What is the different between CDM , HBM and MM test ?
uWhen people walk, they generate some electricity and discharge it to ground. Every step builds up charge that can be represented by:
uΔV/Δt = n Δq/C
uwhere n is the number of steps/second and C is the person’s capacitance. Consider a typical case on an insulating floor, showing a ΔV increase of 300 V per human step and reaching about 3 kV in 10 seconds. (Note: some charge leakage occurs.)
uFor HBM tests, there is a simple series RC network to simulate the discharge from a human body. A 1-MΩ resistor is used to charge a 100-pF capacitor. A 1.5-kΩ resistor is used for discharging. HBM events are most disruptive with fast rise times. Therefore, fast rise time pulses are required to more precisely simulate a HBM discharge event.
ui(t) = i0 exp(–t/τ)
ui0 = VHBM/(RDUT + R)
ut = C(R + RDUT)
uR = 1.5 kΩ
uPower dissipation to the device under test (DUT) is:
uCDM simulates device damage that could not be simulated by HBM testing. It simulates a device charged either directly by triboelectric effect (see “Harvesting Power Using Triboelectric Generators”) or indirectly by electrostatic induction and static charge stored in a part’s body that discharges in an outside environment.
uThis test is used to simulate situations that happen in manufacturing environments such as mechanical device handling where devices slide down shipping tubes or test handlers that build up a charge that’s subsequently discharged to ground. Figure 2 shows the CDM ESD test and typical current waveform characteristic. When an external ground touches the DUT pin of the charged device, the stored charge will be discharged from the device to the outside ground. In the CDM test, the device is kept on its back, facing upward on a test fixture.CDM currents are higher than HBM currents because there is no current limiting resistor in the path to limit the discharge. For a 500-V test voltage, the current waveform rise time is generally around 400 ps with the peak current around 6 A for 1.5 to 2 ns. For a 1000-V test voltage, the peak current magnitude is around 12 A.
uSimilar rise times (i.e., ~10 ns) and total duration for HBM and MM cause comparable joule heating that results in similar failure mechanisms for both models. The failure signature and discharge processes of the MM test are generally the same as that of the HBM test. Thus, the HBM test could guarantee MM ESD robustness.
uUsually, the stress level of MM ESD is approximately 10 times lower than that of HBM ESD. Also, the protection voltage level for HBM typically is ~2 kV while for MM it is ~200 V and for CDM it is ~500 V. CDM is completely different from HBM and MM, so there is no correlation between them. Therefore, CDM and HBM tests are commonly used to test ESD protection circuits. Figure 4 shows current waveforms characteristics for HBM, MM, and CDM. The CDM waveform corresponds to the shortest known ESD event and has a rise time of 400 ps with a total duration of ~2 ns.