Electrical interconnect structure with radial spokes for improved solder void control

Abstract

An electrical interconnect structure includes a bond pad having a substantially planar bonding surface, and a solder enhancement structure disposed on the bonding surface and including a plurality of raised spokes each elevated from the bonding surface. Each of the raised spokes has a lower wettability relative to liquefied solder material than the bonding surface. Each of the raised spokes extends radially outward from a center of the solder enhancement structure.

Description

Background Technology

[0001] Solder is commonly used in electronic products to form electrical connections between two components (e.g., wires, bonding pads, etc.). In semiconductor applications, solder is used to mechanically couple and electrically connect the conductive bonding pads of a semiconductor die to external components. For example, a semiconductor die may be mounted in a flip-chip arrangement, in which the terminals of the semiconductor die are soldered to a carrier (e.g., leadframe, PCB (printed circuit board), etc.). In another example, the semiconductor die may have terminals facing away from the carrier, and these terminals may be soldered to metal clips, bonding wires, strips, etc. In either case, the solder joint is formed through thermal cycling, in which the solder material is heated, liquefied, and hardened. Modern semiconductor processing techniques involve the parallel formation of many small-perimeter solder joints. In some cases, gases may be trapped in the solder material during the formation of the solder joint. These gases may originate from ambient air or may be products of chemical reactions within the solder material. In either case, these gases may be trapped in the solder material, thus creating voids in the completed solder joint. This can cause performance and reliability issues, for example, in high-density and small-footprint solder joints. Summary of the Invention

[0002] An electrical interconnect structure is disclosed. According to an embodiment, the electrical interconnect structure includes: a bonding pad including a substantially planar bonding surface; and a solder reinforcement structure disposed on the bonding surface and including a plurality of raised spokes, each of which rises from the bonding surface and has a lower wettability relative to a liquefied solder material than the bonding surface. Each of the raised spokes extends radially outward from the center of the solder reinforcement structure.

[0003] Independently or in combination, each of the plurality of raised spokes includes an upper surface and a side surface extending perpendicularly from the mating surface to the upper surface, the plurality of raised spokes including a first raised spoke and a second raised spoke, and the side surface of the first raised spoke is offset from the side surface of the second raised spoke facing the first raised spoke by at least 90 degrees.

[0004] Independently or in combination, the plurality of raised spokes includes a third raised spoke, and the side surface of the third raised spoke is offset from the side surface of the second raised spoke facing the third raised spoke by at least 90 degrees.

[0005] Independently or in combination, the plurality of raised spokes also include a third raised spoke and a fourth raised spoke, and the side surface of each of the first raised spoke, the second raised spoke, the third raised spoke and the fourth raised spoke is separated from the side surface of the adjacent raised spoke of the first raised spoke, the second raised spoke, the third raised spoke and the fourth raised spoke by at least 60 degrees.

[0006] Independently or in combination, the center of the solder reinforcement structure is a region that rises from the mating surface and is continuously connected to each of the raised spokes.

[0007] Individually or in combination, each of the raised spokes has a substantially uniform width along the length of the raised spoke, which extends from the center of the solder reinforcement structure to the outer end of the raised spoke.

[0008] Individually or in combination, each of the raised spokes tapers inward from the center of the solder reinforcement structure to the outer end of the raised spoke.

[0009] Independently or in combination, the center of the solder reinforcement structure is the area between the raised spokes on the mating surface.

[0010] Individually or in combination, each of the raised spokes is arranged in a spiral pattern relative to the center of the solder reinforcement structure.

[0011] Independently or in combination, the wettability of each of the raised spokes and the mating surface is such that the contact angle of the liquefied solder material on the outer surface of each of the raised spokes is at least 10 degrees greater than the contact angle of the liquefied solder material on the mating surface.

[0012] Independently or in combination, the mating surface is a copper surface, and the outer surface of each of the raised spokes is a silver surface.

[0013] Independently or in combination, the electrical interconnect structure is a lead frame, and the mating surface is the die attachment surface of the lead frame.

[0014] Independently or in combination, the electrical interconnect structure is a metal interconnect clip, wherein the mating surface is the die attachment surface or lead attachment surface of the metal interconnect clip.

[0015] According to another embodiment, the electrical interconnect structure includes: a bonding pad including a substantially planar bonding surface; and a solder reinforcement structure disposed on the bonding surface and including a plurality of raised spokes, each of the plurality of raised spokes rising from the bonding surface. Each of the plurality of raised spokes includes an upper surface and a side surface extending from the bonding surface to the upper surface. The plurality of raised spokes includes a first raised spoke, the first raised spoke being configured to form a first gas channel along the side surface of the first raised spoke when the solder reinforcement structure is covered by liquefied solder material. The plurality of raised spokes includes a second raised spoke, the second raised spoke being configured to form a second gas channel along the side surface of the second raised spoke when the solder reinforcement structure is covered by liquefied solder material, and the first gas channel and the second gas channel are separated from each other by at least 90 degrees.

[0016] Independently or in combination, the plurality of raised spokes includes a third raised spoke and a fourth raised spoke, the third raised spoke being configured to form a third gas channel along its side surface when the solder reinforcement structure is covered by liquefied solder material, and the fourth raised spoke being configured to form a fourth gas channel along its side surface when the solder reinforcement structure is covered by liquefied solder material, wherein the first, second, third, and fourth raised spokes are arranged such that each of the first, second, third, and fourth gas channels is separated from the adjacent gas channel of the first, second, third, and fourth gas channels by at least 60 degrees.

[0017] Independently or in combination, the first raised spoke and the second raised spoke are configured to form the first gas channel and the second gas channel respectively by means of the difference in wettability of the liquefied solder material between the outer surface of each of the first raised spoke and the mating surface.

[0018] A method for forming electrical connections in a semiconductor device is disclosed. According to an embodiment, the method includes: providing a semiconductor die including conductive bonding pads; providing an interconnect structure including a substantially planar and conductive bonding surface and a solder reinforcement structure disposed on the bonding surface and including a plurality of raised spokes, each of the plurality of raised spokes rising from the bonding surface; covering the solder reinforcement structure with a solder material; arranging the semiconductor die such that the bonding pads contact the solder material; and performing a thermal cycle including a reflow phase in which the solder material becomes liquefied. Each of the raised spokes has a lower wettability than the bonding surface, relative to the liquefied solder material. The lower wettability of the raised spokes allows gas channels to form along the side surfaces of the raised spokes during the reflow phase.

[0019] Independently or in combination, during the reflow phase, a meniscus is formed at the transition between the mating surface and the interconnecting structure, and a gas channel is formed between the side surface of the raised spokes and the meniscus.

[0020] Independently or in combination, the plurality of raised spokes includes at least three raised spokes, each of which extends radially outward from the center of the solder reinforcement structure, and a gas channel draws gas away from the center of the solder reinforcement structure during the reflow phase.

[0021] Those skilled in the art will recognize additional features and advantages upon reading the following detailed description and viewing the accompanying drawings. Attached Figure Description

[0022] The elements in the accompanying drawings are not necessarily proportional to each other. Similar reference numerals indicate corresponding similar parts. Features in the various illustrated embodiments can be combined unless they are mutually exclusive. Embodiments are depicted in the accompanying drawings and described in detail below.

[0023] Figure 1 A semiconductor die mounted on a lead frame in a flip-chip arrangement according to an embodiment is shown.

[0024] Figure 2 A semiconductor die mounted on a lead frame according to an embodiment is shown, the lead frame having a metal interconnect clip that electrically connects the semiconductor die to leads.

[0025] Figure 3 An interconnect structure with a bonding surface having a solder-reinforced structure is shown according to an embodiment.

[0026] Figure 4 An interconnect structure with a bonding surface having a solder reinforcement structure covered by a liquefied solder material is shown according to an embodiment.

[0027] Figure 5 The diagram illustrates the directional flow of gas in a channel formed along the side surface of the raised spokes of the solder reinforcement structure during solder reflow, according to an embodiment.

[0028] include Figure 6 A, Figure 6 B Figure 6 C Figure 6 D and Figure 6 E's Figure 6 Various geometries of the solder reinforcement structure according to embodiments are shown.

[0029] Figure 7 A solder-reinforced structure according to an embodiment is shown. Detailed Implementation

[0030] According to the embodiments described herein, the interconnect structure includes a solder reinforcement structure that advantageously improves the performance and reliability of the solder connection between the planar joint surface of the interconnect structure and external components. The solder reinforcement structure includes a plurality of raised spokes that rise from the planar joint surface of the interconnect structure. The raised spokes are configured to form gas channels in the solder material during the reflow phase of soldering. The gas channels appear between the side surfaces of the spokes and the meniscus in the reflowed (i.e., liquefied) solder material. The meniscus, and thus the gas channels, are caused by the difference in wettability between the raised spokes and the joint surface of the interconnect structure relative to the solder material. The gas channels provide a conduit for gas to escape from the solder material during the reflow phase. The raised spokes are arranged in a radial pattern, which causes the gas channels to extend radially outward from the center of the solder reinforcement structure. This promotes effective venting of the solder material by drawing gas away from the center of the solder joint and towards the outside of the solder where gas can escape. This venting of the solder reduces the likelihood of voids or cavitation in the finished solder joint. As a result, the completed solder joint has low resistance and high mechanical strength.

[0031] refer to Figure 1This paper depicts a lead frame assembly for semiconductor packaging according to an embodiment. The lead frame assembly includes a die pad 100 and a first lead 102 spaced apart from the die pad 100. The die pad 100 and the first lead 102 are conductive structures. Exemplary materials for the die pad 100 and the first lead 102 include conductive metals, such as copper, aluminum, and alloys thereof. The die pad 100 and the first lead 102 may be part of a common lead frame structure. Both the die pad 100 and the first lead 102 include a die attachment surface 104. Each die attachment surface 104 is a substantially planar mating surface configured to mate with a terminal of a semiconductor die to form an electrical connection between them. Optionally, the die attachment surface 104 on the die pad 100 and / or the first lead 102 may have a slight bend (e.g., a protruding or recessed shape) designed to collect solder material.

[0032] The leadframe assembly additionally includes a semiconductor die 106. The semiconductor die 106 includes a first bonding pad 108 and a second bonding pad 110 disposed on its main surface. The first bonding pad 108 and the second bonding pad 110 are conductive terminals (e.g., gate, source, drain, etc.) of the semiconductor die 106. According to an embodiment, the semiconductor die 106 is a discrete MOSFET device, the first bonding pad 108 is the gate terminal, and the second bonding pad 110 is the drain or source terminal.

[0033] Semiconductor die 106 is mounted on a lead frame in a flip-chip configuration. In this arrangement, the main surface of semiconductor die 106 faces the lead frame, such that the bonding pads of semiconductor die 106 are directly electrically connected to the lead frame. Specifically, a first bonding pad 108 faces and is electrically connected to a first lead 102, and a second bonding pad 110 faces and is electrically connected to a die pad 100. Once semiconductor die 106 is mounted and electrically connected, an electrically insulating encapsulation 112 can be formed around the lead frame assembly in the depicted shape, for example using molding techniques (e.g., injection molding, compression molding, transfer molding, etc.). Encapsulation 112 may include ceramic, epoxy resin, thermosetting plastic, etc. In this configuration, the outer surfaces of the first lead 102 and the die pad 100 provide externally accessible contact points to the terminals of semiconductor die 106.

[0034] The electrical connection between the semiconductor die 106 and the lead frame is achieved by a solder joint formed by solder material 114. Solder material 114 is a metal alloy that creates a permanent metallurgical bond between two metal surfaces by fusing solder to them. Fusion occurs when the solder reaches its melting point, which is lower than the melting point of the items to be bonded. The completed solder joint provides conductivity and a strong physical attachment between the two metal surfaces. Exemplary solder materials 114 include lead-free solder and lead-based solder. Lead-free solder can be an alloy of metals such as tin, copper, silver, bismuth, indium, zinc, antimony, etc., while lead-based solder can be an alloy of lead with metals such as tin, silver, copper, antimony, etc. Solder material 114 may include non-metallic materials such as flux (e.g., rosin, inorganic, organic, etc.) to prevent oxidation. In a specific example, the solder material is lead-free solder, and more specifically, Pb with a melting point in the range of 287°C to 294°C. 92.5 Sn5Ag 2.5 Solder composition.

[0035] According to an embodiment of the soldering technology, solder material 114 is initially provided at room temperature, for example, as solder bumps or solder balls or as solder paste. Solder material 114 may initially be placed on bonding pads 108, 110 of the semiconductor die 106, on the die attachment surface 104 of the leadframe, or both. Subsequently, the semiconductor die 106 is mated with the leadframe such that solder material 114 contacts the bonding pads 108, 110 of the semiconductor die 106 and the die attachment surface 104 of the leadframe. The assembly is then subjected to thermal cycling, wherein the temperature of solder material 114 rises. During the reflow phase of this thermal cycle, the temperature of solder material 114 reaches its melting point, resulting in liquefaction of solder material 114. During the reflow phase, solder material 114 chemically reacts with bonding partners to form a stable bond. The device is then cooled, causing solder material 114 to harden and form a stable solder joint.

[0036] refer to Figure 2This describes a lead frame assembly for a semiconductor package according to another embodiment. In this embodiment, a semiconductor die 106 is mounted on the lead frame such that the main surface of the semiconductor die 106, including a first bonding pad 108, faces away from the lead frame. In this example, the first bonding pad 108 may be a source or drain terminal of the semiconductor die 106. The first bonding pad 108 is electrically connected to a first lead 102, which is spaced apart from the die pad 100 by an interconnect clip 116. The interconnect clip 116 may be a sheet of metal of substantially uniform thickness (e.g., copper, aluminum, alloys thereof, etc.). The interconnect clip 116 includes a die attachment surface 118 and a lead attachment surface 120. The die attachment surface 118 and the lead attachment surface 120 may be substantially planar surfaces. Alternatively, the die attachment surface 118 and the lead attachment surface 120 may have slightly curved shapes (e.g., protruding or recessed shapes) designed to collect solder material. The die attachment surface 118 is electrically connected to the first bonding pad 108 via solder material 114. The lead attachment surface 120 is electrically connected to the first lead 102 via solder material 114. Both solder connections can be referenced above. Figure 1 The same welding technique described in the embodiments is used to achieve this.

[0037] Reference Figures 1-2 One problem that may arise in any solder joint of the described leadframe assembly is the presence of voids in the solder material 114. These voids can be enclosed cavities or open holes that exist in the solder material 114 after the material has cooled. Voids adversely increase the resistance of the solder joint by reducing the effective cross-sectional area of ​​the conductive path. Furthermore, voids adversely reduce the mechanical strength of the solder joint. Voids can be attributed to gases that appear in the solder material 114 during the solder reflow phase and cannot escape from the central volume of the solder material 114. These gaseous regions can originate from ambient air, which is trapped between the components when they are pressed together. Alternatively, gaseous regions can originate from chemical reactions in the solder material 114 when the solder material 114 reaches higher temperatures. The likelihood and severity of voids depend on a variety of factors, such as the type of solder material, the reflow temperature of the solder material, the geometry of the bonding surface, etc. In particular, bonding surfaces (e.g., the gate pads of the leadframe) can have a slightly concave shape, which tends to exacerbate the problem.

[0038] refer to Figure 3 The image depicts an interconnect structure with a solder reinforcement structure 122 according to an embodiment, which advantageously mitigates the occurrence and / or severity of voids in the solder joint. The solder reinforcement structure 122 is disposed on a substantially planar mating surface of the interconnect structure. Generally, the interconnect structure can be any conductive structure configured to engage with conductive bonding pads via solder. Figure 1 The lead frame in the embodiment illustrates an example of an interconnect structure that may include a solder reinforcement structure 122, wherein the die attachment surface 104 of the die pad 100 and the die bonding surface 104 of the first lead 102 may be substantially planar bonding surfaces on which the solder reinforcement structure 122 is disposed. Figure 2 The interconnect clip 116 in the embodiments illustrates another example of an interconnect structure that may include a solder reinforcement structure 122, wherein the die attachment surface 118 and the lead attachment surface 120 of the interconnect clip 116 may be substantially planar bonding surfaces on which the solder reinforcement structure 122 is disposed. In another example, the interconnect structure may be a printed circuit board with conductive contact pads, which are suitable bonding surfaces for the solder reinforcement structure 122. For illustrative purposes, the solder reinforcement structure 122 is disposed from... Figure 1 On the first lead 102 (e.g., gate lead) of the lead frame in the embodiment. However, the following discussion also applies to the solder reinforcement structure 122 disposed on any of the interconnect structures discussed above.

[0039] According to an embodiment, the solder reinforcement structure 122 includes a plurality of (i.e., two or more) raised spokes 124. Each of the raised spokes 124 rises from the mating surface (i.e., the die attachment surface 104 of the first lead 102 in the depicted example). That is, the raised spokes 124 project vertically from the mating surface to provide a apex or platform above the mating surface. For example, as Figure 3 As shown in the side perspective view on the right, each of the raised spokes 124 includes an upper surface 126 spaced apart from the engagement surface and a side surface 128 extending perpendicularly from the engagement surface to the upper surface 126. In the depicted embodiment, the side surface 128 of the raised spoke 124 is perpendicular to the engagement surface, and the upper surface 126 of the raised spoke 124 is parallel to the engagement surface. Alternatively, the side surface 128 may be oriented at a non-perpendicular angle relative to the engagement surface and / or the upper surface 126 of the raised spoke 124, for example, within a vertical range of + / - 10°. Additionally or alternatively, the upper surface 126 of the raised spoke 124 may be a non-flat surface at different points.

[0040] Each of the raised spokes 124 extends radially outward from the center 130 of the solder reinforcement structure 122. This means that the separation distance between corresponding positions on the centerline 132 of two adjacent raised spokes 124 increases with distance from the center 130 of the solder reinforcement structure 122. Each of the raised spokes 124 includes an inner end closer to the center 130 of the solder reinforcement structure 122 and an outer end further away from the center 130 of the solder reinforcement structure 122. The centerline 132 is a line traveling between the inner and outer ends of the raised spokes 124 and is equidistant from the side surfaces 128 of the raised spokes 124 traveling between the inner and outer ends. In the depicted embodiment, the center 130 of the solder reinforcement structure 122 is the portion of the solder reinforcement structure 122 continuously connected to each of the raised spokes 124. That is, the center 130 of the solder reinforcement structure 122 and the raised spokes 124 form a single continuous structure, wherein each raised spoke is an elongated portion extending outward from the center of the continuous structure. In this case, the center 130 of the solder reinforcement structure 122 can be raised from the mating surface, for example, raised to the same vertical height as the spokes. Alternatively, the center 130 of the solder reinforcement structure 122 can be a region of the mating surface between the raised spokes 124 (i.e., the region of the die attachment surface 104 in the depicted example). In this case, the solder reinforcement structure 122 is provided by a plurality of discrete raised spokes 124 disconnected from each other, and each raised spoke extends outward from the central region of the mating surface between each raised spoke 124.

[0041] exist Figure 3 In one embodiment, the solder reinforcement structure 122 includes a first raised spoke 134, a second raised spoke 136, a third raised spoke 138, and a fourth raised spoke 140, each of which extends radially outward from the center 130 of the solder reinforcement structure 122. In this example, the solder reinforcement structure 122 has a cross-shaped geometry, wherein the centerline 132 of each of the spokes 124 is substantially perpendicular to the spokes directly adjacent at an angle. Furthermore, in this embodiment, each of the raised spokes 124 has a substantially uniform width along the length of the raised spoke 124 extending from the center 130 of the solder reinforcement structure 122 to the outer end of the raised spoke 124.

[0042] According to an embodiment, each of the raised spokes 124 has a lower wettability relative to the liquefied solder material 114 than the mating surface. As used herein, the term "wetting" refers to the ability of a liquid (e.g., liquid solder) to remain in contact with a solid surface. Wetting can be attributed to intermolecular forces, which include cohesive forces within the liquid and adhesive forces between the liquid and the solid surface. These intermolecular forces affect the geometry of the liquid droplet applied to the solid surface. The degree of wettability is determined by the contact angle of the droplet on the solid surface. The contact angle is the angle at which the side surface of the liquid droplet intersects the solid surface. Low or "poor" wettability results in a high contact angle (e.g., between 90° and 180°), which forms a relatively spherical liquid droplet on the surface. High or "good" wettability results in a low contact angle (e.g., between 0° and 90°), which forms a relatively flat liquid droplet on the surface.

[0043] refer to Figure 4 Interconnect elements having solder material 114 covering solder reinforcement structure 122 are shown. Solder material 114 is in a liquefied state that occurs during the solder reflow phase. The liquefied solder material 114 includes a meniscus 142 at the transition between the bonding surface and the solder reinforcement structure 122. As will be understood by those skilled in the art, meniscus 142 refers to the curved surface of the outer surface of the liquid caused by surface tension. Meniscus 142 is caused by the difference in wettability between the raised spokes 124 and the bonding surface. Because the liquefied solder material 114 interacts differently with each surface, meniscus 142 is caused by the difference in surface tension and cohesion in the liquefied solder material 114. Due to this meniscus 142, a gas channel 144 is formed between the side surface 128 of the raised spokes 124 and the meniscus 142 in the solder material 114. This gas channel 144 is an open area in which the liquefied solder material 114 does not contact the raised spokes 124. Gas channels 144 form a path for fluid (e.g., ambient air or gas derived from solder material 114) to move along the side surfaces 128 of the raised spokes 124. Gas channels 144 may be formed along any one or all of the side surfaces 128 of each raised spoke 124. In an embodiment, gas channels 144 extend entirely along the length of the raised spokes 124, i.e., from the center 130 of the solder reinforcement structure 122 to the outer end of the raised spokes 124.

[0044] refer to Figure 5 The description depicts the passage of gas through gas channel 144 during solder reflow according to an embodiment. Figure 4The gas flows in a directional manner (as shown in the diagram). As can be seen, each gas channel 144 provides a path for drawing fluid along the side surface 128 of each of the first raised spokes 134, the second raised spokes 136, the third raised spokes 138, and the fourth raised spokes 140. The gas flows away from the center 130 of the solder reinforcement structure 122 to the outer end of each of the first raised spokes 134, the second raised spokes 136, the third raised spokes 138, and the fourth raised spokes 140. Due to the radial arrangement of the spokes, the gas is drawn from the inner region of the solder material, which tends to trap the gas, to the outer periphery of the solder material, where the gas can escape. The gas accelerates as it moves away from the center 130 of the solder reinforcement structure 122. As a result, the likelihood of encapsulated voids or end-opening holes forming in the finished weld joint after the solder material 114 has cooled is significantly reduced.

[0045] Refer again Figure 4 An exhaust effect occurs when the gas channel 144 is present and large enough to provide an unobstructed path for gas along the side surface 128 of the raised spoke 124. For this purpose, the difference in wettability between the raised spoke 124 and the mating surface can be adjusted to form a meniscus 142 with an appropriate profile for a given solder material 114, thereby creating an effective gas channel 144. The wettability difference can be adjusted by appropriately selecting the material composition and / or surface properties (e.g., roughness) of the raised spoke 124 and the mating surface. The inventors have discovered that, relative to typical liquefied solder materials 114 used in semiconductor applications (e.g., Pb), the wettability difference is significant. 92.5 Sn5Ag 2.5 A solder (with a melting point in the range of 287°C to 294°C) is used to configure the raised spokes 124 such that the contact angle on the outer surface of each spoke (i.e., the surface exposed to the solder material 114) is at least 10 degrees larger than the contact angle on the mating surface, creating a meniscus 142 with a gas channel 144 that effectively disperses gas to escape from the solder material 114. In one embodiment meeting this requirement, the mating surface is a copper surface, and the outer surface of the raised spokes 124 is a silver surface. More generally, by using one type of metal (e.g., aluminum, copper, nickel, etc., and alloys thereof) for the mating surface and by using different metals (e.g., aluminum, copper, nickel, etc., and alloys thereof) for the outer surface of the raised spokes 124, sufficient meniscus 142 can be obtained, and thus effective venting can be achieved, wherein the material of the raised spokes 124 is selected to have a lower wettability than the mating surface.

[0046] In addition to the size of the gas channel 144, the effectiveness of venting also depends on the geometry of the solder reinforcement structure 122. Since the spoke pattern determines the path of the gas channel 144, the geometric features of the spoke pattern can be selected for effective venting. Generally, these geometric features include the height of the raised spokes 124, the length of the raised spokes 124, the orientation of the raised spokes 124 relative to each other and relative to the center 130 of the solder reinforcement structure 122, the number of raised spokes 124, etc.

[0047] The height of the raised spokes 124 can be selected to create a sufficiently large meniscus 142, thereby allowing effective venting. The height difference between the mating surface and the upper surface 126 of the raised spokes 124 is measured. According to an embodiment, each of the raised spokes 124 has a height of at least 3 μm. The inventors have observed that this height difference produces a sufficiently large meniscus 142 to allow effective venting relative to typical liquefied solder materials used in semiconductor applications.

[0048] The orientation of the raised spokes 124 can be chosen to create gas channels 144 that draw gas away from the center of the solder joint in multiple directions. By forming multiple gas channels 144 extending in different directions, better gas flow is provided and the possibility of voids being generated in the solder joint is reduced. Generally, any geometry in which the raised spokes 124 extend radially outward from the center 130 of the solder reinforcement structure 122 will advantageously produce this result, because the diverging paths of the raised spokes 124 will necessarily form gas channels 144 that draw gas away from the center of the solder joint in multiple directions.

[0049] According to an embodiment, the solder reinforcement structure 122 includes at least two raised spokes 124, wherein the side surfaces 128 of the two different raised spokes are offset from each other by at least 90 degrees. This arrangement provides venting from the center of the solder joint along two different directions, wherein at least two gas flow channels are separated from each other by at least 90 degrees. This is generally more effective than unidirectional venting because more paths are available for gas escape. Figure 5 The depicted embodiment illustrates one example of this embodiment. As can be seen, the side surface 128 of the first raised spoke 134 is offset by 90 degrees from the side surface 128 of the second raised spoke 136 facing the first raised spoke 134. As a result, the two gas channels 144 are offset by 90 degrees relative to each other.

[0050] According to an embodiment, the solder reinforcement structure 122 includes at least three raised spokes 124, and the three raised spokes are arranged such that each side surface 128 is offset by at least 90 degrees from the side surface 128 of the adjacent spoke it faces. By increasing the number of gas channels 144 and increasing the radial extension of the gas channels 144, a divergence of at least 180 degrees from the center of the solder joint is achieved, resulting in improved venting in some cases compared to a dual-channel configuration. Figure 5 The depicted embodiment illustrates one example of this embodiment. As can be seen, the side surface 128 of the first raised spoke 134 is offset by 90 degrees from the side surface 128 of the second raised spoke 136 facing the first raised spoke 134, and the side surface 128 of the third raised spoke 138 is offset by 90 degrees from the side surface 128 of the second raised spoke 136 facing the third raised spoke 138 (i.e., the side surface 128 opposite to the side surface 128 facing the first raised spoke 134).

[0051] According to an embodiment, the solder reinforcement structure 122 includes four raised spokes 124, and the raised spokes 124 are arranged such that each side surface 128 is offset from the side surface 128 of its adjacent facing spoke by at least 60 degrees. By increasing the number of gas channels 144 and increasing the radial extension of the gas channels 144, a divergence of at least 240 degrees from the center of the solder joint is achieved, resulting in improved venting in some cases compared to a dual-channel configuration. Figure 5 The illustrated embodiment shows one example of this embodiment. As can be seen, the side surface 128 of each of the first raised spoke 134, the second raised spoke 136, the third raised spoke 138, and the fourth raised spoke 140 forms a perpendicular angle with the side surface 128 of the adjacent spoke it faces. More generally, the raised spokes 124 can be arranged at a non-perpendicular angle (e.g., as an "X" shape) and similar benefits can be obtained.

[0052] refer to Figure 6 Various geometries of the solder reinforcement structure 122 are shown. Figure 6 In embodiment A, the solder reinforcement structure 122 has a cross-shaped configuration, which is substantially similar to, except that the two raised spokes 124 are wider than the two other raised spokes. Figures 3-5 The structure. In Figure 6 In embodiment B, the solder reinforcement structure includes eight raised spokes 124, each having an equal width, and each raised spoke 124 diverging from the center of the solder reinforcement structure 122 at an angle of approximately 45 degrees relative to its adjacent raised spoke 124. Therefore, the solder reinforcement structure 122 has a star shape. Figure 6 In embodiment C, the solder reinforcement structure 122 includes components for use with... Figure 6 In embodiment B, eight raised spokes 124 radiate away from the center of the solder reinforcement structure 122 in a similar manner. However, in this embodiment, each of the raised spokes 124 tapers inward from the center 130 of the solder reinforcement structure 122 to its outer end. Specifically, each of the raised spokes 124 includes a linear side surface that extends away from the center 130 of the solder reinforcement structure 122 and converges at different points, thereby forming a star-shaped geometry. Figure 6 Embodiment D similarly has a star-shaped geometry, but includes 10 raised spokes 124. Figure 6 In embodiment E, the raised spokes 124 are arranged in a spiral pattern, wherein each raised spoke 124 extends to retract from the center 130 of the solder reinforcement structure 122 while bending away from the center 130 of the solder reinforcement structure 122. This differs from the embodiments discussed earlier. Figure 6 In embodiment E, the center 130 of the solder reinforcement structure 122 is the region of the mating surface between the raised spokes 124. Therefore, in this embodiment, the solder reinforcement structure 122 is provided by a plurality of discrete and disconnected raised spokes 124.

[0053] refer to Figure 7 The diagram illustrates a solder reinforcement structure 122 according to another embodiment. In this embodiment, the solder reinforcement structure 122 comprises only three raised spokes 124. In this geometry, the raised spokes 124 extend radially away from the center 130 of the solder reinforcement structure 122 with approximately equal divergence angles. Specifically, as seen in the planar perspective view, the side surfaces of two adjacent raised spokes 124 (having a uniform width in this example) facing each other diverge away from the center 130 at an angle of 120 degrees. As a result, the solder reinforcement structure 122 uniformly draws liquefied solder material away from the center 130 of the solder reinforcement structure 122 in three directions.

[0054] The various geometries depicted in the accompanying drawings are merely examples of spoke patterns for effective venting of solder joints. Various concepts can be combined with each other. For example, other embodiments of the solder reinforcement structure 122 may include those with… Figures 3-5 , Figure 6 A- Figure 6 D and Figure 7 Any of the spokes shown are similar to those in the diagram, but the area of ​​the mating surface is in the central region of the raised spoke 124, for example, to match... Figure 6 A similar approach is used in E. Generally, the choice of one geometry relative to another may involve performance considerations. For example, a greater number of spokes may be preferred because this increases the number of channels for the outflowing gas. Alternatively, a tapered spoke pattern (e.g., as shown in the image) may be preferred. Figure 6 C- Figure 6As shown in E), to provide a better outlet for gas escape. Alternatively or alternatively, a spiral pattern (e.g., as shown in E) Figure 6 (As shown in E) can reduce bottlenecks in the gas channel 144 because the gas velocity tends to increase as it moves away from the center 130 of the solder reinforcement structure 122. Furthermore, the spiral pattern (e.g., as shown in E) can reduce bottlenecks in the gas channel 144 because the gas velocity tends to increase as it moves away from the center 130 of the solder reinforcement structure 122. Figure 6 (As shown in E) can provide a greater density of gas channels 144 spanning the area of ​​the solder joint and / or covering a larger area of ​​the solder joint. Therefore, at least in some cases, this structure can be more efficient in gas removal compared to a linear configuration. On the other hand, performance considerations can be balanced with other considerations such as cost and / or ease of manufacture. For example, a pattern with fewer spokes (e.g., Figures 3-5 and Figure 7 Spoke patterns may be superior to more complex patterns because such structures are generally easier to reliably form using known metal structuring techniques, especially in small areas.

[0055] Generally, the solder reinforcement structure 122 can be formed using any of a variety of metal processing techniques, such as stamping, embossing, punching, etching, etc. According to one technique, the solder reinforcement structure 122 can be formed using an etching technique, wherein a conductive metal sheet (e.g., a metal foil) of substantially uniform thickness is provided, and mask etching is used to reduce the material thickness in selected areas surrounding the solder reinforcement structure 122. According to another technique, the solder reinforcement structure 122 can be formed using a deposition technique, wherein metal is selectively deposited in exposed mask openings. Differences in wettability between the solder reinforcement structure 122 and the bonding surface can be obtained by depositing different material surfaces on the solder reinforcement structure 122. For example, a plating process (e.g., electroless plating or electroplating) can be performed on the solder reinforcement structure 122 before or after the aforementioned etching or deposition steps. In one example of this technique, the bonding surface is a surface area of ​​the lead frame or interconnect clip (e.g., a copper surface), and the outer surface of the solder reinforcement structure 122 is a portion coated with a metal with lower wettability (e.g., silver).

[0056] The embodiments described herein depict a semiconductor die 106. Generally, the semiconductor die 106 can have a wide variety of device configurations. These configurations include discrete device configurations such as MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), IGBTs (Insulated Gate Bipolar Transistors), JFETs (Junction Field-Effect Transistors), diodes, etc. These configurations may additionally include integrated circuit configurations such as amplifiers, controllers, processors, etc. These device configurations include V-type semiconductor technologies (e.g., silicon, silicon germanium, silicon carbide, etc.) and III-V type semiconductor technologies (e.g., gallium nitride, gallium arsenide, etc.). These device configurations include vertical configurations and lateral configurations, in which the semiconductor die 106 is configured to control current flowing between the upper and lower surfaces of opposite faces of the die, and in which the semiconductor die 106 is configured to control current flowing parallel to the upper surface 126 of the die.

[0057] The term "substantially" encompasses absolute conformity to requirements, as well as minor deviations from the ideal state caused by variations in manufacturing processes, assembly, and other factors that may result. Assuming these deviations are within process tolerances to achieve practical conformity, and that the part described herein functions as required by the application, the term "substantially" covers any deviations from these requirements.

[0058] For ease of description, spatial relative terms such as "below," "under," "lower," "above," and "upper" are used to explain the positioning of one element relative to a second element. These terms are intended to cover different orientations of the device, in addition to orientations different from those depicted in the figures. Furthermore, terms such as "first," "second," etc., are used to describe various elements, regions, sections, etc., and are not intended to be limiting. Throughout the specification, similar terms refer to similar elements.

[0059] As used herein, the terms “having,” “comprising,” “including,” etc., are open-ended terms that indicate the presence of the stated element or feature but do not exclude additional elements or features. The articles “a” and “described” are intended to include both plural and singular forms unless the context clearly indicates otherwise.

[0060] Given the variations and applications described above, it should be understood that this invention is not limited to the foregoing description or the accompanying drawings. Rather, it is limited only by the appended claims and their legal equivalents.

Claims

1. An electrical interconnection structure, comprising: A bonding pad, the bonding pad comprising a substantially planar bonding surface; as well as A solder reinforcement structure is disposed on the bonding surface and includes a plurality of raised spokes, each of which rises from the bonding surface. Each of the raised spokes has a lower wettability relative to the liquefied solder material than the mating surface. Each of the raised spokes extends radially outward from the center of the solder reinforcement structure, and Each of the raised spokes tapers inward from the center of the solder reinforcement structure to the outer end of the raised spoke.

2. An electrical interconnection structure, comprising: A bonding pad, the bonding pad comprising a substantially planar bonding surface; as well as A solder reinforcement structure is disposed on the bonding surface and includes a plurality of raised spokes, each of which rises from the bonding surface. Each of the plurality of raised spokes includes an upper surface and a side surface extending from the mating surface to the upper surface. The plurality of raised spokes includes a first raised spoke, which is configured to form a first gas channel along its side surface when the solder reinforcement structure is covered by liquefied solder material. The plurality of raised spokes includes a second raised spoke, the second raised spoke being configured to form a second gas channel along its side surface when the solder reinforcement structure is covered by liquefied solder material. The first gas channel and the second gas channel are separated from each other by at least 90 degrees.

3. The electrical interconnection structure according to claim 2, wherein, The plurality of raised spokes includes a third raised spoke and a fourth raised spoke, the third raised spoke being configured to form a third gas channel along the side surface of the third raised spoke when the solder reinforcement structure is covered by liquefied solder material, and the fourth raised spoke being configured to form a fourth gas channel along the side surface of the fourth raised spoke when the solder reinforcement structure is covered by liquefied solder material.

4. The electrical interconnection structure according to claim 3, wherein, The center of the solder reinforcement structure is a region that rises from the joint surface and is continuously connected to each of the raised spokes.

5. The electrical interconnection structure according to claim 3, wherein, Each of the raised spokes has a substantially uniform width along the length of the raised spoke, which extends from the center of the solder reinforcement structure to the outer end of the raised spoke.

6. The electrical interconnection structure according to claim 3, wherein, Each of the raised spokes tapers inward from the center of the solder reinforcement structure to the outer end of the raised spoke.

7. The electrical interconnection structure according to claim 3, wherein, The mating surface is a copper surface, and the outer surface of each of the raised spokes is a silver surface.

8. The electrical interconnection structure according to claim 3, wherein, The electrical interconnect structure is a lead frame, and the bonding surface is the die attachment surface of the lead frame.

9. The electrical interconnection structure according to claim 3, wherein, The electrical interconnect structure is a metal interconnect clip, and the mating surface is the die attachment surface or lead attachment surface of the metal interconnect clip.

10. The electrical interconnection structure according to claim 2, wherein, The first raised spoke and the second raised spoke are configured to form the first gas channel and the second gas channel respectively by means of the difference in wettability of the liquefied solder material between the outer surface of each of the first raised spoke and the mating surface.

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