1. The birth of PCB.
Before the advent of PCBs, circuits were composed of point-to-point wiring, and the reliability of this method was low, because as the circuit aged, the rupture of the circuit would lead to an open circuit or short circuit in the line node. Winding technology is a major advancement in circuit technology, which improves the durability and replaceability of the wire by wrapping small-diameter wires around the posts at the connection points.
When the electronics industry develops from vacuum tubes and relays to silicon semiconductors and integrated circuits, the size and quality of electronic components are also declining. Electronic products are appearing more and more frequently in the consumer field, prompting manufacturers to look for smaller and more cost-effective solutions, and as a result, PCB was born.
2. Composition of PCB.
A PCB looks like a multi-layered cake or lasagna – layers of different materials are pressed together by heat and adhesives.
3. PCB substrate.
The substrate of PCB is generally glass fiber, and in most cases, the glass fiber substrate of PCB generally refers to the material FR4, which is a solid material that gives PCB hardness and thickness. In addition to FR4 substrates, there are also flexible circuit boards produced on flexible, high-temperature plastics (polyimide or similar), and so on.
Cheap PCBs and cavitated boards (pictured above) are made from materials like epoxy or phenol and don't have the durability of FR4, but they're a lot cheaper, and you will smell a lot when you solder things on such boards. This type of substrate is often used in very low-end consumer products, where phenolic substances have a low thermal decomposition temperature, and too long a welding time will cause them to decompose and carbonize, and give off an unpleasant smell.
4. Copper foil. 
The next step is to introduce a thin layer of copper foil, which is pressed onto the substrate by heat and adhesive during production, and on double-sided boards, the copper foil is pressed to both sides of the substrate. In some low-cost situations, copper foil may only be pressed on one side of the substrate, and when we refer to "double-sided board" or "two-layer board", we mean that we have two layers of copper foil on the lasagna.
Of course, the number of copper foil layers may be as small as 1 layer or more than 16 layers in different PCB designs.
There are many types of copper thicknesses, and they are measured in weight, which is generally expressed by the weight (ounces oz) of copper covering one square foot evenly. Most PCBs have a copper thickness of 1oz, but some high-power PCBs may use 2oz or 3oz copper thickness, which is about 35um or 14mil copper thickness.
5. Solder mask. On top of the copper layer is a solder mask, which makes the PCB look green or Sparkfun's red.
The solder mask covers the traces on the copper layer to prevent the traces on the PCB from coming into contact with other metals, solder, or other conductive objects that may cause short circuits.
The presence of a solder mask allows for soldering in the right place and prevents solder bridging.
As you can see in the image above, we can see that the solder mask covers most of the PCB, including the traces, but the silver hole ring is exposed as well as the SMD pad for easy soldering, in general, the solder mask is green, but almost all colors can be used to do solder mask.
6. Silk screen printing. 
On top of the solder mask, there is a white silk screen layer, and letters, numbers and symbols are printed on the screen layer of the PCB, which can facilitate assembly and guide everyone to better understand the design of the board.
We often use the symbol of the silk screen layer to indicate the function of some pins or LEDs, etc., the most common color of the silk screen layer is white, and the same silk screen layer can be made into almost any color.
Black, gray, red, or even yellow silkscreen layers are not uncommon, however, it is rare to see multiple silkscreen layer colors on a single board.
7. Terminology. Now that you know the structure of PCB, let's take a look at PCB-related terms.
Hole ring:Copper rings on metallized vias on PCBs.
drc：Design rule checking, a procedure that checks if a design contains errors, such as short circuits, traces that are too thin, or drilled holes that are too small.
Drill hit:It is used to indicate that the deviation between the required drilling position in the design and the actual drilling position, and the incorrect drilling center caused by a blunt drill bit are common problems in PCB manufacturing.
As shown in the image above, it is not a very accurate drill hit schematic.
Goldfinger:A metal pad exposed on the edge of a board is typically used to connect two circuit boards, such as the edge of a computer's expansion module, a memory module, and an old game card.
Stamp Hole:In addition to the V-cut, another alternative to the split board design method is to easily split the board from the imposition by using a few successive holes to form a weak connection point.
Pads:A portion of metal that is exposed on the surface of the PCB is used to solder the device.
Puzzle:A large circuit board composed of many small circuit boards that can be divided, and the automated circuit board production equipment often has problems when producing small boards, and combining several small boards together can speed up the production.
Stencil:A thin metal template can also be plastic, and when assembled, it is placed on the PCB to allow the solder to pass through certain parts.
pick-and-place：A machine or process for placing components on a circuit board.
Planar:A continuous length of copper on a circuit board, which is generally defined by boundaries rather than paths, is also known as copper pour.
Metallized vias:A hole in the PCB, containing the hole ring and the plating hole wall, the metallized via may be a plug-in attachment point, a signal relayer, or a mounting hole.
A plug-in resistor on the FABFM PCB, the two legs of the resistor have passed through the vias of the PCB, and the plating hole wall can connect the traces on the front and back sides of the PCB together.
pogo pin：Refers to a spring-supported temporary contact point, typically used for testing or programming procedures.
Reflow soldering:Melt the solder so that the pads (SMDs) and device pins are joined together.
Slotting:Refers to any hole on the PCB that is not round, slotted can be plated or not, because slotting requires additional cutting time, sometimes increasing the cost of the board.
Note: Since the grooved cutter is rounded, the slotted edge cannot be made at a right angle.
Solder paste layer:Before a component is placed on the PCB, a layer of solder paste of a certain thickness is formed on the pads of the surface-mount device through a stencil.
During the reflow process, the solder paste melts, creating a reliable electrical and mechanical connection between the pad and the device pins.
Before placing the components, there is a brief layer of solder paste on the PCB, remember to understand the definition of stencil.
Soldering Furnace:The furnace for soldering plug-ins generally has a small amount of molten solder in it, and the board is stuck on it and passes through quickly, and the exposed pins can be soldered with tin.
Solder mask:To prevent short circuits, corrosion, and other problems, the copper is covered with a protective film.
Lian Xi:The two connected pins on the device are incorrectly connected together by a small drop of solder.
Surface mount:An assembly method in which the device is simply placed on the board, and does not require the device pins to be threaded through the vias on the board.
Thermal pads:It refers to a short trace connecting the pad to the plane, if the pad is not properly designed for heat dissipation, it is difficult to heat the pad to a sufficient soldering temperature during soldering, and the improper heat dissipation pad design will feel that the pad is sticky, and the reflow soldering time is relatively long.
On the left, the pads are connected to the ground plane by two short traces (hot pads), and on the right, the vias are connected directly to the ground plane, without the thermal pads.
Routing:On the circuit board, the path of copper is generally continuous.
A thin trace connects the reset point to the rest of the board, and a thicker trace connects to a 5V power point.
v-score：If the board is cut incompletely, the board can be broken through this straight line.
Vias:A hole in the board is usually used to switch the signal from one layer to another.
Plugging refers to covering the solder mask on the vias to prevent them from being soldered, and the vias of the connector or device pins are generally not plugged because they need to be soldered.
On the front and back sides of the same PCB, this via transmits the signal from the front to the back by drilling holes in the board. Wave soldering:A method of soldering plug-in devices passes the board through a molten solder furnace that produces a stable wave at a constant speed, and the soldering wave peak solders the device pins and exposed pads together.
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