Rigid Flex PCB
In electronics, we sometimes encounter seemingly new technologies that have roots in the past. Rigid Flex PCB technologies trace back approximately 50 years to the need to replace wiring harnesses in spacecraft. The first commercially available mobile computer (which weighed a little over 25 pounds!) used rigid flex technologies.
Rigid Flex PCB is an excellent combination of rigid boards and Flexible Circuits. Flex Rigid PCB is connected by PTH (plated through holes). Higher component density and better quality control can be guaranteed.
Today, laptop computers, wearable technologies, medical devices, test equipment, and satellites are a few of the applications that rely on rigid flex PCBs.
WHAT IS RIGID FLEX PCB? Rigid Flex Printed Circuit Boards are boards using a combination of flexible and rigid board technologies in an application. Most rigid flex boards consist of multiple layers of flexible circuit substrates attached to one or more rigid boards externally and/or internally, depending upon the design of the application. The flexible substrates are designed to be in a constant state of flex and are usually formed into the flexed curve during manufacturing or installation. Rigid Flex designs are more challenging than the design of a typical rigid board environment, as these boards are designed in a 3D space, which also offers greater spatial efficiency. By being able to design in three dimensions rigid flex designers can twist, fold and roll the flexible board substrates to achieve their desired shape for the final application's package. As with conventional PCBs, you can mount components on both sides of the rigid board. Because of the integration that occurs between rigid and flex circuits, a rigid flex design does not use connectors or connecting cables between the sections. Instead, the flex circuits electrically connect the system together. The lack of connectors and connecting cables accomplishes several things:
Every rigid flex PCB is divided into zones that feature different materials and varying layer counts. Rigid zones may have more layers than flexible zones, and materials shift from FR 4 to polyimide in transition zones.
- Improves the ability of the circuit to transmit signals without loss
- Accommodates controlled impedance
- Eliminates connection problems such as cold joints
- Reduces weight
- Frees space for other components2,4,6
TYPES OF RIGID FLEX PCB
A four layer combination rigid flex circuit has four conductive copper layers. Typically, a four layer has two flexible layers and two rigid layers. A 6 layer combination rigid flex circuit has six conductive copper layers. The two most common design types are as follows:
- 6 Layer Rigid Flex – 2 flex layers and 4 rigid layers
Rigid flex circuits combine the best of both rigid boards and flex circuits integrated together into one circuit. The two in one circuit is interconnected through plated thru holes. Rigid flex circuits provide higher component density and better quality control. Designs are rigid where extra support is needed and flexible around corners and areas requiring extra space. RIGID FLEX PCB APPLICATIONS
- 6 Layer Rigid Flex – 4 flex layers and 2 rigid layers
Rigid Flex PCBs offer a wide array of applications, ranging from military weaponry and aerospace systems to cell phones and digital cameras. Increasingly, rigid flex board fabrication has been used in medical devices such as pacemakers for their space and weight reduction capabilities. The same advantages for rigid flex PCB usage can be applied to military weaponry and weapon control systems. In consumer products, Rigid Flex doesn't just maximize space and weight but greatly improves reliability, eliminating many needs for solder joints and delicate, fragile wiring that are prone to connection issues. These are just some examples, but Rigid Flex PCBs can be used to benefit nearly all advanced electrical applications including testing equipment, tools and automobiles. RIGID FLEX PCB Manufacturing
The birth and development of FPC and PCB have given birth to the new product of rigid flex PCB. Therefore, the combination of flexible Circuit Board and rigid PCB Board is a kind of circuit board with FPC and PCB characteristics, which is formed by the combination of flexible circuit board and Rigid Circuit Board through pressing and other processes and according to the relevant technological requirements. Because Rigid flex PCB is the combination of Flexible PCB and rigid PCB, the production of Rigid-flex PCB should have both FPC production equipment and Rigid PCB production equipment.
Firstly, the electronic engineer draws the circuit and outline of the flexible circuit board according to the requirement, and then sends it to the factory which can produce the flexible and rigid PCB. After the CAM engineer processes and plans the relevant documents, then arranges the FPC and PCB production lines needed for FPC production line to produce PCB. After the two kinds of flexible and rigid PCB are produced, the FPC and PCB are passed through according to the planning requirements of the electronic engineer. After seamless pressing and a series of details, the rigid flex PCB are finally made.
RIGID FLEX PCB FABRICATION PROCESS
PCB is experienced in producing custom Rigid-Flex PCB, welcome your inquiry. Please check our Rigid Flex PCB manufacturing capabilities below.
1 - 12layers
Flexible part: DuPont PI, Shengyi PI
Rigid part: PI/FR4
Maximum PCB Size(Length x Width)
Finished board thickness tolerance
0.3oz - 1.0oz or higher
Min. Annular Ring
Min. Drilling Hole Diameter
Min. hole size
Min. finished via diameter
Tolerance of dimension
Solder Mask Color
Green, White, Blue, Black, Red, Yellow
White, Black, Yellow
HASL(Hot Air Solder Leveling)
ENIG (Electroless Nickle/Immersion Gold)
Peelable solder mask
A very important link is that the rigid flex PCB is very difficult and has many details. Before shipment, it is generally necessary to carry out a full inspection, because of its high value, so as to avoid the loss of related interests caused by both suppliers and demanders. BENEFITS OF RIGID FLEX PCB
- Material selection
- Control of Production Process and Key Parts
- Production process
- Graphic Transfer of Inner Monolithic
- Multilayer Location of Flexible Materials
- drill hole
- De-drilling contamination and protrusion
- Electroless Copper Plating and Copper Plating
- Surface Weldability Protection Layer and Weldability Protection Layer
- Contour processing
- Space requirements can be minimized by applying 3D
- By removing the need for connectors and cables between the individual rigid parts the board size and overall system weight can be reduced.
- By maximizing space, there is often a lower count in parts.
- Less solder joints assure higher connection reliability.
- Handling during assembly is easier in comparison with flexible boards.
- Simplified PCB assembly processes.
- Integrated ZIF contacts provide simple modular interfaces to the system environment.
- Test conditions are simplified. A complete test prior to installation becomes possible.
- Logistical and assembly costs are significantly reduced with Rigid Flex boards.
RIGID FLEX PCB FABRICATION MATERIALS
- It is possible to increase the complexity of mechanical designs, which also improves the degree of freedom for optimized housing solutions.
- Conductors – Copper is the most widely used conductor and comes in various thicknesses to meet each customer`s requirements. Conductor options include:
- Rolled annealed (RA) copper
- Electro deposited (ED) copper
- Adhesives – Adhesive selection depends on customer needs and conductor thickness. Common adhesives include:
- Pre preg
- Pressure Sensitive Adhesive(PSA)
- Adhesiveless base material
- Insulators – Flexible substrate (base) and cover lay materials are available in a variety of thicknesses. Common insulators include:
- FR 4
- Polyester, Polyethylene Naphthalate (PEN), and Polyethylene Terephthalate
- Solder mask
- Flexible solder mask
- Photo image able cover lay (PIC)
- Finishes – The final finish depends on each customer`s assembly requirements and the application of the finished product. Common finishes include:
- Solder (Tin/Lead or RoHS compliant)
- Immersion nickel/gold
- Hard nickel/gold
- Wire bondable gold
- Organic: Entek or Organic Solderability Preservative (OSP)
As the Rigid flex circuit market continues to expand, there have been many advances in technology including:
- Air Gap – Through the process of selective bonding, increased flexibility is achieved by [unbonding" layers so they are allowed to flex freely. At JHY PCB, we are proud to be a leading designer of this air gap technology allowing your designs more flexibility.
- Component Assembly – JHY PCB offers through hole and surface mount capabilities, as well as in circuit testing, conformal coating and electrostatic protective packaging.
- Controlled Impedance – With increasing signal switching speeds, engineers need to understand and control the impedance of traces. With short signal transition times and high clock rates of modern digital circuitry, traces need to be considered transmission lines instead of simple interconnections. With today`s higher speed requirements, controlled impedance traces are designed to minimize electrical reflections and ensure an error free transition between the track and interconnections. Controlled impedance, if perfectly optimized, allows control of the physical dimensions and material of the cable. Controlled impedance signal transmission requires flexible circuit materials to be uniform in both thickness and electrical properties. It is necessary that the circuit manufacturer accurately etch the copper foil to optimize impedance.
- Panelization – Multiple circuits are partially die cut with break out tabs to allow them to remain in the panel for component assembly during the [pick & place" and wave soldering processes. Once the panel of rigid flex circuit boards is assembled, simply clip them out by cutting the breakout tabs and they are ready for assembly into your final product.
- Pressure Sensitive Adhesives (PSAs)– PSAs with a release liner are used in applications where a portion(s) of the circuit needs to be secured to a specific location within the final product. During assembly, the release liner is peeled away and the exposed adhesive allows the assembler to press the circuit into place and keep it there.
RIGID FLEX PCB DESIGN GUIDE
- Shielding – Shielding is applied when an application requires limits in electromagnetic and/or electrostatic interference. Protective shielding can be patterned or solid. Either way, it reduces noise and controls impedance of signal lines. Repeatability is ensured through etching.
Complex designs often transition from rigid to flex and back to rigid multiple times. As these intersections occur, the overlap of rigid flex materials requires keeping holes away from the transition zone to maintain integrity. In addition, many rigid flex designs include stainless steel or aluminum stiffeners that provide additional support for connectors and components. Different challenges offset the versatility and flexibility that allow you to build three dimensional designs and products. Traditional rigid flex PCB designs allowed you to mount components, connectors, and the chassis for your product to the physically stronger rigid part of the assembly. Again, in terms of traditional designs, the flexible circuit only served as an interconnect while lowering the mass and improving the resistance to vibration. New product designs coupled with improved flex circuit technologies have introduced new design rules for rigid flex PCBs. Your design team now has the freedom to place components on the flexible circuit area. Combining this freedom with a multilayer approach to rigid flex design allows you and your team to build more circuitry into the design. However, gaining this freedom adds a few challenges in terms of routing and holes. Flexible circuits always have bend lines that affect routing. Because of the potential for material stress, you cannot place components or vias close to the bend line. And even when components are properly located, bending flex circuits places repeated mechanical stresses on surface mount pads and through holes. Your team can reduce those stresses by using through hole plating and by bolstering pad support with additional coverlay to anchor the pads. As you design your trace routing, follow practices that reduce stress on your circuits. Use hatched polygons to maintain flexibility when carrying a power or ground plane on your flex circuit. You should use curved traces rather than 90° or 45° angles and use teardrop patterns to change trace widths. These practices decrease stress points and weak spots. Another best practice distributes stress across traces by staggering the top and bottom traces for double sided flex circuits. Offsetting the traces prevents the traces from laying over each other in the same direction and strengthens the PCB. You should also route traces perpendicular to the bend line to reduce stress. When moving from rigid to flex and back to rigid, the number of layers from one medium to the other may differ. You can use trace routing to add stiffness to the flex circuit by offsetting the routing for adjacent layers. Electromechanical Factors Influence Design When you design rigid flex PCBs, think in terms of electromechanical factors that affect both the flex circuit and the rigid board. As you build your design, focus on the ratio of bend radius to thickness. With flex circuits, tight bends or an increased thickness at the bend area increase the chances for failure. Fabricators recommend keeping the bend radius at a minimum of ten times the thickness of the flex circuit material and building a [paper doll" of the circuit to determine where bends occur. You should avoid stretching the flex circuit along its outer bend or compressing it along the inner bend. Increasing the bend angle beyond 90° increases stretching at one point and compression at another point on the flex circuit. Another key issue in rigid flex reliability is the thickness and type of conductor found in the bend region. You can decrease thickness and mechanical stress by reducing the amount of plating on the conductors and using pads only plating. The use of heavy copper, gold, or nickel plating decreases flexibility at the bend and allows mechanical stress and fracturing to occur. YOU MAY ASK: What is HDI PCB ? HDI PCB is defined as a PCB with a higher wiring density per unit area than conventional PCB. They have finer lines and spaces, smaller vias and capture pads and higher connection pad density than employed in conventional PCB technology. What is Metal Core PCB? MCPCB, Metal Core PCB, thermal PCB. Metal core pcb is abbreviated as MCPCB, it is made of thermal insulating layer, metal plate and metal copper foil, which has special magnetic conductivity, excellent heat dissipation, high mechanical strength and good processing performance. What is MCPCB? A Metal Core Printed Circuit Board (MCPCB) is a type of printed circuit board that contains a base metal material. The core is designed to redirect heat away from components which produce a substantial amount of heat. Helpful Resources