What happens when you under expose a PCB?

therecordingart · Jul 25, 2005

I bought some photo + PCB's and when attempting to develop them the traces came through fine, but the image was fuzzy and there was still a light green "haze" within the layout. I left the PCB in the developer for quite some time and shook the hell out of it, but no dice. Money down the toilet!

Does this sound like my developer has gone bad, not the right mixture, or under exposure?

gyraf · Jul 26, 2005

Most likely underexposure from your description. Did you make a test-strip for this type photo-pcb and this developer?

Jakob E.

therecordingart · Jul 26, 2005

It would've made sense to do that....I'm such a newbie! Thank you for the response. Right now I want to make all of the PCB's for the projects I'll be doing, and just get parts as I go. Since I'm a newbie I'm starting with guitar pedals, then will move on to my Green pres I ordered, and then onto Fabio's API. Damn, I can't wait for that API!!!!!

Svart · Jul 26, 2005

i've left stuff under the lamp for hours before. make sure your art is FLAT against the pcb. sometimes you think it's flat and it's not. I place a mouse pad under the pcb and put the art over it, covered by thick clear glass to hold it down. something else that could be causing the haze.. check the artwork before you print it. sometimes PDFs have a habit of having small amounts of color data where there should only be white, such as if the pcb was scanned into a printer. make sure that any open areas are pure. this has jacked my art many times!

make your developer a little weak. not tooo weak but a little weaker than normal and over expose the PCB. this gives you a little more time with the solution as to not start to eat off the traces too but the over exposure will cause the stuff you want gone to come off quicker.

:thumb:

therecordingart · Jul 26, 2005

Thanks for the help!!!

EZ81 · Jul 26, 2005

Hi recordingart,

be sure to change only one thing at the time when testing exposure time to get reproducable results. I found it useful to start with a fixed developer concentration (1% NaOH) and fixed developing time (1 min) (depending on pcb brand) using the test pattern linked below. Exposed one field, waited a minute, removed the cover from the next field, waited a minute, ... (this was with 500W halogen lighting which takes 12min, UV is way faster)
http://img177.imageshack.us/img177/2633/expostest1dh.png (600dpi, the outer frame should be ~100mm wide). Wasted two of these before getting good results. I make fresh developer for every PCB, it seems to hate being stored. Sometimes a soft brush used during developing helps removing the exposed material.

HTH
;Matthias