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IoT PCB considerations for startups

Since IoT devices are so new, you would think that getting an IoT printed circuit board (PCB) project off the ground starts by reinventing the wheel and going through a lot of technical hassle. That is definitely not true.

But it doesn’t mean IoT startups have a clear path to stardom. Facing them is a number of design and manufacturing considerations that are unique to these small products. These considerations must be taken into account for the new IoT product to be successful.

On the plus side, it’s important for IoT startups to know that the basic foundation for a successful new product does exist. This means experience and knowhow involving the design, fabrication and assembly of these advanced products are available. And the best advice is for prudent IoT product entrepreneurs and innovators to heed the advice that experienced electronics manufacturing services or EMS providers have to offer. These companies and their engineering staffs have already performed this work with pioneering IoT companies in Silicon Valley entering the early stages of this emerging industry.

The PCB of an IoT device is a different beast than the traditional one, which is substantially larger and flat. IoT devices, on the other hand, consist mostly of either rigid-flex or flex circuit assemblies, which come with their own sets of design layout, fabrication and assembly considerations and nuances.

Layout

A foremost consideration is to seek out experienced designers who’ve done a lot of rigid-flex PCB designs. PCB space for an IoT device is at a premium. So you want the designer to have firsthand layout experience to effectively design key components on that small space.

Also, most IoT devices aren’t stationary; they incur considerable movement and twisting. Here, the experienced designer plays a major role in calculating bend ratios and lifecycle iterations as a significant part of a design. Other key design layout considerations include signal trace thickness, number of rigid and flex circuit layers, copper weight and stiffener placement. Stiffeners are used on flex circuits to assure components mounted on the flex circuit remain tightly in place to avoid movement.

Another consideration is through-hole component placement in rigid-flex circuits. Why is that important? A majority of IoT devices are based on surface mount device placement. But there can be through-hole components, which are normally placed on either the rigid portion or the flex portion of the board. Through-hole components are normally used to communicate input/output or I/O signals to the outside world. That way, those signals can be displayed using an LCD or LED monitor. Through-hole component placement is an important consideration in an IoT device because when used on the flex section of the board, proper stiffeners need to be designed and implemented for proper assembly.

Lastly in the layout category, the heat that components generate must be considered. IoT devices are becoming more complex with rigid-flex and flex circuits featuring upwards of 12 to 14 layers. Some devices are digital. But increasingly analog devices are being used in IoT devices. Analog circuitry generates considerably more heat than digital ones. This means heat expansion and contraction rate must be considered. In tech lingo, this is referred to as the Coefficient of Thermal Expansion or CTE and the proper management of it.

Fabrication

Choosing the right fabricator is critical and is linked to the EMS company you’ve selected. The fabricator you want must have IoT PCB fabrication experience. Among key considerations here are assuring strong adhesions between layers on both rigid and flex circuit sides, knowing all the critical calculations and having a solid understanding of when current transfers from the rigid side to the flex side.

These fabricators must also possess an in-depth understanding of remarkably small components like 0201 and 00105 device packages, package-on-package, and the use of fine-pitch ball-grid array or BGA packaged devices.

They also should have experience in designing boards with very tight tolerances in terms of footprint for those types of BGA devices, in terms of up-to-date capabilities like laser direct imaging for putting the solder mask on the board. They should have laser drills for via drilling with sizes of 5 mils or under because these IoT devices could be so small that a regular drill size of 5 to 8 mils might not suffice. They may need to go to a 3 mil, which means that you need to have an advanced laser drilling capability in house.

If you are placing via-in-pad, it is a good way to use the small real estate that is available on the rigid-flex board, yet it poses problems for assembly. If vias are not completely planar or flat in shape, it becomes a challenge during the assembly of those tiny BGA packaged devices. That is because non-planar surfaces can jeopardize the integrity of solder joints.

Sometimes via in pads leave bumps if they’re not scrubbed properly after placing the vias and gold finish on top. If there are bumps, then the solder joints in the assembly for those tiny BGA balls in those IoT devices would not be a perfect joint. This might create intermittent connections, which might be a bigger issue to address and fix. It all boils down to which EMS company you are using because they’re the ones who will select the fabrication house to make a successful IoT product for you.

Assembly

It’s important to go to experienced EMS companies that have successfully assembled IoT and wearable PCBs as they have specialized tooling and fixtures already available, which are necessary for assembly to assure components are placed properly, accurately and the printing is performed correctly.

Printing can be a challenge for IoT devices. If it’s a rigid-flex board, then there is a change between thicknesses of the rigid and flex circuit portions, meaning a special fixture is required to keep the complete rigid-flex board planar or completely flat to allow effective printing to be achieved.

Startups should be well prepared to select the right manufacturing partners and EMS companies. This way they can make sure they have enough experience ahead of time to get the multitude of design, fabrication and assembly details successfully performed as they are key to a successful and timely IoT product launch.

All IoT Agenda network contributors are responsible for the content and accuracy of their posts. Opinions are of the writers and do not necessarily convey the thoughts of IoT Agenda.

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