Product Testing Services

Temperature is by far the most common stress applied to electronic devices.  This is due to its ease of control and direct relationship to electronic reliability over time.  Put another way, it is an excellent stress to age products to determine failure modes (and thus design or safety margin) and to assess classical reliability parameters such as failure rate and mean time between failure (MTBF).  It is also commonly combined with other stresses such as humidity, altitude, and power cycling.

How is temperature applied in the testing of products, electronic and otherwise?

Temperature storage tests are generally long-term, non-operational tests.  They are to simulate the degenerative effects of storing a product at a temperature extreme such as in a warehouse environment.  The temperatures specified for storage are typically greater than those the product is expected to operate in. 

• Temperature extreme testing examines at what temperature, cold and hot typically, will a device cease to function properly.  This may be done with a slow linear profile, or a step-stress profile.  As the temperatures of interest are the extremes, test efficiency is improved by stabilizing the device just shy of the area of interest and then ramping or stepping from there.

• Temperature cycling is the process of cycling through two temperature extremes, sometimes at relatively high rates of change.  It is used to age products through fatigue.  As components heat up and cool down, they expand and contract.  This causes failure over time.  In addition to evaluating designs, it is also used in manufacturing to screen products to catch early-term, latent defects.  This is known as environmental stress screening (ESS) but is sometimes improperly referred to as "burn-in" testing.

Temperature or Thermal Cycling

1. High temperature soak.
2. Transition to low temperature.
3. Low temperature soak.
4. Transition to high temperature

Cycle Repeats...

• Two categories of thermal testing to be mentioned, but not covered in detail here are Thermal Shock and Highly Accelerated Life Testing (HALT).  Thermal shock is thermal cycling at a very high rate of temperature change, typically 30 degrees C per minute or higher.  This stress will be covered in a separate section (see Thermal Shock).  HALT testing involves very high rate thermal cycling (typically accomplished using LN2 based systems) and multi-axis hammer-table vibration.  This stress is coupled with very thorough product parameter monitoring to determine instantly when a failure occurs.  The function of HALT is to rapidly expose a product's weakest link in terms of its design.  This weak link can then be fixed and the process repeated to reveal the next most likely point of failure.  Repeating this cycle results in a product with greater and greater reliability.  Although it would appear that the failures uncovered during such extreme testing might not match those in the real world, it has been shown that on average, 90 to 95% of the failures found during HALT would have occurred in actual product usage.

How are these tests specified?

Temperature storage tests are specified by the minimum and maximum storage temperatures and the duration that the units should be held in that environment.

Temperature extreme testing is just a matter of specifying the minimum and maximum operating temperatures plus specific guidance on how the device under test should be powered, loaded, and monitored.

Temperature cycling involves specifying the profile in addition to power, loading, and monitoring requirements.  Definition of the thermal profile includes the temperature extremes, soak times, transition times, and when power and loading should be applied.

Test Specification Template (Static Temp/Humidity/Altitude/Power)

Test Specification Template (Temp/Humidity/Altitude/Power Cycling)