PCB Interface Control

Key Takeaways

• The value of interface control for complex systems or development spread across multiple teams.

• The OSI model of organization for interface compliance.

• Some common physical areas of board design and manufacturing that can contribute to interfacing issues.

PCB interface controls include the connectors that enable communication between different devices

PCBs are defined by connectivity. Whether that’s a network protocol to handle the exchange of information between devices or the conductor itself, modern electronic systems need to be able to effectively transfer data from multiple I/O streams. This task of tracking and implementing communication has become more difficult as systems have grown more robust; there are not only more data streams to account for, but more protocols and layers as well. Disasters can strike in electronic development when these communication channels are neglected or unaccounted for.

PCB interface control provides a necessary framework for multi-disciplinary teams to work in parallel without constantly needing to check the work of others for compatibility. Instead, compatibility is covered by ensuring the communication system between different aspects of the system with a methodical check and evaluation of all of the I/O structures in use. By handling only the modes that different systems or sub-systems can interface with, the design remains lean and focused without compromising performance.

PCB Interface Control Keeps Independent Teams Synchronized

PCB interface control simplifies inter-team design by assuring all outgoing connections meet requirements. Instead of designing for all possible cases or standards, design is focused only on those that are in use. In essence, interface control can be thought of as simplifying a system down to I/O, where the in-between process is of reduced importance than that of the start or end points.  As a principle design document, interface control keeps design teams laser-focused on multiple levels of system integration and allows them to trim extraneous information that would otherwise slow down product development.

The Open System Interconnection (OSI) model is a 7-layer organization of the different levels of interfacing. Design teams can use this heuristic to plan out every element of a PCB that requires a compliance check.

Open System Interconnection Model

Data levels can be thought of as a series of baton passes from most to least and then least to most abstract. Does every layer of the OSI model need to apply to every interface? Rarely is it the case that a connection spans every possible data style, as these are often sequential stages. Instead, design teams will want to center the parameters of the interface as well as its intended method of communication as a guide for interface control structure. Some additional considerations:

• Security - With an increasing amount of data exchanged wirelessly or stored and accessed remotely as IoT continues its growth, data protection has become more prominent for financial and safety purposes. Security measures inhibit the ability to interface by placing extra constraints on design teams (justifiably so). 

• Structure - Different network topologies will allow or forbid access between communication nodes. For interfacing, this may slow down communications by forcing messages to follow sub-ideal hierarchical pathing.

• Format - What elements or objects comprise the data being shared? Depending on how the data is formatted, packaged, etc., different interfacing methods may be more or less suitable.

Where Physical Layer Failures Can Disrupt Interfacing

Connectors are the obvious point to search for disruptions to interfacing, but considering the levels of structure the OSI model spans, they are not the only space to search for defects or poor performance. Seeing as the physical layer is the point where all communications ultimately originate or arrive (depending on the perspective), PCB design rules need to be thorough and complete to avoid an abbreviated service life:

• Solder - The junction between board and component has some of the highest rates of failure for PCBs. Poor soldering practices like insufficient temperature resulting in cold joints that lack ductility or even a placement that impedes the flow of molten solder in the wake of components with tall profiles can lead to abbreviated service life due to solder joint failure.  

• Vias - The difference in the z-axis CTE between the substrate and via barrels is a common stressor during manufacturing and occasionally during operation in high-heat environments. Designers can minimize this effect by keeping the aspect ratio (drilled hole circumference to board thickness) low. Additionally, the suppression of some non-functional pads can boost mechanical reliability.

• Opens, shorts, impedance issues - Unintended connections or disconnections can form at many points in the manufacturing process (rule checks make them unlikely to leave the design stage). Detection has become more difficult as components and pitches have shrunk with improvements in IC technology. JTAG/Boundary-scan sidesteps this problem while maintaining full testability with an in-system programming model, making it a critical tool for interfacing.

Cadence ECAD and Simulation Solutions Easily Interface for Performance

PCB interface control is all about simplifying the workflow that different teams have to account for in electronic systems. Concentrating only on the possible ways a system or sub-system can accept or transmit data means a minimal amount of time is spent harmonizing the semi-independent sections of the design without sacrificing performance or quality. With interface control mapped out, all that remains for design teams is robust simulation and modeling before manufacturing and testing to assure a seamless transition from design to production. A comprehensive DFM approach with Cadence’s PCB Design and Analysis Software provides users with a fully capable design environment where teams can rapidly gauge electronic system development at the pre-production stage. And with the fast and powerful OrCAD PCB Designer, the layout for complex HDI boards can be turned in record time to improve design responsiveness.

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