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Chip On Board (COB)

COB PhotoToday electronic miniaturization is one of EMS major challenges. For nearly 50 years, éolane has guaranteed its technological and industrial sovereignty by developing its expertise in advanced electronics to support its customers in their product development to make them more efficient. The electronic function of assemblies is no longer the exclusive performance element of the system. Indeed, the mechanical characteristics such as size, weight, and the capacity of integration in a case designed for the intended uses of the product, are more and more preponderant and the miniaturization of the devices is today an important quality and performance axis of electronic systems.
To respond to changing demand, éolane has 2 COB lines at its CENTER Region Angers site. Chip On Board (COB) technology is an LED chip assembly technology that offers more functions in a limited volume compared to other processes. The advantages of this technology are varied:

  • Increase in thermal performance
  • Reduction in weight, volume and consumption
  • Improved signal performance
  • Parasitic impedances reduction
  • Radiofrequency and microwave

Specificities of this technology

Wafers picture

The electronic chips are all made from silicon. First, cylinders of silicon are made which are then cut into disks called wafers. The wafer is then modified on its surface by chemical and photographic processes, and after a number of processing steps, a wafer coated with chips is obtained. It is possible to put up to several thousand chips on a single wafer. 
These chips are very fragile and very sensitive to dust and light. They cannot be used as is. They have to be removed from their support (the wafer) and connect to the outside world to use their functions. The most common way is to put each chip on a small support, and attach the chip to legs to allow contact with the outside. The chip is then immersed in insulating and protective material to obtain a classic electronic component, contained in a small case.
COB uses the same chips initially but the assembly technique is different and more complex. Instead of putting the bare and fragile chip in a plastic box which will then be soldered onto an electronic card, the same bare chip taken on the wafer is directly placed on the electronic card, which is why this technology is called COB, meaning Chip On Board. The connections are then made between the chip and the electronic card (this is called wire bonding). 

Clean room picture
éolane Angers cleanroom ISO 8

This complex assembly must be carried out in a clean room (room where the number of dust per cubic meter of air is controlled and limited). The chip and its contact wires must then be protected by either covering them with a gel or by putting a cover on top.
The chips thus placed directly on a card take up less space, they are more resistant to vibrations and offer better performance to users than the chips placed in a package which are then themselves placed on an electronic card.

Manufacturing process

Thanks to high-precision industrial equipment and expertise in carrying out various assembly techniques, éolane always adapts itself as closely as possible to customers’ needs. 

  • Die attach, chip bonding process used when the product requires the integration of several components into a single electronic assembly or sub-assembly 
  • Process reflow, chip bonding process with the use of solder paste which, subjected to controlled heat (using a reflow oven or infrared lamps) welds the joints 
    • convection
    • convection vacuum
    • phase vapour vacuum
  • X-ray
  • Cleaner
    • HFE
    • Vigon A200
  • Wire Bonding 
    • Al / Au: (fine wire) 17,5 up to 60µm
    • AL: (heavy wire) de 100 up to 600µ

Photo process ball bonding

  • Ball bonding Au: 20 up to 50 µm, flip chip assembly process
  • Underfill
  • Dam & fill, process of creating a cavity using a dam, this technique minimizes the stresses exerted on the wire connections
  • Glop top, final assembly process individually covering the chips and its wire links with a plastic molding to provide them with protection and enable them to resist in severe environments (dust, organic matter, corrosion, oxidation, thermal shock, reverse engineering, etc.).   
  • Top cover sealing, perfect sealing process participating in OEE (Overall Equipment Effectiveness).