Connection member with bulk body and electrically and thermally conductive coating

Abstract

A connection member for connecting an electronic chip, wherein the connection member comprises a bulk body, and a coating at least partially coating the bulk body and comprising a material having higher electric and higher thermal conductivity than the bulk body, wherein a ratio between a thickness of the coating and a thickness of the bulk body is at least 0.0016 at at least a part of the connection member.

Claims

1. A connection member for connecting an electronic chip, wherein the connection member comprises: a bulk body; a coating at least partially coating the bulk body and comprising a material having higher electric conductivity and higher thermal conductivity than the bulk body; wherein a ratio between a thickness of the coating and a thickness of the bulk body is at least 0.0016 at at least a part of the connection member; wherein the coating comprises or consists of at least one of the group consisting of copper, a copper alloy, zinc, and zinc alloy.

2. The connection member according to claim 1, wherein at least a portion of the coating has a thickness in a range between 4 m and 100 m.

3. The connection member according to claim 1, wherein the coating has a thickness of at least 7 m.

4. The connection member according to claim 1, configured as a leadframe.

5. The connection member according to claim 1, configured as a clip.

6. The connection member according to claim 1, wherein a thickness of the bulk body is in a range between 100 m and 2500 m.

7. The connection member according to claim 1, wherein the bulk body comprises or consists of iron.

8. The connection member according to claim 7, wherein the bulk body comprises or consists of one of an iron alloy, a steel alloy, and steel.

9. (canceled)

10. The connection member according to claim 1, comprising at least one further coating on at least part of the coating, wherein the further coating and the coating are made of different materials.

11. The connection member according to claim 109, wherein the at least one further coating comprises at least one of the group consisting of Ag, Ni, Ni/NiP, Ni/NiP/Ag, Ni/Pd/AuAg, Ni/Pd/AuPd, Ni/Pd/Au, Sn, and SnPb.

12. The connection member according to claim 1, wherein the coating is applied directly on the bulk body.

13. The connection member according to claim 1, wherein the coating coats the entire surface of the bulk body.

14. A method of manufacturing a connection member for connecting an electronic chip, wherein the method comprises: providing a bulk body comprising iron; at least partially coating the bulk body by a coating ; forming at least a portion of the coating with a thickness between 4 m and 100 m, wherein the coating comprises a material having higher electric conductivity and higher thermal conductivity than the bulk body and the coating comprises or consists of at least one of the group consisting of copper, a copper alloy, zinc, and zinc alloy; forming the connection member with a ratio between a thickness of the coating and a thickness of the bulk body of at least 0.0016 at at least a part of the connection member.

15. (canceled)

16. The method according to claim 14, wherein forming the coating comprises at least one of the group consisting of plating, physical vapor deposition, chemical vapor deposition, rolling at least one copper comprising sheet onto the bulk body, and sputtering.

17. An electronic component, wherein the electronic component comprises: a leadframe comprising a non-copper bulk body at least partially coated with a coating comprising copper, the coating having a thickness of more than 4 m; an electronic chip coupled with the leadframe: and an encapsulant encapsulating part of the leadframe and the electronic chip; wherein a portion of the leadframe extending beyond the encapsulant comprises a further coating on the coating, wherein this further coating is not formed on another portion of the leadframe being encapsulated by the encapsulant.

18. The electronic component according to claim 17, wherein at least part of the coating is coated by a further coating.

19. The electronic component according to claim 17, configured as a power package.

20. The electronic component according to claim 17, wherein the electronic chip is a power semiconductor chip.

21. The electronic component according to claim 17, wherein the electronic chip is configured for an operation with a vertical current flow.

22. (canceled)

23. (canceled)

24. A method of manufacturing an electronic component, wherein the method comprises: providing a leadframe with a non-copper bulk body at least partially coated with a coating, the coating having a thickness of more than 4 m, the coating comprising a material having higher electric conductivity and higher thermal conductivity than the bulk body, and the coating comprises or consists of at least one of the group consisting of copper, a copper alloy, zinc, and zinc alloy, wherein a ratio between a thickness of the coating and a thickness of the bulk body is at least 0.0016 at at least a part of the bulk body; and coupling an electronic chip with the leadframe.

25. The method according to claim 24, wherein coupling the electronic chip with the leadframe comprises mounting the electronic chip on the leadframe.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The accompanying drawings, which are included to provide a further understanding of exemplary embodiments and constitute a part of the specification, illustrate exemplary embodiments.

[0047] In the drawings:

[0048] FIG. 1 schematically illustrates a cross-sectional view of a connection member according to an exemplary embodiment in which a bulk body of steel is coated with a copper coating.

[0049] FIG. 2 to FIG. 8 show cross-sectional views of portions of connection members according to exemplary embodiments in which a bulk body of steel is coated with a copper coating which is, in turn, coated by one or more further coating layers.

[0050] FIG. 9 illustrates a three-dimensional view of an electronic component according to an exemplary embodiment comprising a first leadframe-type connection member and a second clip-type connection member both electrically and mechanically connecting an electronic chip.

[0051] FIG. 10 illustrates a cross-sectional view of the electronic component according to FIG. 9.

[0052] FIG. 11 illustrates a three-dimensional view of an encapsulated electronic component according to an exemplary embodiment.

[0053] FIG. 12 illustrates a three dimensional view of the electronic component according to FIG. 11 without encapsulant.

[0054] FIG. 13 illustrates a cross-sectional view of an electronic component according to an exemplary embodiment.

DETAILED DESCRIPTION

[0055] The illustration in the drawing is schematically and not to scale.

[0056] FIG. 1 schematically illustrates a cross-sectional view of a connection member 100 (such as a leadframe or a clip) according to an exemplary embodiment in which a bulk body 104 of steel is directly coated with a copper coating 106.

[0057] The connection member 100 is provided for electrically, mechanically and thermally connecting an electronic chip 102 in various applications (see for instance FIG. 9 to FIG. 13). As can be taken from FIG. 1, the entire surface of the steel bulk body 104 is covered with copper coating 106 so that copper material forms the entire exterior surface of the connection member 100 in the embodiment according to FIG. 1. In other words, the steel bulk body 104 is completely encapsulated by the copper coating 106. The copper coating 106 is applied on the bulk body 104 as a thin film of homogeneous thickness, d. The thickness, d, of the copper coating 106 is much lower than a thickness, D, of the bulk body 104. Preferably, a ratio between the thickness, d, of the coating 106 and the thickness, D, of the bulk body 104 is at least 0.0016. This ensures an improvement of the thermal and electric performance of the connection member 100 so that it becomes suitable for use in power semiconductor applications such as power packages. The mentioned ratio should at the same time be preferably not more than 0.4, because otherwise a plating procedure used for forming the coating 106 on the bulk body 104 would take too much time and would reduce the efficiency of the manufacturing procedure. An absolute value of the thickness, d, of the coating 106 may for instance be in a range between 4 m and 100 m, preferably in a range between 10 m in 30 m. For instance, the absolute value of the thickness, D, of the bulk body 104 may be 250 m.

[0058] Hence, FIG. 1 shows a cross-section of a steel core leadframe as connection member 100 with copper metallization as coating 106. In the shown embodiment, the bulk body 104 made of steel is coated with the coating 106 in form of one layer of copper metallization with a certain thickness, d, to improve the electrical and thermal performance of a power package or other electronic component 114 in which the connection member 100 is implemented.

[0059] Besides steel bulk material with copper metallization, alternative materials for both the bulk material (for instance other metals or even non-conductive materials) and the metallization layer (for instance other metals) are also possible in other exemplary embodiments. Some examples are listed in Table 1.

TABLE-US-00002 TABLE 1 Overview of possible bulk materials and metallizations layer Metallization Bulk Material Layer (s) Preferred Iron, steel Cu or Cu-alloys (iron-alloy), (for instance steel-alloys CuZn, CuSn) Alternatives Various types of Zinc and zinc- steel, such as: alloys a) Carbon Steels b) Alloy Steels c) Stainless Steels d) Tool Steels

[0060] FIG. 2 to FIG. 8 show cross-sectional views of connection members 100 according to exemplary embodiments in which a bulk body 104 of steel is coated with a copper coating 106 which is, in turn, coated by one or more further coating layers 108.

[0061] In particular, further coating of one or more metal layers on a copper-coated steel leadframe surface makes it possible to adjust the properties of the connection member 100 for a respective application. Examples for such applications are wire-bonding, die attach or adhesion purposes.

[0062] For example, various plating procedures can be applied on the top of a steel leadframe with copper metallization, as shown for instance in FIG. 1. The choice of one or more plating layers as further coating layers 108 depends on the assembly technology and materials used (for example die attach materials, wire bonding, mold compound, etc.) and also on an application of an electronic component 114 such as a package. As examples, FIG. 2 to FIG. 8 show some plating layers as further coating layers 108 which can be applied onto for instance a steel leadframe with a copper metallization. The thickness of at least one further coating layer 108 can follow a current thickness for a copper based leadframe.

[0063] Thus, as shown in each of FIG. 2 to FIG. 8, the connection member 100 may comprise one or more further coatings 108 on at least part of the coating 106. The further coating 108 and the coating 106 may be made of different materials to provide different functions. As can be taken from FIG. 2 to FIG. 7, the at least one further coating 108 may comprise one of Ag, Ni, Ni/NiP, Ni/NiP/Ag, Ni/Pd/AuAg, Ni/Pd/AuPd, Ni/Pd/Au, Sn, and SnPb, depending on a desired application. The respective one or more further coatings 108 according to FIG. 2 to FIG. 7 are as follows:

[0064] Referring to FIG. 2, a single further layer is applied as a further coating 108 on an exterior surface of the coating 106 and is made of Ag so that the exterior surface of the connection member 100 of FIG. 2 is highly appropriate for wire bonding, and in particular for attaching gold or copper material.

[0065] Referring to FIG. 3, a single further layer is applied as a further coating 108 on an exterior surface of the coating 106 and is made of Ni so that the exterior surface of the connection member 100 of FIG. 3 is highly appropriate for aluminum wire bonding.

[0066] Referring to FIG. 4, a double layer is applied as further coating 108 on an exterior surface of the coating 106 and is made of a first layer of Ni and a second layer (as surface layer) of NiP. Also with this double layer, the exterior surface of the connection member 100 of FIG. 4 is highly appropriate for aluminum wire bonding.

[0067] Referring to FIG. 5, a layer stack is applied as further coating 108 on an exterior surface of the coating 106 and is made of a first layer of Ni and a second layer (partially as surface layer) of NiP. Only a portion of the second layer of NiP is additionally covered with a third further layer (as surface layer), made of Ag. With this three layer stack of further coating 108, the exterior surface of the connection member 100 of FIG. 5 is highly appropriate for the purposes described above referring to FIG. 2 and FIG. 4.

[0068] Referring to FIG. 6 and FIG. 7, a three layer stack is formed as further coating 108 on an exterior surface of coating 106. According to FIG. 6, the three layer stack is composed of Ni/Pd/AuAg or Ni/Pd/AuPd, whereas the three layer stack of FIG. 7 is composed of Ni/Pd/Au. With each of these three layers stacks, the exterior surface of the connection member 100 of FIG. 6 and FIG. 7 is highly appropriate for gold or copper wire bonding.

[0069] A further coating of metal layers on the external leads of a Cu-coated steel leadframe after molding and post-mold curing process (for solderability purpose) is possible as well. For the external leads after a molding and post-mold curing process, Sn or Sn/Pb plating can be applied at the external leads (see FIG. 8). The thickness of Sn or Sn/Pb can follow the same thickness used for a copper based leadframe. If a Ni/Pd/AuAg-plated or Ni/Pd/Au-plated stack is used for external leads during a leadframe plating process, it is optional to plate Sn or Sn/Pb after molding and post-mold curing process.

[0070] The further coatings 108 shown in FIG. 2 to FIG. 7 may all be located at least partially in the interior of an encapsulant (compare for example reference numeral 116 in FIG. 13) when a power package-type electronic component 114 is readily manufactured. In contrast to this, FIG. 8 described in the following in further detail illustrates a further coating 108 on coating 106 of a connection member 100, which further coating 108 is arranged (and preferably is applied) after encapsulation on a portion of connection member 100 extending beyond encapsulant 116 (compare FIG. 13).

[0071] Referring to FIG. 8, the shown further coating 108 is applied on only a part of an exterior surface of coating 106 and comprises for instance Sn or SnPb. This further coating 108 may for instance be only formed on a portion of the connection member 100 extending beyond encapsulant 116. Only this portion of the connection member 100 is then to be connected by soldering, as promoted by the further coating 108 being made of a solderable material, with a mounting base such as a printed circuit board (compare reference numeral 118 in FIG. 13). Hence, the embodiment of FIG. 8 provides an Sn or SnPb-plated steel leadframe with Cu metallization (external leads).

[0072] FIG. 9 illustrates a three dimensional view of an electronic component 114 according to an exemplary embodiment comprising a first (here leadframe-type) connection member 100 (i.e. configured as leadframe 110) and a second (here clip-type) connection member 100 (i.e. configured as clip 112). Both connection members 100 electrically and mechanically connect an electronic chip 102 such as a semiconductor power chip. FIG. 10 illustrates a cross-sectional view of the electronic component 114 according to FIG. 9 embodied as power package.

[0073] Thus, the electronic component 114 shown in FIG. 9 and FIG. 10 comprises, as the first connection member 100, the leadframe 110 formed on the basis of a punched and bent planar metal sheet. The leadframe 110 comprises an iron comprising (for instance steel) bulk body 104 with thickness, D, of for instance 250 m coated with coating 106 comprising copper and having a much smaller thickness, d, of for instance 10 82 m. In the shown embodiment, the leadframe 110 comprises two different and separate sections, i.e. a mounting section 180 for mounting the electronic chip 102, and a pin section 182 comprising pins for an electric coupling with an electronic environment of the electronic component 114.

[0074] A lower main surface of the electronic chip 102 is mounted on the mounting section 180 of the leadframe 110 to thereby establish an electrically conductive and thermally conductive connection between the electronic chip 102 and the leadframe 110. For instance, the electronic chip 102 may be configured as a transistor chip having a transistor (in particular field effect transistor) monolithically integrated therein. For example, a drain pad of the electronic chip may be located on the lower main surface and may be coupled with the leadframe 110 by the described mounting.

[0075] As mentioned above, the electronic component 114 additionally comprises, as the second connection member 100, the clip 112 which may also be formed on the basis of a punched and bent planar metal sheet. The clip 112 comprises an iron comprising (for instance steel) bulk body 104 with thickness, D, of for instance 250 m coated with coating 106 comprising copper and having a much smaller thickness, d, of for instance 10 m.

[0076] An upper main surface of the electronic chip 102 is connected with one terminal of the clip 112 having another terminal being mounted on the pin section 182 of the leadframe 110. Thereby, a further electrically conductive and thermally conductive connection is established between the electronic chip 102 and the leadframe 110 via the clip 112. As mentioned above, the electronic chip 102 may be configured as a transistor chip having both a source pad and a gate pad located on the upper main surface thereof, both of which being coupled with the leadframe 110 via the clip 112. In the shown embodiment, the electronic chip 102 may be configured for an operation with a vertical current flow, i.e. along a vertical direction of FIG. 10.

[0077] A detail 184 in FIG. 9 and a detail 186 in FIG. 10 show the thermally conductive and electrically conductive coating 106 of the clip 112 improving the electric and thermal performance of the power package-type electronic component 114 with the power chip-type electronic chip 102 with vertical current flow. Correspondingly, a detail 188 in FIG. 9 and a detail 190 in FIG. 10 show the thermally conductive and electrically conductive coating 106 of the leadframe 110 also improving the electric and thermal performance of the electronic component 114 with the electronic chip 102. Thus, current flowing in the electronic component 114 may be conducted in a low ohmic way also by the connection members 100. Moreover, heat generated by electronic chip 102 during operation may be efficiently removed by the connection members 100 from the electronic component 114.

[0078] Two types of simulations have been carried out to show that exemplary embodiments improve both the electric and thermal performance of connection members 100 and corresponding electronic components 114:

[0079] To assess the electric performance of exemplary embodiments, package RDSon simulations and actual sample evaluations were conducted. RDSon hereby refers to the source to drain resistance of an electronic component 114 of the type shown in FIG. 9 and FIG. 10 when the device is on. The smaller the RDSon value, the better is the electric performance.

[0080] The simulation results are shown in Table 2. The thickness of clip materials and leadframe bulk material is the same, namely 250 m. The scenarios use Cu materials for the clip, while they use Fe material or SPCE materials as leadframe bulk materials. SPCE is one type of steel material (SPCE =Steel Plate Cold deep drawn Extra non-ageing) which has been used for actual sample evaluations. For some of the scenarios, Fe is considered as bulk material with the thickness of Cu metallization of 1.5 m, 7 m and 20 m, respectively. Similarly, for the other scenarios, SPCE is considered as bulk material with the thickness of Cu metallization of 1.5 m, 7 m and 20 m, respectively.

[0081] Table 2 shows that package RDSon reduces as the thickness of Cu metallization increases. In particular the results obtained for scenarios 2, 3, 5 and 6 are within the specification of many package types. When the thickness of the coating 106 is at least 4 m and/or the ratio between the thickness of the coating 106 and the thickness of the bulk body 104 is at least 1.6%, good results are obtained for many package types.

TABLE-US-00003 TABLE 2 Summary of simulation results vs. actual sample experiments Scenario 1 2 3 4 5 6 Leadframe Fe Fe Fe SPCE SPCE SPCE 250 m 250 m 250 m 250 m 250 m 250 m with with with with with with 1.5 m 7 m 20 m 1.5 m 7 m 20 m Cu Cu Cu Cu Cu Cu Clip Cu Cu Cu Cu Cu Cu 250 m 250 m 250 m 250 m 250 m 250 m Total 1.660 1.598 1.534 1.735 1.638 1.550 RDSONon (m) Measured 1.55-2.0 Ron range from experiments (m)

[0082] Hence, the RDSon simulation for TDSON 8 shows that, as the copper thickness increases, the RDSon decreases.

[0083] Moreover, thermal simulations have been performed using a TO263 package. Such a package or electronic component 114 is shown with encapsulant 116 in FIG. 11 and without encapsulant 116 in FIG. 12. It turned out that proper small thermal resistance (Rth) values can be obtained by exemplary embodiments. More specifically, Rth simulations have been conducted for TO263 package. The chip size has been 3.82.6 mm.sup.2 and the chip thickness is 70 m. The simulation results are shown in Table 3.

TABLE-US-00004 TABLE 3 Summary of Rth simulation results (Rth relates to the bottom of the package fixed to 85 C.) Scenario 1 2 3 4 5 6 Leadframe Fe Fe Fe SPCE SPCE SPCE 1270/500 1270/500 1270/500 1270/500 1270/500 1270/500 m with m with m with m with m with m with 1.5 m Cu 7 m Cu 20 m Cu 1.5 m Cu 7 m Cu 20 m Cu Rth 1.346 1.329 1.292 1.716 1.687 1.624 [K/W]

[0084] The thickness of leadframe bulk material is the same. The various scenarios use Fe material or SPCE materials as leadframe bulk materials. For other scenarios, Fe is considered as bulk material with the thickness of Cu metallization of 1.5 m, 7 m and 20 m, respectively. Similarly, for the other scenarios, SPCE is considered as bulk material with the thickness of Cu metallization of 1.5 m, 7 m and 20 m, respectively.

[0085] The values in Table 3 show that, in particular with a sufficiently high thickness of the coating 104, the obtainable thermal resistance is compatible with specifications of many package types. In particular, the Rth simulation for TO 263-3 shows that as Cu thickness increases, the Rth of the electronic component 114 is advantageously reduced. A corresponding concept can also be applied to other power packages/devices, such as TO, TPAK, etc. This means that it is possible to use in particular a steel leadframe with Cu metallization to reduce the manufacturing effort while at the same time meeting the specification of many package types.

[0086] FIG. 13 illustrates a cross-sectional view of an electronic component 114 configured as an encapsulated electronic chip 102 on a leadframe 110 as chip carrier according to an exemplary embodiment. More specifically, FIG. 13 illustrates a cross-sectional view of an electronic component 114, which is embodied as a Transistor Outline (TO) package, according to an exemplary embodiment of the invention. The electronic component 114 is mounted on a mounting base 118, here embodied as printed circuit board.

[0087] The mounting base 118 comprises an electric contact 134 embodied as a plating in a through hole of the mounting base 118. When the electronic component 114 is mounted on the mounting base 118, electronic chip 102 of the electronic component 114 is electrically connected to the electric contact 134 via the leadframe 110 of the electronic component 114.

[0088] The electronic component 114 comprises an electrically conductive connection member 100 (here embodied as leadframe 110), the electronic chip 102 (which is here embodied as a power semiconductor chip) adhesively or by soldering mounted on the connection member 100 (see solder structure 158), and encapsulant 116 (here embodied as mold compound) encapsulating part of the connection member 100 and part of the electronic chip 102. As can be taken from FIG. 13, a pad on an upper main surface of the electronic chip 102 is electrically coupled to the connection member 100 via a bond wire 150. Chip pads 196, 198 are provided on a lower and on an upper main surface of electronic chip 102.

[0089] During operation of the power package or electronic component 114, the power semiconductor chip in form of the electronic chip 102 generates a considerable amount of heat. At the same time, it should be ensured that any undesired current flow between a bottom surface of the electronic component 100 and an environment is reliably avoided.

[0090] For ensuring electrical insulation of the electronic chip 102 and removing heat from an interior of the electronic chip 102 towards an environment, an electrically insulating and thermally conductive interface structure 152 may be optionally provided which covers an exposed surface portion of the connection member 100 and a connected surface portion of the encapsulant 116 at the bottom of the electronic component 114. The electrically insulating property of the interface structure 152 prevents undesired current flow even in the presence of high voltages between an interior and an exterior of the electronic component 114. The thermally conductive property of the interface structure 152 promotes a removal of heat from the electronic chip 102, via the electrically conductive connection member 100 (of thermally properly conductive copper), through the interface structure 152 and towards a heat dissipation body 146. The heat dissipation body 146, which may be made of a highly thermally conductive material such as copper or aluminum, has a base body 154 directly connected to the interface structure 152 and has a plurality of cooling fins 156 extending from the base body 154 and in parallel to one another so as to remove the heat towards the environment.

[0091] As can be taken from a detail 177, a portion of the leadframe 110 extending beyond the encapsulant 116 comprises copper coating 106 on steel bulk body 104 and a further coating 108 on the coating 106. The further coating 108 may for example be made of tin. This further coating 108 is not formed on another portion of the leadframe 110 being encapsulated by the encapsulant 116 (see detail 179). The solderable material of the further coating 108 allows the formation of a solder connection between the leadframe 110 and the mounting base 118. The continuous coating 106 increases the electric and thermal performance of the electronic component 114, while the spatially selectively applied further coating 108 simultaneously promotes a reliable solder connection with the mounting base 118.

[0092] According to FIG. 13, the electronic chip 102 may be coupled with the leadframe 110 by mounting the electronic chip 102 on the leadframe 110 with a solder connection between the electronic chip 102 and the leadframe 110.

[0093] With the migrating of bonding wires from gold to copper wire in recent years, leadframe materials become one of most costly materials in the package assembly. Thus, a reduction of the effort in terms of manufacturing of a leadframe becomes more and more important.

[0094] In order to reduce the effort for leadframe manufacture, leadframe materials may be changed. Also the manufacture of high density leadframes (such as larger strip size, etc.) is an option. It is also possible to convert an etched leadframe to a stamped leadframe for high volume parts. However, such concepts result only in a moderate reduction of the effort of manufacturing leadframes.

[0095] Exemplary embodiments implement bulk leadframe materials on the basis of iron, in particular steel and improve thermal and electric performance by an appropriate coating.

[0096] Steel can be obtained and processed with reasonable effort but involves the challenge of a lower electrical and thermal conductivity compared with copper material. In order to overcome this shortcoming, an exemplary embodiment provides a connection member such as a leadframe including an iron comprising bulk body with a coating or metallization (for instance manufactured by plating or by other methods). The coating may be made of a material which properly adheres on the iron comprising bulk body and at the same time increases the thermal and electrical conductivity of the manufactured connection member as a whole. The coating, which is preferably made of or comprises copper, may be applied directly onto a steel-based leadframe surface to improve the electrical and thermal performance of the leadframe. A correspondingly manufactured connection member can therefore be used also for power packages as well as other integrated circuit (IC) packages as examples of electronic components of exemplary embodiments.

[0097] Table 4 shows a comparison of electrical conductivity and thermal conductivity for copper and steel materials.

TABLE-US-00005 TABLE 4 Electrical conductivity and thermal conductivity at 20 C. Base Electrical Thermal conductivity Material conductivity [S/m] [W/(m*K)] Pure Cu 5.8 10.sup.7 385~401 Pure Fe 1.03 10.sup.7 72.7~79.5 Stainless 1.1 10.sup.6 16.3~24 steel Carbon 6.99 10.sup.6 36~54 Steel Zinc 1.69 10.sup.7 116

[0098] As seen in Table 4, the electrical conductivity of steel is about 50 times lower than that of copper material. The thermal conductivity of steel is about 5 to 10 times lower than that of copper material. In order to improve both electrical and thermal conductivity of a steel-based leadframe for power package application, a copper metallization may be applied onto the steel-based leadframe surface in an exemplary embodiment.

[0099] It should be noted that the term comprising does not exclude other elements or features and the a or an does not exclude a plurality. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs shall not be construed as limiting the scope of the claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.