The PCB Artwork
Every artist needs a medium. This holds true even in the world of electronics design and engineering. Yet instead of wood, canvas, and paint, electronics engineers create their master works out of fiberglass, copper, and special lacquer coatings.
Ah, Printed Circuit Boards (PCBs), where would we be without them?
Surely, we here at ENA Electronics would be nowhere without PCBs. That’s because our electronic engineering and repair specialists are dedicated to circuit board design, circuit board reverse engineering and circuit board analysis on a daily basis. Whether it’s for wind repair, AC drive repair, or industrial electronics repair, we succeed by understanding your circuit boards inside and out.
So, in this installment of the ENA Short-circuit Finding Brush series, we would like to share our own PCB “artwork” and teach you what makes (or breaks!) a circuit board.
So What’s in a PCB?
It’s all in the layers.
In case you didn’t know, a PCB is a thin, flat board made of fiberglass material, upon and throughout which thin copper tracks are printed. These tracks connect various components on the board, such as transistors, resistors, and integrated circuits, allowing the components to communicate and function together as a single electronic device.
There are several layers to a PCB, each with a specific purpose.
As electronics designers, we draw out these layers with the help of PCB CAD (computer-aided design) applications. The CAD program produces Gerber Files (artwork) which tell the PCB factory how to make our circuit board. We generated images from the Gerber Files to illustrate our design and all the different layers of a PCB. Note that the layers shown below are shown as if the top side of the board faces our eyes, so the bottom layers appear to be flipped.
Now let’s take a look!
The Substrate and Board Outline
The base layer of a PCB is called the substrate. It’s usually made of fiberglass. The substrate provides structural support for the other layers and protects the circuit from external damage. In order to get the desired board shape, the substrate is cut out from a large panel based on a board outline. Our board outline is shown below in black:
You can see that we’ve specially designed the board outline to fit the 3D printed case that we demonstrated in Part 2 of this series.
The Copper Layers
Thin layers of copper foil are applied to the substrate, serving as the conducting material for the circuit and allowing electricity to flow through the board. Complicated boards may contain many internal copper layers, but many boards have simply 1 or 2 external layers upon which the components are soldered. The red and orange regions below determine where the copper gets deposited on the top and bottom of our substrate:
The Drills and Plated Holes
Although not really a “layer”, almost all boards are also peppered with numerous drilled holes. Some or all of these holes may be copper plated so they act as wires which connect the various copper layers. The gray areas below show where holes or slots are to be drilled through and possibly copper plated:
The Solder Mask
Solder mask is a thin film of insulating material applied over the external copper layers and substrate. It is traditionally green in color. The mask protects the copper from corrosion and accidental contact, and also helps to reduce the risk of short circuits. The purple and turquoise regions below specify where not to apply the coating so that in those areas we can intentionally expose the underlying copper:
The Silk Screen
The silk screen or legend is a thin layer of ink applied over the solder mask. Silk screen ink is usually white in color. It contains labels and markings that identify the various components on the board and their corresponding connections. The green and blue regions show us where to print the Top side and Bottom side silkscreen:
The Surface Finish
After the board has been fabricated, all exposed copper is protected with a surface finish. The surface finish usually consists of either a thin layer of solder–producing a shiny tin color–or a gold plating is applied.
The Final Product
After all these layers are put together, we are left a functional masterpiece!
What’s not to like?
Conclusions
Overall, we’ve seen that the PCB artwork defines the layers of the PCB. These layers work together to create a functional electronic device by providing a structured and organized way to connect and power various components.
And that’s how we get a short-finding brush that works!
Stay tuned for Part 5 where we’ll cover the final element of the design–the Bill of Materials (BoM)!