Before computer graphics became staples in science fiction movies and television productions, your favorite starship was a conglomeration of metal, plastic, fiberglass, and wood crafted together by gifted model makers. The main concern for those artists was balancing the design of the model so that it would film well under stage lighting, while at the same time making it look powerful and fast to hold the audience’s attention. The models also had to match the interior stage sets and be robust enough to build in lights, explosions, and other effects. And all of this had to be done within time and budget constraints, or the producers might just delete the ship out of the script.
When you think about it, there are a lot of similarities between what went into building one of those movie models back then and laying out a printed circuit board today. Not only do we face time and budget constraints as they did, but we have a critical balance to maintain in our designs as well—the components must be placed so that our boards have the best operational performance while also having the ability to be easily assembled.
How can you create a component placement in your PCB layout that balances the needs of both performance and assembly? By paying close attention to the PCB component-to-component spacing when laying out your design. Here are some ideas to keep in mind that can help you with that.
The Importance of PCB Component-to-Component Spacing
Placing the components on your printed circuit board design is the key to creating a PCB that performs as expected. Bypass capacitors must be close enough to their associated devices to provide an immediate reservoir of power and reduce parasitic inductance between them. Schematic signal paths must be recreated in the layout by placing the components precisely so that the high-speed signals can travel the shortest distance possible between pins. The placement must also be organized so that critical routings doesn’t cross split power planes and thereby lose their return paths.
These are important considerations for designing a successful high-speed printed circuit board, but as we said, there is a balance that must be maintained as well. Parts that are placed close together for performance may end up impacting the ability of the contract manufacturer to easily assemble the board. This may result in added time and cost, or at worst, costly redesigns. To avoid manufacturing problems like these, there are some things you can do with your component placement to help ensure the success of your PCB assembly.
Tips For Optimum PCB Component Spacing
Component placement standards will vary depending on the capabilities of the fabrication vendor and the assembly processes used by your contract manufacturer. There is, however, a lot you can do during layout to make your component spacing and placement more assembly-friendly:
- IC’s that have their supporting components, such as capacitors and resistors, placed unnecessarily close can impact the flow of solder and make rework difficult. Although these parts need to be close for board performance, being too close can cause solder problems plus make it more difficult for a technician to clean up a solder anomaly.
- Multiple components placed close together that all connect to a large strip of metal may help electrical performance, but it also creates a large heat sink. This could adversely impact the ability for a good solder flow. These components should have smaller width traces connecting to the strip of metal for thermal relief.
- Components that have their pads covered with a large metal plane will have the same heat sink problem, which could lead to bad solder joints due to uneven heating. The use of thermal reliefs from the pad to the plane will help solder integrity and placement accuracy.
- Place your components with consideration as to which solder process is going to be used. Boards that are going to go through solder reflow can have a tighter placement than those that are being wave soldered.
- Find out the type of solder mask is being used and the capabilities of the fabrication vendor that is building the raw board. Their ability to accurately print the solder mask will determine the minimum pad-to-pad spacing.
- Part of the assembly process is plugging in connectors and probing test points. Make sure that you give these components plenty of room in your placement for human interaction to avoid physical abuse when attaching a cable.
There are many other design for manufacturing (DFM) techniques that your CM can recommend to you to best design a PCB for error-free assembly. These tips listed here, however, will give you a good start for better placement.
Partner with Your Contract Manufacturer to Optimize for Assembly
When it comes to component-to-component spacing considerations, you have a great resource available to you in your contract manufacturer. By using a CM that specializes in prototype, pilot, and low-volume assemblies, they will have a clear idea of what will work best for your specific project. A high-volume CM has to force more constrained placement requirements to support their equipment and processes, whereas a low-volume CM can work directly with you on the specific placement needs of your circuit board.
At VSE, we excel at working with clients to get their designs assembled while at the same time offering them recommendations for layout enhancements that will support their future high-volume goals. We can do this because of the following benefits we offer our customers:
- Our relationship with our fabrication vendors gives us the advantage of being able to get designs through a semi-customized assembly process to help your design constraints.
- Our engineering team can make simple adjustments to your layout if so authorized by you to help streamline assembly and testing.
- We have new state-of-the-art SMT placement automation that can place components with ultra-accurate precision.
- Our selective soldering system can handle components with 1.5mm component-to-component spacing.
All of these benefits mean we help you achieve the best results in your PCB assembly by helping to optimize your design while employing the highest-quality manufacturing processes.
