Dispensing

Dispensing can be used for creating stacked structures which can consist of multiple materials. For packaging, dispensing is used for depositing encapsulants on the die, interconnect and package/PCB. It is also used for underfilling a flip chip arrangement. It offers a precise, accurate and repeatable method of depositing an encapsulant in digitally defined areas of a substrate. As a dispenser can deposit the material in any pattern, it is ideally suited to glob-top encapsulations and conformal coatings.

Dispensing technology

A robotic dispenser system consists of a pneumatic dispenser unit, XYZ movement stage, a syringe and a computer. A material to be dispensed is placed in the syringe, one end of the syringe is connected to an air hose which directs compressed air to the syringe and the other end has nozzle which directs the flow of ink on to the substrate. The dispenser unit controls and coordinates the air pressure applied to the contents of the syringe including the length of time the pressure is applied to the syringe. XYZ stages control the movement of the substrate and define area of substrate for material deposition. A computer coordinates the function of the dispenser unit and the movement stages. They are often determined by the application requirements of the electronics to be encapsulated.

The volume of a deposition is controlled by the following parameters.

• Dispensing pressure
• Time for which the pressure was applied
• Speed of movement of the stages
• Nozzle orifice diameter
• The gap between consecutive dots/lines (in case of multiple dots/lines)

Nozzles attached to the syringes can be broadly divided into two categories; Blunt end and tapered. The blunt end nozzles are compatible with low viscosity materials as they offer better control over the volume of the ink dispensed. Tapered nozzles are better suited to high viscosity materials as they aid the flow of the materials. Nozzles are commercially available in a range of diameters. Nozzle selection is based on the particle size, ink rheology and encapsulation requirements.