Answer Key
- The primary purpose of Test Method A115-A is to provide a standard procedure for testing and classifying microcircuits based on their susceptibility to damage or degradation from a Machine Model (MM) electrostatic discharge. The objective is to generate reliable and repeatable MM ESD test results, allowing for accurate classifications.
- The test method requires an ESD Pulse Simulator, a Device Under Test (DUT) socket equivalent to the circuit in Figure 1, an oscilloscope with at least 350 MHz bandwidth, and a current probe with at least 350 MHz bandwidth. Evaluation loads like a shorting wire and a 500 ohm resistor are also necessary for calibration.
- The component C1 in the typical MM ESD equivalent circuit is a 200 pF capacitor with a tolerance of +/- 10%. The switch S2 should be closed 10 to 100 milliseconds after the pulse delivery period to ensure the DUT socket is not left in a charged state.
- Recalibration is required whenever equipment repairs are made that may affect the waveform and must be performed at a minimum of every 12 months. This ensures the equipment continues to meet the specified requirements for accurate testing.
- A “worst-case pin” is the socket pin that has either the shortest or longest wiring path from the pulse generating circuit. This pin is used for waveform verification because it represents the extremes of parasitic inductance and capacitance in the test fixture, ensuring the test signal meets specifications under the most challenging conditions.
- When using the shorting wire, the waveform verification measures several key parameters as defined in Table 1. These include the Positive Peak current for the short (Ipsl), the Maximum Ringing Current (expressed as a percentage of Ipsl), and the Resonance Frequency for the short (tfr).
- To classify a device, a sample of 3 devices is stressed at each voltage level. The procedure involves applying 1 positive and 1 negative pulse with a minimum interval of 1 second between pulses for all specified pin combinations.
- For Pin Combination 1, all pins are connected one at a time to Terminal A (the pulse source), with the exception of the pin(s) connected to Terminal B. The first power pin(s) are connected to Terminal B (Ground), while all other pins (except the Pin Under Test and first power pin) are left floating.
- A part is defined as a failure if, after exposure to the ESD pulses, it no longer meets the device data sheet requirements. This is determined by performing parametric and functional testing; if testing is required at multiple temperatures, the failure determination is made at the lowest temperature first.
- The classifications are defined as follows: Class A includes any part that fails after exposure to an ESD pulse of 200 volts or less. Class B includes any part that passes a 200 volt pulse but fails after exposure to a 400 volt pulse. Class C includes any part that passes after exposure to an ESD pulse of 400 volts.