PCB Board Fabrication Produce Flexible PCBs
PCBs are the foundation of electronic devices from computers and mobile phones to heart rate monitors and rockets. They connect components and conduct electricity with a myriad of copper connections deposited directly on insulating substrates, known as printed circuit boards. Standard designs now feature advanced high density interconnect (HDI) chips that have thousands of connections and multiple electrical interfaces. This makes it impossible to manually connect them with soldered wires, so copper connections are deposited on flexible substrates in a process called PCB board fabrication.
A pcb board fabrication has a rigid base material, usually FR4 or Rogers 4003 polyimide, that is overlaid with a layer of photoresist. The photoresist is patterned with the circuit artwork patterns. This pattern is transferred to production panels using collimated ultraviolet light, exposing the copper for etching. The copper is then etched away to leave behind the desired circuit pattern and expose the solder mask. The solder mask protects the copper from oxidation while providing a surface for soldering components. Lastly, the panel is finished with an electrically conductive metal coating like ENIG to improve conductivity and durability.
Flex circuits can bend and flex without damage, making them ideal for use in 3D-shaped products like wearable electronics and medical devices. They also resist vibration and abrasion, improving product durability and usability. They can take on a variety of shapes, allowing manufacturers to design more ergonomic devices that fit into tight spaces and replace bulky connectors.
Can PCB Board Fabrication Produce Flexible PCBs?
There are two types of flex PCBs: single-sided and multilayer. Both types are fabricated using the same processes. The difference is in the structure of the layers. Single-layer flex circuits have a rigid core material that is surrounded by flexible circuits. Multilayer flex circuits have both flexible and rigid layers, with some being copper and others being dielectric.
Both types of flex PCBs are durable and reliable, and they can handle repeated bending and flexing. A key factor for determining a flex circuit’s strength and flexibility is the minimum bend radius required. This is determined by the thickness and materials of the substrate, copper layer, and coverlay. For example, a thin polyimide film can provide good flexural endurance, while a thicker dielectric can provide better dimensional stability.
In addition to meeting the minimum bend radii, a flex circuit must also pass a number of other inspections and tests during PCB board fabrication. These include visual inspection to identify defects and other issues, and electrical tests to determine if the circuit meets essential customer requirements.
To ensure a quality flex circuit, designers should consult with their fabricator to understand the fabrication processes and equipment used. This will help them optimize their design for manufacturing (DFM), which is the process of modifying a product’s design to reduce assembly time and cost while meeting minimum design standards. Ideally, the designer should work with the fabricator to develop a set of DFM guidelines that they can follow during the design process to ensure a reliable flex circuit.
