Highly accelerated life test, halt reliability testing

What is reliability?

The best quantitative measure of the integrity of a designed part, component, product or system
The probability that parts, components, products, or systems will perform their deigned-for functions without failure in specified environments for desired periods data given confidence level
Theoretical and practical tools

Discovery testing

HALT testing is a process that is for discovery, specifically looking for failures
It is NOT a life test
The true value of a life parameter is never known, only it's distribution about an expected value, so we cannot say when failure will occur. Sometimes we can say that the likelihood increases, but we can very rarely predict the time of failure.

Who should be involved in the Halt Test

Design Engineer
Product Engineer
Management
Customer or end user
It is important to remember that a HALT process should be continuously monitored, both by data acquisition equipment and by personnel.

What should be tested?

At least 3 samples as a minimum
- Gold cards
- Lemons
Products likely to have be exposed to and possibly suffer from temperature, vibration, power cycling, or some combination

Not a drop or classical shock test

Where should the HALT be performed?

Your lab
Another test lab in your company
An outside test lab

What is a failure?

Failure or the absence of failures is heavily dependent upon human actions and perceptions.
What may be a failure to one company may not be to another:
- Scratched paint (Cisco)
- Circuit boards (Honeywell)
- Transients (Motorola)

Why perform HALT?

To get a better knowledge of your product
A single tool in the toolbox
To save ££££

Logic for use of Unrepresentative Stresses

The causes of failures that will occur in the future are often very uncertain
The probabilities of and durations to failures are also highly uncertain
Time spent on testing is expensive so the more quickly we can reduce the uncertainty gap the better
Finding causes of failure during development and preventing recurrence is far less expensive that finding new failure causes in use

When do you HALT?

Should be started as soon as the hardware is available for test
For action to be taken to analyse and correct failure modes before production
As a way of tracking down causes of field failures

How do you run HALT?

Actually A series of Tests
- Cold only
- Heat only
- Vibration only
- Temperature swings
- Heat with vibration
- Swings with vibration

Preparation for the process

Temperature:
- Laboratory ambient
- Expected usage temperatures
  - Operating
  - Transportation
  - Storage
- Margins
- Melting point

Understanding margin

Operating range
Shipping range
Storage range
Testing range

Ignoring failures outside the margins

Wrong question: At what stress do we decide that the level is so high that we can ignore the failures?
Right question: Could this failure occur in use?
- On other items
- After longer times
- At other stresses
- etc.

Additional preparation

Monitoring
Data acquisition
Time to market
Cabling suitable for test environments

Talk to people

Talk with end users
Find out how they expect to use the vehicles
Get horror stories on the worst things that have ever happened
Find out the things that they have been most satisfied with
An engineer and an end user will look at the same product or system in very different ways

Cold test

Least destructive environment
Start at room ambient
N2 will remove extra humidity
10° steps

Cold chart

Start with 10 degree steps.
Bring temperature up at the first sign of failure to see if it may be intermittent because of certain temperature.
Control the return to room temperature since this may cause it's own failure.

Heat test

Still single environment
5° steps for assemblies
Know melting limits ahead of time

Heat chart

Start with 10 degree steps.
Change to 5 degree steps as you get closer to suspected failure temperature (or melting point).
Bring temperature down at the first sign of a failure to see if it may be intermittent because of a certain temperature.

Vibration test

Single Environment but multi-axis random
- On product
- On fixture
- On table near product

Vibration chart

Start with 2 g steps.
Keep temperature constant, preferably at laboratory ambient, so that vibration is your only stress.
Bring g level down at the fist sign of a failure to see if it may be intermittent because of a certain acceleration.

Temperature swings

Hot and cold Test
- Cold first (removes humidity)
- Hot first (retains humidity)
5 or 10° steps depending on earlier results
Rapid ramps (thermal mismatch and conductivity effects)
Short dwells

Swings chart

Assuming a failure at 85 degrees we go 10 degrees lower
Give a 125 degree difference giving -50 as the cold range
According to Harry McLean in HALT HASS & HASA explained 3 to 5 cycles with 5 being preferred
According to Gregg K Hobbs in Accelerated Reliability Engineering he has not found any product to be rate sensitive so there is no need to limit the speed of the change rate

Heat with vibration

Heat
- Start at laboratory ambient
- Compare with heat only test
Vibration
- Duration
  - Bursts
  - Full time
- Level
  - Lower than failure rate
  - Higher than expect in real life

Heat with vibration chart

Assuming a failure at 85 degrees we start at 65° giving a margin
Assuming a failure at 14 gs we use 10 giving a margin
Vibration can be either pulsed or constant depending upon expected end usage
The same principal would work with a combination of cold and vibration
Thermal swings:
- Closest to real world conditions
- Compare to earlier results
- Rapid ramps
- Short Dwells
Vibration
- Duration
  - Bursts
  - Full time
- Level
  - Lower than failure rate
  - Higher than expect in real life

Swings with vibration chart

Use data based on baseline and earlier swing test
Assuming a failure at 50 gs we divide that into fifths (because of five swings) and increase with each vibration burst
- 10
- 20
- 30
- 40
- 50 g's

Other environments

Humidity
Corrosions
Dust
Power cycling

Review

Remember that testing is a form of experimentation
Good guesses are valuable but need to be backed with real data
HALT is a way of getting a lot of data in a little time and for a comparatively small cost

View previous features

HALT (HIGHLY ACCELERATED LIFE TEST)

What is reliability?

Discovery testing

Who should be involved in the Halt Test

What should be tested?

Where should the HALT be performed?

What is a failure?

Why perform HALT?

Logic for use of Unrepresentative Stresses

When do you HALT?

How do you run HALT?

Preparation for the process

Understanding margin

Ignoring failures outside the margins

Additional preparation

Talk to people

Cold test

Cold chart

Heat test

Heat chart

Vibration test

Vibration chart

Temperature swings

Swings chart

Heat with vibration

Heat with vibration chart

Swings with vibration chart

Other environments

Review