International Business Machines Corporation

Barbara L Gutierrez

Janet M Sickler

Cheng-Yuan Yu

An easily reworkable circuit module is provided that allows unusable electronic components that have been encapsulated to be removed from a printed circuit board. A chip or MCM attached to a carrier using direct chip attach methods (DCA), such as C4 or SBC techniques that leave a space between the chip/MCM and carrier, due to the height of the solder balls, connection pads and the like. The present invention places a non-stick release coating on all surfaces intermediate of the chip and carrier. That is, the release coating of the present invention is placed by spraying, or the like between the chip and carrier to form a thin liquid film which inhibits the adhesion of a subsequently applied and cured rigid polymer encapsulant. Thus, when a chip or MCM tests as 'bad', rework is a relatively simple matter. The solder connections between the chip and carrier of the module are reflowed and the chip is lifted off. The solder reflow temperature will be below the melting point of the encapsulant, and since the encapsulant did not stick to the chip or carrier, it can be merely wiped away with a dry cloth.

Component rework

A no-clean, thermally dissipated soldering flux is shown which includes hydroabietal alcohol as a flux base, an organic activator and an organic diluent. The hydroabietal alcohol provides a tacky medium which holds a precisely aligned chip in place both during placement and reflow. The nature of the formula renders a reducing atmosphere unnecessary. The composition is thermally dissipated during soldering and leaves no undesirable residue which would require a post-cleaning step.

Tacky, no-clean thermally dissipated soldering flux

Water soluble soldering preflux compositions are shown which include gum arabic, modified polysaccharides and other natural resins as a carrier, an oxidation inhibitor and water. The compositions are useful in the assembly of precisely aligned electrical components during multiple step, electronic card assembly techniques. Use of the preflux compositions according to the method of the invention permits a flexible, site-specific method for joining electronic components to a printed circuit board with a fewer number of steps.

Water soluble soldering preflux and method of application

A water soluble soldering flux is shown which includes gum arabic, modified polysaccharides and other natural resins as the carrier, an organic activator and water. The carrier provides a tacky, yet fluid medium capable of holding precisely aligned electrical components during solder reflow and allows aqueous removal of the flux after reflow. The flux composition can be used to solder precisely aligned integrated circuit chips onto a circuit board.

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Austin, TX, United States of America

Barbara L Gutierrez