What Is the Difference Between Flex, Rigid, and Rigid

by BOSS Editorial | Published: January 23, 2023 | Updated: January 23, 2023 11:26 am

Printed circuit boards (PCBs) range in styles and purposes, whether someone is an engineer in the medical field or an aspiring Thocky keyboard crafter. They are integral to all technology, and many humans use them constantly without notice.

Flex, rigid, and rigid-flex PCBs are named after their most distinguishable differences, but other qualities make each type superior for unique applications. How do these types of PCBs function in their optimal environments?

Most types of PCBs have a similar foundation, like a layer of copper circuits. PCBs arguably have more similarities than differences. Here are their qualities:

Circuit board vendors have sturdy PCBs regardless of how flexible they are — they are merely strong in different circumstances. Flex PCBs can withstand shock and movement, while rigid PCBs have more heft and weight. The more a PCB can manipulate in shape, the better it is at temperature regulation, though it could be damaged from excess warping.

Every PCB variation has standards to follow to fall under these definitions. Each design was intended for different market needs because not all electronics need the same class of PCB. Not all companies have the same internal standards for circuit board creation. These standards are crucial for PCB designers because following the guidelines ensures the circuit board can handle and distribute electrical and thermal currents and has sufficient conductivity. This standard is known as IPC-2221.

Other standards, like IPC-2223 and IPC-2222, analyze how much the boards can bend or if the hole sizes are up to code.

Other PCB types exist for even more particular projects, such as single and double-sided, multilayer and high-density interconnect PCBs. They can include more wiring in concentrated areas or withstand greater frequencies without overheating.

Depending on whether the electronic can support a circuit board will inform manufacturing decisions because some PCBs are easier to manufacture and others are more cost-efficient. For example, fewer layers of copper mean less layers of substrates, minimizing costs — but makers understand what PCB infrastructure their technology should have.

All types of PCBs are layered, interchanging between copper, substrates and other materials. Copper tends to be surrounded by nonconductive substrates based on how much electricity it can store and its thermal conduction capabilities. The structure is the same for all types, even between rigid and flex. However, the copper type tends to vary based on how much the circuit board will need to bend. In some cases, circuit boards can even be printed with 3D technology.

The recognizable green solder masks generally protect the copper wiring and substrate for rigid PCBs. They come in various forms and material makeups, including epoxy and ink, but the purpose of covering the exposed wiring is the same. They could also have coverlays, a thin layer of additional protection, but they enhance flexibility for rigid-flex and flex boards. The supplementary material tends to increase the expense of more flexible PCBs, even though they’re lighter in weight despite the extra thickness of the other layers.

Rigid-flex boards contain flexible and rigid manufacturing elements, like flexible substrates and layers of rigid board. Developing a happy medium makes them ideal for unusual positions, with some parts remaining static while others can twist. PCBs are highly susceptible to frequent vibrations so manufacturers will run them through a high frequency DoF test system to ensure quality.

PCB assemblers also need to review other performance and assembly components like hole sizes or how accurately they need to position the wiring. Knowing the board's destination is critical for understanding how lax makers can be.

However, more flexible constructions may not be able to rely on these elements as heavily, as they could change with board warping and positioning. If parts of the board will twist, hole accessibility or how far other features are from each other could change.

Manufacturers assign PCBs a classification based on their application. The class doesn't determine any aspect of the circuit board other than the intended purpose. There are three classes:

Specific sectors that obtain PCBs with classifications inform decision-making when connecting them to technology. It also helps manufacturers meld them into products based on how rigorous inspection standards will be, given the intensity of its application. These are examples of the wide array of technologies containing PCBs:

Flexible types of PCBs tend to be smaller, so they can fit in more niche technologies like wearable medical devices. They have premium prices because they’re more complex to manufacture, befitting the target markets.

However, online DIY keyboard-building communities have popularized awareness of PCB types, as gamers want their keyboard to have specific reactivity and buoyancy while precision gaming.

The smaller circuit board size also contributes to more impactful sustainability initiatives, as flexible PCBs could change the market's carbon footprint. Flexible types of PCBs could use up to 95% less water and significantly less heat, especially since they aren't reliant on glass. These considerations are making environmentally conscious tech companies reconsider how to implement flexible PCBs in their potentially antiquated technology.

Most electronics require the right style of PCB to operate with maximum efficiency. Some tools need more structure, while others need better heat distribution. Despite some manufacturing and construction differences, there is a PCB for all applications. Knowing the distinctions between these circuit boards will better inform electronics designers how their products will work best based on PCB implementation.

Emily Newton is the Editor-in-Chief of Revolutionized, an online magazine discussing the latest industry innovations and trends.

Category: Manufacturing