Microdispensing

Microdispensing is the technique of producing liquid media dosages in volumes of less than one microlitre. The continuing miniaturization in almost all technical areas creates constant challenges for industry, development and research facilities. Microdispensing is one of those challenges. Ever smaller amounts of adhesive, liquid, oil, grease and a multitude of other media must be dispensed reliably and accurately in dosage and placement with short cycle times. The precise positioning and quantity of fluids such as glue, reagents or any other substance has a great influence on the overall quality of a medical device. A few examples are:

Microdispensing is also used in non-medical applications, like on-demand soda flavoring (the Coca-Cola Freestyle and Pepsi Spire), inkjet printing, and 3-D printing.

There are two basic types of dispensing techniques: classic contact dispensing and non-contact dispensing.

In contact dispensing, the drop forms at the exit of a nozzle, and is deposited by contact, while the drop is still on the nozzle. The technique is as old as the wish to divide a medium, stored in a big container, into smaller amounts. A good example for this is applying adhesive with a tube: To apply the adhesive requires contact between the tip of the tube and the part for the bead of adhesive to be transferred. This method has disadvantages:

Despite all of these disadvantages, contact dispensing is still used in the majority of automated processes today, because of:

Gear pump

Pressure-time systems

In non-contact dispensing, the drop also forms at the end of a nozzle, but far enough away from the target area that the drop separates from the nozzle before it hits. This, too, is a very old technique, as old as squirting liquid from a tube.

Because of increasing requirements in regards to cycle time and accuracy in almost all areas of production, non-contact dispensing is constantly gaining importance. A good example for this is the attachment of very small electronic parts (SMD parts) onto printed circuit boards and substrates. For this, the part carrier only needs to be positioned in one plane - after that the adhesive can be transferred without contact. The following examples show the advantages of non-contact dispensing:

Non-contact dispensing can be divided in two different methods:

Jet-forming dispensing exists when the flow velocity of a medium at the nozzle exit is high enough that the effects of gravitation and surface tension on the separation of the fluid from the nozzle are of secondary importance. This state is characterized by the Weber number:

...
Wikipedia