TEC Microsystems - Miniature Thermoelectric Coolers and Sub-Assemblies

ISO9001:2015 Certified

Z-METER - WHY IT IS NECESSARY WHEN YOU WORK WITH TE COOLERS


Thermoelectric cooling is now common in many applications. Thermoelectric coolers are widely used in many areas - from simple consumer applications like wine chillers or huge automotive industry with HVAC systems to hi-tech laser and optoelectronics applications with temperature stabilization applied in optical transceivers or for deep cooling of X-Ray and IR detectors.


TEC is a solid-state heat pump. TEC has no moving parts, available in a very wide dimension range from 1x1mm2 to 50x50mm2, highly reliable and flexible in design to meet particular requirements. With recent advanced miniaturization achievements, thermoelectric coolers have become standard for semiconductor lasers in the telecom industry, mainly in applications with fiber-optical transmitters, where TECs stabilize the laser's temperature inside. One of the thermoelectric cooler's key advantages is its long lifetime, 25-30 years and even more continuous operating. And what is essential - it's maintenance-free operating.


In terms of construction, TEC is quite simple at first sight - in most cases it's about two ceramics plates (for a single-stage TEC), BiTe posts in between and terminal wires or WB pads for power supply. In some cases, the visually simple construction suggests that a thermoelectric cooler is as simple and easy to handle and mount as some brick. But dozens of small and big factors may influence TEC lifetime and create severe damage or improper operating risks.


single stage TE Cooler construction

Let’s take a simple example from some X-Ray detector applications. A thermoelectric cooler is mounted by epoxy on the TO-8 header with the following detector unit mounted on TEC cold side, all related wire bonding applied, baking processing and final sealing with a cap.

There is also a certain risk of TE cooler damage inside a final product during transportation to the end customer - for example, a heavy object attached on TEC cold side with vibration or occasional drop during the transportation. There are other factors, sometimes invisible - for instance, assembly solder diffusion in BiTe material inside TEC, solder cold joint connections, partial cracks or detachment of pellets in TEC and many others. These factors are not considered and not appropriately checked, leading to significant risks, reduced TEC lifetime, risks of poor

cooling performance, and TEC failures.


A thermoelectric cooler is a key component of active temperature stabilization. Once TEC is a part of more complex and way more expensive components/systems, its failure at the final assembly stage or after delivery to the end customer leads to severe losses in resources and reputation. If it’s installed properly, it operates for years; but once it fails, the entire system fails as well. Thus TEC is a subject of detailed 100% inspection during every stage of the manufacturing/integrating process. It means you need to check and control TEC parameters before and after every assembly stage with impacts that may have a risk to affect TEC conditions.  


And here comes a question - what TEC parameters to control and how? The most common method is TEC AC Resistance (ACR) checking. Significant TEC AC Resistance (ACR) growing means mechanical damages inside TEC in most cases. A sudden ACR drop may indicate a partial shortcut between pellets inside - for example, dew point and moisture inside or some electroconductive material getting inside TEC. Profound ACR change (more than 5% from nominal value) points to serious TEC problems.


Electronics Industry Standard Telcordia GR-468 (based on MIL-883) set 5% ACR change as a failure criterion. In fact, it means that TEC may continue to operate, but specific destructive processes are already present. For example, micro-cracks in BiTe posts material, which will grow with time and lead to complete failure. So, ACR change beyond the 5% limit already means that TEC should be rejected in proper quality control. In practice, TEC ACR is to be checked and compared on a “before-after” basis for any impact to TEC. This allows identifying damages and all risky mounting procedures with TEC. It is important to note here that TEC ACR always to be compared at the same ambient temperature because it depends on the ambient temperature. TEC ACR grows with ambient temperature roughly by 0.5% per 1ºC. It means that if you checked TEC ACR at 22ºC before mounting process, you should measure it again after - also at 22ºC, or recalculate the value to the same ambient temperature. Otherwise, there will be a distortion.

Possible risks and impacts to TE Cooler during handling and integrating

But there are situations with ACR staying pretty much stable, while thermoelectric cooler performance is getting worse. For example, this can result from thermoelectric material degradation, connected to the operating at too high temperature, or TEC electrical power supply exceeding recommended TEC Imax/Umax limits. For this case, it is not sufficient to check ACR only. There should be additional criteria for TEC testing.


Finally, there are situations with TEC conditions OK, but overall performance is far from expected. For this case (if skipping an excessive heatload and similar factors), TEC mounting can be a problem. For example, poor contact to a heatsink, voids in glue or solder layer between TEC and heatsink, TEC detachment from the heatsink. For such a case, a simple ACR check doesn’t work. There should be other testing criteria. Thus we are back to the main question - what are the key TEC parameters to control, and how to check them. And the reply here is - Peltier Z-Meter.

Z-Meter is a device for express TEC quality control and testing, developed by our specialists experienced with all aspects in TECs manufacturing and handling. Z-Meter uses the Harman method and directly measures three key parameters of the thermoelectric cooler: TEC AC Resistance (ACR), Figure-of-Merit (Z) and Time Constant (t). ACR value is required for comparative analysis. Figure-of-Merit (Z) value characterizes TEC quality and performance level. Time Constant shows the "TEC cooling rate" in simple words - the time TEC requires from start till the stable cooling mode level.


The combination of these three parameters gives detailed info about TEC performance, quality and conditions. TEC ACR, Z and t are required for proper and thorough quality control by thermoelectric coolers manufacturers and users. Here is the table with key parameters combinations:


Z-Meters can be used both - by TEC manufacturers and TEC consumers. The most significant benefit of Z-Meter is implementing express testing for all TECs in the manufacturing or assembly process and applying 100% QC in manufacturing. The measurement process takes 20 to 180secs (depending on TEC type), it’s non-destructive, has no effect on TEC visual conditions and gives the complete info about TEC with three key parameters. With Z-Meter you may test all mounting/assembly processes with TECs, analyze the risks and develop the most optimal and safe TEC mounting methods.


What is also essential - Z-Meter allows analyzing TEC quality and performance level using Figure-of-Merit as a key criterion. This is important for big projects where several TEC suppliers are involved. All provide the same solution, but the certain difference in quality and performance always present. It’s possible to compare the same TEC solution from multiple TEC vendors in your project and select the best one. Figure-of-Merit (Z), being measured directly by Z-Meter, allows calculating actual TEC dTmax level for a single-stage TECs.


FOR SEPARATE (NOT MOUNTED) THERMOELECTRIC COOLER

#

Reasons of Defect

AC Resistance ACR

Figure-of-Merit Z

Time Constant τ 

Comment

1

Metal junctions detachment

~ const

~ const

 


2

Confused p-n pellets polarity

~ const

 

 τ ~ const @ low current

3

Thermal Contact between Pellet Side Wall and Solder Meniscus

~ const

 

 


4

Thermal and Electric Contact of Pellet Wall and Solder Meniscus

 

~ const

 


5

 TEC Pellets Short Circuit

 

 

 


6

Two-stage TEC: confused stage polarity

~ const

~ const

 τ twice lower to nominal value 

7

TE material Degradation

 

 

~ const



FOR MOUNTED (INTEGRATED) THERMOELECTRIC COOLER

#

Reasons of Defect

AC Resistance ACR

Figure-of-Merit Z

Time Constant τ 

Comment

1

Operational Degrading of a TE module

 

 

or  


2

Poor integrating of a TE Module into the Package

~ const

 

 

twice lower τ means total detachment 

3

Faulty mounting of a cooled object onto the TE module

~ const

~ const

 


4

Environment violation in a TE module construction

~ const

 

 



With Z-Meter you may build efficient income TEC QC, check and analyze all the aspects of your TEC integrating process, study difficult moments in your TEC mounting process and analyze impacts that affect TEC conditions. Z-Meter helps to reduce or eliminate the risks of TEC damages during mounting/handling. It saves time and money. With Z-Meter you may check every assembly step using “before-after” criteria and be sure that TEC was not damaged. It means that after final assembling/sealing you get confidence in TEC actual operating parameters, cooling performance and expected lifetime.


Z-Meters are necessary for failure analysis as well. It’s possible to identify mechanical or overheating reasons of TEC failure. This is important if you deal with some already sealed device having TEC inside but not accessible for visual inspection. For example, a portable X-Ray detector with a thermoelectric cooler inside was dropped, TEC has malfunctions and poor cooling performance after - it’s possible to identify with Z-Meter the character of damage w/o entire device disassembly. ACR check will point to mechanical damage of TEC. TEC Time Constant reduction will tell about a partial or complete TEC detachment from a header inside the device.


Here is another use-case - LD optical transmitter with TEC inside, a particular drop of cooling performance, while TEC ACR is OK. Check TEC Figure-of-Merit (Z). If it’s lower than initial Z values, you probably deal with BiTe material degradation resulting from operating at too high temperature. Thus Z-Meter allows identifying the reasons of failures for warranty service. Z-Meters are the ultimate instruments for TECs analysis and QC, with many possible methods and ways to use them.


Z-Meter devices are available in four versions.  There are Z-Meter Mini (DX4095), Z-Meter DX4090, multi-position Z-Meter DX4190 and portable autonomous Z-Meter Tester (DX4085).  The measuring methodic is the same for all Z-Meters. The differences are in application purpose, some extra features and TEC terminal interfaces.


Same TE Cooler solution from different manufacturers

DX4095 Z-Meter Mini is a pocket-size TEC tester, as small as a USB flash drive. DX4095 is optimal for small TEC batches testing, R&D analysis, an occasional quick check of suspicious TEC or assembly with TEC. The device has only external clips for terminal connection to TEC.


DX4090 Z-Meter is a universal laboratory device suitable for R&D analysis and occasional QC testings or regular QC procedures for small and mid-size batches in manufacturing. DX4090 has two terminal interfaces - external clips (the same as Z-Meter Mini) and an internal chamber with clips for the batch measuring process. In brief words, separate (not mounted TECs) are easy to control with internal chamber testing, while mounted (integrated) TECs you can reach using external clips. DX4090 has a stable metal housing that works as a passive thermostat during measuring in the internal chamber. This is important if you check very miniature TECs, so small that they are sensitive even to air flows in the room.


DX4085 is a portable autonomous Z-Meter, developed as a stand-alone TEC Tester. It has a built-in Li-Ion battery, 2.4" LCD screen for the information output. Additionally to ACR, Z and Time Constant DX4085 can monitor TEC operating voltage and temperature (using the external thermal probe).

Finally, DX4190 is a 10-position Z-Meter, a must-have device for volume manufacturers with large TEC batches testing. It measures 10x TECs at once, which significantly accelerates the QC process. And it's more efficient and affordable by price and usage than 10x separate Z-Meters in the lab or QC department.


All Z-Meters can be equipped by request with extra accessories for additional measuring process simplification - special clips for TECs w/o wires (with WB pads or posts), sub-assemblies in standard headers (for example, "Butterfly" package with TEC inside, or TEC on TO-8. It's possible to provide even special heating tables to use with Z-Meter and analyze for example, TEC ACR dependence on the ambient temperature.


TEC Microsystems GmbH provides the entire range of Z-Meter devices with all necessary instruments for efficient TEC quality control.

Z-Meter DX4090 with Measurement Chamber opened
Z-Meter DX4090 with Measurement Chamber opened
Z-Meter DX4090 with 2-stage TEC setup for measurement process
Z-Meter DX4090 with 2-stage TEC setup for measurement process
DX4090 Z-Meter with external clips cable attached
DX4090 Z-Meter with external clips cable attached
DX4090 Z-Meter USB and external measurement cables attached
DX4090 Z-Meter USB and external measurement cables attached
TEC on a header measuring process with Z-Meter external clips
TEC on a header measuring process with Z-Meter external clips

Z-Meter is a must-have device for any company that seriously works with thermoelectric coolers or devices with integrated TECs. TEC Microsystems provides an entire range of Z-Meter devices with accessories and, if required, customization for customer application.


TEC Microsystems also develops and integrates the comprehensive TEC R&D and quality control systems for customers working with thermoelectric coolers and generators.

How many risks may be available here? Quite a lot of them:

  • First, there is a certain risk of improper TEC quality provided by vendor - manufacturing and quality control level risks. Even in case of very reliable and well-known TEC manufacturer, certain risks are present and have to be taken into account.
  • There is a transportation from manufacturer to customer with all related risks of possible impacts and damages (packing conditions, ambient conditions, vibration, mechanical shocks, unexpected accidents/drops and etc)
  • TEC Storage conditions after delivery and before assembly (stock temperature and humidity, mechanical impacts, unexpected accidents).
  • Thermal shocks, mechanical impacts, overheating during TEC mounting (all the related soldering processes, heating and cooling impacts, WB processes, baking/annealing - can be applied to TE cooler multiple times).
  • Material CTE mismatches (for example, TEC mounting on Copper or Aluminum), multiplied by thermal shocks during soldering or baking processes.
  • All mechanical impacts during mounting and/or WB processes (compression forces, shear forces, vibration and etc).
  • Thermal and mechanical impacts during final sealing (header cap welding process, for example).
Z-Meters (TEC Testers) - instruments for TE Coolers quality control

DX4190 - 10position Z-Meter for volume manufacturers


Z-Meter DX4190 is the must-have device for TEC manufacturers or consumers with serious TEC volumes. DX4190 provides 100% Quality Control for thermoelectric coolers in all stages of mass production with no compromises. The device  measures TEC key parameters  for up to 10 thermoelectric coolers simultaneously. DX4190 can be used with separate (not mounted) TECs by manufacturers or consumers at income/outcome control, or TECs quality control and performance testing in the end-product with thermoelectric cooler integrated.


DX4085 TEC Tester - compact stand-alone Z-Meter


DX4085 Z-Meter Tester is a portable measuring device for thermoelectric coolers express analysis. The device measures directly three key parameters (AC Resistance, Figure-of-Merit and Time Constant) of separate or integrated (mounted)  thermoelectric coolers. DX4085 has 2.4" LCD screen, built-in Li-Ion battery for up to 8 hours operating, it is autonomous and doesn't require a constant connection to PC. All necessary settings, measuring process results and history are displayed and adjusted on LCD screen. The device has a miniature, pocket size form-factor and it's ideal for engineers and researchers dealing with TECs every day.  


DX4090 Z-Meter Classic


DX4090 device has two measurement interfaces - an internal chamber (works as a passive thermostat) with connectors and an external interface with clips. DX4090 has also a built-in temperature sensor for accurate TEC ACR calculations and a heating element for TEC quick polarity. DX4090 is recommended for regular express quality control of small and mid-size TEC batches, R&D analysis and TEC integrating/assembly process control and optimization.


DX4095 Mini - Z-Meter in USB-stick


Z-Meter Mini DX4095 is a portable TEC tester for thermoelectric coolers express analysis. The device has ultra-miniature, pocket size form-factor and it's ideal for engineers and researchers dealing with TECs. Due to a very small size DX4095 has only external measurement interface - external clips - connected to Z-Meter.  DX4095 has also a built-in temperature sensor for accurate TEC ACR calculations.  DX4095 is recommended for regular express quality control of small TEC batches, occasional QC testing, R&D analysis and TEC integrating/assembly process control and optimization.