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“ Reliability Stress-Test Method: Impact on the New-Product Introduction Process, Time to Market, Field Reliability Impact, and Reliability Assessment ”

2002 PROCEEDINGS Annual RELIABILITY and MAINTAINABILITY Symposium
January 28-31

Abstract: A comprehensive Reliability Stress Test program must not be considered as a trivial undertaking for it to be effective and efficient. The shake and bake approach without a complete understanding of the processes, failure modes and mechanism, technology, and reliability objectives may buy a few short term gains and success stories, but for a longer term, could be a costly proposition and undertaking.

It is highly recommended that prior to implementing any stress test strategy, the purpose of the tests are clearly defined, field reliability goals are established, and a reliability growth road map is planned in advance.

“ Design Evaluation & Product Reliability assessment using Accelerated Reliability Fatigue Life Tests”
Shams Jawaid, Jon Ferguson
2000 PROCEEDINGS Annual RELIABILITY and MAINTAINABILITY Symposium
January 24-27

Abstract: Inherent product design, process, or manufacturing latent defects can be exposed as hard detectable failures by the application of proper accelerated reliability stress tests. Accelerated Reliability Stress Tests should be an essential part of the different phases of the product design, development, manufacturing and shipment. With failure analysis and corrective action programs in place accelerated reliability stress tests can drastically reduce the product design and development cycle time. In addition, higher reliability or lower field failure rate, higher customer satisfaction, lower warranty and repair field cost can be achieved. This can potentially increase market share.

“ Accelerated Reliability Test Results: Importance of Input Vibration Spectrum
and Mechanical Response of Test Article”
2000 PROCEEDINGS Annual RELIABILITY and MAINTAINABILITY Symposium
January 24-27

Abstract: Repetitive Shock (RS) and Electrodynamic (ED) vibration systems produce substantially different vibration conditions at the input point to the test article. These differences are most evident in terms of peak G level and spectrum content.

The “RS” System produces vibration in short bursts which contain extremely high G amplitudes at the leading edge of each air hammer impact. The frequency content of the “RS” spectrum is non-uniform and exhibits many “holes” in the best spectrum.

The “ED” System produces a continuous vibration time history that contains peak G amplitudes that vary within a moderate, programmable range. The distribution of vibration energy over the test spectrum is uniform and easily programmed using accelerometer feedback (closed-loop) control.
“ Accelerated Reliability Tests: Solder Defects Exposed ”
1999 PROCEEDINGS Annual RELIABILITY and MAINTAINABILITY Symposium
January 18-21

Abstract: This paper describes a methodology to perform risk assessment and establish the quality and reliability of solder joints utilizing accelerated reliability life testing techniques. Temperature cycling tests were performed on equal number of 100-pin Quad Flat Pack [QFP] package mounted on printed circuit board assemblies [pcbas] from a reworked and non reworked soldering process. The data showed that the accelerated reliability tests exposed the latent defects inherent in reworked solder joints. The projected field failure rate and the percentage of reworked solder joint failures of the total pcbas shipped were high and unacceptable to meet the product MTBF target.

Accelerated reliability test is a powerful engineering tool and the techniques can be used to establish fatigue life of product or force latent defects as hard failures. Reliability tests are designed specifically to target a known failure mode; although a black box approach can also be taken if failure mode and mechanism are not known. A stress portfolio may include the application of individual or combination of one or more stresses such as thermal, sine or random vibration, shock, electrical voltage, humidity, or power cycling. A fatigue plot similar to S-N curve can be generated for a type and magnitude of stress[es] in which frequency of failure or a degradation in a parameter can be measured against the number of stress cycles. A good example can be change in electrical resistance, or degradation in mechanical strength, or an increase in detectable failures against the number of cycles of applied stress. The key to designing an effective reliability test lies in the proper selection of stress type and stress magnitude, and an understanding of the underlying failure mode and mechanisms.

Accelerated Reliability tests can also be used to perform a risk assessment on new product prior to scheduled shipment to the market. The risk assessment can provide a good estimate of the field failure rate and MTBF of the product with a high degree of confidence. The data from the accelerated reliability tests can be used to stop shipment of a product and also prevent latent defects to appear in the field by taking appropriate corrective action. These defects otherwise if not identified and corrected have the potential to adversely impact the quality, performance and reliability of the product.
“ technical brief- disk drive reliability and thermal management ”
Electronic Cooling Volume 4, Number 3. September 1998.

Abstract: The thermal management requirements for a good design are; power budget specifications, power de-rating factor, thermal resistance measurements èja and èjc, junction temperature measurements and temperature control, and optimum board layout.

Drive form factor restriction requires drives to stay within the industry specified dimensions for height, length, and width for each class of drives. Thermal design and thermal management becomes extremely difficult since the use of heat-sinks, cooling fans, or any other cooling method may violate the form factor requirements set by the electronic industry. Ingenuity and thermal design experience are key factors required to maintain a drive’s overall operating temperature within limits, and junction and case temperature within each device specification.

Thermal management and thermal design margins are critical factors and must not be ignored if high standards of performance and reliability in the field are desired for disk drive products.
“ ESS –Linear Ramp Chambers and Thermal ESS ”
Shams Jawaid, Kevin Crook
EE EVALUATION ENGINEERING, Volume 31, No 6, June 1992

Abstract: Optimized equipment performance is essential in developing the stringent ESS technology needed to succeed in today’s highly competitive electronics marketplace. To meet the demands of an effective program, thermal stress screening chambers must deliver linear ramp rates with high volumetric air flow and air velocities.
“ Wearout Evaluation of Soldered Interconnections for surface Mounted Leadless and Leaded Components”
Soldering & Surface Mount Technology
Journal of the SMART ( Surface Mount & Related Technologies) Group. Number 4
February 1990

Abstract: One of the most significant problems associated with the implementation of SMT is the integrity of soldered interconnections, especially in high reliability environments. Accelerated thermal cycling is commonly used to evaluate the attachment reliability of various leadless and leaded SMT soldered junctions. Thermal cycling is also utilized as a means to precipitate incipient manufacturing defects before the product is shipped.

Thermal fatigue caused by repeated power on/off cycles, which results in cyclic temperature variations during the life of a product, is perceived to be responsible for the majority of the field failures. These temperature variations induce cyclic thermal stresses which may consume a significant useful life of the product or even cause catastrophic failure.

A number of criteria have been proposed and utilized to determine the soldered joint failure. Some of the widely followed failure criteria in the electronic industry are: a resistance increase of 1%, 10%, 100% and 1000%; an open in the electrical circuit continuity ( i.e., infinite resistance); the first interruption of electrical continuity even of very short duration; and a percentage decrease in the applied load required to sustain a prescribed strain level. However, only continuous monitoring during cyclic testing can give an accurate and repeatable indication of failures and is expected to correspond closely to the failure threshold in actual product operation.
An inevitable inquiry, often raised, is the extent to which thermal cycling degrades the quality of acceptable soldered joints while serving to highlight incipient defective ones.