Stress relieving technique for plastic packages in a high volume manufacturing environment.

摘要

The roadmap for the electronics manufacturing industry follows a simple mantra of "Smaller, Faster, Better, and Cheaper". Improving device functionality and performance of an analog or digital Integrated Circuit (IC) is primarily driven by design innovations and smaller feature size. Materials, design and processes for packaging these ICs play a major role in meeting the demands of next-generation electronics. As electronics trend towards rigorous and high-stress applications (under the hood automotive, etc.), and the industry focuses on environmentally friendly materials, the challenges faced by packaging grow enormously. In particular, protecting the stress sensitive electronics (such as precision analog devices) can be extremely challenging as they require protection from internal (packaging and assembly processes) and external (end application) environments. These devices have shown a parametric shift in performance due to stresses induced during the packaging process as well as during real life operations in high stress environments.;Package stress related concerns have been around for years, and many solutions have been proposed to alleviate these concerns. However, the search for a better and improved solution persists. Low stress die attach materials, molding compounds, dispensable silicone gel, polyimide and many other stress relieving remedies have been able to ease the effect of package stress on the device performance but they all have certain issues and concerns that present poor yield in a high volume manufacturing environment. The solutions available at present to lower the failures induced by package stress are not sufficient to deal with high (Pb free) assembly temperatures and automotive applications that demand stringent reliability conditions. For these reasons, it is important to continue researching the ideal stress buffering solution for a plastic package that will be able to provide a low cost solution and also sustain the high volume manufacturing requirements of the future. This research is one such effort in this regard. It envisions achieving a robust stress relieving solution for the future trends in the electronics industry.;The primary objective of this research is to understand the effectiveness of the screen printable silicone gel as a stress buffering solution with respect to enduring stringent assembly and reliability conditions that are posed by internal and external conditions. The test vehicle for this research is a stress-sensitive device (precision operation amplifier) that shows parametric shifts during assembly processes and during accelerated stress testing. This research effort investigates the effect of material (dispensable and screen printable silicone gel, mold compound/die attach material) and design (coating thickness, die thickness, package type) variables on reducing package stress. In addition, it correlates the trend between the statistically analyzed experimental data and the results from finite element modeling of material and design variables. The impact of the buffering solution to withstand stringent reliability conditions posed by high end applications is studied based on the package characterization results. The package characterization included JEDEC specified accelerated reliability testing to simulate stringent external environments. In conclusion, this research effort contributes towards the development of a fundamental understanding of the various factors involved in reducing package induced stress.