How to use "UV curable solder mask repair paint"? - Page 1
Forum section: electronics / repair

author: analogix
author_rank: Frequent Contributor
timestamp: January 09, 2020, 10:07:11 pm
content: I've been repairing an old PCBs where I discovered that corrosion had slightly damaged a trace, so I scraped the green solder-mask away from a section (in order to solder a "wire bridge" for repair).Wanting to seal the exposed PCB trace from moisture etc. I bought something called"PCB curable solder mask repair paint" from eBay. The package is labelled "Mechanic Type: LVH900-GY Mechanic UV curing solder mask ink". There are no instructions on the package itself and the eBay page has some very vague info:Capacity : 10ml(10cc)This paint is used to protect PCB traces from corrosion, moisture.It is also used for repairing PCB after soldering, rework.Usage:Apply paint on your PCBSpread it on the PCB with covering the transparent mask filmExpose it under UV light ( or sun ) for a few minutesWash away the extra paint by gasoline or oil base solventColor: GreenI have an EPROM eraser lamp with a 15cm long fluorescent tube (National 4W GL-4).Is this suitable, and if yes -how long should I expose the repair-paint to that light? The eBay page says "expose under UV light (or the sun) for a few minutes". But how close? How powerful a UV source? And for how long exactly?

author: Gyro
author_rank: Super Contributor
timestamp: January 09, 2020, 10:13:58 pm
content: Quote93 Million miles?

author: helius
author_rank: Super Contributor
timestamp: January 09, 2020, 10:20:02 pm
content: EPROM eraser lamps are UV-C, "germicidal UV" lamps that emit at the spectral wavelength of mercury at 253.7nm. They have clear tubes since there is no phosphor. This type of light is very hazardous to the eyes and skin and needs to be confined to a sealed enclosure with safety interlocks. If your PCB will fit in the EPROM eraser tray, you might be able to use it to cure the soldermask.The more common "black light" is a UV-A or UV-B wavelength that is less dangerous (although eye protection is usually still necessary). The tubes with dark blue-black phosphor are blacklights. This is normally the type of UV used to cure UV-curing adhesives and inks because the lamp can be held in the hand or set up in the open in the factory without endangering workers. A watt or less of UV radiance will cure most adhesives in less than a minute, sometimes as fast as several seconds. There is no danger from exposing too long.

author: analogix
author_rank: Frequent Contributor
timestamp: January 09, 2020, 10:43:08 pm
content: Thanks. I did know that EPROM erasing lamps are dangerous, but just not how much, and I didn't know about the skin hazard (which on second thought should be obvious of course, given that too much sun exposure is dangerous to your skin).I built mine into a metal enclosure with a loose tray underneath where I put the EPROM(s), then I put the box on top of it. Not exactly failsafe with safety interlocks, but with common sense there should be minimal exposure towards myself.There is a small (1cm diameter) hole on the end of the box which does allow some of the UV-light to come out, but I don't look straight at it, it doesn't reach far and I try to keep physically away (a couple of metres) from the box when it's on. Is that safe enough, or is just seeing any of the light harmful?Without the tray I can put it right above the PCB, resting on the components although that won't totally block out all the UV-light coming out of it. Maybe a towel over it will help considering exposure might be for just a little bit. From what you're saying here I'm assuming that 4W of that light will cure in just a few seconds?I don't have any other UV-light source unfortunately, and for this one time job of fixing a PCB it would be good to use what I already have. If not however I'll look for a "regular" UV light. Are "blacklights" the types used in discos and such, and that's what is safe to use for this sort of thing without any eye/skin protection?

author: TopLoser
author_rank: Unknown
timestamp: January 09, 2020, 10:47:41 pm
content: LE UV Torch, 9 LED 395nm Ultraviolet Flashlight, Blacklight Detector for Pet Urine, Stain, Bed Bugs and More, 3 AAA Batteries Includedhttps://www.amazon.co.uk/dp/B00GU55270/ref=cm_sw_r_cp_api_i_h06fEb0SYFD1SSomething like this cures DLP UV resin in seconds, then a quick wipe with IPA to clean away any residue.Bright sun does the same thing but takes a bit longer.

author: Zucca
author_rank: Unknown
timestamp: January 09, 2020, 10:52:54 pm
content: in youtube there are plenty of videos

author: mvs
author_rank: Frequent Contributor
timestamp: January 10, 2020, 08:22:48 am
content: Quote from: analogix on January 09, 2020, 10:07:11 pmUV curable solder mask is useful for creating own PCBs, since you can expose it through film with solder mask layer and wash out uncured areas afterwards.For repair work I would recommend solvent based lacquer, like nail lacquer of your girlfriend...

author: Haenk
author_rank: Super Contributor
timestamp: January 10, 2020, 09:26:50 am
content: I'd suggest using Kontakt Chemie "Plastik 70" spray, should be available through amazon or ebay.(Other brands are available as well, like Teslanol 26027 or 3M 1601...)

author: sean0118
author_rank: Frequent Contributor
timestamp: November 21, 2020, 08:19:52 am
content: Sorry to resurrect an old thread, but I've also been looking into how to repair solder mask.I came across the Mektronics CircuitWorks Overcoat Pen, I haven't used it yet but I'll order one to try out.It's probably pretty similar to nail polish (as recommended by mvs above):https://www.mektronics.com.au/circuitworks-overcoat-pen-green.html

author: Radioman23
author_rank: Newbie
timestamp: November 13, 2021, 10:05:50 am
content: Question I wanted to put here since it is relevant and might help another noob at this without getting lost in badly named threads in a search:I have been trying to use this very same solder mask to anchor 34 Ga/ 0.1601mm wire to both repair a trace (it works well to mask the wire) and to (attempt) make a wire loop to replace a torn pad.No matter how thin I have tried applying the mask,it does not hold the wire worth a damn. I can't get it to hold a wire loop long enough to tin it for use as a pad. When the mask joint fails, I can see uncured mask where the wire was, and I suspect that the UV can't penetrate all of the oil. I bought the right UV light, and I let it sit for about 2 minutes, but still no luck. I just tried burning away the enamel coating with a solder blob, and for a moment I thought that it would grab the wire , but the mask failed again. I thought this stuff is what you would use to make a wire loop pad on a PCB? Should I use the overcoat High temp epoxy for this? ( Here in the US its sold by chemtronics).

author: DavidAlfa
author_rank: Super Contributor
timestamp: November 13, 2021, 10:34:30 am
content: - Clean the board with alcohol to remove any dirt and grease- I give a touch of hot air to completely dry the board after cleaning.- Try to mask the area. Removing it after cured is not easy! Only mechanical ways.- Remove the mask before curing, or you'll have some trouble.- Apply a THIN layer. If too thick, the UV won't get through it and it will peel off.You will need some practice, I've found that up to 0.2-0.3mm it's ok (But takes a little more curing time)- Expose it to UV. Even a single cheap UV LED makes the job in few seconds for thin layers. No fancy equipment needed.If the layer is thicker, leave it for few minutes, even if it looks ok, the bottom could be still fresh.

author: abdulbadii
author_rank: Frequent Contributor
timestamp: November 14, 2021, 11:28:28 am
content: Imho choose between using Varnish or Lacquer whichever easier, while Lacquer clearly is better quality

author: Radioman23
author_rank: Newbie
timestamp: November 14, 2021, 08:45:37 pm
content: Would lacquer have enough adhesive/mechanical strength to hold a micro wire loop and hold up to soldering temps long enough to make a good replacement BGA contact point?