Printed Circuit Board (PCB) design has evolved into a specialized domain within the electronics industry. PCBs are indispensable components, providing the electrical pathways for electronic components, offering robust support for mounting these components, and enabling compact integration within a final product. Essentially, they are the core element in any electronic device, dictating its form and functionality, and facilitating high-speed communication between advanced semiconductors.
Understanding the Printed Circuit Board
A printed circuit board (PCB) is fundamentally an electronic assembly utilizing copper conductors to establish electrical interconnections between various components. Beyond connectivity, PCBs also serve as a mechanical backbone, securely holding electronic components, which allows the entire assembly to be housed within a protective enclosure.
PCBs are constructed from layered materials, alternating between conductive copper layers and electrically insulating layers. The conductive elements on a PCB include copper traces (wires), pads (connection points), and conductive planes (large copper areas for power or ground). The structural integrity is provided by the insulating material, laminated between these conductive layers. The entire structure is then plated and coated with a non-conductive solder mask, and a silkscreen layer is printed on top of the solder mask, providing component identification and other helpful markings. Once fabrication is complete, this bare PCB is ready for the printed circuit board assembly (PCBA) stage, where electronic components are soldered onto the board, and the completed PCBA undergoes testing.
During the PCB manufacturing process, the inner copper layers are selectively etched. This etching process removes unwanted copper, leaving behind the intended copper traces that form the circuit connections. Multiple etched layers are then carefully laminated together, one after another, to build up the complete printed circuit board stack-up. This layered approach is the standard process in PCB fabrication, resulting in the bare board that is subsequently used in the printed circuit board assembly process.
A Look Back: PCBs Then and Now
To fully appreciate modern PCB design, it’s helpful to understand the historical context.
In earlier days of electronics, circuits were built using discrete components and small integrated circuits (ICs). These components were interconnected with wires and mounted onto a rigid base. Initially, bakelite, a type of early plastic, served as this base, replacing plywood in some applications. The sheer volume of wiring became a significant problem, leading to tangled connections and bulky designs. Debugging circuits was a complex task, and overall system reliability was often compromised. Manufacturing was also a slow, manual process involving soldering numerous components and wires by hand.
Older PCBs often resembled the example below, characterized by exposed copper traces and numerous through-holes to accommodate larger, through-hole components.
Modern PCB designs, however, often incorporate a vast number of miniaturized components. This includes tiny ICs, extremely small passive components, and advanced chips with a high density of pins. Manually wiring these components is simply impractical. Instead, copper connections are deposited directly onto insulating substrates, as described in the manufacturing process outlined earlier. Many of today’s electronic devices are based on advanced high-density interconnect (HDI) designs, featuring thousands of connections and multiple electrical interfaces. These PCBs power a wide array of devices, from smartphones and wearable health monitors to sophisticated aerospace systems.
Exploring Different PCB Types
While rigid PCBs are the most common type, built on solid substrates, a variety of other circuit board types exist, constructed from diverse materials. Key PCB types include:
- Rigid PCBs: These are the standard, firm PCBs we’ve primarily discussed. They are made from solid, inflexible materials like fiberglass-reinforced epoxy resin.
- Flexible PCBs (Flex PCBs): Fabricated on flexible substrates like polyimide film, these PCBs can bend and flex, ideal for applications requiring movement or tight spaces.
- Rigid-Flex PCBs: Combining rigid and flexible sections, these PCBs allow for three-dimensional design, integrating the advantages of both rigid and flexible boards.
The fabrication and assembly methods for these PCB types differ. However, contemporary ECAD software empowers designers to create any of these board types, provided that the appropriate PCB design rules are implemented within the software.
An older circuit board with through-hole components
Older circuit boards predominantly utilized through-hole components in their design. The image above illustrates an older circuit board largely reliant on through-hole components for its functionality. In contrast, modern printed circuit boards have largely transitioned to surface-mount devices (SMDs). SMDs are better suited for high-density, double-layer designs. They have become the standard component type for applications prioritizing small size, low power consumption, and cost-effectiveness. Nevertheless, through-hole components still find use in certain applications where their greater reliability and ease of assembly, including manual assembly, are advantageous. The image below showcases a modern PCB featuring high-density SMD components.
A modern PCB with surface-mount components
Modern printed circuit board designs can incorporate various solder masks and commonly feature numerous SMD components.
PCB Structure and Diverse Applications
Many crucial performance characteristics of a PCB are determined by its layer stack-up, which is the arrangement of conductive and insulating layers within the PCB. The layer stack-up is composed of alternating layers of conductive material and insulating material, and typically includes core and prepreg layers (both types of dielectric materials). The dielectric and mechanical properties of the core and prepreg materials significantly impact the reliability and signal/power integrity of the PCB design. Therefore, careful selection of these materials is paramount, especially for high-reliability applications. For instance, PCBs intended for military or medical equipment, which must operate reliably in harsh environments, or PCBs for telecommunications systems requiring low-loss signal transmission in a compact form factor, might utilize specialized materials like PTFE laminates.
An example of a typical PCB stack-up is shown below. This example illustrates a 4-layer structure with two internal plane layers: one for ground (L02_GND) and one for power (L03_PWR). This stack-up configuration is well-suited for IoT devices, compact embedded systems, and numerous other designs employing high-speed communication protocols. The internal plane arrangement enhances power integrity and provides shielding against external electromagnetic interference (EMI). These internal planes also serve as a consistent reference for controlled impedance signals, which is crucial for signal quality. This type of stack-up is a common starting point for many contemporary printed circuit boards.
Example of a 4-layer PCB stack-up
Example stack-up drawing created with Draftsman in Altium Designer.
High-Density Interconnect (HDI) PCB Design
Modern advanced electronic devices frequently utilize high-density interconnect (HDI) PCB design techniques. HDI designs involve extremely small feature sizes on the PCB. While the fundamental engineering process for HDI PCBs is similar to that of standard PCBs, they are employed in more sophisticated systems that require a high component count and numerous interconnections. Prominent examples of products utilizing HDI PCBs include:
- Smartphones and mobile computing devices
- Data center infrastructure, such as server motherboards
- Expansion cards for servers and embedded computing platforms
- Miniaturized medical wearables and implants
Ball grid array (BGA) packaging, along with related packaging types like land grid array (LGA), is a primary driver for the adoption of HDI design and manufacturing in PCB fabrication. Many microcontrollers, microprocessors (MPUs), and field-programmable gate arrays (FPGAs) are offered in BGA packages because this packaging method efficiently accommodates a large number of input/output (I/O) pins within a small component footprint. BGA packages are key enablers of miniaturization in many electronic devices, and many consumer products incorporate custom processors in BGA packages. For example, the image below shows the underside of an older CPU, revealing the supporting components on the IC substrate visible from below.
IC Substrate example
Ultra-High Density Interconnect (UHDI) PCBs: The Cutting Edge
The next advancement in PCB design and fabrication is converging with component packaging technology used for semiconductor chips in ICs. Chips in advanced processors and digital/RF modules are mounted on an IC substrate, which provides the interconnections between the chip’s electrical contacts and the PCB. The feature sizes in state-of-the-art ICs are approaching the feature sizes found in IC substrates. Consequently, similar manufacturing processes are now used to produce both IC substrates and ultra-high density interconnect (UHDI) PCBs.
The extremely small feature sizes in UHDI PCBs are pushing the boundaries of manufacturing capabilities. Currently, large-scale UHDI production is primarily concentrated in Taiwan. However, global UHDI capacity is expanding due to substantial investments in Western nations. The manufacturing processes for UHDI PCBs are primarily additive. Traces and vias are formed through metal deposition processes rather than the subtractive etching methods used in conventional PCB fabrication. UHDI PCBs will be essential for the most advanced systems operating at the highest data transmission rates. Although the manufacturing techniques are significantly different, the design process for UHDI PCBs shares many similarities with conventional PCB design.
Embarking on a New PCB Design Project
When initiating a new design, printed circuit boards progress through a series of well-defined stages. Production-quality PCBs are designed using ECAD software, which is specialized CAD software equipped with tools specifically for circuit board design and layout. ECAD software guides designers through a structured PCB design process, starting with basic electrical schematics and culminating in the generation of manufacturing files. The typical circuit board design process encompasses these key stages:
- Schematic Capture: Creating the electrical diagram of the circuit.
- Component Placement: Arranging components on the PCB layout.
- Routing: Defining the conductive pathways (traces) to connect components.
- Design Rule Checking (DRC): Verifying the design against manufacturing and performance rules.
- Manufacturing File Generation: Creating files needed for PCB fabrication and assembly (e.g., Gerber files, drill files).
To navigate these stages efficiently, utilizing robust design software with an intuitive user interface and a comprehensive suite of PCB design features is crucial.
Altium Designer: Your All-in-One PCB Design Solution
The best ECAD software should be user-friendly, easy to learn, and encompass a complete set of design functionalities. Altium Designer stands out as a unified application, integrating all necessary tools within a single program. No external programs are required to complete a design and prepare it for manufacturing.
3D view of a PCB layout in Altium Designer
3D view of a finished PCB layout in Altium Designer
Altium Designer’s integrated environment provides everything needed for designing and manufacturing high-quality printed circuit board assemblies. In contrast, other software programs often fragment design tools across multiple programs with disparate workflows, hindering productivity and increasing software licensing costs. Altium Designer is consistently recognized for its ease of learning and use, making it an ideal choice for both novice and experienced PCB designers.
Altium Designer on Altium 365 elevates collaboration and efficiency to unprecedented levels within the electronics industry. It brings software development-style integration to PCB design, enabling designers to work remotely and achieve new levels of productivity.
This overview has only touched on the vast capabilities of Altium Designer and Altium 365. Explore further by starting your free trial of Altium Designer + Altium 365 today.
