Let's first consider building complex boards for production volume. A number of pc-board fabricators claim the ability to build complex, high-layer-count boards. But, it is important to qualify their expertise and experience in this area. Find out, for example, whether the fabricator has built these boards in production numbers.

Building complex boards in prototype quantities does not guarantee success for volume-production requirements. For the inexperienced fabricator, moving from the prototype stage to production volume can lead to problems with quality and yields. Also, if the building of complex boards is not part of the routine process, there can be problems with the equipment, the chemical processes and the level of expertise of the personnel involved in producing complex boards.

Design rule checking is another issue. The fabricator must have the capability to extract a netlist from the Gerber data provided for a board to show how the pc board will be connected if it is built based upon that data. Comparing this netlist with the CAD netlist is a critical step in the process for the production of all complex pc boards. If there is a discrepancy between the two sets of information, production must stop until the discrepancy is resolved.

Next comes panel sizes. As complex pc boards are often built using large panel sizes, it's important to ensure that the fabricator has the panel size tooling in place for the pc boards being considered. As the panel size increases, the number of fabricators that will have the right size tooling decreases.

Then there's lamination. For high-layer-count pc boards with very tight component lead pitches, maintaining layer-to-layer registration becomes a major challenge. It is important to take into account materials shrinkage during lamination; to plot the working film sets with sufficient accuracy; to align the film layers to one another; and to align all the inner layers to one another.

Finally, aligning the drill to the images on the inner layers must be done with great care. All of that requires a great deal of process control and materials knowledge.