[KOVAR parts] Annealing of Kovar alloy in metal shell sealing

u200bKOVAR (KOVAR parts) alloy (4J29) is the most commonly used metal housing material in the electronic packaging industry, because it has the closest linear expansion coefficient to the molybdenum group glass, and it is in the process of sealing (melting) with the molybdenum group glass. It can produce the smallest sealing stress, so as to obtain good air tightness. In order to achieve airtight sealing of the metal shell, the annealing process undoubtedly plays an important role in the entire sealing process. It not only eliminates the internal stress generated in the pre-manufacturing process of metal parts, It also prepares the material structure for the implementation of the metal parts in the subsequent process-the sealing process. 2 Annealing Purposes The main purposes of annealing Kovar shells before sealing are: (1) To eliminate mechanical processing stress. When Kovar undergoes plastic deformation during cold working, about 10% to 15% of the applied energy is converted into internal energy [1], which is commonly referred to as internal stress, so that the Kovar material structure is in an unstable state , At room temperature, this state 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, 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, that 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 influence; (3) Make the material structure uniform, refined, stable and consistent; (4) Decarburization of the metal surface. As a reducing substance, carbon has strong reducibility. At high temperatures, it will deprive oxygen to generate C0, which will generate bubbles on the metal-glass sealing surface or in the glass, which not only reduces the metal-glass sealing strength, but also Seriously affects the performance of the glass, which is never allowed in the sealing process; (5) Remove the internal adsorbed gas. In addition to the above five functions, high-temperature heat treatment in a suitable atmosphere can further clean the metal parts.