Method of manufacturing a substrate for a semiconductor device, corresponding substrate and semiconductor device

Abstract

Various embodiments of this disclosure relate to methods of manufacturing substrates for semiconductor devices, corresponding substrates, and semiconductor devices. A pre-molded leadframe for a semiconductor device is manufactured by molding an electrically insulating material onto a layered engraving structure of conductive material including die pads for semiconductor device components. A first die pad and a second die pad are coupled at adjacent locations on the front surface of the leadframe via a first extension from the first die pad and a second extension from the second die pad, and a bridging member couples the first and second extensions at the rear surface of the leadframe. The bridging member provides a sacrificial connection between the first and second extensions, which is selectively removed after molding the electrically insulating material to decouple the first and second die pads from each other. The removal of the sacrificial connection leaves cavities formed on the second surface of the leadframe without affecting the shape of the die pads.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to Italian Patent Application No. 102021000017231, filed on June 30, 2021, the contents of which are incorporated herein by reference in their entirety to the fullest extent permitted by law. Technical Field

[0003] This specification relates to the manufacture of semiconductor devices.

[0004] One or more embodiments can be applied to the manufacture of pre-molded lead frames for semiconductor devices. Background Technology

[0005] Semiconductor devices may include one or more semiconductor integrated circuit chips or dies disposed (attached) on a substrate such as a lead frame.

[0006] Plastic packages are commonly used for semiconductor devices. Such packages may include a lead frame that provides a base substrate comprising a conductive material, such as copper, the size and shape of which are adapted to accommodate a semiconductor chip or die, and provides pad connections (leads) for these chips or dies.

[0007] The term “leadframe” (or “lead frame”) is currently used (see, for example, the USPC Combined Glossary) to refer to a metal frame used to support an integrated circuit chip or die, and electrical leads that interconnect the integrated circuit in the die or chip to other components or contacts.

[0008] Leadframes are typically produced using techniques such as photolithography. Using this technique, metal material in the form of foil or strip (e.g., copper) is etched onto the top and bottom sides to create various pads and leads.

[0009] The so-called “pre-molded” leadframe includes, for example, an electrically insulating resin, such as epoxy resin, molded onto the engraved (e.g., photo-etched) metal leadframe structure using a flat molding tool.

[0010] The space left in the etched metal material is filled with pre-molded resin, and the resulting lead frame has the same total thickness as the original etched lead frame.

[0011] After pre-molding (e.g., curing the molding resin by heat or UV curing), deburring and coating processes can be applied to provide a clean top / bottom metal surface for the lead frame.

[0012] This pre-molded leadframe is used in a variety of semiconductor devices.

[0013] Some pre-molded leadframes (e.g., for power semiconductor devices packaged in square flat no-lead (QFN) packages) may include multiple die pads for arranging semiconductor chips or dies and associated components.

[0014] These die pads are intended to be isolated from each other. However, when the pre-molded resin is molded onto the sculpted metal structure of the leadframe, connecting rods can be used to mechanically couple these pads to a metal (e.g., copper) frame within the leadframe and / or to other die pads within the leadframe.

[0015] These connecting rods can be used to avoid negative phenomena such as undesirable displacement of bare die pads or "flash" of pre-molded resin on the metal surface of the leadframe.

[0016] The connecting rod is then removed, for example, during a subsequent (semi)etching process, and applied to the pre-molded lead frame to form wettable sides for soldering.

[0017] However, this process may leave some defects that are difficult to control in production and may lead to scrapped parts or quality problems at the customer board level.

[0018] There is a need in this field to help avoid the aforementioned defects. Summary of the Invention

[0019] One or more embodiments relate to a method.

[0020] One or more embodiments involve a corresponding (pre-molded) lead frame.

[0021] One or more embodiments relate to corresponding semiconductor devices. A square flat no-lead (QFN) power device may be an example of such a device.

[0022] One or more embodiments provide a metal (e.g., copper) bottom and top side design for a leadframe that provides removable temporary (sacrificial) connecting rods without negatively impacting, for example, the die pad profile on the back or bottom side of the device package.

[0023] One or more embodiments do not include additional process steps beyond those required for conventional pre-molded leadframe manufacturing.

[0024] One or more embodiments may provide a multi-die pad pre-molded leadframe, including die pad connecting rods having bridge-like portions on the back (or bottom) side of the leadframe. These bridge-like portions are arranged away from the die pads thus connected and can be removed during subsequent processing (such as a second half-etch step after molding) without adversely affecting the die pad profile.

[0025] One or more embodiments effectively reduce partial rejection due to defects in the die pads. Therefore, visual inspection of a semiconductor device (e.g., a power QFN package) including a pre-molded leadframe according to an embodiment will identify die pads (e.g., die pads for low-voltage dies) with a regular (virtually perfect) rectangular profile that has recessed portions (cavities) in the molding that expose the sides of the bridging, which are "disconnected" due to the removal of the connecting rods. Attached Figure Description

[0026] One or more embodiments will now be described by way of example only with reference to the accompanying drawings, in which:

[0027] Figure 1A and 1B It is a plan view of the pre-molded lead frame;

[0028] Figure 1C Showing overlapping Figure 1A and 1B The view;

[0029] Figure 2 It is reproduced at a magnified scale. Figure 1C The view of the portion indicated by arrow II;

[0030] Figure 3 It is along Figure 2 A cross-sectional view of line III-III;

[0031] Figure 4 After removing the connecting elements as discussed in this article, it is essentially the same as Figure 1C A view of the corresponding pre-molded lead frame;

[0032] Figure 5 It is reproduced at a magnified scale. Figure 4 The view of the portion indicated by arrow V; and

[0033] Figure 6 It is along Figure 5 The cross-sectional view of line VI-VI in the diagram. Detailed Implementation

[0034] Unless otherwise specified, corresponding numbers and symbols in the different figures generally refer to corresponding parts. The figures are drawn to clearly illustrate relevant aspects of the embodiments and are not necessarily drawn to scale. The edges of features drawn in the figures do not necessarily indicate the termination of the feature range.

[0035] In the following description, various specific details are shown to provide a thorough understanding of various examples of embodiments according to the description. Embodiments may be obtained without one or more specific details, or by utilizing other methods, components, materials, etc. In other instances, known structures, materials, or operations are not shown or described in detail so as not to obscure the various aspects of the embodiments.

[0036] References to "embodiment" or "one embodiment" in the structure of this specification are intended to indicate that a particular configuration, structure, or feature described with respect to that embodiment is included in at least one embodiment. Therefore, phrases such as "in an embodiment," "in one embodiment," etc., that may appear at various points in this specification do not necessarily refer precisely to the same embodiment. Furthermore, specific configurations, structures, or features may be combined in any suitable manner in one or more embodiments.

[0037] The headings / references used herein are provided for convenience only and therefore do not limit the scope of protection or the scope of the embodiments.

[0038] Semiconductor devices (such as, for example, power devices) include a substrate (lead frame), on which semiconductor chips or dies and other electrical components are mounted using solder adhesive or other processes, wherein wires and / or “ribbons” provide electrical connections to the semiconductor chip.

[0039] Encapsulation with molding resins (such as epoxy resins) binds these components into the (plastic) body of the semiconductor device.

[0040] The substrate or lead frame 12 is produced, for example, from a foil or strip of a metallic material (copper), on which a “carved” structure is provided, for example, by photolithography.

[0041] In a pre-molded leadframe, pre-molded resin is molded onto the sculpted metal structure of the leadframe to fill the spaces left therein. The resulting "pre-molded" leadframe has the same thickness as the original metal sheet or foil.

[0042] Further processing (e.g., a second etching step) can be applied to the pre-molded leadframe to remove additional copper for various reasons (e.g., to provide wettable sides of the leadframe for soldering or connecting rods).

[0043] Pre-molded leadframes can include two or more die pads (i.e., areas on which semiconductor chips and / or other components are intended to be attached) and can present complex designs.

[0044] This makes connecting to the external rods in the lead frame difficult, especially when maximizing the number of solder pads is the goal.

[0045] Stability, i.e., avoiding unwanted deformation / displacement during pre-molding, and saving space for additional pads, are factors that indicate the formation of temporary (sacrificial) connecting rods between adjacent die pads at the bottom or rear of the engraved metal structure of the leadframe.

[0046] These bars are eventually removed, for example, through a chemical reaction during the second etching step, so that the die pads are eventually isolated from each other (mechanically and electrically).

[0047] The process can be detected by visual inspection of the back or bottom of the pre-molded lead frame, where void spaces (cavities) are visible where metal (e.g., copper) has been removed, thus exposing the pre-molded resin.

[0048] Unless otherwise specified, leadframe treatment as discussed above is standard practice in the art, which makes it unnecessary to provide a more detailed description herein.

[0049] Problems encountered in performing the operations discussed above involve tolerances inherent in the etching process, which ultimately affect the final shape (profile) of the die pads.

[0050] For example, undesirable etching may result in residual metal material exceeding (i.e., undesirably protruding) the desired rectangular shape of the die pad.

[0051] Alternatively, in the case of over-etching, the metal material can be undesirably removed from the periphery of the bare die pad, thereby reproducing an undesirable irregular rectangular bare die pad shape.

[0052] In other words, in the case of poor etching, unwanted metallic material may remain attached; and in the case of over-etching, more material than expected can be removed.

[0053] In both cases, the shape of the bare die pads will exhibit undesirable, uncontrolled protrusions or gaps that are considered defects in the pre-molded leadframe.

[0054] These defects are visible on the surface of the bare die pads, and deviations from the desired (e.g., substantially rectangular) shape can adversely affect the reliability of the packaged resistors and / or solder.

[0055] This drawback can be mitigated by more precisely controlling, for example, the parameters of the second etching process, and / or by modifying the solder etching mask on which the semiconductor product is mounted on the substrate (e.g., a printed circuit board or PCB).

[0056] These solutions may unintentionally increase the cost of manufacturing leadframes and corresponding semiconductor devices, and cannot completely overcome the aforementioned drawbacks.

[0057] Figure 1A and 1B This is a plan view of a portion of the pre-molded lead frame 12 (at the top or front horizontal level and at the bottom or rear horizontal level, respectively).

[0058] As previously discussed (and in other conventional ways in the art), leadframe 12 includes an engraved metal (e.g., copper) structure formed by etching metal foil or strips, comprising a plurality of die pads, one or more semiconductor chips and associated components intended to be mounted onto the plurality of die pads, for example via die attachment material.

[0059] For simplicity and ease of explanation, the specification and drawings refer to the presence of (only) two die pads, designated 12A and 12B respectively. As described above, one or more embodiments can be advantageously applied to leadframes containing a larger number (three or more) of die pads.

[0060] Only in Figure 1A As shown, die pads 12A and 12B are used to accommodate semiconductor chips or dies attached thereto, or possibly components such as “strips”, especially in the case of power devices.

[0061] Those skilled in the art will further appreciate that the embodiments discussed herein are largely "transparent" to the nature and configuration of components such as C, R1, R2, etc., intended for mounting onto die pads such as 12A, 12B, etc.

[0062] In the example described herein, it is assumed that two bare die pads 12A and 12B are (temporarily) connected via one (or advantageously, multiple) sacrificial connecting rods while pre-molded resin 14 is molded onto the metal structure of leadframe 12 to provide a pre-molded leadframe, as is otherwise conventional in the art.

[0063] The sacrificial connector is then removed at least partially, so that the two die pads 12A and 12B are eventually isolated.

[0064] For simplicity and ease of explanation, the example shown relates to a connecting rod comprising: respective extensions 120A, 120B of (conductive) die pads 12A, 12B at one of the surfaces of the lead frame 12 (e.g., the front surface or the top surface), and (conductive) bridging elements 120C of coupling the extensions 120A, 120B, the bridging elements 120C being provided on the opposite surface of the lead frame 12 (e.g., here the back surface or the bottom surface).

[0065] Component 120C extends in a bridging manner between extensions 120A and 120B, and is actually integral, thus providing (temporary) mechanical and electrical connections between die pads 12A and 12B.

[0066] Furthermore, although for simplicity, only two extensions 120A, 120B from the die pads 12A, 12B and a connecting element 120C extending therebetween are shown as a single group, multiple such groups can be provided in the lead frame 12 at locations where it is desired to (temporarily) connect multiple die pads such as 12A, 12B during pre-molding.

[0067] exist Figure 1C The spatial relationship between the intermediate extensions 120A and 120B (on one side of the lead frame) and the bridging element 120C (on the other side of the lead frame) is further illustrated.

[0068] Figure 1C In essence, it reproduces as Figure 1B The plan view of the lead frame 12 shown is at the level of the back or bottom surface, wherein the layout of the metal portion of the lead frame 12 at the front or top surface of the lead frame 12 is reproduced by dashed lines.

[0069] exist Figure 2 This spatial relationship is further illustrated in the magnified view, while Figure 3 The cross-sectional view further details the relative positions between the extensions 120A, 120B and the bridging portion 120C.

[0070] It should be understood that: Figure 3 The cross-sectional view is along Figure 2 The wire is cut from line III-III, and this wire has a 90° bend at extension 120A (where the end portion of bridging element 120C is located in a corresponding position on the opposite side of lead frame 12); and in Figure 3 In the cross-sectional view, the bottom or back surface of the lead frame 12 faces upward, while the top or front surface faces downward.

[0071] Moreover, while maintaining the connection between them, both extensions 120A and 120B, as well as the bridging element 120C, can have a certain degree of freedom in shape and size.

[0072] Advantageously, the extensions 120A and 120B are formed at adjacent positions such that the distal ends of these extensions are located at a short distance between them.

[0073] A straight or basic straight (quadrilateral) shape was found to be advantageous for extensions 120A and 120B.

[0074] Similarly, linear (e.g., rectangular) shapes with rounded edges have been found to be advantageous for bridging connectors 120C.

[0075] Figure 3The cross-sectional view illustrates the possibility of pre-molded encapsulation material 14 filling the voids in the sculpted metal (e.g., copper) structure that penetrates the lead frame 12.

[0076] therefore, Figures 1A to 1C , Figure 2 and Figure 3 This is an example of molding an electrically insulating material 14 onto a layered engraved structure of a conductive material to produce a lead frame 12, which includes a plurality of die pads 12A, 12B configured to have semiconductor device assemblies C, R1, R2 mounted thereon.

[0077] The leadframe 12 has opposing first and second surfaces and a pair (or more pairs) of die pads 12A, 12B. As shown, these die pads 12A, 12B are coupled via at least one sacrificial coupling formation designed to be at least partially removed; thereafter, when an electrically insulating material (i.e., pre-molded resin 14) is molded onto the layered engraved structure of the conductive material of the leadframe 12, these sacrificial coupling formations have helped to counteract undesirable displacement of the die pads.

[0078] In this way, the bare die pads 12A and 12B can be decoupled as expected.

[0079] As shown, a first extension 120A of the first die pad 12A and a second extension 120B of the second die pad 12B are provided on a first surface (e.g., front or top surface) of a layered engraved structure of conductive material, for example during the fabrication of the metal (e.g., copper) structure, as is conventional in the art (e.g., by photolithography).

[0080] As shown, extensions 120A and 120B are provided (formed) at adjacent positions on the first surface of the lead frame 12.

[0081] As shown, a (conductive) forming element 120C is provided on the second surface (e.g., the back or bottom surface) of the layered engraved structure of the lead frame 12. Similarly, this can occur during the fabrication of the metal (e.g., copper) structure, as is conventional in the art.

[0082] like Figure 3 As can be seen, for example, the forming 120C extends in a bridging manner between the first extension 120A and the second extension 120B, thereby providing a sacrificial coupling forming (connecting rod) for the die pads 12A, 12B.

[0083] As shown, the first extension 120A and the second extension 120B are advantageously provided as finger-like extensions and / or advantageously have distal ends located at a distance from the die pads 12A, 12B, while the element or forming 120C extends between these distal ends in a bridging manner.

[0084] As a result, component 120C is eventually located at a distance from the bare die pads 12A and 12B.

[0085] Advantageously, the first extension 120A and the second extension 120B are provided as mutually converging extensions from the die pads 12A and 12B.

[0086] As discussed, after molding (and curing, for example, via heat or UV curing) the insulating premolded material 14, at least partially, the (multiple) sacrificial coupling forming elements (such as 120A, 120B, 120C) are removed to isolate the bare die pads 12A, 12B, and the insulating premolded material 14 penetrates (e.g., see...). Figure 3 ) into the gaps in the layered engraved metal structure of the lead frame 12.

[0087] Such at least partial removal may include at least partial removal (e.g., during a further etching step for forming solder-wettable sides) of a bridging-like forming 120C extending between the first extension 120A and the second extension 120B.

[0088] For simplicity, skip this step. Figure 6 It can be noted that: as a result of removing the bridging form 120C (whose outline is shown in dashed lines), the die pads 12A and 12B are located at adjacent positions on the front or top surface of the lead frame (in Figure 6 The first extension 120A and the second extension 120B are still present (pointing downwards); and conversely, the back surface or bottom surface of the lead frame 12 has a recessed portion (cavity) 120C' that extends in a bridging manner between the first extension 120A and the second extension 120B (the latter provided at the front or top surface of the lead frame) (at the back or bottom surface of the lead frame 12).

[0089] like Figure 4 and 5 As illustrated in the view, removing the bridging form or element 120C (e.g., via a “secondary” etching) leaves a very “clean” surface N in the cavity 120C’ facing the surrounding metal components.

[0090] Therefore, the die pads 12A and 12B are separated without creating unwanted defects in their outlines (e.g., protrusions due to poor etching or gaps due to over-etching).

[0091] like Figure 4 and 5As shown in the example view, the bridging element 120C is thus removed without adversely affecting the outline of the die pads 12A and 12B. In other words, since the connecting rod represented by the bridging element 120C is removed, no defects are generated on the exposed surfaces of the die pads 12A and 12B.

[0092] It should be understood that the bare die pad extensions 120A, 120B provided on the opposite (here, front or top) surfaces will never be affected by the removal of the bridging element (connecting rod) 120C.

[0093] Without violating the basic principles and without departing from the scope of protection, the details and embodiments may vary significantly from what has been described for the purposes of this example only.

[0094] The claims form an integral part of the technical teachings provided herein regarding the embodiments.

[0095] The scope of protection is determined by the appended claims.

Claims

1. A method for manufacturing a pre-molded lead frame for a semiconductor device, comprising: A layered engraved structure of conductive material is provided, the layered engraved structure having opposing first and second surfaces, and including a first die pad and a second die pad configured to have semiconductor device assemblies mounted thereon; In the layered engraving structure of the conductive material, a first extension from the first die pad and a second extension from the second die pad are provided at a location adjacent to the first surface of the lead frame. In the layered engraving structure of the conductive material, a bridging formation is provided at the second surface of the lead frame to couple the first extension and the second extension, wherein the first extension and the second extension, together with the bridging formation therebetween, provide a coupling formation for the first die pad and the second die pad; Electrically insulating material is molded onto the layered engraved structure of conductive material to create a lead frame. as well as After the molding, the bridging member between the first extension and the second extension is at least partially removed to decouple the first die pad from the second die pad.

2. The method according to claim 1, further comprising: Semiconductor device assemblies are mounted to the first die pad and the second die pad at the first surface of the lead frame.

3. The method according to claim 1, wherein: Providing the first extension and the second extension includes: forming distal ends of the first extension and the second extension, respectively, the distal ends of the first extension and the second extension being located at a distance from the first die pad and the second die pad, respectively; and Providing the bridging member includes forming the bridging member between the distal ends of the first extension and the second extension, wherein the bridging member is located at a distance from the first die pad and the second die pad.

4. The method of claim 1, wherein providing the first extension and the second extension comprises: The first extension and the second extension are respectively formed as finger-shaped extensions from the first die pad and the second die pad.

5. The method of claim 1, wherein providing the first extension and the second extension comprises: The first extension and the second extension are respectively formed as mutually converging extensions from the first die pad and the second die pad.

6. The method of claim 1, wherein at least partial removal of the bridging formation is performed in conjunction with the formation of the wettable side of the lead frame.

7. The method of claim 1, wherein at least partially removing the bridging formation leaves a cavity at the second surface of the lead frame.

8. A pre-molded lead frame for a semiconductor device, comprising: A layered etched structure of conductive material, including opposing first and second surfaces and a plurality of die pads configured to have semiconductor device assemblies mounted thereon; Molding an electrically insulating material onto the layered engraved structure of a conductive material; in: The first and second die pads of the plurality of die pads respectively exhibit a first extension and a second extension at adjacent positions on the first surface of the lead frame; and The second surface of the lead frame has a recessed portion in which the electrical insulating material is missing, the recessed portion extending in a bridging manner between the first extension and the second extension.

9. The pre-molded leadframe of claim 8, wherein the plurality of die pads are configured to have semiconductor device assemblies mounted thereon on the first surface of the leadframe.

10. The pre-molded lead frame according to claim 8, wherein: The distal ends of the first extension and the second extension are respectively spaced a distance from the first die pad and the second die pad; and The recessed portion is located at a distance from the first die pad and the second die pad extending between the distal ends.

11. The pre-molded lead frame of claim 8, wherein the first extension and the second extension each include finger-shaped extensions from the first die pad and the second die pad, respectively.

12. The pre-molded lead frame of claim 8, wherein the first extension and the second extension comprise converging extensions from the first die pad and the second die pad, respectively.

13. A semiconductor device, comprising: Pre-molded lead frame, including: The conductive material has a layered etched structure, including opposing first and second surfaces and multiple bare die pads; Electrically insulating material, molded onto the layered engraved structure of conductive material; in: The first and second die pads of the plurality of die pads respectively exhibit a first extension and a second extension at adjacent positions on the first surface of the lead frame; and The second surface of the lead frame has a recessed portion in which the electrical insulating material is missing, the recessed portion extending in a bridging manner between the first extension and the second extension; and Semiconductor device assemblies arranged on the first die pad and the second die pad.

14. The semiconductor device of claim 13, wherein the semiconductor device assembly is mounted to the first die pad and the second die pad at the first surface of the lead frame.

15. The semiconductor device of claim 13, wherein the distal ends of the first extension and the second extension are respectively located at a distance from the first die pad and the second die pad.

16. The semiconductor device of claim 15, wherein the recessed portion is located at a distance from the first die pad and the second die pad extending between the distal ends.

17. The semiconductor device of claim 13, wherein the first extension and the second extension each include finger-shaped extensions respectively from the first die pad and the second die pad.

18. The semiconductor device of claim 13, wherein the first extension and the second extension comprise converging extensions from the first die pad and the second die pad, respectively.

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