Let’s break down the PCB assembly process before we start our optimization quest. Whether it’s an HDI or a flexible PCB, production starts as soon as the design is approved and takes the design to a physical form. But the “bare board” is only a skeleton waiting for its organs and sinews—the electrical parts that give it life and functionality.
A common problem with printed circuit boards (PCBs), especially for those who are still learning about them, is that the assembly process isn’t taken into account in the board’s original design. They just think about the board’s design, not the bigger picture of how the board will work within the product or application.
The idea of PCB design for assembly
The availability of components is another crucial factor to take into account. The assembly vendor needs to have the required parts on hand when the boards are received in order for the assembly process to go well and for the overall production to be efficient. The benefits of a fast-turnaround approach to board production are diminished because these components must be easily accessible in order for the entire process to be finished on time.
DFA advises designers to take assembly into account from the very beginning of PCB design. The arrangement of components is crucial; if they are placed too closely together, they may malfunction or perform less well. Here’s how to stay clear of these dangers:
Placement of strategic components
Your PCB’s components can be thought of as chess pieces. Enough room is required for every piece to maneuver comfortably and tactically. Components also require space for simple assembly, soldering, and possible rework. Enough space is incorporated to prevent short circuits and improve heat dissipation, both of which are critical to the PCB’s dependability.
The main problem with assembly is that it is hampered by the requirement for pin 1 indicators or polarity/orientation indicators on the silkscreen. A facility receives orders on about 75 percent of them that require accurate pin 1 position identification for integrated circuits (ICs) or exact polarity representation for components like capacitors, diodes, and LEDs.
To prevent future issues, you must establish component regulations, requirements, and proximity rules in your design program. Specific recommendations for the distance between various component kinds are provided by board specialists. Discrete components, such resistors and capacitors, should, for example, always be placed at least 10 mils apart, however 30 mils is the ideal spacing. By taking this preventive measure, proximity-related problems that could cause delays or difficulty during assembly can be avoided.
Most PCBs are filled with components by machines, although people also work with them. Designing with both in mind guarantees a procedure that is both user-friendly and machine-efficient. Breakout tabs and hand-soldering spaces are examples of features that can really make an impact.
Making the PCB design simpler
In PCB design, complexity is not necessarily a good thing. There are frequently fewer assembly faults in simpler designs. Reducing the number of components minimizes assembly time and complexity.
TIP: Because of the potential for additional complexity and expense, it is generally not advised to combine several technologies on a PCB, such as through-hole and surface mount. Using standard technologies across the board is more efficient. Using a through-hole makes production simpler when all of these parts are located on one side. Electrical engineers and PCB designers have to choose the right component package sizes early in the design process, balancing the ease of assembly against the need for reduced sizes. Important components that satisfy design specifications, facilitate assembly, and boost yield are frequently chosen.
Lead times for components should also be carefully considered. If possible, this work should be assigned to the assembly vendor to expedite the process; items with longer lead times should be identified early and ordered in advance to assure they’ll be available when needed.
Accepting design in production
Conversely, DFab is all about making sure the board can be built without any issues. This includes:
Relevant factors
By selecting the right base materials, problems like warping and delamination can be avoided. When subjected to assembly and operating environment stressors, various materials will exhibit distinct behaviors.
It’s crucial to refrain from combining lead-free parts with non-lead-free assembly parts. The entire board must be assembled using lead-free techniques and all components must be compatible with lead-free assembly when a component needs to be assembled using lead-free methods and conventional lead-based solder is not appropriate.
Layer stacking and planning for impedance
The stackup, or layer layout, and meticulous impedance planning are key factors in influencing the performance of a printed circuit board (PCB). A thorough understanding of your design’s electrical requirements and careful stackup planning will have a significant impact on power distribution effectiveness and signal integrity. By doing this, designers can reduce problems that are essential to the dependable operation of high-speed circuits, such as electromagnetic interference and signal loss. Furthermore, by guaranteeing that the PCB will adhere to all electrical requirements and work well with other parts in a system, appropriate impedance planning also maximizes the overall performance of the finished product.
Availability of components: A crucial aspect
More important than design details is component availability. The timely manufacture of PCBs can be hampered if essential components are not present when the board is received.
The key to mastering PCB design is striking a balance between DFab and DFA. It involves imagining the final result, accepting the constraints and potential of manufacture and assembly, and incorporating these aspects into the design process.
By concentrating on DFA and DFab, designers can ensure a smooth and effective production process that produces high-quality, functional PCBs by optimizing their board designs on the first try.
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