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Printed Circuit Board Assembly & PCB Design Forum

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Corrosion

Adam

#25971

Corrosion | 6 October, 2003

Please help, we have by mistake repaired some boards using the wrong flux (water soluble on a no clean board). Unfortunatly we found out later on while we are testing the boards. The lab anyalysis clearly showed that the flux has eaten through the copper at the failed location. The problem is we are having difficulty bounding the issue to a certain lot. is there any test method that we can subject the assembly to in order to bound the problem? Is washing the boards enough???

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#25972

Corrosion | 6 October, 2003

If the flux is already eating thru Cu it must have been some time since the boards were soldered with the OA flux. Ionic contamination testing (with OmegaMeter or IonoGraph)can be done to find contaminated boards and cleaning the boards can be done as well, but I feel its too late. Cleaning the boards would be effective only if they were built not too long ago.

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Adam

#25974

Corrosion | 6 October, 2003

Thanks Pete, yes, we have built up some inventory, the boards have been around for sometime. So are you saying if we run the omega test, we'll be able to contain or detect the problem boards?

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#25975

Corrosion | 6 October, 2003

Yes, the OmegaMeter and IonoGraph are test equipment to measure ionic contamination. Either of those units should enable you to sort your inventory boards. for more info about this equipment, go to: www.cooksonee.com/products/scs/CoatingSystems/Ionic/index.htm

EMS and OEM PCB assembly houses tend to have this equipment if they're running OA fluxes. Maybe you can find one in your area to buy time on it.

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Hoss

#25980

Corrosion | 7 October, 2003

Adam,

I can't disagree with Pete that an Ionic contamination test may ID the affected boards. However, if you have a large number of boards to test, this may not be the answer. Omegameter testing takes 10-15 minutes per unit if memory serves. On top of this, the DI H2O and IPA solution used in the equipment will turn your no clean residue a cloudy white. This may be a cosmetic issue for your customer.

I don't have a better idea on this but you may consider visual inspection as an option. If the damage already identified is easy to detect, you may need to go that route.

I feel your pain.

Hoss

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Adam

#25989

Corrosion | 7 October, 2003

The Omegameter (or Ionograph) detect contamination by measuring the conductivity of the solution used to extract the board. This conductivity number reflects the sum of all of the ionics in the extraction solution. Unfortunately, we can't sort out the contribution of chloride ion from other ions in the extract. We would need to establish a cut-off limit for the conductivity above which the board is scrapped. The problem in setting this limit might be that a low level of chloride ion (or no chloride ion) with a high level of organic acid (from several reworked locations on the board) could be above this cutoff limit and we will be scrapping good boards. If this is possible, the limit would have to be set by measuring known good and bad boards in the Omegameter. The failure sometimes is under the part, so it is hard to to detect visually.

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MA/NY DDave

#26006

Corrosion | 9 October, 2003

Hi

If I read things correctly you have quite a problem. I am inclined to scrap the entire LOT.

I will give some hints at what to do as others have, yet you might want to bring someone in if the loss in revenue is high. I don't know your lot or run size.

Statistical Analysis of how big this problem is would be my first thought. Take a proper sampling.

If things don't look like a total loss you are going to have to create an overly agressive triple or greater cleaning process.

Now when you are done with this agressive cleaning then and only then will the omega meter be useful. You certainly don't need it to say "Hey I got a problem"

YiEngr, MA/NY DDave

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Dean

#26011

Corrosion | 9 October, 2003

You could send the boards out for contract cleaning. Saponification and DI wash. I take it your rework process does not keep track of serial or ID numbers?

What about tracking lot codes on the replacement part? maybe it's unique enough to isolate?

Just a thought. Feel for ya man.

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Terry Munson

#26140

Corrosion | 22 October, 2003

Yes Ion Chromatography can when using a isolated extraction system called the C3 tester. Please email me or call of-line and we can show you what we have done for others to not only idendity the flux cleanliness levels but to qualify the cleaning protocol. 765-457-8095 Foresite Inc.

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#26249

Corrosion | 4 November, 2003

Blimey that's a problem and a half. Water Solubles will look completely different residue wise than No Cleans, pending age and solids contents No Cleans will go white powdery - watersolubles will stay oily Alternatively process reworked PCB's through Glue profile in Reflow oven MOST good no Cleans will Volatise off at 150C and Watersolubles will not - should be painless test for you to try and it works very well.

You could also contact SCOPE Labs out of Chicago and ask for IC Work or even Chemical Extraction followed by IR bulk analysis of extracted residue's. Problem with Ionic testing is some wetters used will be NON IONIC and therefore pass with good results but fail once in the field. Speak with Jim Hevel he knows his contamination at SCOPE Labs

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Reflow Oven

SMT in-printer dispensing