Application of a Novel Flip Chip Solder Joint Inspection System to Chips on an FR-4 Substrate

Abstract

Because the trend in electronic interconnection technology is toward the development of solder bump technologies, that include flip chips, chip scale packages, multi-chip modules (MCMs), and ball grid array (BGA) packages, solder bump inspection methods must be developed to allow rapid, accurate, and high resolution on-line inspection of joint quality. Although traditional methods can detect some manufacturing defects, they do not actually test the mechanical quality of the connection. A novel solder-joint inspection system has been developed based on laser ultrasound and interferometric techniques. A pulsed laser generates ultrasound on the chip’s surface and the whole chip is excited into vibration modes. An interferometer is used to measure the vibration displacement of the chip’s surface. Solder joints with different qualities cause different vibration responses, acting as constraints on the system. The system was used to inspect the quality of solder joints on a group of flip chips mounted on FR-4 substrates, and the results show the ability of the system to detect defects such as missing solder balls, cracked chips, and gross misalignment.