When designing PCBAs, what is your primary objective? Of course, getting it to work is the foremost concern; however, what is your chief focus during the design process itself? Perhaps it is board performance or quality once deployed. Or maybe the speed, efficiency, or flexibility of the development cycle are most important to you. All of these are highly desirable attributes of a good PCBA or board development process. And they do require a concerted effort during design to be realized.
Today, in contrast to a few years ago, it would be difficult to find a PCB designer unfamiliar with the need for targeting manufacturing during design or the benefits of DFM for development. These include better quality boards, faster iteration speed, and increased efficiency. This targeting of the PCBA manufacturing process during design is essential for the best board build. When coupled with DFA and DFT, your entire development process can be optimized. The same is true for PCBA reliability once put into operation. Let’s define the design principles that have the most impact on your board’s performance and why it is important that design for reliability be included to optimize your PCBAs.
Requirements for Optimal PCBA Performance
How a PCBA performs is determined after development and production, once it is placed into operation. The objective during this phase is for the board to consistently perform its functions over its lifetime or be reliable. Having a 0% failure rate for all boards produced is a very high bar, as the board may be subjected to unforeseen circumstances that were not taken into consideration during design or manufacturing. Therefore, we should modify our objective of minimizing the failure rate and maximizing the operational lifetime. Although performance is a post-production metric, it is determined by actions taken during development.
An effective PCBA development process is essential to producing the best boards with a low probability of failing in the field. The responsibility for this reliability is shared between the designer and the contract manufacturer (CM). Primarily, this means that your design should incorporate rules and guidelines provided by your chosen CM that fall within PCB tolerances for the actual equipment that will be used to build your boards. By partnering with your CM and applying the best design for excellence (DFX) principles, as listed below, you can achieve optimal PCBA performance.
DFX (Design for Excellence)
DFX can be thought of as the leveraging of other targeted design rules and guidelines (i.e. DFM, DFA, DFT, DFR) into a single unified strategy to achieve the overall best PCBA.
For more information on DFX, see IPC-2231 DFX Guidelines.
DFM (Design for Manufacturing)
Manufacturability is the reason to apply DFM. Failing to incorporate your CM’s DFM rules and guidelines can result in boards that cannot be built, at least not without several back and forths to make design changes, which can result in a waste of time and money.
See The Best Methods to Perform a DFM Check for information on using DFM during design.
DFA (Design for Assembly)
DFA is the utilization of your CM’s rules and guidelines for assembly in your design process. These choices facilitate the best assembly with well-connected components, adequate clearances, and spacing, best use of vias, and other decisions that are in sync with your CM’s equipment and processes.
DFT (Design for Test)
For some designs, it may be necessary to perform testing in addition to the normal functionality testing performed during the prototyping phase. And this additional testing may require that you augment your design to accommodate the testing equipment, for example adding test points, or that a testing apparatus be built as necessary for ROSE testing.
For more information on DFT, see Design for Testability (DFT): Is it Really Necessary?
DFR (Design for Reliability)
For DFR, which should also be included as part of your DFX, the objective is to institute design decisions that will tend to aid your board’s reliable performance once installed and operational. These choices impact your board’s fabrication, assembly, and the components used, as discussed in the next section.
Maximizing Performance with PCBA Design for Reliability (DFR)
For end-users, your boards’ ability to perform their intended function(s) is a basic requirement. Even more important is that they do so consistently for their expected operational lifetime. Achieving this performance level is best accomplished when your design process targets reliability, which includes incorporating the following.
Guidelines for PCBA Design for Reliability
|Design Choices||What to do||Why it’s important|
|Components||Choose components that are not susceptible to moisture and are as derated as much as possible.||Minimizes the probability of failure due to operational or environmental issues.|
|Fabrication Options||Select materials where CTE is matched throughout the temperature cycling range and the glass transition temperature rating is well below expected temperatures. Also, ensure traces have a high safety factor.||Reduce the probability that boards will suffer delamination, shorts or arcing due to excessive heat or overcurrents.|
|Assembly Options||Choose adequate solder mask clearances, make sure footprints match component packages, ensure that traces align properly with component pin pad pins, clean boards and apply conformal coating.||Promote good solder joint connections. Include guards against contamination, which could lead to oxidation and premature failure.|
|Tempo's Custom PCB Manufacturing Service
As shown in the table above, following good design for reliability guidelines has distinct advantages. And, if instituted with the aid of your CM, it will result in high quality, reliable boards. Building high-quality PCBAs quickly is what we specialize in at Tempo Automation.
And to help you get started on the best path, we furnish information for your DFM checks and enable you to easily view and download DRC files. If you’re an Altium Designer or Cadence Allegro user, you can simply add these files to your PCB design software. For Mentor Pads or other design packages, we furnish DRC information in other CAD formats and Excel.
If you are ready to have your design manufactured, try our quote tool to upload your CAD and BOM files. If you want more information on how to design for reliability and the advantages of doing so, contact us.