In low-volume segments, microvias were often added to a lay-up when routing a design using a conventional structure proved difficult or impossible. Adding microvias to a given lay-up adds cost, so microvias are often regarded as a cost driver to be avoided if possible. However, designers in the consumer segment use HDI and microvias aggressively to achieve cost reductions.
HDI’s cost saving potential stems from its efficient use of space and area which in turn results in higher routing density. The via structure itself has smaller diameter and consumes less space. The primary advantage, however, comes from the small vertical extension of the microvia, which leaves larger routing channels on other layers. Judiciously employed it allows a reduction of the number of layers in the board for a given circuit, which more than offsets the cost added by the inclusion of microvias.
Published case studies claims PCB cost reductions in the order of 50% by layer reduction (from 18 layer to 10 in some examples), and reduction in overall board area. When shipping millions of boards the savings are well worth the extra effort.
None of this comes easy, however. An entirely different regime is required to make the right design decisions in terms of construction type, material choice, lay-up and the use of the chosen build before board routing may even start. The wider variety of construction types and methods demands close technical contact with a capable board shop or broker up front.
The board must be designed for the process it will be manufactured with, requiring a far deeper understanding of process and materials on the part of the designer than with conventional boards.