What Are the Key Matters That PCB Designers Should Focus On

For PCB manufacturers, there is a high probability that they will want to provide feedback on the received PCB designs, and there are all-too-familiar and long-standing pain points around the design work.

Therefore, this interview invited several PCB manufacturing experts to share their insights on the challenges that PCB designers need to understand more thoroughly. Which side of these arguments do you agree with?

Q: What is your top concern when it comes to PCB designers? Dana Korf: Impedance and signal loss variability. In recent years, signal integrity, which was once a key focus for RF designers, has now become a mandatory requirement for standard digital and analog designs. Simulation tools are used to characterize the nominal characteristics of the design, as well as the upper and lower limits of the major specification tolerances, to enable rapid prototype fabrication and testing. Prototypes can be built and assembled multiple times until the desired results are achieved.

Korf: Signal performance can be affected by drilling, laser via inner diameter, post-plating diameter, material dielectric thickness and electrical properties, solder mask, Dk and thickness, and trace width tolerances, while trace thickness has a relatively minor impact on signal performance. However, manufacturers are rarely required to provide this information to designers. As a result, designers have no way of knowing whether the PCB was fabricated at the upper limit, lower limit, or midpoint of the tolerance range. Designers often complain that a new revision or fabricated PCB does not perform as well as the previous version. Of course, this may not always be the case, but it is most likely caused by manufacturing tolerances.

Korf: When a design has strict impedance or loss requirements, designers should request access to more information on the key parameters of the received PCB, to better correlate the actual performance with the expected performance.

Q: What are the main matters that PCB designers should focus on? Korf: Over-specification. Over-specification requirements will lead to a significant increase in costs. One of the most common reasons is that requirements are copied from one design to another, without the designer fully understanding whether the requirements of other designs are applicable to their own. Another reason is that PCB hardware engineers and designers have not received sufficient education on cost impacts early in their careers. How many PCB manufacturing courses are taught in community colleges and four-year universities, after all?

Korf: I still use a 20-year-old Apple iPod every day. It is a consumer product that was probably not designed or expected to have such a long service life. I can't help but wonder how much cost is incurred by the extra specifications for a PCB that only needs to have a service life of around 5 years.

Korf: One common example of over-specification is the failure to use IPC Class 1 product requirements where applicable. These requirements are designed to provide sufficient margin for systems operating within a short service life. However, most designers of non-Class 3 products default to specifying PCBs as Class 2 products. Reducing the product class from Class 2 to Class 1 has the potential to improve production yield, reduce processing and material costs, and thereby lower the overall product cost.

Q: What are the key issues that PCB designers should focus on? Korf: The quality of the documentation package. Designers use Gerber-based file packages to send data to manufacturers and assemblers, requiring the manufacturer to manually interpret drawings and specifications, and manually correlate and input the requirements into their CAM systems. For example, a separate netlist is required under the assumption that the data may be incorrect, and trace thickness is also entered manually.

Korf: The PCB industry has had intelligent data formats for 25 years, namely Siemens ODB++ and IPC-2581. Studies show that less than 25% of all file packages are based on these formats.

Korf: These are intelligent data formats for transferring smart data from CAD systems to CAM systems, enabling automatic loading of large volumes of data without manual intervention. These intelligent formats also eliminate the need for extensive supporting documentation, such as fabrication drawings, BOM spreadsheets, and stack-up drawings. There are often discrepancies between the provided documentation and the duplicate information sent, which extends production or prototype cycles and introduces errors.

Korf: Designers should immediately collaborate with their suppliers and switch to IPC-2581 or ODB++ to shorten design cycles and improve the quality of data transmission.

Q: What is your top concern when it comes to PCB designers? Qandeel Sheikh: Understanding the purpose and application of the PCB. Designing a PCB involves far more than just creating a layout. It is essential to consider the purpose and application of the PCB, including its interfaces, technologies, form factor, and electronic circuit design. When designing high-density applications with ultra-fine pitch components (such as 0.4mm BGA), designers must have a clear understanding of the fan-out techniques used to escape component I/Os and route these components on the PCB, such as stacked microvias, laser vias, skip vias, HDI, and VIPPO (vertical interconnect process with plated over).

Sheikh: PCB designers should have a thorough understanding of electronic circuit design and schematics to ensure that the PCB layout meets its intended purpose. For example, a PCB designed for a communication system has different requirements from one designed for a power supply system.

Sheikh: For complex PCB technologies, designers should consider various factors that affect the production cost of the PCB, including material selection, copper weight, PCB dimensions, layer count, coating options (ENIG, HASL, etc.), as well as minimum trace width and line spacing requirements.

Q: What are the main matters that PCB designers should focus on? Sheikh: Thermal management, as well as signal and power integrity, are the primary issues that require focused attention during the PCB design process. EMI compliance, power handling for high and low voltages, and ensuring signal integrity are all core aspects of PCB design. For example, isolating digital and analog signals in miniature devices can become challenging, and the same issue is observed for high-voltage and low-voltage power rails.

Sheikh: Transmitted data may be distorted, interfered with, or attenuated, leading to inaccurate or unreliable results. PCB designers must design PCBs in accordance with best practices for signal integrity, proper grounding, shielding, and routing techniques to prevent issues such as signal reflection, crosstalk, and electromagnetic interference (EMI).

Sheikh: High-power PCBs with high-density and high-speed signals also face heat-related issues that require careful management. When increasing the size and thickness of copper, designers need to ensure an appropriate balance between heat dissipation and power-related issues. PCB designers must carefully consider the placement of heat-generating components (such as processors, power chips, or high-power LEDs), and design appropriate thermal management solutions (such as heat sinks, thermal vias, and copper pours) to effectively dissipate heat and maintain the optimal operating temperature.

Q: What technologies or processes should PCB designers learn more about? Sheikh: Manufacturing and assembly processes. PCB designers need to take manufacturing and assembly processes into account during design, especially when designing for assembly and test (DFx). This can be achieved by ensuring that the physical layout does not violate process capabilities, considering how the physical layout will interact with the assembly process, and making design considerations for board testability. In addition, designers must ensure that the assembled PCB does not interfere with mating PCBs and other mechanical components. For example, designers must understand how to design a PCB with sufficient tolerances and clearances for the correct installation of heat sinks and enclosures.

Sheikh: In short, PCB design requires a comprehensive consideration of the purpose and application of the board, thermal management, signal and power integrity, as well as manufacturing and assembly processes. Designers should have a clear understanding of the fundamental principles and values that drive these considerations, to ensure that their designs are robust not only technically but also functionally. This will improve the accuracy, reliability, sustainability, efficiency, and simplicity of their designs.

Q: What is your top concern when it comes to PCB designers? Dave Hoover: Today's PCB designers need to have a better understanding of actual manufacturing tolerances and production capabilities. They need to collaborate with the manufacturer's application engineers to fully understand the production capabilities of the PCB fabrication facility.

Q: What are the main matters that PCB designers should focus on? Hoover: When selecting materials, designers should pay attention to the support and services provided by the material supplier. Remember: the focus is not entirely on price.

Q: What are the key issues that PCB designers should focus on? Hoover: Designers need to understand the difference between short-term NPI (Quick Turn Around, QTA) and mass production volumes. There can be significant differences between the two; maintaining tighter tolerances for QTA batch sizes is straightforward.

Q: What is your top concern when it comes to PCB designers? Gerry Partida: More designers must pay attention to the minimum conductor thickness of internal buried layers and blind layers.

Q: What are the main matters that PCB designers should focus on? Partida: Calculating pad dimensions to meet the requirements of Class 2 or Class 3 products.

Q: What are the key issues that PCB designers should focus on? Partida: Non-functional pads, drill-to-copper clearance, and the elimination of redundant routing space.


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