About failure reasons
Reliability and product life is decided by the solder connections.
Thermoelectric cooler (module) is constructed of numbers of P-type and N-type thermoelectric chips and soldered together with copper electrode formed on ceramic.
The number of soldering connections of thermoelectric coolers (modules), in the most common case 127 pairs module, is 508 points. If the lead wire portion is included, there are 510 points of soldering connections. Because the electrical circuit is in series, 1 point of 510 solder connection’s life will decide a whole thermoelectric module’s life.
Typical failure reasons
Depending on use conditions for application, the reasons for failure of thermoelectric coolers (module) are different. Typical failure reasons are in the following table. Please refer to the detailed description of each failure reason.
| Failure Reason | Phenomenon | Happening Condition | Solution |
|---|---|---|---|
| Thermal cycle fatigue | Cracks happen and intensify on the connection between the thermoelectric chip and the copper electrode, or on the thermoelectric chip itself, and finally, burn out and cannot be operated by electricity. | Temperature difference (ΔT) at operation is large or the machine with high thermal cycle frequency. | GL structure |
| Corrosion | Copper electrode connection solder, lead wire, or solder, etc. become eroded and cannot be operated by electricity. | Machines with a structure that can be penetrated by humidity like condensation water, etc are vulnerable. | Humidity protection sealing |
| Migration (short ~ breaking of wire) |
With condensation, the solder between thermoelectric chip and copper electrode causes migration with cooper electrode, gradually internal resistance is goes down, and finally results in no cooling ability. | Machines with a structure that can be penetrated by humidity like condensation water, etc are vulnerable. | Humidity protection sealing |
| Crystal defect of thermoelectric element | In case of inclined cleavage plane of thermoelectric element it may lead to burning out of TE element due to concentrated joule heat. | Is vulnerable if there is a TE element which includes inclined cleavage plane. | Carry out QC fully |
About thermal cycle fatigue
This is the most typical failure of thermoelectric coolers (modules), which happens naturally on the solder connection between thermoelectric chip and copper electrode or around thermoelectric chip itself. Because a thermoelectric cooler is a device utilizing the temperature difference (ΔT) between the heat absorption (low temperature side) and heat dissipation (high temperature side), it generates thermal stress naturally. The largest thermal stress is located on thermoelectric element or junction at the corner of thermoelectric cooler (module), which starts causing cracks from thermal cycle fatigue and intensifies intensive slowly. Along with cracks developing, the crack surface will be oxidized, the resistance of that portion will go up, and due to the increasing joule heat, the partial temperature goes up. Finally it will burn out or the solder and thermoelectric elements will be melted and cause the breaking of wire.
About corrosion
If the machine needs to be operated at a lower temperature than room temperature, dew formation is unavoidable. This dew water stays in the thermoelectric cooler (module), and corrosion will happen on solder parts first. Since the solder connecting part has contact with different metal and solder includes base metals, it will be corroded first. If the corrosion intensifies, copper electrode will be corroded as well. Finally, no matter which case happened, the circuit will be cut off and its life ended.
About Migration (short ~ breaking of wire)
Same as corrosion, this happens under the use condition that promotes dew formation. When the dew water is in series with electrodes, the solder component elutes and moves due to the difference in potential existing between electrodes, and metallic ion density will increase, then precipitation will form on the ceramics. The short circuit will be caused by this repeating elution movement and precipitation. As a result, the internal resistance of the thermoelectric cooler (module) decreases gradually, and then the cooling ability decreases as well. The solder connecting section area between the thermoelectric element and electrode will become smaller, so that electrical resistance and joule heat will both go up, then finally burn out or melt the connection and cause the breaking of the wire to end its life.
Crystal failure of thermoelectric element
In case the cleaved surface along the direction of crystal formation of thermoelectric element is inclined largely, once the chip is cleaved by thermal stress or mechanical strength, separation will be caused on elements by relationship of geometric position and electrode, which will cause some sparks between cleaved surfaces which might be melted partially, and disconnection might happen due to increased joule heat.