I tend to be overly cautious when planning my routes on new long-distance backpacking trips. I’ll start with detailed route reviews that pour over elevation maps. These reviews, combined with approximate pack weight, indicate how strenuous each hour of the trip will be and when to plan my breaks. With the wealth of geographical information available, it’s easy to determine how long I can expect to spend on a trail each day. I can also effortlessly discern the best spots to set up camp to average my overall exertion and avoid excessively long or short days. Essentially, I’m building a mental prototype of my backpacking itinerary to minimize difficulties. It may come as no surprise, but a heuristic process such as this does not differ much from industry approaches to building prototypes: use the knowledge available to quickly plan out the best possible approach to fabricate a board.
“What is rapid PCB prototyping?” may seem like an easy enough question to answer – after all, rapid prototyping does not differ significantly between industries. More specifically, however, this moment of development for a project exists as an intersection of many intertwining short and long-term goals of the board. Design and manufacturing departments must be in lockstep from planning to fabrication to keep turnaround time to an absolute minimum and best solve the design and production issues of prototyping.
“What is Rapid PCB Prototyping?” – Improving Speed with Focused Development
Rapid prototyping is an example of agile manufacturing, a further refinement of lean manufacturing. While a lean architecture aims to reduce waste (and therefore cost), agile manufacturing goes one step further by considering development speed and fluctuating market needs. Prototyping denotes a stage of development where a design’s core functionality is prioritized above all else.
PCB prototyping looks to minimize the time a design spends in pre-production and consciously chooses design and manufacturing processes that reduce turnaround time. A board must also meet all of its specifications, so it becomes a careful balancing act of hitting critical design targets within the shortest reasonable time. All designs feature communication between the engineering, layout, and manufacturing departments. Individually, each team can work to optimize the build and reduce the time spent between the design and the finished product.
- Engineering: Due to supply chain issues, complex work has become even more involved. Procurement needs to be as much of a consideration as the design itself as semiconductor backlogs slowly diminish and standard circulation reoccurs. In supporting this goal, engineers must carefully focus the scope of work to accurately capture core functionality without introducing unnecessary features that will have a knock-on effect on turnaround time at all levels of design testing. Simulation conditions must accurately capture available devices and materials used in board construction. DNI components may play a prominent role in keeping board parameters malleable while adjustments are made during the evaluation phase.
- Layout: The designer acts as a go-between for the functionality and performance of the board as requested by engineering and the material and technical realities of the fabrication. An emphasis on manufacturing efficiency in design is reduced but not eliminated. Furthermore, tolerancing mechanical and electrical features found in design rules is unlikely to yield, yet some guiding best practices for ECAD can be relaxed in pursuit of a more expeditious turnaround time.
- Manufacturing: Any manufacturing decision involves a trade-off between different properties of the board; manufacturers may want to elevate those for a greater cost or less efficient use of board space. As many of these features can be repeated hundreds or thousands of times per board, mass production would need to weigh both performance quality and efficiency. Still, the latter can be relaxed when dealing with the small lots traditionally associated with prototyping.
Some of these tradeoffs include:
- Annular ring. Increased annular ring dimensions can be used to prevent instances of breakout between the hole and edge of the ring. However, larger annular rings also reduce the total amount of usable space on outer layersa.
- Spacing. Insufficient spacing results in incomplete metal removal, potentially resulting in unintended connectivity between nets. Once more, larger than necessary spacing could result in routing difficulties.
- Aspect ratio. Smaller aspect ratios (larger hole sizes and thinner boards) provide more reliable plating and performance. However, as these are generally more long-term issues, the immediate benefit for prototyping may be less of a concern. Regardless, aspect ratios should remain below the upper 8:1 limit, as recommended by IPC.
- Board thickness. Depending on the density of the board, design teams may want to add additional thickness to the board for improved structural reinforcement. Additional thickness reduces yield by increasing the prevalence of registration errors; this becomes a yield issue that is less emphasized during small prototyping runs.
- Trace width. A thinner cross-sectional area is more liable to breakage during production and throughout a product’s lifespan. For the former reason, design teams may find it beneficial to increase conductor width wherever routing constraints allow it.
Board Testing for Process Verification and Validation
Testing is at the base of any sort of prototyping; feedback on all levels of the design can be used to qualitatively measure processes to ensure a board is meeting critical goals and improving performance in future revisions.
There are a few steps engineering and layout can undertake to reduce runtime issues for a quicker testing stage:
- Don’t leave logic pins floating – connect a pullup resistor to dissuade coupling from noise and other transients.
- It’s easier to evaluate multiple, smaller logic dataflow circuits than fewer, larger ones. Beware of repeating logic functionality that can be exceptionally difficult to diagnose.
- Edge connectors will likely be the location of many offboard I/O connections and test pins used to probe nets to verify manufacturing processes. However, care should be taken when routing sensitive signals (victim signals) near the edge connectors due to the speed and likelihood of coupling.
- Do not tie signal outputs together, which at best muddles the signals flowing throughout the lines. At worst, this can damage components being driven by the output.
- Provide ample clearance and spacing for any location where probing may be necessary (oscilloscope, function generator, etc.).
Your Contract Manufacturer Can Push Prototyping Speeds to New Heights
Answering the question of “what is rapid PCB prototyping?” involves familiarity with a design and all the processes involved that make a theoretical build tangible. Importantly, you want a high level of cooperation and coordination between the different departments responsible for design and fabrication to create a board that meets all core competencies in the shortest possible period.
VSE and our valued manufacturing partners are well-equipped to navigate this point in the development roadmap with years of experience. Here at VSE, we’re a team of engineers that take pride in building electronics for customers. No matter what stage of production or revision your build is at, we’ll lend our expertise to improve its time-to-market, quality, and performance.
If you are looking for a CM that prides itself on its care and attention to detail to ensure that each PCB assembly is built to the highest standards, look no further than VSE. Contact us today to learn more about partnering with us for your next project.