Pneumatic fluid dispensers or “time/pressure” dispensers were once the dominant means in delivering small quantities of adhesives and solder paste for electronics assembly. They are simple in design and consist primarily of a plunger, or piston, and a syringe.
Pulsed air from a compressor “slaps” the top of the plunger in a rhythmic pattern moving the plunger forward in the syringe resulting in a degree of turbulence as material is pushed out through the needle tip at the end of the syringe.
Pneumatic fluid dispensers are relatively inexpensive, however this one advantage is overshadowed by many distinct disadvantages.
Disadvantages of pneumatic fluid dispensing include:
Precise control is impossible to achieve
The pulsed air supplied to the syringe stresses the material. The turbulence created by the blasts of air heats the adhesive in the syringe, which causes the viscosity to decrease. With pre-mixed and frozen syringes, the thawing process begins to cure the adhesive, increasing viscosity and making dispensing difficult.
The material isn’t in a “released” state
To control flow and minimize fluctuations technicians often use the smallest needle size. This adds to the problem by stressing the material and adding even more viscosity problems that will cause even more dispensing issues.
Changing the homogeneity of certain materials
Adhesives with fillers begin to separate out, and suspended particles can actually become compressed along the inner walls of the syringe. This results in variations in viscosity in the mix and affects flow behavior and bonding properties.
“Over” or “Under” dispensing
“Over” or “under” dispensing happens because of problems with control. Over dispensing wastes material and often makes stenciling of encapsulated components impossible. Under dispensing can lead to components falling off or shifting position before or during reflow.
The amount of vacuum cannot be pre-set
With pneumatic systems the amount of vacuum cannot be adjusted. This is a considerable disadvantage because being able to adjust the vacuum is a crucial component of efficiency.
Air contains moisture
When the pulsed air is blasted against the plunger in the syringe, both the air and moisture can be forced around the sides of the plunger and into the material. The moisture can then negatively impact the product that is being dispensed.
Even though they are inexpensive, pneumatic fluid dispensing has many disadvantages. The Fishman’s SmartDispenser® offers a solution to this issue because it offers multiple solutions to control the process of dispensing fluids without the limitations that many other dispensing solutions that are on the market possess. Contact us for more information about how Fishman Coporation can help.