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Printed Circuit Board Assembly & PCB Design Forum

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Chip Resistor Failure

Bob Willis

#12172

Chip Resistor Failure | 22 March, 1999

Has any one seen failures of chip resistors after 1-2 years where the junction between the silver termination and the restive element on the top of the ceramic has corroded through. This results in a high resistance failure after this period of time.

I understand that some people in the automotive industry have seen this even on conformally coated boards, the example I have been examining is not in the same type of environment.

Look forward to hearing from a few people, many thanks.

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Ben Kirk

#12173

Re: Chip Resistor Failure | 22 March, 1999

| Has any one seen failures of chip resistors after 1-2 years where the junction between the silver termination and the restive element on the top of the ceramic has corroded through. This results in a high resistance failure after this period of time. | | I understand that some people in the automotive industry have seen this even on conformally coated boards, the example I have been examining is not in the same type of environment. | | Look forward to hearing from a few people, many thanks. | | What kind of flux was used when the board was built? Sometimes organic fluxes can cause corrosion if they are not cleaned off properly. Also if a component overheats often enough it can cause oxidation. I'm not sure if I understood the question the way you intended. Please respond if this helps.

Ben K.

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Bob Willis

#12174

Re: Chip Resistor Failure | 23 March, 1999

| | Has any one seen failures of chip resistors after 1-2 years where the junction between the silver termination and the restive element on the top of the ceramic has corroded through. This results in a high resistance failure after this period of time. | | | | I understand that some people in the automotive industry have seen this even on conformally coated boards, the example I have been examining is not in the same type of environment. | | | | Look forward to hearing from a few people, many thanks. | | | | | What kind of flux was used when the board was built? Sometimes organic fluxes can cause corrosion if they are not cleaned off properly. Also if a component overheats often enough it can cause oxidation. I'm not sure if I understood the question the way you intended. Please respond if this helps. | | Ben K. | | It is a corrosion failure ie the connection between the silver termination and the resistive element has been eroded. There is no evidence on other areas of the board that flux is the cause. Normally dendrite growth provides a low resistance path and not a open or high resistance. The corrsion site shows silver salphide at the area of failure. The silver is from the termination which also has a tin lead coating. The failure is occuring at the junction with the resitive element on the top of the device.

Many thanks.

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P.L. Sorenson - Technical Consultant

#12175

Re: Chip Resistor Failure | 24 March, 1999

| | | Has any one seen failures of chip resistors after 1-2 years where the junction between the silver termination and the restive element on the top of the ceramic has corroded through. This results in a high resistance failure after this period of time. | | | | | | I understand that some people in the automotive industry have seen this even on conformally coated boards, the example I have been examining is not in the same type of environment. | | | | | | Look forward to hearing from a few people, many thanks.

Your problem may be related to silver migration (leaching) into the solder. I had what seems to be a similar problem. The solution was using solder with 2% silver content. See these pages for a bit more information:

http://www.ferroemd.com/page7.html http://www.ferroemd.com/page12.html

Regards, Pete Sorenson

| | | | | | | | What kind of flux was used when the board was built? Sometimes organic fluxes can cause corrosion if they are not cleaned off properly. Also if a component overheats often enough it can cause oxidation. I'm not sure if I understood the question the way you intended. Please respond if this helps. | | | | Ben K. | | | | It is a corrosion failure ie the connection between the silver termination and the resistive element has been eroded. There is no evidence on other areas of the board that flux is the cause. Normally dendrite growth provides a low resistance path and not a open or high resistance. The corrsion site shows silver salphide at the area of failure. The silver is from the termination which also has a tin lead coating. The failure is occuring at the junction with the resitive element on the top of the device. | | Many thanks. | |

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Dave F

#12176

Re: Chip Resistor Failure | 24 March, 1999

| Your problem may be related to silver migration (leaching) into the solder. I had what seems to be a similar problem. The solution was using solder with 2% silver content. See these pages for a bit more information: | | http://www.ferroemd.com/page7.html | http://www.ferroemd.com/page12.html | | Regards, | Pete Sorenson | Pete: Help me understand:

If the "problem may be related to silver (from the component terminations??) migration (leaching) into the solder," then how does using solder with a greater silver content improve the situation?

Thanks

Dave F

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P.L. Sorenson - Technical Consultant

#12177

Re: Chip Resistor Failure | 25 March, 1999

| | | Your problem may be related to silver migration (leaching) into the solder. I had what seems to be a similar problem. The solution was using solder with 2% silver content. See these pages for a bit more information: | | | | http://www.ferroemd.com/page7.html | | http://www.ferroemd.com/page12.html | | | | Regards, | | Pete Sorenson | | | Pete: Help me understand: | | If the "problem may be related to silver (from the component terminations??) migration (leaching) into the solder," then how does using solder with a greater silver content improve the situation? | | Thanks | | Dave F | Dave, I'm not a chemist, but I believe the problem is the lead content. I did a little digging and came up with the following from Kester's site at http://www.metcal.com/kester/

Quotation from http://www.metcal.com/kester/sldrelec.html "The 62/26/02 TIN/LEAD/SILVER alloy is for special applications where surfaces being soldered are plated with silver or silver-palladium. Ceramic chip components and ceramic hybrid microcircuits are soldered with this alloy containing silver so that the silver metallizeation is not dissolved by the solder."

Regards, Pete

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Bob Willis

#12178

Re: Chip Resistor Failure | 25 March, 1999

| | | Your problem may be related to silver migration (leaching) into the solder. I had what seems to be a similar problem. The solution was using solder with 2% silver content. See these pages for a bit more information: | | | | http://www.ferroemd.com/page7.html | | http://www.ferroemd.com/page12.html | | | | Regards, | | Pete Sorenson | | | Pete: Help me understand: | | If the "problem may be related to silver (from the component terminations??) migration (leaching) into the solder," then how does using solder with a greater silver content improve the situation? | | Thanks | | Dave F | Thanks for the inputs so far but this is not the problem. Silver leaching is see on terminations that are produced with a silver palladium paste. During soldering it is slowly disolved in to the solder. The 2% silver is close to the theoretical saturation of the silver in solder so by its addition is slows down the rate of termination loss. The same thing happens on ceramic hybrid circuits.

The problem again I have is silver sulphid corrosion on the silver to resistive element. As it corodes the resistance goes up as the cross sectional area decreases. The sulphid corrosion blooms, black spots can also be seen on the exposed terminations of capacitors but they will not fail.

Look forward to further in put from automotive guys as they are some of the people who have seen the failure as well !!!!

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