Patent Application
20160379953
High voltage circuits are being manufactured smaller and are required to operate at higher voltages. The smaller circuits cause conductors of different potentials to be located proximate each other. The close proximity of conductors of different potentials combined with the higher voltages increases the voltage gradients between the conductors. The higher voltage gradients degrade the device performance.
Circuitry is disclosed that includes a conductive portion of a die and a conductive pillar electrically and physically connected to the conductive portion. The conductive pillar includes a conductive pillar surface. A bond connects the conductive pillar surface to an end of a bond wire.
The bond wire 102 is bonded to the first pad 106 by way of a ball bond 130. The ball bond 130 enables an end portion 132 of the bond wire 102 next to the ball bond 130 to have a steep angle. The steep angle causes the end portion 132 of the bond wire 102 to intersect the ball bond 130 substantially perpendicular relative to the surface 134 of the first die 110. The steep angle enables the portion of the bond wire 102 extending over the first die 110 to be located a distance 140 from the surface of the dielectric material 117, wherein the distance 140 is relatively large. The bond wire 102 is bonded to the second pad 108 by way of a stitch bond 142. In many fabrication applications, one end of a bond wire is bonded by way of a ball bond and the other end is bonded by way of a stitch bond. The stitch bond 142 does not provide for the steep angle in an end 146 of the bond Wire 102 as provided by the ball bond 130 because a steep angle at the stitch bond 142 may lead to failure of the stitch bond 142. Accordingly, the distance 148 between the second die 112 and the bond wire 102 is relatively small and the portion of the bond wire 102 located over the second die 112 is relatively close to the second die 112.
The stitch bond 142 shown in
Device geometries, such as those in the circuitry 100, are becoming smaller and operating at higher voltages. The smaller devices cause the bond wire 102 to be located closer to critical areas of the first die 110 and the second die 112, which puts the bond wire 102 in close proximity to conductors (not shown) on or in the first and second dies 110 and 112. The higher voltage in the circuitry 100 causes higher voltage gradients between the bond wire 102 and the first and second dies 110 and 112. The voltage gradients become even higher as the distances 140 and 148 become smaller and the circuitry 100 is made smaller. The combination of the higher voltages and the smaller distances 140 and 148 results in higher voltage gradients between the bond wire 102 and the first and second dies 110 and 112. These higher voltage gradients degrade the performance of the circuitry 100. For example, the high voltage gradients cause shorts and/or arcs through an encapsulant material (not shown) between the bond wire 102 and conductors (not shown) located in the first and second dies 110 and 112.
The circuitry and methods described herein overcome the above-described problems with high voltage gradients by the addition of pillars that raise the bond wire higher over conductors located in or on circuits proximate the bond wire. The raised bond Wile is further from conductors on and in the dies, so the circuitry can withstand higher voltages. Reference is made to
The first circuit 204 has a first dielectric material 226 applied to the surface 212 of the first die 208 and the second circuit 206 has a second dielectric material 228 applied to the surface 224 of the second die 220. A first conductive pillar 230 is fabricated onto the first pad 210 and a second conductive pillar 240 is fabricated onto the second pad 222. The first and second conductive pillars 230 and 240 may extend onto the first and second dielectric materials 226 and 228 such that they are wider than their respective first and second conductive pads 210 and 222. For example, the first conductive pillar 230 has a top surface 244 that has an area that may be greater than the area of the conductive pad 210. Likewise, the second conductive pillar 240 has a top surface 246 that has an area that may be greater than the area of the second conductive pad 222. Accordingly, small conductive pads 210 and 222 conduct between the pillars 230 and 240 and the dies 208 and 220, wherein the pillar surfaces 244 and 246 are large. These smaller conductive pads 210 and 222 decrease the capacitances to underlying circuitry and enable more room for conductors to be routed. The pillars 230 and 240 further enable the conductive pads 210 and 222 to be located close to the edges of the dies 204 and 206. For example, the larger surfaces 244 and 246 enable the bonds attached thereto to be located close to the edges of the dies 208 and 220. In some examples, the diameter of the pillars 230 and 240 narrows proximate the dielectric materials 226 and 228 so that the openings in the dielectric materials 226 and 228 are larger than the diameters of the pillars 230 and 240 in those locations.
The stitch bond 404 results in a low angle a between the bond wire 202 and the surface 246 of the second pillar 240. Therefore, without the additional height provided by the second pillar 240, the height 408 would be low, which results in the bond wire 202 being in close proximity to the die 220 and/or conductors (not shown) located on or in the die 220. The low height creates a high voltage gradient between the bond wire 202 and the conductors on the surface 224 or within the die 220, which eventually may cause degradation in the performance of the die 220 and/or the circuitry 200. It is noted that the distance between the first and second dies 208 and 220 and the bond wire 202 has increased in all locations, not just where the heights 308 and 408 are shown. Therefore, the additional height provided by the first and second pillars 230 and 240 increases the distance between the bond wire 202 and all the conductors in and on the first and second dies 208 and 220. Furthermore, no stitch on ball bond (SBB) is required because the pillars 230 and 240 provide the additional height of the SBB or greater height than provided by the SBB. The pillars 230 and 240 also provide a more robust target for the stitch bonds which improves the yields of the bonds. Both the elimination of the SSB and the higher yields reduce the costs of the dies.
The pillars 230 and 240 may be fabricated from virtually any conductive material, such as copper, nickel, gold, and aluminum. In some embodiments, the pillars 230 and 240 are fabricated by an electroplating process. In some embodiments, the first and second pillars 230 and 240 are fabricated directly onto the first and second dies 208 and 220 and not on the first and second conductive pads 210 and 222. For example, the first and second pillars 230 and 240 may be fabricated on other conductive portions of the first and second dies 208 and 220. The pads 210 and 222 have been described herein as being conductive pads or bonding pads on the surfaces of dies. In some embodiments, the pads 210 and 222 are plates of capacitors, such as galvanic isolators. Accordingly, the pillars 230 and 240 are fabricated onto the plates of the capacitors.
The bond wire 202 may be formed into a bent profile before bonding that causes it to rise, especially proximate the stitch bond 404 so as to provide maximum heights 308 and 408. Referring to
A method for fabricating the circuit 200 is described by the flow chart 500 of
Certain embodiments of dies and die fabrication methods have been expressly described in detail herein. Alternative embodiments will occur to those skilled in the art after reading this disclosure. The claims are intended to be broadly construed to cover all such alternative embodiments, except as limited by the prior art.
