Hassle-Free Rigid-Flex PCB Bending EM Analysis

The functionality, safety, and effectiveness of devices using rigid-flex PCBs are highly critical, especially for devices used in advanced medical implants, high-precision critical military equipment, and similar regulated and classified devices, making it crucial to leave no stone unturned in simulation. Devices designed to operate at smaller footprints must have high packaging density to accommodate various components. With increased component density, Electromagnetic (EM) issues spike and degrade electrical performance. The complexity of 3D designs makes EM analysis of rigid-flex PCBs a challenge. The bending possibility of the rigid-flex circuits allows designers to create multiple stacked-up space-efficient designs at lower costs, making them highly popular. These EM simulations are challenging or even unsolvable for most legacy simulation technologies.  The 3D structure requires simulators that can handle complex designs, large systems, and multiple technologies to minimize risk and ensure design success.

With unique contours, high-speed interconnects, lightweight, and highly reliable flexible substrates laminated together, rigid-flex PCBs reside in a wide range of electronic devices, from wearables to mobiles, military, and medical devices. The world of miniature electronics is evolving rapidly and is a big business; this segment also has the most prominent applications for the rigid-flex PCB market. With rising demand and the upward trend in consumer electronics, the need for rigid-flex segment is predicted to soar in the years ahead. The global rigid-flex PCBs market is expected to reach $5.8M in 2028.

Source: Cadence 

The reasons that lead to respins can be innumerable. Surveys show that each respin can cost around $25M, which can vary significantly depending on the complexity of the chip. Consider IC packaging, which has now been elevated to a prominent level. It can be electrical, yield manufacturing, package assembly, EMI/EMC, and many more. The overwhelming increase in high-speed data transmitted across the package causes EM radiation creating radiative and conductive emissions. Transmission line structure and frequency of operation can also impact product performance. When complex heterogeneous design becomes mainstream, striking a balance in quality over capacity becomes vital. For chip manufacturers, the simulation of intricate designs to analyze behavior in real-world situations is exhausting but unavoidable.

Rigid-Flex PCB Bending Challenges

Miniature, handheld, and wearables that need to hold components together in compact casings require light and flexible rigid-flex designs. Bending the board and importing the bent board file for 3D EM simulation is quite challenging. A rigid-flex environment uses unique materials with varying thickness, flexibility, surface finishes, and protective materials across the designs. They also need specific bending criteria that must be defined like criteria for bending, bending definition and location, and restriction like the interference expected with that bending is highly critical.

With rigid and flex technology bonding, new validation challenges also sprouted. The thin layers of the flex circuit expose the routing on the top and bottom layers. The high-frequency signal transmission through these layers creates EMI radiations due to less shielding resulting in increased near-fled and far-field leakages in the bending area. The intricate 3D design makes the simulation more complicated due to the bending of the board into small spaces, defining material properties, creating the ports, and using hatched ground and power planes, making it challenging for legacy FEM and FDTD 3D numerical solver technologies. The legacy tools involve cumbersome manual processes. Bending is prone to via and layer misalignment errors; material properties, components, and net definitions are lost in CAD translation. Furthermore, dirty geometry makes meshing the bent structure complex. The hybrid dynamic 3D board needs a new error-free approach for bending. A workflow that provides tool interoperability, enabling designers to accurately verify the electrical signals of the rigid-flex traces using 3D finite-element method (FEM) analysis for a fast time-to-market product development process.

Bend it Like Cadence

Laborious pre-processing takes hours to days with low simulation success versus a two-step process that runs in minutes with 99% simulation success. That is what we offer, a new workflow to mitigate the challenges of rigid-flex bending. To meet today’s design complexity and challenges, EM engineers require innovative technologies for 3D EM modeling.  Our new innovative workflow works seamlessly with IC, package, PCB, and system tools to reduce design cycle time and improve overall productivity. The intricated traditional workflow is prone to human errors and CAD translation misses.

Source: Cadence

The Clarity 3D Solver turns the complex rigid-flex design workflow into a simple two-step design process. Our PCB editor, Allegro, captures the defined bending information in the database without any manual process, saving time and effort in translating CAD and fixing the associated issues. Without any intermediate translations, the board can be imported into the Clarity 3D Solver, which translates the entire database, including bending the 3D geometry, material properties, component, and net definitions. As no mechanical tools are involved in managing geometrical information, it is easy to mesh and parametrize the bending angle. Clarity runs your simulation to view the S-parameters, near field, and mesh results and lets you make any adjustments to the bend without the need to go back to the PCB editor.

The Two-Step Process

Modern miniature electronic devices need compact packaging offered by rigid-flex PCBs. Even though concerning time and cost optimizations, these boards are a savior compared to the densely populated chips, rigid-flex circuit boards necessitate special materials and additional layering; hence, the cost of respins is way higher. Also, medical, military, and similar regulated and classified devices using rigid-flex PCBs cannot stand a chance of failure; hence, the functionality and safety of these devices are incredibly critical. The bending area in rigid-flex PCBs causes stronger radiative leakage making EM analysis critical. Our Clarity 3D Solver integrated with the Allegro PCB designer offers a two-step flow that is less error-prone and minimizes the effort and time required for rigid-flex PCB bending EM analysis.