The purpose of HALT and HASS testing is to build robustness into your products from the earliest stages in their development cycle.
They greatly reduce or even eliminate the failures (infant mortality) of a new product.
HALT, Highly Accelerated Life Test, is based on a series of thermal and mechanical tests carried out on equipment during its design phase.
The methodology applied makes it possible to detect design defects and weaknesses in electronic systems and sub-components. Not corrected, these defects may appear during qualification in environments (when this step exists) or once the product is on the market.
The HASS testing, Highly Accelerated Stress Screen, is a screening test. In production, all or part of your equipment is subjected to thermal and mechanical stresses with severity levels resulting from HALT tests.
When compared to a product's life cycle, HALT & HASS tests allow you to influence the 3 phases described by the bathtub curve model representing variations in failure rate as a function of the product's life duration.
HASS methodology
The HASS methodology implements combined vibration, temperature and rapid change temperture testing applied in cycles.
The equipment used to do HASS is similar to that used in HALT, although often a larger chamber is used to accomaodate production quantities.
The fixturing can be quite different in HASS simply o accomodate the production flow (speed with which products can be fixtured, number of products, ...)
Avant de systématiser l'application du HASS en tant que procédé de contrôle de la chaîne de fabrication, le profil de test définissant les contraintes à appliquer doit être défini, le montage de la chambre destiné à accueillir tout ou partie de la production doit être optimisé et le Proof Of Screen (POS) doit être validé.
The HASS profile is deduced from the tests carried out in HALT (detection screen, precipitation scree and Proof of Screen)
The HASS profile is deduced from the HALT after all the corrective actions have been taken into account.
For example, the initial profile before validation of the POS can be built around a temperature excursion at 20% of the operational limits detected in HALT with a minimum delta of 100°C and with a vibration acceleration level half the level leading to destruction in HALT.
The HASS profile must be validated by a POS which takes into account the mounting arrangement of the products in the chamber. This assembly is one of the most delicate elements to be carried out within the framework of the HASS since it must allow a simultaneous passage in test of a maximum of products by guaranteeing that each one of them will be subjected to the same mechanical and thermal stresses.
As soon as the HALT characterization reveals sufficient margins between the functional limits and the destruction limits, the HASS profile is broken down into two phases, one called precipitation screen, which, by using stress levels above the functional limits but below the destruction limits, transforms latent defects into obvious defects, and the other, detection screen, with exposure times at high and low temperatures sufficient to prevent them from occurring.
The PoS is performed once the HASS parameters have been determined. It consists in applying to the same number of products as foreseen by the assembly 20 to 50 times the test cycle defined in HASS by combining test products incorporating manufacturing defects (such as improperly welded wires) with products from the series production. The goal of the PoS is to adjust the HASS profile so that defects can be detected as early as possible in the first cycle, but without causing failures on "healthy" products or significantly reducing their shelf life.
This last aspect is verified by counting the number of cycles required for healthy products to develop symptomatic end-of-life defects.
Once the PoS is completed, HASS can be applied in production.
Emitech Group - Legal information