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Glob Top Jet Process Evaluation for CoB Sensor Packaging
Keywords: Jet Dispensing, Chip on Board, Glob Top
During the last years, jetting processes for higher viscosity materials have gained widespread interest in microelectronics manufacturing. Main reasons for this interest are high throughput/productivity of jetting, contactless material deposition, high volume precision and freely designable deposition patterns. In previous studies we have demonstrated the jetability of different resin-based materials, being exemplary for unfilled adhesive, for low viscous Underfill resin and for higher viscosity Glob Top materials. The focus of our previous work was on the dosing of Underfill material, where this study is dealing with more complex materials " Glob Top resins. These materials are non-newtonian fluids - the flow curves of the filled materials can be described by models of Cross or Herschel/Bulkey. Furthermore, highly filled and paste-like mixtures show a significant time dependency of formation of structural equilibrium after deformation, so process development needs to take this into account, so detailed material analysis is described within this study. To illustrate the potential of jetting as a flexible and powerful tool for Chip on Board encapsulation, both, simple test-structures (dots, lines, dams) but also more complex demonstrators have been assembled using wire bonded ICs on ceramic substrates and encapsulants showing viscosities ranging from 10 Pas to > 100 Pas. Not only basic process data on droplet diameter, resulting material depot size and positioning accuracy have been evaluated, but also statistical means have been employed to determine process homogeneity and stability depending on the respective parameter set. Additionally, the whole process was followed by a high-speed camera system, providing detailed information on actual jetting behaviour during droplet release, flight and impact. Summarized this paper gives a detailed insight into jet process development for high viscosity GlobTop materials and describes process design rules and limitations and thus allows the optimized use of advanced jetting technology for Chip on Board assemblies.
Karl-F. Becker, Group Manager Assembly & Encapsulation
Fraunhofer IZM
Berlin, Berlin

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