Chip on Board is a way to attach a processor directly to a circuit board without a protective case
Chip on Board (CoB) means the actual processor or memory chip is glued directly onto the circuit board and then covered with a blob of epoxy resin. Instead of the chip sitting inside a plastic or ceramic package with pins sticking out, the bare silicon die gets mounted flat on the board, connected with tiny wires, and sealed with that protective coating. You see this in phones, smartwatches, and budget electronics because it saves space and money compared to traditional packaging.
The alternative is a packaged chip, where the silicon die sits inside a protective case (like a square with pins around the edges) that then plugs into the board. Packaged chips take up more room and cost more to manufacture, but they're easier to replace if something breaks. Chip on Board is permanent — if the chip fails, you're replacing the whole board.
The blob you see is not the chip itself. It's epoxy resin covering the chip and the wires that connect it. The actual silicon is underneath, invisible. This coating protects the delicate wires and die from moisture, dust, and physical damage during manufacturing and use.
Key Takeaways
- Chip on Board glues the bare processor directly to the circuit board and seals it with epoxy, saving space and manufacturing cost.
- The visible blob is protective resin, not the chip — the actual silicon die is underneath, connected by hair-thin wires.
- Chip on Board is common in phones, smartwatches, and budget devices because it lets manufacturers make thinner products and reduce assembly time.
- Once sealed, a Chip on Board component cannot be removed or replaced without destroying the entire circuit board.
Why manufacturers choose Chip on Board
Space is the main reason. A packaged chip with pins takes up vertical space on the board and horizontal space for the pins themselves. Chip on Board eliminates both — the die sits flat, wires go straight down, and the whole assembly is thinner. In a smartphone or smartwatch where every millimeter matters, that adds up.
Cost is the second reason. Packaging a chip — putting it in a protective case, adding pins, testing it separately — takes time and materials. Gluing the bare die directly to the board and sealing it with epoxy is faster and cheaper once you have the equipment to do it. The savings are small per unit, but across millions of devices, they matter.
Manufacturing speed is the third. A packaged chip has to be made, tested, and shipped to the board manufacturer as a separate component. Chip on Board skips those steps — the die goes straight from the fab to the board assembly line. This also means fewer supply chain delays.
Where you'll see Chip on Board
Smartphones use it extensively. The main processor, memory chips, and power management chips in most phones are mounted this way. If you've ever opened a phone (which you shouldn't, because it voids the warranty), the black or white blobs you see are Chip on Board assemblies.
Smartwatches and fitness trackers use it because they need to be thin and light. The processor and sensors are often glued directly to the main board. Budget tablets and low-cost laptops also use Chip on Board to keep manufacturing costs down.
High-end gaming laptops and desktop computers rarely use it for the main processor — those chips are usually packaged because they generate more heat and need to be replaceable. But you'll find Chip on Board in the power delivery circuits and memory controllers even in expensive machines.
The tradeoff: size and cost versus repairability
The main disadvantage is that you cannot replace a Chip on Board component without destroying the board. If the processor fails, the entire board is scrap. With a packaged chip, a technician can desolder it and install a new one. This is why repairing phones is expensive — the processor is soldered to the board, and replacing it requires specialized equipment and skill.
Heat dissipation can also be trickier. The epoxy blob does not conduct heat well, so chips mounted this way have to be designed to run cooler or the board has to have extra thermal management. Packaged chips often have a metal case that spreads heat more efficiently.
For the manufacturer and the consumer buying a new device, Chip on Board is a win — thinner phones, lower prices. For someone trying to repair an old device or keep it running longer, it's a loss.
How Chip on Board is made
The process starts with a bare silicon die fresh from the wafer fab. A technician places it on the circuit board using a pick-and-place machine, positioning it precisely. Then a wire bonder connects the tiny pads on the die to the traces on the board using wires thinner than a human hair — usually gold or copper.
Once the wires are in place, the whole assembly gets dipped in or sprayed with epoxy resin. This hardens into the protective blob you see. The resin is usually black or white and opaque, so you cannot see the die or wires underneath.
After the epoxy cures, the board goes through testing to make sure the connections are solid and the chip works. Then it moves on to the next stage of assembly — adding more components, soldering, and final testing.
Chip on Board versus other packaging methods
A Ball Grid Array (BGA) is a packaged chip with hundreds of tiny solder balls on the bottom instead of pins around the edges. It takes up less space than a traditional pinned package but more than Chip on Board. Most modern processors use BGA packaging.
A Quad Flat Package (QFP) is an older style with pins on all four sides. It's larger than BGA and rarely used in new devices, but you'll see it in older electronics and some industrial equipment.
Chip on Board is the smallest and cheapest but cannot be replaced. BGA is a middle ground — compact and solderable with the right equipment. QFP is the largest but easiest to work with if you have basic soldering skills.
What Chip on Board means for device lifespan
If the processor or a critical chip fails, the device is usually not worth repairing. The cost of replacing the entire board often exceeds the value of the device, especially for phones and budget electronics. This is one reason why phones are harder to repair than older computers, where chips were packaged and replaceable.
For everyday use, Chip on Board is reliable. The epoxy seal protects the connections from moisture and dust. The main failure mode is usually the solder joints under the board failing from thermal stress over years, not the Chip on Board assembly itself.
If you want a device that can be repaired or upgraded, look at the specifications or teardown reviews to see what packaging the main components use. Devices with packaged chips are more repairable, but they're also thicker and more expensive.
Frequently Asked Questions
Is the black blob on a circuit board the actual chip?
No. The blob is epoxy resin covering the chip. The actual silicon die is underneath, connected to the board by hair-thin wires. The resin protects those wires and the die from damage and moisture.
Can a Chip on Board component be removed and replaced?
Not without destroying the board. The chip is glued down and sealed with epoxy. Removing it requires heating the epoxy until it softens, which also damages the board underneath. This is why phone repairs are expensive — the processor cannot be swapped out like a replaceable component.
Why do some devices use Chip on Board and others don't?
Manufacturers choose Chip on Board to save space and reduce manufacturing cost. Phones and smartwatches use it because they need to be thin. Devices where repairability matters more, or where heat dissipation is critical, use packaged chips instead.
Does Chip on Board fail more often than packaged chips?
Not inherently. The epoxy seal is reliable and protects the connections well. Failures usually come from solder joints under the board failing from thermal cycling over years, not from the Chip on Board assembly itself. Both types fail at similar rates in normal use.
What does CoB stand for?
CoB is the abbreviation for Chip on Board. You'll see it used interchangeably with the full term in technical specifications and repair guides.