Starting with the application of a flexible polyimide insulating film that is more malleable than copper foil and is coated with rolled copper, a rigid-flex circuit board is constructed. The base material with a copper coating will then be perforated, and the electrical layers will be separated by selective plating on the drill holes. An insulation layer of Bondply, a two-sided adhesive polyimide film, is then applied to the stack up of the flexible circuit. The flexible stack-up and rigid PCB part of the circuit board are connected by extending the ribbon during the final stage.

What is a Rigid-Flex PCB Fabrication?

A flexible circuit board with a stiff core makes up the rigid-flex printed circuit board (PCB), which combines two different types of PCBs. Compared to conventional circuit boards, this novel design has many advantages, such as easier installation and more effective packaging. Rigid-flex printed circuit boards are a well-liked option for dense electronic applications due to their affordability. The rigid-flex PCB is a widely sought-after option for many electronics applications thanks to a variety of benefits that make it a flexible choice.

For industrial & commercial applications, rigid-flex printed circuit boards are an excellent choice since they maximize space efficiency and improve dependability. These boards are a great option for applications that demand a high degree of dependability since they improve electrical functionality and service endurance by incorporating the circuit into the PCB’s general design. Rigid-flex printed circuit boards are a great choice for areas with harsh circumstances or high-density applications.

Rigid-flex PCB designs may be more complex than their flexible-flex equivalents, but the advantages outweigh the added work. The alignment of numerous layers on rigid-flex PCBs must be carefully planned, but the enhanced electrical performance and reliability of this integrated circuit board make the extra effort well worth it. For high-reliability systems, rigid-flex printed circuit boards are the favored option in both industrial and commercial applications.

Types of Rigid-Flex PCB Fabrication

The classification of rigid-flex PCBs is based on the method used to connect the rigid & flexible circuit boards. They are divided into two groups:

• Composite PCB – Based on how the firm and flexible PCBs are joined, several types of circuit boards are distinguished. Both the two primary groups share a blind and buried layout. These use blind vias, which connect two internal layers without piercing the outer ones and feature a more compact circuit design. By connecting component pads, buried vias, on the other hand, enable wire routing and increase circuit space. Rigid-flex printed circuit boards should be built with few vias and thoughtful placement for the best outcomes.
• Rigid-Flexible PCB – Circuit boards that are hard and flexible are created separately and fused after that. This technique does not employ through-hole technology.

A more complex technique requiring more resources and personnel are used to create rigid-flex printed circuit boards. Despite being more expensive, rigid-flex PCBs offer excellent performance in products like TVs & medical equipment. These PCBs’ flexibility allows them to fit snugly into restricted spaces and remove design flaws, making them versatile and used in primitive, bendable equipment like kitchen cabinetry & LED lighting.

The support material is the primary difference between stiff and flexible circuit boards. Flexibility in PCBs distinguishes them from rigid PCBs’ durability. While flexible circuit boards can work in a temperature range, rigid ones can withstand extreme heat. Both alternatives provide excellent performance, but stiff boards are typically heavier. In terms of consumer electronics, rigid-flex printed circuit boards are frequently a better option.

Step-by-Step Process for Rigid Flex PCB Fabrication 

To get a successful end, rigid-flex circuit board construction comprises numerous steps. For instance, careful consideration must be given to the substrate substance to ensure lifespan and durability. Additionally, it must be able to withstand chemicals and heat. The base must also be pliable enough to make it simple to access circuit components. The flexible film, adhesives, and substrate are combined to form cover layers, which offer thorough defense while maintaining access to landing pads.

1. Preparing the Rigid-Flex PCB Fabrication material

We first clean the copper-clad boards and cut the necessary amounts of coverlay, polyimide, prepreg, stiffeners, & the previously cleaned CCL before starting the production of our rigid-flex PCB.

2. Creating the Rigid-Flex PCB Fabrication inner core

To construct rigid-flex PCBs, an internal flex PCB must first be made. An inner core must be made for the flex PCB. If the rigid-flex layout only requires one flexible polyimide layer, we will enclose it in a thin sheet of copper foil. Several outside copper foils will be bonded to the PI if the design necessitates two or more layers.

3. Creating the Rigid-Flex PCB Fabrication inner core circuits

A certain copper trace pattern is what we want to achieve in this stage, and the remaining copper should be taken out. To do this, we cover a copper foil sheet with a UV-activated, curable photoresist. The visible connections on the PCB are then highlighted, and a nontransparent coating is subsequently placed over the copper. The dry film cures and covers the copper wiring that follows the layout of our circuit when exposed to UV light. Next, a chemical solution is used to rinse the unhardened photoresist away. A NaOH solution is then used to dissolve the copper, leaving only the appropriate copper pathways on the inner core.

4. Laminating and drilling holes 

How we adhere to the polyimide layers depends on the rigid-flex design’s number of flexible layers. If the design demands more flexible layers than two, copper foil & PI layers are alternately bonded to the flexible inner core. The construction of circuits then starts. If the design merely calls for two or one bendable layers, we go straight to circuit development.

Creating the network on the outer flex layers is the last step in the process. To start, we keep the copper & eliminate the copper paths from the printed circuit board pattern. To do this, the area of the circuit is first electroplated with copper, followed by tin, protecting the circuit from the subsequent procedure. After removing the photoresist, NaOH is used to dissolve the extra copper in the non-conductive area. All that is left are the copper traces that were electroplated on the flex layers. After drilling holes through the plate with a laser, we cover the flexible layers with a coverlay. The flexible region has now reached its conclusion.

5. Rigid layer lamination and circuit board generation

We alternately laminate prepreg layers & copper foil when creating a rigid-flex printed circuit board with PTHs. The circuit is then created, and holes are mechanically drilled into the board. For rigid-flex PCBs with HDI requirements, we drill alternate prepreg layers & copper foil using a laser. The circuits are then created on the stiff layers of the board after laminating the alternating flex layers.

6. Cut off excess prepreg in the Rigid-Flex PCB Fabrication.

To reveal the desired flexible section, we utilize a laser to remove the prepreg material outside of the circuit.

7. Finalize Rigid Flex PCB Fabrication process and Testing Functions.

We apply a silkscreen, surface finish, and solder mask to the board’s surface to finish the creation of our rigid-flex PCB. The panel’s partial edge holes and V-cuts are then treated. Then, for components intended for use in sectors like the military, healthcare, aircraft, and automotive, we perform fundamental tests like the nail-in-bed and flying probe tests as well as, in unique circumstances, a 4-point sensing test. The production procedure is now finished with it.

Major Applications for Rigid Flex PCB Fabrication

Rigid-flex circuits’ main advantages are their durability, portability, and minimal weight. They can also be created to properly fit the target device. Rigid-flex circuits are a wonderful answer to the need for integrating cutting-edge technology into constrained locations. They maintain flexibility while allowing for a more compact device design with lighter conductors.

When compared to conventional circuit boards, rigid-flex circuits have several benefits, such as reduced cost and improved connection and polarity dependability. Due to their adaptability, they may be used in a wide range of applications, and their small design enables higher technology consumption densities. These circuits offer a fantastic substitute for traditional circuit boards because they are very easy to make and perfect for high-density applications.

Rigid-flexible circuits can provide flexibility by coming in a variety of sizes and component densities. This makes it possible for circuit routing to be more effective on polyimide PCBs with higher-density connections. Rigid-flexible circuits are an excellent choice for applications that undergo significant levels of shock & vibration because they reduce system weight as well.

Other regions of utilization include:

• Monitoring of vital signs in medical wearables
• Use in RF devices and power distribution in industrial settings
• Traceability & tracking of e-commerce deliveries