| 摘要 |
PURPOSE:To improve junction strength so that it becomes stronger than that of a part welded with solder consisting of pure solder composition by performing soldering with a soldering paste which is kneaded with fine metallic lines and dispersing the fine metallic lines in a welded part which is formed by the foregoing soldering after welding these fine lines. CONSTITUTION:Once a screen printing process is performed on a paste 1 in which fine metallic lines are kneaded on a resin printed board 2, the printing deposit 3 of the paste containing the fine metallic lines is three-dimensionally formed on the resin printed board 2. Generally, pure copper wires or alloy wires are used for the most part of the fine metallic lines and especially alloy wires comprise iron and nickel in which surface treatment is performed to provide wettability with respect to the solder to their surfaces. Then they consist of each line diameter of the order of 5mum and each length of the order of 100mum. Further, a leadless chip carrier 4, that is, a component to be soldered is loaded and is attached on the printing deposit 3. As it is welded at a high temperature, a junction part 5 with solder which is in a completely welded state is obtained after performing reflow. After that, even though a temperature cycle test is performed, no breaking occurs in a junction part and no variation caused by a difference in thermal expansion coefficient takes place. |
