Whenever I’m planning how to design a circuit board, I’m reminded of the famous quote by Laozi, “A journey of a thousand miles begins with a single step.” Perhaps I’m being dramatic – layout design is not a thousand-mile journey. Still, it can be arduous and demanding, especially with the increase in complexity of modern slot machine boards. PCBs are engineered products spanning many disciplines and specialties, and communication between teams is key to maximizing the final product’s performance. While general best practices are near-universally applicable to all boards, the most crucial step at the outset of design is determining what the board aims to attain and prioritizing the associated design qualities.
How to Design a Circuit Board? Begin at the End
Form follows function. If a board’s meant to work in a slot machine, it and the adjoining system must provide specific features. To determine them, start at the end. First, ask, “What is the board trying to accomplish?” From there, a design team can work backward to accommodate these features.
Security: Many external systems are in place to prevent and catch those attempting to defraud a gaming machine. However, the machine requires some anti-cheating technology. For example, older slot machines could have optics systems overwritten and run a routine for payout by flashing a light at a specific frequency placed within the coin slot or slowing down mechanical reels with heavy magnets. These two methods are holdovers from the antiquated electromechanical systems that existed before complete digitization. Still, they underscore that those able to gain knowledge of the machine’s inner workings can exploit it. Modern-day players can piece together the pseudo RNG by capturing a segment of the display’s video, giving the player information on when to stop the reels for a payout. As much as possible, the board’s operations must present opaquely to users.- Reliability: The expectation for most machines is to run without interruption, 24/7/365. While these boards are not high reliability in the traditional sense of board classifications, uptime and minimal maintenance mean greater profitability. Design teams need to account for the longevity of the board’s design, primarily with heat dissipation, but also the quality of the fabrication, assembly, and testing processes. Because a slot machine is a self-contained unit that dabbles in many different areas of board design, such as pseudo RNG/logic, audio/visual systems, and power, designers must exhibit the best design practices. These could include topics like signal integrity on logic lines to prevent false jackpots and designing power circuits and pours with ample current-sinking capabilities.
- Rugged: A slot machine board can be subject to much abuse if proper precautions are not provided. The area in which a board operates is often smoke-filled, meaning particulates can accumulate on the board if the enclosure does not effectively filter out air channels. Along with reliability, enclosures must provide stability to protect against shock and vibrations caused by an unruly user. Altogether, a board design, including its enclosure, must anticipate the operation environment.
Security: Many external systems are in place to prevent and catch those attempting to defraud a gaming machine. However, the machine requires some anti-cheating technology. For example, older slot machines could have optics systems overwritten and run a routine for payout by flashing a light at a specific frequency placed within the coin slot or slowing down mechanical reels with heavy magnets. These two methods are holdovers from the antiquated electromechanical systems that existed before complete digitization. Still, they underscore that those able to gain knowledge of the machine’s inner workings can exploit it. Modern-day players can piece together the pseudo RNG by capturing a segment of the display’s video, giving the player information on when to stop the reels for a payout. As much as possible, the board’s operations must present opaquely to users.Improve Performance With Some Best Manufacturing Practices
With the goals of a well-functioning slot machine board in mind, how can designers and manufacturers collaborate to produce the best board possible? Every board begins with design rules, and these reflect the manufacturing constraints of the board shop. Boards then pass on to a QA and testing team that verifies the manufacturing process at multiple stages to ensure compliance with standards, with more demanding standards reducing the yield. Fortunately, slot machine boards do not require the exacting high QA of other industries like medical and aerospace.
Still, the objective for any board should be optimal performance within the design goals set forth by the engineering team. Here are a few tips designers can adopt to achieve that goal:
- Solderability: The connections between devices are often early points of failure in a design after fatigue. First, land patterns must be designed carefully to the manufacturer’s specifications to ensure excellent solder profile forms. Designers should also be mindful of any thermal load inequalities between pins that can result in different wetting rates, a cause of tombstoning in some packages. Be aware that tightly spaced components cast shadows behind them when passing through a wave solder machine. To prevent gaps in the solder wave, arrange components in parallel orientations and beware of placing shorter packages behind taller packages relative to the orientation of the traveling wave.
- EMI: EMI should be a concern of every board. While it may not manifest itself to appreciable levels without a sufficient driver, EMI testing is an expensive process due to the dedicated lab setting where tests are conducted. Neutralizing EMI begins during plane design: ensure signals have a solid reference and do not cross split planes, which increases the return path and resulting current loop. Care should also be taken of routing around high-switching devices that can induce current inductively onto nearby traces. Similarly, avoid routing traces in parallel for extended lengths to prevent coupling. Use the 3W rule or a center-to-center spacing of three times the trace width, which is usually adequate.
- Stackup: The arrangement of signal and plane layers in the board must provide a consistent ground to all signals, distribute power to components across different nets, and allow enough space for routing. The stackup should be a mirrored layout across the board’s core, with signal planes remaining as close to ground planes as possible.
An Experienced Contract Manufacturer is No Roll of the Dice
Learning how to design a circuit board is both an art and a science, but a design for manufacturability approach should help beginners to their end goals. Always utilize information from engineers or manufacturers to guide the layout process, and collaborate with fabricators early to agree upon design rules that will not inhibit production. Optimal performance, however, often comes with experience, and our team is ready to provide it for your next board. At VSE, we’re a team of engineers dedicated to building electronics for our customers. Coupled with our exemplary manufacturing partners, we strive to provide high-quality PCBA, cabling, and box-build solutions.
