Fleshing out ECAD and MCAD.
The case for a holistic approach to CAD systems.
Specific tools and methodologies to enhance interlaced CAD results.
Creating complex electronics takes careful planning and meticulous attention to detail. A design environment must be able to match the complexity of the board or multi-board assembly effectively, and both the mechanical and electrical aspects of the design must be crafted simultaneously to ensure compatibility.
To achieve this goal, teams rely on computer-aided drafting, or CAD, to perform the heavy lifting of translating a design from documents to actionable manufacturing files following user input. More specifically, the role of CAD in design ensures projects successfully integrate the various aspects of a box build – e.g., electrical connectivity, enclosure, mechanical housing, etc. – with powerful simulations, renders, and additional tools to fully model the device’s intricacies and form.
From ECAD to MCAD: The Role of CAD in Design
To keep up with the increasingly complex design demands of today’s electronics, PCB designers are having to incorporate new technologies and processes into their design workflows. One such example is the combination of both electrical and mechanical design of multiple system boards within the same PCB design CAD tool.
The main purpose of CAD is to provide a robust toolset to facilitate the design of features necessary to optimize the performance of the board. ECAD – electronic/electrical CAD – is the first step sequentially and is the primary scope of designing box builds.
ECAD supports the translation of a circuit schematic into a PCB with a series of overarching design stages:
- Stackup build – Dependent on the physical requirements of the board (e.g., thickness, targeted impedance, etc.), materials will be selected and additional features like the via structure(s) will be outlined.
- Land pattern creation – The unique components of the schematic either need to be generated with wizard software, by hand following IPC and manufacturing best practices, or sourced from an already vetted internal land pattern file.
- Assignment and netlist extraction – Land patterns then need to be correctly associated with the appropriate part in the schematic before the land patterns and connection information is extracted in preparation for the board.
- Placement – Components are arranged in such a way that maximizes space and keeps net crossings in the rat’s nest at a minimum. Via fan-outs are used to preemptively allow traces to pass through internal layers if necessary and prevent blocking traces’ escape paths on outer layers.
- Routing – Shapes for power nets are poured on appropriate internal layers and signals are connected in the most direct fashion possible.
- DRC and Output – Adjustments are made to optimize the layout, artwork, and manufacturing files. Barring design rule check corrections, this concludes the current board revision layout.
MCAD Supplements Board Design
MCAD, or mechanical CAD, is a more straightforward process, though it still presents a critical juncture. For PCBs, MCAD is responsible for creating the enclosure the board or boards occupy. Primarily, the enclosure acts as protection for the board or multi-board assembly, mitigating shock and vibration while also providing additional support for cooling, grounding, and other critical safeguards. Since enclosures are defined by the board dimensions, the overall MCAD process is severely constrained compared to ECAD for PCBs. Nevertheless, its presence is crucial and can become complex in its own right with certain multi-board builds.
Traditionally, system design involved developing each printed circuit board individually, while the mechanical engineering team was creating the system enclosure. For systems with multiple circuit boards, each board was designed and prototyped individually. Once the boards were verified to run correctly, the boards and the system enclosure would be brought together and the testing of the entire system would begin.
An Integrated CAD Approach Saves Time, Money, and Circumvents Production Headaches
While the circuit boards had been verified individually during their initial testing, new problems were often found when interfacing with the rest of the system electronics and mechanical design. This would ultimately force another re-design of the affected boards to iron out these problems.
Designers no longer have the luxury of going through lengthy and costly redesign cycles and prototype builds to work the bugs out of the system, especially when multiple circuit boards are involved. Electrical CAD and mechanical CAD co-design tools give the designer the ability to find and correct many of these problems before going through PCB and mechanical prototype builds.
PCB designers can see the effect their parts placement will have on the mechanical design as well as how the electrical connectivity between the boards matches up. Finally, using advanced ECAD-MCAD co-design tools, they can fold all of the multi-board PCBs virtually into the mechanical enclosure to verify the fit and function of the entire system. If this sounds too good to be true, hold on, there’s more.
ECAD-MCAD co-design tools can help with multi-board system design like this laptop
A Comprehensive CAD Procedure for Multi-Board PCB Design Flow
In the old traditional system design workflow, the different printed circuit boards of the system would be developed as individual projects. When all the PCB designs of the system were completed, they would then have to be tested together to verify system operation and compatibility. Some purposes for these tests included:
All the circuit boards would be connected together to verify the system worked as it was designed to.
Individual PCB design details would have to be looked at for system compatibility, such as the pinouts of intra-board connectors to make sure that the wiring harnesses correctly connected one board to another.
Connectors, switches, and other human interfaces would be verified for easy access once all the system boards were assembled together.
All PCB designs would have to be confirmed to be at the same version, and there weren’t any changes made to one design that hadn’t been incorporated into the others.
Although these concerns wouldn’t be problems for each individual PCB design, they do become very important when all the circuit boards are brought together in the mechanical enclosure of the system. And here is where ECAD-MCAD co-design tools can really help.
By bringing all the different system boards and mechanical designs into one design environment, PCB designers can virtually simulate the concerns listed above instead of building a prototype. They can confirm in a 3D environment that each board connects correctly to the rest of the system, that all connectors and interfaces are accessible, and that all portions of the design are at the same version as the rest.
For successful ECAD-MCAD collaboration, however, there must be several essential factors in place first. These include starting with a plan for engineering prototyping workflow management and addressing form factors in multi-board circuits. Additionally, the PCB designer should take into account the multi-board PCB edge clearances all the way through design by utilizing all the tools available, such as the PCB design grid.
One of the key advantages of ECAD-MCAD co-design tools is verifying interface accessibility
Additional Information on ECAD-MCAD Co-Design of Multi-Board PCBs
To make ECAD-MCAD co-design of multi-board PCBs a design success for you, here are some important points to consider.
The Key Is MCAD/ECAD Collaboration
A successful ECAD-MCAD co-design environment can save a lot of time and money by reducing the number of redesigns and prototype builds that you will need. But there are some essential requirements that you need to observe to achieve this – starting with the type of tools you are working with. It is imperative that the CAD systems you are using have the ability to seamlessly communicate bi-directionally with each other to transfer data between them. Without this, you will be fighting with trying to read and write data to synchronize it between tools.
Here is more about MCAD-ECAD collaboration.
Start the Job Right With Engineering Prototyping Workflow Management
Once you have the tools in place to do the job, you need a plan. Without a workflow process in place, before you begin, you may end up wasting as much time as you did with your older, more traditional system design workflows. You need to develop your engineering workflow for prototyping multi-board system design before you start the design. This way, you can minimize the possibility of wasting time by identifying any potential problem areas of your workflow before you begin.
Try this for more information on engineering prototyping workflow management.
Advanced ECAD-MCAD co-design tools are essential for multi-board PCBs like this
Utilize MCAD & ECAD in Addressing Form Factors in Multi-Board Circuits
Working with the advanced tools required for MCAD and ECAD multi-board design will require a new set of design skills and tool savvy. These tools will give you the ability to create and work with 3D component models and imported 3D mechanical models of cases or enclosures as well as perform 3D collision checks for your components, the boards, and the system enclosure. To maximize the effectiveness of the tools, you will need to be able to work as smoothly as possible with these features to rapidly move your design into production.
Here is further reading on addressing form factors in multi-board circuits.
ECAD-MCAD Confirmation of Multi-Board PCB Edge Clearance
Using your 3D ECAD-MCAD tools for system-level design also extends to making sure these designs are manufacturable. As with any PCB, your system boards will have to be manufactured on a panel and then successfully removed from it. Your design needs to make sure that there is sufficient clearance between the components and the edges of the boards that they are mounted on to facilitate breaking the boards out of their panels. Without these clearances, your manufacturing costs may go up or you may have to redesign the board.
This will help you to find out more about multi-board PCB edge clearances.
The PCB Design Grid Is Your Friend
There are a number of features and functions available to you in today’s advanced PCB design tools, and by leveraging them, you can help your design efforts. One of these is the good ol’ standard design grid. Especially when working with multiple board designs where pairing up mating connectors is critical, it is important to use the design grid to locate your connectors precisely where you want them.
Look here to find further reading on using PCB design grids.
Being able to move mechanical objects aside is a key benefit of 3D ECAD-MCAD tools
ECAD-MCAD Co-Design Tools Support Quality Multi-Board Designs
The role of CAD in design environments individually provides the requisite toolkit to fashion an idea into a manufacturable reality and cooperatively engage in the system-level assurance of intricate productions. To create the best designs, you need the best tools. You need design software that can handle multiple PCB designs and 3D mechanical models simultaneously. You need tools that will give you the ability to interact with these important designs and models so that you can move them in and out and maneuver them as required. You also need powerful 3D capabilities that will show you the design as it will truly appear, and will also report back to you DRC collisions and other system-level problems.
Allegro PCB Designer from the Cadence line of premium EDA tools is the design system you need to support your multi-board design needs. With the features and capabilities we’ve been talking about, Allegro can make the difference between getting your system design up and running and ready for market before the rest of your competitors.
If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.