Reliability

Introduction

• Introduction to Reliability

• Historical Perspective

• Current Devices

• Trends

The Bathtub Curve (1)

Time

Failurerate,

Constant

Useful life Wear outInfant

Mortality

The Bathtub Curve (2)What is the "bathtub" curve?

In the 1950’s, a group known as AGREE (Advisory Group for the Reliability of Electronic Equipment) discovered that the failure rate of electronic equipment had a pattern similar to the death rate of people in a closed system. Specifically, they noted that the failure rate of electronic components and systems follow the classical “bathtub” curve. This curve has three distinctive phases:

1. An “infant mortality” early life phase characterized by a decreasing failure rate (Phase 1). Failure occurrence during this period is not random in time but rather the result of substandard components with gross defects and the lack of adequate controls in the manufacturing process. Parts fail at a high but decreasing rate.

2. A “useful life” period where electronics have a relatively constant failure rate caused by randomly occurring defects and stresses (Phase 2). This corresponds to a normal wear and tear period where failures are caused by unexpected and sudden over stress conditions. Most reliability analyses pertaining to electronic systems are concerned with lowering the failure frequency (i.e., const shown in the Figure) during this period.

3. A “wear out” period where the failure rate increases due to critical parts wearing out (Phase 3). As they wear out, it takes less stress to cause failure and the overall system failure rate increases, accordingly failures do not occur randomly in time.

Introduction to Reliability

• Failure in time (FIT)Failures per 109 hours

( ~ 104 hours/year )

• Acceleration Factors– Temperature– Voltage

Introduction to Reliability (cont'd)

Most failure mechanisms can be modeled using the Arrhenius equation.

ttf - time to failure (hours)

C - constant (hours)

EA - activation energy (eV)

k - Boltzman's constant (8.616 x 10-5eV/°K)

T - temperature (ºK)

ttf = C • eEA/kT

Introduction to Reliability (cont'd)Acceleration Factors

ttfL

A.F. = ------ ttfH

A.F. = acceleration factor

ttfL = time to failure, system junction temp (hours)

ttfH = time to failure, test junction temp (hours)

Introduction to Reliability (cont'd)Activation Energies

Failure Mechanism EA(eV)

Oxide/dielectric defects 0.3

Chemical, galvanic, or electrolytic corrosion 0.3

Silicon defects 0.3

Electromigration 0.5 to 0.7

Unknown 0.7

Broken bonds 0.7

Lifted die 0.7

Surface related contamination induced shifts 1.0

Lifted bonds (Au-A1 interface) 1.0

Charge injection 1.3

Note: Different sources have different values - these values just given for examples.

Acceleration Factor - VoltageOxides and Dielectrics

• Large acceleration factors from increase in electric field strength

A.F. = 10 • / (MV / cm)

k - Boltzman's constant (8.616 x 10-5eV/°K)

T - temperature (ºK)

= 0.4 • e 0.07/kT

Acceleration Factor: Voltage

Median-time-to-fail of unprogrammed antifuse vs. 1/V for different failure criteria with positive stress voltage on top electrode and Ta = 25 °C.

Device and Computer Reliability1960's Hi-Rel Application

• Apollo Guidance Computer– Failure rate of IC gates:

< 0.001% / 1,000 hours ( < 10 FITS ) – Field Mean-Time-To-Failure

~ 13,000 hours

• One gate type used with large effort on screening, failure analysis, and implementation.

Device Reliability:1971

Reliability Level of Representative Parts and Practices MTBF (hr)

Commercial 500 Military 2,000 High Reliability 10,000 (104 hours)

MIL-M-38510 Devices (1976)

Circuit Types Description FITS

5400 Quad, 2-input NAND 60 5482 2-bit, full adder 44 5483 4-bit, full adder 112 5474 Dual, D, edge-triggered flip-flop 72 54S174 Hex, D, edge-triggered flip-flop 152 54163 4-bit synchronous counter 120 4049A Inverting hex buffer 52 4013A Dual, D, edge-triggered flip-flop 104 4020A 14-stage, ripple carry counter 344 10502 Triple NOR (ECL) 80 HYPROM512 512-bit PROM 280

Harris CICD Devices (1987)

Circuit Types

HS-6504 - 4k X 1 RAM HS-8155/56 - 256 x 8 RAMHS-6514 - 1k x 4 RAM HS-82C08RH - Bus TransceiverHS-3374RH - Level Converter HS-82C12RH - I/O PortHS-54C138RH - Decoder HS-8355RH - 2k x 8 ROMHS-80C85RH - 8-bit CPU

Package Types

Flat Packs (hermetic brazed and glass/ceramic seals)LCCDIP

FITS @ 55°C, Failure Rate @ 60% U.C.L.

43.0

UTMC and Quicklogic• FPGA

– < 10 FITS (planned)– Quicklogic reports 12 FIT, 60% UCL

• UT22VP10UTER Technology, 0 failures, 0.3 [double check]

• Antifuse PROM– 64K: 19 FIT, 60% UCL– 256K: 76 FIT, 60% UCL

Xilinx FPGAs

• XC40xxXL– Static: 9 FIT, 60% UCL– Dynamic: 29 FIT, 60% UCL

• XCVxxx– Static: 34 FIT, 60% UCL– Dynamic: 443 FIT, 60% UCL

Actel FPGAs

Technology FITS # Failures Device-Hours

2.0/1.2 33 2 9.4 x 107

1.0 9.0 6 6.1 x 108

0.8 10.9 1 1.9 x 108

0.6 4.9 0 1.9 x 108

0.45 12.6 0 7.3 x 107

0.35 19.3 0 4.8 x 107

RTSX 0.6 33.7 0 2.7 x 107

0.25 88.9 0 1.0 x 107

0.22 78.6 0 1.2 x 107

RAMTRON FRAMs

Technology FITS # Failures # Devices Hours Device-Hours

1608 (64K) 1281 1 100 103 105

4k & 16K Serial 37 152 4257 103 4.3 x 106

Note: Applied stress, HTOL, 125ºC, Dynamic, VCC=5.5V.

1 The one failure occurred in less then 48 hours. The manufacturer feels that this was an infant mortality failure.

2 12 failures detected at 168 hours, 3 failures at 500 hours, and no failures detected after that point.

Actel FIT Rate Trends

Skylab Lessons Learned58. Lesson: New Electronic Components

Avoid the use of new electronic techniques and components in critical subsystems unless their use is absolutely mandatory.

Background:

New electronic components (resistors, diodes, transistors, switches, etc.) are developed each year. Most push the state-of-the-art and contain new fabrication processes. Designers of systems are eager to use them since they each have advantages over more conventional components. However, being new, they are untried and generally have unknown characteristics and idiosynchracies. Let some other program discover the problems. Do not use components which have not been previously used in a similar application if it can be avoided, even at the expense of size and weight.

Reliability - Summary

• Covered device reliability basics

• Design reliability is another set of topics– Advanced Design: Designing for Reliability– Fundamental Logic Design: Clocking, Timing

Analysis, and Design Verification– Fundamental Logic Design: VHDL for High-

Reliability Applications - Coding and Synthesis– Fundamental Logic Design: Verification of

HDL-Based Logic Designs for High-Reliability Applications