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There is no more complex and challenging component
technology than microcircuits. The diversity of technologies and the pace of
their advances present a bewildering range of design choices to the engineer.
This information on microcircuits can be used as guidance or as a
The microcircuit industry has been driven by a
progression of marketplaces: the military in the 1970’s, personal computers in
the 1980’s, and networking in the 1990’s. This market progression has fostered
two common trends in microcircuit chip characterization: 1) increased
functionality and complexity and 2) increased speed and density.
These trends have placed a great deal of pressure on
the microcircuit interconnections and packaging. They have made it more
difficult to lay out the interconnecting system with microcircuit chips
increasing in size, I/O, power dissipation and frequency. In addition, with the
demand for increased functional density, smaller package sizes, and the use of
plastic encapsulated microcircuits (PEMs), the microcircuit’s package
reliability risk has grown tremendously.
Microcircuits have had significant technological
advances resulting from these market drivers. For instance, the number of
microcircuits on a motherboard has decreased as more functionality is being
integrated into the microprocessor. As 0.5µm gate lengths are reached and
surpassed, supply voltages are decreasing; this decrease has allowed power
dissipation to be decreased. In addition, smaller microcircuits that are more
capable are permitting reductions in equipment size and weight.
Through the advances of the microcircuit, the pace at
which products are introduced has accelerated. A PC can be on the street in 9 to
12 months from the initial design through assembly to market. The total life
cycle of a PC is just two years. This is all caused by the rate of change of the
microprocessor technology. Every two years or less an old generation of
microprocessors are being replaced by new ones.
The Microcircuits sections describes changes to the
industry, products, and how to design and select microcircuits. Included are
reliability, derating, and assessment requirements, failure mechanisms and
design concerns to support insertion of microcircuits into
When using microcircuits in the “normal” or “severe”
environments, recommend using QML-38535 qualified microcircuits.
For all military applications using microcircuits,
the performance specification, MIL-PRF-38535, should be used.
Recommend applying the requirements in these
microcircuit sections when using PEMs. EIA/JEDEC and IPC Standards to use
a. SSB-1 “Guidelines for Qualifying and Monitoring
Plastic Encapsulated Microcircuits and Semiconductors”.
b. EIA/JESD22-A112-A “Moisture-Induce Stress
Sensitivity for Plastic Surface Mount Devices”.
c. EIA/JEP113-A “Symbols and Labels for
d. JESD22-A113-A “Preconditioning of Plastic Surface
Mount Devices Prior to Reliability Testing”.
e. JEP124 “Guidelines for the Packing, Handling, and
Re-packing of Moisture-Sensitive Components.
f. J-STD-020A “Moisture/Reflow Sensitivity
Classification for Non-hermetic Solid State Surface Mount Devices”.
g. J-STD-033 “Standard for Handling, Packing,
Shipping, and Use of Moisture/Reflow Sensitive Surface Mount
PEMs packages are probably the most discussed subject
in microcircuitry. Some general recommendations and commons are:
a. Use PEMs in the “protected” environment. Use PEMs
in the “normal” environment only when: (1) the sensitivity level is acceptable,
(2) it is thermally packaged to control heat dissipation, and (3) the PEM is
qualified to the environment and application. Do not use PEMs in the “severe”
b. Through-hole PEMs are generally a level 1-2
sensitivity, which is good. They can usually replace standard hermetic packaged
microcircuits. Their replacement is usually for DMS situations only.
c. Surface mount PEMs are used for new designs and
are usually a level 5-6, which is the most sensitive to moisture. In addition,
the consumer industry continues to push this package smaller, which makes it
even riskier. These parts are extremely sensitive and must be handled carefully.
Recommend using them in the “protected” environment only. If used in the
“normal” environment, the application must be one that is easily accessible for
replacement or the applications life cycle must be short, 3 years or
d. Do not store any non-hermetic part beyond its
recommended sensitivity level (1-6) shelf life.
e. Do not use parts in a long-term dormant
application, beyond 7-8 years maximum.
Try to design an application for a 3 to 5 year life
cycle. This will eliminate a number of problems and align with non-military
industries, which lead the industries’ technology changes.