As the demand for smaller, more powerful electronics continues to grow, the importance of flexible circuit boards has never been greater.
Modern electronic devices increasingly rely on these types of PCBs, which provide an unparalleled blend of resilience and adaptability that conventional circuit boards cannot rival.
For designers seeking to create sophisticated electronics that are robust, efficient, and adaptable, a grasp of the Rigid-Flex PCB manufacturing process is imperative.
In this guide, we will explore the 13 essential steps involved in producing high-quality Rigid-Flex PCBs, from initial design and material selection to fabrication and assembly.
Rigid-Flex PCB Introduction
By combining flexible circuitry with rigid sections, these types of PCBs offer a durable and versatile solution that is well-suited for today’s electronic devices.
In contrast to conventional circuit boards, these kinds of PCBs provide a host of benefits such as enhanced dependability, decreased weight and size, and simplified assembly.
A thorough comprehension of the exceptional attributes and manufacturing procedure of the Rigid-Flex PCB manufacturing process is crucial to design high-functioning electronics that fulfill the requisites of contemporary industries.
Rigid-Flex PCB
Material Used in Rigid-Flex PCB Manufacturing Process
These advanced circuit boards require a combination of flexible and rigid materials to achieve the desired properties, such as bendability, strength, and resistance to wear and tear.
Here are common materials used in its manufacturing process:
Substrate Materials
The substrate material provides the base for the circuit traces and components, and it also affects the mechanical properties of the board.
When selecting a substrate material used in the Rigid-Flex PCB manufacturing process, it is important to consider the specific application requirements and the environmental conditions that the PCB will be exposed to.
The right choice of substrate material can help ensure that the PCB performs reliably and has a long lifespan.
Polyimide
This material is renowned for its exceptional thermal and mechanical characteristics, which comprise elevated temperature endurance, superior dimensional steadiness, and more.
Polyimide substrates are often used in applications that require high reliability, such as aerospace and defense electronics, medical devices, and automotive systems.
Polyester
Polyester, on the other hand, is a lower-cost material that offers good flexibility and resistance to moisture and chemicals.
It is often used in consumer electronics and other applications where cost is a primary concern, and the circuit design does not require high-temperature resistance or extreme mechanical stress.
Substrate Material
Conductor Material
Apart from the substrate material, the conductor material is employed in fabricating these kinds of PCBs. This is also crucial in determining the flex circuit’s dependability and effectiveness.
The conductor material is used to create the conductive paths and connections between the different components of the PCB, and it must be carefully selected to meet the specific requirements of the application.
The right choice of conductor material can help ensure that the PCB performs reliably and has a long lifespan while minimizing costs and optimizing performance.
Conductor Material
Adhesives
To merge the rigid and flexible components and generate a single, working unit, adhesives play a crucial role in constructing these kinds of PCBs.
The choice of adhesive material is an important consideration in the design of Rigid-Flex PCBs, as it affects the mechanical, electrical, and thermal performance of the circuit.
Polyimide Adhesives
Polyimide adhesives are based on a high-performance polymer that offers excellent thermal and chemical resistance.
They are commonly used in applications that require high-temperature resistance, such as aerospace and defense electronics, and in flexible circuits where high flexibility is required.
Polyester Adhesives
Polyester adhesives are based on a lower-cost polymer that offers good flexibility and resistance to moisture and chemicals.
They are commonly used in consumer electronics and other applications where cost is a primary concern, and the circuit design does not require high-temperature resistance or extreme mechanical stress.
Acrylic Adhesives
Acrylic adhesives are based on a polymer that offers good adhesion to a wide range of surfaces, fast curing time, and good peel and shear strength.
They are commonly used in applications that require fast assembly and processing, such as automotive and consumer electronics.
Epoxies
Epoxies are two-part adhesives that offer high bond strength, excellent chemical resistance, and good electrical insulation properties.
They are commonly used in applications that require high reliability and durability, such as aerospace and defense electronics, and in high-performance consumer electronics.
Adhesives
Protective Coatings
Protective coatings help to protect the circuit from environmental factors such as moisture, dust, and heat.
The choice of protective coating material is an important consideration in the design of Rigid-Flex PCBs, as it affects the mechanical, electrical, and thermal performance of the circuit.
Coverlays
A kind of protective film that on top of the flexible circuit regions of these kinds of PCBs. They are typically made of polyimide or polyester film and are bonded to the flexible circuit areas using a pressure-sensitive adhesive.
Covercoats
Another type of protective film is used to protect the rigid areas of Rigid-Flex PCBs. They are typically made of acrylic, epoxy, or silicone material, and are applied to the surface of the PCB using a spray or dip-coating process.
Protective Coatings
Types of Rigid Flexible PCBs
Numerous varieties of these kinds of PCBs exist, each possessing distinct qualities and benefits tailored to specific applications.
Rigid-Flexible Composite PCB
These types of PCBs are composed of multiple layers of rigid and flexible materials that are bonded together through lamination, resulting in a single connected circuit.
The rigid layers provide support and stability for the circuit, while the flexible layers allow for bending and flexibility.
This type of Rigid-Flexible PCB is often used in applications that require complex shapes and sizes, as well as high-density circuitry.
Rigid-Flexible PCB
Similar to the Rigid-Flexible Composite PCB, but is typically made up of fewer layers and is more flexible overall.
This type of Rigid-Flexible PCB is often used in applications that require both flexibility and durability, such as wearable technology or medical devices.
13 Steps in Demystifying the Rigid-Flex PCB Manufacturing Process
The Rigid-Flex PCB manufacturing process involves several steps, each of which is critical to the final product. Here are the 13 steps of the manufacturing process:
Step 1: Base Material Preparation
The first step in the Rigid-Flex PCB manufacturing process is to prepare the base materials.
This involves selecting and preparing the rigid substrate and flexible material that will make up the Rigid-Flex PCB.
The rigid substrate is typically made of a fiberglass-reinforced material such as FR4, while the flexible material is made of a polyimide or polyester film.
Step 2: Circuit Pattern Process
The circuit pattern process is a crucial step in the rigid-flex PCB manufacturing process, where computer-aided design (CAD) software is employed to create the circuit layout with meticulous precision and specifications.
The CAD file is then exported to a photoplotter, which uses lasers to produce a photomask that will be used in the photolithography process.
This step lays the foundation for the subsequent stages of the production process and is critical in ensuring the functionality and reliability of the final product.
Circuit Pattern Process
Step 3: Screen Printing
After the circuit pattern has been generated, the next step is to apply the conductive material to the base material.
This is done through a process called screen printing, which involves using a stencil or screen to apply the conductive ink in the desired pattern.
The screen is made of a mesh material that is stretched over a frame, with the pattern cut out of the mesh.
The screen is positioned over the base material, and the ink is forced through the mesh and onto the surface of the material using a squeegee or other tool.
The ink is then cured using heat or UV light to create a solid, conductive layer.
Screen Printing
Step 4: Photo Imaging
This is after the conductive ink has been applied to the base material through screen printing.
This is done through a process called photo imaging, which selectively removes the conductive ink from the surface of the material.
The base material is coated with a layer of photoresist material, which is sensitive to UV light. The photomask is aligned over the material, and the surface is exposed to UV light.
The areas of the photoresist material that are exposed to the light become chemically hardened, while the areas that are not exposed remain soft and can be dissolved in a developing solution.
Step 5: Adhesive/Seed Coating Application
The adhesive or seed coating is applied using a process called spray coating, which involves spraying a fine mist of the coating material onto the surface of the material.
The coating material is carefully formulated to ensure that it adheres to the surface of the material and provides a good base for the electroplating process.
Step 6: Addition of Copper Foil
Once the circuit pattern has been created through photo imaging, the next step in the rigid-flex PCB manufacturing process is to add a layer of copper foil to the surface of the material.
The copper foil serves as the conductive material that will carry the electrical signals through the finished Rigid-Flex PCB manufacturing process.
The copper foil is placed over the surface of the material, and a layer of adhesive material is applied between the copper foil and the material to bond them together.
Step 7: Drilling
After the addition of the copper foil layer, the next step in the rigid-flex PCB manufacturing process is to drill holes in the Rigid-Flex PCB.
These holes will be used to mount electronic components and connect different layers of the circuit.
The drilling process is performed using a computer-controlled drilling machine. The machine is programmed with the specific locations and sizes of the holes needed for the Rigid-Flex PCB.
Drilling
Step 8: THT Plating
After the holes have been drilled and plated, the next step in the rigid-flex PCB manufacturing process is to add a layer of conductive material to the surface of the Rigid-Flex PCB using through-hole technology (THT).
THT is a process that involves inserting electronic components through the drilled holes and soldering them onto the surface of the Rigid-Flex PCB.
THT Plating
Step 9: Etch-Resist Printing
After the THT plating step, the next step in the rigid-flex PCB manufacturing process is to apply a layer of etch-resistant ink onto the surface of the Rigid-Flex PCB.
The etch-resistant ink is applied to the surface of the Rigid-Flex PCB in the areas where the circuit traces and pads should remain after the etching process.
The ink is designed to resist the etching solution, which will be applied in the next step, and protect the copper traces and pads from being etched away.
Step 10: Etching and Stripping
After the etch-resist ink has been applied to the surface of the Rigid-Flex PCB in Step 9, the next step in the rigid-flex PCB manufacturing process is to remove the excess copper from the surface of the PCB using an etching solution.
The etching solution is typically a mixture of acid and other chemicals that dissolve the exposed copper, leaving behind only the copper traces and pads protected by the etch-resist ink.
Etching and Stripping
Step 11: Coverlay Application
Once the etching and stripping process is complete, the next step in Rigid-Flex PCB manufacturing process is the application of a coverlay.
A coverlay is a thin layer of insulating material that is applied over the copper traces and pads on the surface of the Rigid-Flex PCB to protect them from damage and to provide electrical insulation between the different layers of the PCB.
The coverlay is typically made from a flexible polymer material such as polyimide or polyester and is applied using a lamination process.
The coverlay material is first coated with an adhesive and then placed on top of the Rigid-Flex PCB, covering the copper traces and pads.
The PCB is then placed in a laminator, where heat and pressure are applied to bond the coverlay to the surface of the PCB.
Coverlay Application
Step 12: Cutting Out the Flex
The cutting process is typically carried out using a laser cutter, which allows for precise and accurate cuts in the rigid-flex PCB manufacturing process.
The laser cutter is programmed to follow the desired cut pattern and carefully cuts through the coverlay and PCB layers without damaging any of the copper traces or pads.
Cutting Out the Flex
Step 13: Electrical Testing and Verification
The final step in the rigid-flex PCB manufacturing process is to inspect the Rigid-Flex PCB for defects and ensure that it meets all required specifications.
This is typically done using automated optical inspection equipment, which can detect defects that might be missed by human inspectors.
Electrical Testing and Verification
Rigid-Flex PCB Manufacturing Standards
This is a set of standards that govern the rigid-flex PCB manufacturing process. This standard defines the requirements for the design, materials, and manufacturing processes used in the production of rigid-flex PCBs.
It includes specifications for base materials, conductor and adhesive materials, coverlay and covercoat materials, and plating and finishing processes.
Compliance with IPC 6013 Type 4 ensures that the rigid-flex PCBs meet the industry standards for reliability, functionality, and durability.
It provides a common set of guidelines and specifications that manufacturers can use to ensure that their products are of high quality and meet customer expectations.
Adhering to these standards can also help to reduce manufacturing costs by minimizing errors, improving yields, and increasing process efficiency.
Final Words
In conclusion, the rigid-flex PCB manufacturing process is a complex and multi-step process that involves various materials, techniques, and equipment.
From base material preparation to final testing and inspection, each step in the process is critical to ensuring that the final product meets the desired specifications and quality standards.
