Learn the Fundamentals of CAM: Manufacturing Your PCB
Computer-aided manufacturing (CAM) is a critical part of modern electronics production. It’s helpful to understand the process and how advanced CAM processing tools enable a smooth transition to the production phase.
Gone are the days of drawing circuit board artwork on paper, transferring these drawings to copper boards, etching the patterns, and soldering the components by hand. All of these tasks have been replaced by their digital counterparts, each guided by some combination of electronic and physical machines.
As a whole, this process of digitizing and automating the manufacturing process of printed circuit boards (PCBs) is known as computer-aided manufacturing or CAM (Figure 1). CAM is the intermediate step between the electronic design phase and the physical manifestation of the product.
Figure 1. PCB pick and place machine used in CAM
What’s Required for PCB Manufacturing?
Modern printed circuit boards are manufactured in a complex, multistep process. Laminates of conductors and insulators are etched and sandwiched to create the base board, known as a stackup. The electrical parameters of the conductor and the insulator are required so that the manufacturer can source the appropriate raw materials.
The conductor artwork for each layer must also be provided in one of several formats, the most common being OBD++ and Gerber. Finally, a drill table and locations must be provided for every via and hole in the design.
In addition to these basic requirements, a variety of other data might be used in the manufacturing process. This includes artwork for protective solder mask layers, artwork for silk screen layers, specification of areas to apply solder paste, test points and a netlist for verification, and component pick and place coordinates, to name a few. All of this information is managed and generated by sophisticated software called a CAM processor.
The CAM Processor
CAM processing is not limited to the world of printed circuit boards. In the design of mechanical parts, CAM processing is also used to translate a physical object into the commands that guide a machine to produce it. The machine might be subtractive, as in CNC milling, or additive, as in 3D printing.
Fusion 360’s CAM processor includes all of these mechanical capabilities along with the aforementioned electrical ones. The goal is to eliminate several steps from the traditional multi-platform process and ensure data integrity and preservation along the way.
With regard to the manufacturing of PCBs, the CAM processor can be distilled into three main areas of focus. Design rule checking (DRC), design for manufacturability (DFM), and PCB output packaging. DRC happens early and continuously in the design process to ensure that the various features created by the PCB designer meet the rules set forth for a particular application.
Those rules may come from the manufacturer or, more commonly, from the best practices known in effective PCB engineering and can include items like creepage, clearance, via density, signal integrity, and so on.
DFM rules, on the other hand, tend to originate at the manufacturer and are intended to minimize the risk of manufacturing issues. These rules may include physical requirements specific to the manufacturer's equipment or higher-level rules surrounding testability and yield.
Finally, the last and primary task of the Fusion CAM processor is to convert all of the native PCB data into any of the many file formats expected by the manufacturer. All of these various files are packaged up and released from the design in a stand-alone folder that can be sent for review. Fusion 360’s CAM processor supports all of the industry standard file formats, including OBD++.
The Process of CAM
The first step in CAM processing for a PCB is to review the design. In Fusion 360, there is a CAM preview button for this purpose (Figure 2). Engineers can review the board's copper layers from this view and also have the option to change various parameters, such as the solder mask color.
Figure 2. PCB Preview view in Fusion 360
The OBD++ data format has become the industry standard and aims to exchange information between design and manufacturing facilities within a PCB fabrication unit. Fusion 360 supports OBD++ export with a single click and will use any valid CAM job file to control the configuration (Figure 3).
Figure 3. Shown here is the one-click OBD++ export feature.
For more traditional CAM export, there is a dedicated CAM export tool to generate Gerber files, Excellon files, pick and place tables, and a bill of materials (BOM). These are the industry standards used to have your board manufactured. Based on your DRC Layer stackup setup, the CAM export will load the respective CAM job.
For the example shown in Figure 4 below, it loads a 4-layer CAM template and previews the list of files that will be generated in Gerber format in the CAM export dialog notice. The CAM export tool is a one-click solution that prompts you for the location to save the files. After a few seconds, all manufacturing files will be created and compressed in a specific folder.
Figure 4. CAM export
For more refined control over the CAM output, the CAM processor tool can be invoked. Both ODB++ and Gerber formats are available as output options. Once activated, the CAM processor automatically chooses a CAM template appropriate for the design. For example, on a 4-layer board, the template_4_layer.cam will be chosen.
These templates can be modified to suit a designer engineer’s particular needs, or even shared among a team to standardize manufacturing outputs. Custom CAM configurations can be saved and loaded directly into the CAM processor as shown below in Figure 5.
Figure 5. Loading and saving CAM configurations
Finally, once the CAM processor is configured, simply clicking the Process Job button will initiate the process of creating all the output files as specified (Figure 6). The resulting files can be compressed and emailed to the PCB manufacturer to begin production of a fully assembled board immediately.
Figure 6. CAM completion
CAM Bridges the Gap
The tools used to design PCBs are distinctly different in their focus from the tools used to manufacture them. CAM processing bridges this gap, and presents the important elements of a PCB design in the proper way. Fusion 360 is a fully integrated PCB solution that offers a featured set of front-end design tools and a highly capable and configurable CAM processor for seamless manufacturing support.
With only a handful of clicks, a design engineer can send off their latest creation to be prototyped or mass-produced anywhere in the world. More about Fusion 360 and its manufacturing features can be found here.
All images used courtesy of Autodesk
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