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SMT electronics assembly manufacturing forum.


Transient Voltage Suppressors

Ray Morford

#12315

Transient Voltage Suppressors | 12 March, 1999

AVX and a few other companies make these chip transient voltage suppressors (TVS) parts that are a real *PAIN* to use. According to AVX: "Due to the semiconducting nature of the doped Zinc Oxide (ZnO) ceramic material, SMT TransGuards are not sutable for plated nickel termination. The entire chip becomes plated with nickel rather than just the termination. Therefore, AVX uses a platinum-enhanced palladium silver thick film termination."

"The TransGuard PdPtAg termination will always exhibit a dull color and smaller filet height than a nickel barrier component. Typically, Transguards will have a 30% to 50% fillet height... Fillet height variations are due to the colloidal surface tension and wetting characteristics of the PdPtAg material system. The fillet height variations relative to nickel are not due to process problems or termination integrity."

All of the above means that the solder joint looks very suspect and it is very difficult to detect defects. The joint sort of looks "cold". We're using the 30% to 50% fillet criteria to pass/fail them along with the "other components near it look ok" criteria. To top it off, there isn't really a good way to test the part once it's in the circuit.

Has anyone else had any experience with these parts? If so, how have you handled the inspection problem. Could you do anything to your process to improve the solderability?

Ray

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Dean

#12316

Re: Transient Voltage Suppressors | 12 March, 1999

| AVX and a few other companies make these chip transient voltage suppressors (TVS) parts that are a real *PAIN* to use. According to AVX: | "Due to the semiconducting nature of the doped Zinc Oxide (ZnO) ceramic material, SMT TransGuards are not sutable for plated nickel termination. The entire chip becomes plated with nickel rather than just the termination. Therefore, AVX uses a platinum-enhanced palladium silver thick film termination." | | "The TransGuard PdPtAg termination will always exhibit a dull color and smaller filet height than a nickel barrier component. Typically, Transguards will have a 30% to 50% fillet height... Fillet height variations are due to the colloidal surface tension and wetting characteristics of the PdPtAg material system. The fillet height variations relative to nickel are not due to process problems or termination integrity." | | All of the above means that the solder joint looks very suspect and it is very difficult to detect defects. The joint sort of looks "cold". We're using the 30% to 50% fillet criteria to pass/fail them along with the "other components near it look ok" criteria. To top it off, there isn't really a good way to test the part once it's in the circuit. | | Has anyone else had any experience with these parts? If so, how have you handled the inspection problem. Could you do anything to your process to improve the solderability? | | Ray | I dealt with this part last week. Due to the poor wetting characteristics of the terminations I had tombstoning. My process DPMO increased from 50 to 150 overnight. I compensated by profiling my product to the upper limit of the solder pasted 230 C rather than 210C. This eliminated the tombstoning. However, the solder "looked different" in comparison to standard chip resistors / caps. However, it had evicence of wetting on all sides. - and under IPC 610B it was a pass. So, now I'm back down to 50 DPMO... Just because it looks different doesn't mean it fails electrically or mechanically. The different look merely is evidence of different metalurgical properties of the alloys. Regards, Dean

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Charles Stringer

#12317

Re: Transient Voltage Suppressors | 16 March, 1999

| | AVX and a few other companies make these chip transient voltage suppressors (TVS) parts that are a real *PAIN* to use. According to AVX: | | "Due to the semiconducting nature of the doped Zinc Oxide (ZnO) ceramic material, SMT TransGuards are not sutable for plated nickel termination. The entire chip becomes plated with nickel rather than just the termination. Therefore, AVX uses a platinum-enhanced palladium silver thick film termination." | | | | "The TransGuard PdPtAg termination will always exhibit a dull color and smaller filet height than a nickel barrier component. Typically, Transguards will have a 30% to 50% fillet height... Fillet height variations are due to the colloidal surface tension and wetting characteristics of the PdPtAg material system. The fillet height variations relative to nickel are not due to process problems or termination integrity." | | | | All of the above means that the solder joint looks very suspect and it is very difficult to detect defects. The joint sort of looks "cold". We're using the 30% to 50% fillet criteria to pass/fail them along with the "other components near it look ok" criteria. To top it off, there isn't really a good way to test the part once it's in the circuit. | | | | Has anyone else had any experience with these parts? If so, how have you handled the inspection problem. Could you do anything to your process to improve the solderability? | | | | Ray | | | I dealt with this part last week. Due to the poor wetting characteristics of the terminations I had tombstoning. My process DPMO increased from 50 to 150 overnight. I compensated by profiling my product to the upper limit of the solder pasted 230 C rather than 210C. This eliminated the tombstoning. However, the solder "looked different" in comparison to standard chip resistors / caps. However, it had evicence of wetting on all sides. - and under IPC 610B it was a pass. So, now I'm back down to 50 DPMO... | Just because it looks different doesn't mean it fails electrically or mechanically. The different look merely is evidence of different metalurgical properties of the alloys. | Regards, | Dean | Glad to see we are not the only ones with problems on these devices. Without wishing to slag off (english term for critisise) suppliers by name, AVX in our opinion are the best of a bad bunch. We have been using AXV for about 5 years with a "reasonable" joint quality and no ICT failures (we check capacitance). Then our supplier told us one day that they could no longer supply us as the mobile phone boys were taking all that AVX could make. What followed was the usual scramble to get a second source approved only this time it turned out to be more than just a data sheet exercise. Samples we received from other manufacturers (no names here but mail me for details) were not as solderable as AVX. To cut a long story short, we ended up changing paste along with the associated requalification program. We have however had promises from more than one manufacturer that they are working on Nickel plated terminations and will be suppling soon. We have seen and processed samples and they are much better than the standard termination. We still cannot get a date for when they plan to start shipping. If you need any more details mail me.

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