Plated Through Hole PCBs

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srw
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Joined: Tue Oct 30, 2012 10:02 pm

Plated Through Hole PCBs

Post by srw » Tue Jul 15, 2014 1:12 pm

A collection of thoughts that hopefully can form into a working process for PTH PCBs at Techworks.

1. Drill on Goliath.
2. Flash plate holes using "Russian Method"
3. Electroplate
4. laminate resist
5. print transparencies
6. expose, develop, etch
7. strip resist.
8. Tin
Optional:
9. laminate solder mask, repeat 5+6 for mask.

More details:
Step 1: I've used the converter at http://eng-serve.com/cnc/excellon_gcode.html to take Excellon drill files and convert them for use on Goliath. It works.

Step 2: This is described in detail at: http://www.instructables.com/id/Inexpen ... -solution/
I have started acquiring the required chemicals.

Step 3: This process requires plating solution (largely sulfuric acid and copper sulfate) and a variable DC power supply. Some details are available at: http://www.thinktink.com/stack/volumes/ ... latmix.htm

Step 4: I have a laminator already at the space. Photoresist can be purchased on ebay. I have some as well.

Steps 5-8: no big deal. We've all done this already.

Step 9: see Step 4. Same process, different stuff.

An alternate method (and the one I used in school) is to:
1. Drill
2. Laminate (or, it's okay to use pre-laminated boards in this process)
3. expose, develop a "negative" version of the artwork. In this process, you want the traces exposed!
4. flash plate, electroplate copper.
5. electroplate Tin/Lead.
6. strip the resist.
7. etch with etchant that does NOT attack the tin/lead. (I seem to recall Ferric Chloride does not work for this method.)
8. soldermask if desired

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srw
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Re: Plated Through Hole PCBs

Post by srw » Tue Jul 15, 2014 1:24 pm

Chemicals required.
Russian Method:
Copper Sulfate (bluestone -- available at Co-op Agro Store? Kills algae in ponds)
Calcium Hypophosphite (on DEA list... tried ordering from China on Aliexpress. We'll see how it goes.)
25% Ammonium Hydroxide. (Prolab Scientific has 29%)
Dish Soap.

Electroplating solution:
Copper Sulfate
Sulfuric Acid (battery acid is about 35%, sufficient for this process. Apparently it is also available as a commercial cleaner in stronger concentration.)
Polysorbate 20 (optional? available on Ebay or, apparently, at a compounding pharmacy. It's used in cosmetics as well.)
(all sorts of proprietary additives are available)

Developing etch resist:
Possibly Sodium Carbonate (Washing Soda - any grocery store)
Sodium Hydroxide. (Lye. Home Hardware.)

Developing solder mask:
Same as etch resist?

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tonyarkles
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Re: Plated Through Hole PCBs

Post by tonyarkles » Mon Aug 04, 2014 8:44 am

This is something I've been mulling over for quite a while!

If you have a hard time getting ahold of the hypophosphite, I've seen a method that uses conductive ink instead. Drill, coat holes with ink, electroplate, laminate with positive resist (that covers holes), etch, good to go! I've never tried it, but I'd like to!

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srw
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Re: Plated Through Hole PCBs

Post by srw » Sun Aug 17, 2014 3:08 pm

I have a bottle of Ca Hypophosphite sitting right beside me. Now, I just need the Ammonium Hydroxide and some time to play.

Of course, I'll also need some sulfuric acid for the electroplate step.

I might also need some more bluestone... I don't have a lot.

Time. Mostly I need time.

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srw
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Re: Plated Through Hole PCBs

Post by srw » Tue Aug 19, 2014 6:30 pm

So, bluestone (Copper(II) Sulfate - Pentahydrate) isn't as easy to buy as it used to be. I can get a 50lb bag from Early's for about $150, or buy reagent grade from a chemical supply for $11.50/500g. I have 250g. (The price on the bag says it was $2.50/lb) This is enough to make a batch of the flash plating solution plus about 3 litres of the electroplating solution. It doesn't leave any room for experimenting with the plating solution or replenishing either solution.

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srw
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Re: Plated Through Hole PCBs

Post by srw » Tue Aug 19, 2014 6:33 pm

Oh, and I got some sulfuric acid. (90%+) Not sure what the other 10% is in this "drain opener" but it's not clear like it's supposed to be. Also got some 31% Hydrochloric. We could start experimenting with electroplating any time.

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srw
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Re: Plated Through Hole PCBs

Post by srw » Wed Aug 20, 2014 3:43 pm

So, after nearly giving up on the copper sulfate, I discovered "Root Away" available at Home Depot for $13/2lb. It appears to be 99% Copper(II) Sulfate - pentahydrate.

Confirmed: The MSDS for this product states that it is 99% Copper(ii) sulfate pentahydrate.

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srw
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Re: Plated Through Hole PCBs

Post by srw » Fri Aug 29, 2014 10:28 pm

Electroplating notes:
First of all, I think I miscalculated my dilution of sulfuric acid. The solution I made is probably almost twice as strong as it should be. That said, I made some attempts at plating a small board today.

The board was 1.5" x 6" double sided. That's about 18 sq in or 0.125 sq ft. The industry target for current seems to be around 20A/sqft. So, my target should be 2.5A

My plating tank is a 2l plastic juice jug.
Anodes are copper ground wire (#6?) unravelled and fanned out. (7 strands on each side.)
The board was cleaned with an sos pad and suspended mostly into the solution. (so, really, I was over 20A/sqft)
The first run of 1h @ 2.5A only deposited particles of copper (fluffy sludge) on the board, but it didn't adhere at all.

I washed the board off and cleaned one side with a scrubber and comet -- not SOS pad. I noticed that on the side washed with comet the water sheeted while on the sos side it beaded. I decided to try again in this condition.
After 15 minutes at 2.0A both sides had the fluffy copper again. The comet side seemed to have just a bit of new copper actually on the board.

I washed the board off and scrubbed both sides with comet. This next time I made two changes, so I don't know yet which made the difference.
First, I ran the current in reverse at 0.5A for a minute before switching it to the correct way. Now I plated at 0.75A for 50 minutes. This time I had NO copper fluff. It appeared to actually plate onto the board. The new copper was dull, not shiny like it is supposed to be.

I cleaned the board up one more time with comet.
I plated at 1.5A for about 25 minutes before shutting it down. The fluff was back.

There is no dark sludge on my anodes. Apparently, the proper HCl level should cause a black film on the anode.

Possible problems:
1. I probably have an Inadequate anode to cathode ratio.
2. My workpiece is too close to the anodes. (My tank is too small)
3. My solution is wrong. (too much sulfuric acid)
4. I have nothing other than hydrochloric acid as carrier/brightener/leveler.

For next time: I need a better tank. I need to unravel more anode. I need to re-mix the solution.

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