Determination of thermally induced deformations in electronic packages by Moire interferometry

Abstract

Thermally induced deformations in specimens taken from AT&T 1MB DRAM devices were measured using moire' interferometry. Specimens were heated uniformly from room temperature to 90 C. Resulting moire' fringe patterns were recorded, analyzed using Digital-Image-Processing and axial displacements in the device were computed. It was observed that severe displacement gradients occurred at the silicon chip comers while minimal gradient was Seen at and above the chip. A relatively high gradient occurred at and beneath the copper lead frame. The technique proved to be extremely successful in detecting full field displacement patterns necessary for reliable stress analysis in actual devices. 0Detection of thermally induced deformations in elecmnic devices either during normal operating conditions or testing has become of great concern lately. Due to the mismatch in the coefficients of thermal expansion of the different materials coexisting in a device, severe strain concentrations may occur thus leading to the ultimate failure of the device. Many analytical and numerical assessments of devices under such loading conditions were carried out in an effort to predict thermally induced deformations [l]. However, the accuracy of the obtained results has been limited by the complexity of the device details and many simplifying assumptions that had to be made. This, of course, has limited the faithfulness of such models in representing actual packages. Actual measurements of such deformation fields have not been very successful due to lack of proper, sensitive and global methodologies. Relatively small deformations in electronic devices made them very difficult to be detected by many of the traditional experimental techniques.It is the objective of this paper to innoduce an accurate and highly sensitive experimental procedure to measure actual deformations in a device. The technique used here is Moire' Interferometry with a Digital-Image-Analyzer added to enhance sensitivity by evaluating Fractional Fringe Orders. Moire' InterferometrvInterferometric moire' has been recently introduced [2] as a sensitive full field deformation measuring technique. It is based on the formation of fringes by the coexistence of light wave fronts diffracted from a specimen grating of high frequency (e.g. 1200 lines/ mm). These specimen gratings are created on the specimen surface using a sknpli: replication technique from a specially prepared mold. TWO beams of coherent laser light illuminate the specimen grating obliquely from an angle +a anda to create a virtual reference grating in front of the specimen. The creation of this virtual grating is due to the holographic formation of walls of constructive and destructive interferences when two coherent beams intersect at an angle, Fig. 1. The frequency f of this grating is given bywhere h, is the wave length of the light used. f is typically chosen to be 2400 lines/ mm for a specimen grating frequency of 1200 linedmm. This corresponds to a sensitivity of 0.417 pm per fringe order. On the other hand, sp...

A Study of Hygrothermal Behavior of ACF Flip Chip Packages With Moiré Interferometry

“…Kyung-Wook Paik received the Ph.D. degree from the Department of Materials Science and Engineering, Cornell University, Ithaca, NY, in 1981and 1989, respectively. From 1982to 1985, he was with the Korea Advanced Institute of Science and Technology (KAIST), Seoul, as a Research Scientist, and was responsible for various materials developments, such as gold bonding wires and non-ferrous alloys.…”

“…In this paper, microdeformations of ACF packages are measured by Moiré interferometry [8]- [10]. Optical methods are used for the measurement of the thermal and swelling deformations.…”

Micro-deformation characterization of electronic packaging materials and assemblies

“…Considering the small scale of these objects to be measured and the whole field data to be required, only a few methods are available for that purpose. As reported in the literature, moire interferometry has been applied to measure in-plane deformations [52][53][54][55][56][57][58][59][60] in electronic packaging. Digital image correlation (DIe) technique is suited for micro-deformation characterization of electronic packages and assemblies [61][62][63] because of its non-contact feature, easy specimen preparation, and vibration insensitivity.…”