PCB at home guide

[Fred27]

I haven't done any PCBs for a while and a screw up with my process left me a bit worried that my solder mask had expired. After some proper testing I can confirm that 1.5 years stored in a cardboard tube in a garage has had no impact on it at all - even though the light levels, temperature and humidity (tumble drier) vary greatly.  2-3 minutes under a UV nail lamp worked as well as ever.

I did try tinning after the solder mask and this damaged the mask. However, I hadn't bothered with the final post-developing cure step (a UV blast for 30 minutes and 150C for an hour). That was probably all it was.

The offer of some to try out still stands if you want to compare the two.



I was happy enough with my cheap nail lamp and thought that LEDs were unnecessarily complicated and expensive, but your exposure unit has inspired me. I've just ordered the same LED strip you used - although only one as I plan to make a smaller unit. I'll pop some white LEDs in there too so it can double up as a light box for aligning transparencies for double-sided boards.

[kurt]

I haven't done any PCBs for a while and a screw up with my process left me a bit worried that my solder mask had expired. After some proper testing I can confirm that 1.5 years stored in a cardboard tube in a garage has had no impact on it at all - even though the light levels, temperature and humidity (tumble drier) vary greatly.  2-3 minutes under a UV nail lamp worked as well as ever.

I did try tinning after the solder mask and this damaged the mask. However, I hadn't bothered with the final post-developing cure step (a UV blast for 30 minutes and 150C for an hour). That was probably all it was.

The offer of some to try out still stands if you want to compare the two.

That is great news about shelf life. I'm very tempted to try out the film. Seems so much more convenient than the gel. Where did you buy the film? And what do you use to develop it?
 

I was happy enough with my cheap nail lamp and thought that LEDs were unnecessarily complicated and expensive, but your exposure unit has inspired me. I've just ordered the same LED strip you used - although only one as I plan to make a smaller unit. I'll pop some white LEDs in there too so it can double up as a light box for aligning transparencies for double-sided boards.

Awesome to hear that you got inspired from it I built a dedicated light box for white light. If you are going to combine them I guess you have to halve the LED density in one direction. And you will get a less uniform distribution (unless you use the 60 LED/meter strip and get ¹/₄ of the density). And you will have to double the distance between the light panels and the PCB.

I prefer two separate units since it give higher density which means more power, slimmer design, and more uniform lighting. And I used plexiglass on the UV box since it is more transparent to UV and easier to machine for the more complex mounting. For the white light box I used picture frame glass since it is much more scratch resistant and I do more handling of items on top of it than on the UV box. And the box is much simpler so I don't need to do any machining to mount it.

The high density comes with a price though. None of the boxes are able to dissipate enough heat to stay on permanently without overheating. The UV box have the LEDs mounted on metal plates which help. I never need to run it more than 10 minutes at a time, and that seems to be fine. But the white light box have them mounted on the MDF back plate from the same picture frame I stole the glass from. And the LEDs get worryingly hot in a hurry. If I where to build it again I would use a metal plate instead. And I want to make it dimmable. For most things it is to bright and I usually put one of those milky white cutting boards that you use in the kitchen over it to dampen the light. Would be much better to dim the lights and reduce power dissipation than to run it at full power and block 70% of the light

[Anks]

Here is one I did using the film as solder mask. It looks all scratched in the picture but to the naked eye it looks fine.

Ill try and get a better picture tomorrow when I don't have to use the flash or the light on my desk. I'm sure that is what's bringing the scratches from cleaning the copper out.

[Fred27]

If you are going to combine them I guess you have to halve the LED density in one direction. And you will get a less uniform distribution (unless you use the 60 LED/meter strip and get 1/4 of the density). And you will have to double the distance between the light panels and the PCB.

Thanks for the extra info. I will play around with spacing and distance and see what I come up with. Your UV box seems lightning fast so something lower power would probably be fine. I will probably stick a diffuser layer in there, so maybe that would help. The usual 4 x fluorescent tube style commercial light boxes don't seem to have a problem with light distribution despite clearly having bright tubes with gaps between them, so maybe it won't be an issue.

That is great news about shelf life. I'm very tempted to try out the film. Seems so much more convenient than the gel. Where did you buy the film? And what do you use to develop it?

I got mine from octamex.de. I bought a load to make the shipping cost to the UK seem more reasonable. There's usually a few people selling smaller pieces on eBay. Sodium Carbonate is used to develop it. Nothing nasty or expensive.

And I want to make it dimmable. For most things it is to bright and I usually put one of those milky white cutting boards that you use in the kitchen over it to dampen the light. Would be much better to dim the lights and reduce power dissipation than to run it at full power and block 70% of the light

Surely a 555 and a potentiometer is about 10 minutes work? 

[kurt]

Thanks for the extra info. I will play around with spacing and distance and see what I come up with. Your UV box seems lightning fast so something lower power would probably be fine. I will probably stick a diffuser layer in there, so maybe that would help. The usual 4 x fluorescent tube style commercial light boxes don't seem to have a problem with light distribution despite clearly having bright tubes with gaps between them, so maybe it won't be an issue.

I opted out of using a diffuser for the UV box to reduce the amount of light that gets under the edges of blocked areas. Without one the max angle light can enter at with the LEDs I use is 30 degrees. And at that angle it will have very little intensity. And I believe the commercial fluorescent type light boxes have curved reflectors to make the light as unidirectional as possible. That being said, my old UV nail curing lamp didn't have any of that and it still worked pretty well. And yes, with 1188 LEDs the box emits a lot of light. Without any mask over the photoresist it is fully cured in 6 seconds

I got mine from octamex.de. I bought a load to make the shipping cost to the UK seem more reasonable. There's usually a few people selling smaller pieces on eBay. Sodium Carbonate is used to develop it. Nothing nasty or expensive.

That was a bit more reasonable than the prices I have seen on eBay. Depends on how much it will cost to have it shipped to Norway though. Will have to check that out. Thanks for the link.

And I want to make it dimmable. For most things it is to bright and I usually put one of those milky white cutting boards that you use in the kitchen over it to dampen the light. Would be much better to dim the lights and reduce power dissipation than to run it at full power and block 70% of the light

Surely a 555 and a potentiometer is about 10 minutes work? 

If only I could find someone that could make a PCB for it

[Zepnat]

Like your tutorial especially the part on making the solder mask. Using a vacuum to spread it is genius. That was the only part I had trouble with, getting a consistent finish with that uv ink all the same shade. I love the photo resist method it's so controllable and if you make a mistake it's easy to go back a step and carry on.


Excellent well done best tutorial I've seen.

[kurt]

Excellent well done best tutorial I've seen.

Thanks a lot for the very encouraging comments