Learn to Make a PCB

We live in the Golden Age of hobby electronics. Electronic parts are cheaper and more powerful than ever. Never before has it been easier to make a wider variety of interesting electronic things. For any of you who has wanted to expand your electronic construction skill set beyond an Arduino and a plugboard, this class will provide an introduction to creating your own, full custom printed circuit boards (PCBs).

The class project will be to construct a solder reflow controller, a device that will turn a cheap toaster oven into a solder reflow machine capable of manufacturing all your future surface mount PCB design projects.

The reflow controller will be designed as an Arduino shield for a Sparkfun Artemis Redboard. The Artemis Redboard is a hugely capable bit of hardware which you might find useful for future projects. Not only that, the reflow controller board will be designed in a fashion that will allow it to be reused for other projects. Specifically, the controller board will contain a small color LCD display and some buttons that would serve well as the basis for a nice user interface (UI) for future projects. There will also be an 8-pin JST connector that can be used to get additional I2C, SPI, UART, GPIO, PWM, and analog signals to external hardware.

Class Project

Here is a working example of the oven controller that you will make in the class.

The temperature graph is plotted in red while the oven is ramping, green while it is in the soak phase, and blue in the cooling phase. The temperature reading turns red when oven interior is above the liquidus temperature (the temperature where solder becomes liquid). This was a run with leaded solder so the liquidus temperature is 183C. Lead-free solder melts at 217C. The blue LED indicates when the oven heaters are turned on. A full reflow run takes roughly 7-8 minutes, depending mainly on how fast your specific oven can raise its internal temperature.

Just so you know, the little LCD display looks better than this in real life. Shooting a run with my phone clamped in a vise was not the greatest setup, but it's what I had.

The software to drive the controller will be included as an Arduino sketch. Feel free to rewrite any or all of it!

The class will be spread over three sessions, each a week apart. The reason for needing two weeks between the first and last session is that it usually takes around 6-8 days from submitting a design to receiving the circuit boards from the fab house. While the boards are being shipped, the middle session will prepare the toaster oven and associated electrical wiring while the boards are being shipped back.

Each student will receive 5 copies of their own board, because JLCPCB won't make less than that. The 5 boards are only $4 total, so give one to your mom. If you want to buy extras of your board to use as UI displays for use on other projects, you can do that anytime.

The guarantee: in the unlikely event that your own reflow controller board doesn't work, we will make sure you go home with a functional board for no extra charge. The result of these classes will be a lot of functional designs, so we will have lots of spares to choose from.

A description of the sessions and what they involve can be found below. For further information, see the class FAQ.

Reflow Controller

Here is final layout for the version 1.2 reflow controller design. Students will be making their own versions of this proven design.

Session 1: PCB Design and Fabrication

This session will cover going from an idea to a design, then using Eagle CAD program to create a schematic and a PCB layout that will get sent to a fabrication house. Topics will include:

Defining goals and requirements for a design
Schematic capture and verification
Board layout & verification, including mechanical and electrical considerations
- If time permits: Creating custom library parts for Eagle
Preparation and submission of data to a fabrication house

Session 2: Toaster Oven Preparation

It takes approximately 6-8 days for the boards to be constructed by the fabrication house in China and then shipped back via DHL Express. In the meantime, a toaster oven needs to be modified, and some electrical work needs to be performed so that the oven will be ready when the boards come back:

Electrical modifications (if required)
Extra insulation (if needed)
Solid-State Relay and heatsink mounting
Electrical box and power cord construction
Thermocouple mounting for interior temperature sensing
If time permits: oven thermal profile testing
- Using an existing controller, set up the control software to manage the desired reflow profiles for the specific oven being used

Session 3: PCB Construction and Bringup, Oven Testing

This session will cover:

PCB inspection
Board construction
- Solder application using a solder syringe
- Installation of components
- Soldering your board using the classroom reflow oven
Board bringup
- Initial testing
- Validation of all components via Arduino test software
- Debugging techniques to identify faults
Initial heating tests
Validating oven temperature profiles using your own controller and oven

Below, are some descriptions of the basic steps involved in making a custom board.

Schematic Capture

A schematic represents a logical description of a design, as opposed to the layout which is a physical representation of a design. A logical description defines that an electrical connection should exist between some point A and point B. A physical description needs to explain exactly how the wire gets from A to B. A physical description also needs to explain things like how wide the wire should be in order to handle the expected amount of current, or how close the wire should be allowed to get to other wires.

PCB Layout

Here is a sample of what a board layout looks like as you design it using the CAD tool, Eagle. This design is for a LoRa Radio utilizing a SparkFun Artemis compute module. More info on this project can be found here.

The different colors have different meanings. Red is for the copper wires on the top of the board. Blue, for the copper wires on the bottom. Green typically means a "via", which is a hole that goes through the board in order to make a connection between wires on the top and the bottom. The thin teal colored line is the dimensional outline. The fab house will computer route the outside dimensions of the board to match that line to within a few thousandths of an inch.

After Fabrication

This is the top side of the above design, after coming back from the fab house. It's easy to see how the red (top side) wires in the layout photo have been translated into real wires on the top of the physical board. It's also clear to see how the teal colored dimension lines in the PCB layout photo correspond to the final shape of the board.

Finished Hardware

Of course, a bare PCB is just a means to an end. The real goal is to get parts soldered down and start writing software!

This is the result of running the radio project board through my own toaster oven reflow machine.

Bonus Points!

Here's a fundamental truth: If you're not having fun, you shouldn't be doing this.

Incorporating this logo on the backside of the radio board took me three solid days of work. It was totally worth it!

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