Last year, my team struggled to build a postage-stamp-sized glucose monitor. We needed a battery, sensor, microcontroller, and wireless chip—but rigid PCBs and bulky SMD parts wasted too much space. “We either make it bigger or find a better way,” our engineer Leo said.
Then we tried rigid-flex PCBs + COB (Chip-on-Board) packaging. Rigid-flex bent around components to cut wire use; COB mounted chips directly on the PCB (no plastic casings). Six weeks later, we had a working prototype—all parts fit, and it performed better than expected.
This taught us: for tiny devices (wearables, medical sensors), traditional tech fails. Rigid-flex + COB isn’t just space-saving—it’s the key to better integration. Below’s how it works.
Tiny devices need more function in less space—but old-school designs can’t deliver:
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Rigid PCBs Waste Space: They’re flat, need wires/connectors, and force bulky stacking. Leo’s first design used 3 rigid PCBs—wires took 25% of space.
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SMD Packaging Is Bulky: SMD chips have plastic casings 3x bigger than the chip itself. Raj, a wearable engineer, said: “Our tracker’s SMD chip was 1.2mm thick—too thick for our 3mm device.”
Together, these two techs fix old problems—here’s how:
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No Wires: Flexible PI sections link rigid FR4 parts (for sensors/batteries), cutting space by 20–30%.
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3D Mounting: Fold rigid sections (e.g., sensor on top, battery below) to use vertical space.
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Thin: PI sections are 0.1mm thick—thinner than multiple rigid boards.
Our Win: We replaced 3 rigid PCBs with one rigid-flex. It bent to fit the battery, freeing 30% space.
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Smaller: COB chips take 50–70% less space than SMD (e.g., 2mm×2mm vs. 4mm×4mm).
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Thinner: 0.3–0.5mm thick (vs. 1–1.5mm for SMD).
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Better Heat Flow: Chips connect directly to PCB—critical for tiny devices with no fans.
Our Win: COB shrank our microcontroller/wireless chip footprint. We even added a signal amp.
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Fewer connections (no wires/SMD joints) = fewer failures.
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3D stacking (rigid-flex) + small chips (COB) = more function in less space.
Raj’s team used this for a fitness tracker: “We went from 5mm thick (4 parts) to 3mm thick (6 parts). Users actually wear it now.”
A medical firm had a 20mm×15mm, 4mm-thick heart rate sensor—patients hated it. Here’s their fix:
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2 rigid PCBs + wires = 60% space use.
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SMD parts added 1.5mm thickness.
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8% failure rate (wire issues).
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Rigid-Flex: One board with top rigid section (LED sensor) + flexible bend to bottom (battery).
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COB: Switched microcontroller/processor to COB (3mm² vs. 8mm²).
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Flexible Epoxy: Covered COB chips to handle bending.
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Size: 15mm×10mm (33% smaller).
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Thickness: 2.5mm (37% thinner).
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Failures: 0.5% (down from 8%).
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90% of patients called it “comfortable.”
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Design for COB First: COB needs bigger PCB pads—plan rigid sections around chips.
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Choose the Right Epoxy: Flexible for wearables, medical-grade for skin contact.
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Test Bending/Durability: Simulate 1,000+ bends to ensure COB epoxy doesn’t crack.
Rigid-flex + COB lets you have small size AND function—traditional tech can’t do that. As devices get smaller (implantable sensors, tiny IoT trackers), this combo becomes essential.
Next time you think “we can’t fit everything,” try rigid-flex + COB. It worked for our glucose monitor, Raj’s tracker, and that heart rate sensor—and it’ll work for you.
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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.
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