My family and friends will often see me working on a printed circuit board design and joke that the colorful lines and shapes look more like a video game than real work. I can forgive their humor because they don’t know all of the effort that goes into the creation of a PCB.
Those of us in the industry, however, know that PCB design and manufacturing is no game. The cost of engineering and manufacturing time is enormous; the engineering software and manufacturing equipment are expensive to operate and maintain; and the cost of PCB materials and components isn’t cheap. This makes it extremely important to design boards that can be manufactured efficiently and correctly, without adding costs for assembly rework and corrections.
To design a PCB that can be assembled without problems means that the PCB designer needs to understand the requirements of the assembly process up front. Too often, design for assembly (DFA) practices are viewed as simple checks the manufacturer makes after they receive the PCB design data. Instead, these guidelines are critical for the PCB designer to observe during layout. Let’s take a look at why these PCB design for assembly guidelines are so important, what you should know about them, and how your contract manufacturer can help you with them.
Why Are PCB Design for Assembly Guidelines Important?
When it comes to anything you do—whether it’s cutting the grass or cooking a meal—we usually want the end result to turn out the way we planned. The same can be said when designing a PCB—we should worry first about getting it to work first, right? The answer here is both yes and no.
Not only do we need our PCBs to work the way that we’ve designed them too, but those boards must be manufacturable for a reasonable price as well. There are several factors that can contribute to a board not being considered manufacturable. Here are the main categories of problems:
- Components: Parts that are unique or not readily available will have higher costs attached to them. Also if the lead times on some parts cause delays in the board build, that will add to the expense as well.
- Placement: How you place your parts can affect how the board is manufactured and drive up costs. Even simple things such as how a component is rotated can affect its solderability.
- Layout: Your PCB design will usually connect to other boards or interfaces. If these considerations haven’t been accounted for up front, it could add to the expense of manufacturing the entire system.
If it costs too much to manufacture a board the way it was designed, then the design may end up not being used due to its overall expense.
Some might argue then that this kind of thinking doesn’t hold true for prototypes, but remember that a prototype will usually transition into high-volume production at some point. If the design isn’t optimized for efficient assembly during prototyping, it will eventually have to be redesigned for mass production. This will result in yet another round of expensive prototyping to re-verify the integrity of the design. It is a much better practice to follow good design for assembly guidelines from the very beginning of the design.
PCB Design Guidelines for Assembly You Should Know
For the most efficient assembly of your printed circuit board, there are certain design for assembly guidelines that engineers should know:
- Use components in your design that are readily available for manufacturing. Parts that are going end-of-life (EOL) or are not recommended for assembly can cost more and delay your build.
- Surface mount technology parts (SMT) on both sides of the board will add costs for stencils and assembly challenges. If possible, try to put all SMT parts on one side of the board.
- Unusually sized or tall parts can cause problems with solderability of the board. Avoid placing smaller SMT parts next to these parts if possible.
- Avoid placing components too close to the board edges on smaller boards to minimize problems when breaking these boards out of their panels.
- Component orientation can cause problems with the automated inspection if polarized capacitors and diodes are facing different directions. Try to maintain an orthogonal placement where possible.
- Place parts for best soldering results. Parts should be oriented correctly for best results as well as provide room for soldering fixture development.
- Provide test probe points to critical circuitry nets for engineering debug and testing.
- Optimally place connectors in relation to other system-level boards and interfaces. Make sure to allocate room for plugging and unplugging cables during assembly.
These are just some of the assembly guidelines that will help your PCB design to be more successful during assembly. The best way to understand the specifics of these guidelines though is to work together with your contract manufacturer before you begin a design.
Assembly Guidelines for PCB Design: How Your CM Can Help
Working together with your CM before and during your design will give you both the best opportunity to be successful in building your PCBA. Your CM should review your design to help you to make the best component selections to avoid the cost and delay of EOL parts. They should also work with you on your component placement to enhance your design’s manufacturability. By helping you to design your board according to good design for assembly practices, your design will enjoy better yields, costs, and cycle times.
At VSE, we excel at manufacturing low-volume, high-complexity printed circuit board assemblies. We hold ourselves to the highest standards to help our customers design their boards to be ready for high-volume production. This way, they can take the design and documentation that we create and easily transition into a higher-production volume facility with no impact on the design.
