Suggestions on chip removal

[hammerdown]

Hi all!

I have a couple totes of SDRAM style memory sticks as pictured (fingers previously removed and recovered foils this past summer) that I had been stashing up and now about ready to tackle de-chipping. My question is... what seems to be the "easiest / best" method for most of y'all when having such a load to work? I've contemplated just submerging in excess CuCl2 that's already partially FeCl2, or just in a batch of excess CuCl2 only, and then recover the chips (and possibly the tiny MLCCs and chip resistors... already popped off the bigger MLCCs) and rinse afterwards... but concerned with so much possible soldermask material "trash" to have to tackle as well. Not to mention how cumbersome it would be to try and recover any of the trace amounts of gold that comes off as well that litters some the PCBs (not the fingered part). Plus, my local scrap yard will sill give me $0.60 lb for these boards depopped… so trying to avoid leaching the copper substrate would be more of a loss I think. I would consider a straight edge blade to manually remove the chips, but given the stock pile I've accumulated... that would be very time consuming and laborious. Airhammer chiseling these sticks don't work very well for me verses larger area sized boards. Any other methods y'all can think of that I haven't thought of? Or would chemically removing the chips still be the better way? Perhaps a different chemical process if so? I just finished de-chipping my full tote of older EDO-style memory sticks which was way easy... thin flat head screw driver in the gap between the chip & PCB and twist off. I hope the 4+ lbs of those chips are worth a hoot to have collected vs SDRAM chips in yield since they're from an even older era of electronics, even though less contact legs.

Side question, but kind of relevant... what's the best way to de-chip RDRAM (RAMBUS) style memory stick BGA chips? They seem to be adhered to the boards by some sort of glass and doesn't pop off easily without busting up the chips themselves in the process. I only have 30-40 sticks of those.

Thanks guys!

 

[miroman]

For chip removal from RAMs I used a mixture from a Russian guy. Unfortunately it was long ago, I remember the proportions, but can't remember the quantity of sticks I succeed to depopulate with it.

So the mixture is:
In 350 gr. water put 6 gr. citric acid crystals and stir until completely dissolved.
Add 250 gr. nitric, and stir again.
Put the sticks upright, tightly in a vessel, then add the solution, to cover them at 2-3 cm. above.
Wait 24 hours. Most of the chips will have fallen. Some other will be very easy to remove. The rest can be removed too, but with more effort.
Of course, all the small elements (capacitors, resistors, small ICs) will be removed too.
All the paper sticks will remain - on sticks or on chips, you'll have to remove them manually.
As an extra, most of the IC legs will be dissolved by nitric, also most of the tin.
As a disadvantage, some of the gold plated contacts will be released too.

If I remember correctly, the solution was enough for about 50 - 60 sticks, but I'm not sure.
You can try, and if it doesn't work enough well, you can repeat the procedure.

Regards, Miro.