Matching Fluid Dispensers To Materials for Electronics Applications
Understanding the technology behind popular non-contact dispensers for electronics assembly.
There are four basic dispensing technologies being used today in Electronics Assembly. Although all the technologies can theoretically dispense almost all materials in most configurations (fills, beads, dots), each excels when used with certain materials (Fig. 1) and when used in specific applications (Fig. 2). This article will try to match the basic dispensing technologies to the types of material they are best suited to dispense.
Most manufacturers have special models of dispensers available for use with abrasive materials. Because these materials do not affect the basic dispensing technology but are more dependent on materials used to construct the pump or valve, the various types of abrasive materials are not included in this comparison
Within the basic technologies, there are many versions of specific pumps and valves that are available. A dispenser must be compatible with the material and be efficient in delivering the deposition configuration required. By comparing the basic design and theory of operation of each technology to the specifications available on all manufacturers’ product sheets, it becomes a simple task to see which design is appropriate for any specific use. This will help select the correct product for the application.
There are many other things to consider when deciding on the best overall dispensing system to use for an application. However, all the “bells & whistles” of the system will not compensate for using the wrong dispensing technology for the application.
Time/pressure dispensers: The basic time-pressure syringe (Fig. 3a) is probably the oldest dispensing method. Operation is very simple: The syringe holds the material, and air or a plunger applies pressure to the material to push it through the tip. The higher the pressure and the longer it is applied, the greater the quantity dispensed. It is an open technology because material is always present to the dispensing tip. The only thing keeping the material from continuously’ running out of the tip is the shear resistance of the material, combined with the lack of air pressure.
These valves are typically very low cost. They are popular because they may be used with a variety of materials and they are economical because they can be discarded after use. Syringes are best used for dispensing homogeneous materials in manual applications, although the valve is adaptable for attachment to automated equipment (Fig. 4).
The syringe valve dispenses in patterns of fills, beads and dots and works best with materials of medium viscosity. It lacks the precision and repeatability offered by other dispensers, and volumetric accuracy is not one of its key features. However, for dispensing homogeneous materials in non-critical patterns, it does an adequate job.