Solder corrosion and possible causes?

DaveV101 · Mar 23, 2022

Hello all,

I'm new and apologize in advance if this is not the correct forum to post this type of situation.

Attached are two photos of CPU boards from two different devices. One photo shows a section of the board where the solder points appear to have corroded away. The other photo shows a board that has the solder points intact. I am being told that the device with the damaged board was in an office environment where it was not exposed to harsh elements. I am trying to understand what could cause this type of damage to occur over time.

Thank you in advance!

SparkyChick · Mar 23, 2022

I'm not convinced it's corroded... I suspect it's down to a simple case of manufacturing tolerances.

If by solder points you mean the through hole via's... the non-corroded board appears to be of a better quality... the via's appear larger and are not solder masked meaning they will be tinned throughout.

As for statements about being in an office environment meaning it's not been subjected to harsh conditions... someone should perhaps consider simple things like condensation that can form if the board is in a colder area. It's also entirely possible that it wasn't cleaned thoroughly during manufacture and there is some flux residue which can be corrosive, but if I was quality assurance for the company than produced it, I would have flat out rejected the 'corroded' one because of the size and quality of the via's.

DaveV101 · Mar 23, 2022

SparkyChick said:
I'm not convinced it's corroded... I suspect it's down to a simple case of manufacturing tolerances.

If by solder points you mean the through hole via's... the non-corroded board appears to be of a better quality... the via's appear larger and are not solder masked meaning they will be tinned throughout.

As for statements about being in an office environment meaning it's not been subjected to harsh conditions... someone should perhaps consider simple things like condensation that can form if the board is in a colder area. It's also entirely possible that it wasn't cleaned thoroughly during manufacture and there is some flux residue which can be corrosive, but if I was quality assurance for the company than produced it, I would have flat out rejected the 'corroded' one because of the size and quality of the via's.

Thank you for the feedback. This is very helpful.

The client stated the office environment was air conditioned and these devices do produce a good amount of heat so the condensation is a good consideration I had not thought of. I will also discuss the possibility of flux residue with the engineers of the device. This is the only client reporting this type of failure on several devices over the past couple of years.

I appreciate your insight.

pc1966 · Mar 23, 2022

Those photos are not really clear enough to show the PCB joints and construction in enough detail. At least for my eyes!

Avo Mk8 · Mar 23, 2022

As above, I'm afraid much more crisp photo's are needed to make detailed observations.
The only point I would make is that the two boards have been made with slightly different PCB manufacturing processes.
The first photo shows plated through holes the same colour as the tracks, so not additionally plated. Those PTH are overlaid with solder resist.
The second photo shows PTH that have, I think, been additionally plated, and then (I think) are overlaid with solder resist, but the image is a bit unclear.
So the pads and holes look different between the boards, but that is down to how they were made.

I also see the right-hand pic shows ground plane strips down each side of the PCB, with lots of PTH strapping them to some layer in the board, presumably to solve a problem (maybe EMC / susceptibility?) that was evident with the earlier design on the left?

I cannot see any evidence of solder "corroding away", I must be missing what the problem is

Could you give any more details of what has led to 'corrosion' being considered as the issue?
I feel there are many more likely explanations of a PCB failing than that it was through corrosion

DaveV101 · Mar 23, 2022

Avo Mk8 said:
As above, I'm afraid much more crisp photo's are needed to make detailed observations.
The only point I would make is that the two boards have been made with slightly different PCB manufacturing processes.
The first photo shows plated through holes the same colour as the tracks, so not additionally plated. Those PTH are overlaid with solder resist.
The second photo shows PTH that have, I think, been additionally plated, and then (I think) are overlaid with solder resist, but the image is a bit unclear.
So the pads and holes look different between the boards, but that is down to how they were made.

I also see the right-hand pic shows ground plane strips down each side of the PCB, with lots of PTH strapping them to some layer in the board, presumably to solve a problem (maybe EMC / susceptibility?) that was evident with the earlier design on the left?

I cannot see any evidence of solder "corroding away", I must be missing what the problem is

Could you give any more details of what has led to 'corrosion' being considered as the issue?
I feel there are many more likely explanations of a PCB failing than that it was through corrosion

Thank you both for the feedback. Apologies for the initial photos. I had cropped them and didn't realize the resolution got reduced as well. Attached are hopefully some better ones from the same photo samples. 1.png is damaged and 2.png is not damaged. And by damage I mean all the silver looking parts on 2.png should be seen on 1.png

From past conversations with the Engineers, both boards were manufactured with the same process. I know they were manufactured from the same facility, just not sure of the dates. I will find out to see if the manufacturing process was changed between the two. However, my understanding is that the process was the same. That is why the first photo was so shocking to us when we receive the board. Both boards were originally suppose to have overlay with solder. Same with the ground plane strips on each side, both boards are suppose to have it.

A couple of years ago, one board was analyzed to have phosphate residue on the board, which the Engineers stated attributed to the damage. Now the client is coming back saying the device is in an office environment, but the damage looks the same as previous failures. This damage prevents the device from functioning/powering up.

I appreciate the time and consideration!

Avo Mk8 · Mar 24, 2022

DaveV101 said:
From past conversations with the Engineers, both boards were manufactured with the same process. I know they were manufactured from the same facility, just not sure of the dates.

Just to be clear, normally the bare fibreglass board with its tracks will be made by one company (a subcontractor), to their own interpretation of the build up of the board as supplied by the pcb designer, and then the population of the board with components and the soldering will be carried out by "the manufacturer", presumably the party you are talking to.

PCB manufacture has distinct phases, starting with taking the clients circuit, layout and component/ library data, and massaging it to feed into the manufacturing processes, intitially manufacturing individual layers, essentially using lots of amps and horrible chemicals, and then glueing all the layers together, drilling and milling them to shape etc.
Whereas electronics assembly needs cleanliness and no static etc! So not normally done at the same site, or even the same company.

The norm is for the manufacturer to purchase the number of boards required for the current/ forseeable batch. There's a shelf life for solderability so it wouldn't be for more than say a year, if that. Then the next time boards are required, they get quotes for the next batch. Even if they choose the same pcb supplier again, and hadn't changed the artwork (which they have in this case - clearly the pcb layout has been changed), it might still be made differently.

I'm sorry but the bare pcb's have been built differently. I can see that the earlier one without the tinning of the holes, seems to have lost copper plating to the holes. As an example, the pads of the top right connector (no component) seem to have disappeared, assuming they were there originally!
That's nothing to do with solder! There isn't any on those PTH's. It seems to be copper that's missing!

The PTH pads are very small on the older board, and the holes are not well aligned, some seem to break through the annulus, which would be unacceptable in my world. I'm afraid I still can't work out what's up, but it looks like copper has been eaten away somehow. That could be a combination of poor design (pad size), poor manufacture (drilling alignment) and poor cleaning of the bare pcb's.

You might ask what cleaning regime the manufacturer uses on the assembled boards, and whether they measure residual contamination after cleaning. In particular was the same regime used on the older faulty board?

I'm more inclined to think there was a problem with the bare pcb's as originally supplied. Worth talking to an informed chemist at a pcb manufacturer (not the board assembler/manufacturer)

Avo Mk8 · Mar 24, 2022

Dave V101
I feel there is a limit from what can be divined from the photo's. I do see that the daughter board on the damaged unit is more severely affected than the mother? board beneath it, except for the group of PTH in the middle.

I don't understand how a correctly specified and constructed bare pc panel can apparently be eroded like this just by pollutants in the atmosphere. I suspect either plating faulty, top plating layer(s) missing, or contamination in/on the substrate. But I'm no expert in this field.

Edit: I see that in use, the daughter board lives quite close to a backup battery, separated only by a perforated plastic shield. Is it possible a damaged or faulty battery could emit fumes that could erode a board that was not correctly made in the first place?
Given this video is 2016, and shows the more recent design of daughter board with the edge ground plane, the faulty board you ask about, without the ground plane, must be somewhat earlier.

I'm not sure what your role is here, but if you are seeking an authoratitive analysis of the failure, it's time to go to an organisation that specialises in printed board fabrication failure analysis.
I've used such in the UK, but I don't have knowledge of who offers this service near you.

DaveV101 · Mar 24, 2022

Avo Mk8 said:
Just to be clear, normally the bare fibreglass board with its tracks will be made by one company (a subcontractor), to their own interpretation of the build up of the board as supplied by the pcb designer, and then the population of the board with components and the soldering will be carried out by "the manufacturer", presumably the party you are talking to.

PCB manufacture has distinct phases, starting with taking the clients circuit, layout and component/ library data, and massaging it to feed into the manufacturing processes, intitially manufacturing individual layers, essentially using lots of amps and horrible chemicals, and then glueing all the layers together, drilling and milling them to shape etc.
Whereas electronics assembly needs cleanliness and no static etc! So not normally done at the same site, or even the same company.

The norm is for the manufacturer to purchase the number of boards required for the current/ forseeable batch. There's a shelf life for solderability so it wouldn't be for more than say a year, if that. Then the next time boards are required, they get quotes for the next batch. Even if they choose the same pcb supplier again, and hadn't changed the artwork (which they have in this case - clearly the pcb layout has been changed), it might still be made differently.

I'm sorry but the bare pcb's have been built differently. I can see that the earlier one without the tinning of the holes, seems to have lost copper plating to the holes. As an example, the pads of the top right connector (no component) seem to have disappeared, assuming they were there originally!
That's nothing to do with solder! There isn't any on those PTH's. It seems to be copper that's missing!

The PTH pads are very small on the older board, and the holes are not well aligned, some seem to break through the annulus, which would be unacceptable in my world. I'm afraid I still can't work out what's up, but it looks like copper has been eaten away somehow. That could be a combination of poor design (pad size), poor manufacture (drilling alignment) and poor cleaning of the bare pcb's.

You might ask what cleaning regime the manufacturer uses on the assembled boards, and whether they measure residual contamination after cleaning. In particular was the same regime used on the older faulty board?

I'm more inclined to think there was a problem with the bare pcb's as originally supplied. Worth talking to an informed chemist at a pcb manufacturer (not the board assembler/manufacturer)

Very informative, thank you. This will provide good speaking points. I plan on asking for this board back from the client to have it analyzed further. I hope our Engineers will take the extra effort to determine cause of failure.

I appreciate the time you took to respond.

DaveV101 · Mar 24, 2022

Avo Mk8 said:
Dave V101
I feel there is a limit from what can be divined from the photo's. I do see that the daughter board on the damaged unit is more severely affected than the mother? board beneath it, except for the group of PTH in the middle.

I don't understand how a correctly specified and constructed bare pc panel can apparently be eroded like this just by pollutants in the atmosphere. I suspect either plating faulty, top plating layer(s) missing, or contamination in/on the substrate. But I'm no expert in this field.

Edit: I see that in use, the daughter board lives quite close to a backup battery, separated only by a perforated plastic shield. Is it possible a damaged or faulty battery could emit fumes that could erode a board that was not correctly made in the first place?
Given this video is 2016, and shows the more recent design of daughter board with the edge ground plane, the faulty board you ask about, without the ground plane, must be somewhat earlier.

I'm not sure what your role is here, but if you are seeking an authoratitive analysis of the failure, it's time to go to an organisation that specialises in printed board fabrication failure analysis.
I've used such in the UK, but I don't have knowledge of who offers this service near you.

Just seeing this response after I responded to the earlier one. Kudos for finding that video... quite the Sherlock Homes

Agreed, it is difficult to make any clear determination from the photos. The device will need to come back to be analyzed further. I did look at some devices that we have here in the office that were manufactured during the same period as the one in the photo and the tinning is present. This client doesn't use the battery as seen in the video.

I'm a support manager so I try to do right by the client, balancing that with what is right for the company. This is not my area of expertise, but I wanted to go the extra step to understand better the situation so that I can be better prepared when speaking with the Engineers and the client. I will post an update to this post if anyone is interested in the findings.

Cheers

Lucien Nunes · Mar 30, 2022

On the first board (1.png) it looks to me like there is a mismatch between the via pad size and drill size, and also poor and inconsistent registration between the two, so that most pads have been partially drilled away. Some have only the part of the edge in contact with the trace likely to be making contact from the top layer to the via plating. This kind of defect makes the PCBs much more vulnerable to damage and failure over time, even if they passed a full electrical test initially.

The pad size issue is down to the design, the poor registration to the manufacture. It suggests there may be other subtle faults that are not obvious from the pics. Corrosion might be a factor - a badly made board might be much more vulnerable - but I agree with the above posters that it doesn't look serious. Normally PCB corrosion is due to leaking electrolytic capacitors, salt water ingress etc, where electrolyte gets under the solder mask and eats through the copper. The mask is usually blistered and there are recognisable signs of chemical attack, before the device stops working. I am not seeing that here although there are funny black marks on some of the vias, that look like someone has touched them with a fine felt tip pen. It would be nice to have a really high-res pic of some of those.

Solder corrosion and possible causes?

DaveV101

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