International Business Machines Corporation

Motorola Corporation

Julian P Partridge

Karl G Hoebener

Eric M Hubacher

Charles H Crockett, Jr

Ku Ho Chong

Bhavyen S Sanghavi

Chengjun Julian Chen

Issa S Mahmoud

Richard Ian Kaufman

A product created through the reflow of low melting point solder on select contacts of a printed circuit board. In one form, the printed circuit board has fine pitch devices, including flip-chip integrated circuits, connected to a board having conventional coarse pitch surface. 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, 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. The fine contact pitch and coarse contact pitch differ by nominal factor of two or more.

Print circuit board product with stencil controlled fine pitch solder

A method, and product created thereby, by which low melting point solder suitable for reflow connection of components is formed on select fine pitch contacts of a printed circuit board. The method is particularly suited to the attachment of flip-chip die to printed circuit boards which also include coarse pitch surface mount components. Controlled volumes of solder are formed onto fine pitch contacts of the printed circuit board through selective holes in a mask formed onto the board. The deposit is accomplished by molten solder immersion preferably using conventional hot air solder level manufacturing equipment. The volume of solder is related to the thickness of the mask. The mask is then removed, the deposited low temperature solder is flattened, and the coarse pitch contacts are covered with solder paste in a conventional screening process. Flux is applied to the fine pitch contacts. After component placement, the solder reflow connects in one operation both the fine and coarse pitch components to their respective printed circuit board contacts.

Fine pitch solder formation on printed circuit board process and product

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.

Fine pitch solder deposits on printed circuit board process and product

A fusible conductive adhesive for making electrical and mechanical contact is provided. The fusible conductive adhesive contains a polymer having a glass transition temperature and a thermal expansion co-efficient. The thermal expansion co-efficient of the polymer is in the range of about 5 parts per million per degree centigrade to about 10 parts per million per degree centigrade along a z-axis. The polymer is loaded with a conductive material having a sintering temperature range overlapping the glass transition temperature of the polymer. In addition, the loading of the conductive material in the polymer is in the range of about 15% to about 20% conductive material by weight based on the total weight of the polymer and the conductive material.

Method and composition for making mechanical and electrical contact

An apparatus and method for plating metal on a conductor and/or across gaps on insulating substrates is described incorporating two probes, a probe positioner, first circuitry for applying alternating-current electrical power wherein the magnitude of the voltage is controlled as a function of time, and second circuitry for applying alternating-current electrical power wherein the magnitude of the current is controlled as a function of time. The invention overcomes the problem of providing an automatic apparatus for reliably repairing defective wiring or completing seeded sections of wiring having a wide range of initial thermal and electrical characteristics.

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Austin, TX, United States of America

Julian P Partridge