Tests ESS HALT / HASS, TELCORDIA  [ Return towards  Applications  ]

AST accelerates fatigue life and exposes defects that would otherwise take years to appear under normal conditions. AST systems rapidly cycle devices under tests through high and low temperature extremes while subjecting to them electrical voltage. With the increasing concerns over quality and reliability, AST is becoming more predominant and gaining in adoption.

There is various type of Environmental Testing equipment to choose from when considering ESS and AST. Lab bench test, test chambers, or walk-in chambers all offer various features that are more suitable to a given process. If your cooling rate is rather modest, a closed-loop mechanical refrigeration unit may be sufficient. For lower temperature, liquid carbon dioxide (CO2) or the cooler and more environmentally friendly liquid nitrogen is necessary.

Other concerns when selecting the cooling medium is equipment uptime and maintenance. Besides cooling faster, Environmental Testing Chambers using liquid nitrogen offer greater reliability over mechanical refrigeration systems. Testing interruption due to faulty mechanical units can be costly and introduce production delays and bottlenecks. Field retrofits or conversions from mechanically refrigerated equipment to liquid nitrogen are possible (see NITROCOOL™ by AIR LIQUIDE).

In addition, a new design now allows the recycling of evaporated liquid nitrogen. Field retrofits are also available to equip existing equipment of that feature. The use of gaseous and dry nitrogen elsewhere in the plant in other processes such as dry cabinet storage, inert reflow or wave soldering can be done at virtually no cost.

• Reasons to use liquid N2 for ESS / AST applications:

N2 is safe, non-toxic, and extremely cold (-195° C or -320° F)
N2 provides the fastest cooling rate of all methods
N2 provides a dry and inert atmosphere in the chamber
N2 saves precious space in your plant
No maintenance is necessary (unlike mechanical cooling units)
No downtime will affect production (unlike freon-cooling units)
N2 cooling is easy and practical
N2 can be recycled and used in other plant applications
The efficiency and safety of an Environmental Testing process using liquid nitrogen depends greatly on the liquid distribution installation. The choice of the right insulated piping, the location of the Environmental Testing equipment vs. cryogenic liquid storage, the number of piping bends, valves and safety valves all impact the process efficiency and cost. Making the wrong decision can increase liquid nitrogen consumption up to 50% while slowing the process. It is therefore important to seek advice of a professional in order to ensure the optimization of the process.

For more information on Environmental Testing with nitrogen cooling vs. mechanical-refrigeration, please consult the attached document :

Cryogenic Cooling
Sigma Systems, San Diego, CA, USA 2000