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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