What is Rigid Flex PCB?
A Rigid flexible printed circuit board, also known as a rigid-flex PCB, is a combination of both flexible and rigid substrates. It can be used to connect multiple subcircuits. These PCBs are usually produced using a copper cladding substrate and are connected to a rigid FR4 board.
The flexible part of a rigid flex PCB is usually built with holes that are designed to secure the interconnectivity between the layers. This type of board has grown from being used as a replacement for wire harnesses to having actual subcircuits inside it.
Why Rigid flex popular?
Compared to conventional rigid PCBs, designing a rigid flex board is significantly more challenging. However, there are some advantages to using rigid flex in certain designs. For instance, it can be used in tight spaces.
When there’s a need to remove a wire harness from a printed circuit board, connectors are typically used. However, adding them to the board can increase the risk of failure. For instance, in a design with multiple subcircuits, adding connectors can lead to failure.
A flexible design eliminates the need for connectors on a board. This eliminates the risk of failure, and it can be easier to test.
Sometimes, the design of a rigid flex board that requires space is one that’s ideal for a certain application. For instance, a handheld thermal scanner can benefit from a flexible design as there isn’t a lot of room for high-profile connectors and wire harnesses. With an interconnected circuit built into the flexible substrate, you can route the traces easily.
Compared to rigid PCBs, flexible ones are generally cheaper. However, they’re also more cost-effective when it comes to producing the product. With the use of conductive layers, you can lower the cost of assembly.
Unlike other types of PCBs, a rigid flex board doesn’t require a wire harness to be installed in its enclosure. This eliminates the time and effort required to install a wiring harness in a device.
One of the most important advantages of a rigid flex board is its ability to automate the testing of its components. This eliminates the need for manual testing and ensures that the finished product is fully functional.
Our Rigid Flex PCB Capability
| Contents | Rigid-flex |
| Smallest Mechanical Drill Diameter | .0071″ (.180 mm) |
| Max Panel Size | 12×18 |
| Max Finished Copper thickness (O/L) | 9 micron (.009 mm) (only for O/L) |
| Max Finished Copper Weight (I/L) | 3 oz (89 ml) |
| Min Core thickness | .002″ (.051 mm) |
| Max Layer Count | ≤ 16 |
| Min Layer Count | 1 |
| Max Blind Via Aspect Ratio | .75:1 |
| Max through Hole Aspect Ratio | 10:01 |
| Min Finished Hole Size | .006″ (.152 mm) |
| Smallest Laser Drill Diameter | .005″ (.127 mm) |
| Process Pad Diameter | D + .014″ (.356 mm) (1-mil (.025 mm) annular ring) |
| Min Pad Size for Test | .005” (.127 mm) (rigid) |
| Min Trace and Space | ≥ .0035”(.089 mm)(rigid) |
| Stacked Vias | No |
| Controlled Impedance Tolerance | 5% |
| Min Wire Bond Pad Size | > .006″ (.152 mm) |
| Solder Mask Registration | Within .002″ (.051 mm) |
| Solder Mask Feature Tolerance | .001″ (.025 mm) |
| Solder Mask Min Dam Size | .001″ (.025 mm) |
| Mechanical Routed Part Size Tolerance | .010″ (.254 mm) |
| Bow and Twist Tolerance | As per spec |
| Thickness Tolerance | 10% |
| Min Diameter Route Cutter Available | .024″ (.610 mm) |
| Sequential Laminations | 2 |
| Non Conductive Filled Vias | Yes |
| Conductive Filled Vias | Yes |
| Blind Vias | Yes |
| Buried Vias | Yes |
| Surface finishes | HASL (Vertical or Horizontal), Lead Free HASL, OSP (Shikoku F2), OSP (Entek), ENIG (Electroless Nickel/Immersion Gold), Immersion Silver , Electrolytic Soft Gold, Electrolytic Hard Gold, Selective Gold |
| solder mask color | Amber, Green, Black, Red, Blue, Yellow, White, Clear, Bright White, Purple, |
| Fab | Routed Array, V Score, Edge to Copper .01″ (.254 mm) , V Score Angles, Countersink, Counterbore, Bevel, Milling, Edge Castellation, Edge Plating |
| Electrical test | 10 Volt, 40 Volt (Burn-In Boards), 250 Volt, 500 Volt |
| Material | Flexible Poyimide, Hybrid Constructions, Isola FR406, Isola FR408 HR, Isola P95, Isola P96, Iteq IT180, Panasonic R1766, Panasonic R1755, Panasonic Megtron, Nelco N4000-13, Nelco N4000-29, Nelco BT N5000, Nelco N7000-2, No Flow Prepreg, Isola 370HR, PSA Bond Film |
Benefits of rigid flex PCB
3D printing can reduce the space requirements of PCBs by up to 90%. The flexible nature of these PCBs allows for placement of various components around edges and folds.
The use of flexible PCBs can reduce the overall system weight and board size. They also eliminate the need for wires and connectors between the various rigid parts. Compared to traditional wires, the use of flexible cables can take up less space.
By reducing the number of parts, the space requirements of PCBs can be increased. This eliminates the need for solder joints, which provides better connection reliability.
The use of integrated ZIF contacts can help reduce the assembly process and improve the quality of the system. These contacts provide a simple and flexible interface to the system.
The cost of assembly and logistics are significantly reduced with the use of flexible PCBs. Compared to traditional boards, flexible PCBs offer a more complex mechanical design.
Compared to traditional boards, flexible PCBs offer a better overall reliability and are more resilient. They can withstand thousands of bending cycles.
The use of flexible PCBs can be done in harsh environments. They can be built with various materials that are suitable for harsh conditions. Some of these include shock-proof, moisture-proof, and corrosion-resistant.
Difficulty of Design control Rigid-Flex PCB
Due to the increasing number of miniaturization activities in the electronics industry, there is a demand for skilled individuals who are able to design rigid flex PCBs. Before you start working on a rigid flex PCB, it’s important to understand that there are varying skills required.
Instead of following a traditional electrical approach, you should start thinking about the design of a rigid flex PCB in a 3-D environment. This method will allow you to visualize the design’s mechanical elements.
The flexible part of a rigid flex PCB can bend to a certain degree, which means that it’s important to weigh the material’s mechanical stress. This bend line is also important to prevent premature failure.
If you plan on using pads and vias in the bend areas, avoid them as the mechanical stress could weaken the pads’ support. To ensure that the structure of the rigid flex PCB is stable, you should also add dummy traces to the area.
If you’re planning on using a flexible flex PCB, then it’s important that the area around the surface is also designed to have a hatched-polygon. This can be done easily by using OrCAD PCB Designer, which is an easy-to-use tool for designing PCBs.
The size variations of the rigid flex PCB during the design process should be taken into account. Due to the nature of the flexible polyimide core, it will shrink once the copper foil is removed. This variation should be taken into account during the design phase.
The final assembly stage of a rigid flex PCB involves bending the various components into shape. This process can cause stress fractures in the flex laminations.
Rigid-Flex PCB Fabrication Technique
An embedded flexible circuit is created by embedding it into a rigid board, then going through the Building Up Process. The connecting points between the flexible circuit and the rigid board are not always available in the same layer. With the use of flexible substrates, such as PCBs, the waste rate can be reduced significantly. Compared to rigid and HDI PCBs, the embedded flex-rigid variants offer significant advantages.
Compared to traditional flex-rigid PCBs, the embedded flexible circuit is produced by layering it up and embedding it into a rigid board. This method allows for a larger flexible area and a better utilization rate of the flexible substrates. Since the electrical connection between the flexible circuit and rigid board is not always available at the same layer, various advanced manufacturing techniques can be easily obtained by connecting the two through holes.
Due to the advantages of embedded flex-rigid PCBs, they can help solve various problems related to the manufacturing process of flexible PCBs. One of these is the reduction of the waste rate. This method can also be used to improve the performance of the flexible substrates. In addition, the mature manufacturing techniques of rigid boards can be used to further develop the technology.
Rigid flex PCB Fabrication process
- Coating applied
- Adding Copper foil
- Drilling
- Through-hole plating
- Etch-resist printing
- Etching
- stripping
- Copper Plating Process
- Coverlay
- Lamination and Routing
- Stiffener Application
- testing
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