White "fungus" around a ni-cad

"N_Cook" wrote in news:jjcori$q5$ snipped-for-privacy@dont-email.me:

It is potassium hydroxide electrolyte, and it is very corrosive. Put on rubber gloves, and carefully wash the affected area with water. Follow up with vinegar to neutralize what's left, and then rinse with water again.

I once had to clean up an old (really old, it had miniature vacuum tubes in it) H23BAM police radio with NiCd wet cells. I skipped the rubber gloves, and despite being careful, I had no finger prints when I was done. The residue etched the ridges right off.

Doug White

Pineapples remove fingerprints also, but we eat them

I can't see how KHO creates tendrils or matting or whatever the 3D tracery structure is

Relevant looking signal (alternate time slices varies with varying DC at ch

1 and ch2)gets to the analogue data-in of the ZN449 , enable, clock etc ok but invariant data out on the 8 data lines.

I've some SMD ZN449 , any tips for converting to 18 pin conventional DIL? Start with a turned pin socket in the pcb to receive another one to carry the SMD, yes but any other tips ?

Will have to deal with the conductive contamination on the pcb around the nicad, down to 300K over the polyester of the pcb, soaked in capilliary-wise?. Removing 4x 74HC as well as the ADC

Conc. aqueous potassium hydroxide (KOH) attacks E glass (alumino-borosilicate glass fibre) leaving an insoluble white amorphous deposit of potassium silicates and aluminium hydroxide. This deposit will be conductive if contaminated with residual KOH as KOH is both ionic and hygroscopic and will be extremely difficult to remove as it has probably etched its way below the board surface. After aggressive cleaning, neutralisation, thorough washing and oven drying, you will still probably need to grind away the affected PCB surface until the track to track resistance remains acceptably high after 24 hours exposure to normal atmospheric humidity, then wash, re-dry and rebuild the ground away areas with epoxy.

KOH also attacks a number of common plastics to a greater or lesser degree. Polyester is likely to be moderately affected, Epoxy is resistant. If you are very lucky, it may simply have made the resist on the PCB surface conductive and not attacked the underlying fibreglass significantly.

--
Ian Malcolm.   London, ENGLAND.  (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk
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Maybe I'll be lucky. Removed 5 ICs and the nicad from that area. Washed locally with meths and while still wet dremmel and rotary wire brushed over that area . Now I cannot find any conduction to/between any isolated pads or the plastic/glass less than the 30Meg of my DVM. Made good the IC holes ready to receive 5 turned pin sockets

ps I also have a > 30K filter on my (valid) email inbox. It is me who decides who clogs up my inbox /HD

Sounds like it was just surface contamination or leaky resist. I would wet scrub it with deionised water with some IPA as a wetting agent using a abrasive pencil type glassfibre brush to be certain the dremel wire brush hasn't left any metal contamination that may give you trouble with metal salts later, Rinse well with dry alcohol and dry thoroughly with forced air circulation at an elevated temperature. Finally coat the damaged area with a good brand of solder-through PCB lacquer before refitting any components.

If I think there is any chance of future battery leakage I usually fit the new battery through a piece of polyethylene, silicone or ptfe sheet between it and the board to limit the damage next time.

--
Ian Malcolm.   London, ENGLAND.  (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk
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over

pads or

decides

Well I suppose that is progress. Back to exactly the same malfunction as before , but with the 5 original ICs in sockets now. Varying activity on the analogue side of the ADC and no variation at any of the 8 output digital lines . Will try a SM ZN449 , which strangely is wider package than standard DIL. so looks like it will have to be a skewed adaption to fit . Using the original nicad at the moment, slung underneath. I like the idea of a silicone bund. I think , if I get this working, I will replace with a new one , stout-wired upside down, right side of the board , over a silicone sweet or cupcake mould

My tip for a SM IC to DIL adaption.

3/8 inch wooden dowel , cut a small flat to receive the SM IC neatly. 0.2mm tinned copper wire, free end looped around first pin , around the dowel with a bias so the wire lays tight against the up-side of the opposite pin and wind biased spiral fashion over the top of the IC and around the dowel. Finish with a final loop around the last pin. Clamp free end of dowel in a vice and solder each pin to its wire. With a razor cut the wires over the top of the IC close to the pins and cut along the centre back of the dowel. straighten wires. Some 1mm PTFE spaghetti tubing , small length pushed over every other wire and glued to the IC body. Fan out the wires and solder to the pins of a turned pin socket. Continuity check for contacts and bridges.

Wow, that's a lot of work. Why not just use a footprint adapter, e.g. the ones from Bellin?

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net

opposite

dowel

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and

I was not aware of them but can they adapt from wide .45 inch SM down to .3 inch DIL for this purpose and 18 pins ? And for one offs,? thats more for production environment at 40 squid a pop . My free "adaptors" are fully adaptable to any contingency, just don't look so pretty, and probably a bit higher profile due to use of a socket.

I don't think you'd use them in production, because you could lay out your own and they'd probably be cheaper. The Bellin ones work out to be under a buck each. They're dead useful for protos and repairs--I have a couple of sheets of them, about $70 worth, and use them with some regularity. You do need a couple of rows of pins to connect to the main board.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net

the

the

wires

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.3

for

look

Come to think of it, my method would look neater without the intermediary socket. Larger dowel and longer cut 0.2mm wires, so can pass through the original board. Just that over the years I've got in the habit of socketting any replacement IC I've desoldered, there's always been the height available with the stuff I deal with .

He has to do everything the hardest possible way. Can you imagine that cobbled together mess in a really sensitive circuit, as the humidity changes?

--
You can't have a sense of humor, if you have no sense.