Assembly of TEGWAY's FTED (Flexible Thermoelectric Device)

TEGWAY's FTED (Flexible Thermoelectric Device) has a unique structure compared to conventional thermoelectric devices in that it does not use a ceramic substrate. Therefore, the assembly procedure and method differ from the general assembly methods based on conventional thermoelectric devices such as clamping and epoxy bonding. Special management is required in the assembly process.

1) Considerations

FTED (Flexible Thermoelectric Device) does not use a ceramic substrate and has exposed electrodes on both sides of the thermoelectric device. Therefore, it should not be directly attached to surfaces with electrical conductivity, such as heat sinks and cooling targets. In particular, in the case of thermoelectric cooling, it can cause serious damage to the system as well as electric shock and injury to the human body.

Fig 1. A photo of the FTED product (Tegway, model S090A021079)

○ In addition, in the case of thermoelectric power generation, current can bypass through the conductive junction surface, reducing the risk of bodily harm, but the power generation efficiency is greatly affected. 

○ Therefore, to manufacture a thermoelectric system using FTED, an insulation layer must be formed on the surface of the heat sink (and the target object) or a new insulation layer using insulating film must be introduced onto the FTED surface for assembly of the system.

 Fig 2. Assembly of thermoelectric devices using insulation films 

2) Assembly on an insulating surface. (for Aluminum Heat Sink)

○  Aluminum heat sinks can easily create an electrically insulating film by anodizing treatment. Anodizing is a method of forming a stable, passive insulating film and allows for control of film thickness through process control. It is an economically efficient way to form an insulating film.

○  In the case of attaching FTED to the heat sink with an insulating film, the system can be assembled using a clamping method with thermal grease. The standard clamping procedure can be followed.

○  It is recommended to apply the thermal grease with a minimum thickness of ~20 μm, filling the roughness (surface unevenness) of the joining interface. Increasing the thickness of the thermal grease increases the interfacial thermal resistance, and excessive thickness can penetrate the polymer layer inside the FTED and decrease the thermoelectric performance.

Fig 3. Assembly of Anodized Heat Sink and FTED 

3) Assembly on Conductive Surfaces

○ When the joining surface of the heat sink or target object has a conductive surface, the system is assembled using a high-heat conductive and electrically insulating film.

○ The insulation film joining method uses a double-sided adhesive film as the basis for assembling the thermal system, and a graphite film for heat diffusion can also be placed between the product (heat sink, target object) and the insulation film attached to the FTED surface.

 - Double-sided insulation film(tape)

 - Graphite film(sheet)

○ First, the double-sided insulation film can be purchased as a 'high-heat conductive double-sided tape' made of a high-heat conductive electrical insulation film. To reduce the thermal resistance at the joining interface, a thickness of around 5 μm is recommended, and a product with an insulation resistance of 20 mΩ or more (50DCV) should be selected.

○ The attachment sequence involves first attaching the double-sided tape to the FTED by removing one side of the protective film of the double-sided tape. At this time, if the double-sided tape is first attached to both sides of the FTED, the flexibility of the FTED cannot be expected since the same tension will act on both sides of the thermal element.

Fig 4. The attachment order of the double-sided tape

○ Therefore, after attaching the tape to one side of the FTED and peeling off the remaining protective film, attach it to the heatsink (or product), and then sequentially attach the tape and product (or heatsink) to the opposite side of the FTED to complete the system assembly.

○ If mechanical fastening (clamping) is possible between FTED and the product, the system can be assembled by applying thermal grease and clamping while not peeling off the opposite protective film of the double-sided tape attached to the FTED. (In this case, a single-sided tape can be used instead of the double-sided tape.)

Fig 5. The attachment order of the double-sided tape 

○ Next, a graphite film (graphite/protective film) can be attached on top of the double-sided insulating film (tape) to assemble the system. Alternatively, an insulated graphite film composed of graphite/insulating film (PET)/protective film can be used alone by attaching it directly to the thermoelectric element.

○ Graphite film has excellent horizontal thermal conductivity, allowing for uniform heat absorption (or dissipation) over the entire attachment surface of the thermoelectric element, which can improve the overall efficiency of the thermoelectric system.

○ After peeling off the protective film of the film, it can be attached to the surface of the thermoelectric element on top of the double-sided insulating film, or in the case of an insulated graphite film, it can be attached directly to the thermoelectric element to secure insulation and enable uniform heat diffusion. Depending on the configuration of the system, it can be applied to one or both sides of the thermoelectric element simultaneously.

○ The attachment method always starts from one side of the thermoelectric element, and care should be taken to prevent air bubbles from entering the joint. If different types of films (double-sided insulating film vs. graphite film) are used on both sides of the thermoelectric element at the same time, caution should be exercised as the element may bend during use.

Fig 6. Assembling thermoelectric modules using graphite film