Tag: rigid-flex pcb

Categories
PCB Blog

Complete Guide on Flex PCB Stiffener

Printed circuit board stiffeners provide important mechanical support for PCBs and are often used for flexible circuit boards.

When flexible circuit board components are placed in curved areas and pressure is applied to the flexible material, stiffeners are required to add mechanical strength.

But we need to understand that the PCB stiffener is not part of the board design. Let’s learn more about the role of stiffener and its use.

Where to use stiffener?

Simply put, when the PCB needs to increase the stiffness of the place will need to use stiffener.

  • Support areas with SMT or PTH components
  • To maintain the proper thickness of the flexible circuit
  • Connector areas
  • Areas to keep the circuit stable
  • When limiting flexible parts to a certain position
  • Increasing the bending radius of the circuit at the intersection of rigid and flexible parts
  • Protects solder joints
  • Comply with ZIF connector specifications

How to choose the right PCB stiffener material?

Flexible PCB currently commonly used stiffener materials are polyimide (PI), FR4 and steel sheet.

  1. Polyimide (PI), composed of PI, cover film and adhesive release paper, but the PI layer is thicker.
  2. FR4, mainly composed of glass fiber cloth and epoxy resin adhesive, the same as the FR4 material used in PCB
  3. Steel sheet. The components are steel, with strong hardness and support strength, requires manual assembly, and the process is more complex assembly costs are higher.

How to use printed circuit board stiffener?

In the case of plated through-hole components, the PCB stiffener is located on the same side of the flexible board as the components. This makes it easier to access the pads on the flex circuit. Stiffeners can also be attached to both sides of the part.

Heat and pressure are used when attaching the stiffener to the circuit. Connecting PCB stiffeners requires the use of pressure-sensitive adhesives, commonly used are

  • Pressure sensitive adhesives
  • Thermal bonding adhesives

The type of adhesive depends on the location and/or construction of the stiffener. For example, if the stiffener does not extend to the circuit outline, in most cases it will require a PSA attachment with additional stiffener outline added to the screen for precise placement.

How to distinguish between rigid-flexible PCBs and rigid PCBs using FR4 stiffener?

  1. A circuit board with stiffener is still essentially a flexible PCB, with FR4 stiffener bonded to it to increase rigidity during assembly
  2. Rigid-flexible circuits are known as hybrid flex circuits that include both rigid and flexible substrates, and by definition, rigid-flexible boards are not flex circuits.
  3. The use of stiffener of the flexible PCB stiffener part is no trace, only to enhance the rigidity of the location, they are only mechanical connection between. While the rigid-flexible PCB are designed traces for electrical connections.

To summarize

Use PCB stiffener to protect the components and connectors of flexible circuit swell, to ensure that the circuit does not bend and protect the integrity of the solder joints.

Explore KingPCB’s services

KingPCB, one of the leading PCB manufacturers in China, has extensive experience in manufacturing and assembling rigid PCBs, flexible PCBs and rigid-flex PCBs.

For more information about our PCB supply capabilities, please feel free to email us at sales@kingpcb.com or contact us now!

Categories
PCB Blog

Manufacturing Process for Rigid-flex PCBs

With flexibility and the ability to assemble in 3D, the demand for rigid-flexible PCBs is on the rise. We can say that the importance of rigid-flexible PCBs in PCB manufacturing can not be overemphasized

What is Rigid-flex PCBs?

Rigid-flex PCBs connect rigid PCB materials to flexible materials.

The result is bending only in certain places, making the board more rigid but still flexible.

If you want signals to be transmitted between the rigid and flexible sections, you will need to design a rigid-flex PCB.

In a rigid-flex design, the flexible part of the board resembles a typical flex circuit. At the same time, the material of the rigid part is similar to that of a standard rigid PCB. Like standard PCBs, these rigid areas are usually made of glass fiber as the base material.

Multilayer rigid-flex PCBs also include prepreg glass fibers as an intermediate substrate layer.

However, not all PCB manufacturers can meet the complex flexible printed circuit board manufacturing process. The following are some of the characteristics of rigid-flexible PCBs.

Features of rigid-flex PCBs

  1. Flexibility
  2. Lightweight
  3. Cost effective
  4. Save design and assembly process time
  5. Low noise and high reliability
  6. Resistant to high and low temperatures and fire
  7. Prevent electrostatic interference

Rigid-flex PCB manufacturing procedures

– Material cutting

– Dry film coating

– Automatic optical inspection

– Browning

– Lamination

– X-Ray Inspection

– Drilling

– Electroplating

– Graphic Conversion

– Etching

– Screen Printing

– Exposure and Development

– Surface Finishing

– Depth Control Milling

– Electrical Testing

– Quality Control

– Packing

Rigid-flex PCB design rules considerations

Rigid-flexible boards are much more complex in design than standard PCB design. In particular, we should pay attention to the special places, including the transition area of rigid-flexible, alignment design, over-hole design, etc. All of these items need to follow the requirements of the corresponding design rules.

Over the hole location.

In the dynamic use of the case, especially when the soft board is often bent. It is necessary to avoid as far as possible the soft board over-hole, which is prone to breakage and damage.

The design of the solder pads and vias.

Solder pads and vias in line with the electrical requirements, win the maximum, the connection between the pad and the conductor using a smooth transition line, avoid right angles. Independent pads should be added disk toe to strengthen the support role.

Alignment design.

In the flex zone (Flex) alignment design requirements are best to go rounded lines, rather than angled lines. The opposite of the hard board (Rigid) area recommendations. This can protect the flexible board part of the line in the bending is not easy to break. 4.

Lay copper design.

For enhancing the flexibility of flexible bending of flexible board, laying copper or flat layer is best to use the mesh structure.

The distance between the drill hole and the copper skin.

For the rigid-flexible combination area, the two most important distances must not be ignored. One is the hole to copper distance (Drill to Copper) described here, following the minimum standard of 10 mil. The other is the previously mentioned hole to the edge of the flexible board distance (Hole to Flex), generally recommended 50mil. 6.

The design of the rigid-flexible area.

The line should be a gentle transition, the direction of the line should be perpendicular to the direction of the bend. Wires should be evenly distributed throughout the bending area.

Applications of rigid-flex PCB

Industrial use: industrial, military, medical

Automotive: automotive components, in-car video systems, audio systems, radar imaging systems, satellite navigation, temperature sensors, etc.

Consumer electronics: folding cell phones, video modules, keypads, RF templates, etc.

Explore KingPCB’s Services

KingPCB’s customer support team can help you find the best material and structure for your flexible or rigid-flex PCB. Visit our contact page to send us a message online.