Many ESD standards such as Human Body Model (HBM), Machine Model (MM), Charged Device Model (CDM) and IEC 61000-4-2 have been developed to test the performance and robustness of electronic devices. Unfortunately, these standards are frequently misunderstood and often used interchangeably. This ultimately results in failures of supposedly protected systems in the consumer’s hands. The designer needs to understand the difference between manufacturing environment and end user environment ESD testing. Most designers are familiar with the classic device level tests that are applied to integrated circuits (IC), but the most common misunderstanding occurs between the human body model and the IEC 61000-4-2 standards. These two standards are designed for very different purposes. Only the stringent IEC 61000-4-2 standard is acceptable to identify real world ESD stress conditions.
The purpose of this brief is to indicate the differences between the HBM and IEC 61000-4-2 Standards and test methods.
There are three important changes in today’s systems that have increased ESD vulnerability.
Smaller Manufacturing Geometries: most ICs have decreased to less than 90nm and the voltage and current levels have decreased. ESD damage can occur due to excessive voltage, high current levels or a combination of both. High voltages cause gate oxide punch-through and high current levels cause junction failures and melting of metalized traces. This decrease in geometries has made it very difficult to provide adequate on-chip ESD protection.
Reduction of On-Chip Protection: The Industry Council on ESD Target Specifications announced a move to reduce the standard level of on-chip protection. Their focus is providing adequate protection for manufacturing environments and to maintain protection levels of today’s market.
The Changing Application Environment: many laptops, cell-phones (smartphones), MP3 players, digital cameras and other handheld devices that are used in uncontrolled environments require additional ESD protection. In these environments people touch I/O connecter pins – such as USB, HDMI, etc. – when plugging and unplugging cables. The devices are subject to constant ESD stress levels when this happens. The portable device can also build up a charge and will discharge when plugged into a grounded device such as a TV or computer. The simple act of walking across a carpet can generate up to 40kV of this level of discharge through a port that can cause latent and permanent defects of so-called protected ICs.