Could this flux resedue cause a faulty connection?

I am having very uncontrollable problems with a stepper driver. I soldered on the headers myself, but I am not very good at this.

The stepper driver behaves erratic and touching the board sometimes causes a reaction. Thats why I belive this is a soldering problem. I removed the plastic from the pins and found some resedue looking like flux. (top right pins) Could this be the cause? Is it reccomended to clean solder points?

If you have used rosin core electrical solder, then it's not a problem.

Sounds like a "bad decoupling" problem.
I had a look at your other posts, and I did not see any supply decoupling near the module on your breadboard.
Leo..

What Wawa says +

While the flux residue will not cause a bad connection the solders joints do not look good. Why is there so much flux? It looks to me like the wrong flux has been used and the joints have not been hot enough.

Joins should look smooth and bright, yours look dull and rough.

If that board has plated through holes it is only necessary to solder one side of the board and I suggest the other side. Solder will wick through when the temperature is right giving you minimum solder on the side that is going to get plugged in to something.

The solder job doesn't look great, no; somethings systematically wrong with his technique - but none of them look bad to me.

I'd wager he's using lead-free solder, which doesn't make it any easier. Go snag some of the good stuff (60-40 leaded), and you'll understand why they used leaded solder in the first place :wink:

He's also soldering on the wrong side, as Mike mentioned - when you solder pin header, you typically want to put the short end of the header through the holes, so the plastic spacer is on the same side as the long part of the pin, and then you solder from the opposite side. Soldering pins on the end that goes into the connector just makes life much harder on yourself, since you have to be careful about getting solder on the side of the pin.

Check the connections with an ohm meter to be sure if you suspect that, though.

You should use one of these with IPA (IsoPropal Alchohol)
Trim the brush in half to get stiffer bristles.

If you used solder with rosin flux, only the upper right pins got hot enough to activate the flux. So, as suggested, clean all the flux off using IPA.

Did you assemble the rest of the board? Probably not. The board must have been washed after the SMt parts were soldered and the pot on the right side would have been added hand after that. I suggest the pot may have a cold solder joint or may not be working properly and that is the source of the problem.

Paul

What about the missing part? Is that just a DNP (do not place)? Anyway, try reflowing all the connections.

spooner777:
I soldered on the headers myself, but I am not very good at this.

:slight_smile:

You (really) need to practice with your soldering iron. Experiment on a scrap pcb rather than ruin the perfectly good components you have to pay for.

Could this be the cause?

Your joints are 'cold' They are all 'bad joints' The three pins at the bottom of the chip, have not 'whetted' properly and may be the cause of interrmittent connection. The excessive flux residue at the top right, occurs because the melting point of flux is lower than the solder. The joint was hot enough for the flux to melt and flow out the solder wire but not hot enough to melt the solder.

You need a hotter iron or bigger bit. There is a wireman's trick, which is to put the iron on the pin (not the pad) but it takes real care and risks melting the plastic spacer.

Is it reccomended to clean solder points?

If you are using rosin cored flux, yes. Rosin is corrosive. Neglecting to clean the excess from joints may cause premature failure, as the Rosin continues to corode the metal. Hook up wire joints left uncleaned fail much sooner, within weeks or months even.

When I worked as a wireman in the 1980s, it was all 60/40, rosin flux and IPA. Green Legislation introduced in the 1990s lead to the development of lead free solders and so called 'no clean' fluxes, which are water soluble.

It's painful to look at those photos.

Also, SMD components can fall off the board if they are cold soldered.

Thank you for your messages. I used Lead Solder and Zinc type flux that looks like grease.

I did solder as you are supposed to from the top, but somehow there was still a bad connection. I then reflowed them severall times to make sure the solder wicks through. Thats why it looks like I soldered from the other side.

Do you really think the soldering is the problem? The joints look reasonable to me. I mean if this is so difficult, how can you ever be sure that the joint is made?

spooner777:
Thank you for your messages. I used Lead Solder and Zinc type flux that looks like grease.

I did solder as you are supposed to from the top, but somehow there was still a bad connection. I then reflowed them severall times to make sure the solder wicks through. Thats why it looks like I soldered from the other side.

Do you really think the soldering is the problem? The joints look reasonable to me. I mean if this is so difficult, how can you ever be sure that the joint is made?

Oh, NO!!!! You used plumbing solder and flux. NO! No!

The flux will continue to clean the joint forever! May be better to start over!!

Paul

Once you have used acid flux, throw the board away.
You will not get it stable anymore.

I don't know what people have with flux.
In my 45+ years working in the consumer electronics repair industry I NEVER used flux.
Flux was for plumbers.

Use electrical solder. It is hollow. It has a core of rosin flux that is safe for electronics.
No added flux needed.

That said, I have some SMD flux and a flux pen for "difficult" jobs.
This stuff is made for electronics, and relatively safe.
But I still wash it off.
Leo..

At work we use the flux pen, liquud flux in a little squuze bottle with a needle dispenser. It helps with SMD rework.

raschemmel:
At work we use the flux pen, liquud flux in a little squuze bottle with a needle dispenser. It helps with SMD rework.

Yes, I know some people need it.
I hand solder shiploads of MCUs WITHOUT gel flux.
Good thin solder and experience, and you don't need the sh#t.

You certainly DON't need it to solder pinstrips.
Leo..

Wawa:
Good thin solder and experience, and you don't need the sh#t.

Well now, that is the critical item. Expensive, too!

The zinc type flux is made by dissolving zinc in hydrochloric acid. I can remember my father making flux to solder copper water pipe right after WWII. I am sure the HCL is not neutralized. The flux and solder are made to be used with a torch. Now they use propane. Dad used oxy-acetelene. After soldering, copper pipe joints are always wiped clean with a wet cloth. Inside the flux will be washed away by the water flow. That is why improperly cleaned copper pipe joints have "green" growing on them.

And that is why the OP needs to start over with all new board and components.

Paul

We're soldering 168 pin fine pitch chips.

raschemmel:
We're soldering 168 pin fine pitch chips.

I also hand solder fine pitch chips with stainless stencil, silver solder paste (not flux), and hot air.
Leo..

Yeah, the hot air gun is indespensible.