A printed circuit board, or PCB, is a blank circuit board upon which circuit-mounted components such as capacitors, resistors, transistors and potentiometers are mounted. Blank boards are typically used in self-assembly projects, to make circuit assembly quicker and easier for the end-user. A fabrication drawing tells the board manufacturer exactly how you want your board to look, including information about dimension, connection, and holes. Each board has its own connection and dimension specifications. It's prudent to follow certain best practices when having your board fabricated. This reduces the chances of design flaws and manufacturing mistakes in your PCB. The Fabrication Drawing fulfills several important functions to support the circuit board manufacturing process: It provides enough information about the design for the bare board fabricator to prepare a quote; Technology is the knowledge of how to create, produce, or perform some object or function. In PCB design the term technologies is no more than a categorization of values or capabilities of a manufacturer. These values are based on capabilities of the manufacturer's equipment and the overall process. The three controlling points are etch, drill, and registration. Other capabilities influence the overall category, but these are the most important. •Table/legend of drill sizes, tolerances, and quantity with a symbol legend. •A drawing of the board with the respective symbols representing the holes in the board. •Graphic representation of the board cross section detailing the layer number, type, and thickness. •Manufacturing notes specific to only the manufacturing process and not the assembly process. •Additional information such as revision and data and company information should also be placed on this drawing as well as any other internal tracking data. •Detail of all cutouts, slots, and notches that are to be created during the manufacturing process. •Outline or border of the board. •Dimension, in x- and y-coordinates of the overall board. •A hole to edge dimension for one hole near the edge, in the x- and y-coordinates for drill alignment verification. (If there are no holes in the board, this is not necessary since there are no holes to align.) To discuss processes and details of a PCB and the fabrication process, the designer should be familiar with many of the terms used within the industry. Also, there are several levels of fabrication according to the level of technology. These are known as the fabrication technologies. The process for each technology is similar, but the capabilities are different. The manufacturer must know what processes the designer requires and the required values for each process. Starting with material selection and controlling specifications, the designer must specify limits and values for these steps: Plot Signal Chain Left to Right Use a Gerber File Dimension Outline Define Hole Location Use PC-6012 Specifications For more information about PCB, or to learn more about the online quote and ordering process, please visit //www.PCBway.com.
It adds all the extra details about the build that aren't easily incorporated into the data files, like material and final finish;
It lists the criteria by which the finished product will be evaluated for acceptability;
It serves as a tool to be used during final inspection;
It is a record or document to store the history of a product by title, part number and revision; physical dimensions, and lists the name of the designer and possibly several other supporting entities as well as the company name and address, etc.;
The notes area is like an Instruction Manual for manufacturing your product. Many of them will reference acceptability requirements.
The Fabrication Drawing
To provide the PCB manufacturer with a clear description of the requirements and the limitations of a design, the designer should supply the manufacturer with fabrication notes and a fabrication drawing, along with all data files. These notes may be supplied in paper form, but a Gerber format (an electronic drawing format) is preferred so it may be maintained with the customer's files. The fabrication notes should contain the following essential items:
1. Set-up
2. Imaging
3. Etching
4. Multilayer pressing (multilayer boards only)
5. Drilling
6. Plating
7. Masking
8. Board finishing
9. Silk screening
10. Route
11. Quality control
12. Electrical test
The signal chain refers to the sequence of components from power supply through to the output. A circuit may not always be linear, for example it may have branches. But for the purposes of accuracy, your fabrication should denote the intended signal chain in a linear fashion. This way the manufacturer knows exactly where to include copper conductor strip material. This is metal the runs along the base of the PCB, between the turrets. The conductor strip carries current between the board-mounted components. If portions of conductor strip are missing, the fabricated circuit won't work.
Gerber files are the industry standard file type of PCB fabrication drawings. Gerber files are specifically configured to allow you to include layered drawings. This permits you include various drawings which the manufacturer can superimpose on each other to create a complete representation of the board layers, including solder mask, hole size and connection type. A Gerber file generator lets you select industry-standard specifications, so rather than drawing each hole to size, you select from a drop-down menu of industry recognized hole dimensions.
Your drawing should include board dimensions in millimeters. While this sounds like an obvious step, if the information is missing the fabrication software used to cut your board may revert to default dimensions and cut your board to the wrong size.
The location of the holes on the board are crucial to the success of any circuit board assembly project. Position them too close and components won't fit onto the board, position them too far apart and the end-user may run out of room on the board during the population stage.
These are a set of industry-standard PCB board fabrication specifications. Using terms, for example "table 3-9" when referring to conductor thickness, you remove the potential for misinterpretation. These specifications are clearly defined by the Association Connecting Electronics Industries.
