# Presentation: 543650

## COTS PEMs Procurement & Acquisition Concerns and Issues

- Dr. Henning W. Leidecker
- GSFC/Code 562
- 301-286-918021 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”.