Description:

HASS testing, also known as Highly Accelerated Stress Screening, is conducted on the production line after determining the operational or destruction limits through HALT (Highly Accelerated Life Test). It is generally required that 100% of the products undergo the HASS screening. The purpose is to ensure that the manufactured products are free of any hidden defects or at least identify and address these defects before the products leave the factory. HASS employs accelerated stress methods to quickly identify defective products and shorten the corrective action period while identifying other products with similar issues.

Objective: HASS is applied during the production phase of the product to ensure the implementation of all improvement measures identified during HALT. It also ensures that no new defects are introduced due to changes in production processes and components.

Scope of Application: 

Electrical and electronic products and equipment. It is used for pre-screening to eliminate latent defects that may develop into significant flaws, detect obvious defects, perform failure analysis, and implement improvement measures.

Three Stages of the Test:

1.HASS Development (HASS Test Planning Phase):

The HASS test plan should reference the results obtained from the preceding HALT test. Generally, the operational limits for high and low temperatures in the combined stress of temperature and vibration are reduced by 20%, and the vibration conditions start with 50% of the G value of the destruction limit as the initial conditions for the HASS test plan. Then, based on these conditions, temperature and vibration combined stress tests are conducted to observe if any failures occur. If failures occur, it is necessary to determine whether they are caused by excessive environmental stress or by the quality of the tested object itself. If it is the former, the temperature and vibration stress can be relaxed by another 10% before further testing. If it is the latter, it indicates that the current testing conditions are effective. If no failures occur, the test environment stress should be increased by another 10% before further testing.

2.Proof-of-Screen (Plan Verification Phase):

When establishing the HASS Profile (HASS procedure), two principles should be considered: firstly, the ability to detect potential equipment faults and secondly, avoiding equipment damage or “internal injuries” after testing. To ensure that the results obtained in the HASS test planning phase comply with these two principles, three test samples must be prepared, and certain defects not conforming to standard processes or assemblies, such as loose parts, soldering voids, and improper assembly, should be introduced in each sample. The conditions obtained in the HASS test planning phase are used to test each sample to determine if the artificial defects on each sample can be detected. This helps decide whether to tighten or relax the testing conditions to achieve the desired effect of the HASS Profile. 

Once the effectiveness testing is completed, the adjusted conditions should be used to test 30-50 times with new test samples. If no destructive failures occur due to inappropriate stress during these tests, it can be concluded that the HASS Profile has passed the plan verification stage and can be used for Production HASS. Otherwise, a reassessment is required and the test conditions need to be adjusted to achieve the optimal combination.

3.Production HASS (HASS Execution Phase):

Any HASS Profile that has passed the Proof-of-Screen validation is considered a rapid and effective quality screening tool but requires appropriate adjustments based on customer feedback regarding anomalies observed during product usage. Additionally, when there are design changes, corresponding modifications to the test conditions are necessary.

Image of HASS Testing Equipment: