A Chip-on-Board (COB) package is a method of circuit board manufacturing in which integrated circuits (ICs), such as microprocessors, are directly attached (wired or bonded) to a printed circuit board (PCB) and covered by a blob of epoxy. Here are the key points about COB:
1. Advantages of COB:
- Cost-Efficiency: COB eliminates the need for individual semiconductor device packaging, resulting in a completed product that is less costly, lighter, and more compact.
- Improved RF Performance: In some cases, COB construction enhances the operation of radio frequency (RF) systems by reducing the inductance and capacitance of integrated circuit leads.
- Merging Packaging Levels: COB effectively merges two levels of electronic packaging: level 1 (components) and level 2 (wiring boards), often referred to as "level 1.5."
2. Construction Methods:
- Flip Chip on Board (FCOB): In FCOB, the device is inverted, with the top layer of metallization facing the circuit board. Small balls of solder are placed on the circuit board traces where connections to the chip are required. The chip and board are then passed through a reflow soldering process to establish electrical connections.
- Wire Bonding: In wire bonding, the chip is attached to the board with an adhesive. Each pad on the device is connected with a fine wire lead that is welded to the pad and to the circuit board. This method directly wire-bonds the chip to the PCB.
- Glob-Top: Glob-top is a variant of conformal coating used in COB assembly. It involves depositing a drop of specially formulated epoxy or resin over a semiconductor chip and its wire bonds. This provides mechanical support and excludes contaminants that could disrupt circuit operation. Glob-top is commonly used in electronic toys and low-end devices.
- Flexible Circuit Board (Tape-Automated Bonding): Thin flat metal tape leads are attached to the semiconductor device pads and then welded to the printed circuit board. The chip and connections are covered with an encapsulant to reduce moisture entry, protect wire bonds or tape leads, and dissipate heat.
3. Final Product Assembly:
- The printed circuit board substrate may be assembled into the final product, such as in a pocket calculator.
- In the case of a multi-chip module, the module may be inserted into a socket or attached to another circuit board.
- Heat-dissipating layers may be included in the substrate wiring board where mounted devices handle significant power, such as in LED lighting or power semiconductors.
COB packaging offers a balance of cost-effectiveness, compactness, and improved performance, making it suitable for various applications!
For more details, you can explore the [Wikipedia page on Chip on Board](https://en.wikipedia.org/wiki/Chip_on_board).¹²
(1) Chip on board - Wikipedia. https://en.wikipedia.org/wiki/Chip_on_board.
(2) What is a Chip On Board? - Its Application, Packaging and Function. https://www.pcbasic.com/blog/chip_on_board.html.
(3) COB封装（板上芯片封装Chips On Board,COB）简要介绍 - 知乎. https://zhuanlan.zhihu.com/p/503508839.
(4) COB vs BOX transceiver packaging technology – what’s the difference?. https://atgbics.com/blogs/tech-talk/cob-vs-box-transceiver-packaging-technology-what-s-the-difference.
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