Limitations of flexible PCBs
The use of flexible PCBs allows for a more compact and lighter design, which can be a significant benefit in applications such as automotive electronics. However, the flexibility of flex circuits also carries some limitations that need to be considered when selecting this type of board for an application.
Flex PCBs may be less suited to certain types of components, particularly high-density surface mount components that can create excessive mechanical stresses due to their thickness. In addition, large and heavy components can strain the flexible substrate and impose stress on critical areas of the PCB that can compromise the reliability of the circuit.
In addition, the flex material may degrade under certain environmental conditions. This can lead to poor electrical performance and shortened lifespans. In order to overcome these limitations, a careful cost/benefit analysis needs to be conducted in the selection process.
Flex cracks – Repeated bending and flexing can cause cracking of the conductor traces, leading to circuit failures. This can be prevented by planning appropriate bending radii and using design margins to ensure sufficient strength. Via reliability – Plated through hole (PTH) reliability is generally lower on flex boards than on rigid ones, especially in dynamic conditions such as high-speed signal transmission. The difference can be partially mitigated by designing flex circuits with higher trace widths and spacing, but this is not always possible due to manufacturing constraints.
Insufficient shielding – A lack of physical protection can make a flex PCB susceptible to electromagnetic interference (EMI) from ambient environments and other sources, which may negatively affect performance and reliability. This can be addressed by the use of shielding materials, but these add to the total cost of manufacture.
What are the limitations of flexible PCBs
Difficulty in assembling and repairing – The flex material can make it difficult to align and attach components to the board, which can increase assembly and maintenance costs. In addition, some components are not suitable for a flex circuit, and the flexibility of the substrate can lead to damage during handling.
Environmental limitations – The flexibility of a flex circuit can make it vulnerable to damage from moisture, dust and temperature extremes. This can lead to shorting, corrosion and other defects that can impact the integrity of the circuit.
Limitation of layer count – The number of layers on a flexible pcb is limited compared to a rigid PCB, which limits routing capabilities and complexity. This can be overcome by planning a circuit with adequate layers and utilizing simulation tools to determine the physical behavior of the board under various bending scenarios.
Other considerations – The number of layers on a flexible pcb can affect the performance of the board, and the size and shape of components must be taken into account when designing the circuit. In addition, if the board is going to be exposed to moisture or chemicals, the fabricator will need to consider additional protection measures.
In addition, it’s important to note that a flex circuit requires different materials than a rigid PCB. These can include coverlay, insulating and solder masks, stiffeners and adhesives. These can add to the overall cost of the circuit and impact its performance.