First etched surface mount PCB

Well, after experimenting with CNC milled PCBs I decided to give etched boards a ago. As I have a “UV exposure box” (i.e. a cheap eBay thing for drying dragons’ fingernails) for the soldermask, I decided to try photoresist board. Odd then, that I found this was far too stong for the PCBs. Even a minute would appear to give a good exposure when I started developing the, but it turned out to be so overexposed I stripped all the resist off the boards. An expensive way to end up with plain copper boards.

Etching the boards was also not as simple as I thought. Sodium Persulphate seemed useless. Using Freeic Chloride and a sponge seemed too rough for the delicate photoresist. Sloshing Ferric Chloride didn’t do much until I heated it up – by putting the containing (including PCB) in the microwave. Anyway, enough of my woes and failed attempts.

Image

PCB after etching

When I eventuallly got a combination that worked this is what I came up with. This is the board post-etch. It’s not quite as good as I hoped but definitely good enough for the MPS430 microcontroller (TSSOP) and the 0805 LEDs, resistors and capactiors.

ImageAnd this is the end result after applying the Dynamask 500 solder mask that I’ve used before.

I’m hoping I don’t ruin it when I come to try surface mount soldering…

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2 thoughts on “First etched surface mount PCB

  1. Very nice looking result. I’m also using one of the eBay fingernail UV boxes (36W), but haven’t had trouble with exposure times. I guess that is mostly because I use paper instead of transparencies, as my printer is less accurate on the transparencies.

    Looking at your etching results, I would suggest trying different concentrations of the developer. Mostly, I think your developer may be a little bit too strong, resulting in the ragged edges on traces while not all of the background has etched away.

    I’m also trying to set up a soldermask process myself, but it’s not working too well so far. I guess part of the problem may be that I’m using white soldermask paint, which apparently is not as sensitive as green.

  2. Thanks for your comments. I had a lot of trouble using the UV box for exposing the etch resist (Bungard pre-sensitised boards) as it seemed to completely overexpose it. I’m currently using a standard fluorescent tube for 20 minutes and Seno (sodium metasilicate based) developer with much better results.

    My Canon MG5200 inkjet printer on “T-shirt transfer” settings does an excellent job – and even mirrors automatically.

    I can really recommend this soldermask. I bought more than I need. I notice you’re in Europe. I’ll drop you an email and post some over to you.

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