I’m glad to report I’m getting even better result with my PCB etching. Results do seem a bit up and down each time I get back to it but I feel I’m narrowing it down and getting more polished.
One. I’ve started using Ziplock vacuum bags to evenly press the transparency against the PCB. A really nice cheap substitute for a vacuum light box! I can thoroughly recommend them.
Two. I’m now able to get even better exposure with 3.5 minutes under the UV box rather than using the fluorescent tube. Maybe my developer solution used to be too strong. Maybe ditching the glass in favour of the Ziplock helped. Regardless, I’m getting a really good result. Here’s the partially etched board showing great definition.
Three. I got some Tin plating solution. No idea why I didn’t do this before, as it’s really easy and gives a great finish. The instruction say to carefully clean the copper with an abrasive. However, I assumed that as I’d just removed the etch resist from the copper with acetone and it had to be just about as clean as it could be. I popped it straight in the tinning solution before I got fingerprints all over it.
I had to mess something up and I removed the protective layer on the soldermask before exposing. Some of it dulled a little on contact with the transparency. Oh well. Otherwise I’m very happy. The ridiculously small negative text even came out a little. Here’s the board before drilling and populating. It a simple MSP430 based alarm for when my two year old son opens the front door. He can now just reach the handle.
When I’ve got it all sorted (and have tried the via rivets too) I think I might do a proper write-up.