10. How do you mount Peltier modules?
1. Important Installation Notes
Peltier modules contain a relatively fragile thermoelectric material and ceramics, they require careful handling and strict compliance with the installation rules. Failure to meet these rules may result in reduced Peltier module performance, lower life time or complete breakdown.
When installing Peltier modules, pay attention for the following recommendations:
1) Impacts, dropping of the module on a hard surface etc. may cause irreparable damage to the module.
2) The mounting surfaces (between which modules are to be clamped) should be flat to within 0.025 mm (0.001 inch).
3) Module surfaces must have a good thermal contact with the cooled object and heat-eliminating surface.
4) Avoid excessive mechanical loading of the module for（since） the modules are relatively strong in compression and weak in shear.
5) Do not use acuminate tool to position the modules to avoid break the thermoelectric material.
6) The force on the wire cannot be in the direction of up and down or left and right besides the Lead-Out direction.
7) Accurately spot the hot side and cold side of the module.
The "hot" and "cold" sides of standard Peltier modules may be identified by the position of the wire leads. Wires are attached to the hot side of the module, which is the module face that is in contact with the heat sink. For modules having insulated wire leads, when the red and black leads are connected to the respective positive and negative terminals of a DC power supply, heat will be pumped from the module's cold side, through the module, and into the heat sink. Note that for Peltier modules having bare wire leads, the positive connection is on the right side and the negative connection is on the left when the leads are facing toward the viewer and the substrate with the leads attached presented on the bottom.
2. System Assembly
Several methods for installing Peltier modules have been developed, including: mechanical lamping, epoxy bonding, and direct solder bonding. The individual requirements of the application will determine which method is most appropriate, however, mechanical clamping is by far the most common.
Mechanical Clamping Method:
The following is a list of guidelines for using mechanical clamping:
1) Lap or grind all the mounting surfaces flat to within 0.025 mm (0.001 inch).
2) Clean the mounting and module surfaces to ensure all burrs, chips, etc have been removed.
3) If more than one module is to be used in the assembly, all modules should be within 0.025 mm (0.001 inch) in height/thickness.
4) Coat the hot side of the module with a thin layer of thermal grease, then place it on the heat sink. Applying firm but even downward pressure, move the module in clockwise/counter clockwise motions. Do this until a slight resistance is felt and excess thermal grease is squeezed out.
5) Coat the cold side of the module with a thin film of thermal grease. Repeat the process described in step 4.
6) Apply a light load in line with center of module by using clamp or weights, and locate bolt holes in your assembly such that they are at opposite sides of the center of the module between 1.6 mm to 12.7 mm (0.063 to 0.5 inches) from the sides of the module as Fig. 4.
7) Bolt the object to be cooled and heat sink together using stainless steel fasteners with washers or split type lock-washers. Insure an even pressure across the module surface when tightening the screws. The recommended compression for a TEC assembly is 70~130 Kg per sq. inch of module surface.
Fig. 4 Diagram of mechanical lamping installation
Calculation of Peltier module clamping force
Torque (Т) of the torque wrench may be calculated with the following formula:
T (torque) = (2.8 × 10-4 × p × d)/n, (kg × m)
where: p is required clamping force (kg)
d is screw diameter (mm)
n is number of screws (2-4) used for module installation.
Example: Installation of a 40 × 40 mm module (e.g. TEC1-12708) requires a total hold-down force of 210 to 240 kg.
Peltier modules that have metallized external faces may be soldered into an assembly provided that reasonable care is taken to prevent module overheating. Soldering to a rigid structural member of an assembly should be performed on one or two side of the module in order to avoid excessive mechanical stress on the module. Note that with a module's hot side soldered to a rigid body, however, a component or small electronic circuit may be soldered to the module's cold side provided that the component or circuit is not rigidly coupled to the external structure. Good temperature control must be maintained within the soldering system in order to prevent damage to the Peltier module due to overheating. Thermonamic`s Peltier modules are rated for continuous operation at relatively high temperatures (100 or 270°C) so they are suitable in most applications where soldering is desirable. Naturally these relative temperatures should not be exceeded in the process. Since the coefficients of expansion of the module ceramics, heat sink and cooled object vary, we do not recommend soldering modules larger than 15 × 15 mm. Soldering should not be considered in any thermal cycling application. For module mounting with solder, the following steps should be observed:
1) Machine or grind flat the mounting surface on which the module(s) will be located. Although surface flatness is not highly critical with the soldering method, it is always desirable for mounting surfaces to be as flat as possible. Obviously, the heat sink surface must be a solderable material such as copper or copper plated material.
2) Clean and degrease the heat sink surface and remove any heavy oxidation. Make sure that there are no burrs, chips, or other foreign material in the module mounting area.
3) Pre tin the heat sink surface in the module mounting area with the appropriate solder. The selected solder must have a melting point that is less than or equal to the rated maximum operating temperature of the TE device being installed. When tinning the heat sink with solder, the heat sink's temperature should be just high enough so that the solder will melt but in no case should the temperature be raised more than the maximum value specified for the TE device.
4) Apply soldering flux to the Peltier module's hot side and place the module on the pre tinned area of the heat sink. Allow the module to "float" in the solder pool and apply a back and forth turning motion on the module to facilitate solder tinning of the module surface. A tendency for the module to drag on the solder surface rather than to float is an indication that there is an insufficient amount of solder. In this event, remove the module and add more solder to the heat sink.
5) After several seconds the module surface should be tinned satisfactorily. Clamp or weight the module in the desired position, remove the heat sink from the heat source, and allow the assembly to cool. When sufficiently cooled, degrease the assembly to remove flux residue.