Appendix A I Appendix B I Appendix C

The HALT/HASS methods have been in use for some time and are being successfully used by many companies. In particular aerospace and military manufacturers have used it to weed out latent defects and marginal designs. This method was greatly pioneered by Gregg Hobbs Ph. D. ¹

The object of HALT is to subject the operating product to increasing temperature and shock levels by step-wise increasing the stress level until failure. These limits typically far exceed the normal operating range of the device. After this initial failure has been corrected by improved or redesign, the HALT test is continued with higher stress levels until the next failure. When the product survives the limits of the test, it is considered a robust design. First the product is subjected to a temperature step stress test with increasing higher limits to detect the defects. A typical example is the following scenario ²;

Start at 20°C, decrease in 10°C steps to -50°C, dwell 10 minutes at each step. Increase temperature to 30°C, increase in 10°C steps to 100°C, dwell 10 minutes at each step, return to 25°C.

After all the defects are identified and corrected, the product is subjected to a thermal cycling test to confirm that it can withstand the extremes of the test. A typical scenario is as follows:

Start with a transition to low temperature extreme, -30°C maximum, and then transition to high temperature extreme, 80°C minimum. Transition rates set at 50°C/minute. Extremes must be within destruct limits found in step stress. Dwell for 1 minute at extremes.

Then the product is subjected to vibration step stress test. A typical example is the following scenario;

Start with 10Grms vibration, increase by 5Grms increments after 10-minute dwell at each level. Continue
increasing vibration level until device destruction or maximum chamber vibration limit reached.

After all defects are mitigated, the product is subjected to a combined temperature and vibration profile. The same limits as above are applied as seen in figure 1.

Figure 1

A HASS stress profile is developed using operating and destruct limits found in the HALT testing. Maximum stress levels must be greater than normal operating limits and less than destruct limits. This HASS test is used as a screening in manufacturing and each product is subjected before being shipped. This HASS test also can be used as a P/F test for product qualification.

A HALT/HASS test is performed in a HALT chamber that is capable of very rapid thermal cycling and at the same time vibrating the product. Although there are many versions of these HALT chambers, depending on manufacturer, a common type made by Screening Systems in Aliso Viejo has a six-axis pneumatic powered vibration table. The major advantage of using a HALT chamber is that both temperature and vibration testing can be done in the same piece of equipment.

More information on HALT/HASS fundamentals can be found in Appendix A.