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QUICK ANSWER  Chip-on-board mounts a bare die directly onto a PCB, connects it by wire bonding or flip-chip, and protects it with encapsulation. COB can reduce height and interconnect length, but success depends on pad finish, die attach, moisture control, thermal design, and inspection.

Key Takeaways

• This approach saves space by removing the IC package but moves packaging risks onto PCB assembly.

• Align die attach, pad finish, wire clearance, encapsulant, thermal paths, and test access.

• Quote with die data, a bond diagram, materials, inspection criteria, and tests.

Introduction

A compact PCB can fail for reasons absent from the schematic. In chip-on-board assembly, finish, cleanliness, flatness, heat flow, and moisture protection directly affect reliability.

This guide covers COB structure, manufacturing, design choices, supplier inputs, and production checks.

What Is Chip on Board

Chip on board attaches a bare semiconductor die directly to a PCB. Fine bond wires usually form the connections, although flip-chip bumps can connect the die face-down; encapsulation protects the assembly.

Unlike a packaged IC, chip-on-board eliminates the molded body and external leads. The PCB and assembly process must therefore provide support, electrical fan-out, environmental protection, and heat removal.

COB Overview

COB is a board-level packaging system, not a substitute footprint. Fix these decisions before layout release.

Chip on Board Manufacturing Process

The chip-on-board manufacturing process combines a known-good die, prepared PCB, and controlled materials in this flow:

• 1. Review the die data. Confirm dimensions, pad map, orientation, temperature limit, storage, and ESD controls.

• 2. Prepare the PCB. Clean or bake as required, verify pad finish and coplanarity, and keep solder mask and contamination outside the bonding zone.

• 3. Attach the die. Place the adhesive and die, control bond-line thickness, cure correctly, and inspect for shift, tilt, squeeze-out, and voids.

• 4. Form interconnects. Wire-bond die pads to PCB bond fingers, or place a bumped die by flip chip. Check position and loop clearance.

• 5. Encapsulate and cure. Apply glob top, dam-and-fill, or molding without disturbing wires. Control flow, bubbles, shrinkage, and coverage.

• 6. Inspect and test. Use visual and functional tests; add bond pull or shear, X-ray or acoustic inspection, thermal cycling, and moisture tests when risk requires them.

Core Advantages of COB

COB is strongest when size, signal path, optical output, or thermal integration outweigh easy component replacement.

• Smaller form factor: Removing the package body allows a thinner assembly and tighter die placement.

• Shorter interconnects: Direct connections can reduce parasitic resistance and inductance compared with long package leads.

• Flexible integration: Bare dies, sensors, passives, and emitters can share one custom substrate.

• Designed heat flow: Stack-up, copper, thermal vias, and base material can match die power density.

Poor pad finish, long wires, mismatched encapsulant, moisture, or weak thermal spreading can erase these gains.

PCBgogo Focuses on COB Technology

A reliable COB project starts with joint review of the PCB and build package. PCBgogo supports prototype and production PCB fabrication and assembly, including rigid, flex, rigid-flex, metal-core, HDI, fine-line, controlled-impedance, sourcing, inspection, and testing needs.

For a chip-on-board quote, provide Gerber or ODB++ data, stack-up, die drawing, bond-pad map, orientation, attach and encapsulant specifications, wire material, inspection limits, test method, and volume. State the bondable finish, keep-outs, handling limits, and moisture-sensitive steps; an SMT BOM does not define them.

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Chip on Board Applications

Chip on board is useful where direct die integration creates a measurable advantage.

• LED and display modules: Dense emitters can share a compact thermal and electrical platform for COB LED, OLED driver boards, and MicroLED modules.

• Sensors and optoelectronics: Photodiodes, imaging dies, and optical sensors benefit from low profiles and precise alignment.

• Compact electronics: Wearables, toys, calculators, and controllers use COB when area and cost are constrained.

• Industrial and medical modules: Custom modules combine dies with short interconnects, but qualification must match the end-use environment.

• RF and high-speed circuits: Short paths can reduce parasitics when return paths, impedance transitions, and encapsulant are modeled together.

Conclusion

Chip on board works when the die, interconnect, PCB, protection, thermal path, and test plan are engineered as one system. Complete manufacturing data and early DFM review prevent avoidable yield and reliability problems.

Frequently Asked Questions

Is COB the same as a packaged IC mounted on a PCB?

No. COB places a bare die directly on the PCB, while a packaged IC is first enclosed in a separate package and then soldered to the board.

Which PCB surface finish suits chip-on-board wire bonding?

Select the finish for the wire and bonding process, not by copying an SMT design. Confirm bondable metallization, thickness, cleanliness, storage life, and supplier process.

Can a COB assembly be reworked?

Limited rework may be possible before encapsulation, but removing an encapsulated die or damaged bond wires is usually difficult and may harm the PCB. Plan test points and screen the die and board before final encapsulation.

What files should I send for a COB quote?

Send PCB data, stack-up, BOM, assembly and die drawings, bond diagram, coordinates, materials, inspection limits, test method, and volume. State who supplies the die and whether it arrives as a wafer, waffle pack, or tape.