PCB Through Hole Plating at Home - Polyethylene Glycol?

[Dumble]

Hi,

I think I've posted this in the right forum / section? Forgive me if I haven't!

Anyway, a little background info first:-

I make my own PCBs at home. I used to etch single sided boards using the Toner Transfer method ironed directly on to the board or as transparencies for UV Photo Resist Film.

Last year I purchased a CNC3040 Milling and Engraving machine and now I do all of my PCBs on that. I mastered single sided milling pretty quickly and just recently, together with a friend, we're just getting to grips with milling double sided boards using FLATCam and the alignment pins method.

Two days ago, I milled out my first ever double sided board and with the exception of the top side milling a tad bit too deep, the board was a complete success. I don't yet have Z height mapping so I have to set my cutting bit at a compromise so some areas of the board go a tad deeper than others but nothing major.

Now that I'm getting to grips with double sided milling, I am able to produce more complex boards that are smaller in size than their single sided counterparts. The only problem now is when it comes to VIAS and Through Hole Plating in general to ensure good connectivity between top and bottom layers / traces.

The double sided PCB I've just milled out must have a couple of dozen VIAS which I'm not looking forward to hand soldering and because I've got to hand solder them, I've had to make compromises such as using VIAS right near headers so I can connect top and bottom pads where I can't get in to solder the top pads. This is all well and good on relatively simple designs but not so much fun for more complex ones.

ENTER Through Hole Plating by Electrolysis ....

I've been doing some research into Copper Plating Through Holes and Vias at home and have found some great resources / methods / techniques so I jumped on eBay today to order what I need.

For the Electrolyte Solution, I picked up a liter of 38% Sulfuric Acid (Battery Top Up), a liter of 35% Hydrochloric Acid (Muriatic Acid) and 1Kg of High Grade Copper Sulphate Pentahydrate (99.9% Pure).

To activate the holes for plating, I've got two techniques to try. One involves waterproof Ink and Graphite while the other involves a chemical process which requires a long hot bake. I plan to try the Ink method first before getting into more chemicals for the latter.

The ONLY thing missing from my shopping list which I can't find in the UK for a decent price by volume is Polyethylene Glycol (PEG 200) 
This is used as a brightening agent which helps to give a nice shiney flat coating and prevents the build up of large copper crystal clusters leaving a rough ugly finish.

In the videos I've watched and in the write ups I've read, everyone seems to use MiraLax but here in the UK that stuff seems to be near on the price of Gold Dust by weight.... I would ideally like a cheaper source but I can't find any.

The pricing of this stuff makes no sense. I can get 5 liters for £20 but if I want a small quantity, the price gets stupid. I only want half a liter of the stuff max but I can't find it anywhere that's cost effective. I would buy the 5 liters but I wont ever get through that much so it's a waste. I think the Polyethylene Glycol makes up about 1 - 2% of the final plating solution so 5 liters would last an eternity and would probably reach its shelf life before I got through it.

So, after a very long winded explanation, does anyone know where I can get a small quantity, say 500ml for a reasonable price? Or does anyone know of anything I can use as a substitute / equivalent???


Thanks!

[Ian.M]

Hows 1L for £3.11 + £5.50 P&P for price?
http://darrantchemicals.co.uk/index.php?route=product/product&path=61_69&product_id=106

[Dumble]

Hi,

After posting this, I went back to hunting for the stuff and found it.
I couldn't find it anywhere last night with hours of looking and then I came across it at a good price - just like that... 

Anyway, for those interested, a company in the UK called Darrant Chemicals stock it. It's PEG 300 and not PEG 200 so I don't know how the extra molecular weight will affect the plating process but it's the closest I could find.

I picked up a liter of PEG 300 for just a tad over £8 delivered - which will do me for a good while and if the idea / experiments don't work out, it's not cost me a fortune to try.

I also picked up a medium sized plastic fish tank from eBay to use as my plating bath. It measures roughly 23x15x17cm and holds approx 2.5 liters. This should be a good enough size to allow me to plate a 100mm x 160mm board without requiring gallons of electrolyte.

The last thing I need to think about, which I've not done yet, is a good source of copper for my anodes. In many of the tutorials I've been watching / following, they use regular copper water pipe but one guy in another video said that it's not the best stuff to use. It is copper but you want the best grade of purity you can get and also to encase the anodes in polypropylene filter bags to stop the copper sulphate formed around the anodes contaminating the electrolyte solution which results in a poor finish.

So while I wait for my orders to arrive, I'm going to give some consideration into what to use as my anodes.

I want the best chance of success so I'm trying to repeat exactly as I've read / seen demonstrated as closely as possible.

Thanks! 

[Dumble]

Hows 1L for £3.11 + £5.50 P&P for price?
http://darrantchemicals.co.uk/index.php?route=product/product&path=61_69&product_id=106

LOL... great minds and all that!

Thanks for replying BTW..

Just as you were posting, I was also posting that I'd just found Darrant Chemicals so how's that for a coincidence?
I searched for hours last night and never found Durrant Chemicals and then today, after I posted my original post I went looking and found it straight away....

I've ordered some and hopefully, everything I need will be here next week and I can have a go at plating Can't wait!!!

[Ian.M]

It would be nice to have the exact chemicals for whatever plating process you've found the recipe for.

I linked to their PEG 200 product.   If you read this soon enough, give them a call to see if you can change your order from PEG 300 to PEG 200 before it gets dispatched.  The PEG 200 is slightly cheaper so if you are happy to ignore the difference they may oblige.

On the subject of anodes - they need to be copper.   Copper is $expensive$ - there's no getting around it.   Talk to a non-ferrous scrap metal merchant to see if they have a copper water heater tank you could buy off them, or strip scrap 30A ring main cable for the bare copper wire if you are only going to be doing small scale experiments, though that will be a PITA with it breaking off as it is etched away, so you'll want multiple wires. e.g. suspend them from a scotchbiock terminal strip with as many in each terminal as will fit and one wire bent into repeated U shapes the other side to cnnect them all together.

The other thing that's going to be a PITA is plating bath analysis to maintain acceptable copper and acid concentrations.  How good are you at inorganic chemistry?   The glassware and reagents alone to titrate for the acids and copper ion aren't cheap . . . .

[phil from seattle]

When I was making my own boards at home, I tried a grommet like product for vias.  I looked but couldn't find the info on it. Basically it is a little tube with a flare on one end. The length was slightly more than the PCB thickness.  I think it took a 40 mil hole.  The tube was pressed into the hole and then spread by a tap on the other side. It worked but was such a PITA that I only did 2 boards.

When the cost of getting PCBs made in China dropped, I never looked back.

[T3sl4co1l]

Let us know how well PEG works. I hadn't heard of it before.

What I had heard of, and used before, is thiourea, which is available in such products as Tarn-X (a metal polishing mix).  This has the effect of turning a useless crystalline deposit (dendrite crystals) into an adherent, flat, dense, matte deposit.

I don't know if PEG will serve the same purpose, or act to further level/brighten the deposit.

I've also heard of xanthates and related, being used for this purpose; or you can get fully formulated brighteners, but you'll probably have to do a lot of looking to find way too much (gallons?) as this would be an industrial product...

For PCBs specifically, all I hear is long-throw plating, that needs alternating current.  This is a square wave, duty cycle > 50%, probably with I(fwd) and I(rev) adjustable, as well as the frequency, which for whatever reason acts to deposit uniform thickness, even in narrow holes and trenches.

(The reason is probably proactive removal of material around corners, because all of these brighteners -- which are attracted to the cathode -- don't do much on the inversion phase, and material is removed preferentially from the peaks, and not from the valleys and crevices, hence giving, on average, a more uniform deposit.  Downside?  Bad efficiency.  The frequency should be below the ion diffusion rate for the maximum hole depth, I think?  So, not like 50Hz, but maybe on the order of 1Hz.)

Tim

[cowasaki]

When I was making my own boards at home, I tried a grommet like product for vias.  I looked but couldn't find the info on it. Basically it is a little tube with a flare on one end. The length was slightly more than the PCB thickness.  I think it took a 40 mil hole.  The tube was pressed into the hole and then spread by a tap on the other side. It worked but was such a PITA that I only did 2 boards.

When the cost of getting PCBs made in China dropped, I never looked back.

Pretty much in the same boat....  I have a 3 tank MegaPCB kit when doing vias I used their "rivets" which I fitted by placing the board on a solid steel plate then dropping the via through and then using a broken micro drill bit which I placed into the rivet from the other side and tapped with a tiny toffee hammer rounding it off.  I then soldered it both sides.  I worked but was a pain. Having just paid £13 for 11 boards I might well get rid of the PCB making stuff.