The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Feb. 20, 1996
Filed:
Aug. 31, 1994
Karl G Hoebener, Georgetown, TX (US);
Eric M Hubacher, Austin, TX (US);
Julian P Partridge, Austin, TX (US);
International Business Machines Corporation, Armonk, NY (US);
Abstract
A method, and product created thereby, by which low melting point solder suitable for reflow connection of components is formed on select contacts of a printed circuit board. The method is particularly suited to the fabrication of populated printed circuit board having fine pitch devices including flip-chip devices, connected on a board including conventional coarse pitch surface mounted components. The fine pitch contacts of the board are exposed through holes in a stencil characterized in its ability to withstand solder reflow temperatures, not be wettable by solder, and have a coefficient of thermal expansion relatively matching the printed circuit board. Low temperature solder paste is screen deposited into the stencil openings. With the stencil fixedly positioned on the board, the solder paste retained by the stencil pattern is reflowed to selectively form on the underlying contacts of the printed circuit board. Thereafter, according to a preferred practice of the invention, the stencil is removed from the board and the board is subject to previously practiced depositions of flux and paste in preparation for fine and coarse pitch component placement and ensuing solder reflow. Alternate practices of the invention involve concurrent deposition of fine and coarse pitch solder and retention of the stencil following fine pitch solder fellow.