The key to good ESD-tolerant designs is to understand the basic causes, to understand the various solutions to different requirements and to perform a good first-order analysis of possible paths of the ESD energy for non-standard designs.
Although the implementation approach may change for each new technology,
the fundamentals remain the same for all technologies:
- Identify all current paths from the test pin to any other pin or any other supply pin other than the pin being tested.
- All designs must have robust performance to both positive and negative ESD pulses.
Therefore good substrate clamp diodes must be employed.
- The best ESD solutions utilize symmetrical/balanced current paths for the ESD energy.
Therefore it is very important how the I/O pads are laid out.
- The best ESD solutions also make use of a combination of primary and secondary protection.
- Deep sub-micron technologies utilize shunt devices as well as NMOS breakdown (snap-back) devices
because SCR protection is less effective than in the older 0.5- and 0.6-micron technologies.
As design experience increases and new I/Os are developed in new technologies, it is necessary to test all I/Os to failure. Failure analysis must also be performed on all failures, and the results must be fed back to the design community so that new and improved methods can be implemented in future designs.