22 Solvable Design Problems in PCB Manufacturing and DFM Analysis Reference
During the planning phase of a new project, companies of all types typically focus on the technical and financial aspects of PCB mass production. In this process, PCB manufacturing costs must be minimized, and design modifications should be avoided, otherwise profit margins will be impacted. To avoid revisions, engineers must meticulously design the PCB layout to ensure a smooth PCB manufacturing process. After receiving the CAM data, suppliers often correct minor errors, which incur additional costs and time. This article summarizes 22 Design for Manufacturing (DFM) issues that can improve PCB manufacturing, helping product designers, engineers, and purchasing managers quickly analyze potential manufacturing problems in current PCB design projects.
What is DFM in PCB?
DFM stands for Design for Manufacturability. It’s a topic that helps reduce manufacturing problems. In design rules, we define clearances and tolerance tolerances. Therefore, in PCB DFM, we prepare the board for real-world applications. Tolerances should match the actual system. During the PCB layout phase, designers follow a PCB DFM checklist. This process helps optimize the PCB’s design for the manufacturing stage. It reduces costs and quality and serves as a reminder for designers to follow DFM checks every time they want to manufacture a design. PCB DFM is a core component of cross-functional teamwork and collaboration with teams in the supply chain , and it’s also an integral part of the overall product design process.
22 PCB Design Questions and DFM Analysis References
The following are 22 PCB design mistakes that can be avoided before PCB manufacturing, summarized by the engineering team at Geyuan Electronics . As engineers, we’ve all had this experience: after painstakingly completing a project and getting the board finished, we send it for prototyping, only to find the sample arrives and all our efforts are wasted. Specific problems with the board can be design-related or manufacturing-related. Of course, many problems can be avoided before manufacturing. Our summary of 22 avoidable PCB design mistakes can help you build efficient and defect-free PCBs.
1. Incomplete and invalid design documents
Whether it’s Gerber, ODB++, or a BOM file, the input files contain crucial information such as layer images, bill of materials, board outlines, IPC netlists, master drawings, and layer order. Any confusion in the specifications can cause problems in later stages. Therefore, all mandatory documents should be reviewed before submission to production.
2. Inappropriate substrate material
Some circuits require special materials depending on their function. For example, typical substrates cannot handle high-frequency signals well. In such cases, manufacturers need to discuss material requirements and select appropriate PCB substrate materials in the initial stages.
3. Improper cable width
Copper traces connect all components in a circuit. Any defects in the traces can lead to short circuits, signal distortion, and overheating. The current-carrying capacity of a conductor (trace) increases with its width. If a higher current flows through the trace, more heat will be dissipated, causing the board to overheat. Therefore, optimize conductor width according to your circuit requirements and ensure that the outer layer trace width is kept above 4 mil. You can use online tools to optimize trace width, current capacity, and temperature rise.
4. Improper cable spacing
Ensure that conductor spacing is not sacrificed for a more compact circuit layout, as insufficient trace spacing can lead to flashover and crosstalk. You should follow standard guidelines and provide sufficient clearance between conductors. Similar to trace width, you can use a conductor spacing and voltage calculator to calculate the optimal spacing between conductors.
5. Acid trap
During routing, if any trace forms an acute angle (below 90°), an acid trap will be created. During etching, residual acid can become trapped in the bend, leading to over-etching of the trace. Acid traps can be avoided in PCB design by preventing acute angle bends during routing.
6. Insufficient distance between the trace or drill hole and the edge
You should maintain optimal spacing between edges and traces in your circuit layout. If you reduce space for any reason, external conductors may be partially shaved or cut during demetallization. Insufficient spacing between copper and the circuit board edge can result in exposed copper and burrs on the edges.
7. Drilling process error
In printed circuit boards (PCBs), manufacturers drill holes for various purposes, such as vias, alignment, and component placement. Drilling is an irreversible process, and any unnecessary drilling can ruin your design. Other factors to consider include size, spacing, aspect ratio, number of holes on the board, and machine type (laser/mechanical). Common errors affecting drilling include hole rings and insufficient distance between the drill bit and the copper.
8. Defects of the ring
The annular ring connects the via to the trace. If the diameter of the annular ring is insufficient, it will interrupt the signal flow between the conductor and the via. Finished drilled holes may have a tolerance of ±2 mils, so when it is less than 2 mils, the annular ring may break. This will result in an open circuit. Furthermore, an insufficient annular ring for a component hole can lead to poor solder joints after assembly.
9. solder mask error
The solder mask on a PCB protects the surface from contamination and isolates connections. Manufacturers expose areas (footprints and pads) for component placement during the soldering process. If there isn’t proper clearance between the via mask opening and the adjacent component opening, solder bridges can form during assembly, leading to poor solder joints and inefficiency. Therefore, a necessary solder mask layer must be maintained between the via opening and the adjacent component opening. On the other hand, an inappropriate solder mask layer can cause solder holes, exposing the copper to corrosion.
10. Copper and solder resist
Copper strips are loosely bonded, thin residual copper segments formed during the printing stage. During electroplating, these loosely bonded strips can detach and fall into the plating solution. These photoresist fragments can co-deposit anywhere on the circuit board, causing short circuits. Simultaneously, areas where photoresist is removed can result in unwanted copper on the circuit board, potentially affecting its functionality. Solder mask strips are formed during the solder mask imaging process, leaving the solder mask layer in place to prevent solder bridging. When the dam is less than 4 mils, these loosely bonded dams can potentially become strips and be washed away during the development stage.
11. heat sink
The soldering process generates excessive heat, which can damage the circuit board. To avoid this, you must provide sufficient thermal pads. Thermal pads consist of small copper spokes called “heat plates” to aid in heat conduction. If these heat plates are disconnected from the solder pads or plane, they are called starved heat plates. Insufficient heat plates result in poor thermal conductivity and cause the circuit board to overheat.
12. Screen printing error
Screen printing is performed late in the manufacturing process. If the screen print overlaps with pads, PCB surfaces, holes, etc., it can cause problems during assembly. For example, if the screen print is applied to pads, it can melt into the solder joints and create discontinuities.
13. Assembly-oriented PCB design
Design for Assembly (DFA) bridges the gap between the designer’s vision and the reality of the production process. You need to check component availability and placement; DFA can help simplify PCB layout to reduce overall project costs and the probability of design failure .
14. Data inefficiency
Similar to DFM, you should verify all basic datasheets and key parameters, such as package dimensions, XY data, DNI specifications, SI data, and part numbers, before the design enters the assembly process. This will help avoid subsequent corrections and confirmations.
15. Selecting the wrong component
The choice of components affects the assembly process. For example, through-hole components require more complex manufacturing processes compared to surface mount technology (SMT). Therefore, it’s best to use them only when necessary. Always choose standard components over custom components, as standard elements are readily available from multiple suppliers. Custom parts, on the other hand, are often unsuitable for high-volume production and increase costs because you can only source them from selected suppliers.
16. Component availability
Before creating a Bill of Materials (BOM), the availability of components should always be confirmed. If supply is insufficient, you should be prepared to use alternative components from different suppliers. Currently, there are many websites available for querying BOM materials, providing information on materials and out-of-stock alerts.
17. Incorrect object packaging
The Bill of Materials (BOM) specifies all the components required to assemble the circuit board. If the component dimensions specified in the BOM do not match the CAD package data, it will be difficult to complete the circuit. This will cause significant difficulties for automated assembly lines. Correcting this situation will be time-consuming and costly. Therefore, component dimensions should be carefully checked during the design phase.
18. Insufficient component spacing
Insufficient spacing during component placement can lead to component overlap and solder bridges. Providing adequate clearance between components also facilitates manual soldering and rework. Pay special attention to the spacing of sensitive components such as QFP/QFN, POP, or BGA. Sometimes, elements are placed very close together to achieve a smaller form factor. It is best to follow spacing guidelines to ensure zero tolerance in component spacing.
19. Insufficient spacing between components and edges
After assembly, the panel undergoes a depaneling process. During this process, components at the ends of the circuit boards will have to withstand high stresses that could damage them. Therefore, sufficient spacing must be provided between components and edges. Furthermore, spacing options vary depending on the assembly process. In manual assembly, compared to automated assembly, you can place units closer to the edges.
20. Incorrect pad size and spacing
Choosing smaller pad sizes can result in poor solder joints in SMT components and may even lead to breakage when applied to through-hole components. Making the pad size as large as possible is probably not a solution. Wider pads take up more space and can cause SMT components to shift from their positions during soldering. Similar to pad size, pad spacing should not be too close or too far apart, as they can cause problems when placing components.
21. silkscreen error
The silkscreen layer contains a wealth of important information. Examples include component orientation markings, pin 1 markings, polarity markings, cathode markings, and so on. If these details are missing or unclear, the assembly plant will waste time verifying the correct data. In the worst-case scenario, if the polarity or other data is printed incorrectly on the silkscreen, and the assembler installs components accordingly, the circuit board may malfunction. You need to ensure the silkscreen is legible before assembly begins.
22. High temperature error
Manufacturers need to exercise caution during the soldering process, as it generates excessive heat that can damage the circuit board. Controlling the heat generated during this process is crucial. Provide sufficient thermal pads for effective heat dissipation. DFM and DFA guidelines can help you avoid some PCB design problems and minimize the impact of design errors. There are several DFM design tools available on the market, and I have personally tried some that I found quite good. You can choose one that suits your needs.
The main role of DFM in PCB design
DFM is an essential process for manufacturing high-quality PCB products. Only after a good manufacturability analysis can products that meet design requirements be produced, thus ensuring the quality of the final product. The following is the role of DFM in PCB design.
Ensure manufacturability
Review whether the design complies with the physical capabilities and process limitations of the production equipment (such as etching lines, drilling machines, pick-and-place machines, reflow ovens, AOI, etc.) (such as minimum line width/spacing, minimum hole diameter, pad size, solder mask bridge width, etc.).
Improve production yield
Identify and correct potential problems in the design that may lead to manufacturing defects (such as insufficient spacing that is prone to short circuits, weak traces that are prone to breakage, pad designs that are prone to tombstoning, and excessively small package spacing that can cause solder bridging), thereby reducing scrap and rework in the production process.
Reduce manufacturing costs
Reducing defective products and rework means less direct waste of materials and labor. Optimized design facilitates the use of standard materials, standard apertures, and standard dimensions, avoiding the use of special or expensive processes. It also facilitates automated production and improves production efficiency.
Shorten product launch cycle
Addressing manufacturing issues early in the design phase significantly reduces production delays caused by design rework, enabling products to be launched to market more quickly from the design stage.
Improve product reliability
By avoiding design flaws that may lead to potential problems (such as thermal stress concentration points, poor heat dissipation, and vias with insufficient mechanical strength), the long-term stability and reliability of the final product can be improved.
Promote collaboration between design and manufacturing
Introducing manufacturing rules and experience early in the design process facilitates smoother communication between the design and manufacturing teams, reducing problems caused by information asymmetry.
Reduce the number of design iterations
DFM analysis can identify a large number of potential manufacturing problems during the design phase (even before PCB fabrication), allowing design engineers to make timely modifications and avoiding the lengthy process of designs being sent to manufacturers for revisions in the traditional model.
Significantly improves the success rate of first production.
A design optimized with DFM has a high success rate on its first production run, greatly reducing the risk of mass production failure due to design flaws.
Significantly improve the yield rate of production
This is the most direct economic benefit. Avoiding common defects such as short circuits, open circuits, poor soldering, and tombstoning significantly increases the proportion of qualified PCBs produced out of the total input. Improved yield directly translates into lower costs.
Effectively reduce unit production costs
Reduced material waste (fewer defective products) , higher equipment uptime (smoother production line operation) , lower labor rework costs , and easier achievement of bulk discounts.
Optimize processes and improve production efficiency
For example, a reasonable design facilitates board assembly and maximizes material utilization; appropriate component layout and orientation help high-speed pick-and-place machines achieve optimal performance; uniform copper distribution and balanced wiring layers help control board warping.
Enhance product reliability and reduce after-sales failures (reduce field failure rate).
Eliminating design flaws such as thermal management issues, electromagnetic compatibility (EMC) risks, and mechanical stress points makes products more durable at customer sites, reducing maintenance costs and brand reputation losses.
Promote process standardization
DFM (Design, Manufacturing, and Equipment) standards can often help companies or suppliers develop a unified design and manufacturing rule base and inspection standards, thereby improving the overall design and manufacturing level.
PCB manufacturers and turnkey EMS suppliers
Geyuan Electronics is a professional PCB manufacturer and EMS supplier, providing PCB manufacturing, PCB assembly, component sourcing, and turnkey electronic manufacturing solutions. We produce multilayer PCBs, HDI PCBs, high-speed PCBs, RF and microwave PCBs, thick copper PCBs, ceramic PCBs, aluminum PCBs, flexible PCBs, and rigid-flex PCBs, from prototyping to mass production. Please contact us for a project quote if you require any type of PCB.
Conclusion
Only through Design for Manufacturing (DFM) analysis can truly high-quality PCB products be produced. This applies whether the design is for a simple project or a complex, high-speed industrial circuit board. Keeping DFM in mind in every PCB design will bring countless benefits to the projects you are responsible for, and it will also benefit designers and the company’s future orders. These procedures control the manufacturing process. It reduces the overall cost of circuit board manufacturing. If you need high-quality PCBs, please contact the team at Geyuan Electronics. Our engineers and manufacturing team have extensive experience in manufacturing all types of PCBs.