best Regards:
                     Baron.
Reply to
Baron

I have never been happy with the tin dip. After I remove the resist from my boards I spray them with a light coat of "clear Krylon". You can get it from a craft store or hardware store. This blocks oxidation and still is solderable. Been using it for 40 years.

Reply to
Herman

How is it solderable? wouldn't the it interfer with the solder? (unless it vaporized from the heat)

Reply to
Jon Slaughter

I redid the boards and it seems the the discoloration has to do with the unevenness of the plating. In some spot on the second board there is copper showing through. I guess they have to be cleaned extremely well for it to work. I also did a test board where I put a small drop of the stuff and it tinned up nicely. I think tried to tin the rest of it and the drop's outline is clearly seen with the inside being a different color than the rest.

I guess it's simply the method not being very good(either too critical to achieve good results or simply a bad way).

Reply to
Jon Slaughter

It vaporizes. I have used it with rosin and water soluble flux solder.

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Reply to
Herman

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