In hindsight, it’s incredible how much I learned about manufacturing as a child while building model airplanes. For instance, most models begin with building sub-assemblies, like an airplane engine and propeller. These sub-assemblies are then set aside to integrate into the complete model later. There was always a risk of losing them in my messy room, but they had to be built in a specific order and precisely if they were going to fit. Now, as an adult, I’m finding the same principles of model building apply when manufacturing circuit boards designed for assembly into full systems.
We are all familiar with the need to design a circuit board for performance and functionality. If the board doesn’t fulfill the function it was designed for, the entire system will ultimately fail. Most PCB designers understand the need for design for manufacturability (DFM) rules. But do designers understand the importance of full system design? If the PCBs we design doesn’t work with the rest of the system, it can be expensive to correct them. In this article, we will look further into DFMA and reducing manufacturing overhead costs.
What is DFMA?
Design for manufacturability, or DFM, has long been part of circuit board design and layout. When PCB layout was in its infancy, the wider trace widths and spaces in use and the more manual aspects of circuit board assembly didn’t require tight manufacturing tolerances. Later, as trace and space widths narrowed and circuitry densities increased, the tighter tolerances demanded more attention from designers. Today’s DFM requirements include the design for fabrication (DFF), design for assembly (DFA), and design for test (DFT), and each of these is critical to the success of the circuit board.
DFMA, on the other hand, stands for design for manufacture and assembly. DFMA ensures the buildability of an individual part and that the individual part will work with others to complete the final assembly. In electronics manufacturing, DFMA guarantees that a board is designed to be manufactured and integrated into the entire finished system. Some of the concerns for DFMA that extend past the standard DFM checks include:
- Board to board connections
- Cabling and wiring
- Flex circuits
- Human interfaces (switches, etc.)
- 3D clearance to other system obstacles
Next, let’s look more into some of the specific requirements for DFMA checking and how they can save time, expense, and labor.
Considerations for DFMA and Reducing Manufacturing Overhead Costs
Ensuring that a circuit board design is manufacturable according to standard DFM rules can save time and money by checking for some of the following design problems:
- The parts ordered for the board are correct and match all of the land patterns.
- Placed components have sufficient space between them for automated and manual assembly.
- The components are also oriented correctly for automated soldering systems.
- Spacing between traces and other metal board objects conforms to the minimum requirements to avoid solder bridging and shorts.
- The board is set up with a test strategy that includes accessible test points for automated testing.
These are a few of the conditions that a PCB contract manufacturer will be looking for when they conduct a DFM review of a circuit board design before the board enters production. If the board fails any of these areas, the PCB CM will recommend alterations to the layout to ensure the best assembly yields.
To ensure that the board is designed for system assembly, it should be checked for these additional problems:
- Accessibility: The circuit board must be installed, configured, and operated in its designated system.
- Mechanical fit: The board must also fit where it is designed to go. These checks include correctly interfacing to support brackets, braces, connectors, and wire harnesses.
- Adequate clearance: The board must have enough clearance to other parts of the system. Will it interfere with the movement of any other system components, and will it have adequate cooling where it is positioned?
- Electrical connectivity: Even if all of the physical connections are a match, it is still important to verify that the pin-outs of the connectors match electrically. It is not uncommon for board-to-board connectors to be mistakenly pinned out backward.
To verify that the board is ready for manufacturing and full system assembly, many designers rely on 3D PCB CAD systems with mechanical import capabilities. 3D CAD systems give the designer the ability to create a virtual prototype before getting the board built for the first time. After that, a prototype is usually ordered and used for both board and system debug. By the end of this DFMA review cycle, the production will avoid some of the more common problems affecting system builds, saving time, money, and production labor.
There is a lot involved in a complete DFMA check, and fortunately, your PCB contract manufacturer is prepared to do the job.
How Your PCB CM Can Help with Cost Cutting Ideas on Your Next Project
Many PCB CMs today are set up to do full box builds in addition to standard circuit board manufacturing. There are many advantages to using this approach for your system build:
- The single-vendor approach to system builds centralizes project management.
- Processes such as part procurement and design reviews are also centralized, removing the need to coordinate multiple vendor participants.
- With all of the system assembly happening in one location, periodic system reviews can be conducted during any phase of production.
- The system can be built together from the ground up instead of building individual parts and then sending them back to their originators for any needed changes or corrections.
At VSE, we have included box builds and cable and wiring harness assembly as part of our full-feature manufacturing services for many years. We will ensure that all of your system’s components pass the expected DFMA rules to ensure they operate as designed.
