TEC Microsystems - Miniature Thermoelectric Coolers and Sub-Assemblies

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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

     ◻ The qualification is made regularly, every two years

     ◻ 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 any moving parts.  Many thermoelectric coolers (TECs), miniature types in particular, 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 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.

All 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 to products of microelectronics 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)


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
Cycle per axis – 4 minutes Cycles number – 4 per axis 


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
plane. Pull force – not less than 2.22 N 


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 

Hot temperature +85 °С Transfer time – no more than 1 min Soaking time at each temperature – 10 min
Cycles number - 500 


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±10oС; 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, п.4.2.9 


Residual pressure not more than 

1×10-3 mm Hg.
TEC hot surface temperature 27±1
ОС 


TEC Parameters Imax, Umax, Qmax, dTmax.  Compliance with estimated values and specifications  data.


Thermoelectric Cooler  Failure Criteria


According to Telcordia GP-468-CORE the TEC failure is considered not a TEC full serviceability loss, but the termination of the TEC ability to operate within previously specified parameters values. Therefore a failed TEC can still operate but in a limited way.  Telcordia GP-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 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 as well as their reasons. TEC failure criteria are parameters ACR and Z change of more than 5% in comparison with the initial values (before the test).  It is necessary to note that 5 % criterion is used for the qualification tests.  In the lot-acceptance tests for the method of temperature cycling 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 the measurement of the above-mentioned parameters, 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 per 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'2017 is available by request (subject of NDA).  The results of the finished qualification testing program confirm that thermoelectric coolers provided by TEC Microsystems GmbH, as of the year 2017, fully meet the reliability requirements to thermoelectric cooling modules for optoelectronic applications, established by the Standard Telcordia GR-468-CORE.

The next complex qualification testing program will be carried out in 2019.



Bottom Line


     ◻ All thermoelectric cooler series provided by TEC Microsystems GmbH are Telcordia GR-468 qualified

     ◻ TECs fully meet the reliability requirements testablished by Telcordia GR-468-CORE Standard

     ◻ The qualification is made regularly, every two years

     ◻ The up-to-date Reliability Report (2017) is available by request (subject of NDA)

     



CONCLUSIONS

Up-to-date Reliability Testing Reports

CRITERIA

Reliability testing PASS/FAIL criteria

STANDARDS

Reliability Standards

for TE Coolers

METHODS

TEC Reliability

Testing Methods