DIY pcb contacts - gold-plated? tinned?

[chrisbob12]

I want to make a pcb with some contacts for rubber buttons with conductive rubber like these adafruit items, for example.

I need to etch a contact pattern on the pcb for the conductive rubber to make a circuit, but the exposed copper will tarnish in no time, so I'll need to plate it somehow or other. The simplest way would be to tin it with grated solder - this looks like a workable approach, although I'm sceptical about how long the contacts will be reliable with this method.

Does anyone know of better ways for a one-off DIY-er to tackle this?

[Simon Howes]

Spray the contactors tracks with a little wd40.
It'll stop if tarnishing and it should still work, though you might want to tweak resistance values in your touch circuit.

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[chrisbob12]

Thanks! Not what I was expecting, but sounds like a goer.

[Nigel Worsley]

> The simplest way would be to tin it with
> grated solder - this looks like a workable approach, although I'm sceptical
> about how long the contacts will be reliable with this method.

That looks like a lot of work, and I share your concerns about long
term reliability.

> Does anyone know of better ways for a one-off DIY-er to tackle this?

Depends somewhat on your definition of better. Way back when I did
this for commercial products the standard method was to print a carbon
loaded conductive paint onto the pads, it could also be used to
replace wire links (double sided boards were still considered a
premium product back then!). The modern approach is to use gold
plating, this has become such a common finish for PCBs that a fair few
Chinese manufacturers don't even charge extra for it.

DIY gold plating is possible, but a certain amount of equipment and
chemicals are required. The best approach for this application is what
is known as pen plating (and also brush plating, same thing but a bit
bigger). This uses a 'pen' with an absorbent swab that holds the
plating solution instead of it being in a bath as with conventional
electroplating. As well as reducing the quantities required of the
expensive plating solutions, this also allows for plating of selective
areas instead of the whole item.

The most expensive part of electroplating starter kits is the
'rectifier', even in the good ones this is nothing more than a badged
lab power supply of which the hackspace has plenty. These kits don't
just include gold plating solutions, as it it is normally necessary to
use one or more 'strike coats' of other metals before the final gold
one. The usual sequence is to plate copper, then nickel and then gold,
but as we are starting with copper then only two stages are required.

I have had a pen plating kit on my wishlist for quite a while, if you
are definitely going to go ahead with this project then it may just
find itself at the top of the list :)

Nigle

[Chris Brasted]

Hi Nigel, that's a very interesting proposition! Thank you. I'm definitely going to develop the project, though need to design an appropriate circuit board first.

Absent any further suggestions, I'll revive the thread when I've got something working.

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[Nick Johnson]

Tinned pads is the standard approach for commercially fabricated PCBs. For better quality boards, ENIG is used instead.

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[stephen o'brien]

You could try something like this:-
http://www.ebay.co.uk/itm/SENO-TIN-PCB-Tin-Plating-crystals-for-500ml-solution-Immersion-tin-plating-/111779804358?hash=item1a069874c6:g:BFEAAOSwjVVVhVQG