X‐ray Inspection of Flip Chip Attach Using Digital Tomosynthesis

To accommodate increasing levels of device integration at the chip level, circuit line densities in electronic packages are continually increasing. Greater circuit line density, in turn, necessitates a corresponding increase in package‐to‐board interconnection density, with I/O counts expected to reach over 600 by 1995. In conjunction with the upward trend in I/O counts are a complementary upward trend in clock speed and an opposing downward trend in package sizes driven by the need to provide more functionality in less space, particularly in notebooks and PCMCIA cards. To satisfy the requirements of increased I/O counts and clock speed, and reduced package sizes, various package‐to‐board interconnection technologies are being developed, such as flip chip attach (FCA) using C4 joints. However, FCA interconnections have a disadvantage of being very difficult, if not impossible, to visually inspect. Though automatic test equipment (ATE) can determine whether the package is functional, it cannot determine th...