You may choose between stiff, flexible, and flex-rigid printed circuit boards.
Rigid boards are well-known for their joint appearance. Even though PCBs are now in huge demand, flexibility is the most recent innovation to hit the industry. Flex-rigid and flexible PCBs are a consequence.
A flex-rigid board combines stiff and flexible layers, while a flex board uses exclusively flexible materials. Flex PCBs, on the other hand, are ones that allow for complete customization. In the end, the decision is up to you and your application’s demands.
Using flexible and Rigid-Flex PCB has the following advantages:
- They may be used in a wide variety of settings.
- Reduced board weight and size may be achieved using high-density layouts, where components are crammed together in a small space.
- The smaller and thinner boards you create will lower the project’s total cost since they are less expensive than traditional PCBs.
- This board’s security is already superior to that of a standard PCB.
How to Manufacture a Flexible PCB?
In this section, we will see the main points of manufacturing a flexible board. Flex circuits have specific properties with rigid printed circuit boards; however, each panel’s manufacturing process is vastly different.
You have to focus on the following things:
- Capabilities and processes for handling thin materials
- Preparation of Specific Pads
- The Production of Polyimide Coverlay.
- Tolerances in Material Dimensions
- Laser Cutting of a Profile
- Electromagnetic smearing and etching
Capabilities and Procedures for Thin Material Handling
Flexible PCB fabrication relies heavily on material management to provide a high production yield and dependable completed circuits. Handling is responsible for most scrap and reliability concerns in the manufacturing process. Flex materials are substantially thinner and unreinforced than rigid board materials. Cover lays, and flex cores are generally 1.5–2 mils thick, with copper thicknesses of 12 oz. or 1 oz.
Processing Materials for Flex PCB Production
To transport flex materials securely and damage-free, a significant portion of the process equipment must be customized for this purpose. In addition, employees must be taught how to properly handle themselves while doing physical labor. Any kinks or folds in a manufacturing panel will result in discarded components or reliability difficulties in the completed circuits.
- Selective Pad Plating
An essential production method is how and where copper is plated on the pieces. A Pad Plate technique is required for Rigid-Flex PCB, which restricts the amount of plated copper to the region within the holes and a small circle around them.
There is no additional copper plating on any of the traces. When working with high-density designs, it may be necessary to plenaries the circular area of the surface to get an optimal pad and trace imaging results.
- Production of Polyimide Coverlays
Solid Polyimide sheets with adhesive backing are used in the same way as Soldermask on rigid boards as Coverlays. Still, they must be made using a separate manufacturing process since they are solid polyimide sheets.
Laser cutting, drilling/routing, CNC knife cutting, punch and die sets, or a combination thereof, must be used to manufacture all needed apertures to expose the SMT and PTH pads.
- Tolerances in Material Dimensions
Since flexibility is needed, flex materials are significantly thinner and do not need any additional support to maintain their shape (i.e., glass weave in rigid boards). This leads to substantially less dimensional stability in the materials, which has to be accounted for in the tooling/registration systems used in production. Flex materials will expand or contract when exposed to moisture, heat, and pressure.
It’s typical to employ smaller manufacturing panel sizes than rigid boards in order to reduce the influence of the material’s dimensional stability,
- Laser Cutting of Profiles
Lasers can readily cut polyimide materials. As a result, very detailed and intricate profiles may be generated. There is no need for expensive hard punch and die tooling at smaller manufacturing numbers, which saves money. It is possible to employ routing, but the intricacy of the profile will be limited, and the edge of the component will be ragged. A sufficient quantity of carbon residue will be left on the component edge after laser cutting, according to IPC requirements.
- Electromagnetic Smearing and Etching
Desmear and etch-back processes are crucial for dependable plated holes, and inner layer interconnects in multilayer flex systems.
Polyimide and flex adhesive, utilized to laminate layers together, have significantly different material qualities than the rigid board. On stiff boards, standard chemical-based etch-back techniques are simply too harsh. In the end, this leads to uneven outcomes, dependability concerns, and a limited and difficult-to-control process window. Plasma-based etch-back is the method of choice because of the excellent quality and consistency of the results it produces.
Important Manufacturing Tips
Now we will see important things that are involved in the manufacturing of a Rigid-Flex PCB
- Choosing the suitable material
High-quality materials are essential if you want your printed circuit board to work optimally. The following are some of the materials required to make flex PCBs:
In terms of substrates, polyimide is the most preferred choice. It’s a beautiful blend of good features and a reasonable price that makes it more appealing.
A polyether ether ketone acronym is PEEK. Based on PEEK, the content is not pure PEEK. We find this material used in sophisticated applications because of its high temperature and radiation resistance.
When it comes to Teflon-coated pans, polytetrafluoroethylene (PTFE) is short for polytetrafluoroethylene. It can withstand extreme temperatures and dissipate very little heat. Other materials necessary for the design of your boards, such as cladding and conducting, should be taken into account as well.
- Conventional Equipment: How do we choose flex-rigid PCB?
The performance and dependability of your flexible PCB will be significantly enhanced if it is assembled using high-tech machinery. The most outstanding design and materials are available to you. Unless you use current technology, your efforts will be for nothing.
Only the most excellent PCB firms make it a point to employ skilled workers and the most up-to-date technology. So, make sure to choose the right firm for your product and manufacture the correct type of board.
- Importance of Stack Management in Flex-Rigid PCBs
Stack management is one of the most critical aspects of flex PCB design. Your board’s faultless assembly and performance will be guaranteed if you specify your stack up appropriately. Putting it that way, it sounds like a breeze. On the other hand, an exact template is not a simple task.
Stackup management relies heavily on the expertise and an understanding of the proper design software. You can only learn to build trustworthy PCBs by hands-on experience and studying successful stacks.
Printed circuit boards need to distinguish between two forms of flexibility:
- Flexion in motion
The board must be folded and bent every time the product is utilized since it has standard flexibility.
- Install-anywhere PCB
As the name says, you simply need flexibility and bendiness throughout the installation procedure. Using the board’s elastic characteristics is no longer possible after being placed in its intended location.
A flex-to-install board is simpler to design if the two kinds of panels are compared because only the mechanical stress of the ground planes has to be taken into account while setting up the board.
A flexible PCB‘s signal and ground-plane integrity with dynamic bending must be satisfactory. Keeping the integrity of the message in mind while focusing on the substrate materials would be beneficial.
Bend Management on a Flexible-Rigid PCB
If you’re going to use flexible layers on your boards to transport ground planes and power, you shouldn’t only focus on trace routing. Those opting with a design that has to fold frequently will need to consider through-holes and surface-mounted pads, too.
Plated through-holes are nearly commonplace when building flex PCBs. For the pads, industry experts recommend securing them with additional overlay. It might enhance the board’s durability and sturdiness.
Vias and components should not be placed near bends on a flex-rigid PCB. The performance of neighboring vias and features may be impacted if the bows are repeatedly subjected to mechanical stress. The board’s dependability and durability may be compromised as a result.
PCB Trace Management Using Flex-Rigid PCBs
In the end, we will discuss how to layout your traces. Make sure you’re placing them perpendicularly to your curve. Because it reduces trace stress, this is especially important in flex-rigid PCBs. Consider offsetting the traces if your design is double-sided.
Stagger the traces at the bottom and the top of the circuit. You’ll be able to obtain more uniformity and resilience to constant bending and mechanical stress as a result. The strength and dependability of your boards will be improved.
The signal path’s impedance should be maintained at a consistent value throughout the length of the traces. Aim for a mark that is appropriate for your board’s flexible and stiff layers.
The design of any kind of PCB is the starting point for everything since it is there that assembly may be made more efficient. You have to look closely at all the steps involved in manufacturing flex-rigid or just flex PCB. Remember that developing a Rigid-Flex PCB is more complicated than a flex PCB. Your PCB will operate better if you use the proper materials, control the stackup, and more.