Molded-in isolation bushing for semiconductor devices

Claim 2

A semiconductor device with an integral insulated mounting bushing, comprising: an electrically and thermally conductive base member having a planar first surface for thermal coupling to an external heat sink, a second surface opposite said first surface, and a first aperture penetrating said base member from said first surface to said second surface, wherein said aperture has a first portion adjacent said first surface and a second portion adjacent said second surface, and wherein said first portion is of larger cross-sectional extent than said second portion; and a hollow insulating sleeve fixed within and substantially filling said aperture, having a first end substantially flush with said first surface and of a cross-sectional extent corresponding substantially to said first portion of said aperture, and a second end extending beyond said second surface to form a boss of predetermined height and a cross-sectional extent larger than said first aperture and having a second aperture penetrating said base member, and wherein said second aperture is substantially coaxial with said first aperture.

Claim 3

The semiconductor device of claim 1 wherein said first and second apertures are substantially cylindrical, wherein said second portion of said first aperture has a predetermined first internal radius, and wherein said sleeve has a second internal radius corresponding to said second aperture, a first external radius at said first end, a second external radius of said boss, and a third external radius corresponding substantially to said first internal radius of said second portion of said first aperture, and wherein said height of said boss is not less than a predetermined surface flash-over distance, and wherein said first and second external radii exceed said third external radii, and wherein said third external radius differs from said second internal radius by at least a predetermined bulk breakdown distance.

Claim 4

The semiconductor device of claim 2 wherein said first external radius differs from said second internal radius by not less than said predetermined flash-over distance.

Claim 5

The semiconductor device of claim 1 or 3 wherein said sleeve is bonded to said conductive base member and said first surface has an insulating layer bonded thereto.

Claim 6

The semiconductor device of claim 4 wherein said semiconductor device comprises a semiconductor chip enclosed by an encapsulation of molded plastic, and wherein said insulating sleeve is molded in said aperture from said plastic substantially simultaneously with said encapsulation.

Claim 7

The semiconductor device of claim 5 wherein said insulating sleeve and said encapsulation are separated so as to avoid transfer of mounting stresses through said plastic material from said insulating sleeve to said semiconductor device.

Claim 8

The semiconductor device of claim 6 wherein said first end of said sleeve is recessed from said first surface a predetermined relief distance.

Claim 9

A plastic encapsulated semiconductor device with insulated mounting means, adapted for mounting to an external heat sink by means of an electrically conductive fastener, comprising: a metallic base having a substantially cylindrical first through-hole of a first radius penetrating said base from a first planar surface of said base adapted for thermally contacting said heat sink to a second surface of said base opposed to said first surface, wherein said first through-hole is chamfered to a predetermined depth adjacent to said first surface so as to have a larger second radius at said first surface of said base; a semiconductor die coupled to said base; external leads coupled to said semiconductor die; an insulating plastic encapsulation molded around said semiconductor die; and an insulating plastic bushing molded with but separated from said encapsulation, substantially filling said first through-hole so as not to protrude beyond said first surface, and having a centrally located second through-hole substantially coaxial with said first through-hole and of a third radius smaller than said first radius, and having a flange on said second surface of a fourth radius larger than said first radius.

Claim 10

A plastic encapsulated semiconductor device with insulated mounting means, adapted for mounting to an external heat sink by means of an electrically conductive fastener, comprising: a metallic base having a substantially cylindrical first through-hole of a first radius penetrating said base from a first planar surface of said base adapted for thermally contacting said heat sink to a second surface of said base opposed to said first surface, wherein said first through-hole is chamfered to a predetermined depth adjacent to said first surface so as to have a larger second radius at said first surface of said base; a semiconductor die coupled to said base; external leads coupled to said semiconductor die; an insulating plastic encapsulation molded around said semiconductor die; and an insulating plastic bushing molded with but separated from said encapsulation, substantially filling said first through-hole so as not to protrude beyond said first surface, and having a centrally located second through-hole substantially coaxial with said first through-hole and of a third radius smaller than said first radius, and having a flange on said second surface of a fourth radius larger than said first radius.

Claim 11

The device of claim 7 wherein said flange has a first height above said second surface not less than a predetermined surface flash-over distance, and wherein the difference between said second and third radii is not less than said surface flash-over distance.

Claim 12

The device of claim 8 wherein said plastic bushing is received below said first surface for a distance less than said depth of said chamfer.