2. Checking the resistance value of elements
The slant element end can result in forming a large contact resistance, and elements with internal defects can lead their resistance value to change. Before brazing, the resistance value of elements should be measured by using contact electrode. If there are abnormal components in the element, it will be removed so as to reduce the contact resistance. It can not only improve the consistency of component performance parameters but also the consistency of electric pile performance. During measuring, the shape of electrode is the same as the substrate and the clamping force is the same as when brazing.
3. Ensuring the clamping force, flatness and parallelism
In order to reduce welding resistance, the length deviation of elements should be as small as possible. At the same time, it should be ensured that clamping force is moderate, surface flatness deviation is equal to or less than 0.03mm and the correlation deviation is equal to or less than 0.05mm. When brazing, the electric pile in the fixture is compressed by compression spring and the clamping force is guaranteed by the elastic force of compression spring. The number of compress spring is 4 instead of 2, so that clamping points increase from 4 to 8 points, which can ensure the press forces of its two ends are the same.
4. Optimization of welding process
When welding, the temperature field should be uniform. In the condition of meeting welding requirements, the melting time of solder should be as short as possible, which can reduce the thermal shock of elements. The cooling curve should be selected reasonably and optimized so as to reduce temperature stress generated by cold shrinking. The cooling rate is related to the solder types, and the key is the cooling rate of liquid to solid transition temperature region. Due to the segregation of liquid to solid transition, the temperature stress needs to be determined by experiment.
5. Reducing the amount of solder
Based on meeting the requirements of welding strength and resistance, the amount of solder is as small as possible. In order to reduce the copper infiltration effect, tin bismuth can be used for braze.
