Conducting PCBs?  - Page 1
Forum section: electronics / projects

author: psteichen
author_rank: Contributor
timestamp: October 10, 2016, 05:01:15 pm
content: I am trying to transfer a circuit from breadboard to perfboard. I've triple checked all the connections, and it just won't work. Voltages are appearing on traces that are completely isolated from power. So I tried introducing voltage to various parts of the board. The crazy thing is that I can introduce a meager 9V to almost any part of the board and read as high as 90% of that value many holes away, with no connections. The PCB is conducting current! And not just a little bit either. I get readings in the KOhm range in some parts of the board between adjacent unconnected holes. Is this condition something I caused by applying too much heat during soldering? Or is this something that can happen with low quality boards? I already suspected the flux, so I cleaned the whole board with Heptane & Acetone. No better.

author: ataradov
author_rank: Super Contributor
timestamp: October 10, 2016, 05:58:13 pm
content: Do you have pictures of the board? Have you tries to measure actual resistance between the parts that must be insulated?That would be a VERY poor quality board. It would be also reasonably hard to do intentionally, so I have no idea how this can happen by accident.

author: ajb
author_rank: Super Contributor
timestamp: October 10, 2016, 06:06:18 pm
content: I've gotten boards even from reputable fabs with "bonus" copper before--it happens, but you wouldn't expect to be nearly every net unless they simply forgot that whole etching step.

author: ataradov
author_rank: Super Contributor
timestamp: October 10, 2016, 06:07:50 pm
content: Quote from: ajb on October 10, 2016, 06:06:18 pmWell, naturally board defects happen. But 90% of the value suggests some resistance value, not just a dead short.

author: Zero999
author_rank: Super Contributor
timestamp: October 10, 2016, 06:12:03 pm
content: Yes, if it were a dead short, I would have also suggested it was a solder bridge but the fact it's in the kOhm range eliminates that possibility.Have you tried washing the flux off using methylated spirit, then baking it at 60oC for an hour or so? It's possible the flux is soaking up some moisture from the atmosphere and becoming conductive.

author: psteichen
author_rank: Contributor
timestamp: October 11, 2016, 02:08:33 am
content: Thanks for the thoughts. Yeah I thought too that it could be the flux, so I used brake parts cleaner to clean both the soldered side as well as the component side. But I can still probe holes that are clearly free of any bridges and get continuity to most of the rest of the board. Adjacent holes are around 10s of KOhms, while several holes away runs in MOhms. I assume that my flux cleaning, while perfect visually, must still be the issue. I'll try some other cleaning agents and report back.I've attached a photo, so that you can all laugh at my soldering jobHonestly, I've checked all adjacent traces, and there are no bridges. Just this crazy conductivity all over the board. Even on the left edge with no soldering nearby.I will be creating only a few prototypes with perfboard and assuming good performance will etch proper PCBs for future generations.By the way, I tested another raw board from the same batch and it has no continuity. So either I caused it with the soldering heat, or more likely, this is still a flux issue. I just hope the flux hasn't somehow soaked into the board permanently saturating it.

author: ataradov
author_rank: Super Contributor
timestamp: October 11, 2016, 02:13:25 am
content: Quote from: psteichen on October 11, 2016, 02:08:33 amYou've got to be kidding. That stuff is toxic. Don't use it for anything but brakes. Use IPA for electronics.This is a very good type of PCB, so I would assume that this resistance if from the film formed by the brake cleaner.Also, your soldering is horrible, but it should work.

author: psteichen
author_rank: Contributor
timestamp: October 11, 2016, 02:19:06 am
content: Quote from: ataradov on October 11, 2016, 02:13:25 amHahaI thought I might get that response. It was what I had laying around,and I've read that others have good luck removing flux with it.The continuity was an issue before applying the cleaner, so it didn't cause it, but I will take your advice and look for the IPA.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: October 11, 2016, 02:20:31 am
content: Looks like the usual milky white residue of water soluble flux to me. So, what kind of flux was it?

author: ataradov
author_rank: Super Contributor
timestamp: October 11, 2016, 02:21:17 am
content: Quote from: psteichen on October 11, 2016, 02:19:06 amDo you have the remainder of the board this fragment came from? Can you test this?Also, what did you use for a flux?

author: psteichen
author_rank: Contributor
timestamp: October 11, 2016, 02:28:11 am
content: Quote from: ataradov on October 11, 2016, 02:21:17 amThe rest of the unused boards in the batch test with no continuity. I used a water soluble, non-acid, lead free paste.

author: ataradov
author_rank: Super Contributor
timestamp: October 11, 2016, 02:29:12 am
content: Quote from: psteichen on October 11, 2016, 02:28:11 amYou actually used solder paste? With solder balls in it?That's not a flux. And possibly the reason for your problem.

author: psteichen
author_rank: Contributor
timestamp: October 11, 2016, 02:29:48 am
content: I think I need to throw out the flux. Just tested it by probing the paste, and it conducts right in the jar!

author: ataradov
author_rank: Super Contributor
timestamp: October 11, 2016, 02:30:29 am
content: Quote from: psteichen on October 11, 2016, 02:29:48 amBecause it is a solder paste. It has solder in it and it is designed for reflow soldering.Lead free should have been your clue. There is no reason for lead to be in a flux in a first place.

author: psteichen
author_rank: Contributor
timestamp: October 11, 2016, 02:35:20 am
content: Well that's why I posted here. I knew someone would figure out my mistakesThanks. Any chance this board can still function if I clean the solder paste well enough?

author: ataradov
author_rank: Super Contributor
timestamp: October 11, 2016, 02:38:09 am
content: Quote from: psteichen on October 11, 2016, 02:35:20 amI don't know, I don't think anyone will have a lot of experience doing that.You can try IPA + a lot of physical brushing (to the point where you at least fully remove flux residue, not like now).The stuff you have used is a paste of tiny soler balls suspended in the flux. Your goal is to remove those balls.

author: psteichen
author_rank: Contributor
timestamp: October 11, 2016, 02:44:07 am
content: Well that sucks. Must be microscopic solder balls, because it looks like a cream.

author: Mr.B
author_rank: Unknown
timestamp: October 11, 2016, 02:45:36 am
content: A photo of the container and its label would help a lot.

author: ataradov
author_rank: Super Contributor
timestamp: October 11, 2016, 02:48:47 am
content: Quote from: psteichen on October 11, 2016, 02:44:07 amThey are typically 5-50 microns (differs by types).

author: Mr.B
author_rank: Unknown
timestamp: October 11, 2016, 02:50:07 am
content: The indicated parts of the photo look suspiciously like paste balls (or grouped paste balls) to me.

author: ataradov
author_rank: Super Contributor
timestamp: October 11, 2016, 02:51:59 am
content: Quote from: Mr.B on October 11, 2016, 02:50:07 amI think they are balls already combined under heat. You can't really see balls from the paste with a naked eye.

author: Mr.B
author_rank: Unknown
timestamp: October 11, 2016, 02:53:15 am
content: Quote from: ataradov on October 11, 2016, 02:51:59 amAgreed.I just added (grouped paste balls)...

author: psteichen
author_rank: Contributor
timestamp: October 11, 2016, 02:57:03 am
content: The photo is from before I cleaned it up, thus the excess flux. I agree that the solder balls are visible on the board, although they are not visible in the paste. Since cleaning the board the excess flux is visibly gone, but I'm guessing that a residual film is still causing the continuity.

author: psteichen
author_rank: Contributor
timestamp: October 11, 2016, 03:00:52 am
content: By the way, this was my first attempt at using perfboard, and it was awfully tough to make all of those connections without bridging. Looking forward to making a real etched board for this.

author: ataradov
author_rank: Super Contributor
timestamp: October 11, 2016, 03:03:18 am
content: Quote from: psteichen on October 11, 2016, 03:00:52 amThat's not going to help. Perfboard are just as easy to solder as regular boards, you just need to practice soldering.Also, don't tell us that you have some $10 soldering iron directly plugged into the mains

author: ataradov
author_rank: Super Contributor
timestamp: October 11, 2016, 03:07:10 am
content: Quote from: psteichen on October 11, 2016, 02:57:03 amThat's because the ones you see are formed from 1000s of the ones in the paste. That's the point of the paste - you place it on the board (only on the pads), place components and heat the whole thing. Tiny balls from the paste recombine into big solder blobs and solder the components.

author: psteichen
author_rank: Contributor
timestamp: October 11, 2016, 03:08:11 am
content: Well I have a soldering station plugged into mains, but I can adjust the temperature.Soldering individual pins is no problem, but some of the traces/bridges I had to create span a dozen pins or more. I suppose with practice it gets easier. I found that low heat worked best for the bridging. Higher temps caused the solder to flow onto the copper only, and wouldn't bridge.

author: psteichen
author_rank: Contributor
timestamp: October 11, 2016, 03:17:19 am
content: This is the stuff...

author: ataradov
author_rank: Super Contributor
timestamp: October 11, 2016, 03:23:20 am
content: Quote from: psteichen on October 11, 2016, 03:17:19 amIt is even worse. It is not a solder paste, but:QuoteYou really need to re-think your approach to electronics, you can't just use plumbers flux and brake cleaners. You need to use proper tools and materials.

author: ataradov
author_rank: Super Contributor
timestamp: October 11, 2016, 03:28:48 am
content: Also, here are a couple of boards I have around. Yours should look similar if you don't use pluming supplies for soldering.

author: BradC
author_rank: Super Contributor
timestamp: October 11, 2016, 03:30:19 am
content: Quote from: ataradov on October 11, 2016, 03:23:20 amNot disputing the spirit of what you are saying, but the contents of brake cleaner (even the chlorinated kinds) are essentially what we were using as flux remover 25 years ago. It cleans well and leaves no residue. Can be a bit nasty, and you don't want to be soldering around Chlorinated cleaners lest they decompose into Phosgene. IPA is nice, but even the (fairy tree hugger unicorn pee useless) flux cleaner I have here now is a considerably better solvent than IPA.As for plumbers flux, yeah. Not quite the right tool for the job, but hey it's a learning experience and we all start somewhere.

author: psteichen
author_rank: Contributor
timestamp: October 11, 2016, 03:31:10 am
content: Well, apparently that's true. But I tend to use what I have laying around. Apparently this stuff doesn't work well with electronics.Now the brake cleaner was recommended on several other forums, so I won't take all the blame on that one...

author: BradC
author_rank: Super Contributor
timestamp: October 11, 2016, 03:33:11 am
content: Quote from: psteichen on October 11, 2016, 03:31:10 amIt's not *that* bad. Honestly a toothbrush and some methylated spirits, rubbing alcohol or any fairly strong/pure alcohol will do the job.

author: psteichen
author_rank: Contributor
timestamp: October 11, 2016, 03:34:45 am
content: Quote from: ataradov on October 11, 2016, 03:28:48 amI see you used a lot of jumpers rather than bridging. I might have to try that. They look good.

author: ataradov
author_rank: Super Contributor
timestamp: October 11, 2016, 03:36:26 am
content: Quote from: psteichen on October 11, 2016, 03:34:45 amThat's actually PTFE wire. Expensive, but wonderful stuff for prototyping, since insulation does not melt and shrink.

author: psteichen
author_rank: Contributor
timestamp: October 11, 2016, 03:37:31 am
content: Quote from: BradC on October 11, 2016, 03:33:11 amThanks, I'll try the rubbing alcohol tomorrow. Apparently there is still a residue that the BPC didn't remove.

author: psteichen
author_rank: Contributor
timestamp: October 11, 2016, 03:50:37 am
content: BTW: Is this stuff any good?MG Chemicals 835 Liquid Rosin Fluxhttps://www.amazon.com/dp/B005DNR01Q/

author: ataradov
author_rank: Super Contributor
timestamp: October 11, 2016, 03:52:04 am
content: Quote from: psteichen on October 11, 2016, 03:50:37 amYep, that's the one you want.You may also want to grab rosin paste while you are at it. RadioShack used to sell the best one I tried. This onehttps://www.amazon.com/dp/B0195UJ9ZC?psc=1&smid=A37PQFY35MDOP9seems to be the closest, but I have not tried it myself. For whatever reason, clear-looking stuff works better than cloudy-looking stuff.

author: KL27x
author_rank: Super Contributor
timestamp: October 11, 2016, 05:05:17 am
content: FYI, if you indeed used plumber's flux, you have to clean the board with WATER. And very well. The zinc chloride and other salts left behind will not dissolve in break cleaner. It is possible to use plumber's flux on copper/tin electrical connections, but it is a pain to remove the flux, sufficiently. You cannot use it on steel/iron, though. You will never remove all of the salts, and the connection WILL definitely corrode over time, because the acid creates tiny pores in the iron where the salts get imbedded.Certain no clean fluxes will also leave a slightly conductive residue, especially when used incorrectly.Rosin flux, you should be cake. I use MG 835, and it's fine. RA flux is sorta well specified. The military came up with specifications for R, RMA, and RA. Anywhere you buy it, it is essentially the same. (This is one reason why flux manufacturers spend so much time coming up with better mousetraps.... they can only charge as much for rosin flux as the next guy; hence, margin on it is relatively small).So your circuit might be salvageable. I don't know what the brake cleaner did to it. But I would try hot water and a toothbrush before disposing of it. That said, I dunno if you really used plumber's flux. The jar says acid-free. Around here, anyway, "plumber's flux" means zinc chloride. And this creates hydrochloric acid when heated.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 11, 2016, 05:37:11 am
content: With high quality solder wire (for example, Multicore brand) and pristine materials (i.e., no badly oxidized vintage component leads from the 1970's), there is really no need for separate flux at all. Modern "no clean" fluxes, meaning cleaning is not needed, are so good that I have accidentally been using Multicore no clean fluxed solder wire for some time and haven't noticed any difference in how it behaves. Well, the smell has been different.Even with more traditional rosin based fluxes, cleaning is not paramount. With proper flux, your flux residues should read resistances like 10-100Mohm or even more, never kohms. Many of my older stuff, some built 20 years ago, without cleaning the flux residues at all, are just fine today.Precision measurement stuff (for example, instrumentation amplifiers for thermocouples or other very weak signals) are sensitive to flux residues conducting in the 10-100Mohm range.I.e., as a beginner, your effort is going the wrong way right now. Get proper solder wire (I REALLY suggest Multicore brand even though it's more expensive, but you know what you get) and forget the flux issue completely for starters. You can come back to adding extra flux - and cleaning the flux residue - later. This is because cleaning the flux residue IS NOT trivial at all and can make matters worse. You need to have a right cleaner for the flux type you are using. I have used IPA and ethanol, and with some fluxes, they leave horrible white mess that tends to accumulate under SMD components where you can't see it. If you want to clean it - you get the commercial flux cleaner from the flux manufacturer, period. If you are not interested in cleaning the flux properly, then you can as well make your life easier and just leave it there, usually it's not a problem at all, unless you are using some specially active, super corrosive flux. Like that plumber stuff - it is of course out of question.

author: KL27x
author_rank: Super Contributor
timestamp: October 11, 2016, 07:38:10 am
content: QuoteWith rosin flux I can't measure even megaohms. I understand the residue can cause problems at around 1GHz frequencies. Aside from that, nothing going on there, IME. If you are measuring anything with rosin flux, I would personally guess/suggest it is your circuit or circuit board.With some of the "low solids" no cleans, you might be able to measure something in megaohms, particularly if humid. These you will want to take care for your opamps and high impedance resistor networks and whatnot. But they are also selling "high solids" synthetic resin flux under "no clean" moniker now, too, which have a thick water-insoluble residue similar to rosin but clear.QuoteThis is what happens with some of the low solids no clean. Alcohol works great on rosin flux. Just use the 91% or 95%, not the 99%. You need a little water to get the trace salts. (The alcohol dissolves the rosin, and the water will dissolve the trace salts embedded in the rosin to keep it from redepositing).This is why a lot of hobbyists prefer rosin flux (or the synthetic resin flux). Low solids no clean has cost savings benefit for many commercial applications where the residue is tolerable, which includes most hobbyist uses, as well. This is primarily for looks and for pogo pin testing, where rosin flux would cause physical impediment to test points. (Rosin residue is essentially a fairly high dielectric insulator, outside of aforementioned GHz frequency range). But in case you ever need to clean off/rework the board, you could have a bad day if you use the low solids no clean. Bad day as in break out the toothbrush to remove the white crust that forms when you try to clean the board off.I suggest you clean the rosin flux if you want. Leave it on if you want. Don't really matter, unless you are doing a very high voltage, high temperature, or high frequency application. Like really high.

author: ataradov
author_rank: Super Contributor
timestamp: October 11, 2016, 03:57:06 pm
content: Quote from: KL27x on October 11, 2016, 07:38:10 amThat's not my experience, there is still white residue after not so thorough cleaning with IPA of any concentration. I mostly use 91% for personal projects because Walgreens is just around the corner, and 99% at work, because that's what we buy. Both leave white "sandy" residue. It does not affects anything and can be removed with better cleaning.At least IPA does not give me cancer and I don't need a fume hood to safely work with it.

author: KL27x
author_rank: Super Contributor
timestamp: October 11, 2016, 06:00:31 pm
content: Yeah, it's true. If you look real close, not all of it dissolves. Some tiny flecks of white precipitate will form in suspension. I have no problem to remove this. If you use a brush and blot immediately, and repeat with flush of fresh alcohol, and immediately blot, it does not really adhere to the board or components and is largely floated and blotted away in suspension. Once the rosin is removed, there is nothing for this to stick to, I think. So long as you don't leave the board wet/damp with the alcohol. Must be all blotted, immediately.With some of the no clean fluxes, the white stuff can be more like solid plaster that completely fills the space between pins like instant casting resin.99% of time, I leave rosin residue alone. I usually clean it when I am going to conformal coat, for stuff that will be handled with bare fingers. And I have no problem removing it. Maybe there IS a difference between brands. Or maybe I'm just not as observant. Although I use a microscope. I have never found flecks/streaks on the board, though I have noticed the teeny white flecks floating, if I dissolve rosin in a dish of alcohol.FWIW, I use 95% denatured ethyl. I find the smell much less objectionable.

author: yngndrw
author_rank: Regular Contributor
timestamp: October 11, 2016, 09:26:03 pm
content: I would have to agree withSiwastaja, forget the extra flux and just use some decent solder. Try using 0.4mm solder with a fine tip and don't forget to keep your tip clean with a wet sponge.Regarding the board, notice thatataradovhas used the legs of the components to jumper nearby pads rather than massive blobs of solder. You may find stripboard / veroboard (See attached) easier to work with as you don't have to worry about jumping pads on the solder side. (I should have put the decoupling cap under the IC socket, but I had already placed the socket before I'd remembered.)

author: psteichen
author_rank: Contributor
timestamp: October 12, 2016, 01:32:53 am
content: Eureka!I took some advice here and cleaned the board thoroughly with 70% rubbing alcohol and a toothbrush. I then soaked it for half an hour to help clean under the components and then rinsed and baked it till golden brown....er, till dry anywayAt first I had the same problem (some residual moisture I think), but this evening, I tried again and everything works as it should. No more bleeding voltage!Thanks everyone for the advice. I have some better flux on order