Everyone in our business knows that the purpose of a prototype is for proof of concept and to iron out the bugs—you want to make sure that what you have created is going to work before you commit to producing it in large numbers. Just like you would try out a new recipe before serving it at a dinner party, or view a mock-up before printing 500 fliers, prototyping your new PCB design allows you to catch errors that could be costly, or make design changes that will improve your device.
Of course, for most designers, the ultimate goal is to eventually scale that proof-of-concept build into full production, so it’s desirable to design the PCB with manufacturing in mind. For a production run in larger quantities, you need to make sure your circuit board can run through the automated manufacturing and testing processes without any problems. To accomplish this, there are several points to consider when designing your PCB prototype. Let’s take a look at some of these and what these requirements to build a PCB prototype mean for you as the designer.
PCB Design Recommendations for Prototype Builds
PCB design requirements for prototype builds can vary a lot depending on what your production goals are. PCBAs that are not going to be mass produced can virtually be hand built, and the design requirements will not be as stringent.
Most circuit board prototypes, however, will be funneled into regular, high-volume production runs once they have been tested and approved. To make this transition, it will be in your best interest to design your PCB prototypes with the following design for manufacturability (DFM) and design for test (DFT) considerations in mind:
- Component-to-component clearances: How close each component is to another could affect automated pick-and-place machines, which require minimum spacing tolerances for optimum performance. Additionally, minimal spacing can also cause problems during the soldering processes, and make manual rework more difficult.
- Component-to-edge clearances: Components that are placed too close to the edge of the board can affect how the board is handled during assembly. The parts may conflict with automated assembly line machinery or vacuum drawdown test fixtures.
- Component locations: How a part is placed on a board can cause problems during soldering processes. Large parts that precede smaller parts through wave solder will cause shadowing of smaller parts directly behind them leading to unsoldered connections.
- Testpoints: In addition to probe points for debugging, your board will eventually need a full complement of in-circuit test points for automated testing. You can add them later, but that may adversely affect critical placement and routing. You can save yourself a lot of time by adding or making allowances for them now.
These are just a few of the DFM and DFT requirements that can make or break the successful production run of a PCB. You can get more complete DFM and DFT information from your contract manufacturer. It is also recommended that you make allowances for any circuitry that is still uncertain in your prototype. This would include adding alternative part footprints and connectors for off-board connections now so that you don’t have to respin the prototype to add additional circuitry later.
The important thing here is to be accurate in your design and to plan ahead for all of the phases of production for your PCBAs. You need to understand all the design constraints that are applicable to your design for it to go through production, and you need to make sure that everything that you are doing is well documented.
Your prototype may not need this level of precision design to test its functional concepts, but for it to eventually transition into mass production, you should be incorporating DFM and DFT requirements from the start. The worst thing that can happen when you are ready to transition into full production is to be forced to completely redesign your board to incorporate missing DFM and DFT requirements. Partnering with a CM with engineers on staff to review your design and help resolve any of these issues before your prototype is produced is the best way to avoid this.
Documentation Requirements to Build PCB Prototypes
In the same way that you should plan ahead with your design requirements so that your PCBA will be ready for full production, you should also plan ahead in the creation of prototype PCB manufacturing documentation. Documentation that is hastily created can be unreadable or even incorrect and will need to be completely re-done to pass the design on to a high-volume manufacturer. However, if your documentation is good from the start, you will only need to focus on changes resulting from prototype testing, which will save you time and effort.
Another important aspect of your prototype documentation is that it needs to be as complete as possible so that you can easily incorporate any required changes. As you test and work with your prototype builds, any hardware modifications that are made will need to be added to the documentation. Working with incomplete or messy documentation at this point can be a major frustration.
Additionally, if the CM makes changes to the design to get it through fabrication, then those changes need to be made to the documentation as well. A quality CM will partner with you on your documentation to ensure these changes are made. Finally, all changes will need to be reintegrated with the main design database so that future iterations of the design can easily be worked on.
Engineering Support from Your CM Can Help Your PCB Prototype
One of the greatest resources that you can use when designing your PCB for a prototype build is your CM. There are a lot of pitfalls that can derail what would otherwise be a successful prototype build, and the engineering experience of your CM can help you to steer around these problem areas.
For instance, your CM should have the latest component information at their fingertips. If the components that you are using in your prototype have a history of being problematic due to availability, price, mechanical problems, or performance, your CM should be able to work with you to resolve these issues.
At VSE, we have built a network of trusted relationships with our component vendors and distributors. With our regular component status updates from these partners, we can advise you immediately if the components that you are using are going to be a problem, and we can recommend part alternatives or help you with a redesign.
We can also work with you on DFM and DFT issues up front so that your design will be ready for full production once the prototype phase is complete. At VSE, we have the skills and knowledge you need to design your board right from the start. Let us help you with the requirements to make your prototype build a success.
