3. Refining the PCB LayoutInitially, the PCB layout is constrained by mechanical considerations related to the Intermediate Data Format (IDF). In 1992, IDF was developed as a neutral format for exchanging PCA (printed circuit assembly) information between PCB layout design (ECAD) systems and mechanical CAD systems; since then, IDF has continually evolved. An IDF file is actually two files: the first file contains information about the physical characteristics of the PCB, while the second file holds data on the size and shape of each PCB component.
Once the ground rules have been established with an ECAD system, a preliminary circuit trace layout is created that indicates the “keep out” areas, as well as the locations for plated and nonplated holes for component placement. Electrical and electronic design optimizations are performed to confirm component selection and placement, circuit traces for power and ground considerations, and general circuit logic. After one or more iterations, a refined layout with components is transferred back via IDF to the mechanical engineers, so they can check against the preliminary packaging design for proper fit.
While MCAD software is getting easier to use, ECAD software ironically is becoming harder to use. Due to the rapid changes occurring in the semiconductor industry, it is also becoming more specialized.