Arguably, the most important electronic component ever invented is the transistor. Invented in the late fall of 1947, this semiconductor device has been the catalyst for the founding of multiple corporations, helped launch Silicon Valley, and revolutionized the electronics industry. Not surprisingly, the invention of transistors earned Bell Labs researchers—William Shockley, John Bardeen, and Walter Brattain—a Nobel Prize in 1956. Today, it is estimated that trillions of these components are functioning in electronic devices throughout the world and billions more aboard systems in space.
The transistor is an example of an active electronic component. Active electronic components require an external power source to operate, which enables the device to manipulate an applied signal to achieve a desired output signal. This ability—or necessity, depending upon your perspective—allows active components to amplify inputs, which is one of the most common applications for which they are used. Due to the widespread manufacturing of active electronic components, matching your design’s library model with the actual component in your bill of materials (BOM) can be a challenge; however, it is critical for the manufacturability of your board and efficient PCBA development.
Let’s take a look at common types and uses of active electronic components, how they impact your PCB layout, and the importance of getting the CAD library right.
Types and Uses of Active Components
Prior to the widespread use of transistors, vacuum tubes were the preeminent active electronic component for many electronic devices, products, and appliances. Although the basics of operation are similar, semiconductor-based active components:
- Do not need a heat supply
- Operate more efficiently
- Use lower voltages
- Consume less energy
- Are smaller (which is why moving a TV set no longer poses the threat of a hernia)
Types of Active Components
The largest group of active electronic devices can be classified as semiconductor-based, as they are made from semiconductor materials—primarily Si (silicon), Ge (germanium), and GaA (gallium arsenide)—and their operation is based on the manipulation of the electrical properties of these materials. There are other types of active components included in the list below, which are also commonly used in electronics applications.
Active Electronic Component Types
- Semiconductors – transistors, diodes, thyristors, ICs, optoelectronic devices
- Displays – liquid crystal display (LCD), LED display, overhead LED (OLED) display
- Power sources – power supplies, solar cells, fuel cells, Piezoelectric generators
- Vacuum tubes – Cathode Ray Tube (CRT), vacuum fluorescent tube (VFT), X-ray, klystron
The list above is a classification of types, within which there are many specific function devices. However, the list is representational of the common uses of active electronic components, discussed below.
How Are Active Components Used on Circuit Boards?
A good general description for an active electronic component is:
Active electronic components are discrete devices utilized to change or modify the flow of current to enable an electric circuit to exhibit a desired functionality. Typically, these components are used as any of the following:
As the above description indicates, active components are versatile and perform important functions. However, the successful operation of a device requires the PCB layout to accurately reflect the physical attributes of the component and makes use of good manufacturability guidelines.
PCB Layout Considerations for Active Electronic Components
Generally, circuit board layout design consists of two stages:
- Schematic generation
- Board layout
The first stage is where the symbol for each component is illustrated. For board layout, each component’s footprint is required. Creating PCB footprints from scratch, which is sometimes necessary for custom components, can be a painstaking process wrought with opportunities for error. A much better option is to utilize a CAD library, such as the one shown in the figure below, for component selection.
The figure above shows the CAD library images, symbol, footprint, and landing pattern for a commonly used diode controller from Texas Instruments. This information is necessary to layout the active component. When doing so, there are manufacturability concerns that must be addressed in order for the contract manufacturer (CM) to build the board accurately.
Manufacturing Requirements for Active Component Layout Design
In most cases, a CM must rely on design files and the BOM to build a PCBA. Therefore, it is important for these files to accurately reflect design intent, which means addressing the following manufacturing issues:
- Placement and Clearances
The placement of your components matter, as it affects heat distribution and dissipation during assembly and operation. There must also be sufficient clearances between component pins, separate component footprints, and the board edge. Otherwise, solder bridges may form, resulting in short circuits, affected depanelization, or operational concerns such as stray capacitance or arcing.
- Trace Routing
Good signal integrity depends on the size, length, and location of trace routes. Limitations such as spacing between adjacent traces and like copper weights on a layer must also be factored in when laying out and connecting components.
- Layer Stackup
Today, most PCBs employ SMDs, which necessitates the use of vias. For these multilayer boards, the number, size, and type of each layer is critically important for proper operation. This includes routing the various DC (power and ground), analog (RF), and digital signals from your active components to the proper layers and planes.
Meeting the manufacturing requirements above is not optional—they must be incorporated into designs. Your ability to meet these requirements depends upon the accuracy of your active component library. The best way to ensure your component symbol, footprint, and landing pattern are correct is to acquire them from a trusted resource where you are assured of no mismatch with the manufacturer’s datafile.
Ultra Librarian hosts the world’s largest CAD library. This includes the most common active electronic components from the leading manufacturers and vendors in the electronics industry, ensuring any design going through production and validation has accurate models and footprints to work from. Register today for free.