COTS PEMs Procurement Acquisition Concerns and Issues

COTS PEMs Procurement & Acquisition Concerns and Issues Dr. Henning W. Leidecker GSFC/Code 562 301 -286 -9180 21 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”.