Corrosion issue with PCB

[TraceurFrenzy]

So I have dipped my toe into the wonderful world of soldering my own electronics projects with the minty boost and bread board power supply. It was great fun putting them together and I look forward to doing more. I even have a few more kits lined up to work on.

The only thing that is stalling me is that I've noticed the solder joints on the underside of the PCB are showing corrosion. The minty boos is the worst to the point that I think the two middle leads of the USB port had a short circuit but I digress. My concern is that am doing something wrong in my soldering process and I don't want to keep repeating the same mistake on the next two projects.

Is corrosion on the solder joints inevitable or is there a protective/preventive step that I am missing besides keeping it dry?

The solder I am using is Aim solder SN63 PB37 , FLUX OAJ 3% diameter is 0.02".

If there is any other information I can provide to help trouble shoot this I would be happy to answer any questions.

[adafruit_support_bill]

Can you post a photo of the suspected corrosion?

[Zener]

Web search shows that is a water soluable core flux. Such flux must be washed with water after soldering since it is corrosive. I use a toothbrush. Just wash it and let it dry. You can blow it with air or use a hairdryer if you are in a hurry. If you want to avoid washing then use a no-clean flux or a rosin core, which doesn't have to be washed even though everyone (except the solder mfg) will tell you it does.

[MrGlass]

I use a toothbrush. Just wash it and let it dry.

I learned soldering primarily on my own (after a quick tutorial at HOPE ages ago), so I don't know that much about this. I keep seeing this mentioned by professionals, that you should "wash" your stuff after soldering. I don't think I should be placing my Ice tube clock in the banned sink, running it under the tap, and scrubbing it with a sponge. So, for my sake, could you explain when and how I should be cleaning my projects after soldering?

[adafruit_support_bill]

If you are using rosin core solder, it is generally not necessary. If the rosin residue starts getting brown and crusty after extensive rework, you can clean up with some gentle scraping and scrubbing with 90+% isopropyl and a toothbrush.

[Zener]

There are basically 3 kinds of flux you can get with your solder:

1) Rosin core /RMA. This is the oldest kind. Many people will insist you have to clean it off with flux cleaner but you don't.

2) Water washable. This came along around 1990. The flux is water soluable so you can clean it with water. Most components are waterproof so it is not a problem. PC boards were washed in water washers for years (and still are) after soldering. The only parts that don't like water are typically switches and some sensors and audio components like speakers and microphones and LCD displays. Most standard parts are fine. No batteries of course.

3) No clean. This is the newest kind and leaves a minimal residue that is fairly hard. You don't clean it. Some don't have very high activity though (cleaning ability).

[TraceurFrenzy]

Thanks for the information everyone. It sounds like Zener hit it on the head but I'll still try to post some pictures soon. Never hurts to double check right?

[philba]

I use a no-clean flux but still clean it off. While it won't damage anything, it's sticky - dust and other things (like little bits of metal) stick to it. I'd hate to have even a high resistance bridge somewhere (dust will absorb humidity). Plus, I care about how my boards look.

[Zener]

If you are going to clean your boards then use water washable flux.

[philba]

isopropyl works pretty good for me.

[MrGlass]

Thanks for all the great info! Really cleared things up for me.

[bearmos]

According to some articles, if you'd like a clean PCB - it's better/safer to use a solder/flux that is designed to be cleaned (e.g. water soluble), rather than try to clean a no-clean solder or flux. The idea is that the no clean solder is designed to encapsulate the corrosive chemicals, so it winds up being harder to dissolve and clean.

I've definitely found this to be true. It's far easier to use water soluble solder/flux and clean afterwards for a good looking assembly.

Also, beware that toothbrushes can cause static electricity - horse hair bristles are what's commonly used in industry to avoid the ESD.

[lyndon]

Finally, a use for the pounds of winter coat that the horses are shedding as the weather warms up

[adafruit_support_mike]

The reason you want to remove some kinds of flux (especially the water-based ones) is that they do corrode the parts over time.

A flux is basically an acid that etches the surface of the parts while you're soldering. It eats oxidation that would keep the solder from making a good bond. Some fluxes (like rosin) are more or less inert at room temperature, but get aggressive up around the temperature where solder melts (300-350C). Others, like zinc chloride, are aggressive all the way down to room temperature. ZnCl2 is *really* good at stripping gunk off of metal, but you want to get rid of it as soon as possible. If you don't, it just keeps on etching.

[Agent_24]

I clean with 99% Isopropyl Alcohol.

Cleaning is best done soon after soldering, the longer you leave it the harder it is to remove.