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soldermask color change around vias

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We're testing this PCB in 40C 93RH to see if we get ECM or C... - Apr 04, 2019 by TeejSD  

#82299

soldermask color change around vias | 4 April, 2019

We're testing this PCB in 40C 93RH to see if we get ECM or CAF. We have failure. I traced it back to the vias on the left (signal & gnd)if I can get the picture to load. We have not yet confirmed or denied CAF. I am wondering if I should be concerned about the ring of lighter colored soldermask around the via and up the traces from the via above. Is that normal? I am seeing it on some other vias on this board. A simple tape test with scotch tape on the other vias did not pull any mask off.

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#82337

soldermask color change around vias | 10 April, 2019

I wonder if this discoloration isn't delamination. I'd discuss it with my board fabricator.

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#82720

soldermask color change around vias | 7 June, 2019

Does look like delam, if its that bad and the board looks like its HASL finish or Silver, it could also be porous absorbing the chemistries of HASL or Nitric from the Silver which will greatly encourage ECM or poor SIR figures or just simply eat the tracks. Well worth checking the cure and delamination

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#82724

soldermask color change around vias | 7 June, 2019

Closer pics at angle would seem to support soldermask delam. And I am now wondering if our no clean flux is getting properly inactivated where it is sitting under the mask.

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#82726

soldermask color change around vias | 7 June, 2019

The Single Solder ball stuck to the mask may indicate undercured as well. The issue is not so much the mild No Clean flux but the potentially major active HASL flux or Silver Process chemistries causing issues. This has been through flow solder hasnt it??

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#82727

soldermask color change around vias | 7 June, 2019

Went thru wave solder, yes

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#82728

soldermask color change around vias | 7 June, 2019

OK good if you get really close to the two small solder balls trapped in that greasy waxy residue and carefully turn the balls over you should see that they are flat on the side stuck to the solder resist.

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#82729

soldermask color change around vias | 7 June, 2019

We also have a Foresite C3 for spot testing for ionic contamination. I didn't use it at this spot, but used it some other spots around the PCB that showed this color change and with our C3 we were passing IPC standard for ionics. But I was wondering if we were able to properly sample whatever's under the soldermask, though maybe I should've beem concerned about sampling whatevers IN the soldermask.

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#82730

soldermask color change around vias | 7 June, 2019

Unfortunately for me, I can't say whether those balls were flat on 1 side or not -- sent this board for x-section to see if we had CAF, since my ionics testing wasn't breaking IPC standard. Unhappily my x-sect results were inconclusive. However I do have 4 more boards showing this issue....

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#82731

soldermask color change around vias | 7 June, 2019

If you have soldered with HASL finish then the worrying chemistry will be more like NON IONIC. They sit there and attract moisture like mad and any chlorides they hold ionize in the moisture attracted and cause electromigration or SIR issues. They can often come and go and only fail when moisture in sufficient quantity is present. Typically these fluxes are made up of Non ionic wetters, Hydrochloric acid or Hydrobromic acid or a mixture of the two. Best to do a PCB extraction and FT-IR analysis looking for Mica - Nonyl Phenol and Chlorides

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#82732

soldermask color change around vias | 7 June, 2019

This does sound like my failure! Failure typically goes away when boards are removed from humidity. Yes we do have a HASL finish. Do I have to do the waterbath alcohol/water extraction to pull these contaminants, or is warm water/steam enough? Because I could sample with our C3 that uses hot water/steam in like 5 minutes.

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#82733

soldermask color change around vias | 7 June, 2019

I feared so. The only thing to be done is to tell the PCB manufacturer to increase the Thermal cure so dont set the oven to 150C but to 170C and actually measure the middle board and once it hits 155C then give it an hour cure from then. Also insist they use an Alakali cleaner to neutralise the Acids left on the PCB after HASL. The extraction process is 80C in 75IPA/25DI Water for one hour in a kapak bag then FTIR and quantative halide test the residue. OR for a quick indication simply rub the green resist with a decent Aerosol flux cleaner and see if you get green off, if you do then that is a very good indication it isnt cured correctly and is still porous. We have formulated a solvent wipe for this but Im unsure where you are in the World.

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#82734

soldermask color change around vias | 7 June, 2019

Sorry meant to say if the C3 is only testing Ionic then typically this material is Nonyl Phenol which is non ionic so may possibly not see it. Im not familiar with that test, hence we carry out FTIR extraction

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#82735

soldermask color change around vias | 7 June, 2019

C3 just uses heated DI water that it applies, then pulls back into a disposable cartridge. Machine then applies a 10V charge to the sample & measures leakage current(nA,I think) over time(sec). If the leakage current is high enough/fast enough, you fail IPC standard. When the sample is dirty, you can even see the dendrite growth across the electrode board in the cartridge. I was just wondering if hot water could collect this type of sample or if you have to have the IPA to rinse them off the board. Sounds like I need the IPA.

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#82736

soldermask color change around vias | 7 June, 2019

These residues are extremely water miscible BUT you will probably need the extraction of heated IPA/Water to get the porous resist to release the residue quicker than it would do releasing it naturally in the field. Why dont you try to soak the circuit in IPA/Di over the weekend then see if that helps release the residue for your test to work?? Worth a try but I must stress this residue bulk is typically non ionic hence why these pass the normal ionic testing

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#82739

soldermask color change around vias | 7 June, 2019

Yes neither our HPLC IC nor our C3 could detect any concerning levels of ionics. Soaking over a weekend sounds like a good idea, though I may still need to cut the board down to fit our Kapak bag size. And get our silicone coating off the surface. Know our FTIR will detect that silicone coating. Hopefully peaks are different enough it will not mask mica nonylphenols. May have to ask our QA Engineers for a bare board to compare to. Thanks for the input! I will update with any findings

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#82740

soldermask color change around vias | 7 June, 2019

If you send me the results happy to take a quick look for you. Ask your guys to look out for Minerals Salts, Polyvinyl Acetates etc. Have a great weekend

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#82741

soldermask color change around vias | 7 June, 2019

Would be well worth testing a bare board first

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#82852

soldermask color change around vias | 21 June, 2019

ask your supplier to make micro-section to check whether it is delamination.

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