Learn more about thermal shock chambers from ESPEC

1. What is a thermal shock chamber and how does it work?
   1. These chambers rapidly change temperature by physically moving the product from a hot zone to a cold zone, or rapidly changing the air temperature by specialized means.
2. What are the different models of thermal shock chambers available from ESPEC?
   1. There are elevator/lift types and air-exchange damper types.
3. What temperature ranges can ESPEC thermal shock chambers achieve?
   1. All are around -65 to 180°C in range
4. How do thermal shock chambers simulate extreme environmental conditions?
   1. Subfreezing temperatures are by a cascade refrigeration,
   2. Hot temperatures are generated by electrical resistance heaters.
5. What safety features are included in ESPEC thermal shock chambers?
   1. Elevator systems have special protections to avoid injury from moving lift.
6. How do ESPEC thermal shock chambers compare in terms of energy efficiency?
   1. The modern TSA series are 50 to 70% more efficient than their predecessors.
7. What international testing standards can be met with ESPEC thermal shock chambers?
   1. https://espec.com/na/chamber_f...

Following are links to the most popular thermal shock testing standards in use today.

EIA, Electronics Industries Association

EIA’s JEDEC Solid State Products Engineering Council has many published specifications for environmental testing. The JESD22 group of specifications include temperature/humidity, thermal shock, and HAST. You must register, but the standards are free!

• The air-to-air thermal shock test is JESD22-A104D “Temperature Cycling”
• The liquid-to-liquid thermal shock test is JESD22-A106B “Thermal Shock”

Mil-Std 883:

The electronics industry has used this Military Standard 883 as theirs. It is what the JEDEC spec listed above is based on. This page offers the entire text of the standard in Adobe Acrobat format, but you don’t need the whole thing. (Note: Current version is “883J Method 1010.8”. Previous versions 883C, 883D, 883E, 883F, 883G, 883H are the same basic standard, which was numbered 1010.6 and 1010.7.)

• Download the 1000 section (covers test method) Print out pages 33-35 to get Method 1010.8 “Temperature Cycling” for air-to-air thermal shock
• Print out pages 37-39 to get Method 1011.9 “Thermal Shock” for liquid-to-liquid thermal shock

Mil-Std 202G:

Another thermal shock method is part of Military Standard 202. Once again, you don’t need the whole specification, just a few pages.

• Scroll down till you find Method 107 “Thermal Shock” for air-to-air and liquid-to-liquid thermal shock methods

Technology Report Downloads:

Our Technology Reports cover thermal shock testing as part of a general review of testing methods, as well as specific articles. These are in the Adobe Acrobat format.

Issue #3 (pdf link)

• Understanding the Technology
  • Thermal shock testing
  • Current trends and example
• Report 1: Confirming reliability of printed circuit boards with temperature cycle and thermal shock

Unfortunately many people use the same name to refer to different tests. Thermal shock is one of those. Let me elaborate:

Definitions:

1. Alternately dipping the product in hot and cold liquids. More precisely, this should be referred to “liquid-to-liquid thermal shock”.

2. Changing the air temperature as quickly as possible in a single chamber. This we would recommend calling “thermal cycling” or “stress screening” and isn’t truly thermal shock.

3. Moving the product from a hot to a cold chamber or other sudden change of the air temperature. This is “air-to-air thermal shock” or “two-zone thermal shock.”

***

Sometimes during transfer as described in 3, there is an intermediate step of exposure to room temperature. This is done to allow manual transfer of the product. This is called a “three-zone thermal shock”. Mil-Std 202F method 107G allows such a step, for example.

So, from the above list, you can see the variations in what people commonly call “thermal shock”. It should also be noted that some specifications call for “thermal cycling” which is actually “air-to-air thermal shock”.

With thermal shock tests, there are also several ways to define and measure the performance. Thermal shock tests focus on “recovery time”, or how long it takes to stabilize after the switch.

Recovery time can also be defined several ways:

1. Time it takes for the product to move from zone to zone. True name: “transfer time”

2. Time for the air temperature to recover in the new zone. This can be measured in the air stream before or after the test load. This can be called “upstream recovery time” or “downstream recovery time”.

3. Time for the physical product to recover, called “product recovery”. This time is dependent on where the sensor is placed on the load. Mil-Std 883 method 1010.7 defines their requirement as “worst-case” product recovery, which is for a sensor embedded in a sample buried among other samples.

***

Of course, some test specifications only make the confusion between thermal shock and thermal cycling worse. One example is Telcordia (Bellcore) GR-468 that states “Method 1010 of Mil-Std 883C with a minimum temperature ramp rate of 10C/min.” Many people assume that a cycling chamber that does 10°C/min. is sufficient, although the Mil-Std clearly defines the transfer time and recover time, which, if you have been paying attention a thermal shock test.

So when you are asked to do a thermal shock test, be sure that you have a clear definition of the requirements, otherwise it is easy to do incorrectly, or buy the wrong equipment.