In my time working with companies in the automotive, telecom/wireless and defense industries, I often hear of the many issues facing design teams as they tackle projects made up of multiple PCBs connected by flexible PCBs, cables, or with a backplane board.
Often, the challenge arises when defining and implementing the interconnects across boards, and managing changes throughout the course of the PCB design process. Today I’m going to share my top tips for overcoming these issues.
1. Partition electronic functionality across multi-boards early in the design phase. Some might ask why this is worth the effort at the start of the product development process. This is my answer: It allows you to generate a bill of material for each board so you can
- Understand the cost associated with each sub assembly/board.
- Decide if different parts of the system design should be outsourced based on the cost (for example, many companies in the defense industry will buy-in a module rather than designing and manufacturing it themselves).
2. Consider signal integrity across the system rather than individual boards. 
Checking signal integrity board by board has its limitations, as the performance of one, can have a knock-on-effect on another. This is where you need multi-board analysis. It means that the complete system electrical net can be simulated in its entirety from end to end, providing accurate signal analysis across the system.
The challenge is in how to achieve this.
Usually, a systems engineer or lead engineer is forced to use non-intelligent tools, such as spreadsheets or PowerPoint slides to communicate the details. So when changes are introduced during logical or physical circuit design, they have to manually update their documentation to reflect these changes. They then rely on communication by either email or paper to inform others on the project to incorporate relevant changes. This sounds tedious and is, but it’s well worth the effort to do as you progress the design, rather than leaving this until the end, which can become costly when problems are found late in the process.
An intelligent method to managing multi-board design starts at the product planning phase, where the key is to use tools that enable system architects and lead engineers to create the functional diagram of the system, place connectors and visualize the connectivity between PCBs, and study the placement and position of the connectors.
Engineers feed this information to their downstream tools, enabling engineers to confidently organize and manage the critical details for that system, and intelligently communicate information for the actual PCB design process.
This also helps overcome mechanical design issues, where sometimes the wrong mating connector is selected, the pin counts or pin names do not match up, or the position or placement side is incorrect.
3) Using 3D to accurately design and visualize a multi-board system.
In a multi-board scenario consider that the motherboard and daughtercard are next to each other, which may feature bulky connectors or components with heatsinks. Understanding the physical space that components take up in situ allows you to make the most of overhangs around these components and avoid clashes. It also helps to know the surrounding as we can choose to avoid routing sensitive signals in these areas.
The right tools create the logical and physical circuits as a complete system in one environment. The knock-on effect will also encourage hardware engineers and PCB designers to collaborate effectively and manage changes seamlessly for interconnects in the system. So if modifications are required on one board, they can be easily reflected and changed on all other related boards.
Also, designers can confirm that the position, placement and types of connectors are correct, and that the signals crossing the connectors are associated to the right pin of the connectors before the design is released to manufacturing.
4. Get a good night’s sleep. Changes made during logical and physical circuit creation should also be communicated to the system architect or any engineers managing the connectivity of the system. With a system-level approach, design teams can work smart, save time, and finish projects faster and with confidence. This will also help managers sleep better at night!
Are you currently designing products with more than one PCB? What challenges are you facing today? I would like to hear from you: This email address is being protected from spambots. You need JavaScript enabled to view it..
Have you registered for PCB West, the Silicon Valley's largest printed circuit board trade show? Sept. 24-26, at the Santa Clara Convention Center. www.pcbwest.com
