A printer includes a print head for dispensing viscous material, such as solder paste. The print head defines a chamber and includes at least one source port and a dispensing slot. Within the chamber, a flexible membrane segregates the chamber into a dispensing region and an activation region. Viscous material flows from a supply mounted to the source port, into the dispensing region and out the slot. A displacement mechanism is positioned to displace the flexible membrane to reduce the volume of dispensing region and to thereby dispense viscous material through the slot. The print head also includes a removable envelope through which the viscous material flows and contacts as it passes through the envelope.