Making a P.C.B. copy - Page 1
Forum section: electronics / repair

author: clay1905
author_rank: Regular Contributor
timestamp: February 08, 2020, 05:00:37 am
content: Hi,I'm not experienced with PCB making and etching. I have a device that is exhibiting peculiar behaviour, and I believe that the circuit boards have been contaminated with something that has rendered them somewhat conductive.I would like to rebuild the device (a rather nice bench power supply) and this will of course involve making reproduction circuit boards. Google searches seem to return results more about part of the design and production of PCB's rather than how to make a single copy of an already existing board.Isn't there software that's clever enough to interpret a photo of the track side of a board these days?Any pointers in the right direction would be much appreciated.

author: tautech
author_rank: Super Contributor
timestamp: February 08, 2020, 05:34:59 am
content: I’d try a scanner then print it in monochrome and adjust scaling to match the original size.Then with a laser printer do a toner transfer for a DIY etch.How big is the PCB ?From your other thread:

author: clay1905
author_rank: Regular Contributor
timestamp: February 08, 2020, 09:59:50 pm
content: Thanks for the pointer.The board's about 8 X 41/2 inches, single sided. And yes, that's it in the picture. There's another with a signal generator and wave shaping circuits, but it's even smaller. After I posted here I started to hit on web pages that were describing what you're talking about. Delightfully simple. I like that.Before then though, I think I'll try another contributors suggestion of giving the board a good wash. I think I might try giving it another wash with isopropyl alcohol. The last one was just for a clean, and not attempting to address leaking. A much more thorough scrub may save the bacon yet. I'll need to wait though. With all this rain, I don't think the alcohol would ever evaporate.

author: tautech
author_rank: Super Contributor
timestamp: February 08, 2020, 11:02:29 pm
content: Toner transfer can be troublesome without prior experience however products like Press N Peel PCB Film from Jaycar can make it lots simpler.https://www.jaycar.co.nz/press-n-peel-pcb-film/p/HG9980You can find similar products for less.They also have cheapish blank PCB's and etchant:https://www.jaycar.co.nz/ammonium-persulphate-250g/p/NC4258I don't think you really need FR4 and could use FR2 phenolic PCB's for this project.FR2 is lots easier to work with too.

author: clay1905
author_rank: Regular Contributor
timestamp: February 08, 2020, 11:34:19 pm
content: Thanks for the info and links. And making me look up what the rating on PCB's is about. I have to admit, I'm not all that enthusiastic about working with fibreglass board either.The press and peel type of resist looks like a good option for a beginner. There's a Jaycar store just down the road, so a small premium is OK for the convenience.Once again, it'll have to wait until fairer weather. It's bucketing down just now, and the highway doesn't look at all appealing.

author: tautech
author_rank: Super Contributor
timestamp: February 09, 2020, 12:16:02 am
content: Yeah spend the shitty weather time doing your homework and getting your ducks all in a row.If it was winter here and I couldn't get outside I'd offer to draw the PCB up in Altium and send you the Gerber files to have it professionally etched but too much to do ATM.You could also possibly use tracing paper if a scan doesn't work out and then Sharpie the traces black so it properly scans and then do the toner transfer bit. Getting a dense layer of toner on the transfer medium is the key with toner transfer so to not have any porosity in the transfer and get pin holes in the traces after the etch.Check each stage to ensure the scaling is correct and adjust printer settings if it's not.Whatever, I look to be fairly generous with pad sizes so to give yourself some come and go for drilling but for the leaded devices you have a bit of tolerance but not so with headers and the like which will require careful marking out.

author: tooki
author_rank: Super Contributor
timestamp: February 09, 2020, 12:55:16 am
content: Maybe others can shed more light, but absent carbonization from severe overheating, I’ve never heard of fiberglass PCBs going conductive. As such, I really, really doubt it’s the problem.

author: clay1905
author_rank: Regular Contributor
timestamp: February 09, 2020, 06:37:53 am
content: Ta.Funny, but the marking out is the least of my concerns. Comes from doing an awful lot in the past. The boards are not densely populated, so some inaccuracies would be easily tolerated. The pin holes for the chip sockets would be attacked under a little drill press with an indexable table.Not about to rush off and do anything just yet. I quite like to be able to predict outcomes as much as I can.

author: clay1905
author_rank: Regular Contributor
timestamp: February 09, 2020, 06:49:32 am
content: I would agree. Fibreglass conducting seems a very weird thing. Your post made me question the idea. I gave the matter some thought, and decided that maybe the supply transformer was somehow to blame, as it's the only other common element.Nope. Infinite resistance between all the windings. I'm really struggling to find another answer to how there is resistance between isolated power supplies. There are only two things in common, they share the same transformer core, and they share the same circuit boards. Or am I missing something, like some proverbial elephant in the room?There is that case where the resistance between two points on one board is only 1500 Ohms, with a distance of about 12mm between points. The return path on the circuit board should be in the order of hundreds of KOhms. There's no charring, no apparent colour change, nothing to suggest why.I'm not happy with the conclusion, but I'm not coming up with a viable alternative, yet.

author: aix
author_rank: Regular Contributor
timestamp: February 09, 2020, 06:53:59 am
content: Quote from: tooki on February 09, 2020, 12:55:16 amAlso, isn't the suspected conductivity something that could be verified using a multimeter?

author: clay1905
author_rank: Regular Contributor
timestamp: February 09, 2020, 08:50:11 am
content: Indeed. It's how I'm able to quantify resistance between certain points on the board that ought to be orders of magnitude bigger, or infinite.

author: JohnPen
author_rank: Regular Contributor
timestamp: February 09, 2020, 01:37:53 pm
content: Have you perhaps had an electrolytic capacitor leakage onto the PCB? I had one years back that caused a TV to lose it's line hold due to low resisistance across the surface of a PCB. The cure at the time was a squirt of detergent and a PCB scrub in very hot water plus a drying session afterwards. It cured the problem beautifully. The particular TV, valve type, had the electrolytic suspended upside down over the PCB just asking for trouble at some time. The capacitor electrolyte is quite good at conducting and only needs a thin film to cause problems.

author: tooki
author_rank: Super Contributor
timestamp: February 09, 2020, 08:39:30 pm
content: Quote from: clay1905 on February 09, 2020, 08:50:11 amAs in, you measure conductivity between two random places ofbarePCB? (NOT between two traces or pads!!!!)

author: george.b
author_rank: Frequent Contributor
timestamp: February 09, 2020, 08:55:59 pm
content: Quote from: tautech on February 08, 2020, 11:02:29 pmI use the good old glossy magazine paper technique (old IEEE newsletters are a favorite of mine) without any trouble. Granted, I've been doing it for years, but I don't imagine anyone should have much trouble with it

author: clay1905
author_rank: Regular Contributor
timestamp: February 09, 2020, 09:28:13 pm
content: No, and I wouldn't expect to either. I've had a couple of leaky items before today, and they tend to be very secretive about it.One is a rotary selector switch. Leaks from the top deck, but you won't measure anything in the manner you're proposing. Between one terminal and the frame you will though, about 5meg.The circuit board was the same, the leaks are rarely (or so I'm reliably informed) on the surface, and consequently, not immediately apparent.Out of curiosity, I broke open the phenolic board, and just like I was told to expect, no evidence of anything other than some phenolic resin. It's a sneaky thing.As for fibreglass though, I wouldn't have expected it, but that's where the evidence is pointing. I have two tracks on a board. They are not physically connected. Current passes between. What would your diagnosis be?

author: tautech
author_rank: Super Contributor
timestamp: February 09, 2020, 09:38:25 pm
content: Quote from: george.b on February 09, 2020, 08:55:59 pmEach to their own recipe.I first used the glossy backing sheets from self adhesive labels and they worked very very well except for some trace porosity due to only a 600dpi laser printer. Using my much better Oki 1200dpi printer to solve the porosity issues caused all manner of other problems namely toner smudging so I had to go to an inferior transfer medium which wouldn't peel clean so then had to be soaked and rubbed off.Toner transfer is not a cut and dried process repeatable for everyone.....expect to have to experiment until a nice dense transfer is achieved.I never worried about pre-etching much instead gently abrading the blank PCB with 00 steel wool and then rinsing in clean water before the transfer. Anyways, there's a few threads here on the process with plenty of good advice on how to do it.

author: Refrigerator
author_rank: Super Contributor
timestamp: February 11, 2020, 06:11:23 pm
content: I once tried making a BGA stencil and my method was to take a high resolution (and high contrast) picture of the PCB, then convert it to monochrome bitmap and fix up in paint.After that you scale it accordingly and replicate the PCB.

author: nardev
author_rank: Unknown
timestamp: February 11, 2020, 06:31:34 pm
content: I have seen this service before :https://dirtypcbs.com/store/pcbclone

author: mariush
author_rank: Super Contributor
timestamp: February 11, 2020, 06:50:30 pm
content: The number of components seems to be low enough that it would be worth taking the time to write them down on a sheet of paper (or on the computer in notepad or whatever) and write down the connections between the chips (or where 2-3+ traces meet, mark that as junction1, junction2 etc). You can make a dot with a permanent marker where pin 1 is or something like that (it can be removed later with isopropyl alcohol)This would also allow you to "optimize" the layout a bit and maybe incorporate bodge wires like that red wire as traces , or to put physical connectors at some points instead of soldering wires directly on the circuit board.You have Kicad which is free, you have Diptrace that's free for 300 pins or less, there's other free solutions as well.

author: tkamiya
author_rank: Super Contributor
timestamp: February 12, 2020, 12:32:24 am
content: I would actually try to repair the board.If it's charred, I would imagine it could conduct to some extent. But the damage should be localized. How about remove the trace around the smoked portion, leaving just the round. Keep digging the PCB material until no more blackened portion exists. Then use insulated wire and reconnect removed portion of the trace.Trying to remake the PC board and repopulate can easily become a very deep rabbit hole.

author: tooki
author_rank: Super Contributor
timestamp: February 12, 2020, 01:01:45 am
content: Quote from: clay1905 on February 09, 2020, 09:28:13 pmI wish you would use the quote feature so that we know what and who you’re responding to.If you’re talking to me, in response to my question, then what I’m trying to figure out is how you came to the conclusion that the board itself has become conductive. From what I can glean from your vague descriptions, I think you’re measuring between two parts of thecircuitthat should be open, but aren’t. But in that case, it’d be acomponentthat is leaking current, not the PCB.If you poke your multimeter probes into two bare (non-copper) areas of the PCB, and no current flows, then the PCB is not conductive, and you’re following a red herring!