# Photoetching: Developed photoresist coating sticks to the PCB

I've been practicing making PCBs using the photoetching process and I've come across a problem which I I haven't seen mentioned much on the Internet.

When I put the exposed board in the developer, some of the negative photoresist coating immediately starts dissolving in the developer and creates a brown cloud in the developer.

For developing, I'm using $10 \mbox{ } g \mbox{ } NaOH$ in $1 \mbox{ } kg \mbox{ } H_2O.$

My problem is that if any parts of that cloud come into contact with the PCB again, they will stick to it and the covered pieces will etch with great difficulty. They start etching just before the parts which were supposed not to be etched.

So any ideas how to prevent that?

• Have you tried wiping it off with a wet kitchen towel? Jun 3 '12 at 11:44
• @Rocketmagnet Yes and it has no effect. Jun 3 '12 at 12:04
• I have never encountered this problem before. Sorry, there's not much I can suggest that isn't obvious. Jun 3 '12 at 12:52
• I haven't experienced this exactly, but it sounds like the particles in the cloud are not fully dissolved. Have you tried upping your exposure time to make sure the exposed photo-resist dissolves as easily as possible? Jun 4 '12 at 2:13
• @Nathan Wiebe Should I try increasing or decreasing it? Jun 4 '12 at 4:32

Riston has a special developer which deals with "developer sludge":

http://www2.dupont.com/Imaging_Materials/en_US/products/dryfilmPhotoresist/developer_technology.html

I put the developer in a shallow bowl, then place the board facing up and gently brush it with a soft paintbrush. This dissolves the brown cloud instantly while the board is developing and prevents it from adhering to the board again. Once the development is complete I immediately rinse the board in pure water. Maybe the temperature is also related; here the temperature is between 15C and 30C, usually. I never had problems with the development process, but also don't remember making any boards when it was below 25C

• One thing I've noticed that whenever I touch the board with a brush, it removes the protoresist there. I've tried some really soft brushes, but still it seems that they are too much. Jun 5 '12 at 21:22
• Maybe the problem is with the quality of the coating in the boards you're using. These are what I used: digikey.com/product-search/… Jun 6 '12 at 14:32
• Could be. Mine were much cheaper. For example a 200 mm x 300 mm one was around \$11. Jun 6 '12 at 14:40
• Also I bought a solution manufactured by Electrolube (p/n PDN250ML). I noticed it's not pure sodium hidroxide, it also contains trisodium phosphate, disodium metasilicate and sodium carbonate. Jun 6 '12 at 14:42

Looks like the temperature of the development solution could be a factor. I noticed that at 40 C, the could did not stick to the board at all.

Some sources recommend temperature between 18 C and 25 C, but I'm not sure how reliable that information is, since tap water temperature here is around 20 C and it appears to have been too cold for the developing to take place.

From my experience, NaOH seems to work best when used with water temperature between 35 C and 40 C.