Qualmark HALT Testing Guidelines
Document: 933-0336

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Qualmark
HALT Testing
Guidelines

The information contained in this paper is Qualmark proprietary information and is copyrighted. No portion
may be copied, modified, distributed or published without the express written permission of Qualmark
Corporation.

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Revision History
Rev

Originator

9/1998

D. Rahe (Qualmark)4/2003

C. Drake (Qualmark)7/2007

C. Drake (Qualmark)04

Description of Change
Original Issue
Updated body of text.
Update text as needed

N. Doertenbach (Qualmark)thReleased: ECO #3007; 9/13/2010
Placed in Document Control. Reorganizedsections, updating text as needed; added
acronym table

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Table of Contents
Section Title

Page

1.

Purpose ................................................................................................ 4

2.

Scope.................................................................................................... 4

3.

Definitions (Also see Acronym Table, Table 1) ...................................... 44.

Basic HALT Test Concepts.................................................................. 10

5.

Staffing Requirements......................................................................... 106.

HALT Test Equipment Requirements .................................................. 12

7.

Test Samples ...................................................................................... 14

8.

Functional Testing Requirements........................................................ 17

9.

Test Reporting and Documentation..................................................... 1810.

HALT Test Procedure .......................................................................... 19

11.

Post HALT Test Requirements ............................................................ 27

12.

Possible Modifications to a HALT Test ................................................ 29

13.

Table 1: Acronyms .............................................................................. 31thQualmark Corporation | 10390 East 48 Avenue | Denver, CO 80238 | phone 303-254-8800 | fax 303-254-8343

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Qualmark HALT Testing Guidelines
1.

Purpose

1.1.

2.

The HALT test process helps product designers create a more robust
and reliable product, thus improving field reliability and reducing warranty
costs. When successfully applied, HALT testing rapidly exposes productweaknesses and gives the designer the opportunity to provide a moremature product at new product launch. The purpose of this guideline isto provide a consistent, efficient and effective description of the HALT
process.
Scope

2.1.

This document defines the process elements necessary to successfully
implement a HALT test program. It identifies technical responsibilities,
facility and equipment requirements, and testing practice competencies.
This guideline applies to a diversified mix of product types, including
electronic assemblies and electro-mechanical assemblies, and certain
mechanical assemblies as well.

2.2.

This document also defines modifications and variations on standard
HALT testing that can be considered in limited circumstances, anddiscusses the effects of these changes on the outcomes of the test.

3.

Definitions (Also see Acronym Table, Table 1)

3.1.

Accelerometer: A transducer that measures acceleration. Typically
based on piezo-electronic technology, the device provides a voltage
output proportional to the acceleration at the location and in the defined
direction of the device. Typically several are attached to the UUT and
are used to monitor the UUT response to the vibration input from thetable.

3.2.

Air Control Thermocouple: A thermocouple that provides air temperature
feedback to the chamber thermal control system. Depending on thecontrol system settings, the air control thermocouple can act as atemperature safety limit controller, or as the control thermocouple for thesystem.

3.3.

Alternating Low Level Vibration: Also referenced as “Tickle Vibration”1: A
vibration test procedure that is typically introduced in HALT Vibration
Step Stressing at input levels of 30 gRMS and higher. At the end of eachthQualmark Corporation | 10390 East 48 Avenue | Denver, CO 80238 | phone 303-254-8800 | fax 303-254-8343

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vibration dwell and functional test, the vibration level is reduced to 5
gRMS and a complete functional test is conducted, without waiting for adwell at that level. Then, the vibration level is increased to the next steplevel. Alternating low level vibration will help detect a failure mode that isprecipitated at a higher gRMS level, but is not detectable at that level,
and is also not detectable when the UUT is at rest. Low levels ofvibration, however, can make the failure mode detectable. Certain typesof cracked solder joints, including through-hole solder issues, can be
identified this way.
3.4.

Broadband Vibration: Vibration that contains energy over a broadfrequency range (i.e. 10 Hz to 5 kHz or greater).

3.5.

Corrective Action (CA): A change implemented in a design or process toeliminate a product weakness or flaw. Corrective actions may include
changes in parts or material sources, product design, and production
process changes.

3.6.

Destruct Limit (DL): The stress level where a failure is identified and
UUT functionality is not recovered when the stress is reduced. This typeof failure is also known as a hard failure. Vibration step stressing will
reveal the Vibration Destruct Limit (VDL), while cold thermal step
stressing will reveal the Lower Destruct Limit (LDL) and hot thermal step
stressing will reveal the Upper Destruct Limit (UDL).

3.7.

ED (Electrodynamic) shaker: A vibration system consisting of a tablestructure that is connected to a ferrous armature surrounded by a coil.
This coil is separated by an air gap from a second coil in the body of the
shaker system. Controlled current is passed through the coils to create
an electromagnetic force between them that moves the table in a single
axis. The UUT is mounted to the table structure. The spectral and realtime content of the driving force is specifically controlled to meet adesired vibration profile.

3.8.

Fast Fourier Transform (FFT): An algorithm for describing a real time
signal in terms of its component frequencies. Used in vibration analysis
to provide magnitude and frequency information about the frequency
components of an acceleration signal.

3.9.

Functional Test: A test of the UUT that measures functionality, UUT
operation, and critical parameters to determine if UUT fails to perform tospecifications or degradation has occurred within the UUT. This test may
include internal diagnostics. Functional testing is to be performed
throughout the thermal and vibration stresses of a HALT test.
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3.10.

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gRMS: The RMS (Root Mean Square) level of an acceleration signal,
normalized to the value of acceleration due to gravity.2 gRMS ismeasured across a specified frequency range, depending on the cutoff
frequency of the filter on the acceleration level. gRMS can be measured
both in the time domain, using analog RMS converter circuitry, andthrough sampling and FFT analysis, then calculating the square root of
the area under the Power Spectral Density curve, cut off at the desired
frequency (Figure 1). gRMS is typically used as a measurement of thevibration energy present in a random vibration signal. For vibration froman RS machine, the frequency cutoff used is typically 5 kHz.

Figure 1: Example of gRMS calculations at two different cutoff frequencies using PSD

3.11.

HALT (Highly Accelerated Life Test), also referenced as “HALT test”: A
process that utilizes a step stress approach to subject a UUT to thermaland vibration stresses of types and levels beyond what it may see in
actual use, but which will rapidly induce failure modes, allowing them tobe detected and corrected. The stresses applied include thermal
extremes, extreme thermal ramp rates, 6DoF RS vibration andcombinations of these stresses.
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3.12.

Hard Failure: A non-recoverable failure mode. A hard failure will not go
away when the stress that induced the failure is reduced or removed. A
hard failure will define the Destruct Limit of a UUT.

3.13.

Isolation; thermal and vibration: Techniques used to protect portions of a
UUT from the stresses of the HALT test system in order to debug failuremodes or to work around a known issue and continue testing the rest of
the UUT.

3.14.

Operational Limit (OL): Also referenced as “Operating Limit”. The stresslevel prior to where a failure is identified but UUT functionality isrecovered when the stress is reduced. This type of failure is also known
as a soft failure. Vibration step stressing will reveal the Vibration
Operational Limit (VOL), while cold thermal step stressing will reveal theLower Operational Limit (LOL) and hot thermal step stressing will reveal
the Upper Operational Limit (UOL).

3.15.

Picket Fencing: A description of the shape of the PSD of an RS vibration
system with actuators that are all striking at the same frequency but atslightly different times. Such a system will result in a table spectrum withhigh vibration levels at the actuator strike frequency and its harmonics,
with little energy between those harmonics. The resulting PSD
resembles a ‘picket fence’.

3.16.

Power Spectral Density (PSD)3: A measurement of the amplitude andfrequency content of a random vibration spectrum, expressed in units ofgrms2/Hz. Also commonly referred to as the Acceleration Spectral Density(ASD). The shape of the PSD graph provides a visual representation of
the relative levels of vibration across the frequency range of interest,
allowing analysis of the effectiveness of vibration fixturing and insight into
the UUT’s transmissive and absorptive characteristics (Figure 2).

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Figure 2: Typical PSD graphs from multiple accelerometers in a HALT test

3.17.

Product Control Thermocouple: A thermocouple that provides producttemperature information to the chamber thermal control system.
Typically the chamber control system is set to use the temperature levelof this thermocouple to control the thermal system, although control fromthe air temperature thermocouple is also possible.

3.18.

Product Control Accelerometer: An accelerometer that provides tablevibration level information to the chamber vibration control system. The
chamber control system uses the vibration level of this accelerometer tocontrol the vibration system.

3.19.

Quasi-Random Vibration: Non-periodic vibration that possesses all
frequencies within a band and having a continuously varying amplitude
and phase that is specified as a probability that it will exceed a given
value during a time interval.

3.20.

Return on Investment (ROI): A calculation used to determine the valueof a proposed investment. It is calculated as the ratio of the amountgained (taken as positive), or lost (taken as negative), relative to thethQualmark Corporation | 10390 East 48 Avenue | Denver, CO 80238 | phone 303-254-8800 | fax 303-254-8343

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amount invested. When considered specifically for HALT testing, it is theratio of the amount of money saved by discovering and correcting faults
by using HALT testing relative to the cost of doing the HALT test,
including capital equipment, infrastructure, personnel, etc.
3.21.

Repetitive Shock (RS) Vibration: Vibration originating from a repeatedshock impulse excitation to a rigid or semi-rigid table supported bysprings. Typically created from pneumatic actuators impacting a vibrationtable to which UUTs are attached.

3.22.

Root Cause Analysis (RCA): Identifying the true cause of a weakness orflaw; fully understanding what failed and why. This process may require
use of failure analysis tools like scanning electron microscopes.

3.23.

Six Degree of Freedom Vibration (6DoF): Vibration that has
simultaneous acceleration energies in three axes (X, Y and Z) and thethree rotations (roll, pitch and yaw) around those axes.

3.24.

Soft Failure: A recoverable failure mode. A soft failure will go away when
the stress that induced the failure is reduced or removed. A soft failure
will define the Operational Limit of a product.

3.25.

Step Stressing: A stress testing process where a stress level isincrementally increased to identify UUT weaknesses and limitations.

3.26.

Thermocouples: Temperature sensors that are created when two
dissimilar metals are fused, creating a thermoelectric current flow and a
resultant voltage potential proportional to temperature.

3.27.

Thermal Ramp Rate: The rate of change of temperature in a system.
When used as a thermal system specification, it is the fastest change
rate the system can achieve. The measurement point is typically in the
air at a centrally located point in the chamber, near the location of a UUT.
It can also be specified and measured on specific areas or components
on a UUT as desired. It can be used to evaluate chamber thermal
performance as well as the effectiveness of the transmission of thermalenergy to the UUT. Higher ramp rates result in more stress on the UUT
and hence a more effective test.

3.28.

Triaxial Accelerometer: Three accelerometers mounted in a single
package with three outputs, to monitor x, y and z axes simultaneously.

3.29.

Unit Under Test (UUT): The device being HALT tested.
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4.

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Basic HALT Test Concepts

4.1.

The goal of a HALT test is to use thermal, vibration and other productspecific stresses, typically at levels beyond the product’s specifications or
intended use environment, to force latent defects in the product’s design
or construction to become patent, allowing them to be corrected before
product release. The stresses are incremented during the test to force
the weakest links in the UUT to fail first. The test is successful when
failure modes are identified, corrective action taken, and theeffectiveness of the correction has been verified. 4,5

4.2.

While HALT testing is typically considered as a tool for evaluating new
designs, it can also be very valuable for evaluating component andprocess changes6, changes to an existing design or evaluating field
failures that are returned with no defect found.

4.3.

Whenever possible, the results from a HALT test should be comparedwith the results from a previous HALT test on a similar product. This will
provide information that can help with failure analysis, corrective action
and decisions on the need for in depth failure mode evaluations. When a
HALT test is conducted for the first time, it may not be possible to do thiscomparison. In this case, a similar, legacy product should be tested
alongside the new product to provide baseline data.

4.4.

Before introducing HALT testing in a facility or product line, it is advisable
to do a rough estimate of the Return on Investment (ROI) that can be
expected. By reviewing the costs of correcting design defects foundduring design verification testing or after release of past products, as wellas the potential value of releasing new products more quickly, versus thecosts of HALT testing implementation, including infrastructure, staffing,training and HALT system requirements, intelligent decisions can bemade on procuring equipment vs. testing at a lab, justification of staffing,
etc.

5.

Staffing Requirements

5.1.

Training in HALT test methods and philosophy is important for all
personnel involved in HALT testing, whether they are implementing thetest itself, performing failure analysis, or implementing corrective action.
HALT is not a ‘cookbook’ or ‘check the box’ test method. It requires good
judgment and decision making throughout the test based on results
found, product characteristics, business considerations and other factors.
These decisions can only be made correctly if the personnel involvedthQualmark Corporation | 10390 East 48 Avenue | Denver, CO 80238 | phone 303-254-8800 | fax 303-254-8343

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fully understand and agree with the goals of HALT testing. Similarly,
retraining is important as personnel change.
5.2.

The HALT test team should include those individuals involved in thedesign and test of the product. HALT testing requires cooperation among
multiple disciplines within the facility. Design engineering will assist in
the development of the UUT functional test. This includes identifying
additional stresses that may help to precipitate defects. They will also
provide support during the HALT test, and the failure analysis process(e.g. troubleshooting defects). These individuals need not be present
during the entire HALT test, but must be available on an as neededbasis. Test Engineering will assist in the definition of functional test
protocols and test hardware design and creation. Other disciplines
include reliability engineering, manufacturing engineering, and thepersonnel who run the HALT test system. Supply Chain Management
should also be involved to help identify and correct design issues related
to vendor selection as well as to oversee HALT test results andcorrective action requirements throughout the supply chain. Eachdiscipline shall take responsibility for their area of expertise as HALT test
result issues arise (Figure 3).7

Figure 3: Disciplines Required For HALT Testing8th

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5.3.

A failure analysis lab (in-house or outside lab) may be required todetermine root cause analysis on failures found during HALT testing.

5.4.

A cross-functional committee should be defined. This committee shouldmeet on a regular basis (i.e. monthly) to define HALT test requirements,
review past HALT test results and develop test plans for future testing.
Records shall be maintained on the outcome decisions of the meetings.
These meetings shall occur prior to and after the HALT test.

5.4.1.

The pre-HALT test meeting agenda should define the HALT test
specifications, the functional test requirements, methods of fixturing
the UUT to the table, and UUT components and/or locations tomonitor with thermocouples and accelerometers.

5.4.2.

The post HALT test meeting agenda should include a review of HALT
test results including discussion of failures and corrective action
planning. It should also include the definition and implementation of aclosed loop process that documents the failure modes found, confirms
and records the corrective actions taken, and record these failuremodes and corrective actions in a database so that similar mistakes
will not be repeated.

6.

HALT Test Equipment Requirements

6.1.

HALT Test Chamber Requirements

6.1.1.

6.1.1.1.

The system required to perform HALT testing must be a single
chamber capable of providing both thermal and vibration energy
stresses as defined below. The equipment must create these stresses
independently and in a combined environment within the samechamber at the same time.
The goal of the vibration system is to provide enough vibrationstress to the UUT to induce failures. This vibration stress level willvary depending on the product being tested and the fixturing used.
The vibration system used should be capable of delivering at least
50 gRMS (measured from 10 Hz to 5 kHz) into an empty vibrationtable. It should use repetitive shock vibration to provide 6DoF
quasi-random vibration, with broadband energy from 10 Hz up to 5
kHz or higher. The actuators used in the vibration system should
impact at differing frequencies in order to avoid picket fencing in thethQualmark Corporation | 10390 East 48 Avenue | Denver, CO 80238 | phone 303-254-8800 | fax 303-254-8343

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PSD and loss of vibration energy in specific low frequency (<200Hz) bands.
6.1.1.2.

The goal of the thermal system is to force rapid thermal change
rates on the UUT. It is additionally important that the chamber has
sufficient air velocity to produce the desired rapid thermal rates ofchange as measured on the UUT and to maintain thermal stability.
For an effective test, the chamber must be able to thermally stress
the UUT sufficiently above the design specifications to uncoverdefects. The thermal system must be capable of minimum airtemperature change rates of 60°C/minute, hot and cold, whenchanging temperature at its maximum possible rate, and must havea minimum thermal range of -100°C to +200°C.

6.1.1.3.

If the product is designed and specified for extreme hightemperature environments, the required upper thermal limit of thechamber will be higher.

6.2.

Laboratory Test Equipment

6.2.1.

UUT response data is acquired during the HALT test process. Thisdata includes thermal, vibration and UUT functional performance.

6.2.1.1.

The collection and storage of thermal data is required to provide
credible evidence that thermal stress was applied to the UUT. Thismay be achieved by utilizing available thermocouple monitoring
channels of the HALT test system or the use of a data acquisition
instrument capable of multiple channel measurements.

6.2.1.2.

The collection and storage of vibration data is required to provide
credible evidence that vibration stress was applied to the UUT. Thismay be achieved by utilizing available accelerometer monitoring
channels of the HALT test system or the use of a spectrum analyzer
instrument capable of measuring sensors (e.g. accelerometers) anddisplaying the data.

6.2.1.3.

The measurement of acceleration levels at various points on the
UUT and fixturing is necessary to understand vibration input andresponse. Accelerometers are used for these measurements.
These accelerometers should be low mass type (e.g.  4 grams),
with frequency response capability of 10 Hz to 5 kHz or higher, anda measurement range of ± 500 g’s. The accelerometers should besmall enough to be mounted in the desired location and lightth

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enough that their mass does not significantly impact or alter thevibration dynamic characteristics of the UUT.
6.2.1.4.

6.2.2.

Thermocouples for the measurement of UUT thermal response.
The use of thermocouple wire is required. Thermocouples used for
HALT testing should have sufficient stability characteristics throughthe temperature range of the chamber (approximately -100°C to+200°C).
Test Equipment Setup Requirements

6.2.2.1.

The HALT test system, ancillary test equipment setup, andoperation is performed in accordance with manufacturer’s
instructions.

6.2.2.2.

Verify that all test equipment to be utilized for the HALT test iscalibrated and operable. Document the test equipment in the test
report including equipment description, model number, serial
number, and calibration status.

7.

Test Samples

7.1.

The UUTs are uniquely identified by a serial number or other means ofidentification.

7.2.

Ideally a total of at least four UUTs should be tested.9 Simultaneous
testing of the four samples may reduce the total test time. However, thismakes the vibration fixturing and functional testing more complex, andmay make failure mode detection, analysis, and isolation more difficult.
Also, limitations on availability of samples may make this approach
impossible. Whenever possible, spare subassemblies should be on
hand to replace failed units when failures occur.

7.3.

Test Sample Setup Requirements

7.3.1.

Thermal control of the HALT test system is achieved through feedback
from the air and product control thermocouples. They must be
properly placed on the UUT(s) to ensure effective control of the UUT
temperature. The system can be configured to use either the air or
product thermocouples as the control feedback to the system control
loop. Monitoring of the thermal response of the UUT is accomplishedusing thermocouples attached at desired locations in/on the UUT, withthe readings recorded with a data logger.
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7.3.1.1.

7.3.1.1.1.

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When operating under product thermocouple control, the productthermocouple is used for temperature control - the control system
drives the chamber air temperature as needed to achieve thedesired temperature setpoint as measured at the productthermocouple. The chamber air temperature will typically exceed
setpoint as necessary to achieve the desired setpoint. When
operating under product thermocouple control, the productthermocouple should be attached to a location that provides anaccurate approximate average of the temperature of the UUT. The
product thermocouple should be placed on an exposed surface on
the UUT, preferably in an area of relatively low thermal mass. This
thermocouple should not be placed on or near a heat-generating
component, or inside a closed portion of a UUT. The airthermocouple is used as an air temperature limit control, keeping
the air temperature from reaching preset levels chosen to prevent
damage to the UUT. The air temperature thermocouple should belocated in the air near any area on the UUT where temperature
limits are of particular concern.
If an appropriate location for the product control thermocouple
cannot be identified, the product thermocouple can be placed ona dummy load. Typically, a washer or other small mass, locatednear the center of the chamber and in the air flow, is used forthis.

7.3.1.2.

If the air temperature thermocouple is used for temperature control,
the control system will maintain the air temperature at the desired
setpoint. In this case, the air temperature thermocouple should belocated near the UUT, in the air where the airstream isunobstructed. Air control can be used when the UUT is sensitive totemperature extremes, and close control of the air temperature isdesired. It will result in slower ramp rates on the UUT itself. In thiscase, the location of the product temperature thermocouple is notimportant. It can be used as an additional thermocouple to monitor
UUT temperature where desired.

7.3.1.3.

Product response thermocouples are attached to adequately
assess the response of the UUT(s) to the thermal environment.
Suggested placement includes components that generatesignificant heat, components that would be sensitive to thermaltransitions, components designed to respond to temperature, andon a high mass portion of the UUT to provide a measure of thedwell time necessary to achieve temperature stabilization.
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Thermal transition rates on the UUT and subassemblies within the
UUT may be improved by modification of the UUT chassis such as
removing panels or covers or drilling holes in the cover to allow air
flow through the UUT. If cable lengths and UUT functionality permit,
consider removing subassemblies from the UUT and fixturing themseparately to the table to maximize both thermal and vibrationstresses on the subassemblies.

7.3.2.

Vibration control of the HALT test system is achieved throughfeedback from the product control accelerometer. This accelerometeris typically located near the center of the vibration table, on theunderside of the table. Unlike thermal control elements, the productcontrol accelerometer should never be placed on the actual UUT or
fixturing. Not only is there a risk of damage to the control
accelerometer due to the thermal extremes of the upper part of thetest system, there is a risk of loss of vibration control if the UUT
breaks or fixturing loosens in such a way that the accelerometer is nolonger monitoring the actual table acceleration. It is never necessary
to change the location of the control accelerometer.

7.3.3.

Secure the test UUT(s) to the vibration table using a suitable test
fixture that maximizes the thermal and vibration energy transfer to the
UUT. The goal is to stimulate the UUT tested to accelerate fatigue
damage to uncover product weaknesses. Therefore, optimization of
maximum stress to the UUT is beneficial. If subassemblies within the
UUT do not receive adequate vibration levels to induce failures, it may
be necessary to remove them and fixture them separately, or perform
a separate HALT test on the subassemblies. Redesign the fixture if
the vibration levels on the UUT or subassemblies are too low to stress
the UUT adequately.

7.3.3.1.

7.3.4.

HALT test fixturing is very different from those used in traditional ED
vibration testing. The rigid, heavy plates typically used in ED
fixturing can dampen the vibration in an RS table, dramaticallyreducing the effectiveness of the vibration. HALT test fixturing
should be flexible, to allow the table to move in its natural resonantmodes.

In some cases, subassemblies of the UUT will be unable to tolerate
HALT test stresses due to specific limitations of the subassembly.
These subassemblies might include hard drives, batteries, etc. In thiscase, these subassemblies should be removed from the chamberusing extension cables to retain functionality while protecting thesethQualmark Corporation | 10390 East 48 Avenue | Denver, CO 80238 | phone 303-254-8800 | fax 303-254-8343

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sensitive devices. If cable length tolerances or other issues make it
impossible to do this, thermal and vibration isolation techniques may
be used to provide low stress environments within the chamber.
7.3.5.

UUT size and weight should be taken into account when determining
feasibility of a particular chamber to properly stress the UUT.

7.3.6.

If multiple UUT’s are being tested, they should be fixtured so that theirlocations are symmetric with respect to the table quadrants. This will
help maintain uniform vibration on the UUTs.

8.

Functional Testing Requirements

8.1.

Functional testing of the UUT while under stress is a critical componentof HALT testing. Transient failures that occur only under stress but are
not detectable at ambient conditions will be identified during thefunctional test. Since the goal of HALT testing is to find and correct
failure modes, a failure mode that goes undetected due to insufficient
functional testing defeats the purpose of the test. Functional testingshould be sufficient to determine the overall performance of the UUT and
detect the occurrence of multiple types of failure modes. The test must
exercise the major functions of the UUT with a feedback measurement of
performance of each function. The goal of the functional test is toachieve as complete test coverage of the UUT as is possible.

8.2.

In addition to the thermal and vibration stresses provided by the HALT
test system, the product should be subjected to any product-specificstresses that may enhance failure precipitation and detection. Productspecific stresses may include power cycling, line voltage margining, line
frequency margining, DC supply voltage margining, on-board oscillator
margining, output loading, and any other stresses that are applicable.
These product-specific stresses are incorporated into the functional
testing and should be performed at each level of stress throughout the
HALT test process.10

8.3.

The functional testing of the UUT must be documented. The
documentation shall provide definition of the amount of test coverage, inpercentage, and include a detailed description of the test performed.
Test documentation shall also provide evidence of how the functional test
objectives as defined in the pre-HALT test meeting were achieved

8.4.

Before beginning the HALT test process, the UUT is subjected to one ormore cycles of functional testing to verify the integrity of the test setup
and obtain baseline performance information for the UUT(s).
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Test Reporting and Documentation

9.1.

The test documentation must be able to achieve two key purposes; 1) itwill provide information to help in failure analysis and corrective action,
including detailed descriptions of the failure modes found, and thespecific stresses under which they occurred, and 2) provide the detailed
information needed to reproduce the test, including thermocouple andaccelerometer placements, functional test method, equipment, software
revisions, and any other necessary information.

9.2.

It is recommended that a defined, controlled test procedure and datacollection template be established for HALT testing.11 This will help
ensure that the process does not change with personnel or facilitychanges, keeping HALT test results repeatable and consistent.

9.3.

The data is compiled and stored in sufficient detail and quantity that theflow of the process can be easily followed and the test sequence
reproduced if required. UUT response measurements and the HALT test
system data including temperature data and vibration data are collectedduring the entire test.

9.4.

It is important to collect and understand response data from the UUT
itself in addition to the input and control parameters of the chamber.
While the control parameters (vibration setpoint and table response,
temperature setpoint and control thermocouple response) provide thenecessary metrics for chamber control, the actual response of the UUT is
the true indicator of the UUT stresses. The thermal and vibration
response on the UUT and key subassemblies within the UUT must be
monitored and recorded in order to understand the true conditions whena failure mode is discovered.

9.5.

The documentation shall accurately and clearly present the test results
and other test related relevant information. The documentation shallcontain:9.5.1.

The identification of the person(s) who performed the HALT test.

9.5.2.

UUTs are identified by a unique identifier (e.g. serial number) including
revision level.

9.5.3.

Deviations from the HALT test procedure.

9.5.4.

Dates of testing.
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9.5.5.

A description of the UUT fixturing used during testing, including
photographs to support the description.

9.5.6.

Specific thermal and vibration data measurements (supported bytables, graphs, photographs as appropriate).

9.5.7.

Locations of UUT response sensors (thermocouples andaccelerometers). This is particularly important, as slight changes inthese locations when a test is repeated can have significant effects on
the readings, making comparisons of thermal and vibration levels
between tests invalid.

9.5.8.

Description of the functional testing performed on the UUTs.

9.5.9.

At each level of applied stress, functional testing is performed on the
UUT to evaluate the operation of the UUT. Documentation shall detailfailure modes and the conditions at which they occurred as well as theoperating and destruct limits of the sample and any other importantcomments.

9.5.10.

The root cause analysis (RCA) information and results.

9.5.11.

Any corrective action (CA) implemented.

10.

HALT Test Procedure

10.1.

Thermal Step Stress Test

10.1.1.

During Thermal Step Stress testing, the goal is to identify failuremodes that are due to temperature extremes. In Thermal Step Stresstesting, the temperature is increased (or decreased) in steps of adefined increment followed by a temperature dwell of a defined length.

10.1.2.

Thermal Step Stress testing shall begin at ambient (defined as 20°C to30°C).

10.1.3.

The thermal step increments are typically 10°C.

10.1.4.

The dwell time is a minimum of ten (10) minutes following stabilizationof the UUT at the setpoint temperature as determined by the UUT
thermocouple response. Ideally the full functional test or a subset ofthe functional test should be performed throughout the dwell tomonitor basic UUT functionality. At a minimum, the full functional test
is performed at the end of the dwell. Any product-specific stressesthQualmark Corporation | 10390 East 48 Avenue | Denver, CO 80238 | phone 303-254-8800 | fax 303-254-8343

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that are being used should be applied in a similar fashion. At the endof the dwell, the thermal stress is incremented and the dwell isrepeated (Figure 4).

Figure 4: Sample Thermal Step Stress Graph10.1.5.

10.2.
10.2.1.

Thermal Step Stress testing is continued until a failure is identified or
the limits of the chamber have been reached. When a failure is
identified, it is handled as described in “Handling Failures in HALT
Testing” below and step stressing is continued. If possible, continue
until the operational and destruct limits for the product have been
identified.
Rapid Thermal Transitions Stress Test
During Rapid Thermal Transition Stress testing, the goal is to identify
failure modes that result from rapid thermal changes. Consequently,
the thermal limits are reduced from the operational limits found inthQualmark Corporation | 10390 East 48 Avenue | Denver, CO 80238 | phone 303-254-8800 | fax 303-254-8343

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Thermal Step Stress testing to avoid finding failure modes alreadyidentified in Thermal Step Stress testing.
10.2.2.

A minimum of five (5) thermal cycles are performed unless a
destructive failure is encountered prior to completion. The thermaltransitions are performed at the maximum attainable rate of change.

10.2.3.

The minimum thermal cycle temperature range is within 10°C of boththe lower thermal operating limit and the upper thermal operating limit
as discovered during Thermal Step Stress testing. Example: if the
LOL was determined to be -50°C and the UOL determined to be
100°C, the thermal transition range would be -40°C to +90°C.

10.2.4.

The dwell time is a minimum of five (5) minutes following stabilizationof the UUT at the setpoint temperature as determined by the UUT
thermocouple response. The dwell time is increased to allow higher
mass components to reach at least 80 percent of the thermal range.

10.2.5.

The full functional test is performed at the end of the dwell. If
possible, the full functional test or a subset of the functional test
should be performed throughout the ramp to monitor basic UUT
functionality. Any product-specific stresses should be applied in asimilar fashion. At the end of the dwell, the thermal stress is ramped
to the next thermal extreme and the dwell is repeated (Figure 5).

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Figure 5: Sample Rapid Thermal Stress Test Graph

10.3.

Vibration Step Stress Test

10.3.1.

During Vibration Step Stress testing, the goal is to find vibration
related failures, and to mechanically fatigue the UUT so that the
weakest portions of the UUT will fail quickly.

10.3.2.

During Vibration Step Stress testing, accelerometers are affixed to the
UUT to monitor the UUT’s response to the table input.
Accelerometers should be placed on major assemblies andsubassemblies in the UUT to evaluate overall transmission of vibration
into these areas, as well as on massive components or components
likely to have significant resonances.

10.3.3.

Since the RS vibration table provides energy in all three axes,
monitoring of vibration in multiple axes is recommended, particularly
when inner boards or subassemblies are mounted in perpendicularaxes to each other. Triaxial accelerometers are useful for thispurpose.

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10.3.4.

Vibration Step Stress testing begins at a chamber setpoint of 5 gRMS,
as measured over a 10 Hz to 5 kHz bandwidth. The vibration level isincreased in steps of a defined increment followed by a vibration dwellof a defined length Then increased in 5 gRMS (recommended)
increments upon completion of the dwell period and subsequentfunctional test.

10.3.5.

The vibration step increments are typically 5 gRMS.

10.3.6.

The dwell time at each level of vibration is a minimum of ten (10)minutes. The full functional test is performed at the end of the dwell.
If possible, the full functional test or a subset of the functional test
should be performed throughout the step to monitor basic UUT
functionality. Any product-specific stresses should be applied in asimilar fashion. At the end of the dwell, the vibration stress isincremented and the dwell is repeated (Figure 6).

Figure 6: Sample Vibration Step Stress Test Graph10.3.7.

Vibration Step Stress testing is continued until a failure is identified or
the limits of the chamber have been reached. When a failure isthQualmark Corporation | 10390 East 48 Avenue | Denver, CO 80238 | phone 303-254-8800 | fax 303-254-8343

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identified, it is handled as described in “Handling Failures in HALT
Testing” below and step stressing is continued. If possible, continue
until the operational and destruct limits for the product have been
identified.
10.3.8.

At input vibration levels of 30 gRMS and higher, alternating low levelvibration should be introduced. At the end of each vibration dwell andfunctional test, the vibration level is reduced to 5 gRMS and acomplete functional test is conducted, without waiting for a dwell atthat level. Then the vibration level is increased to the next step level.
Alternating low level vibration will help detect a failure mode that isprecipitated at a higher gRMS level, but is not detectable at that level,
and is also not detectable when the UUT is at rest. Low levels ofvibration, however, can make the failure mode detectable.

10.3.9.

Once the operating limit is determined, vibration step stressing
continues beyond the operational limit to the destruct limit or thechamber maximum. However, because the UUT may not be
operational, it is necessary to reduce the vibration stress between
each dwell to determine whether the UUT is still functional. This could
include a return to 0 gRMS or a level between 0 gRMS and theoperational limit.

10.4.

Combined Environment Stress Test

10.4.1.

During Combined Environment Stress testing, all of the stresses usedpreviously in the HALT test are combined and applied simultaneously.
The goal is to drive out any failures that require this combination ofstresses to be made patent.

10.4.2.

The accelerometers used during Vibration Step Stress testing should
be removed before beginning combined environment stress testing.
Accelerometers can be damaged by the temperature extremes usedin the combined environment.

10.4.3.

A minimum of five (5) combined environment cycles are required
unless a destructive failure forces the early termination of thestressing. Each combined environment cycle will consist of one
thermal cycle that is conducted while the vibration is held at a single
setpoint. For each of the five combined environment cycles thevibration level is incremented and held at the next setpoint while athermal cycle is conducted.

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10.4.4.

The minimum thermal cycle temperature range is within 10°C of boththe lower thermal operating limit and the upper thermal operating limit
as discovered during Thermal Step Stress testing. Example: if the
LOL was determined to be -50°C and the UOL determined to be
100°C, the thermal transition range would be -40°C to +90°C.

10.4.5.

The dwell time at each temperature extreme is a minimum of ten (10)minutes following stabilization of the UUT at the setpoint temperature
as determined by the UUT thermocouple response. The dwell time isincreased to allow higher mass components to reach at least 80
percent of the thermal range.

10.4.6.

The full functional test is performed at the end of the temperaturedwell. If possible, the full functional test or a subset of the functional
test should be performed throughout the thermal ramps to monitor
basic UUT functionality. Any product-specific stresses should beapplied in a similar fashion. At the end of the dwell, the thermal stressis ramped to the next thermal extreme and the dwell is repeated(Figure 7).
Combined Stress

Vibration, Grms^2/Hz, Temp Deg. C

140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
-10
-20
-30
-40
-50

11
2
11
6

10
4
10
8

96
10
0

92

84

88

76

80

68

72

60

64

52

56

44

48

36

40

28

32

24

16

20

8

12

4

0

-60
-70
-80

Time, Minutes
Temperature Level

Vibration Level

Figure 7: Sample Combined Stress Test Graphth

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10.4.7.

The vibration is maintained at the dwell setpoint until one complete
thermal cycle is finished. At the end of one complete thermal cycle thevibration level is incremented and the thermal cycle is repeated.

10.4.8.

The starting vibration level for the five (5) required cycles isdetermined by dividing the Vibration Destruct Limit by five. The
vibration level is increased by the same number during eachsubsequent thermal cycle. Therefore, if the UUT has a Vibration
Destruct Limit of 35, the initial test cycle would be conducted at a
vibration level of 7 gRMS. The vibration level would be increased by 7
gRMS after each complete thermal cycle - Cycle 1: 7 gRMS, Cycle 2:
14 gRMS, Cycle 3: 21 gRMS, Cycle 4: 28 gRMS, Cycle 5: 35 gRMS.
If a Vibration Destruct Limit was not determined during step stresstesting, then the Vibration Operating Limit is divided by five. Note that
smaller starting vibration and increment levels may be used if the UUT
is particularly sensitive to vibration stresses.

10.5.

Handling Failures in HALT Testing

10.5.1.

During the HALT test process, failure modes will be exposed. The firststep when a failure mode is detected is to carefully document allavailable details about the failure and the associated stresses in thetest report. Then investigation is done to determine if the failure is a
soft failure (operational limit) or a hard failure (destruct limit). This isachieved by first reducing the stress, dwelling at the reduced stress,
and functionally testing the UUT. During this investigation process,power cycling or UUT resets can be used as well. If necessary, theUUT is brought back to ambient and tested at ambient to determine if
a failure is hard or soft. At that point, decisions must be made to
replace components and continue testing, implement thermal or
vibration isolation to work past the identified failure mode, continue
testing and ignore the failure mode, or define the failure as an
operational or destruct limit and continue with the next stress. If an
operating limit is determined, the process of incrementing the stressshould continue beyond the operational limit to the destruct limit or thechamber maximum. However, since the UUT may not be operational,
it will become necessary to reduce the stress between each dwell andfunctionally test at a stress level below the operational limit todetermine whether the UUT is still functional.

10.5.2.

In all cases, the primary goal of HALT testing must be kept in mind –do all that is necessary to push stresses further and find as many
failure modes as possible.
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Post HALT Test Requirements

11.1.

The next step in the HALT test is to determine why failure(s) occurredand deciding what should be done about them. Engineering decisions
need to be made and justified regarding the response to the HALT test
results. This includes root cause failure analysis, corrective action, andVerification HALT testing.

11.2.

Root Cause Failure Analysis

11.2.1.

An integral part of the HALT test process is the determination of theroot cause of the failures identified in the test. This process may
involve the need for a failure analysis lab, whether in-house or
external. Attributing a root cause to a specific failure requires a fullunderstanding of the problem. When the cause is understood, theappropriate corrective action is implemented. Engineering judgment
decisions must be made to assess what corrective action, if any, will
be performed.

11.2.1.1.

A defined process is followed for all root cause analysis
investigations. This should include a procedure and a reporting
structure for review and decision making authority to assess
completeness and accuracy of the analysis.

11.2.1.2.

The root cause analysis process and results for each failure modemust be thoroughly documented, including any applicable picturesor other details that will facilitate understanding of the failure mode..

11.2.1.3.

Root cause analysis will include a review of the HALT test
documentation of the failure modes found and any changes madeto the UUT to work around failure modes during the test. Thermal
or vibration isolation techniques can be used during HALT tofacilitate the root cause analysis..

11.3.
11.3.1.

Corrective Action
When root cause analysis is complete, corrective action is
implemented. Corrective action for each failure mode found during
HALT testing must be thoroughly documented.

11.3.1.1.

Corrective actions are summarized in a cause and effect report forreview by the appropriate decision-makers within the company.
The report shall include a cost estimate/justification of the redesignand estimated product design margin improvement. Based on thisthQualmark Corporation | 10390 East 48 Avenue | Denver, CO 80238 | phone 303-254-8800 | fax 303-254-8343

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assessment a decision is made to implement changes or to leave
the product unmodified.
11.3.1.2.

11.4.

The engineering redesign decision process is defined and followed
for all corrective actions. This should include a procedure and areporting structure for review and decision-making authority toassess completeness and accuracy of the information reported.

Verification HALT Testing

11.4.1.

A Verification HALT test is performed after the corrective action
process when a product is redesigned. The design or processchanges to the product are incorporated in the product samples
subjected to this test. The goal of this test is to assess the impact of
the corrective action changes. Did they improve or eliminate theearlier discovered defects from the previous test, and are there anyother new problems resulting from the changes?

11.4.1.1.

A documented process must exist that defines when a Verification
HALT test needs to be be performed. It is recommended that a
Verification HALT test be performed on all but the least significant ofdesign changes.

11.4.2.

Verification HALT test report documentation is required, and should bein the same format, style and detail as the standard HALT test report.

11.4.3.

For products in production, changes made to the design subsequent
to the last HALT test on the product need to be evaluated for the
possibility of product design degradation. It is recommended thatwhen changes are made to products, a Verification HALT test is
performed to assess the effect of the change. These changes could
be due to redesign or vendor changes.

11.4.3.1.

11.4.4.

A documented process must exist that defines which engineering orprocess changes will require a Verification HALT test (i.e. after one
or more engineering changes, after major subassembly/component
change). It is recommended that this Verification HALT test be
performed on all but the least significant of engineering changes.

HALT testing should be performed periodically, typically every 3 to 9months on production products. This may not be necessary for
products that are submitted to a HASS production process.

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Possible Modifications to a HALT Test

12.1.

While the definition of HALT is rigidly defined as random repetitive shock
vibration combined with rapid thermal stresses, the steps used to drive
the UUT to failure may vary based upon the product type, the experienceof the test engineer, the needs of the company, and other factors. At
many points engineering judgment is used to determine if corrective
action is necessary, when to stop incrementing a stress, how best to
troubleshoot a failure mode, etc. In some cases changes to the process
are made. If these changes are carefully thought out, and are inagreement with the basic philosophies of HALT, then it may bereasonable to modify the procedure. It is important that the risk ofcompromising the effectiveness of the HALT test is fully understood.
That understanding requires a thorough knowledge of HALT philosophy
and purpose. The following are possible modifications to the HALT
process and the factors to take into account when considering suchmodifications.

12.2.

Changing a HALT Test to Decrease Test Time12.2.1.

In some cases, the product’s thermal tolerances across a limited
range are well understood before HALT testing begins. In thesecases, it may be feasible to skip the first few thermal steps, both hot
and cold, perhaps even stepping directly to the highest known
functional limit for the product. This will reduce the test time by
reducing the total number of dwells necessary in the test. Some of therisks associated with this approach are that failures related to theaccumulated fatigue of moving through the elevated thermal stresses,
or failures due to transient conditions that only occur at specificthermal levels, may be missed.

12.2.2.

Similarly, the elimination of the first few vibration steps may beconsidered. There is more risk associated with this change, as theaccumulated fatigue during vibration can be an important factor in the
final failure level, and skipping steps reduces that accumulated
fatigue. Increasing the vibration dwell at the higher gRMS levels mayhelp offset that risk.

12.2.3.

Moving directly to a combined environment rather than performing
separate stress testing is often considered. This is not recommended
for three key reasons. First, there is a decrease in the accumulated
vibration stress as described above. Second, without doing thethermal and vibration step stresses, the limits used in the combinedthQualmark Corporation | 10390 East 48 Avenue | Denver, CO 80238 | phone 303-254-8800 | fax 303-254-8343

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environment are not known. In this case, the limits would have to be
estimated somehow, introducing a possibly significant source of error.
Third, it is more difficult to debug failures found in a combined
environment because the stress that induced the failure is not known.
12.2.4.

12.3.
12.3.1.

12.4.

In general, reduction in dwell times, particularly thermal dwell times,
may be considered if the product has very low mass and good thermaltransition rates, such as a circuit card mounted on standoffs.

Testing Expensive Products or Limited Samples of Products.
If a test sample is expensive relative to the expected revenue streamof the product, the cost of four samples for HALT testing may have anegative impact on the ROI for the testing. In this case, anexperienced HALT test manager can apply changes to the test
procedure accordingly. The primary difference is, before testing
begins, the engineers involved must determine the thermal or vibrationlevels at which there is a high likelihood of hard failures occurring. To
avoid these hard failures, stresses are not increased to those levels.
Instead, stress testing is stopped before those levels are reached, or
earlier if failure modes are found that indicate the possibility ofimminent hard failure modes. At the conclusion of the testing, the unit
can then be tested to failure in the combined environment, or using
the stress determined to be the most valuable based on earlier test
results. The obvious risk with such changes is that hard failure modes
may not be identified.
When a Verification HALT test is done to verify corrective actions, anAbbreviated Verification HALT test may be considered. This decision isbased on the significance of the changes made, the likelihood of thechanges inducing new failure modes, and the necessity of full HALT teststresses to confirm that the changes were effective. This HALT test may
use larger (2 X) increments for the step stress environments and more
attention given to the stress levels that induced failures during the first
HALT test.

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Table 1: Acronyms

ASD:
CA:
DL:
DoF:
ED:
FFT:
HALT:
HASS:
LDL:
LOL:
OL:
PSD:
RCA:
RMS:
ROI:
RS:
UDL:
UOL:
UUT:
VDL:
VOL:

Acceleration Spectral Density
Corrective Action
Destruct Limit
Degrees of Freedom
Electrodynamic
Fast Fourier Transform
Highly Accelerated Life Test
Highly Accelerated Stress Screen
Lower Destruct Limit
Lower Operating Limit
Operating Limit
Power Spectral Density
Root Cause Analysis
Root Mean Square
Return on Investment
Repetitive Shock
Upper Destruct Limit
Upper Operating Limit
Unit Under Test
Vibration Destruct Limit
Vibration Operational LimitthQualmark Corporation | 10390 East 48 Avenue | Denver, CO 80238 | phone 303-254-8800 | fax 303-254-8343

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References1

Hobbs, G., Accelerated Reliability Engineering – HALT and HASS, John Wiley & Sons LTD(2000)

2

NASA Website, Finite element Modeling Continuous Improvement: The Book,
http://femci.gsfc.nasa.gov/random/randomgrms.html

3

Tustin, W., Random Vibration In Perspective, Tustin Institute of Technology (1984)

4

General Motors, Worldwide Engineering Standards, GMW8287, Highly Accelerated Life Testing,
Copyright General Motors Corp., 2002

5

Doertenbach, N., HALT and HASS – Testing with a Different Purpose, Qualmark Corporation
White Paper, http://www.qualmark.com/resources/library-documents

6

McLean, H., Silverman, M., Tulkoff, C. The Use of HALT and ALT when Transitioning to PbFree, Proceedings, ASTR 2006

7

“McLean, H., HALT, HASS and HASA Explained, American Society for Quality, Quality Press(2009)

8

9

Roettgering, M., Kyser, E., A Decision Process for Accelerated Stress Tests, EEP Vol. 26-2,
ASME, 1999.
Mayfield, M., Reliability Optimization Strategy, ASTR proceedings (2009)10

IPC-9592A, Requirements for Power Conversion Devices for the Computer andTelecommunications Industries, p. 26

11

RG.Aéro 000 29, Bureau de Normalisation de l’Aéronautique et de l’Espace (BNAE), Guide For
Defining And Performing Highly Accelerated Tests (2005)

The information contained in this paper is Qualmark proprietary information and is copyrighted. No portion
may be copied, modified, distributed or published without the express written permission of Qualmark
Corporation.

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