Printed Circuit Board Assemblies Differ From Traditional Rigid PCBs
Printed circuit board assemblies (PCB) connect the components in electronic devices to turn them on. They can be rigid, flexible or a combination of rigid and flexible. Each type has its own fabrication methods, assembly considerations and cost structure based on the unique materials and technologies involved. Understanding these differences allows the PCB designer to choose the best solution for the design, engineering and production requirements of a particular project.
printed circuit board assemblies use unmoving substrates like fiberglass or FR-4 and are available in single, double or multilayer formats. They can have copper on one or both sides with internal layers that are typically used for routing signals and power. These layers also protect circuits from interference, electromagnetic emissions and power supply decoupling. The PCB manufacturing process uses additive or subtractive processes.
In the additive method the bare laminate is coated with a photosensitive solder mask film which, when imaged with light, exposes the exposed areas to bond with metal ions. The copper is then plated over the sensitized areas to create the circuit pattern. The excess copper is removed by etching and the remaining exposed areas are plated with tin to form the components contact points. The exposed tin is then soldered to the components, completing the assembly.
How Do Printed Circuit Board Assemblies Differ From Traditional Rigid PCBs?
Flex circuits are made of flexible plastic material and can be used in tight spaces and in contoured shapes. They work exceptionally well in small and lightweight electronic devices. They can also be used in applications that require high flexing or vibration tolerance. In addition to their flexibility, flex circuits have other advantages including less material, lighter weight and lower manufacturing costs.
Unlike rigid PCBs, flex circuits can be fabricated with long ‘jumper wire’ connections using conductive traces on both the rigid and flex layers. This can significantly reduce the number of connectors needed in a design which improves assembly reliability. However, it is important to consider the environmental conditions and mechanical stress the device may be subjected to when designing a flex circuit. Thin flex layers can be vulnerable to damage caused by repeated bending or over-stressing of conductive copper. Selective applications of solder mask or silkscreen epoxy inks can limit flexing range and protect external copper.
Depending on the application, rigid-flex or hybrid rigid-flex boards can have significant cost savings over traditional rigid PCBs and cable assemblies. This is due to fewer connectors, simplified routing and easier assembly steps. Rigid-flex can also provide additional durability and reliability by reducing the number of connection points that can be damaged by vibration or mechanical stress.
This can be particularly beneficial in medical and industrial devices that must withstand harsh environments. Whether a project requires a traditional rigid PCB, a flex circuit or a combination of both, understanding the design considerations for each will ensure successful transformation from concept to finished product. The key is to work with your PCB manufacturer early in the design phase to tailor these considerations to suit a specific design, engineering and production requirements.