I have no direct experience with it but it's probably too abrasive and will damage the slot pins.

SSTV2 wrote on 2024-10-26, 16:58:

Understandable, in such case, the best price-quality ratio for plating bare copper would be achieved by using nickel salts solution (nickel sulfate/chloride) which can be bought or made at home. For the electric current source, you can use any old AT/ATX PSU, 3.3-5V rails should do just fine. Now for the plating method you have two options here - either buss all of the pads together and submerge the edge connector into the nickel solution or you could plate them separately with a swab tip. Swab can be cheaply made from a Q-tip or a depleted marker pen.

Interesting proposal, maybe I could just treat only the most damaged pins and leave the rest as is. So I'll apply +5V to the pin and the swab should be moist with the nickel solution and connected to ground?

vstrakh wrote on 2024-10-26, 17:22:

...
Does this mean the HASL for pcb finish is a hard no-go if I'm about to experiment with making ISA cards, and ENIG is the only way to be considered?

For prototypes is ok.
For the production, if you have an edge connector gold is the way to go.
The gold plating have two purpose. First gold don't oxidize. Second, gold is a "soft" material. I mean it's like teflon, it's a soapy material which prevent the two surface from scratching each other.

vstrakh wrote on 2024-10-26, 17:22:

Does this mean the HASL for pcb finish is a hard no-go if I'm about to experiment with making ISA cards, and ENIG is the only way to be considered?

HASL will ruin the gold plating in any slot you insert the card, since gold readily amalgamates with tin. Afterwards the slot is going to get unreliable, since it has lost the corrosion resistant nature of the original gold plating.
I personally only use ENIG and will never use HASL again for anything going into gold plated slots like ones of game consoles and variety of computer motherboards. It is especially important for game console slots, because this ruined slot will continue to damage the gold plating on the game carts aswell, with computers it is less of a problem since you usually don't change what goes into the slot.

Paar wrote on 2024-10-26, 17:32:

Interesting proposal, maybe I could just treat only the most damaged pins and leave the rest as is. So I'll apply +5V to the pin and the swab should be moist with the nickel solution and connected to ground?

That's the general idea, except pads should be connected to the negative terminal as nickel ions are positively charged. You might also need to add other chemicals into the solution if you'd like to change the appearance of the plated surface and bonding strength.

This is important - if you are going to plate each pad separately, keep in mind that you will have to insulate rest of the pads, as you might fry ICs by accidentally creating circuits with reverse current flow.

Tiido wrote on 2024-10-26, 18:59:

HASL will ruin the gold plating in any slot you insert the card, since gold readily amalgamates with tin.

Yeah, this what I wanted to hear, a strong argument against cheap option that is recommended too often, "good enough for proto".
Obviously it's not just about proto vs product stability when it rots valuables irreversibly once brought in contact.

vstrakh wrote on 2024-10-26, 20:00:

Yeah, this what I wanted to hear, a strong argument against cheap option that is recommended too often, "good enough for proto".
Obviously it's not just about proto vs product stability when it rots valuables irreversibly once brought in contact.

tons of HASL finished 30/72 pin SIMMs back in the day, no evidence of "rotten" simm sockets to date

Yeah never seen any corrosion from it.
I have lots tin soldered (HASL) 30 and 72 pin SIMM and they always work fine. In fact have some gold plated 30pin just do not work well in some of the old 30pin steel/nickel sockets of some 286 and early 386 boards.
There are posts about it here...guess it depends on each person experience over the years.
Added: my time is worth a lot now that I am old and still working/chores/taking care of parents/etc so I would spend $50 and get a new VLB card instead of buying chemicals, messing with a PSU and trying to replate one if the sanded one does not work.
Just my opinion..

Horun wrote on 2024-10-27, 04:41:

Yeah never seen any corrosion from it.

There's no friction when you install HASL SIMMs. It's a different story with expansion cards. It's not about corrosion but abou scratching the slot pins.

Paar wrote on 2024-10-27, 06:14:

There's no friction when you install HASL SIMMs. It's a different story with expansion cards. It's not about corrosion but abou scratching the slot pins.

exactly.
also in humid environments one should match tin socket + tin simms , gold sockets + gold simms because using any mix combo will result is corrosion/fuziness on the contacts and an endless cycle of cleaning every year or two when the connections become unreliable ...

It also generates an electrical potential that can kill ICs when dissimilar metals are in contact, with humidity present.

(Dissimilar, as relates to their electronegativity value, which is related to their oxidation number on the periodic table. Iron and Cobalt are similar metals. Copper and Iron, are NOT. Tin and Gold, are NOT. Copper and Nickel, ARE. (only .01 difference in their electronegativities. Putting those in a salt solution, and putting a volt meter on each, will show very very low voltage generated.)

https://en.wikipedia.org/wiki/Electrone ... data_page)

Note, that gold has an electronegativity of 2.52 and tin has an electronegativity of 1.96. There can be almost a whole volt's worth of electrical potential generated from just a small amount of finger sweat and high humidity, on a junction between these metals.

If there is a very strong/profound difference in the electronegativity of metals, vs a salt of the dissimilar metal, a "replacement reaction" can happen. This happens with say, Aluminium and Copper. Placing aluminum foil in cold copper sulfate (COLD!!), will result in the outer layer of the aluminum foil being replaced with copper, as the aluminum is less electronegative than the copper. Same thing happens with iron nail in copper sulfate. plates the outside of the nail with copper.

In the case of an alkaline earth salt (like sodium chloride, from human sweat), the alkaline earth metal readily falls out of solution, and attempts to plate the metal, especially when there is a voltage generated from the dissimilar metals being present. Being alkaline earth, it READILY oxidizes, the oxide is hyper-reactive with water, becomes a hydroxide, and falls into an equilibrium reaction where the dissimilar metals and the alkaline earth metal rapidly become "Dance Partners", with oxygen from the air grabbing the less electronegative metal, the more electronegative metal entering solution, and the alkaline earth metal just constantly cutting in, then being dished out again. This corrodes the less electronegative metal surface, pits and damages the more electronegative one, and degrades both over time.

Yeah, contact surfaces are supposed to have compatible chemistry for any long term stability and things are done the way they are for a reason.

rasz_pl wrote on 2024-10-27, 02:22:

tons of HASL finished 30/72 pin SIMMs back in the day, no evidence of "rotten" simm sockets to date

SIMM sockets are also nearly always solder plated, I don't think I even have ever seen a gold plated one although they're definitely supposed to exist since I do have a few gold plated SIMMs. The ones I have, I can see little differently colored dots where the contact surface is and I have often had trouble with these SIMMs. I.e I stuck them in my 286 and after some time (few weeks to months) the machine stopped working reliably until the memory was exercised.

Now I live in Norway and right next to sea and that salty air is probably making this type of problem even worse...

One of the boards with gold plated 72pin SIMM sockets is Acer VI15G. Most of the 486 boards have solder plated slots though.

They are probably Nickel-Plated. Nickel is a cheap alternative to gold.