Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

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Corroded ASIC's

David R

#20719

Corroded ASIC's | 16 July, 2002

Hi,

we have recently had some customer returns where the 44 pin j-lead ASIC devices exhibit green corrosion from the copper under the tin plating on the leads. These boards were in the field for around 4 years, with innadequate conformal coating protecting these devices.

Having stripped the conformal coating away, I was wondering if there is any way of chemically removing/ neutralising this corrosion, perhaps by dipping into something. This would save us a huge task of identifying and replacing all the corroded devices. This is problematic not only because the parts have a 22 week lead time, but also because there may be corrosion that we miss when choosing which devices to rework.

A blanket rework whithout removing them would be the most desireable option.

Cheers, Dave.

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#20724

Corroded ASIC's | 16 July, 2002

Questions are: * What is this green material? * What does the green material look like? * What the impact of this material on the long-term reliability of your customer�s product? * What flux did you use to solder these boards? * How were the boards cleaned after soldering? * What is the conformal coating? And what makes you think it was inadequate? * To what degree has the green material affected the copper leads between the lead and tin-plating? * Why wasn�t the copper portion of the leads coated with the tin plating? Or is something consuming the tin-plating to form this green material? Or is this green material causing the tin-plating to loose contact with the copper lead? Erwat? * One more thing, exactly where you are seeing this green growth on the J-lead?

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David R

#20729

Corroded ASIC's | 17 July, 2002

Answers are: *Mainly copper and potassium. *it looks like a soft growth. *customer will not accept this, hence the returns. These boards are either reworked or scrapped. *Flux is not an issue. *The cleaning process has been found to be the cause of the problem, whereby the contraflux saponifier was not cleaned off properly by the wash. *The saponifier residue would possibly not have reacted the way it has, without the insufficient coating allowing exposure to the moisture in the air.(The coating was only innadequate because of the contraflux residue). *unsure *These ASIC's are manufactured with a tiny portion of copper visible at the junction between the lead and component body. *The corrosion is on the edges of the lead at the junction between the lead and the component body.

Dave.

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#20731

Corroded ASIC's | 17 July, 2002

Contact: Terry Munson; Contamination Studies Laboratory (CSL); Kokomo, IN; (765)457-8095; residuguru@aol.com http://www.residues.com

Please keep us updated

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