Chip-on-Glass (CoG)

Chip-On-Glass (COG) is a flip chip technology for direct connection assembly of ICs (Integrated circuits) on glass substrate by using ACF. The IC is an unpackaged, bare chip and the pitch of the bumps (footprint) can be scaled down according to customer requirements (contact pitch of glass substrate). This technology reduces the assembly area to the highest possible packing density and is implemented in applications where space saving is crucial. It allows a cost-effective mounting of driver chips because integrating flex PCB is no longer required. The IC is bonded directly onto the glass substrate and is suitable for handling high-speed or high-frequency signals.

COG is primarily used for source driver ICs within TFT display technologies where they are used for LCD, plasma, e-ink, OLED or 3D technologies. This is essential for consumer electronic products such as notebooks, e-book reader, video and digital cameras or mobile phones with the need for small size and light-weight components.

What are the challenges?

Sensitive, bare chips with long and extra thin dimensions and high packaging density
Specialized tooling, fixtures and optics shifting for wide range of chip and substrate sizes
Miniaturization of chip footprint (for example pitch of 60 µm (line/gap=25/35[µm]) requires high degree of parallelism and alignment accuracy
ACF demands for application of controlled bond-force (for example up to 300 N/cm² needed for specific foils)
Flexible solutions for chips, substrates and ACF with different visibility (reflections, transparency)

The Finetech Solution

I. Stable Substrate Handling

Heating plate with customized vacuum cavities

Typical a heating plate optimized for small substrate sizes up to 100 mm x 100 mm
Special support table for larger panel sizes can be offered
Full-area or individual vacuum clamping solutions for glass substrates
Flexibly designed heating plate with cavities for substrate backside assembly

II. Adapted Tooling & Optics

Gimbal or non-gimbal tooling according to chip dimensions
Quick tool switchover, flexible use for different applications
Contact-heating tools if substrate heating is impossible
Optics shifting allows visual alignment over the complete chip length

III. Flexible Process Technologies

Precision dispensing of an ACP dot

Anisotropic Conductive Film
ACF module supports application of various ACF materials with flexible force and time parameters

Other adhesives possible (ACP, NCA)
Adhesive dispensing is supported

Low-temperature curing
UV curing

Alternative process technologies
Ultra-sonic and thermocompression technologies can be integrated

Integrated Process Management (IPM)

Integrated Process Management (IPM)
Principle of process gas integration
Operating software for bonding

The Integrated Process Management (IPM) is the center piece of a FINEPLACER^® system¹ - the place where it all comes together. IPM is more than just thermal management. It synchronizes the control of all process modules and their related parameters:

Controlled and precisely balanced interaction of top and bottom (pre-)heating and cooling
Control of temperature, time, force, power, energy, flow
Controlled process gas integration for reduced solder contamination, minimized surface tension effects and smooth spherical solder residues

IPM is very complex, yet easy to access. Via the GUI of the operating software, the user has perfect control of all required adjustments. Just drag 'n drop to define temperature ramps or activate process modules. All settings are represented in only one profile, making for a very intuitive work flow.

The operating software provides an ever-growing library of profiles for all kinds of processes. It also offers comprehensive data logging functions essential for statistical process control.

In combination with the system-to-system process transfer capability this is as easy as process development can get.

¹ _{FINEPLACER^® core offers co-ordinated top and bottom heating but does not support IPM}