Conducting PCBs?

[ataradov]

I agree that the solder balls are visible on the board, although they are not visible in the paste

That'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.

[psteichen]

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.

[psteichen]

This is the stuff...

[ataradov]

This is the stuff...

It is even worse. It is not a solder paste, but:

When it comes to soldering and brazing, LA-CO is the brand that plumbers around the world trust to do the job right the first time, every time. LA-CO makes specialty fluxes for all metals including aluminum, stainless steel, brass, iron, tin and zinc

You 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.

[ataradov]

Also, here are a couple of boards I have around. Yours should look similar if you don't use pluming supplies for soldering.

[BradC]

You 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.

Not 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.

[psteichen]

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...

[BradC]

Now the brake cleaner was recommended on several other forums, so I won't take all the blame on that one...

It's not *that* bad. Honestly a toothbrush and some methylated spirits, rubbing alcohol or any fairly strong/pure alcohol will do the job.

[psteichen]

Also, here are a couple of boards I have around. Yours should look similar if you don't use pluming supplies for soldering.

I see you used a lot of jumpers rather than bridging. I might have to try that. They look good.

[ataradov]

I see you used a lot of jumpers rather than bridging. I might have to try that. They look good.

That's actually PTFE wire. Expensive, but wonderful stuff for prototyping, since insulation does not melt and shrink.

[psteichen]

It's not *that* bad. Honestly a toothbrush and some methylated spirits, rubbing alcohol or any fairly strong/pure alcohol will do the job.

Thanks, I'll try the rubbing alcohol tomorrow. Apparently there is still a residue that the BPC didn't remove.

[psteichen]

BTW: Is this stuff any good?
MG Chemicals 835 Liquid Rosin Flux
https://www.amazon.com/dp/B005DNR01Q/

[ataradov]

BTW: Is this stuff any good?

Yep, 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 one https://www.amazon.com/dp/B0195UJ9ZC?psc=1&smid=A37PQFY35MDOP9 seems to be the closest, but I have not tried it myself. For whatever reason, clear-looking stuff works better than cloudy-looking stuff.

[KL27x]

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.

[Siwastaja]

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.

[KL27x]

your flux residues should read resistances like 10-100Mohm or even more, never kohms.

With 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. 

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.

This 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.

[ataradov]

Alcohol works great on rosin flux. Just use the 91% or 95%, not the 99%.

That'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.

[KL27x]

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.

[yngndrw]

I would have to agree with Siwastaja, 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 that ataradov has 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. )

[psteichen]

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 anyway

At 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