By J.R. Wilson
OXNARD, Calif. — One of the more controversial topics among engineers and program managers today is microcircuit upscreening. This involves testing a commercially manufactured microcircuit and declaring it acceptable for use in temperatures and other environments beyond its design parameters.
Central to the debate are the results of a study for the Defense Standardization Program Office (DSPO) at Fort Belvoir, Va. The study determined that upscreening is commonplace in commercial and military aircraft, as well as in weapons systems and platforms. This is despite the opposition to upscreening by members of the Semiconductor Industry Association, individual IC manufacturers, and nearly all end user commands.
The Naval Surface Warfare Center [NSWC] strongly "recommends `never allow uprating/upscreening`," reports Joe Chapman, a microcircuits consultant involved in the study.
The DSPO study has involved interviews with more than 50 companies, agencies, and individuals. Those interviewed include officials of prime contractors Lockheed Martin, GTE, Boeing, Honeywell, Raytheon, and Allied-Signal; government organizations NSWC Crane, Ind., NSWC Port Hueneme, Calif., Naval Air Systems Command, Defense Supply Center Columbus, and the Defense Microelectronics Activity; semiconductor companies and distributors Integra Technologies, Analog Devices, Arrow-Zeus, Texas Instruments, Lansdale Semiconductor, Harris Corp. (now Intersil), Xilinx, National Semiconductor, and Rochester Electronics; as well as electronics suppliers DY 4, Bell Technologies, Philips, and QP Labs.
Interviews show that contractors have procedures in place that permit the use of commercial-off-the-shelf (COTS) and upscreened components in systems and subsystems, even as concern for the process grows in the user community.
Chapman, who had a long career at the military products group of Texas Instruments Semiconductor division, says the upscreening poses several dangers. These include handling damage, non-repeatable lot manufacturing, unreliability at broad temperature ranges, a lack of traceability, and hidden costs.
"Recognition that upscreened components should be the last choice is well documented," he says. "Industry must proactively deal with the risk and the best known engineering practices must be rigidly observed."
Gorky Chin, vice president-advanced technology for Vista Controls Corp. in Santa Clarita, Calif., says an upscreened commercial integrated circuit (IC) usually is just as expensive as the original mil-spec item — and when done without the original manufacturer`s consent or approval, also can be a risky process.
That risk is twofold — the legal implications to the contractor in the event of failure, and the influence of that failure for the end user.
Despite these considerations, contractors turn to upscreened microcircuits because parts manufactured to wide temperature ranges are expensive and difficult to find. Where IC design limits used to be -60 to 130 degrees Celsius, they now tend to fall into a -10 to 80 C range, with normal operating specification limits of zero to 70 C. The full-military temperature range is -55 to 125 C.
"Computer, consumer, and much of the communications market are not concerned about performance beyond zero to 70 C nor moisture or temperature cycle effects," says Jack Stradley, central and southwest regional manager for Rochester Electronics of Newburyport, Mass. "They are obsessed with cost and performance related to data throughput. If an extra capability impacts cost, it may disappear."
Even so, upscreening/uprating "always degrades reliability," he claims. "Typical upgrading insertion causes 0.5 percent fallout for ESD/EOS," Stradley warns about the increased number of parts that fail due to handling during the upscreening process, "plus unknown ESD walking wounded."
life cycle perspective