Adhesive Technologies

Adhesive materials can be applied between two join partners, e.g. dice and substrates in various ways: dispensing, stencil printing, pin transfer or as film working as intermediate connection.

Thermal conductive adhesives can for instance be used to mount chips on boards (COB), dice on substrates and substrates on heat sinks. Electrical interconnections can e.g. be made by wire bonding, if needed.

If the electrical contact is desired to be established by the glue itself, adhesive materials filled with conductive particles can be dispensed as isotropic conductive paste (ICP) for solder replacement as well.

Anisotropic conductive adhesive (ACA) is filled with conductive particles but is not electrically conductive itself. As recently as this adhesive is pressed between two surfaces, the particles will touch them and each other and a conductive layer will be established in one direction. These adhesives are available as paste (ACP) or film materials (ACF).

Another possibility for electrically connecting two contacts is to use unfilled, nonconductive adhesives (NCA) and stud bumps. This means, that conductive material (e.g. gold) is bumped on the pads of one chip. The adhesive is applied between the chip and substrate and then both join partners are pressed together. While pressing, the adhesive is displaced by the gold bumps and cares for the mechanical support and fixation.

For optical applications it may be important to use glue with appropriate optical characteristics, e.g. index of refraction.

Depending on your needs, you can choose between different characteristics of these adhesive materials and suitable curing methods.

Attaching LCD drivers to LCD panels is one example for using ACF with chip on glass bonding (COB). In contrast to most other bonding methods, ACF bonding is reworkable. The defective component can be removed and the glass panel can be cleaned. Then new ACF preforms are placed either by an ACF module or manually by using a pair of tweezers.

In case of using anisotropic conductive film (ACF) materials several process steps are necessary:

• Pre bonding (force and temperature) of the ACF to the substrate after removing of the safety layers of the film
• Alignment of chip to substrate
• Placement of the chip onto the film
• Final bonding by force and temperature

Learn more about FINETECH solutions for rework of ACF bonded devices.

For example in RFID applications anisotropic conductive paste is used to fix dice on antenna films. The dice have only a few pads, which are embossed by bumps or coined bumps. The conductive particles are pressed between the contacts and snap cured within a few seconds by a heated tool and may be supported by a heated chuck.

Merely a suitable dispensing module is required for integrating ACP processes in your flip chip bonding system.

This technique of connecting electrical contacts needs well prepared flip chip dice with gold bumps. These stud bumps can be added by a wire bonder (ball-bonder) working in stud bumping mode. The dice are then mounted by a flip chip bonder and the gold bumps are pushed against the target pads.

After placing the chip into the adhesive, it has to be held by the tool in this particular position and cured by temperature or activated by UV light.