04-10-2012, 11:51 AM
Defect Detection of Flip Chip Solder Bumps With Wavelet Analysis of Laser Ultrasound Signals
Defect Detection.pdf (Size: 2.06 MB / Downloads: 45)
Abstract
Microelectronics packaging technology has evolved
from through-hole and bulk configuration to surface-mount and
small-profile ones. In surface mount packaging, such as flip chips,
chip scale packages, and ball grid arrays, chips/packages are
attached to the substrates/printed wiring board (PWB) using
solder bump interconnections. Solder bumps hidden between the
chips/packages and the substrate/board are no longer visible for
inspection. A novel solder bump inspection system has been developed
using laser ultrasound and interferometer techniques. This
system has been successfully applied to detect solder bump defects
including missing, misaligned, open, and cracked solder bumps in
flip chip packages, chip scale packages and land grid arrays. The
system uses a pulsed Nd:YAG laser to induce ultrasound in the
thermoelastic regime and the transient out-of-plane displacement
response in nanometer scale on the package surface is measured
using the interferometer technique. In this paper, wavelet analysis
of laser ultrasound signals is presented and compared to previous
signal processing methods, such as Error Ratio and correlation
coefficient. The results show that wavelet analysis increases measurement
sensitivity for inspecting solder bumps in electronic
packages. Laser ultrasound inspection results are also compared
to X-ray results. In particular, this paper discusses defect detection
for a