Unisys Corporation

Robert E Rackerby

Jerry Ihor Tustaniwskyj

Steve Joseph Bezuk

Jon Lee Zimmerman

Maria D Alvarez

Patrick A Weber

A method of stretching solder joints between the input/output pads of an electrical component and corresponding input/output pads on a substrate includes the steps of: melting the solder joints; confining the component while the solder joints are melted such that the component can only move substantially perpendicular to the substrate; pulling the component, while the component is confined, by an external force in a direction away from the substrate to thereby stretch the melted solder joints; compelling the movement of the component to stop when the component has moved a predetermined distance; and, solidifying the solder joints while the component is compelled to stop. By stretching the solder joints with the above method, the solder joint shape can be changed from convex to concave; and thermally induced stress/strain in the joint is substantially reduced.

Method of stretching solder joints

A given target temperature profile T is produced in a workpiece as it passes through an elongated passageway of a belt furance by the steps of: (1) determining a set of temperature setting TS.sub.X for the belt furnace thermostats which satisfy an equation f(.alpha.,TS.sub.X,CF.sub.Y).apprxeq.T where .alpha. is a set of thermal parameters for the workpiece, CF.sub.Y is a set of correction factors, and f( ) is a function which approximates the temperature of said workpiece based on TS.sub.X,.alpha., and CF.sub.Y ; (2) measuring an actual temperature profile A(TS.sub.X) of the workpiece in the furnace with the heater thermostats at the settings TS.sub.x ; (3) terminating if the measured actual temperature profile A(TS.sub.X) matches the target temperature profile T within a predetermined tolerance; otherwise, (4) determining a new set of correction factors which satisfies an equation f(.alpha.,TS.sub.X,CF.sub.Y)=A(TS.sub.X); and thereafter repeating the above steps.

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San Diego, CA, United States of America

Robert E Rackerby