Hello all. I'm working with a 4-layer PCB and the two middle layers are power and ground. One of the boards I've been working with just started pulling a lot of current when I connect to power supply. I probed around and notice very low resistance between VDD and ground. Just before this I had done some soldering rework so naturally I thought I created a solder bridge somewhere between a ground and power pin. After scouring over the board for an hour under a lit magnifying glass I could not locate any short that might have been inadvertently created.

Now my suspicion is that heat exposure from the soldering iron might have caused the internal copper layers to expand and either directly short or have decreased the resistance of the material that sits between them. Has anyone ever had an issue such as this?

Anyway to diagnose or treat this problem? Thanks for any insight.

 

Hello all. I'm working with a 4-layer PCB and the two middle layers are power and ground. One of the boards I've been working with just started pulling a lot of current when I connect to power supply. I probed around and notice very low resistance between VDD and ground. Just before this I had done some soldering rework so naturally I thought I created a solder bridge somewhere between a ground and power pin. After scouring over the board for an hour under a lit magnifying glass I could not locate any short that might have been inadvertently created.

Now my suspicion is that heat exposure from the soldering iron might have caused the internal copper layers to expand and either directly short or have decreased the resistance of the material that sits between them. Has anyone ever had an issue such as this?

Anyway to diagnose or treat this problem? Thanks for any insight.

Possible, but not likely that the internal layers have shorted. More likely is the possibility of a solder bridge or a bad component. Post photos of both sides of the board and perhaps someone here can spot a problem.

 

I'll second Trace's thoughts... and add a couple of my own

If the circuit worked before you did the rework then it's possible that there is a solder short somewhere - despite you looking at it. If nothing shows up in an additional inspection then there are also a couple other possibilities: failed part(s) due to ESD, incorrect pinnout, or excessive thermal during soldering. A short between layers can happen, but it is usually due to a improper layout or cracked layers due to dropping the board or something like that.

 

When a board goes bad you look at what happened before it failed.

*Why* were you doing "soldering rework?" Was there an initial failure to cause this?

Did you replace any components? Are the orientated correctly?

Could the fresh parts be shorted?

Did the rework expose a previously untested section of the board?

How mature is this PCB? Is it serial number 0001 or 10,001? You may have uncovered a design deficiency in a new design.

 

When a board goes bad you look at what happened before it failed.

*Why* were you doing "soldering rework?" Was there an initial failure to cause this?

Did you replace any components? Are the orientated correctly?

Could the fresh parts be shorted?

Did the rework expose a previously untested section of the board?

How mature is this PCB? Is it serial number 0001 or 10,001? You may have uncovered a design deficiency in a new design.

Thanks for your reply.

1) One chip on the board was incorrectly swapped out for another when it was initially assembled.

2) I replaced it with the right chip. The chip has two pins on one side and three on the other side, so there is only one way to orient it.

3) I don't see that they are. I could have someone else look at it for a second opinion.

4) That part of the board was tested and working.

5) This is the third revision of the board. This part of the circuit was working in the previous revision and nothing has changed since then.

 

I'll second Trace's thoughts... and add a couple of my own

If the circuit worked before you did the rework then it's possible that there is a solder short somewhere - despite you looking at it. If nothing shows up in an additional inspection then there are also a couple other possibilities: failed part(s) due to ESD, incorrect pinnout, or excessive thermal during soldering. A short between layers can happen, but it is usually due to a improper layout or cracked layers due to dropping the board or something like that.

Hi tindel,

1) I am wearing ESD wrist straps all day and the board sits on an ESD mat.

2) It is a five pin chip, with three on one side and two on the other, so there is only one way to orient it.

3) If I cooked a chip beyond it's recommended temperature, that might be it. I will look at the data sheet and use the right temperature and try soldering on another chip. However, the chip is currently not on the board, and I'm still getting very low resistance between power and GND.

 

Possible, but not likely that the internal layers have shorted. More likely is the possibility of a solder bridge or a bad component. Post photos of both sides of the board and perhaps someone here can spot a problem.

I wish I had a high resolution camera to take the pictures with. Anything I take would come out a little blurry at best.

 

1) One chip on the board was incorrectly swapped out for another when it was initially assembled.

2) I replaced it with the right chip. The chip has two pins on one side and three on the other side, so there is only one way to orient it.

3) I don't see that they are. I could have someone else look at it for a second opinion.

4) That part of the board was tested and working.

5) This is the third revision of the board. This part of the circuit was working in the previous revision and nothing has changed since then.

1) I am wearing ESD wrist straps all day and the board sits on an ESD mat.

2) It is a five pin chip, with three on one side and two on the other, so there is only one way to orient it.

3) If I cooked a chip beyond it's recommended temperature, that might be it. I will look at the data sheet and use the right temperature and try soldering on another chip. However, the chip is currently not on the board, and I'm still getting very low resistance between power and GND.

With no photos and no schematic, we are just shooting in the dark.

Maybe the wrong chip that was installed damaged something else on the board. Maybe one of the SMD resistors is 10 ohms instead of 10k ohms.