Schematic Capture and PCB Layout for Manufacturing

What Is Schematic Capture?

Schematic capture is the process of creating an electronic diagram or an electronic schematic. This is the first step in the design of most printed circuit boards. In many cases, a schematic editor or schematic capture tool is used, though you could in theory use CAD software, as well. Or you may create the initial schematic in schematic capture and PCB layout software.

The Difference between Schematics and PCB Layout Drawings

The 2D layout of a basic circuit is not yet ready to be laid out on the printed circuit board. The printed circuit board consists of layers. The simplest PCB consists of a copper layer and a substrate layer. The copper layer is conductive and creates the circuit, while the substrate provides a surface that components can be glued, screwed, or otherwise attached to. The schematic showing where key components will be mounted doesn’t tell the PCB manufacturer how to make the PCB unless you’re making a basic breadboard.

The design process is more complex when you have a 3D schematic with thru-holes, whether this is necessary for the SMT or surface mount technology component to reach an inner copper layer or connect it to something on the other side of the board. A 3D model of your circuit board won’t necessarily give PCB manufacturers the details they need to make the product, either. This is where schematic capture and PCB layout software comes in.

How Do You Create a PCB Layout from a Schematic Diagram?

The schematic is the basis of your design. You must have this initial outline of the circuit paths and descriptions of key components before you can do anything else. The schematic can be considered the high-level blueprint for the PCB.

PCB editing software can import this schematic unless you import it or replicate it inside of an electronic design automation or EDA application. In some EDA software applications, you’d start the conversion process by selecting the option “convert to PCB.” However, it is your responsibility to make sure that there are no errors in the component footprints, overlaying items, or overcrowding them based on design rules.

The resulting diagram is then used as the basis for the PCB design detailing how thick the PCB layers will be and how the SMT components connect with each. The final design in the PCB editing software becomes the PCB file.

The PCB file is a data file containing the printed circuit board design. The PCB manufacturer doesn’t need the program used to create the file or the original schematic. They need the PCB fabrication data typically contained in the Gerber files. The PCB design tools may create a Gerber file for each layer of the PCB or a single file for the entire PCB to be manufactured.

What Is a Gerber File?

A Gerber file is an open ASCII vector format used for PCB designs. It is the industry standard for PCB software. It contains everything required to manufacture the PCB. This includes the locations and layout of the solder mask, drill data, and the drawing legend. It has all of the information required for photo-plotters, legend printers, solder paste layers, and direct imagers. It provides the information used to create stencils and the location information loaded into automated optical inspection machines. In summary, it contains the necessary information for PCB assembly.

There are two main types of Gerber file formats. The Standard Gerber file format or RS-274-D is now obsolete. The Extended Gerber file format or RS-274X adds meta-information to graphics objects, though a Gerber file doesn’t have to include this information. For example, pads may be labeled as a via pad or SMD pad.

Files with these attributes are called X2 files. Those without this meta-information are called X1 files. Both types typically have the .gbr file extension.

How Do You Turn a PCB into a Schematic?

The PCB design process is an iterative one. You may make changes to the schematic, replacing parts that have become obsolete or deciding to use two capacitors instead of one. In this case, you’d make changes to the schematic drawing and then update the PCB. However, designers may get feedback from the manufacturer and adjust the schematic as a result. It may be easier to import the PCB file and reverse it to get the revised schematic. In some cases, the engineers may have the PCB files for an existing design but not the original schematic.

This process (schematic capture and PCB layout) isn’t as easy to turning schematics into PCBs. There are a few tools that can create schematics from netlists. Another option is studying the PCB files and manually drafting up a schematic. If you already have the schematic drawing, you’ll have to add the components and the nets in the schematic. Just make sure you update the reference designators, parts lists, and other information in your master file.

If you would like to learn more about how schematic capture works with PCB assembly, reach out to the professionals at Geospace Technologies. Since 1980, we have stayed at the forefront of engineering and manufacturing innovation. Contact us or submit a form about your inquiry.