Selective plating of semiconductor package leads

Abstract

The present invention provides a method for forming a semiconductor device, comprising: providing a semiconductor package, the semiconductor package comprising an electrically insulating mold compound body, a semiconductor die encapsulated by the mold compound body, a plurality of conductive leads, and a metal heat sink, wherein each of the plurality of conductive leads protrudes from the mold compound body, and the metal heat sink comprises a rear surface exposed from the mold compound body; coating the outer portion of the leads exposed from the mold compound body with a metal coating; and after completing the coating of the outer portion of the leads, providing a planar metal heat sink interface surface on the semiconductor device, the planar metal heat sink interface surface: exposed from the mold compound body; and substantially free of the metal coating.

Description

[0001] Related Applications

[0002] This application is a continuation-in-part of and claims priority to U.S. Application No. 16 / 036,354 filed on July 16, 2018, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to semiconductor packaging, and more particularly to techniques for forming metal coatings on semiconductor package leads. Background Art

[0004] In many modern applications, semiconductor chips generate a large amount of heat during operation. This heat must be effectively dissipated from the semiconductor chip to maintain the operating temperature of the chip within acceptable limits. For this reason, heat sinks are typically fixed to the outer surface of the packaged device. The heat sink is configured to extract heat from the packaged device and effectively dissipate the extracted heat, thereby reducing the temperature of the packaged device.

[0005] In some applications, the interface between the heat sink and the external surface of the package can be a source of inefficiency. The interface can be substantially thermally resistive, which reduces the heat sink's ability to extract heat from the packaged device. Summary of the invention

[0006] A method of forming a semiconductor device is disclosed. According to an embodiment, the method includes: providing a semiconductor package, the semiconductor package including: an electrically insulating mold compound body; a semiconductor die encapsulated by the mold compound body; a plurality of conductive leads, each conductive lead protruding from the mold compound body; and a metal heat sink, the metal heat sink including a rear surface exposed from the mold compound body; coating the outer portions of the leads exposed from the mold compound body with a metal coating; and after completing the coating of the outer portions of the leads, providing a planar metal heat sink interface surface on the semiconductor device, the surface exposed from the mold compound body and substantially free of the metal coating.

[0007] Either alone or in combination, the planar metal heat sink interface surface and the conductive leads are each formed of a first metal, and the metal coating comprises a second metal having a higher solderability than the first metal.

[0008] Either alone or in combination, the planar metal heat sink interface surface and the conductive leads are each formed of copper, and the metal coating includes at least one of gold, nickel, tin, and silver.

[0009] Alternatively or in combination, the planar metal heat sink interface surface is provided by a rear surface of the heat sink, coating the outer portions of the leads comprises a plating process, and providing the planar metal heat sink interface surface substantially free of metal coating comprises preventing the plating process from depositing the metal coating on the rear surface of the heat sink.

[0010] Either alone or in combination, a lead frame is provided including a peripheral ring and a connecting bar, each lead is connected to the peripheral ring and is physically separated from the heat sink, the connecting bar is connected between the peripheral ring and the heat sink, and preventing the electroplating process from depositing a metal coating on the rear surface of the heat sink includes cutting off the connecting bar before performing the electroplating process.

[0011] Alternatively or in combination, a lead frame is provided that includes a peripheral ring, wherein at least one lead is physically connected between the peripheral ring and a heat sink, and preventing an electroplating process from depositing a metal coating on a rear surface of the heat sink includes applying a non-conductive coating on the rear surface of the heat sink prior to performing the electroplating process.

[0012] Alone or in combination, providing a planar metal heat sink interface surface includes providing a metal attachment separate from the heat sink and attaching the metal attachment to a rear surface of the heat sink after coating an outer portion of the leads with the metal coating.

[0013] Either alone or in combination, coating the outer portion of the lead includes an electroplating process that forms a metal coating on the rear surface of the heat sink, and the metal attachment completely covers the metal coating on the rear surface once attached to the heat sink.

[0014] Alone or in combination, attaching the metal attachment to the rear surface includes directly attaching the metal attachment to the rear surface such that a lower side of the metal attachment interfaces with and covers the rear surface of the heat sink, and an upper side of the metal attachment opposite the lower side provides a planar metal heat sink interface surface.

[0015] Either alone or in combination, the underside of the attachment includes a first set of attachment features, the rear surface of the heat sink includes a second set of attachment features, the first and second sets of attachment features are complementarily formed, and the attachment is secured to the heat sink by forming an interlocking connection between the first and second sets of attachment features.

[0016] Either alone or in combination, a metal coating is formed directly on a rear surface of the heat sink during coating of an outer portion of the leads, and providing a planar metal heat sink interface includes removing the metal coating formed directly on the rear surface of the heat sink.

[0017] Alone or in combination, removing the metal coating layer formed directly on the rear surface of the heat sink includes performing a laser removal process that removes the metal coating layer using a laser beam.

[0018] Either alone or in combination, the metal coating is removed from a central portion of the heat sink such that a ring of the metal coating extending to an outer edge of the heat sink remains on the heat sink after the laser removal process.

[0019] Either alone or in combination, the metal coating is completely removed from the heat sink.

[0020] According to another embodiment, the method includes providing a semiconductor package, the semiconductor package including: an electrically insulating mold compound body; a semiconductor die encapsulated by the mold compound body; a plurality of conductive leads, each conductive lead protruding from the mold compound body; and a metal heat sink, the metal heat sink including a rear surface exposed from the mold compound body. Performing an electroplating process on the semiconductor package, the electroplating process forming a metal coating on an outer portion of the leads exposed from the mold compound body. In the electroplating process, the metal coating is prevented from being formed on the rear surface of the heat sink.

[0021] Either alone or in combination, performing the electroplating process includes immersing the leads and the rear surface of the semiconductor package in an aqueous solution, and preventing the metal coating from forming on the rear surface includes electrically disconnecting the heat sink from the leads before performing the electroplating process.

[0022] Either alone or in combination, a semiconductor package is provided on a lead frame including a peripheral ring and a connecting bar, each lead is connected to the peripheral ring and disconnected from a heat sink, the connecting bar is connected between the peripheral ring and the heat sink, and electrically disconnecting the heat sink from the lead includes cutting the connecting bar.

[0023] Either alone or in combination, preventing the metal coating from being formed on the rear surface of the heat sink includes applying a non-conductive adhesive on the rear surface of the heat sink before performing the electroplating process.

[0024] A packaged semiconductor device is disclosed. The packaged semiconductor device includes an electrically insulating mold compound body. The packaged semiconductor device also includes a metal heat sink having a rear surface exposed from the mold compound body and a die attachment surface opposite the rear surface. The packaged semiconductor device also includes a semiconductor die encapsulated by the mold compound body and mounted on the heat sink. The packaged semiconductor device also includes a plurality of conductive leads, each lead including an outer portion exposed from the mold compound body. The packaged semiconductor device also includes a metal coating covering an outer portion of each lead. The packaged semiconductor device also includes a planar metal heat sink interface surface, which is exposed from the mold compound body, thermally coupled to the semiconductor die via the heat sink, and is substantially free of the metal coating.

[0025] Either alone or in combination, the planar metal heat sink interface surface and the conductive leads are each formed of a first metal, and the metal coating comprises a second metal having a higher solderability than the first metal.

[0026] Either alone or in combination, the rear surface of the heat sink provides a planar metal heat sink interface surface.

[0027] Alternatively or in combination, the semiconductor package further comprises a metal attachment that is separate from the heat sink and secured to the heat sink at its underside, and wherein an upper side of the metal attachment provides a planar metal heat sink interface surface.

[0028] Alone or in combination, the metal coating is additionally formed on the rear surface of the heat sink as a ring surrounding a central portion of the heat sink exposed from the metal coating.

[0029] Alone or in combination, the semiconductor package further includes a recess formed in the body of the molding compound, the recess surrounding a rear surface of the heat sink, and the rear surface of the heat sink is completely free of the metal coating.

[0030] Those skilled in the art will recognize additional features and advantages upon reading the following detailed description, and upon viewing the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The elements of the drawings are not necessarily drawn to scale relative to each other. Similar reference numerals represent corresponding similar parts. The features of the various illustrated embodiments may be combined unless they exclude each other. The embodiments are depicted in the drawings and described in detail in the following description.

[0032] Figure 1 A packaged semiconductor device according to an embodiment is depicted.

[0033] Figure 2 An electroplating process for forming a metal coating on leads of a packaged semiconductor device is depicted in accordance with an embodiment.

[0034] Figure 3 A packaged semiconductor device having a heat spreader interface without a metal coating formed on the package leads is depicted in accordance with an embodiment.

[0035] Figure 4 includes Figure 4A , 4B 4C and 4D depict techniques for preventing an electroplating process from forming a metal coating on the rear surface of a heat sink according to an embodiment.

[0036] Figure 5 includes Figure 5A , 5B and 5C , depicting a technique for preventing an electroplating process from forming a metal coating on a rear surface of a heat sink, according to an embodiment.

[0037] Figure 6 includes Fig. 6A , 6B and 6C , depict a packaged semiconductor device having a heat sink interface without a metal coating formed on the package leads and at least one lead directly connected to a heat sink in accordance with an embodiment.

[0038] Figure 7 Techniques for providing a heat sink interface without a metal coating after performing an electroplating process are described in accordance with embodiments.

[0039] Figure 8 Techniques for providing a heat sink interface without a metal coating after performing an electroplating process are described in accordance with embodiments.

[0040] Figure 9 includes Fig.9A and Fig. 9B , depicting two different laser removal techniques for removing metal coatings from heat sinks. DETAILED DESCRIPTION

[0041] According to embodiments described herein, a semiconductor package is provided having a semiconductor die encapsulated by an electrically insulating mold compound body. The semiconductor package includes a plurality of leads exposed from the mold compound body. In addition, the rear surface of a metal heat sink on which the semiconductor die is mounted is exposed from the mold compound body. Once the semiconductor package is provided, a metal coating is formed on the leads using an electroplating process. Advantageously, processing steps for forming a metal heat sink interface surface without a metal coating on the leads on the exterior of the package are described herein. According to some techniques, measures are taken prior to the electroplating process to prevent the formation of a metal coating on the rear surface of the heat sink during electroplating. In this case, the rear surface of the heat sink can directly provide a metal heat sink interface surface without a metal coating. According to other techniques, after performing the electroplating process, an additional metal sheet is fixed to the rear surface of the heat sink. In this case, the additional metal sheet can provide a metal heat sink interface surface without a metal coating.

[0042] refer to Figure 1 , a semiconductor package 100 is depicted according to an embodiment. The semiconductor package 100 includes an electrically insulating mold compound body 102, a metal heat sink 104, and a plurality of electrically conductive leads 106. A semiconductor die 108 is mounted on a die attach surface 110 of the heat sink 104.

[0043] In general, the semiconductor die 108 can have a variety of device configurations. For example, the semiconductor die 108 can be configured as a discrete device, such as a metal oxide semiconductor field effect transistor (MOSFET), an insulated gate bipolar transistor (IGBT), a diode, a thyristor, etc. Alternatively, the semiconductor die 108 can be configured as an integrated circuit, a processor, a controller, an amplifier, etc. The semiconductor die 108 includes a conductive input / output terminal 112 (e.g., a gate, a source, a drain, etc.), which is electrically connected to the lead 106. In the illustrated embodiment, the electrical connection is provided by a conductive bonding wire. More generally, the electrical connection can be provided according to any known technology, such as a tape, a clamp, etc.

[0044] The mold compound body 102 is formed of an electrically insulating material. Exemplary materials for the mold compound body 102 include any of a wide variety of encapsulation materials, such as ceramics, plastics, resins, epoxies, etc. The mold compound body 102 is formed to encapsulate the semiconductor die 108 and the associated electrical connections between the semiconductor die 108 and the leads 106. In this way, the package components are protected from the external environment.

[0045] Lead 106 includes inner portion 114 and outer portion 116. Inner portion 114 of lead 106 is encapsulated by mold compound body 102 and provides a connection point for terminal 112 of semiconductor die 108. Outer portion 116 of lead 106 is exposed from mold compound body 102 and provides external electrical access to terminal 112 of semiconductor die 108.

[0046] In the depicted example, the outer portion 116 of the lead 106 extends laterally away from the package sidewalls and bends downward to reach the bottom side 118 of the semiconductor package 100. This lead configuration produces a so-called "surface mount" package type configuration. This represents only one exemplary package configuration. More generally, the semiconductor package 100 can have a variety of package configurations, such as through-hole, flat, surface mount, etc., and the techniques described herein are applicable to any of these package configurations.

[0047] The heat sink 104 is formed of a thermally conductive material including metals such as copper, aluminum, and alloys thereof. A rear surface 120 of the heat sink 104 is exposed from the mold compound body 102. In this example, the rear surface 120 of the heat sink 104 is exposed at the top side 122 of the package, i.e., the side of the package opposite to the bottom side 118. This provides a so-called top-side cooling configuration, in which heat is drawn away from the top side 122 of the semiconductor package 100 during device operation. In this configuration, a heat sink 124 may be mounted on the rear surface 120 of the heat sink 104. As a result, the heat sink 124 is directly thermally coupled to the semiconductor die 108 via the heat sink 104. In another packaging configuration, the heat sink 104 may be arranged so that the rear surface 120 (i.e., the surface opposite to the semiconductor die 108) is exposed at the bottom side 118 of the semiconductor package 100. This style of package may be mounted with the heat sink underneath it so that heat can be drawn away in a similar manner.

[0048] refer to Figure 2 , an electroplating process is performed on the semiconductor package 100. Electroplating refers to any process that uses an electric current to form a thin metal coating on the outer surface of a charged component. According to this technology, the semiconductor package 100 is immersed in a water-based solution 126. The water-based solution 126 is a chemical solution containing cations of the metal to be deposited. The cathode 128 is immersed in the water-based solution 126, and a potential difference is generated between the immersed cathode and the immersed conductive article (which acts as an anode). In this case, the exposed portion of the lead 106 and the rear surface 120 of the heat sink 104 are immersed in the water-based solution 126, and therefore represent potential surfaces on which metal can be deposited by an electroplating process.

[0049] refer to Figure 3 , shows the semiconductor package 100 after performing an electroplating process. The electroplating process is performed so that the outer portion 116 of the lead 106 exposed from the mold compound body 102 is coated with the metal coating 130. The electroplating process causes the metal coating 130 to completely cover the lead 106 so that the underlying material of the lead 106 is not exposed.

[0050] According to an embodiment, the lead 106 is formed of a first metal, and the metal coating 130 is a second metal different from the first metal. In general, the metal coating 130 can include any material that produces some benefit related to the surface properties of the lead 106 (e.g., solderability, corrosion protection, adhesion, conductivity, etc.). That is, the metal coating 130 can be selected so that the lead 106 is easier to solder to the printed circuit than a package without the metal coating. In addition, the metal coating 130 can be selected to provide a certain degree of corrosion protection for the lead 106. Alternatively, the first and second metals can include similar or identical materials.

[0051] According to an embodiment, the metal coating 130 has a higher solderability than the lower material of the lead 106. Solderability refers to the ability of a material to be soldered to another component via solder. The degree of solderability used herein can be determined using EIA / JEDEC J-STD-002, the entire contents of which are incorporated herein by reference. Factors affecting solderability include the presence or absence of oxides on the surface of the material and the wettability (i.e., surface tension) of the solder material. In general, coatings that are very suitable for solderability and corrosion protection include tin coatings, silver coatings, gold coatings, nickel coatings, and alloys thereof. These coatings have a higher solderability than copper or aluminum, which are common package lead materials. In a specific example, the lead 106 and the heat sink 104 are formed by copper, and the metal coating 130 is a silver or silver-based coating.

[0052] The inventors have observed that the above-described metal coating 130, while advantageous when provided on the leads 106, can be detrimental when applied to the rear surface 120 of the heat sink 104. In particular, the metal coating 130 can cause problems with the connection between the heat sink 124 and the heat sink 104, such as Figure 1 . The heat sink 124 can be attached to the heat sink 104 using a soldering technique or using a polymer-based thermal interface material. Although the metal coating 130 is generally designed to enhance the solderability of the lead 106 to an external device (e.g., a printed circuit board), this benefit cannot be obtained accordingly when the heat sink 104 is soldered to the heat sink 124 or the heat sink 104 is attached to the heat sink using a polymer-based thermal interface material. Unlike the soldering of the lead 106, the soldering of the heat sink 124 involves applying a larger amount of liquefied solder material over a larger surface area. During solder reflow, the large amount of metal coating 130 present on the rear surface 120 of the heat sink 104 becomes unevenly distributed, with large accumulations in some areas and bare spots in other areas. In other words, the substantial difference in physical properties between the lead 106 and the heat sink 104 means that the metal coating 130 is generally not beneficial on the rear surface 120 of the heat sink 124.

[0053] Figure 3A planar metal heat sink interface surface 132 on a semiconductor package 100 is schematically depicted that avoids the above-mentioned disadvantages of forming a metal coating 130 on the back surface 120. The planar metal heat sink interface surface 132 is thermally coupled to the semiconductor die 108 via the heat sink 104. This means that the planar metal heat sink interface surface 132 has a low thermal resistance connection to the semiconductor die 108, which is at least partially provided by the heat sink 124. In addition, the planar metal heat sink interface surface 132 is substantially free of the metal coating 130. This means that a substantial portion (e.g., greater than seventy-five percent) of the surface area of ​​the planar metal heat sink interface surface 132 is not covered by the metal coating 130. In some embodiments, the planar metal heat sink interface surface 132 is completely free of the metal coating 130. In addition, the planar metal heat sink interface surface 132 is exposed from the mold compound body 102. Therefore, the planar metal heat sink interface surface 132 can be accessed from the outside, for example, to communicate with the semiconductor die 108. Figure 1 A heat sink 124 is provided and connected in a similar manner as shown in .

[0054] The methods described herein allow for providing the above-described properties to the planar metal heat sink interface surface 132 after coating the outer portion 116 of the lead 106 with the metal coating 130, for example according to the above-described electrodeposition technique. Thus, the methods described herein allow for providing the metal coating 130 on the outer portion 116 of the lead 106 without providing the metal coating 130 at the interface between the heat sink 124 and the semiconductor package 100, thereby avoiding the problem of non-uniformly distributed coating material as previously described. In some examples, the planar metal heat sink interface surface 132 may be provided by the back surface 120 of the heat sink 104. Alternatively, the planar metal heat sink interface surface 132 may be a separate structure attached to the heat sink 104. In either case, the planar metal heat sink interface surface 132 is thermally coupled to the semiconductor die 108 within the meaning of the present specification, and thus provides a surface for mounting the heat sink 124 thereon.

[0055] 4 , two different configurations of the semiconductor package 100 are shown, according to an embodiment, along with corresponding lead frames 134 that may be used to form these different configurations of the semiconductor package 100 .

[0056] Figure 4A Depicted as previously referenced Figure 1 A semiconductor package 100 is described. Figure 4BA lead frame 134 for forming the semiconductor package 100 according to an embodiment is depicted. The lead frame 134 includes each of the leads 106 and the heat sink 104 of the semiconductor package 100. The lead frame 134 includes a peripheral ring 136 that forms a closed circle around the heat sink 104. Each of the leads 106 is directly connected to the peripheral ring 136 (e.g., by an integral physical connection). In addition, each of the leads 106 is disconnected from the heat sink 104. That is, the ends of the leads 106 are physically spaced apart from the heat sink 104. The lead frame 134 further includes a connecting strip 138 that extends directly between the heat sink 104 and the peripheral ring 136 and is physically connected to the heat sink 104 and the peripheral ring 136 (e.g., by an integral physical connection).

[0057] Figure 4C A semiconductor package 100 is depicted according to another embodiment. Figure 4C The semiconductor package 100 is compared with the reference Figure 1 The packages described are identical with the following exceptions. Figure 1 All leads 106 in the package are physically separated from the heat sink 104, but Figure 4C The semiconductor package 100 includes a first lead 142 of the leads 106 that is directly physically connected to the heat sink 104. In one example, the heat sink 104 provides a reference potential (e.g., GND) connection to the semiconductor die 108, and the first lead 142 of the leads 106 provides an external terminal for the reference potential. This configuration may require that at least one of the leads 106 from the lead frame 134 (e.g., as shown in FIG. 4 ) is connected between the peripheral ring 136 and the heat sink 104. That is, unlike the previous embodiment, at least one of the leads 106 is in physical contact with the heat sink 104, thereby providing a reference potential such as Figure 4C Configuration shown. Figure 4D Depicted is a method for forming a Figure 4C The lead frame 134 of the semiconductor package 100 . Figure 4D The lead frame 134 may be connected with Figure 4B The lead frame 134 is substantially similar or identical, except that at least one of the leads 106 extends from the peripheral ring 136 directly to the heat sink 104 , thereby providing a first lead 142 of the leads 106 as previously described.

[0058] 5, a technique for preventing the electroplating process from depositing a metal coating 130 on the rear surface 120 of the heat sink 104 is shown according to one embodiment. According to the technique, a lead frame 134 is provided. The lead frame can be connected to the reference Figure 5B The lead frames 134 depicted are substantially similar or identical.

[0059] Figure 5A Leadframe 134 is shown with mold compound body 102 formed over heat sink 104. Prior to this step, semiconductor die 108 is mounted on die attach surface 110 and bond wires are formed using, for example, commonly known techniques. Subsequently, an encapsulation step is performed to form mold compound body 102. This can be done using a variety of techniques, such as injection molding, transfer molding, and lamination, to name a few. Once the encapsulation material hardens, heat sink 104 is physically supported by leads 106. As a result, connecting bars 138 are no longer needed to physically support heat sink 104.

[0060] See also Figure 5B , each of the connecting strips 138 is severed. This can be done immediately when the molding compound body 102 is hardened. By severing the connecting strips 138, the heat sink 104 becomes electrically disconnected from the peripheral ring 136, and thus electrically disconnected from each of the leads 106.

[0061] refer to Figure 5C , a metal coating 130 is formed on the lead 106 by an electroplating process. According to this process, for example, according to reference Figure 2 In the described technique, the lead wire 106 and the peripheral ring 136 are energized by a power source while being immersed in the aqueous solution. As a result, the metal coating 130 is deposited on the lead wire 106. At the same time, the cations in the water-based solution 126 are not deposited on the rear surface 120 of the heat sink 104 because the heat sink 104 is disconnected from the power source that energizes the lead wire 106. Therefore, the severance of the lead wire 106 prevents the electroplating process from depositing the metal coating 130 on the rear surface 120 of the heat sink 104.

[0062] Referring to FIG. 6 , a technique for preventing the electroplating process from depositing a metal coating 130 on the rear surface 120 of the heat sink 104 is shown according to another embodiment. In this example, a lead frame 134 is provided. The lead frame 134 may be connected to the reference Figure 4A The lead frame 134 described or referenced Figure 4C The depicted leadframe 134 is substantially similar or identical. After providing the leadframe 134, the semiconductor die 108 is encapsulated, for example according to the previously described techniques.

[0063] refer to Fig. 6A, a non-conductive coating 140 is applied to the rear surface 120 of the heat sink 104. According to an embodiment, the non-conductive coating 140 covers at least 95% of the rear surface 120 of the heat sink 104. In general, the non-conductive coating 140 can be any of a wide range of materials that can be formed to cover the rear surface 120 of the heat sink 104 and are electrically insulating. Examples of these materials include adhesives, lacquers, and epoxies, to name a few. In some embodiments, the non-conductive coating 140 is preferably provided by a material that is easily applied to the rear surface 120 and can be removed from the rear surface 120 (e.g., an adhesive tape).

[0064] refer to Figure 6B , a metal coating 130 is formed on the lead 106. This can be done using an electroplating process, such as that described above. In this case, the non-conductive coating 140 inhibits cations in the form of an aqueous solution from being deposited on the rear surface 120 of the heat sink 104. Thus, the non-conductive coating 140 prevents the electroplating process from depositing the metal coating 130 on the rear surface 120 of the heat sink 104. Alternatively, the metal coating 130 can be formed using an electroless plating process. In this case, the non-conductive coating 140 prevents any chemical reaction between the electroless plating solution and the rear surface 120 of the heat sink 104.

[0065] refer to Figure 6C After performing the electroplating process, the non-conductive coating 140 is removed from the rear surface 120. As a result, the rear surface 120 of the heat sink 104 is substantially free of the metal coating 130. Thus, the rear surface 120 of the heat sink 104 can provide a planar metal heat sink interface surface 132, as shown in FIG. Figure 2 described.

[0066] The technique of FIG. 6 allows the semiconductor package 100 to be formed without the metal coating 130 at the rear surface of the heat sink 104 without electrically disconnecting the heat sink. This technique can be used to provide a reference Figure 4C 5 to electrically disconnect leads 106 from heat sink 104 (eg, by severing tie bars 138 ) is not feasible because a connection between first lead 142 of leads 106 and heat sink 104 is required.

[0067] refer to Figure 7 , according to another embodiment, a technique for providing a planar metal heat sink interface surface 132 for a semiconductor package 100 is shown. Unlike the previously described embodiments, Figure 7 The technique does not require any measures to be taken prior to the electroplating process to prevent the metal coating 130 from being formed on the rear surface 120 of the heat sink 104, for example, as described with reference to FIGS. 4 and 5. Instead, Figure 7The technique involves processing steps that occur after the metal coating 130 process is performed. Figure 7 In the figure, reference Figure 4A The semiconductor package 100 described above. Alternatively, Figure 7 The technology can be used to provide reference Figure 4C The semiconductor package 100.

[0068] according to Figure 7 According to the technology, a metal attachment 142 is provided that is separate from the heat sink 104. The metal attachment 142 may include the same material as the heat sink 104. For example, according to one embodiment, the metal attachment 142 and the heat sink 104 are both formed of copper. After the metal coating 130 is formed on the lead 106 of the semiconductor package 100, the metal attachment 142 is fixed to the semiconductor package 100. This is done by directly adhering the lower side 144 of the metal attachment 142 to the rear surface 120 of the heat sink 104 so that the lower side 144 of the metal attachment 142 is interfaced with the rear surface 120 of the heat sink 104 and covers the rear surface 120 of the heat sink 104. In other words, the two components are brought into contact with each other and combined. Optionally, a conductive adhesive, such as solder or conductive glue, may be provided between the two components. Once the metal attachment 142 is fixed to the heat sink 104, that is, as shown in the lower figure, the rear surface 120 of the heat sink 104 is covered. According to an embodiment, the metal attachment 142 is at least as large as or larger than the exposed rear surface 120 of the heat sink 104. In this way, the metal attachment 142, when secured to the heat sink 104, completely covers any metal coating 130 formed on the rear surface 120 of the heat sink 104. An upper side of the metal attachment 142, opposite the lower side 144, provides a planar metal heat sink interface surface 132.

[0069] In the depicted embodiment, the metal attachment 142 includes a first group 146 of attachment features on its underside 144 that help form a fixed connection. The first group 146 of attachment features is configured to be combined with a second group 148 of attachment features in the rear surface 120 of the heat sink 104. The second group 148 of attachment features can be formed by a variety of techniques such as stamping, etching, etc. before or after the metal coating 130 process. The second group 148 of attachment features has a shape that is complementary to the first group 146. In addition, the complementary shape can be configured so that the first group can be inserted into the second group and can be received by the second group. As a result, the first group 146 of attachment features and the second group 148 of attachment features form an interlocking connection.

[0070] More generally, the metal attachment 142 can be secured to the heat sink 104 using any of a variety of techniques and structures. For example, the geometry and number of attachment features can be different than shown. Instead of physical interlocking features, conductive adhesives such as conductive glue, sinter, solder, etc. can be used.

[0071] refer to Figure 8 , according to another embodiment, a technique for providing a planar metal heat sink interface surface 132 for a semiconductor package 100 is shown. Similar to the previously described Figure 7 An embodiment of Figure 8 The technique does not require any measures to be taken prior to the electroplating process to prevent the metal coating 130 from being formed on the rear surface 120 of the heat sink 104 (eg, as described with reference to FIGS. 4 and 5 ). Figure 7 The technique involves processing steps that occur after the metal coating 130 process is performed. Figure 8 In the figure, reference Figure 4A The semiconductor package 100 described above. Alternatively, Figure 8 The technology can be used to provide reference Figure 4C The semiconductor package 100.

[0072] like Figure 8 As shown, the metal coating 130 is removed by performing a laser removal process. Performing the laser removal process includes directing a laser beam 154 onto the rear surface 120 of the heat sink 104 using a laser device 152 . Figure 8 The semiconductor package 100 is depicted while a process is being performed to partially remove the metal coating 130 from the heat sink 104. In general, the laser device 152 and the energy density of the laser beam 154 can be selected to provide sufficient energy concentration that destroys the material of the metal coating 130 without substantially damaging the heat sink 104. Thus, after performing the laser removal process, a semiconductor package 100 having a planar metal heat sink interface surface 132 as previously described is provided.

[0073] Referring to FIG. 9 , two different options for the laser removal process are shown. Each of these techniques is performed after the lead frame 134 is coated with the metal coating 130 , for example, according to reference Figure 5C Because no measures are taken to prevent the metal coating 130 from forming on the rear surface 102 of the heat sink, the electroplating process causes the metal coating 130 to initially form directly on and cover the rear surface 102 of the heat sink. Subsequently, the laser device 152 is used to remove the metal coating 130.

[0074] according to Fig.9A, a laser beam is used to remove a substantial portion of the metal coating 130 from the rear surface 120 of the heat sink 104, for example, at least 95% of the surface area of ​​the rear surface 120 of the heat sink 104. The remaining metal coating 130 is disposed at the outer edge of the heat sink 104 and thus forms a ring around the central portion of the heat sink 104, which is exposed from the metal coating 130 and provides a planar metal heat sink interface surface 132 as previously described. The purpose of performing the laser removal process in this manner is to ensure that any energy of the laser beam 152 does not reach the mold compound body 102. That is, the ring of the metal coating 130 acts as a buffer to ensure that the laser beam 152 is only applied to the heat sink 104. To this end, the width of the metal coating 130 in a direction parallel to the rear surface 120 can be selected to be larger than the precise tolerance of the laser process, for example, between about 50 nm and 150 nm, and the thickness of the metal coating 130 in a direction perpendicular to the rear surface 120 can be selected to be between about 0.5 μm and 15.0 μm.

[0075] according to Fig. 9B , a laser beam is used to completely remove the metal coating 130 from the rear surface 120 of the heat sink 104. Thus, the planar metal heat sink interface surface 132 is coextensive with the complete rear surface 120 of the heat sink 104. The laser process may have a precise tolerance window such that all of the metal coating 130 cannot be precisely removed without directing laser energy onto the directly adjacent mold compound body 102. Fig. 9B Depicted is a recess 154 that may be formed in the mold compound body 102, which is immediately adjacent to the heat sink 104 as a result of this effect. Thus, in applications where planarity of the mold compound body 102 is desired, it may be preferred to use reference Fig.9A Alternatively, if the maximum area of ​​the planar metal heat sink interface surface 132 relative to the area of ​​the semiconductor package 100 is more important than forming the recess 154, then reference Fig. 9B The described techniques may be preferred.

[0076] Spatially relative terms such as "under," "below," "lower," "above," "upper," etc. are used to simplify the description to explain the positioning of one element relative to a second element. These terms are intended to include different orientations of the device in addition to orientations that are different from the orientations shown in the figures. In addition, terms such as "first," "second," etc. are also used to describe various elements, regions, portions, etc., and are not intended to be limiting. Similar terms refer to similar elements throughout the specification.

[0077] As used herein, the terms "having", "containing", "including", "comprising", etc. are open terms that indicate the presence of stated elements or features, but do not exclude additional elements or features. Unless the context clearly indicates otherwise, the articles "a", "an", and "the" are intended to include the plural as well as the singular.

[0078] With the above range of variations and applications in mind, it should be understood that the present invention is not limited by the foregoing description, nor by the accompanying drawings. Instead, the present invention is limited only by the following claims and their legal equivalents.

Claims

1. A method for forming a semiconductor device, comprising: providing a semiconductor package comprising an electrically insulating mold compound body, a semiconductor die encapsulated by the mold compound body, a plurality of conductive leads, and a metal heat sink, wherein each of the plurality of conductive leads protrudes from the mold compound body, the metal heat sink comprising a rear surface exposed from the mold compound body; coating exterior portions of the leads exposed from the body of mold compound with a metallic coating; as well as After coating of the outer portions of the leads is completed, providing a planar metal heat sink interface surface on the semiconductor device, the planar metal heat sink interface surface: exposed from said body of molding compound; as well as The metal coating is substantially absent.

2. The method according to claim 1, wherein: The planar metal heat sink interface surface and the electrically conductive lead are each formed of a first metal, and wherein the metal coating comprises a second metal having a higher solderability than the first metal.

3. The method according to claim 2, wherein: The planar metal heat sink interface surface and the conductive leads are each formed of copper, and wherein the metal coating comprises at least one of gold, nickel, tin, and silver.

4. The method according to claim 1, wherein: The planar metal heat sink interface surface is provided by the rear surface of the heat sink, wherein coating the outer portions of the leads comprises an electroplating process, and wherein providing the planar metal heat sink interface surface substantially free of the metal coating comprises preventing the electroplating process from depositing the metal coating on the rear surface of the heat sink.

5. The method according to claim 4, wherein: A lead frame is provided including a peripheral ring and a connecting bar, each of the leads being connected to the peripheral ring and physically separated from the heat sink, the connecting bar being connected between the peripheral ring and the heat sink, and wherein preventing the electroplating process from depositing the metal coating on the rear surface of the heat sink includes severing the connecting bar before performing the electroplating process.

6. The method according to claim 4, wherein: A lead frame is provided comprising a peripheral ring, at least one of the leads being physically connected between the peripheral ring and the heat sink, and wherein preventing the electroplating process from depositing the metal coating on the rear surface of the heat sink comprises applying a non-conductive coating on the rear surface of the heat sink prior to performing the electroplating process.

7. The method according to claim 1, wherein: Providing the planar metal heat sink interface surface comprises: providing a metal attachment separate from the heat sink; and After coating the outer portion of the lead with the metal coating, the metal attachment is attached to the rear surface of the heat sink.

8. The method according to claim 7, wherein: Coating the outer portion of the lead includes an electroplating process, wherein the electroplating process forms the metal coating on the rear surface of the heat sink, and wherein the metal attachment completely covers the metal coating on the rear surface once attached to the heat sink.

9. The method according to claim 7, wherein: Attaching the metal attachment to the rear surface includes adhering the metal attachment directly to the rear surface so that a lower side of the metal attachment interfaces with and covers the rear surface of the heat sink, wherein an upper side of the metal attachment opposite the lower side provides the planar metal heat sink interface surface.

10. The method according to claim 9, wherein: The underside of the attachment includes a first set of attachment features, wherein the rear surface of the heat sink includes a second set of attachment features, wherein the first set of attachment features and the second set of attachment features are complementarily formed, and wherein the attachment is secured to the heat sink by forming an interlocking connection between the first set of attachment features and the second set of attachment features.

11. The method according to claim 1, wherein: The metal coating is formed directly on the rear surface of the heat sink during coating of the outer portion of the lead, and wherein providing the planar metal heat sink interface surface includes removing the metal coating formed directly on the rear surface of the heat sink.

12. The method according to claim 11, wherein: Removing the metal coating layer formed directly on the rear surface of the heat sink includes performing a laser removal process that removes the metal coating layer using a laser beam.

13. The method according to claim 12, wherein: The metal coating is removed from a central portion of the heat sink such that a ring of the metal coating extending to an outer edge of the heat sink remains on the heat sink after the laser removal process.

14. The method according to claim 12, wherein: The metal coating is completely removed from the heat sink.

15. A method of forming a semiconductor device, comprising: providing a semiconductor package comprising an electrically insulating mold compound body, a semiconductor die encapsulated by the mold compound body, a plurality of conductive leads, and a metal heat sink, wherein each of the plurality of conductive leads protrudes from the mold compound body, the metal heat sink comprising a rear surface exposed from the mold compound body; performing an electroplating process on the semiconductor package, the electroplating process forming a metal coating on outer portions of the leads exposed from the body of the mold compound; as well as The metal coating is prevented from being formed on the rear surface of the heat sink during the electroplating process.

16. The method according to claim 15, wherein: Performing the electroplating process includes immersing the leads and the rear surface of the semiconductor package in an aqueous solution, and wherein preventing the metal coating from forming on the rear surface includes electrically disconnecting the heat sink from the leads prior to performing the electroplating process.

17. The method according to claim 16, wherein: The semiconductor package is provided on a lead frame, the lead frame including a peripheral ring and a connecting bar, each of the leads being connected to the peripheral ring and disconnected from the heat sink, the connecting bar being connected between the peripheral ring and the heat sink, and wherein electrically disconnecting the heat sink from the leads includes cutting the connecting bar.

18. The method according to claim 16, wherein: Preventing the metal coating from being formed on the rear surface of the heat sink includes applying a non-conductive adhesive on the rear surface of the heat sink before performing the electroplating process.

19. A packaged semiconductor device, comprising: an electrically insulating molding compound body; a metal heat sink including a rear surface exposed from the mold compound body and a die attach surface opposite the rear surface; a semiconductor die encapsulated by the molding compound body and mounted on the heat sink; a plurality of electrically conductive leads, each of the leads including an exterior portion exposed from the molding compound body; a metallic coating covering the outer portion of each of the leads; as well as A planar metal heat sink interface surface that: exposed from said body of molding compound; thermally coupled to the semiconductor die via the heat sink; and The metal coating is substantially absent.

20. The packaged semiconductor device according to claim 19, wherein: The planar metal heat sink interface surface and the electrically conductive lead are each formed of a first metal, and wherein the metal coating comprises a second metal having a higher solderability than the first metal.

21. The packaged semiconductor device according to claim 19, wherein: The rear surface of the heat sink provides the planar metal heat sink interface surface.

22. The packaged semiconductor device of claim 19, further comprising a metal attachment separate from the heat sink and fixed to the heat sink at its underside, and wherein An upper side of the metal attachment provides the planar metal heat sink interface surface.

23. The packaged semiconductor device of claim 19, wherein: The metal coating is additionally formed as a ring on the rear surface of the heat sink, the ring surrounding a central portion of the heat sink exposed from the metal coating.

24. The packaged semiconductor device of claim 19, further comprising a recess formed in the body of molding compound, wherein: The groove surrounds the rear surface of the heat sink, and wherein the rear surface of the heat sink is completely free of the metal coating.

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