Content:

• UV box (THE box)
• Making board design
• Printing artwork
• Exposing unit to UV light
• Etching
• Source files

UV box:

Into word of home made  PCB’s I have stepped in with UV light.

• UV tubes: local store
• Sockets (G5): local store
• Box: local store

For starters I’ve scavenged “energy efficient fluorescence light bulbs” (the cheapest ones):

The pinout IMO is straight forward so no explaining here, unless you ask. Ok, the basic idea is to connect two grouped pins from the starter chip to one end of UV tube and other two grouped pins to the opposite end.

And actual box:

Board design:

Thirst thing you always have to do prior you have desired PCB is to design it! (captain obvious :-)) I always make my designs (or at least until now I have) with EAGLE. I do not consider myself expert, more like novice so for simplicity reasons I use hobbyist design rules (see files section). Almost always manual routing is needed, but hey, it’s better than nothing. I won’t explain how make board from schematics, IMO pretty good job is already done by instructables: Turn your EAGLE schematic into a PCB

Printing artwork:

You need to generate positive (as in copper track == black ink) artwork. It’s important to print in the best possible quality, because PCB quality depends directly on the artwork quality. The printed side should “touch” the copper when under UV light to avoid blurring. As for medium it’s recommended to use translucent material but as I have figured out default ordinary paper will do the job, just exposure time from 2-5 min. rises up for about 30-45 min. It’s not bad considering the rarity and cost of this type of paper.

Exposing to UV light:

After printing is done secure printed artwork tightly on the copper fiberglass board. Exposure time may vary from 2 to 45 min. it depends a lot on material being used, power of UV tubes, et cetera… For me it’s 30 min. Timer is essential for this kind of work to avoid over-exposure/under-exposure and in both cases quality of PCB decreases dramatically. You have to try yourself to determine the right values for your rig… If exposure time is right you should see yellowish tracks.

Notes:

• Don’t use glass to hold your artwork, use organic glass instead because normal glass stops about 90% of UV light
• DO NOT use short-wave UV lamps (like EPROM eraser tubes) – these emit short-wave UV which can cause eye and skin damage, and are not suitable for PCB exposure
• You have to remove the protective layer from copper to expose photoresist, try to do it in as little direct sun light as possible, the best time to do it is in evening/night.

Etching:

I’ve only used DP50 for positive photoresist development and it worked great. This stuff has many advantages over other solutions, most importantly is is very hard to over-develop. Even then it’s without dramatic quality decrease. Also it’s not temperature critical. Solution has a very long shelf-life so it’s great for home use (although,  I would not recommend to store chemicals at home). Available at my local store: dp50

For actual etching I use chemical B327 (Sodium persulfate (Na2S2O8)). Why B327 over others?

1. Clean – Does not damage clothing or dishes;
2. The solution is clear – you can see etching process;
3. Uniform distribution and dissolve rate

So this is second time when you have to experiment, but after you define times according you it’s all worth it.

That’s it, enjoy Your PCB ;-)

Source files:

• EAGLE design rules: hobbyist.dru
• CAD: soon