Fujitsu Corporation

Theresa M Larson

Michael G Lee

Albert Wong Chan

A method of depositing solder on a conductive region of a substrate comprising providing a substrate having a substrate aperture and a coefficient of thermal expansion. A polymeric stencil is also provided such as to have a stencil aperture and a coefficient of thermal expansion which is approximately equal to the coefficient of thermal expansion of the substrate. The method also includes disposing the polymeric stencil on the substrate such that the stencil aperture is aligned with a conductive region; and reflowing the solder paste while the polymeric stencil remains disposed on the substrate. The polymeric stencil is then removed from the substrate essentially without any solder-paste being removed with the polymeric stencil. A method of forming a polymeric stencil for solder-paste printing comprising forming in a polymeric sheet of plurality of apertures having wrinkles in the polymeric sheet in proximity to the plurality of apertures, and compressing opposing surfaces of the apertured polymeric sheet toward each other. The compressed apertured polymeric sheet is then heated and rapidly cooled to remove wrinkles in proximity to the apertures. A stencil for use in a fine pitch bumping process comprising a releasable polymeric sheet having a coefficient of thermal expansion of less than about 4.0 ppm/&deg;C. and a structure defining a pair of apertures spaced from each other at a distance less than about 0.20 mm.

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Hayward, CA, United States of America

Theresa M Larson