Improved Reliability of Leadfree Flip Chip Assemblies Using Direct Underfilling by Transfer Molding

Abstract

Flip Chip technology has been widely accepted within microelectronics as a technology for maximum miniaturization. Typical applications today are mobile products as cellular phones or GPS devices. For these consumer applications upper temperature limits and reliability demands are not very harsh. To widen the application range of Flip Chip technology and to address the volume market of automotive and harsh environment industrial electronics the development of highly reliable assemblies with high temperature capabilities is as crucial as being able to qualify and predict this very reliability. Transfer molding is the standard process for a highly reliable encapsulation of leaded and area array packages as BGAs or CSPs. Advanced materials and process developments now allow the use of transfer molding technology for direct underfilling and / or overmolding of Flip Chip assemblies. Existing standard equipment for encapsulation can be used and no additional process step for underfill dispensing or jetting is required. Molded Flip Chips have the potential of high reliability as the low CTE of the flip chip molding compound reduces the thermal mismatch. Trends of the market drive towards SIPs with an integration of different devices as e.g. SMD and Flip Chip. Therefore the highly reliable encapsulation of these hybrid packages with inhomogeneous topography is the goal. For testing the reliability limits and the determination of failure mechanism of molded Flip Chips a test vehicle has been designed at Fraunhofer IZM.