How to Implement a HASS Program

This article is a general outline on how to implement a HASS program after a successful HALT has been performed and corrective actions have been completed for any weaknesses found during HALT.  For more information about HASS, please read our blog, What is HASS Testing?  For more information about HALT, please read our blogs

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A Primer for HAST: Highly Accelerated Stress Testing

HAST Chamber: Highly Accelerated Stress Testing

DES’s HAST Chamber

The HAST acronym stands for Highly Accelerated Temperature/Humidity Stress Test and is sometimes shortened to Highly Accelerated Stress Testing. HAST makes use of accelerated temperature and humidity conditions to precipitate failures which could be caused by long term exposure to humid environments.

HAST has been developed to replace Temperature-Humidity-Bias (THB) testing which has typical conditions of 85 ⁰C and 85 % RH along with a bias voltage applied to the sample. A typical THB test time would be 1000 hours. HAST uses increased test temperatures of 110 to 130 ⁰C which decreases the test time to as low as 96 hours compared to a THB test. Thus, by choosing HAST over THB for an accelerated reliability test, testing can be completed in days, not weeks.

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Circuit Board HALT Testing Case Study

HALT Test Setup on Circuit Boards

HALT Test Setup on Circuit Boards

Customer Goal

A customer approached DES looking to perform Highly Accelerated Life Testing (HALT) on a new circuit board design.  DES and the customer agreed to test the circuit boards using DES’s traditional HALT test procedure which calls for hot/cold temperature steps followed by rapid temperature ramping, vibration steps and combined temperature and vibration stresses.  HALT testing on electrical componentry is quite common across industry to expose design weaknesses; both mechanical and electrical (What is HALT and Why Perform HALT?).  Typical failures include poor solder connections, overheating, component failure, etc. (What Kind Of Failures Occur During HALT?)

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Rapid HALT – A Cost Effective Alternative to HALT

Rapid Highly Accelerated Life Testing or Rapid HALT is a reliability test method that is used to expose product weaknesses.  A Rapid HALT procedure is a modification of a Classical HALT procedure.  For more information about Classical HALT procedures, refer to the following blog articles:

A Rapid HALT is an abbreviated HALT, typically one day of tests, making it a great cost-effective solution for those seeking faster qualitative results.  Exposing a product to a Rapid HALT early in the design process can help reduce product development time and cost by enabling manufacturers to identify flaws or areas of improvement before it’s too late.

Rapid HALT’s are a good tool for assessing the reliability of different suppliers of components but can also be used to assess the reliability of less complicated products.  For example, DES has performed Rapid HALT’s to evaluate the reliability of different suppliers of power supplies, cooling fans, and LED’s.  DES has also performed a Rapid HALT to study different fastening methods in order to determine which was more robust.

DES Rapid HALT Profile

Figure 1. DES Rapid HALT Profile

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Cooling Fan Reliability Testing Case Study

Fan Reliability Testing Case StudyCustomer Challenge

A customer approached DES looking to find an accelerated test solution for an AC powered cooling fan used in one of their products.  The product had been established in the marketplace and the company was now looking for ways to reduce cost by looking at different cooling fan suppliers.  Most fans, however, have a mean life rated for over 20,000 hours, so a typical accelerated life test would require a significant amount of time and money.  Continue Reading Cooling Fan Reliability Testing Case Study

What Kind Of Failures Occur During HALT?

Product failures in HALT testing are defined as either the cessation of any functions or an out-of-specification condition for any performance characteristic. When a failure occurs, it is documented in DES’s HALT log. The exact time and test condition when each failure occurred is noted.

If the product fails to operate, the temperature or vibration will be changed toward ambient room conditions followed by a short dwell period to see if the product recovers. If the product is non-operational after dwelling at ambient conditions, trouble shooting will take place to find the failed component. The failed component will then be removed, repaired or replaced with a new component (as is practical) in an effort to expand the test stresses.

Relevant Failures

Figure 1 - Failure of Improperly Designed Mounting Tabs

Figure 1 – Failure of Improperly Designed Mounting Tabs

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What Equipment Is Used For HALT?

HALT Chambers

Figure 1 - DES’s HALT Chambers

Figure 1 – DES’s HALT Chambers

Specialized test chambers are needed to perform a HALT. Typical HALT chambers are shown in Figure 1. The specification for HALT chambers is typically the following:

Liquid nitrogen (LN2) is used to cool the air temperature in HALT chambers. This allows for very rapid temperature changes of 60°C per minute and a cold temperature extreme of -100°C.

HALT chamber heating is provided by high power resistive heating elements that can produce changes of 60°C per minute and a hot temperature limit of +200°C.

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What Is A Typical HALT Procedure?

HALT procedures vary from lab to lab but are typically performed similar to DES’s procedure which is summarized below. DES’s HALT procedure is divided into 5 Stages: Stage 1 – Temperature Step Stresses, Stage 2 – Temperature Ramps, Stage 3 – Vibration Step Stresses, Stage 4 – Combined Temperature &Vibration Stresses, and Stage 5 – Temperature Destruct Limits.

Stage 1 is used to determine the HALT Operational Limits for temperature. The goal is not to cause destruction in Stage 1, but sometimes the operational and destruct limits occur simultaneously. The HALT Destruct Limits for temperature and vibration are typically found in Stages 3 to 5.

Temperature Step Stresses – Stage 1 (Figure 1)

Figure 1. Stage 1 Temperature Steps

Figure 1 – Stage 1 Temperature Steps

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What Is HALT (Highly Accelerated Life Testing) And Why Perform HALT?

Highly Accelerated Life Testing (HALT) is a rigorous reliability test method that is used to expose product weaknesses. The goal of HALT is to proactively find weaknesses and fix them, thereby increasing product reliability. Because of its accelerated nature, HALT is typically faster and less expensive than traditional testing techniques.

HALT of circuit boards in one of DES’s HALT chambers

HALT of circuit boards in one of DES’s HALT chambers

HALT can be effectively used multiple times over a product’s life time. During product development, it can find design weakness when changes are much less costly to make. By finding weaknesses and making changes early, HALT can lower product development costs and compress time to market. When HALT is used at the time a product is being introduced into the market, it can expose problems caused by new manufacturing processes. When used after a product has been introduced into the market, HALT can be used to audit product reliability caused by changes in components, manufacturing or suppliers etc. The bottom line is that HALT can reduce product development time and cost, reduce warranty costs, improve customer satisfaction, gain market share, and increase profits.

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