ABSTRACT
The implementation of lead (Pb)-free technology in microelectronics very much depends on the reliability of interconnections, in addition to other aspects. Thus, the focus of this chapter is on the reliability of lead-free interconnections in electronic assemblies. In the ensuing sections, some reliability fundamentals and reliability requirements are reviewed first. Reliability or long-term product performance under thermal and/or mechanical loading conditions depends on a number of factors. Some of the significant factors include the composition and physical properties of the interconnection alloy, printed wiring board (PWB) surface finish, and component lead termination finish. As the size of package-to-board interconnections becomes ever smaller due to electronic miniaturization and implementation of technologies such as direct chip attachment, additional complexities that affect reliability come into play. Variations introduced in the assembly process can also affect the ultimate product reliability. Reliability-conscious organizations address the issues by utilizing a combination of accelerated testing and modeling methods. Modeling and simulation provide an evaluation of potential reliability and the opportunity to optimize a package design through iterated evaluation of subsequent model validations with input from accelerated test condition findings. Tests are carried out until a sufficient number of failures occur in order to identify different failure mechanisms that may be operating and to obtain statistically significant failure distributions. The test methods selected must mimic actual loads that a product is anticipated to experience in the field, especially in regard to portable consumer products such as cellular phones, personal digital assistants, camcorders, etc. A multitude of thin-walled microvias with a variety of copper thickness, interconnections with extremely small solder volumes, board warpage, and poorly shaped solder joints all become concerns for product reliability. The test methods include cyclical bending, mechanical drop and shock, and vibration caused during product transportation. This chapter provides an overview of these various aspects.
