When the same CDM waveform shown in Fig. 5 is measured with a higher-bandwidth, 8 GHz, rather than 1 GHz, oscilloscope, the true shape of the waveform can be seen more clearly. This is shown in Fig. 5. This waveform shows the higher frequency components of the CDM waveform. When the interpolated data points are removed, the resulting display retains the same characteristic shape. This is also shown in Fig. 5.

Fig. 5.     Current (A) vs Time (ns), 8 GHz oscilloscope, interpolated and actual data points

A 1 GHz oscilloscope with 5 Gigasamples/sec does not have adequate resolution to make accurate measurements on the JEDEC CDM waveform. Because the waveform in the ESDA specification is faster and narrower, there is an even greater need for a higher bandwidth oscilloscope. This is likely to continue to be the case when the joint ESDA/JEDEC CDM specification is released.

EAG CDM Capabilities

To insure that the CDM waveform is measured correctly, take the following actions to minimize variation:

·     Use an 8 GHz oscilloscope in 5 Gigasamples/sec mode to meet old JEDEC and ESDA specs.

·     Correlate 8 GHz/40 Gigasamples/sec s oscilloscope measurements to 1 GHz/5 Gigasamples/sec measurements for the existing JEDEC and ESDA specs. The result will be a revised version of the CDM waveform characteristics table that has the correct waveform parameters for measurements made with an 8 GHz oscilloscope.

·     Set up the existing JEDEC and ESDA tests using the aforementioned new table (optional).

·     Offer the option to capture actual waveforms on client parts to help them understand and model the effects of the CDM event for their products.

·     When the new CDM specification is released, use an 8 GHz/40Gigasamples/sec oscilloscope to verify and center waveforms, as allowed in new specification’s waveform table.

·     Users should move toward the new joint ESDA/JEDEC spec when it becomes available.

References

1.     JESD22-C101F, Field-Induced Charged-Device Model Test Method for Electrostatic-Discharge-Withstand Thresholds of Microelectronic Components

2.     JEP157, Recommended ESD-CDM Target Levels

3.     “CDM Tester Properties as Deduced from Waveforms”, Timothy J. Maloney and Nathan Jack, 2013 EOS/ESD Symposium