Swissbit’s COF process is a special form of COB technology. It is a current trend for high quality solutions in a wide range of sectors that include electronic applications in machine construction, the automotive, medical, and military industries, home automation, and avionics and model construction. The major advantages of using COF consist of their space saving compact design and complex geometries, their reduction in weight, and their thermal durability and flexibility.
The connection options and materials used vary depending on the intended use of the application. For instance, a flexible reinforced board can be used just as a rigid flexible board or even a semi-flexible board. Depending on the version, the material will be suitable for dynamic bending cycles.
For example, when creating the flex connection, polyimide, polyester or polyethylene naphthalate is used. Polyimide, FR4, polyethylene terephthalate, aluminum, and steel serve as reinforcement materials.
Chip bonding allows positional accuracy and positive connection of semiconductor chips to substrates such as boards, ceramics or flexible holders (COF). Besides serving only as a mechanical fixture, insulating and conducting adhesives are used as joining elements, which also serve as thermal contacts to conduct heat losses and if necessary, as an electrical contact (e.g. for diode chip LEDs).
Wire bonding is the establishment of an electrical connection between the connection pads for a semiconductor chip to the wiring level on the substrate. The majority of wires used for this purpose consist of aluminum alloys (metallization of contact surfaces on the chip side) and gold (metallization of substrate contacts, often as nickel-gold layer composition). Their diameter is between 22 and 25 µm and is not allowed to become lower than 15 µm. The inner lead bonding can be characterized as micro-welded connections which are created by two basic technological processes: ultrasound wire bonding and thermosonic wire bonding (ultrasound with temperature support). In this case, the welding parameters are the ultrasound energy, time and contact pressure strength and the mechanical properties of the contact elements and heat to be connected. The wire connections are optimally shaped using a coordinated equipment axis process and the micro-welding connection properties are checked by mechanical inspection procedures (Pull Test) and optical checks.
Chip compound is understood as the freely programmable application of a filled epoxy resin to protect the assembly against environmental influences. Therefore, the processed base materials determine the viscosity and the expansion coefficient or the compound mass to be used.