Over time, experts have disproven numerous myths and misconceptions in PCB design. Here are five of the more common myths we have encountered.
5 Common PCB Design Myths
- Acid Traps Still Pose Risks
- Bigger Traces are Better
- Thicker Copper Always Improves Performance
- Silkscreen Is for Aesthetics Only.
- Solder Mask Is Only for Protection
PCB Design Myth 1: Acid Traps Still Pose Risks
An acid trap refers to an unintended localized irregularity in the copper deposition or etching process of a printed circuit board (PCB). It occurs due to uneven or inadequate removal of etching chemicals and can potentially lead to signal integrity issues or short circuits within the PCB.
In modern PCB design, acid traps are less of a concern. This is primarily a result of improved manufacturing techniques, such as horizontal plating. Furthermore, design software and guidelines emphasizing impedance control and proper spacing have helped reduce acid trap concerns.
Best Practice Implementation:
- Use Horizontal Plating: Horizontal plating reduces the chances of acid traps by ensuring more even and consistent copper on the PCB. More even copper deposition on the PCB reduces the chances of acid traps because it ensures that there are no irregularities or uneven surfaces where etching chemicals can get trapped. When copper is deposited uniformly, it promotes smoother etching during manufacturing, minimizing the likelihood of acid traps and potential issues in the PCB.
- Consider Controlled Impedance: Ensuring that signal traces have consistent impedance values, accounting for the dielectric constant, reduces the chances of acid traps by maintaining uniformity in the electrical properties of the copper traces. When impedance values are consistent, it means that the dimensions and characteristics of the traces are standardized, reducing variations that could lead to acid traps during the PCB manufacturing process. This consistency in trace design helps ensure that etching and plating processes occur evenly, minimizing the risk of acid traps forming due to irregularities in the PCB layout.
- Optimize Trace Spacing: Traces placed too closely together can lead to acid traps when uneven copper etching occurs due to the narrow gap between them. This can cause etching chemicals to get trapped, potentially resulting in acid traps, short circuits, or other PCB performance problems. Proper trace spacing in the design prevents such issues by keeping traces sufficiently apart and reducing the risk of acid trap formation.
Adhering to stringent design rules further mitigates the risk of acid traps by ensuring all design aspects adhere to proven standards.
PCB Design Myth 2: Bigger Traces are Better
Designers used to think “wider traces are better” because they believed it meant less resistance and more current capacity, but this idea didn’t consider important factors like controlled impedance. Over time, as PCB technology advanced, it became evident that trace width should be chosen based on factors like signal quality and manufacturing, rather than just making them wider.
Modern PCB design prioritizes controlled impedance. This means that trace width selection is based on specific requirements rather than simply making traces wider. Controlled impedance ensures signal integrity and minimizes interference, guiding trace width choices for optimal performance.
Best Practice Implementation:
- Controlled Impedance Analysis: Trace widths closely tie to controlled impedance in PCB design. It helps calculate the appropriate trace width needed to achieve specific impedance values. This ensures that the traces maintain consistent electrical properties throughout the design.
- Current-Carrying Capacity Evaluation: Evaluate the current-carrying capacity needs of the traces. Consider factors such as the maximum current the trace should carry and the temperature rise constraints to determine suitable trace widths.
- Signal Integrity Assessment: Check signal integrity needs, including signal delay and noise levels, to decide on trace width and spacing that reduce signal problems while reaching design goals.
PCB Design Myth 3: Thicker Copper Always Improves Performance
Some designers may believe that using thicker copper layers in a PCB design will automatically lead to better performance. However, while thicker copper layers can enhance current-carrying capacity and heat dissipation in some cases, thicker layers also come with trade-offs. These include increased manufacturing cost and potential challenges in fabrication and assembly.
While thicker copper layers can boost current capacity and heat dissipation, they aren’t a one-size-fits-all fix. They can raise manufacturing costs, complicate PCB fabrication and assembly, and make the bare board thicker. A thicker board can be problematic due to increased manufacturing complexity, limited component compatibility, higher costs, heat dissipation challenges, and potential signal integrity issues.
Best Practice Implementation:
- Evaluate Current-Carrying Requirements: Assess the maximum current that traces need to carry to electrically connect components effectively. Consider the resulting temperature rise constraints to determine the appropriate copper thickness for adequate current-carrying capacity and heat dissipation. Copper that is too thick could lead to unnecessary manufacturing complexity, increased costs, and potential compatibility issues with components designed for standard copper thicknesses.
- Consider Manufacturing Capabilities: Consider the capabilities and limitations of the PCB manufacturer. This includes assessing their ability to reliably fabricate PCBs with the desired copper thickness, ensuring manufacturability.
- Optimize Layer Stackup: Consider the layer stackup and copper thickness within the entire PCB design. Ensure that the chosen copper thickness aligns with the overall design goals, including signal integrity, thermal management, and cost-effectiveness. Using overly thick copper layers in a PCB design can result in increased costs, manufacturing challenges, limited component compatibility, potential thermal issues, and signal integrity concerns
PCB Design Myth 4: Silkscreen Is for Aesthetics Only
This myth originated from an oversimplified view of PCB design, where the silkscreen layer was initially considered mainly for aesthetics rather than practical use. This led to the misconception that its sole purpose was visual appeal.
The silkscreen layer in PCB design is actually practicable. While it does provide visual branding and aesthetics, it also plays a crucial functional role by conveying essential information such as component placement, reference designators, polarity markings, and assembly instructions. This information aids in efficient assembly, debugging, maintenance, and troubleshooting processes, making it an integral part of modern PCB design rather than merely a decorative element.
Best Practice Implementation:
- Clarity and Readability: Clear, legible, and properly sized silkscreen markings are vital for easy visibility during assembly and maintenance. Silkscreen provides component placement guides, reference designators, polarity markings, and assembly instructions. These guide assemblers and technicians in correctly placing electronic components, ensuring proper orientation, and troubleshooting any issues. This ultimately streamlines the assembly and maintenance processes and reduces the likelihood of errors or misplacements.
- Consistency and Standardization: Consistency in silkscreen markings, like reference labels and polarity signs, is a top practice for clear PCB assembly and maintenance. Following industry standards helps accurate component placement, reduces errors, and improves assembly efficiency.
- Prevent Overcrowding: Avoiding overcrowding of silkscreen elements is a valuable practice as it ensures that markings and instructions are clearly visible and easily comprehensible during assembly and maintenance. By leaving sufficient space between these elements and prioritizing essential information, designers facilitate efficient and error-free component placement and orientation.
PCB Design Myth 5: Solder Mask Is Only for Protection
The misconception that solder mask layers on PCBs primarily serve for protection likely originated from oversimplified explanations in early electronics discussions. These explanations tend to neglect their multifaceted functions, such as ensuring precise soldering, optimizing electrical performance, and preventing defects. These functions include ensuring precise soldering, optimizing electrical performance, and preventing solder-related defects.
Solder mask layers play a significant role in defining soldering areas, ensuring soldering precision, enhancing electrical performance, and preventing solder-related issues.
Best Practice Implementation:
- Clearance and Spacing: Embracing ‘design for manufacturing’ principlesis a crucial best practice for PCB designers. This will ensure enough space between solder mask openings and nearby components, traces, or pads. This practice prevents solder issues, highlights solder mask layers’ multifunctionality in ensuring precise soldering and preventing defects, and optimizes electrical performance.
- Alignment Marks: Include alignment marks or fiducials in your PCB design, which are specific solder mask openings or patterns placed at strategic locations. These marks assist in the accurate alignment of components during assembly processes, such as pick-and-place machines and reflow soldering. Proper alignment reduces the risk of misalignment and soldering defects.
- Design for Solder Stencil: Collaborate with your PCB manufacturer to design the solder stencil, which is used during the solder paste application process. Ensure that solder mask openings are aligned with corresponding openings in the stencil to facilitate precise solder paste deposition. Proper stencil design contributes to high-quality solder joints and minimizes defects.
In conclusion, the world of PCB design has seen its fair share of myths and misconceptions debunked over time. We’ve explored five common PCB design myths and unveiled the truths behind them.
Today, acid traps in PCB design are less of a worry because of better manufacturing methods and guidelines for controlled impedance and spacing. Horizontal plating, controlled impedance, and optimized trace spacing are key practices for mitigating acid trap risks.
Second, the idea that narrower traces mean more data has evolved to prioritize controlled impedance over wider traces. Designers now select trace widths based on specific requirements, ensuring signal integrity and reducing interference.
Third, the belief that thicker copper layers always lead to improved performance is dispelled as we recognize the trade-offs they bring. Designers should evaluate current-carrying requirements, consider manufacturing capabilities, and optimize layer stackups for the best balance of performance and cost-effectiveness.
Fourth, the myth that silkscreen is purely aesthetic has been disproven, highlighting its practical role in conveying essential information for assembly, debugging, and maintenance. Clarity, consistency, and preventing overcrowding are best practices for effective silkscreen use.
Finally, the misconception that solder mask layers are solely for protection has been refuted. These layers are instrumental in defining soldering areas, ensuring precision, optimizing electrical performance, and preventing solder-related defects. Practicing adequate clearance and spacing, using alignment marks, and designing for solder stencils are essential steps in harnessing the full potential of solder mask layers.
In PCB design, knowing the facts and using best practices is crucial for making efficient, dependable, and affordable circuit boards. Following these guidelines ensures that PCBs work well and contribute to the success of electronic products and systems. Adherence to these guidelines and the proper utilization of gerber files ensures PCBs are built to precise design standards.