Flexible PCBs
The primary differences between a rigid PCB and a flexible pcb are flexibility and bendability. These two features can make or break the performance of your product in harsh environments. In addition, the driving needs that lead you to choose flex or rigid-flex PCBs often have an impact on what types of materials your fabricator uses and how they are fabricated. This is especially true for automotive products that are subject to high heat, moisture, chemicals, shock & vibration.
Rigid circuit boards are solid and inflexible, and they usually consist of a substrate layer, copper layer, solder mask, silkscreen layer, and a layer of adhesives. They can be single-sided, double-sided, or multi-layered and are bonded together with glue and heat. Rigid PCBs cannot flex or twist like a flexible pcbs, and they can be difficult to assemble, especially if the design is complex.
In order to produce a flexible pcb, you must use different layers of material than those used in a rigid PCB. Typically, a flex circuit board consists of a flexible plastic substrate and one or more copper foil layers. In most cases, the plastic substrate is made of polyimide, which can be fabricated into a wide range of shapes. It can also withstand many solder reflow cycles and is reasonably stable in temperature fluctuations.
Flexible PCBs and Rigid PCBs
It’s important to keep in mind that even though a flex circuit board can bend, there is a limit to how far it can be bent without being damaged. Static flexible pcbs can only flex about 100 times, which is why manufacturers typically only bend them during assembly and leave a big allowance of flex cycles for future maintenance or repairs. Dynamic flex pcbs, on the other hand, can withstand thousands or tens of thousands of bending cycles.
A key concern when designing a flex circuit board is maintaining signal integrity and controlling electromagnetic interference (EMI) in the flex section. Depending on the thickness of the substrate and where signals are located in relation to the bending section, the signal quality can change significantly.
Another key consideration is choosing the right types of coverlay, flexible solder mask, and stiffeners. The material choices should be compatible with the substrate, and they should also match those chosen for the rigid sections of the PCB. These factors can influence the final cost of the flex circuit board.
While rigid and rigid-flex circuits have similar manufacturing processes, a flex PCB is usually more expensive than a rigid PCB because it requires more material. However, you may be able to reduce costs by using a stiffener that’s added to specified areas of the flex circuit board to increase its thickness. This will help reduce the number of steps needed to manufacture the circuit board and will save you money. You can find more information about the difference between rigid and flex circuits in this Epec Engineered Technologies webinar.