What is chip on board and how does it develop

What is chip on board and how does it develop
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    Why chip on board has been used

    In the past, chip on board was mostly used in some less complete consumer products. As electronic products become smaller and smaller, more and more companies are considering introducing the chip on board process into their products. After all, there is a lot of space available on the PCB, and the chip on board process can be used in a smaller space than IC. Perhaps the more advanced technology is too expensive, so some are using the chip on board process.

    Manufacturing materials needed for chip on board

    COB requires PCB, di, silver glue,aluminum wire, epoxy resin and other materials. Some materials may have substitutes, but all of them are necessary in principle. The process uses a die attach nozzle, a wire bonding machine, a dispenser, an oven, and a tester.

    It is simple, just build a clean room and buy the necessary machinery to produce, with 99% of successful rate, discipline and process control is definitely needed.

    What is the environment requirement of chip on board

    It is recommended that there must be a clean room and the class is better below 100K. The clean room of IC packaging and testing industry is generally required to be 10k or even 1k, and the wafer factory is of a higher class. Because the process of chip on board is wafer encapsulation grade, any small particles may contaminate the welding points , thus causing serious defects in the quality of the welding wire.
    Basic dust-free clothing and cap protection are necessary, in order to avoid wire bond dust flying around, stained to the welding line position.

    the clean room should strictly control the entry of cartons and any articles

    In addition, the clean room should strictly control the entry of cartons and any articles that are easy to produce dander. All packaging should be unpacked outside the clean room before entering, in order to keep the clean room clean and extend the life of the clean room.

    The development history of electronic chip packaging

    The development history of electronic chip packaging: IC packaging→ COB → Flip Chip (COG)
    The size of electronic chip packaging is getting smaller. COB can only be described as an intermediate product between current technologies. In addition, CSP (chip scale package) should be the intermediate process from chip on board to flip chip.

    COB is to transplant IC encapsulated wire bonding and Capsule operations to the circuit board. In other words, the bare die originally attached to the lead frame is attached to the PCB. Besides, we changed the wires from bonding to the wire frame to the gold-plated welding pad of PCB, and then used epoxy glue to cover wafers and wires instead of the original mold packaging. Chip on board could save the manufacturing process of IC sealing and marking. It can also reduce the cost of the management and pin of the IC sealing factory, so basically its process will be cheaper than the IC packaging process.

    Because it was cheap, early chip on board technology was typically used only in lower-level consumer electronics that were less reliable, such as toys, calculators, small monitors and clocks, because they were so cheap that you could just throw them out and buy a new one. Therefore, the early chip on board process was mostly family-type OEM opened by IC sealing factory employees. The living room was the factory, and there was no environmental control. It was often mistaken that the quality of chip on board was so unreliable.

    But with the progress of the times, there are more and more big factories look at its small size, as well as the trend of thin and short products, the use of chip on board in recent years has been more and more widespread trend, such as mobile phones, cameras and other short products have a lot of products into the chip on board process.

    COB has another advantage that makes some vendors particularly fond of it. Due to the need of sealing glue, common chip on board will seal all external wire connectors in epoxy resin, as those who like to crack other people’s design hackers may need to spend more time to crack because of this feature, indirectly achieving the enhancement of anti-terror security level.

    The design requirement of chip on board for PCB

    The design requirement of COB for PCB

    1.Because chip on board does not have IC packaging lead-frame, but use PCB to replace it, so the PCB welding pad design is very important, and the surface treatment can only use electric gold plating or ENIG(nickel dipped gold), otherwise the gold wire or aluminum wire, even the latest copper wire will not hit the problem.

    The finished surface treatment of PC board must be electric gold plating or ENIG, and to be thicker than the general PC board gold plating layer, can provide the energy required by die bonding, the formation of gold aluminum or gold.

    2. In the layout of the welding pad outside the die pad of chip on board, the length of each welding wire should be fixed as far as possible, that is to say, the distance of the solder joint from the die to the PCB welding pad should be as consistent as possible, so as to control the position of each welding wire and reduce the problem of short circuit of welding wire intersection.

    So a diagonal pad design does not meet the requirements. It is suggested that the PCB pad spacing can be shortened to eliminate the appearance of diagonal pad. Oval pad positions can also be designed to evenly distribute the relative positions of the welding lines.

    3.  It is recommended that a chip on board die should have at least two or more registration points, and it is better to use cross registration points instead of the circular registration points of traditional SMT production line, because the wire bonding machine will basically grasp straight lines for automatic positioning. This is because there is no circular registration point on the traditional wire frame. It’s just a straight frame. Maybe some wire bonding machines are different. It is recommended to make the design by referring to the machine performance first.

    4.  The size of PCB die pad should be larger than the die, to limit the deviation when placing the wafer, but also to prevent the wafer from rotating too much inside the die pad. It is recommended that the wafer pads on each side be 0.25~0.3mm larger than the die.

    5.  It is best not to have pilot holes in the chip on board area where glue is needed. If not unavoidable, PCB manufacturers are required to plug these pilot holes 100% completely. The purpose is to avoid epoxy dispensing from penetrating the other side of PCB by pilot holes and causing unnecessary problems.

    silkscreen marks can be printed on the areas that need dispensing

    6.  It is suggested that silkscreen marks can be printed on the areas that need dispensing, which can facilitate dispensing operation and shape control.

    Conclusion

    COB has been a mature technology in the electronic manufacturing industry, but the general assembly plant is not familiar with its manufacturing process, perhaps because it uses some wire bond IC packaging technology. So many finished products or professional PCB Assembly factories are difficult to find the relevant technical personnel, but IBE is home to bunch of high skilled technicians, which enable us to provide you the chip on board services.

    FAQ

    In the past, COB was mostly used in some less complete consumer products. As electronic products become smaller and smaller, more and more companies are considering introducing the COB process into their products. After all, there is a lot of space available on the circuit board, and the COB process can be used in a smaller space than IC. Perhaps the more advanced technology is too expensive, so some are using the COB process.

    COB requires PCB, die(wafer), silver glue,aluminum wire, epoxy resin and other materials. Some materials may have substitutes, but all of them are necessary in principle. The process uses a die attach nozzle, a wire bonding machine, a dispenser, an oven, and a tester.
    The development history of electronic chip packaging: IC packaging→ COB → Flip Chip (COG)

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