COTS PEMs Procurement & Acquisition Concerns and Issues Dr. Henning W. Leidecker GSFC/Code Nov 2002

See Also: GSFC Plastic Encapsulated Microcircuit (PEMs) Supplement to 311-INST-011, released by the Parts, Packaging, and Technology Branch(Code 562)

How Much Should A Project Spend On Electronic Parts? Baseline: The electronics must work. Additional: They must keep working, in space, without repairs! Reliability is needed. This costs extra. The launch vehicle sets a particular cost and a particular reliability: this sets one level for the extra cost. The worth of the mission also sets a level.

The Material We Work With: Old style --- Hi-Rel: ”manufacturing lot” controls, defined performance with strong protections against fraud, notification of changes, ALERTS, qual and screening programs. New style --- commercial PEMs: no lot controls, vaguely defined performance with no recourse from "bad data", no notification of changes, no ALERTS (better not try it!), mysteries about “qual”ing and about screening. We need several kinds of special care to incorporate commercial PEMs into spacecraft. Detailing some of these is the purpose of this talk.

Why Use Commercial PEMs? Mainly availability! Hi-Rel parts are less than 0.5% of the market => many manufacturers have switched to making only commercial PEMs. Increasingly, we cannot find Hi-Rel parts. High performance in small low-power packages. Cost is almost never a driver. Commercial PEMs cost more per part than the Hi-Rel devices do, after qual and screening. (Swift-BAT an exception.)

COTS PEMs DANGERS (Part 1) The key idea: commercial PEMs are being carefully aimed at a precisely defined market. And it is not the spacecraft market. Desiderata: The lowest possible piece-cost / Highest initial performance. What is sacrificed for Desiderata: Reliability extending past one year (or a few years). ESD hardness / EOS robustness. Not even on the table: Radiation hardness / Operation in a vacuum.

COTS PEMs DANGERS (Part 2) High performance and low-cost * Crowding circuits => "hot electron"degradations. Thinning traces => electromigration-induced breaking of traces giving electrical “opens”. Thinning dielectrics => dielectric breakdown. Passivation layers are being omitted. All the above can lead to "wear-out": a failure probability that says low until after a threshold time, and then rapidly increases.

COTS PEMs DANGERS (Part 3) The ESD/EOS guard circuits are gone in some cases. The physical sizes of the parts are shrinking profoundly. Hence, the capacitance of each pin is decreasing, so that a given amount of charge deposited onto a pin will increase its potential more than used to be the case. The dielectric thicknesses are decreasing, along with their breakdown voltages. ESD/EOS damage is now affecting many devices.

Qual: Can The Part-design work? Possible failure modes are explored using highly accelerated tests. These usually use high temperature, and may use high voltage, and high humidity. Potentially damaging --- these parts are discarded. New parts => new failure modes --- What are they? What tests would reveal them? Cannot increase temperature enough! End-game failures, like radiation softness. Advertising the failures of commercial parts?

Screening: Was This Lot Made Correctly? We do find problems with lots (e.g., memory). Burn-in: what temperatures and times? C-SAM: many PEMs delaminate during burn-in. $50 sockets for 50 cent parts, and other screening expenses.

Screening House Adventures Do not read testing requests. Do not test whether all parameters are OK. Destroy parts using bad burn-in settings. Destroy parts using “bad” equipment. Station a friendly Watchdog at the house!

What To Do? Work closely with the manufacturers: get data. Be vigilant for changes in the parts being supplied: different wafer supplier, different mask, different foundry, different wire bonder, different plastic composition, different encapsulation parameters. Check that the flight parts work in their circuits. Set aside extra time for the qual and for the screening. Ensure alternative choices --- be cautious about committing to a unique part because it is “sweet”.