Microvia hole technologies

TABLE 63.4 Technical Capabilities of Microvia Hole Technologies for Double-Sided Flex Circuits... 

The purpose of this chapter is to examine a variety of microvia hole formation technologies, structures, and materials. 

However, a greater emphasis will be placed on the laser-drilling process laser via hereafter) since it is the most popular process today and it seems its popularity will grow in the future. It must be understood that via hole formation is just one element of fabricating HDI wiring boards. Fabrication of HDI wiring boards with microvia holes involves many new processes not common to conventional board fabrication. Therefore, additional emphasis will be placed upon these new fabrication processes that are common to other microvia technologies. 

FIGURE 63.9 Microvia holes made by chemical etching. The hole diameter is 40 micrometers. (Source Asahi Fine Technology.)... 

Smaller holes and increasing circuit density are drivers that pnsh technology for via-in-pad and stacked microvia designs that help minimize PWB real estate. It has been established that via-in-pad designs, where the via is not filled, can lead to voids in the BGA solder joint that can negatively affect reUabUity. 

HDI technology creates small blind microvias that are plated to provide interconnects to buried layers of circuitry. These small holes can either be coated with solder mask or filled and plated over so that the real estate of the hole can be utilized for a circuit or a component mounting pad (via-in-pad). 

FIGURE 6Z8 Microvia capabilities shown by base thickness and hole diameter. Also shown is the range of technologies from HDI to mechanical drilling required to create the vias. 

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