The present invention relates to an assembly inspection system and method for examining the connected or bonded state of electronic parts of BGA (Ball Grid Array) type or CSP (Chip Scale/Size Package) type.
In recent years, in mounting an electronic part such as an LSI package on a substrate or board, a face bonding method is mainly adopted. BGA type electronic parts and CSP type electronic parts are typically face-bonding type electronic parts. Once an electronic part of the BGA type or that of the CSP type has been mounted in position, a soldered state thereof cannot be visually confirmed. In the process of assembling the board mounted with such a BGA type electronic part or a CSP type electronic part into an electronic equipment, there is a case in which it is impossible to decide whether an equipment failure is due to a defective connection of the BGA/CSP type electronic part or due to another cause. Thus, it is necessary to correctly inspect whether the BGA/CSP type electronic part is correctly bonded on the board. For this purpose, there is proposed an inspection system in which through-hole-provided pads are formed on a printed wiring board in correspondence with ball-shaped solder pads formed on a back surface of the BGA/CSP type electronic part, and in which the state of connection between the BGA/CSP type electronic part and the printed wiring board is inspected after the reflow process according to whether the through-hole-provided pads are filled with solder, as disclosed in Laid-Open Japanese Patent Publication No. 9-127178. Also, as disclosed in Laid-Open Japanese Patent Publication No.7-234189, there is proposed an inspection system utilizing a fine connection inspection device using a sensor.
However, in the former of the above two conventional inspection systems, it is necessary to form on the printed wiring board the through-hole-provided pads corresponding to the ball-shaped solder pads on the back surface of the BGA/CSP type electronic part. Thus, the degree of freedom in designing a pattern deteriorates, which prevents a fine pattern design. In the latter of the two conventional inspection systems, it is necessary to introduce an expensive inspection device and thus the manufacturing cost becomes substantially high.