Preparation method of semiconductor structure

Abstract

The invention provides a preparation method of a semiconductor structure. The preparation method of the semiconductor structure comprises the steps that a lead frame is provided, the lead frame comprises a base island and at least one extension part, and the base island comprises a first surface, a second surface and a plurality of side surfaces; the extension part comprises a connecting rib and a pin connected with the end part, deviating from the base island, of the connecting rib; the pins are located on the sides, away from the first surface, of the base islands; determining the distance between the surface, facing the base island, of the pin and the first surface; providing a plastic package mold comprising a first sub-mold and a second sub-mold, wherein a cavity of the first sub-mold is used for accommodating the base island and the part of the extension part; obtaining the depth of the cavity; and if the difference between the distance and the depth of the cavity is within a threshold range, the lead frame is placed in the first sub-mold, and the second sub-mold and the first sub-mold are closed to form a plastic package layer wrapping the connecting rib and the base island, and the first surface exposes the plastic package layer.

Description

Technical Field

[0001] The present application relates to the field of semiconductor technology, and in particular to a method for preparing a semiconductor structure. Background Art

[0002] The lead frame includes a base island, pins and connecting ribs, one end of the connecting rib is connected to the pin, and the other end is connected to the base island, and there is a height difference between the pin and the base island.

[0003] When the lead frame is plastic-sealed to prepare a semiconductor structure, the surface of the base island facing away from the frame may be covered by the plastic sealing material, which will cause the semiconductor structure to be unable to be electrically connected to other structures through the base island, or the base island cannot play a role in heat dissipation after the semiconductor structure is electrically connected to other structures, thereby affecting the yield of the semiconductor structure. Summary of the invention

[0004] The present application provides a method for preparing a semiconductor structure. The method for preparing a semiconductor structure comprises:

[0005] A lead frame is provided, the lead frame comprising a base island and at least one extension portion, the base island comprising a first surface, a second surface opposite to the first surface, and a plurality of side surfaces connecting the first surface and the second surface; the extension portion comprises a connecting rib connected to the side surface and a pin connected to an end of the connecting rib away from the base island, the extending direction of the connecting rib intersects with the first surface, and the extending direction of the pin is parallel to the first surface; the pin is located on a side of the base island away from the first surface;

[0006] Determine the distance between the surface of the pin facing the base island and the first surface;

[0007] Providing a plastic encapsulation mold, the plastic encapsulation mold comprising a first sub-mold and a second sub-mold, the cavity of the first sub-mold being used to accommodate the base island and part of the extension portion of the lead frame; obtaining the depth of the cavity;

[0008] If the difference between the distance and the depth of the cavity is within a threshold range, the lead frame is placed in the first sub-mold so that the base island and the connecting ribs are located in the cavity, and the second sub-mold is combined with the first sub-mold to plastic-encapsulate the lead frame to form a plastic-encapsulation layer covering the connecting ribs and the base island, with the plastic-encapsulation layer exposed on the first surface.

[0009] In one embodiment, the minimum value of the threshold range is 0.

[0010] In one embodiment, the lead frame includes at least one extending portion, each of the extending portions is connected to the same side surface of the base island, and the threshold range is [0, 10 μm].

[0011] In one embodiment, the lead frame includes at least two extensions, the multiple side surfaces include a first side surface, a second side surface opposite to the first side surface, a third side surface, and a fourth side surface opposite to the third side surface; the base island has a first symmetric plane and a second symmetric plane, the first side surface and the second side surface are symmetrical about the first symmetric plane, and the third side surface and the fourth side surface are symmetrical about the second symmetric plane; each of the extensions is connected to one of the first side surface and the second side surface, and the extension connected to the first side surface is symmetrical with the extension connected to the second side surface about the first symmetric plane; or, the first side surface, the second side surface, the third side surface, and the fourth side surface are respectively connected with at least one extension, the extension connected to the first side surface is symmetrical with the extension connected to the second side surface about the first symmetric plane, and the extension connected to the third side surface is symmetrical with the extension connected to the fourth side surface about the second symmetric plane;

[0012] The threshold range is [0, 50 μm].

[0013] In one embodiment, the lead frame includes at least two extending portions, the multiple side surfaces include a first side surface, a second side surface opposite to the first side surface, a third side surface, and a fourth side surface opposite to the third side surface; the base island has a first symmetric plane and a second symmetric plane, the first side surface and the second side surface are symmetrical about the first symmetric plane, and the third side surface and the fourth side surface are symmetrical about the second symmetric plane; among the at least two extending portions, the extending portion connected to the first side surface and the second side surface is asymmetric about the first symmetric plane;

[0014] The threshold range is [0, 25 μm].

[0015] In one embodiment, the method for preparing the semiconductor structure further includes:

[0016] If the difference between the distance and the depth of the cavity is not within the threshold range, and the distance is less than the depth of the cavity, a cushioning structure is provided in the cavity so that the difference between the sum of the distance and the thickness of the cushioning structure and the depth of the cavity is within the threshold range;

[0017] The lead frame is placed in the first sub-mold so that the base island and the connecting ribs are located in the cavity, and the second sub-mold is combined with the first sub-mold to plastic-encapsulate the lead frame to form a plastic-encapsulation layer covering the connecting ribs and the base island, with the plastic-encapsulation layer exposed on the first surface.

[0018] In one embodiment, the bottom surface of the raising structure is in contact with the bottom surface of the cavity, and the side surface of the raising structure is in contact with the side surface of the cavity.

[0019] In one embodiment, the material of the padding structure is metal or metal alloy.

[0020] In one embodiment, the first sub-mold includes a first abutment portion surrounding the cavity, and the second sub-mold includes a second abutment portion;

[0021] Placing the lead frame in the first sub-mold so that the base island and the connecting rib are located in the cavity comprises: placing the lead frame in the first sub-mold with the opening of the cavity of the first sub-mold facing upward, the base island and the connecting rib being located in the cavity, and the lead being located on the first abutting portion;

[0022] After the first sub-mold and the second sub-mold are clamped, the second abutting portion abuts against the lead.

[0023] In one embodiment, the lead frame further includes a pin connected to the side surface; the second sub-mold is molded together with the first sub-mold to plastic-encapsulate the lead frame to form a plastic-encapsulation layer covering the connecting rib and the base island, and after the first surface exposes the plastic-encapsulation layer, the method for preparing the semiconductor structure further includes:

[0024] The lead frame is connected to an electrical connector; the lead is connected to the electrical connector, and the first surface faces away from the electrical connector; or the first surface is connected to the electrical connector.

[0025] The main technical effects achieved by the embodiments of the present application are:

[0026] The method for preparing a semiconductor structure provided in an embodiment of the present application first determines whether the difference between the distance between the surface of the lead frame's pins facing the base island and the first surface and the depth of the cavity is within a threshold range before plastic-sealing the lead frame. When the difference between the above distance and the depth of the cavity is within the threshold range, the lead frame is plastic-sealed. This allows the first surface of the base island to be exposed to the plastic sealing layer, thereby avoiding the problem of the first surface of the base island being covered by the plastic sealing layer due to the difference between the above distance and the depth of the cavity being not within the threshold range, which helps to improve the yield of the semiconductor structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a flow chart of a method for preparing a semiconductor structure provided by an exemplary embodiment of the present application;

[0028] Figure 2 is a side view of a semiconductor structure provided by an exemplary embodiment of the present application;

[0029] Figure 3 is a top view of a semiconductor structure provided by an exemplary embodiment of the present application;

[0030] Figure 4 is a top view of a semiconductor structure provided by another exemplary embodiment of the present application;

[0031] Figure 5 is a top view of a semiconductor structure provided by yet another exemplary embodiment of the present application;

[0032] Figure 6 is a top view of a semiconductor structure provided by another exemplary embodiment of the present application;

[0033] Figure 7 is a top view of a semiconductor structure provided by another exemplary embodiment of the present application;

[0034] Figure 8 is a top view of a semiconductor structure provided by another exemplary embodiment of the present application;

[0035] Fig. 9 is a top view of a semiconductor structure provided by another exemplary embodiment of the present application;

[0036] Fig.10 is a cross-sectional view of a plastic encapsulation mold provided by an exemplary embodiment of the present application when encapsulating a lead frame;

[0037] Fig.11 is a cross-sectional view of a plastic encapsulation mold provided by another exemplary embodiment of the present application when encapsulating a lead frame;

[0038] Fig.12 is a cross-sectional view of a lead frame being encapsulated by a plastic encapsulation mold provided by another exemplary embodiment of the present application;

[0039] Fig.13 It is a cross-sectional view of a lead frame being encapsulated by a plastic encapsulation mold provided by another exemplary embodiment of the present application. Specific embodiments

[0040] Exemplary embodiments will be described in detail herein, examples of which are shown in the accompanying drawings. When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present application. Instead, they are merely examples of devices and methods consistent with some aspects of the present application as detailed in the appended claims.

[0041] The terms used in this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The singular forms of "a", "said" and "the" used in this application and the appended claims are also intended to include plural forms unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more associated listed items.

[0042] It should be understood that although the terms first, second, third, etc. may be used in the present application to describe various information, these information should not be limited to these terms. These terms are only used to distinguish the same type of information from each other. For example, without departing from the scope of the present application, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information. Depending on the context, the word "if" as used herein may be interpreted as "at the time of" or "when" or "in response to determining".

[0043] Some embodiments of the present application are described in detail below in conjunction with the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0044] The present application provides a method for preparing a semiconductor structure. Figure 1 As shown, the method for preparing the semiconductor structure includes the following steps 110 to 140.

[0045] In step 110, a lead frame is provided, wherein the lead frame includes a base island and at least one extension portion, wherein the base island includes a first surface, a second surface opposite to the first surface, and a plurality of side surfaces connecting the first surface and the second surface; the extension portion includes a rib connected to the side surface and a pin connected to an end of the rib away from the base island, an extension direction of the rib intersecting with the first surface, and an extension direction of the pin parallel to the first surface; the pin is located on a side of the base island away from the first surface.

[0046] In step 120 , the distance between a surface of the pin facing the base island and the first surface is determined.

[0047] In step 130, a plastic encapsulation mold is provided, wherein the plastic encapsulation mold includes a first sub-mold and a second sub-mold, wherein the cavity of the first sub-mold is used to accommodate the base island and part of the extension portion of the lead frame; and the depth of the cavity is obtained.

[0048] In step 140, if the difference between the distance and the depth of the cavity is within the threshold range, the lead frame is placed in the first sub-mold so that the base island and the connecting ribs are located in the cavity, and the second sub-mold is combined with the first sub-mold to plastic-encapsulate the lead frame to form a plastic-encapsulation layer covering the connecting ribs and the base island, with the plastic-encapsulation layer exposed on the first surface.

[0049] The method for preparing a semiconductor structure provided in an embodiment of the present application first determines whether the difference between the distance between the surface of the lead frame's pins facing the base island and the first surface and the depth of the cavity is within a threshold range before plastic-sealing the lead frame. When the difference between the above distance and the depth of the cavity is within the threshold range, the lead frame is plastic-sealed. This allows the first surface of the base island to be exposed to the plastic sealing layer, thereby avoiding the problem of the first surface of the base island being covered by the plastic sealing layer due to the difference between the above distance and the depth of the cavity being not within the threshold range, which helps to improve the yield of the semiconductor structure.

[0050] The following is a detailed introduction to each step of the method for preparing the semiconductor structure provided in the embodiment of the present application.

[0051] In step 110, a lead frame is provided, wherein the lead frame includes a base island and at least one extension portion, wherein the base island includes a first surface, a second surface opposite to the first surface, and a plurality of side surfaces connecting the first surface and the second surface; the extension portion includes a rib connected to the side surface and a pin connected to an end of the rib away from the base island, an extension direction of the rib intersecting with the first surface, and an extension direction of the pin parallel to the first surface; the pin is located on a side of the base island away from the first surface.

[0052] like Figure 2 As shown, the base island 10 includes a first surface 15 and a second surface 16 opposite to the first surface 15; the extension portion 20 includes a connecting rib 21 and a pin 22, the connecting rib 21 is connected to the side of the base island 10, the pin 22 is located at an end of the base island 10 away from the first surface 15, and the orthographic projection of the pin 22 on the plane where the first surface 15 is located does not overlap with the first surface 15.

[0053] like Figure 3 As shown, the base island 10 includes a first side surface 11, a second side surface 12 opposite to the first side surface 11, a third side surface 13, and a fourth side surface 14 opposite to the third side surface 13. The base island 10 has a first symmetry plane and a second symmetry plane, the first side surface 11 and the second side surface are symmetrical about the first symmetry plane, and the third side surface 13 and the fourth side surface 14 are symmetrical about the second symmetry plane. In some embodiments, the first symmetry plane is parallel to the third side surface 13, and the second symmetry plane is parallel to the first side surface 11.

[0054] In one embodiment, the lead frame further comprises a plurality of pins, and the pins are connected to the side surfaces of the base island. Each side surface of the base island 10 may be connected to a pin respectively.

[0055] In one embodiment, the lead frame further includes a frame, the base island 10 and the extension portion 20 are located in the frame, and the ends of the pins 22 of the extension portion 20 away from the connecting ribs 21 are connected to the frame.

[0056] In one embodiment, Figure 3 and Figure 4 As shown, the lead frame includes at least one extending portion 20 , and each of the extending portions 20 is connected to the same side surface of the base island 10 . Figure 3 In the illustrated embodiment, the lead frame comprises only one extension 20 . Figure 4 In the illustrated embodiment, the lead frame includes two extensions 20, both of which are connected to the same side of the base island 10. In other embodiments, the lead frame may include more than two extensions 20, each of which is connected to the same side of the base island 10. Figure 3 and Figure 4 In the lead frame shown, the arrangement of the pins connected to the side of the base island 10 is such that the space between the pins connected to only one side of the base island 10 satisfies the space required for the extension 20 to be connected to the base island, so the extension 20 is only provided on one side of the base island 10. Figure 3 and Figure 4 The lead frame shown includes a small number of extensions, and the setting of the extensions has a small effect on the resistance of the lead frame. The lead frame can be used to connect to devices that are sensitive to resistance, for example, the lead frame can be connected to power devices such as high-voltage isolation devices.

[0057] In one embodiment, Figure 5 and Figure 6 As shown, the lead frame includes at least two extensions 20, and the extensions on both sides of the same symmetry plane among all the extensions 20 are symmetrical about the symmetry plane. In some embodiments, all the extensions 20 may be located on both sides of the first symmetry plane, and the extensions 20 on both sides of the first symmetry plane are symmetrical about the first symmetry plane; or some of the extensions 20 among all the extensions 20 are located on both sides of the first symmetry plane, and the remaining extensions 20 are located on both sides of the second symmetry plane, and the extensions 20 on both sides of the first symmetry plane are symmetrical about the first symmetry plane, and the extensions 20 on both sides of the second symmetry plane are symmetrical about the second symmetry plane.

[0058] Figure 5In the illustrated embodiment, all extensions 20 of the lead frame are connected to one of the two opposite side surfaces of the base island 10, that is, the other two side surfaces of the base island 10 are not connected to the extensions 20. The two side surfaces of the base island 10 connected to the extensions are the first side surface 11 and the second side surface 12, that is, each of the extensions 20 of the lead frame is connected to one of the first side surface 11 and the second side surface 12, and the extensions 20 connected to the first side surface 11 and the extensions 20 connected to the second side surface 12 are symmetrical about the first symmetry plane. Figure 5 In the lead frame shown, the arrangement of the pins connected to the side of the base island 10 is such that, on each side of the base island 10, the space between the pins connected to two opposite sides meets the space required for the extension portion 20 to be connected to the base island, while the space between the pins connected to the other two sides may not meet the space required for the extension portion 20 to be connected to the base island. Figure 5 In the illustrated embodiment, the first side surface 11 and the second side surface 12 of the base island 10 are respectively connected to one extension portion 20. In other embodiments, the first side surface 11 and the second side surface 12 of the base island 10 may be respectively connected to two or more extension portions 20.

[0059] Figure 6 In the illustrated embodiment, at least one extension portion 20 is respectively connected to the first side surface 11, the second side surface 12, the third side surface 13 and the fourth side surface 14 of the base island 10. That is, among the at least two extension portions 20 of the lead frame, at least one extension portion 20 is connected to the first side surface 11, at least one extension portion 20 is connected to the second side surface 12, at least one extension portion 20 is connected to the third side surface 13, and at least one extension portion 20 is connected to the fourth side surface 14. The extension portion 20 connected to the first side surface 11 and the extension portion 20 connected to the second side surface 12 are symmetrical about the first symmetric plane, and the extension portion 20 connected to the third side surface 13 and the extension portion 20 connected to the fourth side surface 14 are symmetrical about the second symmetric plane. Figure 6 In the lead frame shown, the arrangement of the pins connected to the side of the base island 10 is such that the space between the pins connected to each side of the base island 10 satisfies the space required for the extension 20 to be connected to the base island. Figure 6 In the illustrated embodiment, each side of the base island 10 is connected to one extension portion 20. In other embodiments, the base island 10 may have two opposite sides connected to two or two upper extension portions 20, or each side of the base island 10 is connected to two or two upper extension portions 20.

[0060] In one embodiment, Figure 7 and Fig. 9As shown, the lead frame includes at least two extensions 20, and the extensions 20 connected to the first side surface 11 and the second side surface 12 are asymmetrical about the first symmetry plane. Only one of the first side surface 11 and the second side surface 12 is connected to the extension 20, or the first side surface 11 and the second side surface 12 are respectively connected to the extension 20.

[0061] like Figure 7 As shown, the first side surface 11, the third side surface 13 and the fourth side surface 14 of the base island 10 are all connected to the extension portion 20, and the second side surface 12 is not connected to the extension portion 20. Since the first side surface is connected to the extension portion 20, and the second side surface 12 is not connected to the extension portion 20, the extension portion connected to the first side surface 11 and the second side surface 12 is asymmetric with respect to the first symmetry plane. Figure 7 In the illustrated embodiment, the extension portion connected to the third side surface 13 and the extension portion connected to the fourth side surface 14 are symmetrical with respect to the second symmetry plane.

[0062] like Figure 8 As shown, the first side surface 11 and the third side surface 13 of the base island 10 are both connected with the extension portion 20, and the second side surface 12 and the fourth side surface 14 are both not connected with the extension portion 20. Then, the extension portions connected to the first side surface 11 and the second side surface 12 are asymmetric with respect to the first symmetry plane, and the extension portions 20 connected to the third side surface 13 and the fourth side surface 14 are asymmetric with respect to the second symmetry plane.

[0063] like Fig. 9 As shown, the first side surface 11, the second side surface 12, the third side surface 13 and the fourth side surface 14 of the base island 10 are all connected with the extension portion 20, wherein the first side surface 11, the third side surface 13 and the fourth side surface 14 are respectively connected with one extension portion 20, the second side surface 12 is connected with two extension portions 20, the extension portion 20 connected to the first side surface 11 and the extension portion 20 connected to the second side surface 12 are asymmetric about the first symmetry plane, and the extension portion 20 connected to the third side surface 13 and the extension portion 20 connected to the fourth side surface 14 are symmetric about the first symmetry plane. In other embodiments, the first side surface 11, the second side surface 12, the third side surface 13 and the fourth side surface 14 of the base island 10 are all connected with the extension portion 20, and the extension portion 20 connected to the first side surface 11 and the extension portion 20 connected to the second side surface 12 are asymmetric about the first symmetry plane, and the extension portion 20 connected to the third side surface 13 and the extension portion 20 connected to the fourth side surface 14 are asymmetric about the first symmetry plane.

[0064] In step 120 , the distance between a surface of the pin facing the base island and the first surface is determined.

[0065] like Figure 1 As shown, the distance between the surface of the pin 22 facing the base island 10 and the first surface 15 of the base island 10 is d1.

[0066] In some embodiments, the distance between the surface of the pin facing the base island and the first surface can be obtained by measurement, for example, by using a micrometer.

[0067] In step 130, a plastic encapsulation mold is provided, wherein the plastic encapsulation mold includes a first sub-mold and a second sub-mold, wherein the cavity of the first sub-mold is used to accommodate the base island and part of the extension portion of the lead frame; and the depth of the cavity is obtained.

[0068] In one embodiment, Fig.10 As shown, the first sub-mold 30 is provided with a cavity 31, and the first sub-mold 30 also includes a first abutment portion 32 surrounding the cavity 31. The second sub-mold 40 is provided with an accommodating cavity 41, and the second sub-mold also includes a second abutment portion 42, and the second abutment portion 42 surrounds the accommodating cavity 41.

[0069] In one embodiment, the depth of the cavity 31 of the first sub-mold 30 can be obtained by measurement. Alternatively, the depth of the cavity 31 of the first sub-mold 30 is known data.

[0070] like Fig.11 and Fig.12 As shown, the depth of the cavity 31 is d2.

[0071] In step 140, if the difference between the distance and the depth of the cavity is within the threshold range, the lead frame is placed in the first sub-mold so that the base island and the connecting rib are located in the cavity, and the second sub-mold is combined with the first sub-mold to plastic-encapsulate the lead frame to form a plastic-encapsulation layer covering the connecting rib and the base island, with the plastic-encapsulation layer exposed on the first surface.

[0072] In one embodiment, the minimum value of the threshold range is 0. That is, the distance between the surface of the lead frame pin 22 facing the base island 10 and the first surface 15 is greater than or equal to the depth of the cavity 31 of the first sub-mold 30. In this way, after the lead frame is placed in the cavity 31, the first surface 15 of the base island 10 can be fitted with the bottom surface of the cavity 31, thereby preventing the molding material from entering the gap between the first surface 15 of the base island 10 and the bottom surface of the cavity 31 during the process of forming the molding layer, resulting in the final molding layer covering the first surface.

[0073] In one embodiment, the step of placing the lead frame in the first sub-mold so that the base island and the connecting rib are located in the cavity includes the following process: making the opening of the cavity of the first sub-mold face upward, placing the lead frame in the first sub-mold, the base island and the connecting rib are located in the cavity, and the pin is located on the first abutment portion.

[0074] By setting the orientation of the cavity 31 of the first sub-mold 30, after the lead frame is placed in the first sub-mold 30, when the distance between the surface of the lead frame's pins facing the base island and the first surface is greater than or equal to the depth of the cavity 31, compared with the solution in which the opening of the cavity 31 of the first sub-mold 30 faces downward, it is easier to make the first surface 15 of the base island 10 fit better with the bottom surface of the cavity 31, thereby helping to avoid the formed plastic encapsulation layer covering the first surface 15 of the base island 10.

[0075] like Figures 10 to 12 As shown, after the lead frame is placed in the first sub-mold 30, the pin 22 of the extension part 20 is located on the first abutting portion 32; after the first sub-mold 30 and the second sub-mold 40 are molded together, the second abutting portion 42 abuts against the pin 22. When the distance between the surface of the pin 22 of the lead frame facing the base island 10 and the first surface 15 is greater than the depth of the cavity 31 of the first sub-mold 30, the second abutting portion 42 applies a downward force to the pin 22 after the second abutting portion 42 abuts against the pin 22, and the force of the second abutting portion 42 on the second sub-connection 22 is transmitted to the base island 10. When the difference between the above distance and the depth of the cavity 31 is greater than a threshold value, the force transmitted to the base island 10 will cause one end of the base island 10 to tilt up or the base island 10 to deform, so that the first surface 15 of the base island 10 cannot be completely attached to the bottom surface of the cavity 31, and finally the formed plastic encapsulation layer covers the first surface 15 of the base island 10. The above threshold value is also the maximum value of the threshold range. The inventors have found that the extension portion 20 of different types of lead frames is distributed differently on the side of the base island 10, and the force distribution of the second abutment portion 42 on the pin 22 is different, so that the threshold range corresponding to the difference between the distance and the depth of the cavity of different types of lead frames is also different.

[0076] In one embodiment, Figure 3 and Figure 4 As shown in FIG. 1 , when the extension portions 20 of the lead frame are connected to the same side surface of the base island 10 , the threshold range corresponding to the lead frame is [0, 10 μm]. Fig.11 As shown, only one side of the base island 10 is connected to the extension portion 20. After the force applied by the second abutting portion 42 to the pin 22 is transmitted to the base island 10, only one side of the base island 10 is subjected to a downward force, and the base island 10 is prone to one end lifting. In combination with the structural characteristics of the lead frame, the inventors (they) have concluded, based on multiple attempts, summaries, repeated tests, and calculations, that when the threshold range corresponding to the difference between the distance of the lead frame and the depth of the cavity is [0, 10μm], the base island 10 will not lift or deform at one end after the first sub-mold 30 and the second sub-mold 40 are assembled, and the first surface 15 of the base island 10 will expose the plastic encapsulation layer after the plastic encapsulation layer is formed.

[0077] In one embodiment, Figure 5 and Figure 6 As shown, among all the extensions 20 of the lead frame, the extensions 20 located on both sides of the first symmetry plane are symmetrical about the first symmetry plane; or, among all the extensions 20 of the lead frame, some of the extensions 20 are located on both sides of the first symmetry plane, and the remaining extensions 20 are located on both sides of the second symmetry plane, the extensions 20 located on both sides of the first symmetry plane are symmetrical about the first symmetry plane, and the extensions 20 located on both sides of the second symmetry plane are symmetrical about the second symmetry plane; the threshold range corresponding to the difference between the distance and the depth of the cavity of this type of lead frame is [0, 50 μm]. Fig.10 and 12 As shown, after the first sub-mold 30 and the second sub-mold 40 are molded together, any two opposite sides of the side of the base island 10 of this type of lead frame are subjected to uniform force, which can avoid the base island 10 from warping at one end due to uneven force on the two opposite sides; combined with the structural characteristics of the lead frame, the inventors (they) have concluded on the basis of multiple attempts, summaries, repeated tests and calculations that when the difference between the above distance and the depth of the cavity 31 is less than or equal to 50μm, the base island 10 will not deform or will deform very slightly, and the plastic encapsulation material will not enter between the first surface 15 of the base island 10 and the bottom surface of the cavity 31; when the difference between the above distance and the depth of the cavity 31 is greater than 50μm, the base island 10 will deform significantly, making the first surface 15 uneven and unable to fit the bottom surface of the cavity 31, which will cause the plastic encapsulation material to enter between the first surface 15 of the base island 10 and the bottom surface of the cavity 31. Therefore, in this embodiment, the threshold range is [0, 50μm]. Fig.10 In the embodiment shown, the distance d1 is equal to the depth d2 of the cavity 31; Fig.12 In the illustrated embodiment, the distance d1 is greater than the depth d2 of the cavity 31 .

[0078] In one embodiment, Figures 7 to 9As shown, the lead frame includes at least two extensions 20, and the extensions 20 connected to the first side surface 11 and the second side surface 12 are asymmetric with respect to the first symmetry plane. The threshold range corresponding to the difference between the distance and the depth of the cavity of this type of lead frame is [0, 25 μm]. After the first sub-mold 30 and the second sub-mold 40 are molded together, at least two sides of the side surfaces of the base island 10 of this type of lead frame will be subjected to force, and the base island is not prone to warping at one end. Combined with the structural characteristics of the lead frame, the inventors (they) have concluded, based on multiple attempts, summaries, repeated tests and calculations, that when the difference between the above distance and the depth of the cavity 31 is less than or equal to 25 μm, the base island 10 will not deform or will deform very slightly, and the plastic encapsulation material will not enter between the first surface 15 of the base island 10 and the bottom surface of the cavity 31; when the difference between the above distance and the depth of the cavity 31 is greater than 25 μm, the deformation of the base island 10 is more obvious, making the first surface 15 uneven and unable to fit completely with the bottom surface of the cavity 31, which will cause the plastic encapsulation material to enter between the first surface 15 of the base island 10 and the bottom surface of the cavity 31. Therefore, the threshold range in this embodiment is [0, 25 μm].

[0079] In one embodiment, the method for preparing the semiconductor structure further comprises the following steps:

[0080] First, if the difference between the distance and the depth of the cavity is not within the threshold range, and the distance is less than the depth of the cavity, a cushioning structure is provided in the cavity so that the difference between the sum of the distance and the thickness of the cushioning structure and the depth of the cavity is within the threshold range;

[0081] Subsequently, the lead frame is placed in the first sub-mold so that the base island and the connecting ribs are located in the cavity, and the second sub-mold is combined with the first sub-mold to plastic-encapsulate the lead frame to form a plastic-encapsulation layer covering the connecting ribs and the base island, with the plastic-encapsulation layer exposed on the first surface.

[0082] When the distance from the surface of the second extension of the lead frame facing the base island to the first surface is less than the depth of the cavity, the cushioning structure can be provided so that the sum of the above distance and the thickness of the cushioning structure is within the threshold range, so that the first surface of the base island can be exposed to the plastic sealing layer after the plastic sealing layer is formed. That is, the provision of the cushioning structure prevents the lead frame from being scrapped when the distance from the surface of the second extension of the lead frame facing the base island to the first surface is not within the threshold range, and the lead frame can be used to connect with other structures such as electrical connectors after plastic sealing, which helps to reduce the cost of the semiconductor structure.

[0083] Preferably, the sum of the distance and the thickness of the padding structure is equal to the depth of the cavity. This arrangement is more helpful to prevent the base island from being lifted or deformed at one end due to the force of the second abutment portion on the pin after the first sub-mold and the second sub-mold are molded together.

[0084] Furthermore, if Fig.13 As shown, the bottom surface of the padding structure 50 is in contact with the bottom surface of the cavity 31, and the side surface of the padding structure is in contact with the side surface of the cavity 31. This arrangement can prevent the plastic encapsulation material from entering between the padding structure and the cavity, resulting in the padding structure being difficult to separate from the sub-mold after the plastic encapsulation layer is formed. Fig.13 In the illustrated embodiment, the sum of the height h of the elevated structure 50 and the distance d1 is equal to the depth d2 of the cavity 31 .

[0085] Furthermore, the material of the padding structure is metal or metal alloy. With such a configuration, the padding structure can withstand a relatively high temperature, which can prevent the padding structure from deforming during the process of forming the plastic encapsulation layer, thereby preventing the plastic encapsulation material from entering between the base island 10 and the padding structure, and further causing the formed plastic encapsulation layer to cover the base island 10.

[0086] In one embodiment, after the step of closing the second sub-mold with the first sub-mold, plastic-sealing the lead frame to form a plastic-sealing layer covering the connecting ribs and the base island, and exposing the plastic-sealing layer on the first surface, the method for preparing the semiconductor structure further includes the following processes: connecting the lead frame to an electrical connector; connecting the pin to the electrical connector, with the first surface facing away from the electrical connector; or connecting the first surface to the electrical connector.

[0087] When the first surface of the base island is not connected to the electrical connector, the lead frame can be electrically connected to the electrical connector through the pins, and the first surface away from the electrical connector can dissipate heat, which helps to improve the heat dissipation performance of the semiconductor structure; when the first surface of the base island is connected to the electrical connector, the pins of the lead frame can also be connected to the electrical connector at the same time, that is, the lead frame can be connected to the electrical connector through the first surface of the base island and the pins at the same time.

[0088] In one embodiment, the electrical connector may be a circuit board.

[0089] It should be noted that in the accompanying drawings, the sizes of layers and regions may be exaggerated for clarity of illustration. It is also understood that when an element or layer is referred to as being "on" another element or layer, it may be directly on the other element, or there may be an intermediate layer. In addition, it is understood that when an element or layer is referred to as being "under" another element or layer, it may be directly under the other element, or there may be more than one intermediate layer or element. In addition, it is also understood that when a layer or element is referred to as being "between" two layers or two elements, it may be the only layer between the two layers or two elements, or there may also be more than one intermediate layer or element. Similar reference numerals throughout the text indicate similar elements.

[0090] Those skilled in the art will readily appreciate other embodiments of the present application after considering the specification and practicing the disclosure disclosed herein. The present application is intended to cover any modification, use or adaptation of the present application, which follows the general principles of the present application and includes common knowledge or customary techniques in the art that are not disclosed in the present application. The specification and examples are intended to be exemplary only, and the true scope and spirit of the present application are indicated by the following claims.

[0091] It should be understood that the present application is not limited to the precise structures that have been described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof. The scope of the present application is limited only by the appended claims.

Claims

1. A method for preparing a semiconductor structure, characterized in that: The method for preparing the semiconductor structure comprises: A lead frame is provided, the lead frame comprising a base island and at least one extension portion, the base island comprising a first surface, a second surface opposite to the first surface, and a plurality of side surfaces connecting the first surface and the second surface; the extension portion comprises a connecting rib connected to the side surface and a pin connected to an end of the connecting rib away from the base island, the extending direction of the connecting rib intersects with the first surface, and the extending direction of the pin is parallel to the first surface; the pin is located on a side of the base island away from the first surface; Determine the distance between the surface of the pin facing the base island and the first surface; Providing a plastic encapsulation mold, the plastic encapsulation mold comprising a first sub-mold and a second sub-mold, the cavity of the first sub-mold being used to accommodate the base island and part of the extension portion of the lead frame; obtaining the depth of the cavity; If the difference between the distance and the depth of the cavity is within a threshold range, the lead frame is placed in the first sub-mold so that the base island and the connecting ribs are located in the cavity, and the second sub-mold is combined with the first sub-mold to plastic-encapsulate the lead frame to form a plastic-encapsulation layer covering the connecting ribs and the base island, with the plastic-encapsulation layer exposed on the first surface.

2. The method for preparing a semiconductor structure according to claim 1, characterized in that: The minimum value of the threshold range is 0.

3. The method for preparing a semiconductor structure according to claim 1, characterized in that: The lead frame includes at least one extending portion, each of the extending portions is connected to the same side surface of the base island, and the threshold range is [0, 10 μm].

4. The method for preparing a semiconductor structure according to claim 1, characterized in that: The lead frame includes at least two extensions, and the multiple side surfaces include a first side surface, a second side surface opposite to the first side surface, a third side surface, and a fourth side surface opposite to the third side surface; the base island has a first symmetric plane and a second symmetric plane, the first side surface and the second side surface are symmetrical about the first symmetric plane, and the third side surface and the fourth side surface are symmetrical about the second symmetric plane; each of the extensions is connected to one of the first side surface and the second side surface, and the extension connected to the first side surface is symmetrical with the extension connected to the second side surface about the first symmetric plane; or, the first side surface, the second side surface, the third side surface, and the fourth side surface are respectively connected with at least one extension, the extension connected to the first side surface is symmetrical with the extension connected to the second side surface about the first symmetric plane, and the extension connected to the third side surface is symmetrical with the extension connected to the fourth side surface about the second symmetric plane; The threshold range is [0, 50 μm].

5. The method for preparing a semiconductor structure according to claim 1, characterized in that: The lead frame includes at least two extending portions, the multiple side surfaces include a first side surface, a second side surface opposite to the first side surface, a third side surface, and a fourth side surface opposite to the third side surface; the base island has a first symmetric plane and a second symmetric plane, the first side surface and the second side surface are symmetrical about the first symmetric plane, and the third side surface and the fourth side surface are symmetrical about the second symmetric plane; among the at least two extending portions, the extending portion connected to the first side surface and the second side surface is asymmetric about the first symmetric plane; The threshold range is [0, 25 μm].

6. The method for preparing a semiconductor structure according to claim 1, characterized in that: The method for preparing the semiconductor structure further comprises: If the difference between the distance and the depth of the cavity is not within the threshold range, and the distance is less than the depth of the cavity, a cushioning structure is provided in the cavity so that the difference between the sum of the distance and the thickness of the cushioning structure and the depth of the cavity is within the threshold range; The lead frame is placed in the first sub-mold so that the base island and the connecting ribs are located in the cavity, and the second sub-mold is combined with the first sub-mold to plastic-encapsulate the lead frame to form a plastic-encapsulation layer covering the connecting ribs and the base island, with the plastic-encapsulation layer exposed on the first surface.

7. The method for preparing a semiconductor structure according to claim 6, characterized in that: The bottom surface of the raising structure is in contact with the bottom surface of the cavity, and the side surface of the raising structure is in contact with the side surface of the cavity.

8. The method for preparing a semiconductor structure according to claim 6, characterized in that: The material of the padding structure is metal or metal alloy.

9. The method for preparing a semiconductor structure according to claim 1, characterized in that: The first sub-mold includes a first abutment portion surrounding the cavity, and the second sub-mold includes a second abutment portion; Placing the lead frame in the first sub-mold so that the base island and the connecting rib are located in the cavity comprises: placing the lead frame in the first sub-mold with the opening of the cavity of the first sub-mold facing upward, the base island and the connecting rib being located in the cavity, and the lead being located on the first abutting portion; After the first sub-mold and the second sub-mold are clamped, the second abutting portion abuts against the lead.

10. The method for preparing a semiconductor structure according to claim 1, characterized in that: The lead frame further includes a pin connected to the side surface; the second sub-mold is molded together with the first sub-mold to plastic-encapsulate the lead frame to form a plastic-encapsulation layer covering the connecting rib and the base island, and after the first surface exposes the plastic-encapsulation layer, the method for preparing the semiconductor structure further includes: The lead frame is connected to an electrical connector; the lead is connected to the electrical connector, and the first surface faces away from the electrical connector; or the first surface is connected to the electrical connector.

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