Optimizing DFA PCB Designs With OrCAD X

June 12, 2024

Cadence PCB Solutions

Key Takeaways

While DFM focuses on meeting manufacturing specifications, DFA emphasizes easing the assembly process to reduce costs and errors.
Adhering to detailed DFA guidelines such as pad size, solder mask clearances, and component spacing ensures the PCB design supports efficient assembly.
OrCAD X offers specialized tools, such as the Alignment Guide, Basic DRC, and Constraint Manager, which help maintain necessary design constraints.

DFA PCB

Setting up package-to-package spacing DFA rules

Design for Assembly (DFA) for PCBs is a methodical approach used to guarantee that components on a PCB are assembled accurately and function without errors. Additionally, DFA for PCBs aims to reduce the cost of assembling a board by streamlining its design.

DFA vs. DFM

Design for Assembly (DFA) and Design for Manufacturing (DFM) are complementary approaches in PCB production.

DFA vs. DFM

Important PCB DFA Points to Keep in Mind

DFA Point	Description
Component Spacing	Optimal spacing between components such as chips, SOTs, SOICs, PLCCs, QFPs, BGAs, Axial, and PTHs varies from 10 to 150 mils, depending on the type of component, to avoid solder bridging and facilitate easier rework. Smaller board form factors may necessitate reduced spacing.
Solder Mask Clearances	Solder mask clearance dictates the allowable proximity of the solder mask to board features like copper traces to ensure sufficient solder dams and prevent solder bridges.
Pad Size / Annular Ring	Pad size should exceed the finished hole size by at least 10 mils for vias and 14 mils for component holes. Annular rings should maintain a minimum width of 5 mils for vias and 7 mils for component holes.
Component Orientation	Aligning similar components in the same direction facilitates efficient routing and ensures error-free soldering. This alignment significantly affects PCB assembly, impacting turnaround time and device performance related to signal integrity and EMI.
Part-to-Edge Spacing	The distance between components and the board edge is crucial to prevent stress on parts near the board edge, especially during the depanelization process. Adequate spacing is necessary to accommodate clamps during the solder application process, ensuring proper solder paste application and preventing damage to SMT components.
Part-to-Hole Spacing	Ensuring sufficient distance between a component body/pad and any type of hole is essential to prevent assembly issues for both through-hole parts and microvias.
Component Clearance	Specifies the minimum distance around components to ensure no overlap with other parts, hardware, or the board edge, facilitating rework and assembly. Clearance varies by component type, e.g., 1.0 mm for BGA devices, 0.5 mm for connectors and certain capacitors, and 0.15 mm for smaller packages below 0603.

Given the multitude of DFA PCB considerations outlined in the table—from pad sizes and solder mask clearances to component spacing and electromagnetic compatibility—it's evident that manually managing these critical details can be challenging for designers.

This is where the utility of advanced EDA (Electronic Design Automation) software becomes indispensable. Investing in a capable EDA tool that supports comprehensive DFA functionalities can significantly streamline the PCB design process. We’ve compiled an array of OrCAD X tools tailored to enhance DFA PCB creation.

Setting physical constraints in the OrCAD X Constraint Manager

Setting physical constraints in the OrCAD X Constraint Manager

OrCAD X for PCB DFA

Tool/Feature	Description	How It Assists in DFA
Alignment Guide	Guides that assist in aligning components on the PCB layout, ensuring that they are positioned correctly relative to one another.	Helps in maintaining uniform component spacing and orientation, crucial for automated assembly processes like pick-and-place machines.
Basic Design Rule Checks (DRC)	These checks ensure components do not overlap and meet specified clearance requirements according to PCB design standards.	Prevents component overlaps and ensures adequate spacing, crucial for avoiding assembly errors like solder bridging or misaligned parts.
Constraint Manager	A comprehensive tool within OrCAD X that allows designers to set up and manage various design constraints, including those for DFA, to ensure the PCB design adheres to assembly requirements.	The Constraint Manager is essential for setting and managing DFA constraints such as spacing between components and ensuring components fit properly during the assembly process.
DFA Constraint Set Section	A specific section within the Constraint Manager dedicated to defining and managing DFA constraints such as spacing between component packages.	Enables the creation and application of precise spacing rules, ensuring that components have enough space for assembly tools to operate effectively and for manual soldering processes.
Analysis Mode	A feature within the Constraint Manager that enables or disables the active checking of DFA rules during the design process.	Facilitates real-time compliance monitoring with DFA rules, identifying and resolving potential spacing issues before the manufacturing stage.
Package to Package Spacing	A DFA constraint that specifies the minimum distances between different component packages to prevent physical and electrical interference during assembly.	Essential for maintaining optimal spacing, directly affecting assembly process reliability and the functionality of the assembled PCB.
DFA Package Classification	A system for categorizing similar components into classes to which specific DFA rules can be uniformly applied, simplifying the management of these rules across the PCB design.	Grouping similar components, such as all chips or connectors, streamlines the application of DFA rules. This reduces complexity in setting individual spacing rules and enhances overall design efficiency.
Bumpers and DRC Markers	Visual indicators in the PCB layout that appear when components are placed too close together and potentially violate established DFA rules.	Provide immediate visual feedback during component placement, helping designers maintain necessary clearances and avoid DFA violations, which is crucial for effective assembly.
Design Rule Checking (DRC) Window	An interface that updates in real-time to show potential design violations, allowing designers to inspect and correct issues as they design.	This window aids in identifying and rectifying spacing or layout errors promptly, ensuring the design adheres to all DFA guidelines before proceeding to production.
3D Visualization and Export	OrCAD X provides capabilities to export and visualize PCB designs in 3D, facilitating the viewing of the board in different orientations, including bending flex regions and isolating specific areas.	By visualizing the PCB in 3D, designers can assess the physical layout for potential assembly issues, verify component placements, and ensure adequate spacing and clearance.
Collision Detection	This feature within the 3D visualization tools allows for the detection of physical overlaps or inadequate clearances between components.	Collision detection is essential for confirming there is no interference between components, which is crucial for automated assembly processes.
Constraint-Driven Routing	OrCAD X features an advanced routing engine that is powered by real-time, constraint-driven feedback, allowing for the efficient and accurate connection of traces according to predefined constraints.	Constraint-driven routing assists in maintaining necessary clearances and alignments per DFA guidelines, ensuring that the routing does not lead to manufacturability or assembly issues.

To experience the multitude of OrCAD X tools available for DFA PCB creation, sign up for a free trial today and take the first step toward enhancing your design process.

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