Thanks to the rapid developments that have taken place in the electronics industry, a number of printed circuit board types have been invented over the past few years. One of the most inventive PCBs among all the options available in the market are semi rigid-flex PCBs, also known as semiflex PCB design.
Offering a perfect balance between rigidity and flexibility, semiflex PCBs have worked wonders in many modern-day applications such as laptops, industrial equipment and much more. But how exactly does a semi rigid-flex PCB differ from a rigid or flex PCB, you wonder? This article will explain what a semi rigid-flex PCB is, what its benefits are, and some tips for designing it. So, without any further ado, let’s dive in!
What Is a SemiFlex PCB?
The traditional rigid-flex PCBs are manufactured using a combination of flexible and rigid materials. The present-day production techniques typically involve pattern plating for both the flexible and rigid substrates, followed by laminating the two substrates with an adhesive.
The downside of this, however is that the expense of producing flexible materials is extremely high. As such, the development of rigid-flex PCBs is currently inhibited by the high cost of multilayer rigid-flex PCB, which, at present is five to seven times higher than the manufacturing cost of regular multi-rigid PCBs.
Another problem with conventional rigid-flex PCBs is that the variations in flexible materials are significantly greater than those in rigid materials. Because of this, when flexible and rigid materials of the same size are laminated together, uneven expansion or contraction may cause the circuit patterns to move, in doing so, deteriorating the reliability of the finished circuit board.
To tackle the high cost and inconsistencies of traditional rigid-flex PCBs, researchers and R&D teams turned to semi rigid-flex PCB, also known as semiflex PCB design. The PCB manufacturing process of semiflex PCB involves using the bendable FR-4 materials and taking them through the manufacturing process of a conventional rigid PCB.
This is followed by a deep milling process which thins out the bended areas, imparting them with a certain amount of flexibility. This grants the manufactured PCB enough flexibility to facilitate the requirements of assembly bending connections.
The Benefits of Semi Rigid-Flex PCB
Having the characteristics of rigid as well as flexible PCBs, a semiflex PCB design offers several benefits which make it a popular option for many modern-day applications, which we’ll look into later in this article. Here are some of the biggest benefits of using a semiflex PCB:
The manufacturing process of semiflex PCB design is relatively quite simple and generally consists of only a single step. The FR-4 material undergoes normal PCB processing, similar to a typical rigid PCB, after which, depth milling technology thins out the material, granting it flexibility.
In comparison, the manufacturing of multilayer and double-sided PCBs involves multi-step processes which are quite sophisticated. In addition, the semi rigid-flex PCB is a monomaterial circuit board, this means that the entire board is made from a single material, just with varying thicknesses.
All this makes these circuit boards quite affordable compared to the traditional rigid-flex PCBs that have a multi-step manufacturing process and are made from the combination of several materials.
Due to its use in the electronics and automotive industries, semiflex PCB design must adhere to strict specifications and regulations. Furthermore, semiflexible PCBs can help reduce the assembly costs, welding points, and connector tangling when the final assembly calls for stacking of the PCB board.
They also have the advantage of allowing components to be installed in the same state and plane. Since semiflex PCBs are monomaterial boards that do not use any flexible substrate, they are free from the problem of uneven and inconsistent expansion and compression, a problem that typical rigid-flex PCBs commonly face. This enhances the reliability of the PCB making it ideal for high-precision applications.
Special Installation Performance
The semi rigid-flex PCB has the advantage of being flexible and rigid at the same time. This means that the PCB can provide the mechanical and structural support of a typical rigid PCB and at the same time, can be locally bent as per the needs of the product, thereby complying with the installation requirements of a variety of 3D applications. The semiflex PCB design can support different degrees of bending which include 45°, 90°, and 180°.
Enhanced Thermal Rating
Compared to traditional rigid PCBs, semi rigid-flex PCBs have a slightly better thermal rating. This is because the thinned-out sections of the PCB that provide it with flexibility, also enhance the heat dissipation of the circuit board. This means that the PCB can channel away the heat better than normal rigid PCBs and therefore is better suited to demanding applications, especially in electronic devices such as laptops.
Rigid PCBs lack flexibility and instead, they are hard and brittle. This means that mechanical stress induced in the board will likely cause it to fracture and break. Flexible PCBs, on the other hand, have the flexibility required to sustain mechanical stress and dampen vibrations, however, the lack of stiffness means that these boards cannot provide other components with the mechanical support they need.
Semi rigid-flex circuits, however, have stiffness as well as a certain degree of flexibility which allows them to provide other components with mechanical support and sustain mechanical stresses. It is important to note, however, that the durability of a standard rigid-flex PCB will be superior to that of semiflex PCB design.
Tips for Designing a Semi Rigid-Flex PCB
Avoid Sharp Angled Corners
Using small bending radii and sharp angled corners is a common practice for the manufacturing of rigid PCB design. However, having sharp-cornered angles in the flex region of a semiflex PCB design can instill tears in the traces.
Use Hatched Polygon for Copper Planes
The stresses induced in the flex region can cause a solid copper plate to tear or crack. That is why you should use a polygon (hatched) to maintain the integrity of semiflex PCB’s flex region.
Avoid Pads and Vias at Bend Areas
Mechanical strain accumulates along a single line, known as the bend line, when the semi rigid-flex PCB is bent. Any pads or vias on bend lines should be avoided to maintain the durability of the PCB.
Semi rigid-flex PCB offers a cost-effective and simple alternative to typical rigid-flex PCBs. However, it is important to note that the limited flexibility of these PCB types restricts them to only static, bend-and-install applications.
Hemeixin is an industry leading electronics manufacturer that specializes in a variety of PCBs and circuitry. Our services include semi rigid-flex PCB, rigid PCB, Flex PCB, and much more. Call us now to learn how we can help you.