Over the years, the term “virtual” has become associated with many different domains. Virtual machines are now commonplace as a substitute for physical laptops or desktops, allowing for the emulation of computer systems. Of course, virtual reality is in the news daily as new headsets, apps, and games provide a substitute for images and sounds, allowing for the simulation of a three-dimensional environment. In the printed circuit board (PCB) space, some fabrication and assembly information such as artwork, drill, netlist, test, and component placement have been conveyed virtually to manufacturing for more than 30 years.
But what about articulating the very critical fabrication and assembly notes and drawings in an intelligent electronic (virtual) format? Virtual fabrication and assembly documentation has the potential to provide an alternative to the non-intelligent static versions of PCB drawings and supporting specifications. Instead, the requisite manufacturing instructions would be conveyed as data elements that allow the recipient tool to automate the planning and execution of the manufacturing process preparation. In the end, this would streamline the process of new product introduction, and at the same time, increase efficiency.
Virtualization of PCB Data
Prior to the 1970s, PCBs were designed by “hand-taping” components and traces using 4:1 red and blue line vellum. A precision camera then produced the 1:1 negative that became the manufacturing film. Drill information was conveyed via a drill tape. The artwork films and the drill tape were, of course, both physical formats.
During the 1970s, the virtualization of PCB fabrication and assembly information was initiated when Gerber Scientific introduced a machine-based format called RS-274-D that was supported by its vector photoplotters. That was followed by the RS-274X format (Extended Gerber or X-Gerber), released as an enhancement to the RS-274-D format. The new format embedded the aperture information into each Gerber file, eliminating the need for separate and potentially out-of-sync aperture definition information. During this same timeframe, the Excellon Automation Company designed a format to drive computer numerical control (CNC) drill and route machines.
The virtualization continued as specifications and formats were also developed to convey the PCB bill-of-materials, netlist, test, and component placement information to manufacturing. More recently, standards such as IPC-2581 and ODB++ have combined all of that information into a more intelligent xml-based format. During this time, however, a methodology to capture, and a format to convey, the critical fabrication and assembly documentation as intelligent data elements has been lacking (Figure 1).
Potential for More Virtualization
Most engineers and designers would probably agree that the creation of fabrication and assembly documentation is one of the more time-consuming, tedious, and potentially error-prone aspects of the product development process. The fact is, many teams expend a significant amount of time and effort creating and maintaining automation to support the detailed notes and images required in fabrication and assembly drawings. Likewise, the various electronic CAD (ECAD) tool vendors also expend a significant amount of time and effort developing functions to create and maintain items required to be included in the fabrication and assembly drawings, such as drill tables and pictorial representations of board stackups. The ECAD tool vendor's functions, combined with the design team's automation, help ensure a certain level of accuracy and repeatability; however, this information is still non-intelligent and non-virtual.
The single PCB or panel added to the drawing formats with notes, specifications, and dimensions conveys a static and potentially incorrect or incomplete representation of the manufacturing requirements. Furthermore, even in the best-case scenario where all of the notes, drawings, and specifications are created correctly by the product development team, the non-intelligent information is still subject to potential misinterpretation or, in the worst case, not even understood by the fabrication or assembly vendor.
Capturing and Conveying Notes and Specifications
Even the most accurately designed PCB will not be fabricated or assembled correctly if the documentation does not accurately and completely convey all of the unique and specific manufacturing requirements. To mitigate this risk, a structure that not only supports the capture of existing virtualized data such as artwork, drill, and component placement, but also supports the translation of drawings and documentation from the PCB design into electronic format, is required. The bottom line is that the information documented in the drawing notes and specifications must be captured as intelligent metadata. At a minimum, this includes the capture and electronic representation of the following:
- Fabrication notes
- Drill table
- Stackup/buildup and impedance requirements
- Part number and revision information
- Product summary
- Customer/designer information
- Specification sheets
- Assembly drawings
In the best case, critical dimensions should also be captured electronically.
Any system that supports a methodology to capture, and a format to convey, the above information as metadata should also ensure that the fabrication and assembly data would not have to be entered in its entirety for each design. Instead, templates based on design technologies could be established and applied to merge these requirements, along with board-specific information to create a comprehensive data set.
As an example for the board-level requirements, items such as board outline tolerances, board thickness and tolerances, silkscreen color, soldermask color, flammability rating, PCB standards, and plating requirements would all need to be captured. The type of graphical user interface that could be used to acquire this information and represent it as intelligent metadata, is shown in Figure 2.
Along with board requirements, most aspects of the manufacturing process could and should also be captured such as smallest drill size, number of unique drill sizes, and smallest trace. Likewise, most aspects of the assembly information should be represented in metadata such as test points, fiducials, number of components on each side, types of components, and QC information. The underlying concept of this approach is to allow the recipient tool to automate the execution and planning of the manufacturing process preparation. For example, if the solder mask finish type and color are defined electronically, the PCB fabricator could create a process through automation that would include material instructions based on the solder mask settings. Similarly, if the use of buried discretes was defined electronically, the PCB fabricator could create a process through automation that would include routing instructions based on the design's settings.