Four Pillars of PCB Design for Successful IoT Products
By Hieu Duong
Attending conferences on electronics and embedded systems has always helped me stay ahead of the latest industry trends. And in recent years, Internet of Things (IoT) product design has become a major focal point across events.
Printed circuit boards (PCBs) are at the core of almost every IoT product. Successful IoT products require well-designed PCBs. And at AltiumLive 2017, I gave a talk that covered the 4 pillars of PCB design that lead to successful IoT products.
You can check out the slide deck from the talk here. Below, I’ll dive deeper into the challenges and best practices involved with each of the 4 pillars — form factor, connectivity, cost, and time to market.
PILLAR 1: FORM FACTOR
Even in these early days of IoT development, there are already a number of different form factors available in the market. Look at the differences between Nest Cams, Ecobee4 Thermostats, Philips Hue lighting, Fitbit smart watches, and Ring doorbells.
There are four main challenges to keep in mind when choosing a form factor for your IoT device.
- Lightweight: Many IoT products are consumer-focused and your users don’t want to adopt something bulky and heavy.
- Miniaturized: In many cases, IoT devices are carried everywhere. You want it to be unnoticeable, which means the form factor should be as small as possible.
- Ergonomic: If you’re building a wearable device, it needs to be comfortable for the user.
- Ruggedized: Some products are built to operate in extreme conditions. If you expect your device to be abused, it needs a form factor that can hold up for the use case.
I recommend two best practices for overcoming these challenges — streamline MCAD/ECAD collaboration and take advantage of multiple board designs.
The Value of MCAD and ECAD Collaboration
Mechanical and electrical engineers should be best friends when working on an IoT product. Whenever you change something on the electrical side it impacts mechanical design, so you need to maintain alignment at every step.
Collaboration is especially important when your device runs on battery. Power consumption can be demanding and the thermal output from microcontrollers and processors must be kept in check. You need to perform a thermo-airflow simulation, but they can only be done by MCAD tools.
We faced this challenge when Dialexa Labs built Vinli. We had four different radios on the IoT device which produced a lot of heat at maximum performance. Working with the mechanical engineers helped us perform airflow simulations that ensured our designs would minimize overheating.
Working across the aisle is easier than ever with new, advanced CAD tools that have collaboration built in. Mechanical and electrical engineers can work from different sides and verify the effectiveness of design throughout the product development workflow.
Leveraging Multiple Board Designs
Traditional, horizontal PCBs aren’t well-suited for miniaturized, ergonomic IoT products. If you take advantage of multiple board designs, you can overcome your form factor challenges.
One approach is to build smaller modules and stack them together to reduce the overall horizontal footprint.
Another option is to utilize rigid-flex designs. Combining typical rigid PCBs with flexible connectors means you aren’t limited to having parallel boards on top of one another. You could connect vertical and horizontal PCBs to fit different form factors.
You may also want to consider if conformal antennas would help overcome form factor challenges. They can be designed to match the shape of any closure. We used one for the GPS in Vinli, which allowed us to meet the design specs we planned out.
PILLAR 2: CONNECTIVITY
There are so many different wireless technologies and standards to choose from when building an IoT product. The connectivity decisions you make will impact power consumption, compatibility, and certifications, among other things.
You want to take connectivity into account in the architectural stage. And the earlier you can choose the right technology the better. That means deciding if you need Bluetooth, WiFi, ZigBee, or cellular connectivity as well as choosing between star and mesh topologies.
Every decision you make will impact the data rate and range of your IoT device, so making the right choices is important. While it’s easier said than done, these common layout practices can help you produce a PCB that translates data with minimal noise/interference and high throughput:
- Power Analysis: Usage will fluctuate throughout the day and you need a power consumption formula that will accommodate those fluctuations. As you design the PCB, you should have a clear projection of power consumption over the target lifetime of the product. This is especially important when devices are battery-powered.
- PCB Stack-Up: PCB stack-up is extremely important when it comes to RF and thermal performance. Take the time to design a proper stack-up to avoid problems with signal transmission, power delivery, antenna feeds, and more.
- Grounding: The ground area is usually very limited for small devices. Care must be taken to provide proper grounding for thermal dissipation and RF performance.
- Stitching Vias: Efficient via stitching will provide proper current returns and reduce noise interferences. When combined with grounding, you can effectively reduce noise and maximize performance of your RF design.
- Antenna Performance: Orientation, directivity, gain, and form factor are among the most important criteria when selecting an antenna. Also, pay close attention to any object in the antenna’s near field because it can cause detuning.
All of these common practices factor into your ability to obtain certifications for your RF designs. The most common certifications are FCC (in the U.S.), IC (in Canada), and CE (in Europe). However, you’ll also have to pay attention to standards for intentional/unintentional radiators, multiple radios, and the requirements for additional certifications like PTCRB and WEEE.
PILLAR 3: COST
The cost model for your IoT product depends on its overall complexity. However, you can take this common example as a way of framing your own cost challenges:
- Research and Development: You may spend between 6 months and 2 years depending on the complexity of your product.
- MSRP: Make sure you’re selling your product in the right price range. This could fall between $50 and $200 depending on features and functionality.
- Non-Recurring Engineering Fees: Production NRE is the money spent to set up production. Usually this involves a contract manufacturer and you might spend a few months setting up supply chains and testing assembly. This cost component can fluctuate greatly, falling between $30,000 and $70,000 on average. You’ll see costs increase if production requires custom fixtures and/or equipment.
- Certifications: The certifications we discussed above can prove costly. You could spend between $20,000 and $50,000 to fully certify your new PCB design.
The key is to follow best practices that minimize the cost of each component. We recommend frequent testing, designing for manufacturing, and designing for certifications.
Test Early and Often to Minimize Costs
Nobody wants to make mistakes, but sometimes they’re inevitable. The deeper into the hardware development process you get, the more costly any mistakes become. That’s why you’ll want to discover mistakes, if any, as early as possible in the process.
Testing frequently and maintaining an agile mindset can help minimize late-stage mistakes. Reducing design feedback loops also helps. You want to have an iterative approach to provide feedback on minor features so they’re reviewed and approved before you commit to any particular build.
Every bit of effort wasted implementing features will increase the cost of the overall project. Testing may prove you’ve made a mistake, but at least you’ll catch it quickly and minimize impact.
Design for Manufacturing and Assembly
You should engage with your CM as early as possible so there aren’t any surprises when production begins. Aligning on production requirements, standards, and capabilities keeps CMs from having to increase prices due to last minute requests. You can also ease manufacturing and assembly costs by:
- Using Fewer Components: Minimal designs inherently lower costs by reducing the number of components that must be purchased in bulk.
- Build with Standard Components: Common parts are easy to assemble and cost efficient. And when you apply those common components across product lines, you can further drive down costs by purchasing in greater bulk.
- Relax Design Tolerance: Certain designs always require strict adherence. For example, it is very common for antenna feed lines to be 50 ohms for maximum power output. However, other aspects of your design don’t require such strict manufacturing. If your design tolerance is set too high, CMs might charge you more for production.
- Leverage Plastics: Typical electronic products use metal parts for structural support. When possible, replace metal parts with plastic to cut costs and standardize design molding.
Design to Streamline Certifications
Don’t wait until the final stages of development to determine which certifications are necessary for your IoT product. Talk to people in your test labs early to determine what you’ll need ahead of time. Then, you can apply to certifications early and design specifically to meet those requirements.
Other approaches to streamline the certification process include:
- Use Pre-Certified Modules: There are plenty of modules that have already been designed and certified that you can plug into your device to avoid costly certification processes. You may need to make modifications, such as adding an antenna to a pre-certified module. But as long as you follow the specifications, you can avoid having to recertify.
- Reuse Custom Modules: If you have to use a custom-designed module, you can still get more out of it by making it standard across a product family. This avoids multiple certification processes for similar products.
- The 20cm Rule: Always remember that co-located antennas must be 20cm apart for most certifications. Designing with this in mind can prevent rework after specific certifications are set.
- Certify in Bulk: The main PCB certifications set similar requirements. If you test for the outliers all at once, you can perform multiple certifications rather than doing one at a time.
PILLAR 4: TIME TO MARKET
Being the first to market with your IoT product can help establish a solid customer base before competitors flood the space. Look at smart doorbells, for example. The company made it to market first and hardened itself against any competition with its high quality product.
However, everyone wants to be the first to market. Even a couple weeks of delay in development can drop you to second or third, giving you a smaller share of the market. Also, if you take too long to get to market, you risk seeing the technology become obsolete before you ever hit production.
The obvious best practice for accelerating time to market is to avoid mistakes in development. It all comes down to spending more time in the planning stages to avoid extra design cycles down the road. The sooner you can engage with vendors, your CM, and parts providers the better. Determine your requirements quickly and do your market research to make development as fluid as possible.
One thing you can do to further improve time to market is start practicing rapid prototyping. I dove deeper into rapid prototyping in another article. But overall, you should focus on constant iteration to future-proof your product. You don’t want to design something for 2G connectivity only to find that it’s been phased out of existence by the time you finish development.
KEY TAKEAWAYS FOR SUCCESSFUL PCB DESIGN IN IOT PRODUCTS
There’s certainly a lot to take in for each of these pillars of successful PCB design. As you start down the path of IoT hardware development keep these points in mind:
- Do everything you can to choose the right technologies early.
- Maximize collaboration between MCAD and ECAD.
- Always design for manufacturing and assembly.
- Plan early for certifications and manufacturing.
- Shorten design feedback loops. Test early and often.
- Mistakes = time + cost.
I hope these tips help you create a great IoT product. And if you’re looking for help with strategy and development, Dialexa can help. Reach out to us today and let us know what you want to build.