Space may be the final frontier on Star Trek, but in the little universe of printed circuit boards, it seems to get used up in a hurry. It’s not surprising though as PCB form factors keep decreasing in size to fit into smaller devices, the amount of electronic circuitry on them keeps increasing to support new functionality. This has caused PCB designers to push the limits on how close they can place their parts to each other, and in some cases, it has resulted in problems for PCB manufacturers.
To avoid designing a circuit board that isn’t manufacturable, minimum standards for component spacing must be adhered to in the design layout. Of course, there are many other factors to consider as well, including the electrical and thermal performance of the board, but designing for manufacturability (DFM) is just as important. There are industry standards that offer some assistance with this, however, and here we’ll look at how IPC component spacing guidelines can help as you design.
Why PCB Component Spacing is Important for Manufacturing
First, let’s review what some of the assembly problems are for PCB manufacturers when minimum spacing requirements aren’t met:
Component installation: Although automated placement equipment is extremely accurate, those systems still need enough room to operate in. Parts that aren’t candidates for machine placement, will need even more room for technicians to be able to work with them.
- Soldering: For boards that are to be wave soldered, the spacing between parts is extremely important to prevent shadowing of smaller parts by larger. As with component installation, those that are to be manually soldered need enough room for the technician to be able to work with.
- Test: There must be enough clearance between test points and components to allow access for the probes of the test fixture. There also needs to be proper clearance around the perimeter of the board for the test fixture outline.
- Access: Printed circuit boards usually have connectors, switches, and other interfaces that require access for technicians. There needs to be enough clearance to fit fingers and tools in for a test, debug, rework, and normal operations.
In addition to the manufacturing requirements, there are a host of EMI, signal integrity, and thermal reasons for proper component spacing as well. The important thing is to have a list of those different spacings available, and then work from them. Here is where the IPC standards can provide some information.
IPC Component Spacing Guidelines to be Aware Of
Here are some of the IPC standards that are available to PCB designers for access to spacing guidelines:
- IPC-7351B: This standard specifies the land pattern requirements for surface mount parts. Here you will find pad specifications and spacing details for PCB design.
- IPC-SM-782A: This is the original standard for land pattern and surface-mount design. Although it was superseded by IPC-7351 (above), it still has some pertinent information.
- IPC-A-610: This is the general acceptability of printed circuit boards and electronic assemblies standard. It will cover areas such as how hardware is to be assembled onto circuit boards.
- IPC-2221B: This standard covers various aspects of printed circuit board design, including spacing guidelines for voltage and other electrical considerations.
As you can see, there is a lot of information available to PCB designers through these guidelines. So much in fact that trying to pull specific details out can be challenging when you consider the amount of material that has to be researched. Fortunately, there is a more convenient resource for all of this same information available to you from your PCB contract manufacturer.
For many years, your local PCB CM has been building circuit boards to industry standards, and therefore they are well acquainted with the different IPC guidelines. Additionally, the PCB CMs have empirical data based on their processes and experience in building circuit boards that will satisfy the customer’s needs. This combination of knowledge and experience can work the best for giving you the component spacing guidelines you need for the successful manufacturing of your PCB design.
Tips on Following These Placement Guidelines
To leverage the capabilities of your PCB CM, the best thing to do is to work with them ahead of the design to have all the rules and constraints ready before you start component placement. Next, make sure that these rules are loaded into your PCB design CAD system so that you are placing your parts according to the correct spacing standards. Another good use of your relationship with the PCB CM is to work together with them to find components or circuitry alternatives that can give you more space to work with on your board.
At VSE we have an engineering staff that is ready to help you with the correct spacing rules and constraints for your circuit board component placement. Since we specialize in prototype, pilot, and low-volume complex assemblies, our engineers already know what will or won’t work when placing PCB components. The strong working relationships with our component and PCB fabrication vendors allow us to support non-standard constraints on projects that are needed quickly. Our manufacturing experience and capabilities can successfully build these unique boards, while at the same time our engineering staff will help refine those designs to support high-volume production runs in future revisions.
