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Patrick Brandon

Engineering

Electrical & Software Engineering

Mechanical Engineering

Wearable devices keep getting tinier.
The small size, organic lines, and smooth function of high-end wearable devices like Google’s Pixel Buds, Amazon’s Halo and the Ray-Ban Stories have impressed us. 
We just had to find out how they worked! So Delve engineers deconstructed several of our favorites.

INLINE0 Ray Ban Stories Assembly

Taking a device apart is a classic educational technique engineers call a tear down. Tear downs allow us to learn how other designers solved a specific challenge, and can inspire solutions to similar challenges in a new device so it works just as well--or even better.
Here, we'll share the results of several of our recent tear downs of wearables, and find out how they work their magic.
How do the leading wearables manufacturers pack so much functionality into so little a space? 
Here’s what we saw.
<h2>Flexible Printed Circuits</h2>
Wearables need to integrate ultra-tiny electronic processors with sensors that interact with the body, and package them together into small, organic shapes like an ear bud.
One of the most popular ways to do that is with flexible printed circuits (FPCs).
FPCs are the secret weapon of wearables engineering.
<ul><li>They allow you to compactly wrap circuits into 3D forms.</li><li>They are cheaper and easier to assemble than individual wired connections when you manufacture at scale.</li><li>And they keep all the circuits and components neatly confined to a 2D tape, even if your device twists like a Mobius strip.</li></ul>

INLINE 1 tiny electronics Pixel Buds Flex Circuit

Google’s Pixel Buds 2 are a good example of FPC use.
The device includes a speaker, microphones, battery, Bluetooth circuit and antenna, all wrapped into a 5-gram device that fits within your ear.
Using wires for the earbuds would require multiple components and finicky soldering, while FPC allows the whole thing to be manufactured as a single assembly.

INLINE2 tiny electronics Amazon Halo Circuit2

Like in Amazon's Halo, FPCs can also be combined with circuit boards to make hybrid flexible-rigid circuits.
The Halo keeps its main circuit board in a rigid plane, but the microphone, temperature sensor, push button and LEDs are on an FPC, allowing these components to be close to the curved surface of the device, almost touching the wearer.&nbsp;
And hybrid circuits can be manufactured in a single process, retaining the cost and assembly advantages of flexible printed circuits. 
<h2>Making Connections</h2>
No matter how amazingly compact your device may be, occasionally it may need to connect with the outside world. Inside the deconstructed devices, we discovered a diverse assortment of connectors.<h3>Pogo Pin Connector</h3>

INLINE3 A tiny electronics Bose Frames Pogo Pins

A pogo pin connector is a reliable, reversible way to connect a device to exterior components.

INLINE3 D tiny electronics Fitbit Charge5 Pogo Pins

Engineers like to say it’s for “mates and breaks;” pogo pin connectors can disconnect and reconnect many times without damage.&nbsp;This is ideal for devices that need to plug in and out of something else, like a charger.

INLINE3 C tiny electronics Fitbit Charge5 Boardto Board

Board-to-board connectors were also common in the devices we examined.

INLINE3 G tiny electronics Snap Spectacles Boardto Board2

Board-to-board connectors are used to interconnect rigid printed circuit boards or to connect rigid board to FPCs when there are a lot of signals to transmit.&nbsp;Board-to-board connectors can have one to hundreds of pins each

INLINE3 F tiny electronics Ray Ban Stories Camera Boardto Board

Generally, with a small production quantity and a high number of electronic signals that need to be transmit, the more affordable and applicable board-to-board connectors are compared to FPCs.

INLINE3 E tiny electronics Muse2 ZIF

We also found Zero Insertion Force (ZIF) connectors in the devices we deconstructed. ZIFs are designed to mate and un-mate. They’re best for components that need to be connected but remained unattached for a portion of the assembly process.

INLINE3 B tiny electronics Bose Frames ZIF

We found ZIFs in several pairs of glasses and other wearables worn on the head including Bose Frames, Ray-Ban Stories, and the Muse 2 Headband.

<h3>Hot Bar Soldering</h3>
As handy and small as ZIFs and board-2-board connectors can be, they still take up space—they are about the size of a pencil eraser. If you can’t even spare that much, hot bar soldering can be used to connect components. It’s also inexpensive. But the device cannot then be disassembled without unsoldering the joint.

INLINE4 tiny electronics Apple Air Pods Assembly

Finally, a special kind of connector is needed to transfer signals from a radio frequency antenna (which creates analog signals) to the digital circuit board. Called U.FL coaxial connectors, they have shielding to block interference with the radio frequencies as they are converted to digital. 
Apple AirPods uses U.FL connectors with the Bluetooth antenna, for example.

<h2>Lase it Direct</h2>
One of the coolest manufacturing techniques we noticed in our tiny electronics tear down was laser direct structuring. The process is unique.

INLINE5 tiny electronics laserdirectstructuring

Most commonly, we saw it used to incorporate antennae directly into the shell of a device, giving the maximum volume for the antenna without taking up any interior space! It also brings the antenna as close to the exterior of the device as possible, increasing its efficiency. 
To create a device using laser direct structuring:
<ul><li>First, a plastic part is injection molded. Pretty normal for today’s devices—except that this plastic has had a metallic inorganic compound mixed in.</li><li>After the part is molded a laser etches the future track of the circuit or antenna into the plastic. </li><li>The metallic compound interacts with the laser light to roughen the etched surface microscopically. </li><li>The exposed metallic particles in the rough etched area then stick to the copper, nickel, or gold electroplated onto the device to form the circuit. We saw this technique used in the Amazon Halo, Sony WF-1000XM4 Earbuds, and the Apple Pencil 1.</li><li>Leaf spring connectors then make contact with the exposed antenna to bring the signals to the device’s microcontroller.</li></ul>

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<h2>Let Form Follow Function</h2>
The best choices for a wearable design should flow from the device itself. 
The shape of the device may lend itself to FPCs, or not. The number of units you expect to manufacture can also influence that choice, as well as the connectors you use. 
The need to pack a large volume antenna into an otherwise tiny device may cry out for laser direct structuring. 
Carefully considering function, price point, and manufacturing will help you create the best product for your purpose.

Learn more about&nbsp;<a href="https://www.delve.com/services/engineering" target="_blank">Product Development Engineering Services from Delve​.</a>

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What Mini Electronics Are Inside Tiny Wearables?

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