Conducting PCBs?

[psteichen]

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.

[ataradov]

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.

[ajb]

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.

[ataradov]

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.

Well, naturally board defects happen. But 90% of the value suggests some resistance value, not just a dead short.

[Zero999]

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 60^oC for an hour or so? It's possible the flux is soaking up some moisture from the atmosphere and becoming conductive.

[psteichen]

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 job Honestly, 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.

[ataradov]

so I used brake parts cleaner to clean both the soldered side as well as the component side.

You'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.

[psteichen]

You'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.

Haha I 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.

[Alex Eisenhut]

Looks like the usual milky white residue of water soluble flux to me. So, what kind of flux was it?

[ataradov]

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.

Do you have the remainder of the board this fragment came from? Can you test this?

Also, what did you use for a flux?

[psteichen]

Do you have the remainder of the board this fragment came from? Can you test this?

Also, what did you use for a flux?

The rest of the unused boards in the batch test with no continuity. I used a water soluble, non-acid, lead free paste.

[ataradov]

I used a water soluble, non-acid, lead free paste.

You actually used solder paste? With solder balls in it?

That's not a flux. And possibly the reason for your problem.

[psteichen]

I think I need to throw out the flux. Just tested it by probing the paste, and it conducts right in the jar!

[ataradov]

I think I need to throw out the flux. Just tested it by probing the paste, and it conducts right in the jar!

Because 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.

[psteichen]

Well that's why I posted here. I knew someone would figure out my mistakes

Thanks. Any chance this board can still function if I clean the solder paste well enough?

[ataradov]

Thanks. Any chance this board can still function if I clean the solder paste well enough?

I 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.

[psteichen]

Well that sucks. Must be microscopic solder balls, because it looks like a cream.

[Mr.B]

A photo of the container and its label would help a lot.

[ataradov]

Well that sucks. Must be microscopic solder balls, because it looks like a cream.

They are typically 5-50 microns (differs by types).

[Mr.B]

The indicated parts of the photo look suspiciously like paste balls (or grouped paste balls) to me.

[ataradov]

The indicated parts of the photo look suspiciously like paste balls to me.

I think they are balls already combined under heat. You can't really see balls from the paste with a naked eye.

[Mr.B]

The indicated parts of the photo look suspiciously like paste balls to me.

I think they are balls already combined under heat. You can't really see balls from the paste with a naked eye.

Agreed.
I just added (grouped paste balls)...

[psteichen]

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.

[psteichen]

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.

[ataradov]

Looking forward to making a real etched board for this.

That'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