Large area embedding for heterogeneous system integration

Abstract

The constant drive to further miniaturization and heterogeneous system integration leads to a need for new packaging technologies which also allow large area processing with potential for low cost applications. Wafer level embedding technologies and embedding of active components into printed circuit boards (Chip-in-Polymer) are two major packaging trends in this area. This paper describes the use of compression and transfer molding techniques for multi chip embedding in combination with large area and low cost redistribution technology from printed circuit board manufacturing as adapted for Chip-in-Polymer applications. The work presented is part of the German governmental funded project SmartSense. Embedding by transfer molding is a well known process for component embedding that is widely used for high reliable microelectronics encapsulation. However, due to material flow restrictions transfer molding does not allow large area encapsulation, but offers a cost effective technology for embedding on a medium size scale as known e.g. from MAP (molded array packaging) molding (typically with sizes up to 60 × 60 mm2). In contrast, compression molding is a relatively new technology that has been especially developed for large area embedding of single chips but also of multiple chips or heterogeneous systems on wafer scale, typically up to 8” or even up to 12”. Wiring of these embedded components is done using PCB manufacturing technologies, i.e. a resin coated copper (RCC) film is laminated over the embedded components - no matter which shape the embedded components areas are: a compression molded wafer, larger rectangular areas or smaller transfer molded systems (MAP). Typical process flow for RCC redistribution is lamination of RCC, via drilling to die pads by laser, galvanic Cu via filling, conductor line and pad formation by Cu etching, soldermask and solderable surface finish application - all of them standard PCB processes. The feasibility of the technology is demonstrated by the fabrication of a Land Grid Array (LGA) type package with two embedded dies. First step is a high precision die placement on an intermediate carrier. For embedding, both compression molding and transfer molding are used and directly compared with regards to material properties, processing, resulting die shift and warpage after molding. Reliability testing including MSL testing, temperature cycling, and humidity storage has been performed with LGA packages manufactured using the different technologies. The reliability potential and failure modes are intensively discussed and backed by destructive and non destructive failure analysis. Finally, an outlook for the integration of through mold vias into RCC redistribution process flow is given showing also the potential for package stacking.