Chip on Board (COB) is a mature technology in the electronics manufacturing industry, but its manufacturing process is unfamiliar to most electronics assembly plants. This is likely due to the fact that it utilizes integrated circuit (IC) packaging techniques such as wire-bonding. Consequently, many finished product assembly plants and specialized PCB foundries struggle to find skilled personnel.

Please note that this article describes the COB process for traditional IC wafer bonding. The currently popular COB LEDs use a similar process, but with slightly different manufacturing processes.

Previously, COB was primarily used in low-end consumer products. Because COB eliminates the IC packaging process, material costs are relatively low. As electronic products become increasingly smaller, more companies are considering incorporating COB into their products. After all, available space on circuit boards is becoming increasingly scarce, and COB processes can accommodate even smaller spaces than ICs. Perhaps adopting more advanced technologies is too expensive, leading some to consider COB manufacturing.

Here, I'm revisiting my experience setting up and operating COBs from years ago. This serves both as a reminder of the process and as a reference. Of course, some of the information may not be current, so it's for reference only.

The Evolution of ICs, COBs, and Flip Chips (COG)

The diagram above helps you understand the evolution of electronic chip packaging: from IC packaging → COB → Flip Chips (often referred to as COG, Chip on Glass), with ever-shrinking sizes. COBs are merely an intermediate product between current technologies. CSPs (Chip Scale Packages) are probably a process between COBs and flip chips! It's a bit confusing.

To put it simply, COB is simply a migration of the wire bonding and encapsulation processes of IC packaging to the circuit board. This means the bare wafer (die), originally attached to the lead frame, is now attached to the PCB. The wires (wires) originally bonded to the lead frame are then soldered to the PCB's gold-plated pads. Epoxy is then applied to the wafer and wires, replacing the traditional molding process. COB eliminates the traditional IC packaging processes of trimming, forming, and marking, and reduces the IC packaging factory's overhead. Therefore, its manufacturing process is generally cheaper than IC packaging.

Because COB manufacturing is cheap and the environment typically lacks the same high standards as foundries or IC packaging plants, early COB technology was primarily used in low-end consumer electronics, where reliability was less important, and on relatively inexpensive wafers. These products, such as toys, calculators, small monitors, and clocks, were so affordable that people could simply throw them away and buy new ones if they broke. Consequently, early COB manufacturing in Taiwan was largely done by IC packaging factory employees, operating in their living rooms and lacking environmental controls. This often led to the misconception that COB quality was inherently unreliable.

However, as the world progresses, more and more major manufacturers are attracted to its small size and the trend toward thinner and lighter products. COB's use has actually become increasingly widespread in recent years. For example, many products requiring a compact form factor, such as mobile phones and cameras, have adopted the COB process.

COB has another advantage that makes it particularly popular with some manufacturers. Because of the need for "sealing," typical COBs encapsulate all external wires and pins in epoxy resin. This feature can increase the time it takes for hackers to decipher designs, indirectly improving the security level. (Note: The security level is determined by the time and money spent on deciphering the technology; the more time and money spent, the higher the level.)