Pressure control system for printing a viscous material

A stencil printer for printing one of solder paste, epoxy, glue and encapsulant on an electronic substrate, the stencil printer comprising:

• a stencil having apertures formed therein;
• a print head positioned over the stencil and constructed and arranged to deposit one of solder paste, epoxy, glue and encapsulant within the apertures of the stencil, the print head comprising:
• a housing defining a chamber;
• a source port defining a passage having an inlet positioned to allow one of solder paste, epoxy, glue and encapsulant to flow into the chamber;
• a pair of blades defining a slot that provides an outlet from which one of solder paste, epoxy, glue and encapsulant can flow out of the chamber;
• each blade being adapted to bend during a print stroke to solely function as a squeegee so as to force one of solder paste, epoxy, glue and encapsulant into the apertures in the stencil;
• a flexible membrane within the chamber, the flexible membrane segregating the chamber into a dispensing region and an activation region, where the print head is configured such that the passage defined by the source port is positioned to direct one of solder paste, epoxy, glue and encapsulant through a passage through the dispensing region and out the slot and on to the stencil to print one of solder paste, epoxy, glue and encapsulant on the electronic substrate;
• and
• a displacement mechanism positioned to displace the flexible membrane to reduce the volume of the dispensing region.