Electronic Component Guide: PCB Layout & Design

Like an alphabet, combining electronic components in different orders and combinations unlocks different functionality. These components are at the heart of any simulation or schematic design, but deciphering their broader physical characteristics from a symbol of thousands can be daunting. Designers new to circuit board layout or those wishing to review these features can use this electronic component guide as a handy reference.

Electronic components come in many shapes, sizes, and functions – like
an LED, this electronic component guide offers illumination.

ELECTRONIC COMPONENTS GUIDE BREAKDOWN
Common Components	Passive/Active?	Linear?	Semiconductor?*
Resistor	Passive	Yes	No
Capacitor	Passive	Yes	No
Inductor	Passive	Yes	No
Diode	Passive	No	Yes
Transistor	Active	No	Yes
Integrated Circuit (IC)	Both	Depends	Yes

*As a discrete component

Electronic Components Guide Basics: Three Building Blocks

Electronic components begin with the three essential passive components: the resistor, capacitor, and inductor. In the classic water analogy, where the current is the speed of the flowing water, voltage is a waterfall, and resistance is a rock, log, or other object residing in the river, the three passives directly correlate. A resistor offers resistance to the current flow (e.g., the rock or log example), a capacitor acts like a water storage tank, and an inductor is like a water wheel that maintains the inertia of the flowing water. Subsequently (translating back to the world of electronics), the resistor opposes the flow of electrons by dissipating power in the form of heat, a capacitor stores energy in the form of an electric field (it opposes a change in voltage by sourcing current), and an inductor stores energy in the form of a magnetic field (it opposes a change in current by sourcing voltage).

Consider some additional details on these essential passive components:

Resistors act as current limiters by increasing the resistance. According to Ohm’s Law (V = IR), the current drop is proportional to the increase in resistance (thus maintaining the voltage). Resistors use a color code that indicates the resistance and tolerance (the maximum allowable deviation from the targeted resistance). Resistors also use a power rating to indicate the maximum tolerable power dissipation before failure (P = I2R). Variable resistors like the historical rheostat or modern potentiometer allow users or engineers to vary the voltage division (e.g., volume control knobs) to alter circuit performance; varistors are non-Ohmic counterparts (i.e., their behavior is nonlinear). Thermistors are resistors constructed from materials with greater temperature dependency than standard resistors that can increase or decrease resistance with increasing temperature (and vice versa).
Capacitors build up charge between parallel plates separated by a dielectric material until reaching full charge (physically, the capacitor never reaches a full charge, but from an engineering error standpoint, a duration of five-time constants is suitable). After reaching steady-state conditions, the capacitor discharges this stored charge to keep the voltage across the capacitor constant. From a broader circuit outlook, the capacitor fills in the gaps in power delivery when the system demand intensifies. Capacitors also provide an AC short to ground that removes harmonics and other noise from the power network that degrade power integrity. Capacitors are polarized or unpolarized and come in ceramic, film, and electrolytic varieties with multiple voltage/capacitance ratings.
Inductors store magnetic energy in their coils and, acting opposite to a capacitor, exchange it as a voltage source to maintain the current. Like the capacitor, the inductor has many uses related to power generation and storage in circuit applications, with the added magnetic susceptibility/permeability that is useful for sensors, detectors, and transducers. Compared to the capacitor, the real form of the inductor is far less ideal, making its implementation in some circuits more challenging; designers can replicate some functionality of the inductor with other components, like an operational amplifier (op-amps). The transformer, another basic circuit element, is effectively two back-to-back inductors used to change the voltage level of the incoming signal up or down. Lastly, since the inductor opposes a change in current, it passes DC (zero frequency) while blocking AC – the complement of a capacitor.

Each of these passive components individually offers an indispensable circuit function, but combined resistors, inductors, and capacitors provide vast filter networks for signal integrity. The four essential filters – highpass, lowpass, bandpass, and bandstop – all use some permutation of resistors, capacitors, and inductors from the source to the load.

Additional Passive Components
Oscillator	A quartz crystal or ceramic material provides a reliable periodic signal for timing.
Fuse	A sacrificial component that protects sensitive circuits/components from overcurrent conditions by failing and creating an open in the circuit continuity.
Antifuse	An antifuse is a redundant component that shorts to preserve circuit continuity.
Switch	Electromechanical components that control circuit behavior by toggling between two or more electrical contacts.

Semiconductor Components

Semiconductors are another major class of components that created the digital revolution in electronics over the past seven decades. Semiconductors span active and passive components and largely account for the power consumption/size reduction and speed increase in modern devices. Broadly, semiconductor devices are any whose primary functionality derives from the properties of semiconductor materials like silicon, germanium, gallium nitride, or gallium arsenide (to name a few). Consider some of the major families of semiconductor devices:

Diode – In the water analogy, a diode is like a check valve that only allows water to flow unidirectionally. The p-n junction of the semiconductor material (performed by doping impurities into the crystalline structure) creates asymmetrical resistance; ideally, this resistance is zero (perfect conduction) in the forward direction and infinite (perfect insulation) in the reverse direction. Operating the diode in the forward direction requires a minimum voltage threshold (the exact value depends on the material) before conduction occurs. Conversely, the diode blocks the majority of current flow in the reverse direction (there may be microamperes of reverse current leakage, but the exact value is material and temperature dependent) until the voltage is large enough to cause the insulation to “breakdown” and begin conduction (destroying the component in the process). The diode is the simplest semiconductor device as it only requires a single p-n junction, but diodes come in many varieties that build off this structure:
- Avalanche diodes operate in the reverse direction at voltages above the breakdown voltage.

- Light emitting diodes (LEDs) generate light from infrared to ultraviolet.

- Photodiodes sense light for optoelectronic applications.

- Thermal diodes monitor temperature with a forward bias that varies with thermal excitation.

- Schottky diodes have a lower forward bias than traditional silicon diodes. They are excellent for clamping (moving the voltage level up or down to stay above or below a certain threshold).
- Zener diodes allow the diode to conduct at a reverse breakdown voltage without damaging the component; they make excellent voltage references.
Transistor – A transistor switches or amplifies an incoming signal by supplying (or removing) a threshold voltage or current to one of the three terminals of the device that establishes conductivity from input to output. The two fundamental families are bipolar junction transistors (BJTs) and field effect transistors (FETs), with the metal-oxide-semiconductor field effect transistor (MOSFET) extremely popular in modern applications due to its miniscule switching losses.
Integrated circuits (ICs) – These discrete packages contain miniaturized electronic components built directly on the semiconductor die. They range from analog ICs like sensors, operational amplifiers (op-amps), modulation, and filters to application-specific digital ICs like microprocessors, microcontrollers, memory, and power management. The miniaturization and encapsulation of discrete components into a single package is responsible for the electronics revolution.

Achieving the highest level of PCBA development requires optimizing your PCB layout and design process by understanding and incorporating important considerations; such as how your selection of electronic components affects all aspects of board development.

Component Selection Impact on PCBA Development

1: Footprint Management

Designers can use an electronic component guide to acclimate to component function and performance as these characteristics often shape layout requirements (e.g., manufacturer’s datasheets). The first step to translating any electronic design to a board layout is creating the footprints that enable assembly between the bare board and selected components. Looking to streamline your footprint creation process?

2: PCB Layout Management

The next stage of your PCBA design is to convert the schematic to a PCB layout. Similar to drawing the schematic, this stage includes choosing materials, routing, and design verification. Again, for the most efficient process and highest quality results, it is best to follow good design guidelines, including the ones listed below.

PCB Layout Best Practices

Know and follow IPC standards for PCB layout.
Choose board material based on application.
If possible, use a standard board size and shape.
Set up design constraints based on your CM’s DFM rules and guidelines.
Arrange components based on signal type.
Use a consistent trace size and impedance.
Design your stackup to be symmetrical.
Run periodic error checks.
Use simulation to validate power distribution and thermal dissipation.

The guidelines above can be used for any PCBA design, and following the items on the list will help your CM maximize the first pass yield rate for your board build process. However, the overall success of your board development and the quality of the design and manufacturing processes is dependent upon having and following an accurate and effective electronic component guide and the electronic components you choose.

If you’re looking for CAD models for common electronic components or design tips to help improve the efficiency of your PCB layout, Ultra Librarian helps by compiling all your sourcing and CAD information in one place. Working with Ultra Librarian sets up your team for success to ensure streamlined and error-free design, production, and sourcing. Register today for free.