By Christopher Coronel | Aug 5, 2013
Highly Accelerated Stress Screening, also known as HASS testing, is a method for testing the reliability of a product by exposing it to stresses beyond what it would encounter in normal use. The testing is performed in an environmental chamber and can involve a variety of stresses, including thermal cycling, humidity, power cycling, and vibration.
The testing methodology exposes the weak points in a product design so that they can be fixed, and the product quality and reliability can be improved. Nuvation Engineering goes through HASS testing fairly often as part of our New Product Introduction process, particularly for our clients in the defense and medical industries.
Recently we had a prototype board that was failing performance tests at temperatures below -20°C and we needed to investigate to find the root cause of the failure. The board worked perfectly at room temperature, so we had to examine a chilled board for our investigation.
Ideally we would use an environmental chamber for the debug process, but this would involve renting a testing facility and transferring all our equipment there. We would be limited to the available openings and hours of operation of the laboratory, and it could potentially be very expensive, since we’d need to move the Device Under Test (DUT) in and out of the chamber often. It simply wasn’t practical for our client in this particular case.
We could have used a standard freezer for our testing, but it was inconvenient to find a portable freezer that could be moved into the lab area with the DUT and its test equipment. Also, a typical freezer keeps the temperature around -18C, and we wanted the ability to go considerably colder. On the other hand, dry ice (solidified Carbon Dioxide) sublimates — meaning that it transitions from a solid to a gas. Chilling a board with dry ice allows you to create an extremely cold environment for your DUT in the comfort and convenience of your own lab. While this is not the approach we would take with deliverable product, it was a perfect fit for functionality testing on a prototype.
How to make a temperature chamber:
- Get a cooler that’s the appropriate size to fit your DUT. If it’s too big it is more difficult control the temperature, and uses a lot dry ice.
- Put dry ice at the bottom of the cooler, followed by an aluminum sheet (a size that will fit in the cooler). Dry ice can be purchased at a number of grocery and home supply stores; we picked up 20 pounds of it from Smart & Final. 20 pounds is enough to last for 1 to 3 days of experimentation, depending on how well you keep it insulated in the cooler, and how much heat your DUT generates.
- Attach a thermal probe to the DUT to monitor the temperature. We used an Agilent U1272A digital multimeter.
- Set up any equipment you will need for testing and debug.
- Close the lid of the cooler and observe the temperature. Once it reaches your desired level, begin testing!
A few warnings about working with dry ice:
- Dry ice is VERY cold and should only be handled wearing appropriate gloves.
- Cooling your product in a normal atmosphere will cause water vapor to condense and eventually freeze all over your board. Your board will become covered with frost during the experiment, and after it warms back to room temperature, it will be covered with water droplets. Make sure your product can tolerate this before doing this experiment! It’s possible that this can be kept under control using commercial desiccants, but we haven’t tried that.
Nuvation has delivered over 800 projects for customers in a wide range of industries. Contact Nuvation Engineering to learn more about the electronic design services we offer, and how we can improve the reliability of your product and decrease the time to market.