Near Void-Free Assembly Development of Flip Chip Using No-Flow Underfill

• Published in: IEEE transactions on electronics packaging manufacturing 2009-04, Vol.32 (2), p.106-114
• Main Authors: Sangil Lee, Myung Jin Yim, Master, R.N., Wong, C.P., Baldwin, D.F.
• Format: Article
• Language: English
• Subjects: Applied sciences; Assembly; Assembly systems; Assembly yield; Chip formation; Chips; Degradation; Density; Design of experiments; Design. Technologies. Operation analysis. Testing; Electronics; Exact sciences and technology; fine pitch; Flip chip; high I/O density; Integrated circuits; Joining materials; Materials reliability; Materials science and technology; no-flow underfill; Organic materials; Reduction; reliability; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Side effects; Silicon; Soldering; Statistical analysis; Studies; void formation; Voids
• ISSN: 1521-334X; 1558-0822
• DOI: 10.1109/TEPM.2009.2015592

The advanced flip-chip-in-package (FCIP) process technology, using no-flow underfill material for high I/O density (over 3000 I/O) and fine-pitch (down to 150 mum) interconnect applications, presents challenges for flip chip processing because underfill void formation during reflow drives interconnect yield down and degrades reliability. In spite of such challenges, a high yield, reliable assembly process (>99.99%) has been achieved using commercial no-flow underfill material with a high I/O, fine-pitch FCIP. This has been obtained using design of experiments with physical interpretation techniques. Statistical analysis determined what assembly conditions should be used in order to achieve robust interconnects without disrupting the FCIP interconnect structure. However, the resulting high yield process had the side effect of causing a large number of voids in the FCIP assemblies. Parametric studies were conducted to develop assembly process conditions that would minimize the number of voids in the FCIP induced by thermal effects. This work has resulted in a significant reduction in the number of underfill voids. This paper presents systematic studies into yield characterization, void formation characterization, and void reduction through the use of structured experimentation which was designed to improve assembly yield and to minimize the number of voids, respectively, in FCIP assemblies.