Tin plating surface "discoloration"

[Jon Slaughter]

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

http://i36.tinypic.com/30hq5uw.jpg

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?

 

[Jon Slaughter]

BTW, it really looks like some crude on the surface.

 

[legg]

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

http://i36.tinypic.com/30hq5uw.jpg

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 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

 

[Jon Slaughter]

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.

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.

 

[Jon Slaughter]

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.

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.

 

[Baron]

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.

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.

 

[Herman]

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

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.

 

[Jon Slaughter]

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.

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

 

[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).

 

[Herman]

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

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