I'm having a severe problem with solder adhering to the FR4 PCB material. I made my boards (myself, my first time) using positive developer and etchant on a pre-sensitized board. I washed the etchant off with nail polish remover.

It's so bad, I can take the iron and "paint" solder on the board. Flux (kester flux) doesn't seem to help at all. I don't know why this is happening or how to rectify it; searches on google only turn up page after page of people who just don't know how to solder (i.e., "solder won't stick to board."

Any advice or insight is extremely welcome.

I scoured it per the advice given below, and to my surprise, the "PCB" came off and revealed that even though I could see all my traces, the whole thing appeared to be copper. Considering I tried to follow instructions to a T, what could have gone wrong here and how do I fix it (or fix it on the next board)?

  • 4
    \$\begingroup\$ This is one of the reasons why people use solder mask :) It's one of the downsides of etching your own boards in my experience. \$\endgroup\$ – Some Hardware Guy Jul 22 '14 at 16:24
  • 3
    \$\begingroup\$ This is not normal behavior at all - you seem to have some contaminant on your board or low quality stock, as solder will not normally wet bare board materials. Yes, soldermask is used for best results, but can be as much about preventing solder from migrating down traces. It should not be necessary for even moderately skilled hand assembly. Try cleaning that board with an abrasive pad, steel wool or a mildly abrasive cleanser and then plenty of water. \$\endgroup\$ – Chris Stratton Jul 22 '14 at 16:27
  • \$\begingroup\$ Thank you. Could it be because I didn't use non-acetone nail polish remover? Currently I'm giving it an isopropyl bath and then I'll scour it. \$\endgroup\$ – MJXS Jul 22 '14 at 16:30
  • 2
    \$\begingroup\$ Sounds like you didn't etch or agitate it enough. \$\endgroup\$ – Ignacio Vazquez-Abrams Jul 22 '14 at 16:47

You've under-etched the board, or the photo resist was not properly exposed or developed to reveal the copper for etching (so it would definitely be under-etched in that case).

The way it works is that the etch resist prevents the copper from being etched away. When you are done you should be able to see light through the etched areas (and there still should be resist protecting the traces).

A photo would help, but it may be either that you did not recognize the appearance of an etched board or that something is funky with your etchant that is causing the areas being etched to not have a bright matte copper appearance. Here's a partially etched board where you can see the laminate partly exposed and the copper remaining.

enter image description here

  • 1
    \$\begingroup\$ may be caused by under-exposed photo-resist \$\endgroup\$ – jippie Jul 22 '14 at 16:49
  • \$\begingroup\$ My etchant is definitely NOT that dark at all, this is going by the instructions as listed on the bottle. Have I over-diluted it? I etched for a "full" 24 minutes as recommended, diluting with warm water and agitating the whole time (not disagreeing I underetched, merely painting a whole picture). Please let me know what photos would be useful and I can provide them. \$\endgroup\$ – MJXS Jul 22 '14 at 16:50
  • 2
    \$\begingroup\$ That's not necessarily a problem. That etchant is FeCl, there are clear types too. The important thing is what the board looks like. Did you get any laminate exposed on the copper side? It's very temperature sensitive. Also, as @jippie says there could be a problem with the exposure or developing of your photo resist. Suggest you try some test strips to get the process down. \$\endgroup\$ – Spehro Pefhany Jul 22 '14 at 16:52
  • 1
    \$\begingroup\$ Why would you dilute the etchant? Moderate heat is useful, but you can do that by putting the etchant container in a water bath. In any sort of manual-involved etching process, completion will be determined not by time, but rather by observation of the results. \$\endgroup\$ – Chris Stratton Jul 22 '14 at 17:00
  • 1
    \$\begingroup\$ I am trying a longer exposure period as well as a longer time in the positive developer. It already seems a lot clearer than previous. I've left the etchant mostly undiluted and am agitating while it develops. I know what you mean by you can see light through the traces - only a FEW of those occurred on the last board. Thank you both for your advice/guidance, I'll report back hopefully with good news. \$\endgroup\$ – MJXS Jul 22 '14 at 17:00

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.