14: Input Devices (Custom PCB)

Goal: Implement an IMU as before, but now on a custom-ordered PCB
Software: EAGLE in Fusion 360 (PCB design), Arduino IDE (microcontroller code)
Hardware: Microconontroller (SEEED XIAO ESP32-S3) and IMU (BNO-086 on custom PCB)
Prior Experience: Only ever used development boards for IMUs
New Methods: Design custom PCB, Order custom PCB from manufacturer, Order custom stencil from manufacturer, Use stencil, solder paste, and reflow oven to solder components to PCB

Details:

"Wildcard Card" week. I loosely interpretted the assignment this week...
I want to stop being limited by the form factor of IMU devleopment boards
So, I'm building my own IMU circuit
This present several challenges:

PCB design: must design circuit as recommended by Bosch example schematics (not as simple as connecting the 4x I2C pins like before)
PCB manufacturing: must order this PCB from a manufactuer
PCB assembly: must solder very tiny components to the PCB

How tiny?

On the left: the IMU development board I've used previously
On the right: the IMU from that board that I have to design a circuit around and somehow solder
First up, the for circuit design:

For both schematic and wiring, I used EAGLE in Fusion 360
In general for something like this, follow the manufacturer guidelines for how to implement that part in a circuit
The datasheet will contain example schematics for various implementations
My goal is to use the minimum number of pins necessary for I2C communication
From CEVA's BNO-08x datasheet, using Adafruit's development board as a starting point, I arrived at the following:

And, designed the following wiring diagram:

I ordered the PCB via OSHPark's "Superswift" PCB service
And, ordered a matching stencil from OSHStencils along with soldering paste
Received everything within a week
The stencil is patterned to match the pads on the PCB

This enables us to apply soldering paste with precision
To do so, first fashion a jig to hold the PCB in perfect alignment with the stencil

Then, assemble:

Apply soldering paste to the stencil, spreading with a plastic card
Remove the stencil
Remove the PCB from the jig
Place components on the PCB using tweezers

Then, reflow the soldering paste to solder the components to the PCB
I used a specialized reflow station with a hot air gun set to 235°C, but I've heard a hair dryer or toaster oven would work fine
Note: The PCB is sitting on top of another PCB I designed but did not end up using

After reflow, the components are soldered to the PCB
Next, I soldered on header pins as well, and...

Beautiful! Time to test!
To test, I plugged it in to the same custom setup I've been using
The header pins on this new component match those on the IMU development board
So, let's plug-and-play...

And, it worked! Just as expected
No joke, it worked the very first time and hasn't stopped working since.
I'm now empowered to design, order, and assemble custom PCBs with small surface mount components. Huge!

Files:

[next: final project]