To provide circuit board in which the state of a solder bonded part can be judged visually without generating a fillet, by a method wherein conductive through holes are provided in one or both terminals, for external connection, of both circuit boards in which the mutual terminals for external connection are overlapped and phase-bonded by solder.
Inflexible circuit boards 1a, 1a are solder-bonded by overlapping mutual terminals 2a, 2a for external connection. Through holes which are passed to the surface and the rear are bored and formed in one or both of the terminals 2a, 2a, for external connection, of the phase-bonded inflexible circuit boards 1a, 1a. Conductive films 9 are applied to the whole inner walls of the through holes. Thereby, conductive through holes 3 whose continuity and thermal conductivity are ensured over the surface and the rear of the board is formed via the conductive films 9. Through holes 3 are formed in alternate positions in the respective terminals 2a, 2a, for external connection, regarding both phase- bonded circuit boards 1a, 1a. As a result, a region in which a bonded state can be confirmed is made wide, and the reliability of a bonded place is increased. In addition, surface mounting components can be mounted at high density, and their excellent bonding strength can be obtained.
HASHIZUME MICHIYA
KUBO KOICHI
