Last year, I was part of a team designing a compact smart projector for home use. We’d spent months refining the lens (for sharp 1080p images) and the motherboard (for streaming apps like Netflix). But when we tried to connect them, we hit a wall: the rigid PCB we initially used was too stiff to fit between the lens (which needed to tilt for focus) and the motherboard (tucked in the projector’s narrow base). Every time we adjusted the lens, the PCB bent—and the image cut out.
“We need FPCs,” our senior engineer, Mark, said, holding up a thin, flexible circuit. “Rigid PCBs can’t handle the lens’s movement. FPCs will bend with it, keeping the connection stable.” He was right: within a week of switching to FPCs, the lens adjusted smoothly, and the image stayed clear.
That experience taught me why FPCs are non-negotiable in smart projectors. Unlike TVs or monitors, projectors rely on movable lenses (for focus, zoom, or keystone correction) that need to stay connected to the motherboard—often across tight, curved spaces. Rigid PCBs can’t handle the movement or the fit; FPCs (Flexible Printed Circuits) solve both.
In this article, we’ll break down how FPCs enable flexible lens-motherboard connections in smart projectors, share stories from engineers who’ve fixed common issues, and outline the key design tips to make this connection reliable.
Before we dive into FPCs, let’s understand why rigid PCBs don’t work for projector lens connections. Smart projector lenses have two key needs that rigid PCBs can’t meet:
Nearly all smart projectors let users adjust the lens:
- Focus: Twist the lens to sharpen the image.
- Zoom: Slide the lens to make the image larger/smaller.
- Keystone Correction: Tilt the lens to fix distorted “trapezoid” images.
Each adjustment moves the lens—sometimes by 5–10mm, sometimes at an angle. A rigid PCB is fixed; it can’t bend or stretch with the lens. “We tried a rigid PCB for our projector’s keystone correction,” said Lisa, an engineer at a Chinese electronics firm. “Every time we tilted the lens, the PCB pulled at the motherboard connector. After 20 adjustments, the connector broke.”
Smart projectors are getting smaller—think “palm-sized” models for travel. This means the lens and motherboard are packed into narrow, curved spaces (e.g., around the projector’s battery or cooling fan). A rigid PCB is flat and thick; it can’t snake around these obstacles.
Raj, a designer at an Indian projector startup, faced this: “Our compact projector’s lens was 3cm from the motherboard—but there was a cooling fan in between. A rigid PCB couldn’t fit around the fan. We had to either make the projector bigger or switch to FPCs.” They chose FPCs.
FPCs aren’t just “flexible rigid PCBs”—they’re designed to handle the unique demands of projector lens connections. Here’s how they solve the two big issues:
FPCs are made of thin polyimide (PI) film, which bends and stretches without breaking. This lets them move with the lens, whether it’s twisting for focus or tilting for keystone correction.
Mark’s team used this to fix our projector’s focus issue:
- We chose a 0.1mm-thick FPC with a “stress relief loop” (a small U-shape) between the lens and motherboard.
- When the user twisted the lens for focus, the loop flattened slightly—absorbing the movement instead of pulling the connector.
- Result: The lens could be adjusted 100+ times without any signal loss.
“Rigid PCBs fight the lens’s movement,” Mark said. “FPCs work with it. That’s the difference.”
FPCs are as thin as 0.05mm (thinner than a sheet of paper) and can be routed around obstacles like fans, batteries, or speaker grilles. This keeps projectors compact while maintaining the lens-motherboard connection.
Raj’s startup used this for their palm-sized projector:
- They routed a 0.075mm-thick FPC around the cooling fan—snaking between the fan blades’ gap (which was only 0.5mm wide).
- The FPC was so thin, it didn’t block airflow or add bulk.
- Result: The projector stayed 8cm wide (the size of a smartphone) and the lens connected perfectly to the motherboard.
“We couldn’t have made the projector this small with a rigid PCB,” Raj said. “The FPC was the only way to fit the connection.”
Not all FPCs work for projectors—you need to design them for the lens’s specific movement and the projector’s space. Below are the four most important tips, tested in our projector and others.
Thickness determines flexibility and durability. For projectors:
- 0.05–0.1mm thick: Best for lenses with small movements (e.g., focus twists) and very tight spaces (palm-sized projectors).
- 0.1–0.125mm thick: Better for lenses with larger movements (e.g., zoom slides) or heavier components (like small sensors on the lens).
Our projector used 0.1mm FPCs: “Thinner FPCs would have been too fragile for frequent focus adjustments,” Mark said. “Thicker ones wouldn’t fit in the tight gap between the lens and motherboard.”
Stress relief loops (U-shaped bends in the FPC) absorb movement so the connector doesn’t get pulled. Here’s how to design them:
- Size: Make the loop 2–3x the FPC’s width (e.g., a 5mm-wide FPC needs a 10–15mm loop).
- Placement: Put the loop as close to the moving part (the lens) as possible—this minimizes pull on the motherboard connector.
Lisa’s team added loops to their projector’s keystone-correcting lens: “Before the loop, the connector failed after 20 adjustments. With the loop, it lasted 500+ adjustments—way more than a user would ever need.”
Projector lenses move, but other parts (like cooling fans or battery covers) are fixed. If the FPC is routed between moving and fixed parts, it can get pinched—breaking the circuit.
Our team learned this the hard way: we initially routed the FPC between the lens and a fixed plastic bracket. Every time the lens tilted, the bracket pinched the FPC, causing image glitches. We re-routed the FPC around the bracket (using a small notch in the plastic) and the problem stopped.
“Route the FPC where there’s no pressure,” Mark said. “If two parts move past each other, the FPC shouldn’t be in between.”
Projector lenses send high-resolution image data to the motherboard (e.g., 1080p or 4K signals). The FPC’s copper traces need to handle this speed without signal loss.
- Use 2oz copper traces (thicker than standard 1oz) for better signal transmission.
- Keep trace lengths short (under 15cm) to avoid delays.
- Add ground planes (extra copper layers) to reduce interference from the projector’s power supply.
Raj’s startup used this for their 4K projector: “We initially used 1oz traces, and the image had pixel glitches. Switching to 2oz traces with a ground plane fixed it—now the 4K image is crystal clear.”
Let’s look at how Lisa’s team fixed a common projector problem with FPCs. Their company made a portable projector where the image cut out every time the user adjusted the zoom. Here’s what happened:
- The projector used a rigid PCB to connect the zoom lens to the motherboard.
- When the user slid the lens to zoom, the rigid PCB pulled the motherboard connector loose.
- The image cut out 30% of the time during zoom adjustments.
- Switch to FPC: They chose a 0.125mm-thick FPC with a 15mm stress relief loop near the lens.
- Re-Route the FPC: They moved the FPC away from the zoom lens’s sliding track to avoid pinching.
- Upgrade Traces: They used 2oz copper traces with a ground plane to prevent signal loss.
- Image cutouts dropped from 30% to 0%.
- Users could adjust the zoom 1,000+ times without issues.
- The projector’s size stayed the same—no need to make it bigger.
“The FPC turned a frustrating product into a bestseller,” Lisa said. “Users loved being able to zoom without the image cutting out.”
Smart projectors rely on movable lenses to deliver sharp, adjustable images—and those lenses need a flexible connection to the motherboard. Rigid PCBs can’t handle the movement or the tight spaces; FPCs do both, while keeping image quality high.
The key design tips are simple: choose the right thickness, add stress relief loops, route to avoid pinching, and use high-speed traces. These small choices make a big difference in how well the projector works for users.
As projectors get smaller and more powerful (think 4K portable models), FPCs will become even more important. They’re not just a “part”—they’re the reason users can adjust the lens and still get a clear image.
Next time you use a smart projector and twist the lens to focus, remember: there’s probably an FPC working behind the scenes, keeping that connection stable. And that’s the magic of FPCs in projectors—they make the impossible fit (and move) possible.
Founded in 2009, our company has deep roots in the production of various circuit boards. We are dedicated to laying a solid electronic foundation and providing key support for the development of diverse industries.
Whether you are engaged in electronic manufacturing, smart device R&D, or any other field with circuit board needs, feel free to reach out to us via email at sales06@kbefpc.com. We look forward to addressing your inquiries, customizing solutions, and sincerely invite partners from all sectors to consult and collaborate, exploring new possibilities in the industry together.
English
Wechat
+86 13670210335
+86 13670210335
E-mail