Magnetic alignment for semiconductor device bonding

Claim 1

A self-aligning method of automatically transferring integrally leaded semiconductor device chips to a conductive lead frame structure for permanently bonding thereto, said method comprising: placing a semiconductor device chip having a face with a plurality of soft ferromagnetic integral leads thereon on a soft ferromagnetic support so that said chip face is oriented upwardly, positioning the support so that said chip is in closely spaced relation under an overlying conductive lead frame having a soft ferromagnetic convergent cantilevered finger set that has free ends corresponding to said integral leads on said chip, with said integral leads being in close proximity with said corresponding finger free ends, applying a magnetic field generally perpendicularly to said chip and said finger set to precisely align said integral chip leads with corresponding finger free ends and to concurrently magnetically raise said chip from said support up to said finger free ends to produce a uniform intimate engagement between all of said integral chip leads and their corresponding finger free ends, and bonding said integral chip leads to said finger free ends.

Claim 3

A method of producing a uniform low stress bond between an integrally leaded semiconductor chip and fingers of a conductive lead frame including magnetically transferring said chip to the fingers so that the integral leads on the chip are automatically precisely aligned with the lead frame fingers, said method comprising: placing a semiconductor chip having a plurality of soft ferromagnetic integral leads on one face thereof onto a soft ferromagnetic support so that said face is oriented upwardly, positioning said support so that said chip is in spaced relation with an overlying set of soft ferromagnetic lead frame fingers having free ends corresponding to said integral leads on said flip chip, said chip being positioned so that said integral chip leads are in close proximity with said lead frame fingers, applying a magnetic force through said support and generally perpendicular to the underside of said chip and said finger set to precisely align said integral chip leads with said lead frame finger free ends, and to concurrently magnetically raise said chip to said set of lead frame finger free ends to produce a uniform intimate engagement between all of said chip integral leads and their corresponding fingers of said lead frame without significantly stressing any of said fingers, maintaining said low stress aligned engagement between the lead frame fingers and said integral chip leads, heating said integral chip leads and said fingers in engagement therewith to permanently bond said chip to said lead frame finger set, and tErminating application of said magnetic field to said finger set and said chip.

Claim 4

A method of producing a uniform low stress bond between an integrally leaded semiconductor chip and fingers of a conductive lead frame including magnetically transferring said chip to the fingers so that the integral leads on the chip are automatically precisely aligned with the lead frame fingers, said method comprising: placing a semiconductor chip having a plurality of soft ferromagnetic integral leads on one face thereof onto a soft ferromagnetic support so that said face is oriented upwardly, positioning said support so that said chip is in spaced relation with an overlying set of soft ferromagnetic lead frame fingers having free ends corresponding to said integral leads on said flip chip, said chip being positioned so that said integral chip leads are in close proximity with said lead frame fingers, applying a magnetic force through said support and generally perpendicular to the underside of said chip and said finger set to precisely align said integral chip leads with said lead frame finger free ends, and to concurrently magnetically raise said chip to said set of lead frame finger free ends to produce a uniform intimate engagement between all of said chip integral leads and their corresponding fingers of said lead frame without significantly stressing any of said fingers, maintaining said low stress aligned engagement between the lead frame fingers and said integral chip leads, heating said integral chip leads and said fingers in engagement therewith to permanently bond said chip to said lead frame finger set, and tErminating application of said magnetic field to said finger set and said chip.

Claim 5

A method of bonding semiconductor flip chips to conductive lead frame structures including magnetically transferring and concurrently orienting said flip chip so that contact bumps on the chip are automatically precisely aligned with corresponding fingers of said lead frame upon engagement therewith and for producing a uniform low stress intimate bond therebetween, said method comprising: placing a back side face of a semiconductor flip chip having soft ferromagnetic tin and gold-plated contact bumps on an opposite face thereof onto one end of a probe, said contact bumps having a nickel content of at least 30 percent by volume of the total contact bump volume, said probe being constructed of a soft ferromagnetic material having a low magnetic reluctance so as to easily pass magnetic lines of flux therethrough and concentrate the flux lines in the area of said contact bumps, applying a magnetic field to the opposite end of said probe so that magnetic lines of flux flow longitudinally through said probe and generally perpendicularly into said contact bumps of the flip chip thereon, positioning the probe with said flip chip thereon so that said contact bumps are within 2-8 mils of an overlying set of gold-plated soft ferromagnetic fingers of a lead frame having free ends corresponding to said contact bumps, raising said flip chip with the magnetic force from said probe onto said lead frame fingers and concurrently automatically orienting said flip chip while in transit thereto so that said contact bumps are precisely aligned with their corresponding finger free ends upon engagement therewith, said contact bumps being so engaged with said fingers without significantly stressing said fingers, holding the flip chip bumps in aligned engagement with said lead frame fingers with said magnetic force while said fingers are in their low stress condition, applying a hot gas to said contact bumps and said fingers in engagement therewith to form a melt of the tin and gold outer surfaces thereon, removing said heat to solidify said melt and permanently bond said chip to the lead frame, and terminating application of said magnetic field.

Claim 6

A method of bonding semiconductor flip chips to conductive lead frame structures including magnetically transferring and concurrently orienting said flip chip so that contact bumps on the chip are automatically precisely aligned with corresponding fingers of said lead frame upon engagement therewith and for producing a uniform low stress intimate bond therebetween, said method comprising: placing a back side face of a semiconductor flip chip having soft ferromagnetic tin and gold-plated contact bumps on an opposite face thereof onto one end of a probe, said contact bumps having a nickel content of at least 30 percent by volume of the total contact bump volume, said probe being constructed of a soft ferromagnetic material having a low magnetic reluctance so as to easily pass magnetic lines of flux therethrough and concentrate the flux lines in the area of said contact bumps, applying a magnetic field to the opposite end of said probe so that magnetic lines of flux flow longitudinally through said probe and generally perpendicularly into said contact bumps of the flip chip thereon, positioning the probe with said flip chip thereon so that said contact bumps are within 2-8 mils of an overlying set of gold-plated soft ferromagnetic fingers of a lead frame having free ends corresponding to said contact bumps, raising said flip chip with the magnetic force from said probe onto said lead frame fingers and concurrently automatically orienting said flip chip while in transit thereto so that said contact bumps are precisely aligned with their corresponding finger free ends upon engagement therewith, said contact bumps being so engaged with said fingers without significantly stressing said fingers, holding the flip chip bumps in aligned engagement with said lead frame fingers with said magnetic force while said fingers are in their low stress condition, applying a hot gas to said contact bumps and said fingers in engagement therewith to form a melt of the tin and gold outer surfaces thereon, removing said heat to solidify said melt and permanently bond said chip to the lead frame, and terminating application of said magnetic field.