Selective wire coating during wire bonding
A semiconductor device wherein a selected subset of bond wires is coated with an electrically insulating polymer to reduce occurrences of electrical shorts caused by wire sweep in the flow of a molding compound during an encapsulation stage of the manufacturing process. In some examples, the bond wires to be coated are selected based on a set of criteria that flag the bond wires exhibiting a relatively high tendency towards forming such electrical shorts. A specialized wire-bonding tool that can be operated to produce both polymer-coated bond wires and bare bond wires is also provided.
1 . A method for assembling a semiconductor device, the method comprising:
bonding segments of a bond wire between a vertical stack of semiconductor dies and a first main surface of a substrate, the segments of the bond wire providing electrical connections between the semiconductor dies and the substrate, the vertical stack being supported on the first main surface of the substrate and having the semiconductor dies thereof horizontally offset with respect to one another;
coating, with a wire bonding tool during the bonding, a selected subset of the segments of the bond wire with an electrically insulating polymer; and
encapsulating, with a molding compound, the vertical stack of semiconductor dies, the bonded segments of the bond wire attached between the vertical stack of semiconductor dies and the first main surface of the substrate, and at least a portion of the first main surface of the substrate.
2 . The method of claim 1 , further comprising selecting said selected subset of the segments of the bond wire based on one or more selection criteria from the group consisting of:
a set of criteria specifying a relationship between a segment length, a wire diameter, and a direction of the bonding;
an orientation angle of a corresponding bond wire in the semiconductor device with respect to a flow direction of the molding compound during the encapsulating;
a loop height of the corresponding bond wire in the semiconductor device with respect to the first main surface of the substrate; and
a bond-wire pitch in a corresponding part of the semiconductor device.
3 . The method of claim 1 , further comprising attaching a plurality of solder balls to the second main surface of the substrate.
4 . A semiconductor device, comprising:
a substrate having a first main surface and an opposing second main surface;
one or more semiconductor dies attached to the first main surface;
a plurality of bond wires electrically connecting at least one of the one or more semiconductor dies to the first main surface of the substrate, wherein a first bond wire of the plurality of bond wires includes a polymer-coated segment, and wherein a second bond wire of the plurality of bond wire is uncoated with a polymer; and
a molding compound encapsulating the one or more semiconductor dies, the plurality of bond wires, and at least a portion of the first main surface of the substrate.
5 . The semiconductor device of claim 4 , further comprising a plurality of solder balls attached to the second main surface of the substrate.
6 . The semiconductor device of claim 4 ,
wherein the first bond wire and the second bond wire are in physical contact with one another; and
wherein the polymer-coated segment is in an area of the physical contact.
7 . The semiconductor device of claim 6 ,
wherein the first bond wire has a first loop height; and
wherein the second bond wire has a second loop height different from the first loop height.
8 . The semiconductor device of claim 6 ,
wherein the first bond wire is connected between a first contact pad located on a first one of the semiconductor dies and a second contact pad located on the first main surface of the substrate; and
wherein the second bond wire is connected between a third contact pad located on one of the semiconductor dies and a fourth contact pad located on the first main surface of the substrate.
9 . The semiconductor device of claim 6 ,
wherein the first bond wire is connected between a first contact pad located on a first semiconductor die of the one or more semiconductor dies and a second contact pad located on the first main surface of the substrate; and
wherein the second bond wire is connected between a third contact pad located on the first semiconductor die and a fourth contact pad located on the first main surface of the substrate.
10 . The semiconductor device of claim 6 , wherein the first bond wire and the second bond wire have different respective loop shapes.
11 . The semiconductor device of claim 6 , wherein the first bond wire and the second bond wire have different respective lengths.
12 . The semiconductor device of claim 6 ,
wherein the plurality of bond wires includes a third bond wire and a fourth bond wire in another physical contact with one another; and
wherein at least one of the third bond wire and the fourth bond wire has another polymer coat in an area of said another physical contact.
13 . The semiconductor device of claim 4 , wherein a polymer coat of the polymer-coated segment comprises a thermosetting polymer.
14 . The semiconductor device of claim 4 , wherein a polymer coat of the polymer-coated segment comprises a polyimide.
15 . The semiconductor device of claim 4 ,
wherein a polymer coat of the polymer-coated segment comprises a first dielectric material; and
wherein the molding compound comprises a different second dielectric material.
16 . The semiconductor device of claim 4 , wherein the semiconductor dies are arranged in a vertical stack attached to the first main surface and are horizontally offset with respect to one another.