Both PEMs and HSMs, if exposed to environments outside their specification limits, are subject to potential failure. Therefore, it is critical that the design phase consider manufacturing, transportation, and storage environments as well as operational environments. PEMs are generally available in six temperature ranges, shown below, which may vary between available microcircuit functions and suppliers.
PART TEMPERATURE
GRADE RANGE
COMMERCIAL 0 ºC TO +70 ºC
INDUSTRIAL -25 ºC TO +85 ºC
AUTOMOTIVE GRADE 3* -40 ºC TO +85 ºC
AUTOMOTIVE GRADE 2* -40 ºC TO +105 ºC
AUTOMOTIVE GRADE 1* -40 ºC TO +125 ºC
MILITARY GRADE** -55 ºC TO +125 ºC
* Limited availability of device types.
** Several suppliers have achieved "MIL-SPEC"
temperature ranges experimentally by encapsulating circuitry,
originally designed using HSM design rules, in PEM packages.
Some specific observations relating to this consideration are as follows:
- Environmental specifications must include not only operating profiles but also manufacturing, test, transportation, and storage profiles.
A thorough knowledge of application conditions is essential (life cycle functional and environmental profiles).
- Create robust designs, using derating, wide tolerances and other design techniques to allow for variations in part manufacturing processes and temperatures outside part specification ranges.
- Circuit simulations (e.g., stress analyses, failure modes and effects analysis, worst case analysis, etc.) should be performed to evaluate performance and design margins in intended environments.
- PEM costs must consider both the total life cycle and acquisition costs.
Cost advantages of PEMs may erode if life/qualification testing and additional quality screening are necessary. PEM cost advantages may be offset by logistics costs associated with long term dormant storage systems.
