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Old 11th Apr 2017, 12:20 am   #1
MrBungle
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Default Varnish or tin a home made PCB?

I've started making my own PCBs again. Had a moment of non-laziness and knocked one up for a project I'm working on using the old fashioned "nail varnish and paint brush approach" (because I really couldn't be bothered to argue with KiCad or photoresist stuff. However the copper has started oxidising already, something which always annoyed me. For the sake of longevity I should probably do something about this on future boards.

So the question is, what are the relative merits of tinning vs using solderable varnish?

I'm considering either buying tinning crystals or Kontakt SK10 spray. Cost isn't a problem either way. Time, outcome and general mess is however.
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Old 11th Apr 2017, 12:43 am   #2
joebog1
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Default Re: Varnish or tin a home made PCB?

Both is really nice!

I just varnish, and I live in the tropics. BUT I have used tin as well.

Regards, Joe.
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Old 11th Apr 2017, 3:56 am   #3
Terry_VK5TM
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Default Re: Varnish or tin a home made PCB?

My experience with tinning crystals is that the coating also tarnishes over time.

I used to use a spray on, solder through coating (but have got lazy and send my designs out to get made now).


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Old 11th Apr 2017, 9:56 am   #4
David G4EBT
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Default Re: Varnish or tin a home made PCB?

I tried tinning crystal many years ago but it wasn't a success. They were expensive, I wasn't impressed with the result, and once mixed the solution has a short shelf life. Over the years, I've made a habit of tinning boards after drilling, by applying a small amount of solder to the tip of the soldering iron then quickly spreading the solder along all the tracks and pads. A very small amount of solder goes quite a long way. I don't let the iron tip dwell on the tracks for risk of lifting them. A light smearing of flux encourages the flow, but of course the board must be scrupulously cleaned afterwards so that the flux doesn't stay in the holes and risk corroding any component wires at the building stage. (I never tin before drilling as it risks the drill bit skidding).

I've attached three examples of drilled and tinned PCBs not yet made up, for stalled projects which will probably never get built, but they give an idea what the boards look like. The first is the audio amp stage of a home-brew 80 Metre receiver, the second is for the '49er' 40M direct conversion QRP transceiver, the third is for an SSB/CW filter which uses 12 stages of filtering via three TLO84 op amps. All were for amateur radio, in which I've lost interest. Quite scary to note that I made that filter PCB in 1997! (It featured in PW mag Nov 1997).

I never used PCB CAD software - I find it unsuitable for home-brew construction, and for the most part, it isn't intended for that, but to have the boards produced professionally. For DIY use, the tracks are needlessly thin and the pads needlessly small in diameter. One small slip of the drill and the board is a write-off, and thin tracks are all too easily undercut by the etchant. I get by nicely using MS PAINT and Photoshop to either create my own designs, or to modify others designs.

The last pic shows two (at that point, untinned) PCBs I produced to a standard that I'm content with, based on other people's designs, in which I 'beefed up' the tracks and pads to my liking using MS 'PAINT'. Homebrew PCBs is very time consuming of course, and makes no economic sense, but then I don't do it to save money - I do it because I enjoy it and that's what hobbies are about. If I found any aspect of my hobbies a bothersome chore, I'd find something else to do with my time.

I don't kid myself that I can match the quality of commercially produced boards - I aim to attain a good standard of DIY production because I'm a hobbyist - not a pro.I never use Dalo pens or other forms of 'resist' such as hobby paints, nail varnish etc - I'm too much of a fusspot and would find the end results offensive to the eye. That said, I quite understand that not everyone wants to go to all the palaver of gearing up to make the occasional PCB. Electrons aren't fussy - if they can get from where they are to where they want to go, they're unconcerned about aesthetics, but if my projects don't work, at least I can console myself that they look nice - through my eyes, at any rate!

Hope that's of interest.

Have fun.
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Old 11th Apr 2017, 2:15 pm   #5
dominicbeesley
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Default Re: Varnish or tin a home made PCB?

Like David says tin with a soldering iron - I use my largest tip and smear it around. I wet the board with plumbers flux first and the solder flows nicely and leaves a very thin layer, so thin that I now do this before drilling. Be sure to clean all flux off though as it is fierce stuff.

Recently I have sent my first couple of boards off for professional fabrication. I've always done them at home but these ones are quite complex computer boards and I couldn't face all the drilling. The manufacturing costs are way lower than buying the materials ($5 for 5 boards with a $5 discount for the latest design, cheaper than the photo resist board from Farnell) but the duty and delivery came to about £20! However by the time you've bought etchant, varnish and very expensive drill bits that I always seem to snap it still probably works out around the same. Plus these have solder resist and silk screen and look the part! I still make my own boards as the turn around (about 7 days for cheapest option) is a bit too long for my impatient temperament!

D
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Old 11th Apr 2017, 5:54 pm   #6
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Default Re: Varnish or tin a home made PCB?

Hair spray.

Seriously... it dries and is readily solderable (through) not to mention cheap and potentially in the bathroom/bedroom already!
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Old 11th Apr 2017, 6:42 pm   #7
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Default Re: Varnish or tin a home made PCB?

Fit the components, do a couple of 'washes' with both organic and aqueous solvents to take-away any nasty fluxy-residues, then after 24 hours in a "dry tank"[*] apply a modern 'conformal coating' lacquer.

What may seem a 'safe' solder-flux on a PCB can a decade-later turn out to be a corrosion-liability.

'[*]' Negative pressure and less-than-1%-humidity.
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Old 11th Apr 2017, 7:49 pm   #8
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Default Re: Varnish or tin a home made PCB?

A quick lick of shellac seals and is solderable through. Much the same as hair spray but cheaper per unit volume.
 
Old 11th Apr 2017, 9:52 pm   #9
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Default Re: Varnish or tin a home made PCB?

Firstly, a big thank you for all the useful replies above.

I decided to consolidate all the advice and produce a new PCB from scratch for this. So I used the following process:

1. Drill the holes with a paper template and an 0.8mm drill in a Dremel. I did this first as it makes it easier to mark out!
2. Scrub the board down with wire wool.
3. Nail varnish the entire thing by hand. Took about 5 minutes in total. Primark black nail polish (80 pence!) applied using the brush that came with it. Left it for 20 minutes.
4. Chuck in a takeway box with a little ferric chloride in it in a sink of hot water and etch wobbling it constantly.
5. Rinse down with water and pour the FeCl back into the bottle (important).
6. Soak in isopropyl alcohol until all the nail varnish has all dissolved.
7. Rub down with wire wool again.
8. Flux with a flux pen (Chemtronics no-clean stuff)
9. Run a slightly wet soldering tip over it to cover all the copper.
10. IPA wash again followed by water wash.
11. Solder all parts in (multicore/loctite 60/40 rosin)
12. IPA wash again.

Final result. Not perfect but better than the original:

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I used a lumocolor pen to write the date and project number on but this mostly disappeared. The nail polish is orders of magnitude better than any etch resist I've ever used historically!

Top looks better...

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(for reference, it's the FET VOM adapted from Test Equipment for the Radio Amateur. Divider network is 5% parts which was a mistake - awaiting better resistor delivery!)

It slightly pains me the irregularity of the traces but at the same time it pleases the anarchist in me. My wife just informed me that you can get nail varnish pens so I'm going to try one of them as a compromise.

Please excuse the terrible photographs; my DSLR is irreparable apparently which means I'm stuck with a terrible mobile phone camera. Not happy.
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Old 16th Apr 2017, 7:41 pm   #10
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Default Re: Varnish or tin a home made PCB?

I've had good success with tinning PCBs. I was advised by a colleague how to do it such that the tinning coats evenly and stays untarnished. The procedure is to use a fine scouring pad and avoid any contaminants and get the PCB really shiny and grease free before tinning it. Then leave it tinning for much longer than the minimum recommended time.

I've got boards here that I regularly handle (eg MCU programmer/play boards) and these were tinned 10-15 years ago. They still look like they were tinned recently! The added bonus is that a well tinned PCB is really easy to solder, especially with small SMD parts. However, get it wrong and the tinning will not be even and can look smeary or cloudy and will tarnish easily and will not solder as easily.

I use an old version of Eagleware Genesys to do the PCB design of most of my boards. It's as close to freehand as you can get and it was intended for the design of small RF prototype boards. You don't need a schematic to place parts or create a PCB although it will support schematic capture. It is optimised for creating and placing custom shapes, nudging things around and for ease of creating custom component cells and aligning shapes with great precision. It was designed by RF enthusiasts for RF enthusiasts and the PCB layout feature was added in the mid 1990s. That's when I started using their PCB layout tool and nothing else can compete for the stuff I do.
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Old 16th Apr 2017, 8:43 pm   #11
David G4EBT
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Default Re: Varnish or tin a home made PCB?

For those who might wish to go down the tinning solution route, there's a short (2 mins) video here:

https://www.youtube.com/watch?v=wOqkI-S-wdI

SENO PCB Tin Plating powder sufficient for 500ml solution for immersion tin plating can be found on ebay for £12.95 post free.

The suppliers state that the powder is mixed with warm (50°C) water, allowed to cool and used at room temperature (no heated tank is needed). This low operating temperature allows very small tin molecules to be deposited giving a very smooth hard surface. It actually plates tin at room temperature resulting in a deposit of 1.5-2.0 microns in the first half hour and 4.5 microns in up to 2 hours. Working solution has a life of up to 6 months if stored in an air tight plastic container - unmixed powder has unlimited shelf life. It's supplied in powder form to make up to 0.5 ltr of immersion tinning solution. 0.5 litres of fresh solution will plate 15-20 complete copper Eurocards with 1-1.5 microns of tin or 5 Eurocards with 5 microns. As an average etched circuit has 30% copper a figure of 50-65 Eurocards respectively is a more accurate figure. (The ‘Eurocard’ format describes a standardized size of printed circuit boards with dimensions of 100mm x 160mm and the thickness 1.6mm).

The instruction for use can be found here:

http://www.modellingelectronics.co.u...structions.php

The problem I'd have with that is that my PCB making is spasmodic - I might make three or four in a month, then none for six months, so once the solution is made, by the next time I might need it, it would be past its best, if not defunct. Maybe for small boards, less than 0.5L could be made, but even two 0.25L lots of solution would cost £6.50 a pop for the powder, so would cost more than the other costs involved in producing a PCB. Basically, it makes the whole process of homebrew PCB production uneconomical as compared to getting the boards made professionally. But then as we've said before - cost is not the only consideration where hobbies are concerned. (There would be no hobbies if we factored in the cost of our time and materials!).

Hope that's of interest.

I'm in a rut as deep as a grave, so I'll keep bimbling along with the flux and solder method which I've used since days of yore.

"Use what talents you possess - the woods would be very silent if the only birds that sang were those that sang the best".
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Old 17th Apr 2017, 6:16 pm   #12
MrBungle
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Default Re: Varnish or tin a home made PCB?

I'm actually quite happy with the flux and solder method now I've used it a couple of times. Works just as nicely on "cut and peel" boards:

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(Colpitts oscillator for measuring inductors with a frequency counter)
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Old 17th Apr 2017, 6:41 pm   #13
Craig Sawyers
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Default Re: Varnish or tin a home made PCB?

I used to cheerfully make my own boards, and I've still got a UV box, a bunch of laserjet film, a big jar of ferric chloride, and a wide range of carbide drills.

Then the price of PCB's dropped like a stone, so it is dead easy with practice to do a layout and produce Gerber files for a board house. Prices are stupidly low, and quality excellent.

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