The Peltier module is an excellent cooling solution, ideal for high density, high power medical and industrial applications as well as refrigeration and sealed environments where forced air cooling is not an option. This article will show you the functional characteristics of Peltier modules, as well as the features and advantages of the Peltier module offered by CUI Devices.
Gain better cooling capacity from the application of the Peltier effect
The Peltier module, also known as a thermoelectric cooler (TEC) or thermoelectric module (TEM), is a solid-state device with no moving parts that transmits heat when energized, and can operate over a wide range of temperatures. It is theoretically based on the Peltier effect, which was discovered in 1834 by Jean Peltier, a French physicist.
The Peltier module is structurally composed of positive and negative doped pellets of semiconductor material placed between two electrically insulated but thermally conductive ceramic plates. A conductive pattern of metal material is plated on the inner surface of each ceramic plate, on which the semiconductor pellets are soldered. This module configuration enables all semiconductor pellets to be connected in series electrically and mechanically in parallel. The desired thermal effect is provided from the electrical connection in series, while the mechanical parallel connection allows heat to be absorbed by one ceramic plate (cold side) and released by the other ceramic plate (hot side).
Common causes of failure in typical Peltier modules
The most common failure in the Peltier module is the mechanical fracture of a semiconductor pellets or associated solder joints, which does not initially propagate entirely through the pellet or the solder joint and can be detected by the rise in the device’s series resistance. The rise in the resistance of the Peltier module may lead to decreased overall "efficiency", but the fracture rupture that entirely propagates to the semiconductor pellet or the solder joint can cause complete failure.
In a typical application of the Peltier module, the object to be cooled is placed on the cold plate of the module and a heat sink is placed on the hot side. In the case of the heat sink and the object to be cooled adhering to the ceramic plate, the absence of any other mechanical structure to support the cooled object and the heat sink is likely to cause mechanical failure. Supporting the object or the heat sink solely using the Peltier device may impose a large shear or tension load on the module. The Peltier module cannot withstand the high tension or shear force between the heat sink and the cold plate, and may fracture in the event of excessive force.
In most applications, the heat sink is clamped together with the object to be cooled, with the Peltier module placed in between. This mechanical configuration is made possible by the fact that the Peltier module can support large compressive forces from the clamps, which can absorb any shear or tension stress between the object and the heat sink.
Despite the capability of the Peltier module to withstand large compressive loads, the heat sink and the object to be cooled must be clamped even across on the Peltier module, or the torque and compressive forces between the ceramic plates can result in mechanical failure. Mechanical constraints that generate compressive clamping forces on the Peltier module must be carefully and evenly applied to minimize torque stress applied to the Peltier module and minimize the possibility of damage.
In addition, the ceramic plates and semiconductor pellets for constructing the Peltier module have related coefficients of thermal expansion (CTE). A mismatch between the ceramic and the semiconductor CTEs can cause mechanical stress. In the case of modules being heated or cooled, it can cause fractures in the semiconductor pellets and solder joints. In addition to the absolute temperature change of the Peltier module, the thermal gradients on the device and the rapid change rate of its temperature can also cause mechanical stress as a result of the CTE. Operation at extreme temperatures, large temperature gradients and high temperature slew rates can increase mechanical stress and lead to device failure.
Possible external contamination of semiconductor pellets, solder joints, and metalized conduction paths in the Peltier module may also lead to failures. The common solution to minimize contamination exposure is to apply sealant beads around the module between the two ceramic plates. The mechanical flexibility of the material makes silicone rubber a common sealant, but it may not be effective as a vapor barrier in harsh operating environments. Epoxy resins can be used as peripheral sealants in the presence of high vapor concentration, but epoxy resins generally do not have the mechanical compliant of silicone rubber.
Peltier modules with arcTEC™ structure perform even better
As mentioned above, the solder joints and semiconductor pellets of the Peltier module can crack under mechanical stress. CUI Devices has developed Peltier modules with arcTEC™ structure. Their unique structure enables them to resist thermal fatigue, thus improving the module performance, reliability, and cycle life.
Firstly, Peltier modules with arcTEC™ structure from CUI Devices have solder joints on the cold side of the modules replaced with conductive resin. This resin, which is mechanically more flexible than solder, allows thermal expansion and contraction during repeated thermal cycles of the Peltier modules, and helps to minimize the stress and fracture in traditional Peltier module structures, resulting in better thermal connection, superior mechanical bonding, and performance that does not significantly deteriorate over time.
The remaining solder joints in the arcTEC structure are made of high-temperature antimony solder (SbSn, 235°C) in place of the more common low-temperature bismuth solder (BiSn, 138°C). Antimony solder is more resistant to mechanical stress than bismuth solder, and its excellent thermal fatigue resistance and better shear strength contribute to improving the reliability of the Peltier module. The Peltier module from CUI Devices also comes with a silicon rubber moisture-proof layer for mechanical compliance. Other moisture-proof layers, such as epoxy resin, are available on request.
Under the combined action of thermally conductive resin and SbSn solder joint in the arcTEC structure, the reliability and service life of the Peltier module are greatly affected. There is a direct correlation between the life expectancy of the Peltier module and the quality of the bonds, and the failure is mainly due to the increase of resistance in the module from thermal fatigue of the bonds within the module. This effect is further complicated by internal stresses that occur during repeated thermal cycles. At more than 30,000 thermal cycles, the resistance change of the Peltier module with arcTEC structure is negligible, giving it excellent performance.
In addition to superior reliability and module life, the Peltier module with arcTEC structure provides enhanced thermal performance. In the Peltier module, the integrated P/N elements made from premium-quality silicon ingots is 2.7 times the size of the elements used in other thermoelectric modules on the market. Since larger elements produce faster and more uniform cooling, this can have a significant impact on thermal performance. The infrared inspection of the unit constructed by the arcTEC structure shows a uniform temperature distribution on the surface of the ceramic substrate.
In contrast, conventional units exhibit multiple temperature variations, indicating a higher risk of decreased cooling performance and shortened service life. These temperature variations may be caused by inferior P/N element quality, small element size, or poor solder quality within the module. The use of modules with larger P/N elements allows for faster cooling without a drop-off in performance. Field tests show that the modules with arcTEC structure have improved cooling time by more than 50% compared to competing modules. This significant difference can be attributed to the size and quality of the P/N elements and the higher reliability of the arcTEC structure. An increase in the number of thermal cycles and resistance change in conventional modules will widen the gap.
Diversified Peltier module series to meet different application needs
Included in the high-performance Peltier module series of CUI Devices are single-stage Peltier modules with a compact, lightweight shape and solid state without moving parts. Precise temperature control and response allow it to evolve into a highly reliable cooling solution. The additional multi-stage Peltier module is able to achieve higher temperature increments of up to 105°C by stacking two modules to increase heat pump capacity, while maintaining the solid-state advantages of the single-stage thermoelectric cooler. In addition, the better water resistance and thermal stress absorbing leakproof structure of the Peltier cooling unit allows for better heat absorption, improved performance and easier installation without the need for tightening screws.
CUI Devices provides the series of high-performance Peltier modules in sizes from 3.4 mm to 70 mm, a profile as low as 1.95 mm, ΔTmax up to 95°C (Th=50°C), rated current from 0.7 A to 20 A, and temperature increments from 70°C to 105°C. The reliable solid-state construction, precise temperature control, and quiet operation capabilities of these Peltier modules make them ideal for medical and industrial applications and designs where forced air cooling is not an option. For more information about Peltier modules from CUI Devices, please visit the website of Arrow Electronics: https://www.arrow.com/en/products/search?cat=&q=Thermoelectric%20Cooler%20Peltier%20Modules%20CUI%20Devices&r=true
Conclusion
CUI Devices' Peltier modules, which focus on mitigating the effects of thermal fatigue and optimizing P/N elements, perform far better than thermoelectric coolers with conventional structures. Given that these enhancements implemented in the arcTEC structure collectively provide the improved performance and reliability required for the most demanding applications, these Peltier modules become the ideal choice for high-density, high-power medical and industrial applications.