Has anyone seen this before? See the white lines jetting out from the corners of the pads. This board underwent automotive thermal stress testing and is still functional, but I have never seen cracks like these before.

 

It looks like you are looking at the pad with no solder on it.

 

It looks like you are looking at the pad with no solder on it.

Likely just a visual processing artifact from video system level overloading (contrast/brightness).

 

The pad is flat and reflects the light back into the camera. The solder is not flat, it is not at a right angle to the camera, and solder has a texture that reflects less.
I think we agree.

 

Are you talking about this? I don’t think it is a photographic artifact.
If this is an automotive board validation, they may want a better explanation. Automotive QC people are known to be very stubborn.

You may want to do a SEM. If you don’t have an electronic microscope, there are many external labs that will do the work.

 

I think the solder does not flow over the entire pad. The corners are short of solder.
The solder is gray and do not reflect light well. The solder has a verity of surfaces.
The pad is probably gold plated and reflects light very well.

I am not commenting on if this is a problem or not. Just what I see.

 

A quick image demo from a PCB design of mine with a gold plated finish.

Partial solder coverage on connector ground/mount tabs.



Low brightness, gold plating.


High brightness, Whiteout.

 

Looks like cracks in shrinking solder mask layer to me?
Sharp corners create stress risers that love to crack?

 

Has anyone seen this before? See the white lines jetting out from the corners of the pads. This board underwent automotive thermal stress testing and is still functional, but I have never seen cracks like these before.

Looks like stress fractures in the solder mask, probably do to differential thermal expansion during the thermal testing -- corners tend to concentrate stress.

Shouldn't impact functionality and I doubt it would have a significant impact on life expectancy, but they could grow over time and possibly result in pieces of soldermask flaking off or provide a path for moisture to get in underneath it. My guess, though, is that they are benign. But automotive qualification my still have issues with them.

 

those are obviously stress cracks in the solder mask,

 

 

Hi, panic mode, thank you for your reply. Do you know why they developed? Would it be indicative of a poorly applied solder mask or poor-quality material itself?

 

Looks like stress fractures in the solder mask, probably do to differential thermal expansion during the thermal testing -- corners tend to concentrate stress.

Shouldn't impact functionality and I doubt it would have a significant impact on life expectancy, but they could grow over time and possibly result in pieces of soldermask flaking off or provide a path for moisture to get in underneath it. My guess, though, is that they are benign. But automotive qualification my still have issues with them.

Thank you WBahn. We normally run large numbers of samples, and if I understood the engineer correctly, this was the only one that creaked like this. Do you think it has anything to do with supplier quality, or is it more likely that the material is of low quality?

 

Thank you WBahn. We normally run large numbers of samples, and if I understood the engineer correctly, this was the only one that creaked like this. Do you think it has anything to do with supplier quality, or is it more likely that the material is of low quality?

I have no idea, especially based on one picture -- and if explaining/understanding this is important, I wouldn't recommend asking strangers on the Internet, either. There are lots of labs out there that are dedicated to doing fault analysis and investigation, so I would recommend finding one that specializes in PCB quality assurance and engaging them for their professional evaluation. They may offer a fairly low cost preliminary evaluation based on visual examination of the board, detailing potential causes and likely ramifications. They can probably give you some idea of the likelihood that this is indicative of something potentially larger, versus as more-or-less one-off occurrence. They can also give you an estimate of what it would take and cost to pursue a more definitive explanation of the cause.

 

I gave you a valuable suggestion, which you chose to ignore.

I also worked for automotive electronics companies. The auto makers are not looking for guesses or hypotheses. They require a full analysis, together with an 8D report and the corrective action in compliance with whatever standard is in vogue now.

Is this a PPAP failure? Do you have a line down situation? Is this an engine bay or a cabin assembly? Could a failure in the assembly trigger a recall? Is this for a new program or do you have 100,000 units already installed? Would a failure create a safety issue?

 

Looks to me like the pads have been "over stressed"....maybe during an automated placement or electrical test.

 

It would be worth your time and effort to remove the mask from one of the affected areas to see if the cracks extend into the substrate.