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|Direct Die-placement Technology for Component Attach in Thin and Lightweight Electronics|
|Keywords: Die bonding, Pick-and-place equipment, heterogeneous integration|
|High-volume manufacturing of systems based on advanced packaging technologies, including fan-out wafer-level packaging (FOWLP) and interposers, require high bonding yields as well as fast and precise die-placement capability . Current approaches employing die-to-wafer (D2W) strategies to build heterogeneous systems involve die population of intermediate carriers using conventional die-bonding equipment that is based on pick-and-place strategies . The conventional D2W process flow thus poses a challenge for high-volume heterogenous integration, particularly in heterogeneous systems involving components that vary in material composition, lateral size, and thickness . The objective of this work is to develop a single-step process for transferring dies directly from flexible carriers (e.g., dicing and backgrind tapes) to receiver substrates in order to increase the process throughput of D2W assembly approaches. Direct die-placement (DDP) is a new technology for the transfer of high-performance semiconductors from flexible carriers directly onto receiver substrates. The DDP method provides a reduction in process steps for building heterogenous systems by replacing conventional pick-and-place tooling and bypassing the use intermediate carrier substrates. DDP tooling enables a shortening of the tool path due to the handling of the die carrier itself, thereby reducing die-placement times compared to those of conventional pick-and-place processes. A custom tool was developed to implement the DDP process and which allows for aligned direct placement of die from a wide range of carrier tapes onto receiver substrates. The DDP process is mechanical in nature and uses a unique bonding head to deform the carrier substrate locally, thereby sequentially placing dies directly onto a receiver substrate. Finite element modeling was used to investigate the mechanics of the process and establish process parameters (e.g. bonding-head size, contact force, etc.) for transfer of dies with specific lateral dimensions as a function of the properties of the carrier substrate (e.g., geometry, thickness, elastic properties) and the interfaces. The modeling was also used to ensure that the process does not introduce significant strains in the die during transfer or residual stresses after die placement. The finite element results were used to define a process window that guided the experimental conditions under which transfer of thin dies was performed. Using the custom DDP tool, we demonstrate the transfer of thin (30-μm thickness and 20-μm thickness) silicon bare dies with lateral dimensions ranging from 2.5 mm to 5 mm. The dies were transferred from grinding tape and flexible PET carriers onto to various rigid and flexible receiver substrates. Die profile/geometry and electrical connectivity after transfer are characterized to investigate the reliability of the transfer process. Beyond the modeling and experimental results described above, strategies in which DDP technology and accompanying processes can be integrated into a range of device fabrication process flows will be discussed. Specifically, the tailorability of the DDP approach to accommodate carrier and receiver substrates with dimensions and properties that are of particular importance to the advanced packaging field will be highlighted. Advantages and limitations of the DDP approach as an alternative assembly method for high-volume advanced packaging will be discussed.|
|David Grierson, President & CTO