| 摘要 |
PURPOSE:To obtain a package whose airtightness can be maintained even if it is subjected to a thermal load by molding the package with two types of glass materials whose thermal expansion coefficients are different from each other when the thermal expansion coefficients of a base and a cap are different from each other. CONSTITUTION:Thermal stress created in the junction of two types of materials is mainly influenced by the difference alpha between the two thermal expansion coefficients, a junction area S, temperature difference T and rigidities E of the materials. Generally, the thermal sterss sigma is expressed by the formula: sigma=K.E. alpha. T. Therefore, as the thermal expansion coefficients of glasses 13 and 17 are close to that of a base 15 and the thermal expansion coefficients of glasses 12 and 18 are close to that of a cap 11, only thermal stresses at the boundaries between the glasses 13 and 17 and the top 11 and between the glasses 12 and 18 and the cap 15 have to be considered. As the mis-matching area of thermal expansion coefficients is about a half of the area of the package which is molded with one type of glass like in the conventional method, the thermal stress can be reduced without deteriorating the junction strength. |
