This
section details derating requirements for microcircuits.
Derating is the method of reducing stress and/or making
numerical allowances for functional degradation in microcircuit performance.
Non-military parts used in military applications need to be derated more
conservatively than military parts. The microcircuits must meet the performance
and reliability criteria established for their application when used in military
applications. When using microcircuits of different temperature ranges,
reliability levels, and performance characteristics, it is crucial to derate
them properly. Two methods of derating are (1) by reducing heat and electrical
stress and (2) by compensating for functional loss. Heat and electrical stress
derating is applied to the voltage, current, and power stresses of the
microcircuit. Functional loss and/or performance degradation over the part’s
life requires a degree of parametric derating. Derating should be applied
knowledgeably and singly only enough to improve reliability, and only once
throughout the application cycle. The severity of an application and its
environment may require an additional degree of derating.
Tables 1A through 1E detail the type (technology-product), package (hermetic or plastic), derating parameters, and maximum allowable limits (percentage and/or temperature) of operation (in specific environment) for the microcircuit. Tables 1A through 1E are grouped by type of microcircuit: Table 1A MOS and Bipolar Digital, Table 1B MOS and Bipolar Linear, Table 1C MOS and Bipolar Microprocessor, Table 1D MOS and Table 1E Bipolar Memory and GaAs Digital microcircuits.
Table 1A.
Digital MOS and Bipolar Microcircuit Derating Requirement
Type |
|
Environment |
Digital |
Package |
Derating Parameter |
Protected |
Normal |
Severe |
MOS |
Hermetic |
Supply Voltage |
/3 |
/3 |
/3 |
|
|
Frequency |
90% |
90% |
90% |
|
|
Output Current |
90% |
85% |
80% |
|
|
Fanout |
100% |
90% |
90% |
|
|
Junction Temperature
(TJ) |
125°C |
110°C |
100°C |
|
Plastic 1/ |
Supply Voltage |
/3 |
/3 |
|
|
|
Frequency |
90% |
80% |
|
|
|
Output Current |
90% |
80% |
|
|
|
Fanout |
100% |
90% |
|
|
|
Junction Temperature
(TJ) |
90°C |
85°C |
|
|
Plastic 2/ |
Supply Voltage |
/3 |
|
|
|
|
Frequency |
80% |
|
|
|
|
Output Current |
70% |
|
|
|
|
Fanout |
80% |
|
|
|
|
Junction Temperature
(TJ) |
70°C |
|
|
Bipolar |
Hermetic |
Supply Voltage |
/3 |
/3 |
/3 |
|
|
Frequency |
100% |
90% |
85% |
|
|
Output Current |
90% |
85% |
80% |
|
|
Fanout |
90% |
85% |
80% |
|
|
Junction Temperature
(TJ) |
125°C |
110°C |
100°C |
|
Plastic 1/ |
Supply Voltage |
/3 |
/3 |
|
|
|
Frequency |
100% |
90% |
|
|
|
Output Current |
90% |
80% |
|
|
|
Fanout |
90% |
80% |
|
|
|
Junction Temperature
(TJ) |
90°C |
85°C |
|
|
Plastic 2/ |
Supply Voltage |
/3 |
|
|
|
|
Frequency |
75% |
|
|
|
|
Output Current |
70% |
|
|
|
|
Fanout |
70% |
|
|
|
|
Junction Temperature
(TJ) |
70°C |
|
|
Table
1B. Linear MOS and Bipolar Microcircuit Derating
Requirements
Type |
|
Environment |
Linear |
Package |
Derating Parameter |
Protected |
Normal |
Severe |
MOS |
Hermetic |
Supply Voltage |
/3 |
/3 |
/3 |
|
|
Input Voltage |
80% |
80% |
70% |
|
|
Frequency |
90% |
90% |
90% |
|
|
Output Current |
90% |
85% |
80% |
|
|
Fanout |
100% |
90% |
90% |
|
|
Junction Temperature
(TJ) |
125°C |
110°C |
100°C |
|
Plastic 1/ |
Supply Voltage |
/3 |
/3 |
|
|
|
Input Voltage |
80% |
70% |
|
|
|
Frequency |
90% |
80% |
|
|
|
Output Current |
90% |
80% |
|
|
|
Fanout |
100% |
90% |
|
|
|
Junction Temperature
(TJ) |
90°C |
85°C |
|
|
Plastic 2/ |
Supply Voltage |
/3 |
|
|
|
|
Input Voltage |
60% |
|
|
|
|
Frequency |
80% |
|
|
|
|
Output Current |
70% |
|
|
|
|
Fanout |
80% |
|
|
|
|
Junction Temperature
(TJ) |
70°C |
|
|
Bipolar |
Hermetic |
Supply Voltage |
/3 |
/3 |
/3 |
|
|
Input Voltage |
80% |
80% |
70% |
|
|
Frequency |
100% |
90% |
85% |
|
|
Output Current |
90% |
85% |
80% |
|
|
Fanout |
90% |
85% |
80% |
|
|
Junction Temperature
(TJ) |
125°C |
110°C |
100°C |
|
Plastic 1/ |
Supply Voltage |
/3 |
/3 |
|
|
|
Input Voltage |
80% |
70% |
|
|
|
Frequency |
100% |
90% |
|
|
|
Output Current |
90% |
80% |
|
|
|
Fanout |
90% |
80% |
|
|
|
Junction Temperature
(TJ) |
90°C |
85°C |
|
|
Plastic 2/ |
Supply Voltage |
/3 |
|
|
|
|
Input Voltage |
60% |
|
|
|
|
Frequency |
75% |
|
|
|
|
Output Current |
70% |
|
|
|
|
Fanout |
70% |
|
|
|
|
Junction Temperature
(TJ) |
70°C |
|
|
Table
1C. Microprocessor MOS and Bipolar Derating
Requirements
Type |
|
Environment |
Microprocessor |
Package |
Derating Parameter |
Protected |
Normal |
Severe |
MOS |
Hermetic |
Supply Voltage |
/3 |
/3 |
/3 |
|
|
Frequency |
90% |
90% |
90% |
|
|
Output Current |
90% |
85% |
80% |
|
|
Fanout |
100% |
90% |
90% |
|
|
Junction Temperature
(TJ) |
125°C |
110°C |
100°C |
|
Plastic 1/ |
Supply Voltage |
/3 |
/3 |
|
|
|
Frequency |
90% |
80% |
|
|
|
Output Current |
90% |
80% |
|
|
|
Fanout |
100% |
85% |
|
|
|
Junction Temperature
(TJ) |
85°C |
75°C |
|
|
Plastic 2/ |
Supply Voltage |
/3 |
|
|
|
|
Frequency |
80% |
|
|
|
|
Output Current |
70% |
|
|
|
|
Fanout |
80% |
|
|
|
|
Junction Temperature
(TJ) |
70°C |
|
|
Bipolar |
Hermetic |
Supply Voltage |
/3 |
/3 |
/3 |
|
|
Frequency |
90% |
80% |
75% |
|
|
Output Current |
80% |
75% |
70% |
|
|
Fanout |
80% |
75% |
70% |
|
|
Junction Temperature
(TJ) |
125°C |
110°C |
100°C |
|
Plastic 1/ |
Supply Voltage |
/3 |
/3 |
|
|
|
Frequency |
90% |
80% |
|
|
|
Output Current |
80% |
75% |
|
|
|
Fanout |
80% |
75% |
|
|
|
Junction Temperature
(TJ) |
85°C |
75°C |
|
|
Plastic 2/ |
Supply Voltage |
/3 |
|
|
|
|
Frequency |
75% |
|
|
|
|
Output Current |
70% |
|
|
|
|
Fanout |
70% |
|
|
|
|
Junction Temperature
(TJ) |
70°C |
|
|
Table
1D. Microcircuit Memory MOS and Bipolar Derating
Requirements
Type |
|
Environment |
Memory |
Package |
Derating Parameter |
Protected |
Normal |
Severe |
MOS |
Hermetic |
Supply Voltage |
/3 |
/3 |
/3 |
|
|
Frequency |
100% |
90% |
90% |
|
|
Output Current |
90% |
85% |
80% |
|
|
Junction Temperature
(TJ) |
125°C |
110°C |
100°C |
|
Plastic 1/ |
Supply Voltage |
/3 |
/3 |
|
|
|
Frequency |
100% |
90% |
|
|
|
Output Current |
90% |
80% |
|
|
|
Junction Temperature
(TJ) |
90°C |
85°C |
|
|
Plastic 2/ |
Supply Voltage |
/3 |
|
|
|
|
Frequency |
80% |
|
|
|
|
Output Current |
70% |
|
|
|
|
Junction Temperature
(TJ) |
70°C |
|
|
Bipolar |
Hermetic |
Supply Voltage |
/3 |
/3 |
/3 |
|
|
Frequency |
100% |
100% |
90% |
|
|
Output Current |
90% |
85% |
80% |
|
|
Junction Temperature
(TJ) |
125°C |
110°C |
100°C |
|
Plastic 1/ |
Supply Voltage |
/3 |
/3 |
|
|
|
Frequency |
100% |
95% |
|
|
|
Output Current |
90% |
80% |
|
|
|
Junction Temperature
(TJ) |
90°C |
85°C |
|
|
Plastic 2/ |
Supply Voltage |
/3 |
|
|
|
|
Frequency |
80% |
|
|
|
|
Output Current |
70% |
|
|
|
|
Junction Temperature
(TJ) |
70°C |
|
|
Table
1E. GaAs Microcircuit Derating Requirements
Type
|
|
Environment
|
GaAs
|
Package
|
Derating Parameter
|
Protected
|
Normal
|
Severe
|
Digital
|
Hermetic
Plastic 1/
Plastic 2/
|
Channel Temperature
Channel Temperature
Channel Temperature
|
150°C
125°C
90°C
|
125°C
90°C
|
90°C
|
Notes for Tables 1A through 1E
1/ Plastic packaged microcircuit with heat
dissipating mechanisms (e.g. thermal fillers, thermal conductivity plate or a
type of metal substrate) built-in.
2/ Low-power plastic packaged microcircuits with
no heat dissipating mechanism other than through the leads.
3/ The supply voltage must be kept within the
microcircuit specification sheets minimum and maximum limit.
Examples of parameters that may need derating
are:
a. Junction temperature. The microcircuit’s maximum junction
temperature should not go over 115°C. For
example, IBM uses 85°C as its
design guideline and Intel uses 90°C as the
maximum junction temperature specification for the Pentium processor.
Temperature drop between the junction and the ambient is typically 50°C with an
ambient of 40°C
(113°F) inside
an enclosure. Designers should try to design-derate junction temperatures below
90°C
while maintaining, at most, a temperature difference of 50°C.
Junction temperatures increase as energy builds up. The greater the
temperature-difference, the higher the energy flow out of the part. The maximum
temperature of a junction is reached when the heat flow out to the ambient is
able to keep up with the energy being produced by the junction. Performance
risks and speed concerns are associated with increasing junction temperatures.
In addition, all failure mechanisms have activation energy associated with
accelerated increased temperature. For an activation energy, for the failure
mechanism of 0.5eV, typical of punch-through failures for example, every 10°C increase
in junction temperature results in the lifetime of a microcircuit cut roughly in
half. This is diagramed in Figure 1.
Figure 1. Relative MTBF with Activation Energy
of 0.5eV
b. Examples of parametric derating:
1. Use a digital circuit at less than full fanout.
Historically, fanout has been derated by a factor of 20%.
2. Design for extra noise margin and sacrifice some for
derating.
3. Applying the performance level below guaranteed by the
manufacturer.
4. Parameters that depend directly on transistor beta,
resistor value, or junction leakage are more prone to shifting during the life
of the microcircuit. These are detailed in the derating Table 8-5.
5. Parameters that depend directly on the saturation
voltages of junctions and on the ratios of resistors are likely to remain stable
through the life of the microcircuit.
6. Logic noise-margin levels have been derated by a factor
of 10%.
7. AC parameters such as delay times or rates are usually
not derated, as these parameters do not vary greatly over the life of a
microcircuit. The delay times of separate gates within one microcircuit may vary
greatly in many cases. In addition, these parameters are not normally measured
on 100% of the microcircuits, and as such, this variation should be allowed for
in the designing of microcircuits.
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