A circuit board is a network of paths that electricity can flow through to connect different components and devices. These pathways, often made of copper, enable signals to travel accurately and reliably.
Solder paste is a thin layer of metal that lines up with the pads on a PCB before components are soldered. During reflow, the solder in the paste melts and creates an electrical and mechanical connection between the pads and components.
Resistors
Resistors are crucial elements on circuit boards that help safeguard sensitive devices from overvoltage and current. They block the flow of electric current and dissipate electric power as heat. They are also used to influence specific electrical circuit board components characteristics within a circuit. They can be divided into fixed resistors and potentiometers. A fixed resistor has a predetermined resistance value and cannot be altered. They are available in various sizes and types. Carbon film and metal film resistors are among the most popular types.
A fixed resistor can have leads that leave its body axially or radially. They are typically labeled using a color code. A common scheme is the RKM code that uses color bands to display tolerance and resistance values. A first two-digit code indicates the primary digits of the resistance while the last three digits reveal a power of 10. Additional zeros indicate tighter tolerance.
Transistors
Among the fundamental components of circuit boards, transistors serve as electric switches that convert signals to power. They’re also crucial in making logic gates that create microprocessors and other integrated circuits.
Silicon, a chemical found in sand, isn’t a conductor of electricity until it’s doped through a process called deposition. It then gains free electrons that can carry electric current. The inner semiconductor layer is either n-type or p-type, which makes the transistor switch on or off when an electric current flows through it.
The three pins of a transistor are known as the base, collector, and emitter. When it’s in active mode, a current flowing into the base pin amplifies current passing through the collector and emitter. The resulting signal is used for many different functions.
Capacitors
Capacitors are essential for circuit boards to temporarily store energy and release it when needed. They have two conductive plates separated by an insulator and can be sized in microfarads or millifarads (mF). The capacitance of a capacitor is determined by its physical size, dielectric material, and rated voltage.
Capacitor selection is a key factor for stable PCB performance. It is important to understand the trade-offs when comparing different dielectric materials, rated voltage ratings, tolerance ratings, cost, and physical size.
For example, a ceramic capacitor can be smaller than a mica capacitor, but has lower voltage ratings and less storage capacity. Using the right caps in your design will help you avoid problems like short circuits, overheating, and low capacitance values. It is also important to take proper care when handling capacitors to prevent failure. Use anti-static mats and wrist straps to reduce electrostatic damage, double-check polarity indicators before soldering, and avoid excessive heat that can crack or boil ceramic caps or dry out dielectrics.
Inductors
Inductors, which are often made of coils of insulated wire tightly wound around a core, store energy in magnetic fields as current flows through them. The inductor resists changes in current flow, which produces an induced voltage that opposes the change and is measured in inductance units like microhenries (uH).
On a PCB, inductors provide a range of crucial functions, including signal filtration and EMI suppression. They are commonly used in combination with capacitors to create low-pass, high-pass, and band-pass filters that pass some frequencies while blocking others.
When designing PCBs, it’s important to consider the inductor’s size and layout to ensure that it meets your circuit’s specifications. For example, positioning the inductor close to ground planes offers a low-impedance path for current flow and reduces electromagnetic interference from nearby components on the board. Also, be sure to keep the inductor away from power and signal traces because they carry high currents that could generate magnetic fields that interfere with its performance.
Diodes
Diodes allow current to pass through in one direction and are commonly used for protecting circuit wires from overcurrent. They are also essential for the correct operation of LEDs (light-emitting diodes) and other flashing light effects.
Physically, a diode has two terminals extending from a tin can shape in the center. One is called the anode and the other is the cathode. If you connect the positive test lead to the anode and the negative one to the cathode, the diode will conduct current. It takes a certain amount of voltage, known as the forward voltage drop, to make this happen.
The ideal diode has no voltage drop across circuit board components supplier it and consumes no power, but real ones do have a fixed voltage drop that dissipates as heat. They also have limits to how much current they can handle. If a large enough reverse-bias voltage is applied, it can cause a condition known as breakdown and allow current to flow in the opposite direction.
Sensors
Sensors are essential components in PCBs that detect and monitor environmental changes and conditions, converting them into electrical signals for processing by other circuit board parts. They enable electronic devices to interact with and respond to their surroundings, thereby improving functionality and user experience.
Accuracy is the degree to which a sensor’s output corresponds to the true value of its measured variable. A sensor with high accuracy is more precise than one with lower accuracy, but it may also require a larger range to cover the expected operating conditions of a specific application.
For example, a platinum temperature sensor used in calorimetry must be highly accurate to ensure reliable measurements. The response time of a sensor is also important, as it determines how quickly the sensor reacts to changes in the measured variable. This is particularly critical in control systems or real-time monitoring applications, such as detecting gas leaks in industrial environments.