Method for multiple filtration of dispensing liquid in a liquid dispense system

A method for dispensing a liquid onto a substrate using an apparatus, the apparatus comprising:

• a reservoir for storing the liquid to be dispensed;
• a filter comprising a filter inlet and a filter outlet, the filter inlet in fluidic communication with the reservoir via a first valve on a supply conduit;
• a dosing pump having a dosing pump volume and comprising a dosing pump inlet, a first outlet, and a second outlet, the dosing pump inlet in fluidic communication with the reservoir and the second outlet in fluidic communication with the filter inlet via a second valve and a return conduit;
• a trap reservoir being located between the filter and the dosing pump;
• a buffer tank located between the reservoir and the filter;
• a dispense nozzle in fluidic communication with the first outlet;
• and
• the supply conduit extending from the buffer tank to the filter and a second branch extending from a line between the filter and trap reservoir to a point in the supply conduit upstream of the first valve,
• the method comprising:
• performing a dispensing step comprising dispensing the liquid through the dispense nozzle onto the substrate;
• after the dispensing step, flowing the liquid from the dosing pump via the second valve to the filter inlet and from the filter to the trap reservoir to filter the liquid by applying a positive pressure of the liquid at the filter inlet, the flowing of the liquid from the dosing pump to the filter removing particles from the liquid flowing through the filter;
• wherein flowing a first volume of the liquid from the dosing pump via the second valve to the filter and from the filter to the trap reservoir further comprises flowing a second volume of the liquid from the dosing pump to the buffer tank;
• and flowing the liquid from the buffer tank to the filter and from the filter to the trap reservoir, and from the trap reservoir to the dosing pump to filter the liquid again while reloading the dosing pump, the flowing of the liquid from the buffer tank further removing particles from the liquid flowing through the filter;
• calculating the first volume and the second volume of the liquid flowing from the dosing pump to maximize a total filtered volume of the liquid filtered by the filter based on a total pressure (FP) applied to the filter according to
• FP=(FR*VF)/(CF*CT)
• wherein FP is a filtration pressure drop in kPa, FR is a flow resistance across the filter in kPa/(cc/min), VF is the total filtered volume in cc including a return volume and a reload volume, CT is a cycle time in minutes, and CF is a fraction of the cycle used for filtration;
• choosing the first volume and the second volume of the liquid flowing from the dosing pump in order to maximize the total filtered volume of the liquid filtered by the filter based on the total pressure to be applied to the filter.