Bidirectional ESD ESR problems

[破裂的杯]

In our circuit， PESD18VF1BSF and a 68 K ohm resister  was placed in parallel, but when we do the ICT test after SMT, the resistance of some resistor is about 25K (not 68K), I have removed the ESD diode , the cosmetic looks good, and the resistance returned to normal, then detected the resistance of ESD, the data is about 40K(No ESR data was provided in datasheet), but when we left the ESD alone several hours, it changed to infinite,  is there any problems? Then we placed the ESD back to the PCB, this resistance error problem was still appear intermittently. We have test some good samples, this problem would also appear. So is the phenomena OK? Or some other problem? what should be the right resistance?

Tester: Agligent 34401A

[LPP]

The root cause of the problem may be the solder or flux on the sides of the package. The sides of PESD18VF1BSF are not insulated.

>when we left the ESD alone several hours, it changed to infinite

The flux may dried up.

You should follow application note AN11046 where the recommended footprint is described. With this footprint (or a smaller one) it is ensured that there is no solder at the package side.

http://cache.nxp.com/documents/application_note/AN11046.pdf

[sreekanthreddyc]

Hello,

The TVS diode placed is to protect the signal from transients, and its fine with the circuit, Still you are facing an issue with the functionality then adding a PN junction diode between the ESD diode and resistor will solve your issue.

When you check resistance without a PN diode the ESD diode and resistor are in parallel. Hence the resistance would have shown different value or wrong value.

Thanks and Regards

Sreekanth