LASER ASSISTED ASSEMBLY FOR NCP, ACF AND SOLDER INTERCONNECTION

摘要

Flip Chip Assembly has an increased importance in modern microelectronics industry and Advanced Packaging. Flip Chip and miniaturized packaging is being implemented in volume productions in consumer products in mobile telecommunication as well as in advanced high end automotive and aerospace industry. An additional aspect is the implementation of new substrates and especially low cost flexible substrates for 3D - packaging to promote the ongoing the miniaturization in this industry. In the equipment field, the majority of today's Flip Chip Bonders is derived from modified SMD - equipment respectively from modified die bonder equipment. The majority of the Flip Chip Assembly Processes are based on soldering, however adhesive attach is having a stronger and more important impact in Flip Chip Technology. Adhesive attach is especially interesting in applications on flexible circuits, like LCD drivers and smart cards. The methods of flip attach are all using thermal energy by either reflow convection ovens or a thermal based on heated tools (thermode). To address the demands of the newest chip interconnection technology a new Flip-Chip assembly process solution and tool concept is presented implementing an unique laser heating technique into a Flip-Chip bonder (LAPLACE). The advantage of laser instead of direct thermal heating is given by extreme high selectivity and by using a localized heat with an extremely good time control in the milisecond In contrast to infrared ovens where the assembly process takes minutes and to thermodes where the assembly process is taking seconds, the laser attach allows selective assembly process with a duration of milliseconds. By this, the thermal stress induced in the package and on the substrate is minimized allowing implementation of new substrates and new IC's which are thermally more sensitive. Additionally common alignment problems due to different thermal expansion behavior of substrate and chip are reduced. Process cycle times are improved by the equipment concept of performing chip placement and assembly reflow simultaneously and the absence of long heating and cooling cycles of standard thermode FC bonder systems. Especially, in combination with electroless Nickel UBM cost reduction of the overall assembly process can be achieved. Beside of this the process capability for ACF, NCP and solder interconnection techniques illustrates the high flexibility of the laser heating process. New results using Non-Conductive Paste, Anisotropic Conductive Foil materials but also solder connection are presented and sample analysis by cross sectioning and SEM are shown. Finally an overview on advantages of this new technology compared to common assembly techniques is given.