Why PCB Assembly to Edge Clearance is so important

Why PCB Assembly to Edge Clearance is so important

Arguably choosing the components that make up your board is the most important PCB design task. After all, your circuit won't work properly without the right components. The operation of the board also depends on the interconnectivity between components, through-hole or surface mount technology (SMT), via traces and vias. Although on-board operation is required, there is no need to deploy the PCB in the vacuum, and connections to external devices are also required.

Typically, electrical interface to nearby external equipment is through a common connector. However, this means that the edge gap depends on the signal type. In some cases it is desirable to have physical contact between boards, as opposed to wiring or cable connections, in order to receive signals between multiple devices simultaneously. For these cases, one board plugs directly into the other. A popular way to achieve this direct connection is to use golden fingers. Regardless of the connection method, clearance from the edge of the board is an important issue that affects PCB construction. Understanding the importance of edge clearance to PCB components will allow us to make design decisions that help simplify board manufacturing and assembly.

What is PCB component-to-edge clearance?

When considering PCB components, the following are most likely to come to mind:

l Passive Components - Resistors, Capacitors, Inductors, Transformers, Diodes, etc.

l Active Components - Bipolar Junction Transistor (BJT), Junction Field Effect Transistor (JFET), Metal Oxide Field Effect Transistor (MOSFET), Optocouplers, etc.

l Integrated Circuit (IC) - Can contain a single component type, multiple circuits or a complete system.

l Power supply - battery, etc.

l Electromechanical components - piezoelectric devices, switches, etc.

Listing all components that fall into one of the main categories above would be pretty exhaustive. Also, the list would not be complete unless we included wiring, cables, headers, USB, ethernet, and connectors like Goldfinger. Connectors must be included when considering clearance between PCB components, as these are the components most likely to be placed near the edge of the PCB.

Why is PCB assembly-to-edge clearance important?

The manufacture and assembly of circuit boards is carried out in sheet or standard panel sizes. The panel-on-board layout design must be done at the time of manufacture. You can leave this grouping task to the CM or incorporate it into the design phase. By performing panelization during the design process, you can determine the quantity of each board, which affects waste and manufacturing costs, and you can control the orientation of the board, which affects the de-paneling listed below for separating the boards back into individual units method.

lScore

Do it in a straight line. Sufficient clearance between components and edges is required to prevent damage to components during separation.

lRouting

More flexible than scoring. The router bits are used to keep track of odd shapes. Separation results in split sheets and irregular board edges.

Creating the optimal PCB layout design requires your contract manufacturer (CM) ability to tailor it to your specifications. This includes designing PCB assembly-to-edge clearances that comply with the depanelization techniques provided by your board manufacturer. As a PCB development team committed to a smooth and efficient process, high-quality, reliable products should be readily available.