What is HASS testing?
HASS, Highly Accelerated Stress Screening, is a production screen. Every unit runs a short combined temperature and vibration profile derived from the limits found in HALT. It precipitates latent manufacturing defects that a functional test would miss, without removing meaningful life from good product. HASS tests the build; HALT tests the design.
Where the HASS profile comes from
HASS presupposes a design that HALT has matured. The screen runs in the operating margin HALT measured: above the specification, below the operating limits, so the product can be powered and monitored for the whole screen. A design with thin operating margins cannot be screened effectively. A HASS profile has two parts:
- the precipitation screen, at the higher stress, turns latent defects into hard, detectable failures;
- the detection screen follows at lower stress, with the product powered, exercised and monitored, so those failures, including intermittents that appear only under stress, are caught.
A typical profile is a few combined-environment cycles, running from minutes to a couple of hours, and several units are often screened together on the table at once. What is HALT testing? explains where the limits come from, and the methodology guide sets out how to build the screen.
Proof of Screen
A screen aggressive enough to precipitate defects is, by definition, aggressive. Before it is used on saleable product it has to be proven on two counts: effective, because it finds the defects it is meant to find, and safe, because it does not consume meaningful life from good units. What is Proof of Screen? explains how both are shown.
When 100% screening becomes sampling
Start by screening every unit. Once the process has proven stable and the screen has stopped finding defects, production can move to HASA, the same screen applied to a sample of each lot, and it returns to 100% HASS when something changes. What is HASA? covers when to switch, and when to switch back.
In the standards
- IPC-9592B treats HASS as a route to reducing burn-in time for power conversion devices.
- GMW8287, GM’s guideline, covers HASS and HASA as well as HALT.
The standards guide gives each one’s revision and issuer, and what it asks for.
The short answer
What is HASS testing?
Highly Accelerated Stress Screening: a production screen in which every unit runs a short combined temperature and vibration profile, above the specification but below the operating limits found in HALT, to precipitate and detect latent manufacturing defects before shipment.