Thin-Film Packaging

Abstract

Thin film refers to a coating layer of thickness typically in the range of from a few (2–3) atomic layers to a few (1–5) microns. However, film thicknesses up to 20–50 μm are frequently regarded as thin-film in electronic packaging. Thin-film packaging is the technology for conductors and dielectrics deposition and patterning in package fabrication, which resembles the technology used for integrated-circuit (IC) chip fabrication. Thin-film packaging is distinguished from thick-film packaging, mainly ceramic and printed wiring board (PWB) packaging, in two aspects: (a) the typical dimensions of conductors and dielectrics are about 2–25 μm versus 100 μm and above in thick-film packaging; (b) the typical methods of thin-film deposition include sputtering, evaporation, chemical vapor deposition (CVD), more recently electro/electroless plating and polymeric solution coating, and other similar methods, which are all typical sequential processes, whereas in thick-film packaging parallel processes are more common, such as lamination and cofiring of ceramic greensheets. Nevertheless, the current trends in electronic packaging are the enhancement of thick-film technology to fabricate finer feature sizes which are traditionally considered only achievable by thin-film technology and the adoption of some of the parallel thick-film processes for thin-film fabrication. Due to these developments, the traditional division between thin- and thick-film packaging technologies is diminishing and the definition of thin-film packaging is becoming less obvious. Still, the mainstream of thin-film packaging can be well identified which allows a fairly extensive compilation on this technology. In this chapter, the need for thin-film packaging, electrical performance considerations, and typical structures in thin-film packages are first elucidated. Subsequently, the materials, processes, and cost analyses of thin-film packaging are discussed in detail. Repair is especially important in thin-film packaging and is dealt with in the context of cost and yield. Reliability of packages has been discussed in Chapter 5, “Package Reliability,” and reliability issues which are unique to thin-film packages are identified here. Some major commercial applications of thin-film packaging are reviewed, followed by a summary of the emerging technologies. Integration of various passive components is becoming imperative for thin-film packages to enhance electrical performance and packaging efficiency, which is also included in this chapter along with some applications and future predictions. Finally, the current development and future directions of thin-film packaging technology are summarized and projected.