Practical Reliability Engineering 2009

ray.brett@philips.com

Contents

� Why is reliability important?

� Assembleon Reliability program 2007 – 2008

� HALT and basic principles of Reliability

� HALT case overview (Temperature)

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� HALT case overview (Temperature)

� Electrical Transients

� HALT case overview (Transients)

� Shock & Vibration

� Experience with HALT

� Mindset

Why is reliability so important?

�Unreliable products gives:

– Customer dissatisfaction

– Warranty Costs

– Rework of parts (€ )

– Loss of Reputation

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– Loss of Reputation

– Loss of Repeat Business

Assembleon Reliability program 2007-20081/2

� Design reviews, FMEA, functional/duration testing are NOT sufficient.

We still had FP’s (Field Problems).

� A reliability program was set up determine if the HALT technique can

provide answers to the following questions:

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provide answers to the following questions:

– How can we provoke realistic failures during design?

– How to do this within a reasonable amount of time?

– What does reliability cost?

(HALT = High Accelerated Life Testing)

Assembleon Reliability program 2007-20082/2

� Engineering changes had to be made to various electronic boards

because of functionality expansion.

– This gave us the opportunity to try to simulate & solve known FP’s

using the HALT method.

� (Hitch-hike with the ongoing engineering process)

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� (Hitch-hike with the ongoing engineering process)

Find an answer to the unanswered questions:

What is HALT ?� HALT is an engineering step-stress-to-fail process which can reveal

design flaws quickly (within hours of testing).

� HALT is not a compliance test and not limited by component or product

specifications.Failure

Evaluate the relevance of the failure.

Determine if stress-level is acceptible and

implement corrective action if necessary.

6Apply stress

(+/-15min/step)

Failure

Evaluate the relevance of the failure.

Determine if stress-level is acceptible and

implement corrective action if necessary. Increase stress

Basic principles of Reliability:

Reliability of a product is determined by:

– strength (product related)

– stress (user/environment related)

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Reliability (Load & Strength interferences)

1

Excluding wear-out

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Load Strength

Defect!

Ref. Patrick T.D. O’Connor – British Areospace

Reliability (HALT principle)

..

1 • Induce failure

• Find weak-spots

Design

• Improve design

9Load Strength

Ref. Patrick T.D. O’Connor – British Areospace

Design

Margin

HALT tests may include:

� Temperature stress

• under max. loading conditions

• In combination with power cycling

� Temperature cycling

� Voltage stress (in combination with temp.)

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� Voltage stress (in combination with temp.)

� Electric transient susceptibility stress (all cables)

� Shock & vibration

� RH%

HALT case overview – Temperature

+100C

+140C

ModifiedChange FET type Cost: approx. 10ct

ModifiedChange IC type Cost: approx. 10ct

ModifiedChange Diode type Cost: approx. 5ct

ModifiedChange FET type Add 10uF capacitor Cost approx. 20ct

120C

85C

130C140C

X20 PCB’s

80CX20PCB’s

Case 1(Tape cutter)

100C

140C

Case 6(ITBF-EFT) 120C

Modified

Solve in FPGA

Stop test.

100C

140C

Sprocket

140C

Modified2 x pull-down resistors.Cost: negligible

ModifiedChange the BIOS settings.Cost: negligible (Implementation)

ModifiedChange res. values Cost: negligible

140CX14 PCBs130C

80C

140C

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-40C

Case 3(PCU-IC)

+50C

Re-active (learning – correlation with FP’s)

70C

Case 5(re-use F)

Case 2(PCU-FETs)

X20PCB’s

-10C

Case 8(AXPC)

Pro-active

CCB(tray

trolley)

Solve in FPGA

Cost: negligible

Case 7(BA-

Camera)

60C

Sprocket

detector

Case 9(TPR Liftcontroller)

70C

Case 4(PCU-diode)

70C

80C

Summary: Performing Temperature HALT

� Perform Infra-red measurements (Hot-spots)

before performing HALT.

� For HALT; (Rule of Thumb): ensure a margin of at least 40C above

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specification.• (This is NOT a continuous spec!)

� It’s important to analyze all failures and to decide on: • Root cause

• Evaluate the relevance of the failure

• What is the effort/cost for improvement

Electric transients

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� Electronic circuits with cable connections can be affected by electric transients.

� Cables can be excellent antenna’s, depending on impedances, length etc. and can

pick up such transients:

� This phenomenon deals with electromagnetic disturbances inside equipment (intra-EMC)

� The EMC regulations often concern only inter-EMC and has a more legal goal & scope

� Additional EMC performance is often necessary for reliability

Example of an electric transient and effects

Relay switching off a load witha residue voltage.

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Possible resultant transient voltage which can be induced into nearby cables or locally on a PCB.

Possible resultant damage caused by a transient voltage disturbance.

HALT case overview – Transients

6kV

7kV

8kV

9kV

10kV

Modified

Add 10nF cap.

Cost: negligible

Modified

Gnd. connection

Cost: negligible

At approx. 8kV,

Cable isolation gets “tricky”

10kV10kV

Modified

Shield repeater

Cost: 5 euro

8kVdefect

Modified

Gnd. connection

Cost: 10ct

6kV

Modified

Add 2x10nF caps.

Cost: negligible

Case 6(BA-

Camera)

Design integration

EMC

Cost: negligible

Design integration

EMC

Cost: negligible

8kV

Case 8(TPR)

10kV

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1kV

2kV

3kV

4kV

5kV

Re-active (learning – correlation with FP’s)

2kVCase 2

(ITBF)

mP reset

3kV3kV

3kVFET defect

Case 1

0.5kV

2.5kV

Case 4Fire-WireRepeater problem

1.5kVdefect

Case 3(Sprocket detector)

1kV

Pro-active

Camera)

4kV

0.6kV

2.8kV

Case 7(LED pcb)

Case 5(Tape cutter)

mP reset

2kV

Transient “Rule of thumb” targets

6kV

7kV

8kV

9kV

10kV

Soft errorsHard failureEither SW

or HW

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1kV

2kV

3kV

4kV

5kV

Shock & Vibration (placement head)

Example: Placement Head (during operation)

Test:

Vibration:10-1000Hz; 0.1g; 0.2g;… 1g; 1.2g… etc

Shock: 25g; 3msec (Sys. Limit) 30, 60, 100%

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Other tests: Non-operating; transport

Shock & Vibration

BA Camera

Representing Optics

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Representing OpticsRepresenting Electronics

Experience with HALT: (electro.)

� A lot of Field Problems can be provoked using the concept of HALT

testing.

� HALT testing provides results quickly (within a few hours/days).

� Experience shows that realistic failures can be provoked with minimum

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� Experience shows that realistic failures can be provoked with minimum

design impact.� Provided testing is performed early during development (pro-active).

� Now we are performing pro-active HALT testing with success.

Reliability engineering: a matter of mindset

� The principle behind HALT is quite simple and is usually easy to

perform. The biggest challenge is setting the right MINDSET and

applying the right strategy.

� Don’t test for approval but test to find potential failures and make the

necessary improvements (It’s not a Pass/Fail test).

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� Determine HALT: plan/parameters depending on product type &

working environment.

� HALT is not a “magic solvent” but with a good test strategy and the right

mindset, it can be a very effective tool for improving the reliability of

design’s.

� Less failures gives satisfied customers

– Improved quality & less re-work