Everything about Flex-Rigid PCB Manufacturing

Printed circuit boards have evolved from just simple single-layer printed circuit boards to complex ones that can be used in more powerful electronic devices. This means electronic manufacturers are able to design flexible and smaller devices without compromising functionality. 

One common type of PCB used in modern devices is flex-rigid PCB. It has become popular because it is flexible, powerful, and can be used on several devices. Below is everything you need to know about flex-rigid PCB manufacturing. 

What is Flex-Rigid PCB?

Flex-rigid or rigid-flex PCB is a mixture of flex PCB and rigid PCB. These are boards that consist of multiple layers of flexible circuit substrates that are attached to rigid boards. 

Nevertheless, it is a challenge to design and manufacture a flex-rigid board. This is because there are several steps involved. But it is a great board that can be used in various applications. 

A rigid-flex circuit board has features, benefits, and disadvantages of both flex and rigid PCBs. Some of the advantages of rigid-flex PCBs include being easy to assemble and repair, being light in weight, and it enhances flexibility in devices. 

Advantages of Rigid-Flex PCB

1. Provides flexibility in design

Since there are multiple layers of flexible circuits, a rigid-flex circuit offers increased flexibility to ensure it fits well into small devices. Hence, with this type of PCB, you do not need to design an electronic device based on the specifications of a circuit board. 

2. Reduced packaging size

Another benefit of rigid-flex PCB is its small size. Due to their compact size, they can easily fit in small devices and are hence designed even for smaller gadgets. 

Since modern electronics are designed to be flexible and smaller, the flex-rigid PCB serves the requirement. It can be folded to fit smaller and lighter devices.

3. Has unique stability

The bending feature of a rigid-flex PCB is another great advantage for electronic manufacturers. The ability to twist, bend, and roll is a great feature for many applications such as smartphones, computers, and digital cameras among others. 

4. Can withstand high temperature

A rigid-flex PCB is made to withstand high temperatures. Hence, it is a good choice for applications that are used in high climates. It is a board that retains wonderful features for both rigid and flexible circuit boards. 

5. Rigidity movement

There are several parts of the board that are designed to remain static under some conditions such as vibrations and shocks. Hence, rigid-flex circuit boards provide the best option that can be used in gadgets that are prone to vibrations and excess movements. 

Rigid-Flex Design guidelines

Even though there are numerous benefits of rigid-flex PCBs, there are some challenges when it comes to designing. This is because the designers need to consider electrical and mechanical aspects. Here are some of the rigid-flex design guidelines that need to be followed. 

Avoiding plated through holes on the bending areas

One design guideline that designers need to follow is to avoid plating through holes in the bending areas. You need to ensure you do not place vias and pads on the bending area of the board. 

This is because spots near the bending line can cause mechanical stress and can jeopardize the structure of the plated holes. Hence, make sure pads and vias are placed on areas not subjected to bending. 

Avoid bending at the corners

When designing a flex circuit board, it is important to ensure there is no bending at the corners. This is because a sharp bend at the corner can cause wrinkles. In addition, the sharp bend can cause stretching. 

Think about routing across the bending areas

The traces across the bending line need to remain straight. Hence, use narrow traces that can easily spread across the flexible area. When it is a double-layer design, ensure the traces are routed alternatively on the top and bottom layers. 

Steps with Rigid-Flex PCB Manufacturing

Rigid-flex PCBs are complex to manufacture. Nevertheless, most of the boards are designed in a 3D space. Below are the main steps involved in rigid-flex PCB manufacturing. 

1. Base preparation

The first step during rigid-flex PCB manufacturing is base preparation. This involves cleaning and preparing laminates before they are used in the manufacturing process. 

This pre-cleaning process is vital because the copper coil is normally covered with an anti-rust layer. Although the layer is great for oxidation protection, it is a hindrance to rigid-flex manufacturing. 

2. Creating circuit patterns

The next step is creating the circuit patterns. Two methods can be used in this step. The screen-printing method helps to produce patterns on the surface of the laminate. The other method is photographic imaging which is a famous method for drawing circuit patterns. 

3. Etching the circuit pattern

The next step is circuit pattern etching. Here, dipping laminate in a solution or an etchant solution is sprayed over the circuit pattern. The process is done on both sides to ensure desired results are achieved. 

4. Drilling holes

Here, small and large-sized holes are drilled, as well as vias and pads on the flex substrate. This drilling is done using lasers. 

5. Through-hole plating

This is a vital step in the PCB manufacturing process. At this stage, copper is deposited into the drilled holes and the thickness of through-hole plating should be maintained at 1Mil. The step is done to build interconnection on the circuit board. 

6. Protecting rigid-flex with copper plate

Next is covering the top and bottom surfaces of the board with a copper layer. This is to ensure the board is protected from harsh weather conditions, harsh chemicals, and other severe things. 

7. Cutting of rigid-flex board

The final step is to cut the board. The step should be done with extreme care to avoid damage. Happily, there are several cutting methods to consider. For instance, you can use the hydraulic method, CNC milling or use a special blanking knife. 

Final Word

Rigid-flex PCBs are commonly used in modern electronic devices because they offer durability, reliability, and long-lasting results. However, manufacturing a rigid-flex circuit board is not a simple process. Several considerations must be taken into account during the manufacturing process. 

Hence, when manufacturing rigid-flex PCBs, you need to be cautious from the beginning. By following the above steps, it is possible to produce a reliable rigid-flex printed circuit board.