A rigid flex PCB combines a hardboard and a flexible circuit. The manufacturing process involves the use of traditional rigid boards; however, some layers are flexible circuits that run through the hardboards. The board fabricator attaches PTH to connect layers of rigid boards to areas of the flexible circuit.
These pcbs comprise both flexible and rigid circuit substrates. In most cases, rigid flex PCB boards feature flexible substrates of many layers. These substrates are fixed to rigid circuit boards.
The substrates are attached externally or internally. The attachment of these substrates depends on the application of the board. A rigid flex PCB can resist many flex cycles without any failure. The components of a rigid flex board are constantly flexible.
Rigid flex circuit boards offer a greater component density and improved quality control. Rigid designs are useful where support is required and flexible designs come in handy in applications that extra space is necessary.
Rigid Flex PCB Types
Rigid flex boards come in various types which include;
Single side Rigid Flex PCB
These boards come with a layer of conductive material. Its side gives space for the integration of different electronic components. Single side boards feature a layer of flexible and rigid substrates.
Double side Rigid Flex PCB
This type of semi flex pcb is made of a layer of flexible substrate and rigid substrate. Flex substrate helps to enhance flexibility while rigid layer boosts compactness. Double-sided rigid flex PCB ensure greater routing traces due to the via within the two layers.
Multiple-layer Rigid Flex PCB
Multilayer rigid flex pcbs feature three or more conductive layers. The substrates in these boards serve as insulators.
Rigid Flex PCBs Advantages
Rigid flex boards provide a solution for limited space conditions. This type of board ensures the secure connection of components in devices while assuring contact stability and polarity. Rigid flex PCBs have several advantages which includes
Space saving: A rigid flex board is used in applications where space is important. For instance, rigid flex materials are utilized for thermal scanners. This device needs less space to fit in connectors and wire harnesses. Using rigid flex boards enables you to build circuitry that fits your device.
Flexibility: Rigid flex board offer flexibility which makes it easy to produce a board for an existing device instead of producing a device with board’s specifications.
Reliability: These boards are more durable and reliable. Fewer interconnects helps to reduce potential failure, hence, improving reliability. The low mass of these boards also minimizes the effect of vibration and shock.
Low cost: Utilizing rigid flex PCBs helps to reduce the cost of production. Rigid flex boards required a fewmaterials for their assembly. Rigid flex boards are much cheaper than rigid boards. These boards are a complete circuit as there is no need for wire harness installation in the enclosure you mount it on.
Resistance to harsh temperature: Rigid flex circuit boards can withstand varying temperatures. These PCBs can withstand exposures to UV rays and radiation. They also resist harsh oils and chemicals.
Ease of testing: These boards are very easy to test since all the sub-circuits are interconnected. The ability to get rid of connectivity issues before assembling the components prevents unnecessary expenses and wastage.
Great thermal stability: Polyimide is utilized during rigid flex circuit board assembly process. Polyimide is known to have great thermal stability. This makes these boards ideal for defense and military applications.
Rigid Flex Boards Limitations
Although rigid flex boards have several benefits, they also have their own limitations.
Requires intensive labour: Rigid flex boards manufacturing is labor intensive due to the PCB sensitivity and variations in flex and rigid substrates.
Elaborate production: Since two separate substrates are involved in the production of rigid flex board the production is time-consuming and elaborate.
Complex production process: The fabrication of rigid flex boards is complex, unlike other PCBs. It requires the utilization of suitable and effective software which makes production cost expensive.
Rigid Flex Boards Material
Rigid flex pcb comprise several materials which are discussed below;
Substrate and Coverlay Films
Woven fiberglass is one of the commonest materials used in the production of rigid flex boards. Epoxy resin impregnates this woven fiberglass. This makes the fiberglass resistant to sudden shock and constant vibrations. Therefore, these materials are utilized:
- Polyimide:Polyimide has a great thermal resistance and as such can withstand constant movements and vibrations. This type of material that can resist heat. It is a great option for applications that are subjected to fluctuating temperatures. Polyimide is very tough and flexible.
- Polyester: Polyester is a common material for rigid flex boards. Polyester is known for its flexibility. This material resists moisture and chemicals. It is useful in applications exposed to harsh environments. When you use the appropriate substrate, the lifespan and strength of the substrate are guaranteed.
Coatings
- Cover lays:Cover lays are created by combining adhesives with flexible films. Cover lays are very important in rigid flex PCB assembly. They provide inclusive shielding for the assembly.
- Cover coats:Cover coats are coatings applied on a circuitry’s surface. Polyurethane is utilized in this case.
Adhesives
Adhesives play a significant role in the production of rigid flex circuit boards. Adhesives enable secured connections to be formed between the substrate and the materials for conductor. There are different types of adhesives used in the production of rigid flex boards.
- Polyester adhesives:Polyester adhesives are mostly used in the rigid flex boards’ fabrication. These adhesives have low bond strength and are less likely to withstand unpredictable and high temperatures. However, these adhesives are now modified to resist heat.
- Polyimide adhesives: These adhesives have the ability to resist different temperatures. It can withstand about 500°C. This capability makes it an ideal option for use in sensitive applications. It is used in applications such as military and defense.
- Epoxies:Epoxies are a kind of adhesive used for the production of the rigid flex board. They can resist corrosion and varying temperatures. Epoxies are flexible and have bond stability. To enhance flexibility, small amounts of polyester are included in epoxies.
- Acrylic adhesives:Such types of adhesives offer thermal stability. They can withstand chemicals and corrosion. They are much cheaper and easy to use.
Conductor Materials
Copper is the most preferred and commonest material for assembly of this PCB. This is because copper is a good conductor of electricity. The two major types of copper used are rolled copper foil and electrodeposited copper foil.
These foils vary in thickness and weight. Surface treatment of the board is required before the assembly process. Chemical treatment is also important. This helps to enhance bond strength and increase adhesiveness. Chemical treatment on the foil also prevents oxidation and reduces the likelihood of bond degradation.
Insulators
Polyimide film is the most preferred insulator. This film is utilized on the flex circuits’ base. Polyimide is utilized in the internal parts of the multiple layer circuits.
Applications of Rigid Flex PCBs
Rigid flex circuit boards are commonly used in many applications due to their features and benefits. They are utilized in the following applications
Military equipment: Most of the military equipment is designed with rigid flex boards. This is due to the reliability of these boards and their ability to withstand varying temperatures. A rigid flex board is used in communication devices, tracking and surveillance systems, and weapon guidance systems.
Aerospace equipment: Rigid flex PCB manufacturers design these PCBs to withstand harsh temperatures. Therefore, a rigid flex board is made use of in the production of radar communication systems and radar equipment.
Automotive devices: In the automotive industry, rigid flex PCB help in the manufacturing small devices like comfort control units and control modules. Rigid flex boards are used for transmission control, music systems, and navigation systems.
Consumer appliances: Rigid flex PCBs play a significant role in the production of most consumer appliances. Consumer appliances such as washing systems, remote controllers, electronic irons, and lighting systems are made with these PCBs.
Telecommunication systems: The telecommunication industry also utilizes rigid flex boards. These boards are used in applications such as handheld devices, wireless communication devices, routers, base stations, and communication satellites.