Thermoelectric Coolers Reliability testing and qualification
◻ All thermoelectric cooler series provided by TEC Microsystems GmbH are Telcordia GR-468 qualified
◻ TECs fully meet the reliability requirements established by Telcordia GR-468-CORE Standard
◻ TECs with advanced protective coating all withstand additional Damp Heat 85/85 Test
◻ The qualification of thermoelectric modules is made regularly, every two years, and takes 6 months
◻ The up-to-date Reliability Report (2017) is available by request (subject of NDA)
Thermoelectric Coolers Reliability
Thermoelectric coolers are inherently reliable due to their solid-state design with no moving parts. Many thermoelectric coolers (TECs), miniature types, are applied in components and systems where the TEC failure can result in the overall product rejection, whose cost is by far higher than that of the TEC. Therefore the TEC quality and reliability should meet very stringent requirements.
State-of-the-art TECs have high reliability that can be expressed in hundreds of thousands of hours. The Mean Time before Failure (MTBF) of the TECs of modern manufacturers is usually not less than 250K-300K hours at room conditions.
Reliability Standards
In the international practice the reliability standards developed by the company Telcordia are widely used. The TEC requirements are offered in the document Telcordia GR- 468-CORE (Generic Reliability Assurance Requirements for Optoelectronic Devices Used in Telecommunications Equipment). It contains general requirements to reliability of products and components for optoelectronics, as well as methods of their testing.
The TEC test methods stated in Telcordia GR-468-CORE are based on the US military standard MIL-STD-883F. In this standard, the requirements for microelectronics products for military and space applications and test methods of these products are formulated.
Kinds of Tests
Telcordia GR-468-CORE considers two kinds of tests: qualification and acceptance.
The qualification tests are called to establish or confirm quality and reliability of the products. They should include the following tests:
◻ mechanical endurance
◻ environmental factors endurance
◻ reliability (in operating conditions)
Additionally to the list of standard Telcordia GR-468 Tests TEC Microsystems qualifies thermoelectric coolers with Damp Test 85/85 according to IEC61215:2005 and IEC61646:2005 Standards, applicable to PV (photovoltaic) modules.
For thermoelectric coolers manufacturing Telcordia GR-468-CORE established a testing plan included in the program of these qualification tests.
The acceptance tests establish quality of a specific lot of production. The control can be complex (i.e. 100 % products from a lot are controlled) and selective (a sample from a lot is controlled). If the control is 100%, it provides rejection of defective products. If it is selective, it confirms that the quality of products of the given lot is not worse than the average level.
Test Methods
TEC qualification and acceptance tests methods are described in details in the standard MIL-STD-883F. The table below shows the list of Telcordia GR-468 tests applied for thermoelectric coolers in qualification.
|
Method name |
Method type |
Normative document |
Conditions |
Control |
|
Vibration of variable frequency |
Mechanical |
MIL-STD-883F, method 2007.3. Condition А |
Frequency range – 20-2,000 Hz. Pick acceleration – 20g Axis Х,Y,Z |
Visual inspection; Electrical parameters control |
|
Mechanical shock |
Mechanical |
MIL-STD-883F, method 2002.4. Condition B |
Pick acceleration – 1500 g. Pulse duration – 0.5 ms Axis Х,-X, Y, -Y, Z, -Z Number – 5 impacts per axis |
Visual inspection; Electrical parameters control |
|
Lead Integrity |
Mechanical |
MIL-STD-883F, method 2004.5, condition D |
Perpendicularly to the soldering |
Visual inspection |
|
Shear Force |
Mechanical |
MIL-STD-883F, method 2019.7 |
Effort in the parallel plane to the soldering connections. Minimal force – 1.0X Average force – 1.25X Maximal force – 2.0X |
Visual inspection |
|
Temperature cycling |
Environmental |
MIL-STD-883F, method 1010.8 |
Cold Side temperature -40°С Hot temperature +85°С Transfer time – no more than 1 min Soaking time at each temperature – 10 min |
Visual inspection Electrical parameters control |
|
High temperature storage |
Environmental |
Telcordia GR-468- CORE |
Temperature +125 °С Duration 640 hours |
Visual inspection Electrical parameters control |
|
Intermittent Life – Power Cycling |
Operational Reliability |
MIL-STD-883F, method 1006 |
Temperature +85°С On-period – 1.5 min Off-period – 4.5 min Current – Imax Cycles number - 5000 |
Visual inspection Electrical parameters control |
|
Electrical resistance insulation |
Operational Reliability |
MIL-STD-883F, method 1003 |
Ambient temperature 25±10°С; Relative humidity 45 – 80%; Atmospheric pressure 630 – 800 mm Hg DC voltage – not lower than 100 V Time before reading begin – 1 min |
Electric resistance insulation >500 MOhm |
|
TEC electrical and thermal parameters measurement |
TEC Electrical and Thermal Parameters |
ТУ 8420 001 16295994 17, p.4.2.9 |
Residual pressure not more than 1×10-3mm Hg. |
TEC Parameters Imax, Umax, Qmax, dTmax. Compliance with estimated values and specifications data. |
|
Damp Heat Test 85/85 |
Environmental |
IEC 61215:2005 IEC 61646:2005 |
Temperature +85°С Humidity 85% Duration 1000 hours |
Visual inspection Electrical parameters control |
Extensive Temperature Cycling Testing of 1MA10 TEC Series
The 1MA10 Series thermoelectric modules are tested under an extended qualificaton program with a focus on TEC reliability in temperature cycling. Originally designed for cycling applications, the 1MA10 Series modules feature all-metal aluminum circuit boards instead of the traditional TEC ceramic circuit boards. Under typical DNA cycler conditions (ambient/heatsink temperature +40ºC, Heating up to +95ºC 10sec, Cooling down to +45ºC 10sec) the 1MA10 Series modules passed the 1M cycle milestone without failure or loss of key performance parameters.
1MA10 TECs are qualified and tested to real 1M temperature cycles with a median projection of at least 1.5M of operating cycles (using Telcordia GR-468 max 5% ACR change as a criterion of failure).
Thermoelectric Cooler Failure Criteria
According to Telcordia GR-468-CORE, the TEC failure is considered not a TEC complete serviceability loss but the termination of the TEC's ability to operate within previously specified parameters values. Therefore a failed TEC can still function but in a limited way. Telcordia GR-468-CORE suggests the following TEC failure criteria:
◻ An increase of more than 5 % of TEC AC electrical resistance (ACR).
◻ A drop of TEC operational parameters beyond the specified range.
Thermoelectric coolers provided by TEC Microsystems pass through a complex TEC parameters control with the Z-Meter Express Control method. These measured and controlled parameters then are the following:
◻ AC Resistance (ACR)
◻ Figure-of-Merit (Z)
◻ Time Constant (τ)
The measurement of these parameters before and after a test is sufficient for revealing TEC latent defects and their reasons. TEC failure criteria are parameters ACR and Z change of more than 5% compared to the initial values (before the test). It is necessary to note that the 5 % criterion is used for the qualification tests. In the lot-acceptance tests for the temperature cycling method, a more stringent 3 %-criterion of change ACR and Z is applied, which is caused by the accelerated method of these tests with the reduction cycles number down to 10.
Besides measuring the parameters mentioned above, before and after the test, TECs should pass the visual inspection. The failure criterion by the visual inspection after the tests is the appearance of defects that are subject to rejection according to the internal quality control instructions #006-13, regulating the acceptance tests (TEC lot-to-lot inspection. Outgoing control).
Telcordia GR-468 Qualification
The qualification is made once every two years for all Series of thermoelectric coolers provided by TEC Microsystems GmbH. Each qualification takes 6-8 months. The official Reliability Report is released after each qualification. The up-to-date Reliability Report is available by request (subject of NDA). The finished qualification testing program results confirm that thermoelectric coolers provided by TEC Microsystems GmbH fully meet the reliability requirements to thermoelectric cooling modules for optoelectronic applications, established by the Standard Telcordia GR-468-CORE.
Damp Heat Test 85/85
Damp heat test 85/85 is a relatively new requirement for thermoelectric coolers. It's a non-standard test method applied to TECs with a scope on un-sealed open-design applications. It is not included by default in Telcordia GR-468-Core requirements. And it is not described as basic MIL-STD 883 standard.
The test is performed according to IEC61215:2005 and IEC61646:2005 applicable to PV (photovoltaic) modules.
The purpose of the Damp Test is to determine the ability of the thermoelectric modules to withstand the effect of long-term penetration of humidity. Thermoelectric modules are subjected to temperature +85°C and relative humidity 85%RH for 1000 hours in a climatic chamber. Damp Heat Test proves the ability of TECs with a protective coating to withstand the effect of long-term penetration of humidity in un-sealed applications without a controlled environment.
Bottom Line
◻ All thermoelectric cooler series provided by TEC Microsystems GmbH are Telcordia GR-468 qualified
◻ TECs fully meet the reliability requirements established by Telcordia GR-468-CORE Standard
◻ TECs with advanced protective coating all withstand additional Damp-Heat 85/85 Test
◻ 1MA10 TEC Series is tested to 1M cycles in extended qualification with a focus on temperature cycling
◻ The qualification of TE modules is made regularly, every two years, and takes around six months
◻ The up-to-date Reliability Report is available by request (subject of NDA)