Spots on Fully Annealed Copper Pinch Off Tubes 1

[rhmeng]

We use fully annealed C10100 copper tubing as a pinch off tube for hermetic sealing applications. The tubes we are receiving have already been soldered into a housing, and then a mechanical abrasive is used to rub off the oxides created during soldering. On the tubes that we are receiving, we are noticing that after we clean the tubes there are several "spots" that appear on the copper tubes. The cleaning consists of ultrasonic bath in de-ionized water and ultra-sonic bath in high purity IPA. The spots are not on the tubes before cleaning, and only appear after cleaning. We have used the same cleaning process on these tubes for the last year and have never seen this before. Also, it only appears on some of the tubes and not all of them. I was wondering if anyone has seen spots similar to what we are seeing, I attached several pictures. The spots will not come off if you try and rub them with IPA or acetone. The copper tube is 2 inches long with an OD of .125" and ID of .08".

 

[rhmeng]

additional picture

 

[Compositepro]

It seems that your IPA bath is contaminated and that residual solvent was not wiped off after cleaning. So, as solvent dried from the tubes, it left spots. Since the spots do not wipe off this might be caused by water drops corroding the surface. DI water is fairly crrosive to metals. Some uncontrolled variables may include:

The amount of flux applied during soldering.
The amount of contamination inside the tubes.
The amount that comes off in the water bath in comparison to the IPA.
How often The IPA is changed.
How well residual solvent is wiped-off when parts are removed from the bath.
How much water is in the IPA bath.

Ultrasonic baths are good for removing non-dissolving contaminants. Flux that dissolves in the bath will just accumulate and contaminate the bath. A vapor degreasing process is far superior as a final step.

 

[EdStainless]

Are you re-distilling the IPA frequently?
Is the water continuously filtered and polished (keeping purity high and conductivity low)?

The spots do look like residue from impurities, maybe residual flux.

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P.E. Metallurgy, Plymouth Tube

 

[rhmeng]

We use new IPA straight from the bottle every time we clean these. We also use new water every time we wash new parts. After the parts go through the cleaning, they are transported into a clean room while they are submerged in fresh IPA, then they are put on a clean room bench under a hood and allowed to air dry.

As above mentioned, we are thinking that this is more a corrosive thing than it is oxidation. Also we were thinking it does not really matter how much flux was used, since it should be cleaned off during abrasive cleaning and/or the DI water then IPA baths. Possible the flux splashes onto the tube during soldering and then the tube gets hot and flux bakes into the tube?

 

[EdStainless]

Are these just on the surface?
If so then it is your cleaning process.
You say clean IPA, but do mean a bottle that has never been opened in air before. Open IPA will absorb a lot of moisture.
Do you check your water after you rinse? If the conductivity has increased noticeably then you should again start with fresh water and rinse again until the conductivity does not increase.
And what about impurities that are not very soluble in either water or IPA?

If the surface is actually etched then it probably happened because of lubricant residue on the tubes in final anneal. You should be able to find this via metallography.

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P.E. Metallurgy, Plymouth Tube