KOVAR parts are commonly used as metal casing materials in the electronic packaging industry. Because they have a linear expansion coefficient close to that of molybdenum group glass, and can produce less sealing stress during the sealing (melting) process with molybdenum group glass, so To obtain good air-tightness, in order to make the metal tube and shell to achieve air-tight sealing, in the entire sealing process, the annealing process undoubtedly plays an important role as a link between the previous and the next. The internal stress generated during KOVAR machining also prepares the material structure for the implementation of the subsequent process-the sealing process of the metal parts.
The main purpose of annealing Kovar shell before sealing is to:
(1) Eliminate machining stress.
When Kovar undergoes plastic machining deformation during cold working, about 10% to 15% of the applied energy is converted into internal energy, which is commonly referred to as internal stress, so that the Kovar material structure is in an unstable state. Under this condition, it can be maintained for a long time without significant changes. Once it is heated, a series of changes in structure and properties will occur, and the material structure tends to a stable state. This change in structure and properties, especially changes in the structure of the structure, is reflected on the sealing surface The tensile stress on the molybdenum group glass during high temperature sealing may cause the glass to produce small cracks and leak;
(2) Eliminate work hardening.
In the process of cold working, cnc manufacturing and forming of Kovar parts, due to defects such as grain elongation and grain breakage in the internal material structure, crystal defects and dislocation density increase greatly. The smaller the distance between the dislocation and the dislocation, the greater the interference between each other, and the greater the distortion of the surrounding lattice. Each dislocation line has a stress field, and the dislocation and dislocation pass through each The interaction of the stress field causes the hardness and elasticity of Kovar to increase, while the plasticity decreases, which is work hardening. If the work hardening is not eliminated, the stress field of the interaction between dislocations and dislocations will be broken due to crystal recovery or recrystallization during high-temperature sealing, and the balance will be lost. This also affects the sealing of metal and glass. Certain stress effects;
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