Jetting

The major difference between dispensing and jetting is that jetting does not require contact with a substrate for deposition. During deposition a dispenser may have a lot of movement in the z-axis whereas z-axis motion is often not required for jetting depositions. The elimination of the z-axis movement increases the speed of deposition. Jetting offers higher consistency compared to dispensing as the volume of the deposition is precisely controlled by the valve. Jetting also eliminates any dripping, tails or strings as the nozzle contents do not come into contact with the substrate surface. Jetting can offer more accurate depositions in tight spaces without any risk of colliding with surrounding components/depositions.

For packaging applications, jetting is particularly useful for underfills and stacked-die applications where the components are laid out closely together with very small spaces between them. It has been used to manufacture flat panel displays and sensitive MEMS device packaging. Jetting can also be used for conformal coating and glob-top encapsulations. It offers an accurate, repeatable and consistent method of encapsulation. The shape and size of the encapsulation is only limited by the maximum deposition area of the stages and is compatible with a wide range of substrates and materials.

Jetting technology

Jetting technology is based on valves controlled by actuators such as piezoelectric actuators. These actuators control opening and closing of the valve. A jetting deposition involves the jetting valve hovering over a defined area of substrate and then opening for a predefined time period which causes a specific quantity of material to be jetted out through a nozzle. The rapid ejection of the materials is caused by pneumatic pressure applied to the material to be jetted. A series of droplets or a steady stream of a material can be jetted to fill an area on a substrate.

A jetting system consists of a jetting head, jetting controller, a syringe, XYZ axis movement stage and a pneumatic pressure valve. The material to be jetted is placed in a syringe which is connected to the jetting head. The pneumatic pressure valve is connected to the other end of syringe through an air hose to control the pressure applied to the contents of the syringe. The jetting controller controls the opening and closing of the valve and the period of time the valve is opened. The XYZ movement stage digitally defines an area of the substrate where the material is required to be deposited. A computer is an optional component of a jetting system, it can co-ordinate the movement of the XYZ stage, opening and closing of the jetting valve. In some cases the jetting controller receives the signal to open and close the valve directly from the movement stage; in such cases a computer is not essential.

The following are the jetting parameters which are used for defining a jetting deposition.

• Jetting pressure
• Jetting time – period of time where the valve opens
• Speed of movement of stages
• Nozzle orifice diameter
• The gap between consecutive droplets/lines

The nozzle in the case of jetting systems is often an opening in a plate attached to a jetting head. Different diameter nozzles can be applied to the jetting head to gain control over the deposition.