Screen printing apparatus and screen printing method

A screen printing apparatus for printing an electronic part joining paste on printing targets as an upper surface printing area which is set on an upper surface of a substrate and on which upper surface electrodes are formed and a bottom surface printing area which is set on a bottom surface of a recess portion which is opened to the upper surface and on which bottom surface electrodes are formed, the screen printing apparatus comprising:

• a screen mask including a bottom surface printing region which has a fitting portion which is provided so as to correspond to the bottom surface printing area and which fits in the recess portion and patterned holes which are formed in the fitting portion so as to correspond to the bottom electrodes and an upper surface printing region which is provided so as to correspond to the upper surface printing area and patterned holes which are formed so as to correspond to the upper surface electrodes;
• a substrate positioning unit which holds a substrate which is transferred from an upstream side and selectively registers the substrate with either the bottom surface printing region or the upper surface printing region;
• and
• a closed type squeegee mechanism which has a pair of facing sliding contact plates which extend downwards from a lower surface side of a main body portion which stores the paste so as to gradually narrow a distance between the facing sliding contact plates as the facing sliding contact plates extend downwards with their facing direction aligned with a squeegeeing direction and which is adapted to slide in the squeegeeing direction with the sliding contact plates brought into abutment with either the bottom surface printing region or an upper surface of the upper surface printing region while pressurizing the paste stored in the main body portion so that the paste is supplied into the fitting portion or is filled in the patterned holes via a printing opening provided between the sliding contact plates, and
• wherein, among the pair of sliding contact plates of the closed type squeegee mechanism, a first sliding contact plate which is positioned at a rear side in a squeegeeing direction in a squeegeeing operation on the bottom surface printing region as a printing target scoops up the paste which remains in an upper surface side depressed portion of the fitting portion so as to remove it from the depressed portion in the squeegeeing operation, while a second sliding contact plate which is positioned at a rear side in a squeegeeing direction in a squeegeeing operation on the upper surface printing region as a printing target scrapes off the paste sticking to the upper surface of an upper surface of the upper surface printing mask in the squeegeeing operation,
• wherein the first sliding contact plate and the second sliding contact plate have different materials and thicknesses with each other,
• wherein a thickness and material of the first sliding contact plate are selected so that the first sliding contact plate is deflected to be deformed by an impression pressure with which the closed type squeegee mechanism is pressed against an upper surface of the bottom surface printing region in the squeegeeing operation and a lower end portion thereof enters the depressed portion by virtue of a spring-back force resulting from the deflected deformation,
• wherein a thickness and material of the second sliding contact plate are selected so that a lower end portion thereof is closely attached to an upper surface of the upper surface printing region by an impression pressure with which the closed type squeegee mechanism is pressed against the upper surface in the squeegeeing operation so as to separate and scrape the sticking paste off the upper surface.