Rigid-flex board is a semi-rigid and semi-flexible circuit structure so project components can be connected on both parts. Rigid-flex board is rigid in some parts and flexible in other parts, so it has the characteristics of both, taking advantage of it and making up for the shortcomings. For all electronic consumers PCBA, the most obvious application of rigid-flex PCBA is folding mobile phones. Based on the advantages provided by this circuit board, high-quality folding phones can be better folded or permanently bent while maintaining the condition of areas that require additional support.
Why use more expensive rigid-flex PCBA
Rigid-flex PCBA is more expensive than other types of circuit boards, so it is often used in more complex and technical applications. In order to improve functional usability, these boards are created as multiple layers, containing rigid and flexible substrate materials, and the flexible layer is completely covered with internal penetration into the rigid areas of the PCB.
Rigid-flex PCBs support two essential application types: flex to introduce and dynamic flex. More and more applications today are inseparable from it, and more electromechanical assembly companies use it because its structure is thinner than other types of circuit boards. The standard dielectric in flex circuits is 0.001 – 0.002”, which is an excellent choice for ultra-light and lighter harness requirements. Adhesive-free overlays, HDI PCB, and thin copper layers make it ideal for exceptional line innovation, providing small size, lightweight, and solutions for projects.
Flex to introduce is a common type of rigid-flex board application. In this application, there is one time overly board used during the evacuation process. In fact, the flexibility of some parts of the board remains stable throughout use, despite the factor that some progress will occur due to high-vibration applications.
Without considering the cost, it is obviously better than other boards to manufacture rigid-flex PCBA before mechanical assembly. For electronic products, the ability to repeatedly fold, wear, and twist will make their life longer. These boards are the key point to achieve these capabilities. When planned with the correct twist, these perimeter sheets can be trusted to endure a huge number of bending cycles without having any error.
Even though its price is high, it can still be seen in different electronic products because of its unique features and advantages:
- Complete circuit setup, omitting the need for redundant PCB connectors;
- Combination of reliability and flexibility makes it shine in electronic medical devices such as implantable and wearable devices;
- Omission of connectors and the characteristics of three-dimensional space improve space utilization and enhance three-dimensional space cohesion;
- It can viably reduce item volume and convey better;
- Increase board thickness, withstand higher levels of stress conditions, and reduce critical collection tasks;
- Increase flexibility and elasticity, provide the possibility of countless bending cycles, and reduce the weight and volume of the finished product;
How rigid-flex PCBA is made
Material used
The properties of the circuit board are determined by the substrate material, as is the rigid-flex PCB, whose substrate materials include flexible dielectric films and flexible adhesive films. As the main kind of flexible PCB substrate material, flexible dielectric film, for the most part, incorporates polyester (Mylar) that is generally utilized in low-finished results, polyimide (Kapton) that is the commonest type, and fluoropolymer (PTFE) that is normally utilized in military and aviation items.
Polyimide is the most used of the three flexible PCB substrate materials and is widely used for its high dielectric stability and good electrical and mechanical properties as well as high temperature operation compared to the other two. However, in order to make the circuit board have these characteristics, you have to bear higher manufacturing costs.
The main material used in flexible glue film consists of acrylic corrosive, epoxy, and polyester. Acrylic Corrosive and Polyesterimide include incredible adhesion, high flexibility, and generally high synthetic barrier and heat resistance. Nevertheless, it has a slightly enormous coefficient of thermal expansion, therefore its internal thickness should not be more than 0.05 mm. Epoxy rubber has a terrible bond and is mostly applied to the cover layer of the adhesive and the inner layer. In addition, it underlines less value of the coefficient of thermal expansion that it is a drawback to heat to stun the opposition of the plated through gaps.
Manufacturing process
- Manufacturers use FR4 and polyimide to create the rigid and flexible parts of the board, respectively. After this PCB manufacturing process is complete, the copper foil and overlay are kept on the board.
- A high amount of glue is applied to the copper layer at the starting point of rigid-flex PCBA board creation.
- Cover the area where the glue was applied with a layer of copper foil. (Can use copper plating instead)
- Drill holes in flexible substrates by laser penetration. This method can be more precise.
- Copper is deposited in the gaps as they penetrate the flex structure. This process is called through-hole plating, in which the copper is plated synthetically.
- Photosensitive anti-overlap engraving is used on the flexible area. The technique of painting window ornaments is a good option for this technique.
- After the coating is applied, the copper film is suitably cut. From this location to moving forward, the draw against is pushed out of the circuit board.
- Use polyimide as a cover layer and apply it to both sides of the flexible substrate.
- The flexible substrate is cut and bent according to the product requirements using a kick set and hydraulic punch. These techniques involve cutting various flex with high accuracy and precision.
- In the last phase, a flexible board is laid between the rigid layers, created with the use of a blanking process, resulting in a final product that can be electrically tested to be accessible for electronic reasons.
Is it cost-effective to buy rigid-flex PCBA for electronic products?
We can easily find various circuit board cost calculation tools on the Internet, and these calculators can accurately calculate rigid PCBA, flexible PCBA or rigid-flex PCBA. Do these calculators really give the correct answer? FS Technology doesn’t think so, even the most popular cost calculators can’t calculate the truest price, the rationale behind these tools build programs based solely on quantity and physics. We don’t need to do a detailed PCBA cost analysis, we only need to know from the erratic purchase price of PCB components that these tools are unreliable. Although rigid-flex PCB bare boards are expensive to manufacture, according to our observations, most customers will recoup the additional cost in 2000 pieces or less using an assembled rigid-flex PCBA.
The other factor in the expense of tooling pursues comes to volume. For rigid-flex and additionally flex models and little volume runs, most are made with laser cutting or some kind of mechanical directing. This is utilized to make the surface mount includes in the coverlays, part diagram, and whenever required, the framework of the stiffeners.
Electrical testing on these lower volumes is ordinarily finished with a flying test. In volume creation of flex and rigid-flex circuits, you have to switch over to steel rule passes on or male/female punch and bite the dust sets. This steel rule kicks the bucket and is regularly more costly to make refrains the laser cutting system. The electrical test apparatuses are likewise exchanged over to a hard-wired test, which can be more labor serious. Both of these factors can include an underlying forthright cost, yet it considers a generous decrease to the unit cost of the wholesale PCBA when you are managing higher volumes.
- PCB layers are the factor that affects the manufacturing price, don’t try to use more layers if a cheaper single-layer construction can meet the needs of your electronic device;
- Type of Flexible PCB board: Individual pieces or in a panel, when you make a Flex PCB cost estimate, consider the material utilization rate, the flex PCB material is a unit of movement, and one side must be about 250 mm not large when making, the dimensions of the board will be adjusted by us, if there are waste packages, it will find out the cost of flex PCB;
- Minimum Track is about two to three mil;
- The minimum hole size is about 0.25;
- There are 2 options for flex boards gold finger, hard gold or inundation gold, but hard gold is expensive;
- The thickness of copper is about 1/3oz is normal;
- There are three options for flexible PO connectors to select stiffeners: Fr4 stiffener, Aluminum stiffener, and Pi stiffener. If your electronic products need to be plugged and unplugged repeatedly, it is recommended to use stiffer ribs;
- Small batch PCBA is much higher than that of mass assembly.
What are the applicable fields of rigid-flexible combination?
Although these products are expensive, their excellent adaptability is still regarded as the first choice by different electronics industries. They are deeply suited for military, aerospace, and therapeutic aids, yet can also be upgraded to certain trade items.
Some conditions make rigid-flex circuits the most ideal configuration, such as the need for high-speed signal transmission of 5G base stations can not be separated from the use of rigid-flexible 5G PCB. Other smart decisions include:
- It consists of heavy stun and high vibration. Rigid-flex PCBs are exceptionally safe and can get around high-stress situations that would otherwise cause a gearbox to fail;
- It is used for applications where high accuracy is needed then cost observations. In these conditions where connectors can cause problems, a rigid-flex board will be a good option;
- Several assemblies do not have the necessary surface area for all important connectors and cables. A rigid-flex board can streamline the space to take care of this problem;
- It was used for projects that needed different rigid boards. In fact, where congregations are involved with more than four sheet configurations, it will be the best choice more practical to replace them with a solitary rigid-flex board.
Conclusion
In spite of factor that rigid and flexible boards at the basic level fulfill the same requirements by making connections with electrical and mechanical components together and these two boards are used in every aspect of life. Different quantities of the same processes are used for rigid and flexible boards, but flexible boards needed some additional processes and techniques during assembly. With that despite the fact that solid-state circuit boards may seem, at first glance at least, cheaper, the cost of ownership must be considered before declaring that flex circuits are too expensive.