Wire bonding a die to a package has traditionally been performed using either aluminum or gold wire. Gold wire provides the ability to use a ball and stitch process. This technique provides more control over loop height and bond placement. The drawback has been the increasing cost of the gold wire. Lower cost Al wire has been used for wedge- wedge bonds but these are not as versatile for complex package assembly. The use of copper wire for ball-stitch bonding has been proposed and recently implemented in high volume to solve the cost issues with gold. As one would expect, bonding with copper is not as forgiving as with gold mainly due to oxide growth and hardness differences. This paper will examine the common failure mechanisms that one might experience when implementing this new technology.
Conductive adhesives offer lead-free, low temperature attachment for various types of electronics applications. They are composite materials consisting of a polymer matrix (adhesion, strength) and conductive filler (electric conductivity). Due to the nature of polymers, it is relatively easy to tailor adhesive properties to match the specific requirements. Selection of the filler depends on the application.
Conductive adhesives have been used in the electronics industry for a long time. Silver-filled Isotropic Conductive Adhesives (ICA) were first used for die bonding in hybrid circuits. Many other applications have appeared since the introduction of ICAs. Anisotropic Conductive Adhesives (ACA) were developed for attaching driver circuits to Liquid Crystal Displays (LCDs) for calculators. Today, ACAs are a cornerstone for the display industry allowing the use of Chip-on- Glass and Chip-on-Flex technologies and enabling fast, reliable, and lightweight solutions for driving the displays . ICAs are used in various applications from die attach to space applications.