Boiling lye to take off masks but gold going somewhere?

[acpeacemaker]

Hey,

My first time posting, and of course with a question. I've been reading on the site for a couple of months now and still in the middle of Hoke's book. I haven't tried anythying major yet just boiling some chips and boards in lye. The masks came off with ease but on some things that were gold they discolored to the base metal? The cpu chips I left pins on to see what they would do. Half had gold left on them and the others had a mix of gold left but the pins turned silver colored. I ran these in the solution at about five minutes max time. Did the solution get to hot or did I leave them in too long? Will to much lye do something to the gold?

Thank you so much,
Andrew

 

[lazersteve]

Most likely your traces where coated with a yellow colored mask that is very common. When the mask was removed you see the copper.

Steve

 

[acpeacemaker]

Hey thank you Steve.

But what about the pins on the chips?

 

[Anonymous]

I processed several pounds of cards with all gold traces last year the same way and I had the same result.I have never used hot lye to remove the masking since then.Steve can you try and duplicate this result?The cards I ran were mostly sound cards with all gold traces.I would guess there was around 3 pounds total.After running them in AR there was no positive stannous result.

 

[lazersteve]

The pins on the cpus in the photo above are flash plated kovar. Modern technology has found a way to plate gold very thin (think nanometers thick). With gold this thinly plated it takes extremely large masses of material to amount to a recoverable amount of gold.

As for why the plating 'vanished' in the lye treatment, I'll take a guess and say the lye penetrated the thin gold layer and attacked the base metal slightly, causing the gold to dislodge as a super fine film ( they look like tiny particles floating on the liquid) almost like a copper colored scum.

Don't waste your time chasing the flash gold plating on new processors and the thin flash plated boards.

HP boards and some older pc cards and daughter cards do have a fair amount of gold on the traces. Be sure to test a few to see which type your are dealing with before processing a huge lot. If the gold plating holds the shape of the copper trace once the copper is dissolved away, the boards are worth processing if you have enough of them.

When working with any type of escrap it is vital to test samples for yield data before jumping in head first. I like using 100 grams as my test sample size as it makes calculating the yield percentages easy.

Steve

 

[acpeacemaker]

Thank you Steve, that was pretty much my guess about being so thin. I guess I just had to hear it from someone else.

 

[wifitekman]

I have soaked boards in lye and I believe some of the thin plated gold, does come off in the heated lye. To test the theory, I have put lightly plated gold boards in a crock pot with lye, to expose any gold traces underneath the mask (several batches, adding up to about 300 boards). Some of the exposed plating seems to have come off in the heated lye. Next, I scrubbed the boards in a tub of water to remove the solder mask. I have noticed that specs of gold was left in the tub along with the solder mask. I then ran the thinly plated boards in AP. If left too long, portions of the thin plate seemed to go into solution. It had too. If not, it just disappeared. Very little gold recovered. Recently, I put similar boards (solder mask on) in AP for 24 hrs and bubbled them, simultaneously. I found that I was able to recover the thinly plated gold. I was happy to see the tiny gold flakes (that's all you get when it is plated so thin) in the bottom of the tub. I just finished the AP and bubbling step, and the boards are in rinse water. I am reluctant to do the heated lye with thin plate. I think I have the bulk of the gold from the AP process and I think it will take a lot of precious time to try and recover the very thin traces which, are remaining under the solder mask. I have tried this different ways to see what would work best, and for me, this makes some cents