Electrical Overstress (EOS)
In August 2016, the Industry Council on ESD Target Levels released a new white paper on Electrical Overstress (EOS). The Council gathered information via a survey sent to more than 90 companies asking them about the importance of EOS to their business and their methods for addressing EOS issues. One of their first steps—create a universal definition of EOS –
EOS – an electrical device suffers an electrical overstress event when a maximum limit for either the voltage across, the current through, or power dissipated in the device is exceeded and causes immediate damage or malfunction, or latent damage resulting in an unpredictable reduction of its lifetime.
In general, they found that ESD damage was often confused with EOS damage and those responsible for identifying failures were many times either inconsistent or incorrect in their findings. The Council also created multiple goals after gaining insight from the survey and laid out plans for the future.
Industry Council goals –
- Reduce EOS occurrences
- Create a unified global understanding of what constitutes EOS
- Understand how EOS damage signatures can result from a wide variety of root causes
- Address possible preventable failures showing EOS damage
- Explain the non-correlation between EOS return rates and component ESD target levels
- Standardize EOS reporting to reduce mislabeling damage as EOS
- Continue to dispel the notion that EOS can be avoided by making devices more ESD robust (ref. JEDEC publications JEP155  and JEP157)
The white paper contains very detailed explanations and diagrams to help EOS data reporters improve. (IC suppliers, i.e., customers, applications engineers and system builders). One of their most significant findings concerned Absolute Maximum Rating (AMR) and the actual meaning of maximum limit. (see definition of EOS) and the different methods a manufacturer uses to determine a device’s AMR values.
- Some suppliers do not include ESD limits as part of their AMR because testing to establish the ESD limits often does not have the similar statistical data required for setting more traditional items such as voltage.
- Some suppliers do place ESD limits in their AMR definition believing this is part of the overall agreement that must be met between supplier and customer.
- Other suppliers placed ESD limits in AMR sections because it was the only place that made sense to them.
The Council asks manufacturers to go back to suppliers to verify the AMR information published before the release of their EOS white paper.
The white paper concluded –
- EOS has never been fully understood or accurately and thoroughly explained or interpreted.
- Meeting ESD levels beyond the specification targets does not mean a reduced rate of EOS returns. Overwhelming data from the Industry Council supports this assertion.
- Industry-wide surveys indicate a) EOS is the most common attribute of reported returns, b) most respondents indicated they use “damage signature” to determine EOS.
- EOS almost always represents permanent damage.
- Most common cause for EOS – 1) misapplication, 2) violations to absolute maximum ratings, 3) exposure to electrical stress events during assembly and in the field that violate the AMR
- Establishing a universal definition of EOS should foster better communication in the industry when addressing EOS problems
- Absolute maximum rating requires a more in-depth definition informing customers that exceeding the AMR value has risks and can lead to irrecoverable device damage. Also, an EOS event occurs if any AMR is exceeded for any period of time.
- AMR specifications must include constraints for excursions in system operation and environmental conditions needing to be accommodated by system design to allow safe operation and handling of semiconductor components.
- Electrical and environmental conditions for intended AMR values must be documented in datasheets.
- In unique systems requirements, the AMR values must be provided by semiconductor component suppliers according to electrical and environmental conditions given by system manufacturers.
The Industry Council hopes to foster understanding of EOS, the root cause determination for resolving EOS issues and implementation of methods for EOS mitigation.