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

Abstract

Embodiments of the present disclosure relate to methods of manufacturing substrates for semiconductor devices, corresponding substrates, and semiconductor devices. A pre-molded substrate for a semiconductor device includes an engraved conductive (e.g., copper) layered structure having a space therein. The layered structure includes one or more die pads having a first die pad surface configured to mount a semiconductor chip thereon. A pre-molded material molded onto the layered structure extends into the space therein and provides a layered pre-molded substrate including the first die pad surface exposed by the pre-molded material and the die pad(s) interfacing with the pre-molded material. One or more stress relief bends are provided at a periphery of the one or more die pads. The stress relief bends are configured to interface the pre-molded material over a smooth surface to effectively counter cracks formed in the pre-molded material due to bending of the pre-molded substrate.

Description

[0001] Priority requirements

[0002] This application claims priority to Italian Patent Application No. 102021000020111, filed on July 28, 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 semiconductor devices.

[0004] One or more embodiments can be applied to semiconductor power devices, for example, in the automotive field. Background Technology

[0005] In a substrate such as a pre-molded leadframe, sufficient adhesion between the etched conductive structure of the leadframe (e.g., copper) and the pre-molded resin (e.g., epoxy resin) molded thereon should be sufficient to absorb the stress generated when the pre-molded leadframe is pressed or bent, and thus resist the formation of cracks that can also propagate along the leadframe.

[0006] It should be noted that in the case of narrow strips of pre-molded material, stress increases and therefore the risk of cracking increases.

[0007] The above-mentioned problems need to be addressed in this field. Summary of the Invention

[0008] One or more embodiments relate to a method.

[0009] One or more embodiments relate to a corresponding substrate (lead frame) for a semiconductor device.

[0010] One or more embodiments relate to semiconductor devices.

[0011] One or more embodiments rely on modifications to the die pad shape of the substrate, such as the lead frame (optionally only on the front or top side).

[0012] In some examples, a lateral half-etch stress relief (or stress reduction) protrusion is created in the die pad, thereby making the bottom side of the die pad straight.

[0013] This shape helps absorb stress, such as stress generated during wire bonding in response to bending or possible pressing of the substrate (lead frame).

[0014] One or more embodiments facilitate the production of smaller semiconductor device packages. Attached Figure Description

[0015] One or more embodiments will now be described by way of example only with reference to the accompanying drawings, in which:

[0016] Figure 1 This is an example of cracks that may form in substrates such as pre-molded lead frames;

[0017] Figure 2 It is a plan view of the pre-molded lead frame, which highlights the areas more exposed to crack formation;

[0018] Figure 3 This is an example of a measurement that can be attempted to combat crack formation in pre-molded lead frames;

[0019] Figure 4A and Figure 4B It is a plan view of a pre-molded lead frame, illustrating the possible topology exposed to crack formation;

[0020] Figure 5A and Figure 5B This is a description of a pre-molded lead frame according to an embodiment of this specification;

[0021] Figure 6 It is reproduced at an enlarged scale, as indicated by arrow VI. Figure 5A A partial view;

[0022] Figure 7 and Figure 8 They are along Figure 6 The cross-sectional view reproduced at a further magnified scale, showing lines VII-VII and VIII-VIII.

[0023] Figure 9 It is similar to Figure 6 The view of the lead frame portion described herein illustrates possible advantageous features of the embodiment;

[0024] Figure 10 It is along Figure 9 A cross-sectional view of line X-X reproduced at a further magnified scale; and

[0025] Figure 11 and Figure 12 This is a plan view (front view and rear view) of a pre-molded lead frame according to an embodiment of the present invention. Detailed Implementation

[0026] Unless otherwise specified, corresponding numbers and symbols in different figures usually refer to the corresponding parts.

[0027] The accompanying drawings are provided to clearly illustrate relevant aspects of the embodiments and are not necessarily drawn to scale.

[0028] The edges of features drawn in the attached figures do not necessarily indicate the end of the feature range.

[0029] 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 that various aspects of the embodiments are not obscured.

[0030] References to "embodiment" or "an embodiment" in the framework 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.

[0031] 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.

[0032] Semiconductor devices may include one or more semiconductor integrated circuit chips or dies disposed (attached) on a substrate such as a lead frame.

[0033] Plastic packages are commonly used for semiconductor devices. Such packages may include a lead frame that provides a base substrate comprising a conductive material (e.g., copper), the base substrate being sized and shaped to accommodate a semiconductor chip or die and to provide pad connections (leads) for these chips or dies.

[0034] The term “lead frame” (or “lead box”) (see, for example, the USPC Combined Glossary of Terms) refers to a metal frame that provides support for an integrated circuit chip or die, and electrical leads that interconnect the integrated circuit in the die or chip to other components or contacts.

[0035] Leadframes are typically produced using techniques such as photolithography. Using this technique, metal (e.g., copper) material in the form of foil or strip is etched on the top and bottom sides to create various pads and leads.

[0036] Substrates such as lead frames are advantageously provided in pre-molded form, wherein an insulating resin (e.g., epoxy resin) fills the empty space between the die pads and the leads.

[0037] Therefore, the pre-molded leadframe is a substantially flat layered substrate in which a pre-molded material (resin) fills the spaces in the conductive structure of the leadframe (e.g., made of a metallic material (e.g., copper)) and has been given an engraved appearance, which includes empty spaces during formation (e.g., by etching).

[0038] The total thickness of the pre-molded lead frame is the same as the thickness of the engraved conductive structure.

[0039] During the assembly process of semiconductor devices using pre-molded leadframes, the pre-molded leadframes may be exposed to repeated stresses.

[0040] For example, the lead frame may be bent simply due to its weight during transport or when stored in a slot box.

[0041] Furthermore, during lead bonding, the lead frame is clamped, and the bonding tool that places the bonding wire or strip can further stress the lead frame structure.

[0042] Figure 1 An example of a crack C that may form in a pre-molded lead frame is illustrated as generally comprising a conductive (metal, such as copper) portion 10 included in an engraved conductive structure of the lead frame having spaces filled with a pre-molded material (resin) 12.

[0043] For example, such as Figure 1 As depicted, in response to bending of the pre-molded lead frame, a crack C can be formed in the resin 12, wherein the crack may propagate along an elongated portion of the pre-molded material 12.

[0044] The presence of this crack is a source of material repulsion.

[0045] Figure 2 The plan view shows that the formation and propagation of cracks may be related to the fact that in some pre-molded lead frame topologies, the two sides connected by the connecting strip 100 can represent the only part of the lead frame that resists bending stress.

[0046] Figure 3 This is an example of the trend of mounting an increasing number of devices on a lead frame PLF in order to reduce the cost of related units and reduce package size.

[0047] Reducing package size may involve reducing the spacing between adjacent conductive portions of the pre-molded lead frame (e.g., die pad 10). This, in turn, translates to reducing the width of the portion of the pre-molded material 12 included therebetween (see, for example...). Figure 3 (D1 and D2 in the middle).

[0048] Therefore, the pre-molded material 12 between adjacent die pads 10 can be reduced to a very narrow straight line. Reducing the widths, such as D1 and D2, makes the pre-molded material (resin) more susceptible to damage.

[0049] Therefore, if the lead frame PLF is bent, pressed or pulled, the pre-molded material 12 is more likely to be exposed to crack formation, and there is a risk that such cracks may easily propagate across the entire surface of the lead frame.

[0050] Figure 4A and Figure 4B This helps in understanding the linear regions of pre-molded material (e.g.) Figure 4A The area indicated by 12 refers to single-channel power quad-flat no-leads (QFN) packages and even more areas in the pre-molded material 12 that exhibit more complex shapes (e.g., Figure 4B There is a risk of crack formation and propagation in the T-shaped package (indicated by multiple reference numerals 12) (which refers to the dual-channel power QFN package).

[0051] Figure 5A and Figure 5B This is a plan view of the pre-molded lead frame PLF.

[0052] Figure 5A Reproduce the horizontal level of the front or top surface of the lead frame PLF, wherein one or more semiconductor chips or dies C1, C2 (shown in dashed outline) are intended to be mounted on the front or top surface of the corresponding die pad 10.

[0053] Figure 5B It is a plan view of the same pre-molded lead frame PLF at the level of the rear or bottom surface, wherein the die pad 10 can be exposed and is not covered by the pre-molded material 12 (which can promote, for example, the dissipation of heat generated by the chips C1, C2 during operation).

[0054] It should be noted that Figure 5A and Figure 5B It refers to, for example Figure 4B The leadframe topology illustrated (defined as dual-channel pads coupled to the corresponding strips, not visible in the figure) is considered particularly critical in the area involving crack formation.

[0055] Furthermore, it should be understood that Figure 5A and Figure 5B (And the following figures) are examples of pre-molded lead frames comprising (among others conventional in the art): an engraved conductive layered structure having (initially empty) spaces and a pre-molded material (e.g., resin 12) molded onto the layered structure and filling those spaces.

[0056] The pre-molded material is inserted into the spaces within the sculpted conductive structure, and once cured (e.g., by UV or thermal curing), it provides a layered pre-molded substrate (PLF).

[0057] As shown in the figure, apart from other features that will not be discussed here for simplicity, this sculpted conductive layered structure includes one or more die pads 10. Reference Figure 7 , Figure 8 and Figure 10 The die pad 10 includes: a first, front or top die pad surface 10A and a second, rear or bottom surface 10B opposite to the front or top surface 10A, wherein the first, front or top die pad surface 10A is exposed and not covered by a pre-molding material 12 to facilitate mounting one or more semiconductor chips or dies C1, C2 thereon; the second, rear or bottom surface 10B is opposite to the front or top surface 10A, wherein the die pad 10 may similarly be exposed and not covered by the pre-molding material 12.

[0058] As used herein, “may” emphasizes the fact that in some embodiments, one or more of the die pads 10 may be die pads with a thickness less than (e.g., therefore half the current definition of “half-etched”) the total thickness of the pre-molded leadframe.

[0059] In this way, the "semi-etched" die pads will be covered by (electrically insulating) pre-molded material 12 on their rear surface 10B, thereby creating insulating die pads.

[0060] Regardless of the details of the implementation, in the pre-molded leadframe PLF as illustrated herein, the die pad 10 contacts the periphery (i.e., side) of the pre-molded material 12 (strip) molded onto the layered structure of the leadframe.

[0061] In such Figures 1 to 4B In the illustrated solution, die pad 10 is a rectangular pad that borders the pre-molded material 12 along its entire straight boundary line (with at most a slightly rounded tip).

[0062] Even without being bound by any particular theory in this regard, it is found that these straight boundary lines lie at the reference point for crack formation (and propagation), for example... Figure 1 Crack C is shown.

[0063] Figures 5A-12 The example presented in the paper anticipates providing at least one stress-relief (or stress-reducing) bend 100 at the periphery of one or more die pads (optionally (only) at the surface 10A of the first die pad), which is configured to interface with the pre-molded material 12 above a (lateral) rounded surface, i.e., above a smooth bend surface (i.e., a uniform and regular surface without perceptible protrusions, lumps or dents).

[0064] like Figure 6As illustrated, the stress-relief bending portion 100 may include, for example, protrusions of the die pad 10 extending into the pre-molded material 12.

[0065] For example in Figure 6 As can be seen in the diagram, when viewed in a plan view, the stress relief portion 100 can be exhibited as a serpentine profile, having at least a generally sinusoidal trajectory relative to the reference centerline X100 on the side parallel to the die pad 10 (another straight line).

[0066] In other words, the stress-relief bending portion 100 extends along a roughly sinusoidal trajectory in the plane of the layered pre-molded substrate PLF (whose thickness is practically negligible).

[0067] Similarly, without being bound by any particular theory in this regard, it was found that this roughly sinusoidal shape is particularly effective in combating the potential formation and propagation of cracks.

[0068] like Figure 6 As can be seen, for example, the stress-relief bending portion 100 is advantageously located at the same position as the T-shaped (initial) empty space in the sculpted conductive structure of the pre-molded material 12 filling the lead frame.

[0069] like Figure 6 As can be seen, in the case where the stress-relief bending portion 100 is formed by the protrusion of the lead frame 10, this results in a T-shaped space intended to be filled by the pre-molded material 12 (see...). Figure 4B It becomes a Y-shaped space with rounded edges.

[0070] This bending shape is considered particularly effective in absorbing stress generated when the lead frame PLF is bent or pressed (e.g., during lead bonding).

[0071] This result was found to be particularly advantageous when the (straight) resin portion was greater than 50% of the encapsulation width.

[0072] Figure 9 and Figure 10 The stress-relief bending portion 100 is formed by a through hole 102 (see, for example, see...). Figure 10 An example of the arrangement of transverse protrusions, with through holes 102 filled with pre-molded material 12.

[0073] This arrangement has been found to be particularly effective in providing strong locking between the sculpted structure that provides the lead frame (die pad 10) and the pre-molded material 12 that fills the space therein.

[0074] Advantageously, the hole 102 can be an elongated hole (buttonhole) with a main dimension in the lateral direction of the lead frame 10, rather than a round hole.

[0075] Moreover, such as Figure 10 As can be seen, the hole 102 can have a slightly tapered shape starting from the front pad surface 10A. Such a shape can be advantageously provided during the etching process to form the lead frame engraving structure.

[0076] Advantageously, such as Figure 8 and Figure 10 As can be seen, the stress-relief bending portion 100 (recess or advantageously, protrusion) can be provided only near one of the opposing surfaces 10A, 10B of the die pad 10.

[0077] For example, as shown herein, stress-relief bending portions (multiples) 100 can be provided only at the front or top pad surface 10A, while the opposing surface (here, the rear or bottom pad surface 10B opposite to the front or top surface 10A) maintains a generally straight shape.

[0078] In some embodiments, complementary options can be employed, where the stress-relief bending portion 100 is provided only at the rear or lower pad surface 10B, while the front or upper surface 10A maintains a generally straight shape.

[0079] In some embodiments, the stress-relief bending portion 100 can be provided over the entire thickness of the die pad, i.e., simultaneously at the front pad surface or upper pad surface 10A and at the rear pad surface or lower pad surface 10B.

[0080] The above applies regardless of the fact that one or more holes (e.g., 102) are provided in the stress relief section 100.

[0081] For example Figure 7 The accompanying drawings also illustrate that the periphery of the die pad (e.g., 10) may have a stepped profile, wherein the front or top surface 10A is larger than the rear or bottom surface 10B (and therefore protrudes relative to the rear or bottom surface 10B).

[0082] Figure 11 and Figure 12 This is a further view of the pre-molded lead frame PLF at the level of the front or top surface 10A of the die pad 10 and at the level of the rear or bottom surface 10B of the die pad 10.

[0083] Figure 11 and Figure 12 This is an example of the possibility of providing one or more stress-relief bend portions 100, which are adjacent only to the front die pad surface 10A and the rear or bottom surface 10B (see...). Figure 12 The sides of the object maintain a substantially straight shape.

[0084] Figure 11This is also an example of the possibility of providing one or more stress-relief bending portions 100 (with or without holes 102) at multiple locations in the lead frame.

[0085] For example, in Figure 11 The die pad 10, located at the center, has stress-relief bending portions 100 on both of its main (longer) sides, which are perpendicular in the figure.

[0086] also, Figure 11 This is an example of the possibility of providing multiple adjacent stress-relief bending portions 100 (with or without holes 102) on one side of the lead frame.

[0087] same, Figure 11 The die pad 10, which is located in the center, has multiple stress-relief bends 100 on its left main (longer) side and a single stress-relief bend 100 on its right main (longer) side.

[0088] For example, in some embodiments, the die pad 10 may have: a single stress-relief bend 100 on one or more of its sides (a single portion 100 on each side); and / or a plurality of stress-relief bends 100 on one or more of its sides (a plurality of portions 100 on each side); and / or a single and / or a plurality of stress-relief bends 100 on all or only a portion of its side (e.g., a combination of the foregoing).

[0089] Figure 11 This is also an example of the possibility of providing multiple stress-relief bending portions 100 on the mutually facing sides of adjacent die pads 10 with 12 strips of pre-molded material extending therebetween.

[0090] like Figure 11 As illustrated, these multiple stress-relief bends 100 in the mutually facing sides of adjacent die pads 10 can be provided as alternations (e.g., interdigitated) of stress-relief bends 100 (e.g., protrusions), such that the pre-molded material strips 12 therebetween have a generally zigzag or serpentine pattern.

[0091] It has been found that the arrangement illustrated herein helps to lock the pre-molded material 12 to the die pad 10 with a larger adhesion surface, wherein the flexural boundary line therebetween, provided by a structure such as 100, effectively absorbs stress and resists the formation and propagation of collisions therebetween.

[0092] Furthermore, it was found that the protruding stress relief structure 100 facilitates the flow of preformed material into the vertical channel (e.g., see...). Figure 6 and Figure 9As can be seen in the image, this also facilitates (especially when hole 102 is provided) stronger locking of the conductive and insulating (non-conductive) portions of the pre-molded lead frame.

[0093] Advantageously, in packages with dual-channel pads or channels perpendicular to the die pads (see again) Figure 6 and Figure 9 (It was found that these pre-molded materials 12, which are particularly exposed to crack formation, do not follow straight lines and have vertical sections.)

[0094] The bending shape of the stress relief structure at this point significantly absorbs the stress generated when the lead frame is bent or pressed (e.g., during lead bonding).

[0095] As described above, this modification of the boundary of the die pad can occur only at one of the front surface 10A and the rear surface 10B, for example only at the front surface 10A.

[0096] 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.

[0097] The claims are an integral part of the technical teachings provided herein with reference to the embodiments.

[0098] The scope of protection is determined by the appended claims.

Claims

1. A method for manufacturing a substrate for a semiconductor device, comprising: A sculpted conductive layered structure is provided, having a space in the sculpted conductive layered structure, wherein the sculpted conductive layered structure includes at least one die pad, the at least one die pad having a first die pad surface configured for mounting a semiconductor chip. as well as A pre-molded material is molded to penetrate into the space of the sculpted conductive layered structure and to produce a layered pre-molded substrate, the layered pre-molded substrate including the surface of the first die pad, the surface of the first die pad being exposed by the pre-molded material at the periphery of the at least one die pad that is in contact with the pre-molded material. The sculpted conductive layered structure includes providing at least one stress-relief bend at the periphery of the at least one die pad, the at least one stress-relief bend being configured to interface with the pre-molded material molded onto the sculpted conductive layered structure above a smooth surface. The at least one die pad of the sculpted conductive layered structure comprises a pair of adjacent die pads having a pre-molded material strip therebetween, and wherein providing the sculpted conductive layered structure comprises: forming alternating stress-relief bending portions in the pair of adjacent die pads.

2. The method of claim 1, wherein the at least one stress-relief bending portion extends along a generally sinusoidal trajectory in the plane of the layered pre-molded substrate.

3. The method of claim 1, wherein the at least one stress-relief bending portion includes a protrusion extending into the pre-molded material molded onto the sculpted conductive layered structure.

4. The method of claim 3, further comprising providing at least one aperture in the protrusion, the at least one aperture being configured to be filled with the pre-molded material molded onto the sculpted conductive layered structure.

5. The method of claim 1, further comprising providing the at least one stress-relief bending portion located at the position of the sculpted conductive layered structure, wherein a T-shaped space is provided at the position for filling with the pre-molded material molded onto the sculpted conductive layered structure.

6. The method of claim 1, wherein the stress-relieving bending portion is provided with alternating, cross-shaped stress-relieving bending protrusions.

7. The method of claim 1, wherein the pre-molded material strip between the pairs of adjacent die pads has a serpentine pattern.

8. The method of claim 1, wherein the at least one die pad has a second die pad surface opposite to the surface of the first die pad, and wherein providing the etched conductive layered structure comprises: The at least one stress-relief bending portion is provided only on one of the surfaces of the first die pad and the second die pad.

9. The method of claim 8, wherein the periphery of the other of the first die pad surface and the second die pad surface is straight, opposite to the at least one stress-relief bending portion.

10. A substrate comprising: An etched conductive layered structure having a space, the etched conductive layered structure including at least one die pad having a first die pad surface configured to mount a semiconductor chip; A pre-molded material molded onto the sculpted conductive layered structure, wherein the pre-molded material extends into the space and provides a layered pre-molded substrate, the layered pre-molded substrate including the surface of the first die pad, the surface of the first die pad being exposed by the pre-molded material at the periphery of the at least one die pad at the interface with the pre-molded material molded onto the sculpted conductive layered structure; as well as The periphery of the at least one die pad includes at least one stress-relief bend, the at least one stress-relief bend interfaced above a smooth surface with the pre-molded material molded onto the sculpted conductive layered structure, the at least one stress-relief bend extending along a generally sinusoidal trajectory in the plane of the layered pre-molded substrate. The at least one die pad of the sculpted conductive layered structure comprises a pair of adjacent die pads having a pre-molded material strip therebetween, and wherein alternations of the stress-relief bending portions exist in the pair of adjacent die pads.

11. The substrate of claim 10, wherein the at least one stress-relief bending portion includes a protrusion extending into the pre-molded material molded onto the sculpted conductive layered structure.

12. The substrate of claim 11, wherein the protrusion includes at least one aperture therein, the at least one aperture being filled with the pre-molded material molded onto the sculpted conductive layered structure.

13. The substrate of claim 10, wherein the at least one stress-relieved bending portion of the at least one die pad is positioned at the location of the sculpted conductive layer structure, a T-shaped space is provided at the location, the T-shaped space being filled with the pre-molded material molded onto the sculpted conductive layer structure.

14. The substrate of claim 10, wherein the alternating cross-shaped stress-relief bend protrusions are provided in the stress-relief bend portion.

15. The substrate of claim 10, wherein the pre-molded material strip between the pairs of adjacent die pads has a serpentine pattern.

16. The substrate of claim 10, wherein the at least one die pad has a second die pad surface opposite to the surface of the first die pad, wherein the at least one stress-relief bending portion is provided only on one of the surface of the first die pad and the surface of the second die pad.

17. The substrate of claim 16, wherein the periphery of the other of the first die pad surface and the second die pad surface is straight, opposite to the at least one stress-relief bending portion.

18. A semiconductor device, comprising: The substrate according to claim 10; as well as At least one semiconductor integrated circuit chip mounted on the surface of the first die pad.

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