Novel Application and Advantage of Reverse Blind Microvia (RBMV) on PCB
Reverse blind microvia (RBMV) is a upside-down blind microvia that looks similar to a traditional blind microvia; however, RBMV has several features and advantages in real application. RBMV can apply to not only HDI structure but also conventional double side PCB. In multi-layered HDI structure, most 1+N+1 and 2+N+2 structures are accessible by RBMV. In a 1+N+1 HDI structure RBMV will exhibit a flat platform at outer layer after all processes without other complicated processes. With this flat surface, which is also a microvia connecting to the inner layer, via-on-pad or even that via is pad is easy to achieve. This will reduce the board size and increase the circuitry density as well. Due to different processes forming this plane via pad, RBMV could do without the cost of via-filling plating, reducing Cu thickness but still keep the facilitation of image transfer with a adequate Cu thickness. As to the 2+N+2 HDI structure, the second built-up blind microvia can just stand right on the RBMV forming a so-called stacked via. Moreover, even some of the 2+N+2 HDI structures fabricated by only one time lamination are possible. Once applying the RBMV structure to a single-sided or double-sided PCB, since RBMV can form a flat surface on one side of PCB, this flat surface is a good platform for SMD to place on. In addition, with RBMV where one side of a conducting via is sealed, it mask plugging or resin plugging with scrubbing later. And this would be much easier, especially for thinner boards, to prevent molding compound or solder to penetrate through mechanical drilling holes.