Doctoral Abstracts (1990-2001)

HUANG, CHIEN-YI
(August 1996), Assistant Professor, Huafan University, Taiwan
SMT Process Consultant, Universal Instruments, Taiwan

Email: huang107@ms17.hinet.net

Process Research In the Encapsulation Direct Chip Attach Components

Flip Chip On Board (FCOB) technology involves bonding the bare die or dice directly onto the printed wiring board. The interconnections are provided by the solder bumps which are arranged in the area under the chip. This approach maximizes the circuit density that can be achieved. The mismatch in the Coefficient of Thermal Expansion (CTE) is critical in FCOB technology. Encapsulation is one strategy that could be used to reduce the impact of the thermal stress that results from the CTE mismatch. A review of the literature indicated that the encapsulation process for FCOB devices is still far from being optimized with respect to the package quality, reliability, process time and cost. The identification of a robust, highly reliable encapsulant as well as a proper encapsulation process are critical for the widespread use of FCOB technology.

The optimization of the manufacturing process is essential to maximize the throughput while the concurrently satisfying defect level and product reliability objectives. This research characterizes the encapsulation process through the following approaches. The capillary flow of the encapsulant material was rigorously studied. An understanding of the capillary flow of the encapsulant and an effective estimate of the encapsulant's flow time helped to achieve a more robust underfill process. Also, this research evaluates the various underfill related defects and provides possible solutions. Several models that are based on rigorous statistical principles were developed to predict the behavior of the encapsulant material and to define the process windows. Models were developed to determine the optimal substrate preheat temperature, evaluate the dispensing pattern, and to identify other dispensing related parameters. Reliability testing was performed on samples after the underfill process to assess the performance of the materials used and to study the failure mechanisms. Eventually, an (almost) 'optimized' encapsulation process and material combination was suggested.