Introduction
This article explains the role of advanced Via technologies for rigid flex PCB. In rigid-flex printed circuit boards, via holes act as a crucial component of high-density interconnect (HDI). The compactness of electronic devices is increasing with time. As the size of electronic devices is shrinking, the importance of via structures is expanding to ensure proper functionality.
What Is Via In Rigid Flex PCBs?
Vias in rigid flex circuits are small holes that are meant to connect different layers of a board. They usually are 0.010 inches (254 microns) or less in size. For your convenience, here’s the standard via size chart that can help you get optimal performance from printed circuit boards.
Vias play a key role in passing signals between rigid and flexible sections. These holes help in maintaining the connectivity of complex designs. Those where the space is much limited.
Additionally, via holes in rigid flex boards make reliable electrical paths across multiple layers. In their absence, routing signals will become difficult both in rigid and flexible areas.
Why Are They So Complex?
Via holes in rigid-flex circuit boards are complex because they have to connect both rigid and flexible parts. Designers face challenges such as:
- Tight spaces
- Bending stresses
- High-density layouts
Also, the board bends, which can stress the vias. On top of that, designers work with very small spaces and crowded layouts. They need special via designs to keep signals strong and reliable.
Types of Vias in Rigid Flex PCB
There are different types of vias, and each has a specific use:
- Blind Vias: These holes are meant to connect outer layers to inner layers. They don’t go all the way through the board.
- Buried Vias: This one remains completely inside the board. Also, they are invisible from the outside.
- Filled Vias: These via holes are filled with epoxy material. They are plated flat to make a smooth surface for soldering.
- Vias in Flex: Usually, blind vias which are placed in flexible parts of the board.
Blind Vias
Blind vias are used for connecting an outer layer to one or more inner layers. Connectivity goes on without passing through the full board. Designers use them to save space and support complex layouts during rigid flex PCB assembly. As a result, signals route better around tight BGA areas. Plus, they help improve overall signal flow.
However, blind vias bring challenges in rigid-flex designs. For example, manufacturers limit the aspect ratio, which links via depth to hole size. That is why it is necessary to check limits with the manufacturer early. Also, blind vias should start and end only in rigid layers. This approach avoids stress in flexible areas and improves long-term reliability.
Buried Vias
Unlike blind vias, buried vias remain completely inside the board. They are used for connecting internal layers only. These via holes also help to free up space on the outer layers. Also, they support high-density routing. In a rigid-flex PCB, buried vias can improve power plane layout and signal integrity across the board.
However, they add complexity to the stack-up. For instance, manufacturers allow only certain aspect ratios, which vary by process. So, designers must plan carefully and confirm limits early. Also, buried vias should stay within rigid sections and avoid flex areas. Too many buried via layers can also complicate manufacturing. Therefore, smart planning keeps the design reliable and manufacturable.
Filled Vias
The next type is the filled vias. These are especially used for circuits having many small components. Firstly, these are filled with epoxy resin. Secondly, they are plated to create a flat and smooth surface, which helps in efficient soldering. Because of this, designers often place components directly on top of them. This approach helps save space, which matters a lot in small and compact designs.
Filled vias also stop solder from flowing into holes during assembly. In addition, they help spread heat and make component placement cleaner and easier. However, designers usually use filled vias only in rigid areas. High heat and pressure are used while filling and plating them. These conditions can damage flexible materials and cause them to bend or warp.
Most manufacturers support non-conductive-filled vias. This is because they cost less and work well in most designs. Conductive fills also exist. But they do add extra cost and give little benefit. So, designers should always check with their manufacturer first.
Vias in Flex Sections
Vias in flex sections require extra care and planning. Designers use them only in special cases because flex areas bend and move. Most of these vias are blind vias and support specific needs. For example, they help create EMI shielding and add extra grounding paths. Moreover, they connect layers in multi-layer flex designs.
However, vias in flex areas can fail easily. When the board bends near a via, the copper can crack or break. Over time, this damage can cause signal loss or random failures. Because of this risk, design standards advise designers to avoid vias in bending areas.
When vias in flex sections are necessary, designers place them in areas that stay flat. They also add stiffeners or protective materials for support. In addition, designers use these vias as backup paths, not main connections.
How to Design Via for a Rigid Flex PCB?
To get maximum benefit from the via holes in rigid flex circuit boards, follow the practices as suggested in design-for-manufacturing (DFM). First, work with your PCB manufacturer and confirm:
- Via size
- Filling type
- Board design limits
Additionally, you have to avoid placing vias in bending areas of the flex part. Try to keep them in flat and supported zones for better strength. Also, use filled vias only when necessary, as they can increase costs and delay production.
Moreover, do not add too many vias since they can make the board thick and hard to build. Finally, avoid placing vias between rigid and flex parts to prevent drilling problems.
MV Flex Circuit: Your Expert in Flexible & Rigid-Flex PCB Manufacturing
As a professional manufacturer of flexible PCBs and rigid-flex PCBs with over 20 years of production experience, we have extensive project experience in high-demand industries such as wearable devices, foldable smartphones, medical equipment, and aerospace systems.
Our manufacturing capabilities are tailored to tackle complex designs:
- Flexible PCB fabrication: Up to 8 layers
- Rigid-flex PCB fabrication: Up to 20 layers
- Advanced Processes Through Technical Expertise: We specialize in blind vias, buried vias, filled vias, and custom via designs. Meeting your high-density, space-constrained layout requirements.
We strictly adhere to IPC Class 2/3 standards and hold authoritative certifications including ISO, UL, REACH, and RoHS, ensuring our products fully comply with global market access requirements.
Every board undergoes strict quality control through 100% E-test, AOI, X-ray, ICT, flying probe testing, and custom fixture testing to eliminate defects and guarantee reliable performance.
Looking for a reliable flex and flex- rigid PCB supplier? Send your Gerber files to sales@flexiblepcbboard.com. Our engineering team will provide a free DFM check to assess the manufacturability of your via structures and provide you a quote within 24 hours.
Conclusion
Vias are very important in rigid flex PCBs. When you choose the right via type and plan the design carefully, your board works better and lasts longer. Always talk to your PCB manufacturer during the design process. Doing this will help you avoid mistakes and build a board that performs well.
Things You Need to Know
- Blind and buried vias: Use them for high-density designs. Always follow aspect ratio and stack-up limits.
- Filled vias: Keep them in rigid areas only, as flex parts cannot handle the filling process.
- Vias in flex sections: Avoid them in bending areas. Place them only in flat zones as recommended in IPC-2223.
