Creating a Design Constraint Strategy

Estimated reading time: 2 minutes

Feature Q&A With Kris Moyer, Global Electronics Association

Most designers learn how to set their design constraints through trial and error. EDA vendors’ guidelines explain how to use their particular tools’ constraints, and IPC standards offer a roadmap, but PCB designers usually develop their own unique styles for setting constraints.

Is there a set of best practices for setting constraints? That’s what I asked Global Electronics Association design instructor Kris Moyer, who covers design constraints in his classes. In this interview, Kris discusses how to identify PCB design requirements and set design constraints tightly enough for performance but flexible enough for manufacturing limitations.

What pre-layout analysis should be performed before you begin setting constraints?

Kris Moyer: There are several analyses that should be completed before setting constraints. These include the following:

• Timing/signal integrity: Used to set controlled impedance, termination, length matching and max length, and layer restrictions for digital signals.
• SPICE/power integrity analysis: Used to define the power distribution network (PDN) limits, the current requirements (trace widths), and voltage clearance requirements (Cu-Cu clearance).
• Thermal analysis: Used to determine how many plane layers, the copper weight of the plane layers, temperature rise of the traces (also used to define trace width), and any heat-sinking needed.
• Structural/mechanical analysis: This is the vibration, shock, and other environmental impacts to the design. It’s used to trade off between how many copper layers vs. board thickness for the stackup, and it is also used to evaluate the number and locations of mount holes or other support structures for the board. This analysis also leads to placement restrictions, such as specific placement of tall parts due to the design of the enclosure, or heavy/high mass parts due to special support structures designed into the housing, etc.
• Material analysis: This is an investigation of any special materials that may be needed, such as RF materials, flex materials, etc. These all have an impact on the stackup of the PCB and often lead to routing restrictions. For instance, you can only route the RF signals on the RF layers, or you have fewer routing layers available in the flex sections vs. the rigid sections of a rigid-flex board, limiting your ability to route signals from one rigid section to the next.

To continue reading this Q&A, which originally appeared in the July 2025 Design007 Magazine, click here.