ADVANCED MATERIALS & PROCESSES | MARCH 2023 31 5 THICK FILM PVD-BASED MEDICAL DEVICE COMPONENTS Using a physical vapor deposition process to manufacture medical device components reduces post-processing time and improves materials properties. Scott Carpenter* and Christian Palmaz* Vactronix Scientific, Fremont, California Physical vapor deposition (PVD) is used to additively fabricate intermediate materials at the atomic scale. These materials can be further processed into finished device components. This is a relatively new development for medical devices compared to the traditional reductive methods typically used today. PVD fabrication offers advantages in dimensional tolerance control, material properties, surface finishes, and the range of feature sizes. It can also reduce the processing steps needed to achieve a finished device. Although PVD can be used to process metals, ceramics, and polymeric materials, this article will focus on metallic sputter deposition. Likewise, it will not focus on PVD coatings or other vapor deposition processes, such as chemical vapor deposition or reactive sputtering. The PVD processes used for device components differs from the PVD processes used in electronics in that the primary function is mechanical and the films are significantly thicker. These thick films can be upwards of 350 µm wall thickness. THE PVD PROCESS It’s helpful to begin with some background on the PVD process[1,2] itself. In this high energy vacuum transport process, donor material ions from the sputter target are dislodged by the high energy nuclei of an inert gas plasma that strikes the target (Fig. 1). These free donor ions are then attracted onto a sacrificial substrate by an electric field where they reassemble into a new shape, based on the shape of the substrate. Figure 2 illustrates this mechanism. The substrates can be planar, tubular shapes, or fully three dimensional. The material is built up atom by atom until the final desired thickness is achieved. This is similar to the transport mechanism of electroplating, albeit in a plasma state, rather than in liquid. There are different PVD machine chamber configurations, including planar and cylindrical constructions, each producing preferred material formats. The PVD material structure is a function of the processing parameters, and thus the resulting material can be amorphous or crystalline, depending upon the processing parameters[3]. PVD typically produces crystalline films with final properties direct from the deposition by tuning these process parameters. This intermediate material can then be patterned, typically employing laser ablation or photolithography[4]. The components can be electropolished while still on the substrate, if desired. Finally, the substrate material is removed, resulting in a discrete component. This FEATURE *Member of ASM International Fig. 1 — Plasma in a hollow cathode PVD reactor. Fig. 2 — Atomistic view of film growth mechanism.
RkJQdWJsaXNoZXIy MTYyMzk3NQ==