The Charged Device Model (CDM) test method is steadily taking the place of the MM testing method for today’s ESD testing. This method simulates what happens in an automated manufacturing environment when an IC becomes triboelectrically charged, and the part discharges when it comes in contact with a grounded conductor. The CDM discharge is a fast transient, which takes place over a couple of ns at most. This is a more challenging device to model, and is based on the size and the capacitance of the IC being tested, with little impedance to reduce the current. This can result in high currents well above 5 A to 6 A being discharged in a short duration of one ns or less. Thus, this stands as the most practical real world test for ESD issues today. By some estimates, as much as 25% of semiconductor yield loss in production assembly and test is due to CDM.
Charged Device Model testing is defined in several popular industry standards documents. The most widely used test method is defined by EIA/JEDEC JESD22-C101. Additional methods are ANSI/ESDA STM5.3.1 and AEC-Q100-011. These standard test methods are revised frequently, so the most recent revision should be used during ESD testing.
Charged Device Model failures typically occur in two areas on the chip: in the core as dielectric failures due to voltage build-up during the CDM discharge, or in the Input/Output circuitry as metallization or junction failures due to current crowding.
Charged Device Model testing differs greatly from both HBM and MM testing, in that it is an “unsocketed” test, meaning there is no data collected during the testing procedure. The CDM testing procedure consists of the DUT being placed on the tester with the leads or contacts facing up. The metal field plate and the DUT are separated by a thin layer of FR-4 material, which acts as an insulating capacitor between the two objects. The field plate is then raised to the required CDM test voltage level (500 V – 1,000 V typically), and a robotic probe comes into close proximity of the pin under test. A high-current electric discharge takes place, which is verified by monitoring the ground connection of the pin under test. The field plate is then grounded through a 1 MΩ resistor to remove any residual charge. CDM industry standards require that each pin on the DUT receives three positive and three negative pulses, resulting in six total discharges per pin.
The uniformity and repeatability of the CDM discharge is of particular concern, since the discharge occurs in an air gap between the pin under test and the grounded pogo pin. Qualification of a CDM testing service should include a review of the test environment, including calibration of the CDM testers, availability of N2 in the test chamber, and monitoring of temperature and humidity during testing.
Additional Overviews:
- ESD Testing
- Human Body Model
- Charged Device Model
- Machine Model
- Latch up
- Transmission Line Pulse