Leaving the photoresist on after etching - Page 1
Forum section: electronics / projects

author: akis
author_rank: Frequent Contributor
timestamp: December 11, 2013, 09:47:33 pm
content: I noticed that if I do not strip off the photoresist after etching, it provides nice copper protection. But is there a way to remove it just on the pads so I can solder the components? I have noticed that it is possible to apply solder straight on over the photoresist, but it takes time and is much harder than trying to solder on clean copper. Any ideas?

author: Balaur
author_rank: Unknown
timestamp: December 11, 2013, 09:54:15 pm
content: I mainly use Bungard pre-sensitized boards and they describe a technique to use the photoresist as protection/solder mask with an extra expose/develop step.Extract fromthis manual:Quote

author: akis
author_rank: Frequent Contributor
timestamp: December 11, 2013, 10:27:56 pm
content: I had no idea that the photoresist can be developed again (or at least the Bungard one). Would that mean that you'd have to develop and then etch the board in a dark room so as to be able to expose the board once more?

author: Balaur
author_rank: Unknown
timestamp: December 11, 2013, 10:42:08 pm
content: Quote from: akis on December 11, 2013, 10:27:56 pmTypical photoresist is most sensitive at 400nm. Direct sunlight is obviously not recommended.The following picture fromthis sitewould suggest that LED and incandescent bulbs could be OK. CFL are problematic?

author: akis
author_rank: Frequent Contributor
timestamp: December 11, 2013, 10:54:36 pm
content: I was told by Mega to be quick when working with the protective film removed, as sunlight even through windows is enough to compromise the photo resist. I am not sure about fluorescent tubes though and other sources of room lighting. Developing and etching are not very difficult processes so I suppose I could have a yellow or red or whatever low wattage lamp just for this purpose. I will try the Mega photosensitive boards tomorrow to see if they can be redeveloped.

author: nctnico
author_rank: Super Contributor
timestamp: December 11, 2013, 11:12:54 pm
content: I strip the photoresist by exposing the PCB again (for a couple of minutes) and then use the same developer to strip the resist. Much nicer than using ethanol or acetone. After etching I spray the PCB with SK10 (from Kontakt Chemie) which is a flux and protective coating in one product.

author: akis
author_rank: Frequent Contributor
timestamp: December 12, 2013, 07:23:26 am
content: This SK10 looks good.

author: hlavac
author_rank: Frequent Contributor
timestamp: December 12, 2013, 01:00:11 pm
content: Note that sides of the traces will not be protected and solder can still get to the traces, so its not much of a solder mask....

author: akis
author_rank: Frequent Contributor
timestamp: December 12, 2013, 01:21:43 pm
content: Quote from: hlavac on December 12, 2013, 01:00:11 pmWhich one the SK10 or the leftover photoresist?

author: nctnico
author_rank: Super Contributor
timestamp: December 12, 2013, 04:05:41 pm
content: The leftover photoresist!

author: madires
author_rank: Super Contributor
timestamp: December 12, 2013, 04:24:05 pm
content: Quote from: nctnico on December 11, 2013, 11:12:54 pmSK10 works great. I'm using it for over 20 years and my old PCBs still look fine, no visible corrosion.

author: akis
author_rank: Frequent Contributor
timestamp: December 12, 2013, 04:33:43 pm
content: Quote from: nctnico on December 11, 2013, 11:12:54 pmWhy? Dipping it in the stripper takes like 10 seconds and it's all done, why bother re-exposing (ie reusing the UV light box) and then weakening the developer? I reserve the developer for "surgical" operations, and the stripper for "mass effect"