Method for manufacturing semiconductor assembly

Abstract

A method of manufacturing a semiconductor device is disclosed. The method includes securing a die to a die mount with solder, and securing a clip to the die with solder to form a first subassembly. The method further includes heating the first subassembly to at least a melting temperature of the solder and then subsequently removing at least some of the solder from the die pad in a region adjacent the die to expose the die pad in the region. The method further includes molding a housing onto the first subassembly such that the housing at least partially surrounds the die, the die mount, and the clip.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a semiconductor device. Background Art

[0002] Semiconductor components such as transistors are manufactured as layered components including components such as a die pad, a die, a clip, and a housing. The housing provides a protective function and at least partially surrounds the die and other components that form part of the semiconductor component.

[0003] Semiconductor assemblies are manufactured by bonding components together. Once bonded, the assembly defines a laminate structure that forms a number of layers. For example, the die pad, die, clip, and housing may each form a layer of the laminate structure.

[0004] Semiconductor components are subject to stress during use. The stress may arise, for example, due to thermal expansion and / or mechanical deformation of the component. The stress experienced by the semiconductor component may lead to delamination of the component. This is undesirable because delamination may ultimately lead to failure of the component, for example due to moisture ingress.

[0005] There exists a need to overcome the shortcomings associated with existing methods of manufacturing semiconductor components, whether mentioned in this document or otherwise. Summary of the invention

[0006] In a first aspect of the invention, a method of manufacturing a semiconductor device is provided. The method includes securing a die to a die pad with solder and securing a clip to the die with solder to form a first subassembly. The method further includes heating the first subassembly to at least the melting temperature of the solder and then subsequently removing at least some of the solder from the die pad in an area adjacent to the die to expose the die pad in that area. The method further includes molding a housing onto the first subassembly such that the housing at least partially surrounds the die, the die pad, and the clip.

[0007] Removing at least some solder from the die pad in an area adjacent to the die may be understood to mean removing solder from the die pad in an area adjacent to and outside the die's footprint when the first subassembly is viewed in a plan view (i.e., perpendicular to the first major surface of the die pad).

[0008] The solder may be removed from the die pad in an area adjacent to and outside of the footprint of the die.

[0009] Solder is commonly used in semiconductor devices to secure components of the device together. Liquid (molten) solder is applied to the die pad in the area where the die is to be secured, and the die is placed on the liquid solder to create a temporary bond. Then, in a process called reflow, the component is heated to a temperature above the melting temperature of the solder, which creates a permanent bond. During reflow, some of the solder will spread outside the footprint of the chip, covering a portion of the die pad. After reflow, an enclosure, typically an epoxy mold compound, is molded onto the component.

[0010] The diffusion of solder beyond the footprint of the die is undesirable because the bond strength between the housing and the solder is less than the bond strength between the housing and the die pad. The reduced bond strength increases the likelihood of the housing delaminating from other components of the device, which ultimately causes the device to fail due to, for example, moisture ingress. By removing at least some of the solder from the die pad in the area adjacent to the die, the bond strength between the housing and the first subassembly is increased. Advantageously, this reduces the likelihood of delamination of the components.

[0011] The area of ​​the die pad exposed by removing the solder may correspond to the area from which the solder was removed.

[0012] Laser ablation may be used to remove the solder from the die pad.

[0013] Laser ablation allows solder to be removed in an efficient manner.

[0014] The method may further include, simultaneously with removing at least some of the solder from the die paddle, removing at least some material from the die paddle to form a recess in the die paddle.

[0015] In the case where the groove is formed in the die pad, the surface area of ​​the die pad is increased. Increasing the surface area of ​​the die pad improves the bonding strength between the housing and the die pad. In addition, the groove acts as a locking mechanism to better secure the housing to the die pad. Therefore, the groove further reduces the possibility of delamination of the device.

[0016] The groove may extend around at least 50% of the circumference of the die pad.

[0017] The groove may extend around at least 25% of the circumference of the die pad.

[0018] A groove extending around the perimeter of the die paddle may be understood to mean that the groove extends inside the perimeter of the die paddle.

[0019] The groove may extend around at least 50% of the footprint of the die.The groove may extend around at least 25% of the footprint of the die.

[0020] With the groove extending around at least 50% of the circumference of the die pad, the likelihood of delamination is reduced to a desired amount.

[0021] The groove may define a plurality of segments, each segment defining a continuous path or a discontinuous path.

[0022] The segments of a groove defining a corresponding continuous path may be understood to mean that each segment does not define any vertices. The vertices may be defined at the interfaces between the segments of the groove. In some embodiments, one or more segments may define vertices.

[0023] Discontinuities in the grooves present a risk of delamination as stresses may be concentrated at the discontinuities.Thus, where the groove sections define a continuous path, the likelihood of delamination of the component is further reduced.

[0024] The grooves may be non-linear.The grooves may define a wave shape.

[0025] In the case where the groove is non-linear, the length of the groove, and therefore the surface area of ​​the groove, is increased compared to, for example, if the groove is linear. Increasing the surface area of ​​the groove increases the surface area of ​​the die pad, thereby increasing the bonding strength between the housing and the die pad. Increasing the bonding strength between the housing and the die pad advantageously reduces the likelihood of delamination of the device.

[0026] Molding the housing onto the first subassembly may include molding the housing into the recess.

[0027] The groove depth and / or width may be at least 5 μm. The groove depth and / or width may be at least 3 μm and / or up to 15 μm. The groove width may be at least 20 μm and / or up to 40 μm. The groove depth may be up to 10 μm.

[0028] The method may further include applying a protective layer to the first subassembly before removing at least some of the solder from the die pad.

[0029] With the protective film applied to the first subassembly, the likelihood of damage to components of the device when removing the solder from the die pad is reduced.

[0030] The method may further include applying a protective layer to the first subassembly after heating the first subassembly and before removing at least some of the solder from the die pad.The solder may be removed by chemical etching.

[0031] The ratio of the area of ​​the footprint of the die to the area of ​​the footprint of the die pad may be at least 0.75.

[0032] The ratio of the area of ​​the footprint of the die to the area of ​​the footprint of the die pad may be at least 0.5.

[0033] The area of ​​the footprint of the die may refer to the total footprint area of ​​the die.The area of ​​the footprint of the die pad may refer to the total footprint area of ​​the die pad.

[0034] Larger die-to-pad ratios increase the likelihood of delamination because the solder can diffuse to the periphery of the die pad, leaving little or no die pad material for housing bonding. Thus, the present invention is particularly beneficial where the ratio of the cross-sectional area of ​​the die taken in a plane parallel to the major surface of the die to the cross-sectional area of ​​the die pad taken in a plane parallel to the major surface of the die pad is at least 0.75. Having a larger die-to-pad ratio allows for increased functionality of the device compared to a smaller die-to-pad ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Embodiments of the present application will now be described with reference to the accompanying drawings, in which:

[0036] Figure 1 shows a cross-sectional side view of a semiconductor device fabricated in accordance with an embodiment of the present invention;

[0037] Figure 2 FIG. 7 schematically shows a manufacturing method according to an embodiment of the present invention. Figure 1 Method for producing a semiconductor device;

[0038] Figure 8 Shows Figure 1 a first subassembly of a semiconductor device; and

[0039] Fig. 9 Shows the manufacturing Figure 1 The method of manufacturing a semiconductor device includes the following steps. DETAILED DESCRIPTION

[0040] Figure 1 A semiconductor device 2 is shown. The semiconductor device 2 includes a die pad 4. The semiconductor device 2 includes a die 6. The semiconductor device 2 includes a clip 8.

[0041] The die pad 4 serves as a substrate for the semiconductor device 2, on which other components of the device are attached. The die pad 4 defines a first major surface 5 and a second major surface 7. The second major surface 7 is generally opposite to the first major surface 5. The die pad 4 is generally a plate-like component and is generally quadrilateral. The die pad 4 forms a substrate in the manufacture of the device 2. The die pad 4 is made of a conductive material such as copper (including copper alloys).

[0042] The die 6 is fixed to the die pad 4. The die 6 is fixed to the die pad 4 through the first solder layer 10. Figure 1 It is not obvious in the figure, but the tube core 6 includes multiple components (in Figure 1Only one component is visible in the die 6 - the other components are hidden by the visible components). However, in some embodiments, the die 6 may include a single component. The die 6 is made of semiconductor material. The die 6 has functional circuits fabricated thereon. The die 6 is typically rectangular, but may be any other suitable shape. The shape of the die 6 is plate-like.

[0043] Clip 8 is formed of a plurality of component parts 8a, 8b. Each part 8a, 8b of clip 8 is secured to a corresponding component of die 6. Clip 8 is secured to die 6 by a second solder layer 12. Second solder layer 12 may be applied in a plurality of sections, each section being for a corresponding component of die 6, as will be discussed in more detail below. A plurality of leads 14 (in Figure 1 The lead wires 14 may be formed integrally with the respective portions 8a, 8b of the clip 8 or may be formed separately from the clip 8 and secured to the respective portions of the clip 8 using any suitable method, such as by welding.

[0044] The semiconductor device 2 further includes a covering 16. The covering 16 may also be referred to as an insulator, an enclosure, or an encapsulant. The covering 16 encapsulates the remaining components of the semiconductor device 2 (i.e., the die holder 4, the die 6, and the clip 8). The covering 16 is adhered to the die holder 4, the die 6, and the clip 8, which secures the covering 16 thereto. However, as will be discussed in more detail below, the covering 16 may become separated from the components during use due to, for example, repeated deformation of the device 2. The leads 14 of the clip 8 extend through the covering 16. This allows the leads 14, and therefore the device 2, to be connected to an external circuit (not shown). The covering 16 may be made of any suitable electrically insulating material, such as an epoxy resin.

[0045] Now refer to Figures 2 to 9 Let's discuss the manufacture of semiconductor device 2.

[0046] from Figure 2 Initially, the die pad 4 is shown in a form still connected to the surrounding frame 18. The frame 18 may be referred to as a lead frame. The frame 18 is actually a flat plate of conductive material such as copper, from which the geometry of the die pad 4 is stamped or etched. Figure 3 As shown, the closed shapes labeled 21 and 23 are openings in the frame 18 that are not filled with material (ie, they are voids). Figure 2 As shown, the die pad 4 is attached to the surrounding frame 18 only by branches 17, 19. The branches 17, 19 may be otherwise described as attachment points of the die pad 4 to the frame 18. The frame 18 may include, for example, an array of 20 x 5 die pads (e.g., for a batch production process).

[0047] Steering Figure 3 , schematically showing the subsequent steps of the manufacturing process. Figure 3 In the step shown, a first solder layer 10 is printed or dispensed onto the die pad 4. In particular, the first solder layer 10 is printed or dispensed onto the first major surface 5 of the die pad 4. Figure 4 In the subsequent step shown, the first part 6a and the second part 6b of the die 6 are attached to the die pad 4 by means of the first solder layer 10. Therefore, this step can be described as coupling the die 6 to the die pad 4 with solder.

[0048] exist Figure 5 In a subsequent step shown, a second solder layer 12 is dispensed or printed onto the die 6, in particular onto the first component 6a and the second component 6b.

[0049] exist Figure 6 In the subsequent manufacturing step shown, the clip 8 is coupled to the die (at Figure 6 8 is not visible in the figure, it is behind the clip). Therefore, this step can be described as coupling the clip 8 to the tube core 6 with solder. Once the clip 8 is coupled to the tube core, the first subassembly 15 is formed. The first subassembly 15 includes the tube core 4, the tube core, the clip 8, and the first solder layer 10 and the second solder layer 12. In the embodiment shown, the clip 8 is initially attached to the larger copper ribbon in a manner similar to the frame 18, but is separated from the ribbon before being attached to the tube core 4. The clip 8 can be said to be attached to the top of the tube core 6. The bottom of the tube core 6 can be said to be attached to the tube core 4. The clip 8 is also attached to the surrounding frame 18 at points 20a, 20b. At a later step in the process (i.e., at Fig. 9 Afterwards, the clip 8 is cut across the line 22 to isolate the clip 8 from the frame 18 and define the plurality of leads 14 of the clip 8 .

[0050] For completeness, although the illustrated embodiment includes a clip 8, the clip 8 is not a necessary feature of the present invention. In other embodiments, wire bonding may alternatively be used to couple the connector to the die. The connector may include one or more external leads. However, the use of a clip is preferred because the clip has desirable conductive properties.

[0051] In a subsequent step not shown, the first subassembly 15 is heated. The process of heating the first subassembly 15 can be referred to as reflow. When undergoing reflow, the first subassembly 15 is heated to a temperature greater than or equal to the melting temperature of the first solder layer 10 and the second solder layer 12. In other words, the first subassembly 15 is heated to a temperature at least equal to the melting temperature of the solder (the first solder layer 10 and the second solder layer 12). This causes the first solder layer 10 and the second solder layer 12 to melt. The melting of the first solder layer 10 and the second solder layer 12 may cause one or both of the first solder layer 10 and the second solder layer 12 to diffuse. In some cases, the first solder layer 10 may extend beyond the footprint of the tube core 6. When the first subassembly 15 is observed in a plan view (i.e., from above), the footprint of the tube core 6 can be understood to refer to the area defined by the periphery of the tube core 6. The diffusion of the first solder layer 10 may cause a limited area of ​​the first main surface 5 of the tube core seat 4 to be exposed. This is because a large portion of the first major surface 5 of the die pad 4 may be covered by the first solder layer 10. The bonding strength between the housing 16 and the die pad 4 is proportional to the amount of the first major surface 5 of the die pad 4 that is exposed. In the case where the first major surface 5 of the die pad 4 is not exposed or is slightly exposed, the bonding strength between the cover 16 and the die pad 4 is reduced compared to the case where a larger area of ​​the first major surface 5 is exposed. This may cause the cover 16 to separate from the die pad 4 during use. The present invention attempts to solve this problem, which will be discussed in more detail below.

[0052] exist Figure 7a In the subsequent step shown, a protective layer 25 is applied to the first subassembly 15. The protective layer 25 can be a protective material, such as a protective film. The protective layer 25 can be made of a highly purified water-soluble protective material such as a water-soluble film. The protective layer 25 covers at least the top surface of the first subassembly 15 (when viewed in a plan view). The protective layer is preferably water-soluble. The water-soluble protective layer 25 advantageously allows the protective layer 25 to be easily removed in a later step.

[0053] exist Figure 7b and Figure 7c In the subsequent step shown, at least some of the solder of the first solder layer 10 is removed from the first subassembly 15. In particular, at least some of the first solder layer 10 is removed from the die pad 4 in the area adjacent to the die 6. Removing at least some of the solder of the first solder layer 10 from the die pad 4 in the area adjacent to the die 6 exposes the die pad 4 in this area. The solder of the first solder layer 10 is removed using laser ablation. Removing at least some of the solder from the first solder layer 10 from the die pad 4 in the area adjacent to the die 6 can be understood to mean removing the solder of the first solder layer 10 from the die pad 4 in the area adjacent to the footprint of the die 6 and outside the footprint of the die when the first subassembly 15 is viewed in a plan view (i.e., perpendicular to the first major surface of the die pad 4). Housing ( Figure 7b and Figure 7c The bonding strength between the die pad 4 (not shown in the figure - it has not been molded onto the first subassembly) and the die pad 4 is greater than the bonding strength between the housing and the first solder layer 10. Therefore, exposing the die pad 4 increases the bonding strength between the housing and the first subassembly 15, which reduces the possibility of delamination of the device 2.

[0054] Laser ablation may also remove some material from the die pad 4. Removing material from the die pad 4 results in the formation of a recess 24 in the die pad 4. Figure 7b . The groove 24 further increases the bonding strength between the cover 16 and the die pad 4. This is because the surface area of ​​the first main surface 5 of the die pad 4 is increased due to the presence of the groove 24. In some embodiments, the groove 24 may extend around at least 50% of the footprint or periphery of the die 6. However, in some embodiments, the groove 24 may extend around less than 50% of the footprint or periphery of the die 6. The groove 24 extends around the perimeter of the die pad 4. In some embodiments, the groove may extend around at least 50% of the perimeter of the die pad 4. The groove 24 extending around the perimeter of the die pad 4 can be understood to mean that the groove 24 is arranged on the inner side of the perimeter of the die pad 4. The groove 24 can be said to be arranged in a region between the perimeter of the footprint of the die 6 and the perimeter of the footprint of the die pad 4 when the first subassembly 15 is viewed in a plan view (i.e., perpendicular to the first main surface 5 of the die pad 4). The depth and / or width of the groove 24 can be at least 5μm. In some embodiments, the depth and / or width may be at least 3 μm and / or up to 15 μm. The width of groove 24 may be at least 20 μm. In some embodiments, the depth of the groove may be up to 10 μm. In some embodiments, the width of groove 24 may be up to 40 μm. In some embodiments, the width of groove 24 may be greater than 40 μm. The width and / or depth of groove 24 may be selected based on, for example, the size of semiconductor device 2 and the intended application of semiconductor device 2.

[0055] refer to Figure 8, the first subassembly 15 is shown in a plan view after the groove 24 is formed. The groove 24 defines a plurality of segments 24a-c. In the depicted embodiment, the plurality of segments 24a-c includes three segments. However, in some non-depicted embodiments, the groove 24 may define any suitable number of segments. The number of segments of the groove may be determined by, for example, the geometry of the die seat 4, the die 6. For example, the groove may define only a single segment, or may define four or more segments. The segments 24a-c define corresponding continuous paths. The segments 24a-c of the groove 24 that define corresponding continuous paths may be understood to mean that each segment 24a-c does not define any vertices. The segments 24a-c may extend continuously to each other. This may be understood to mean that no vertices are defined at the interfaces between the segments 24a-c of the groove 24. However, in some embodiments, one or more vertices may be defined at the interfaces between the segments 24a-c of the groove 24. In Figure 8 In the embodiment shown, each section of the groove 24 is non-linear. In particular, each section 24a-c of the groove 24 defines a waveform. This further facilitates the die pad 4 and the cover (in Figure 8 The bonding strength between the first subassembly 15 and the second subassembly 15 is not shown in the figure, which has not been molded onto the first subassembly 15). This is because the surface area of ​​the groove 24 increases when it is non-linear compared to if the groove is, for example, linear. In other embodiments, the groove 24 can define any other suitable non-linear or linear form. In some embodiments, the segments 24a-c may not be continuous. For example, one or more segments 24a-c of the groove 24 may be dotted lines, may define a zigzag shape, or may be formed by multiple points. In some embodiments, grooves do not need to be provided, and laser ablation can be performed to remove solder only from the first solder layer 10. That is, laser ablation does not remove any material from the die seat 4.

[0056] exist Figure 7c In the subsequent step shown, the first subassembly 15 is washed. The step of washing the first subassembly 15 may be referred to as 'flux cleaning', or simply as a 'cleaning process'. The first subassembly 15 may be washed with water. Since the protective layer 25 is water-soluble, washing the first subassembly 15 with water dissolves the protective layer. In other embodiments, the protective layer 25 may not be water-soluble, and the first subassembly may be washed using an alternative substance. Washing the first subassembly 15 also removes any residue that may be present on the first subassembly 15 after laser ablation.

[0057] exist Fig. 9In the subsequent step shown, the housing 16 is molded onto the first subassembly 15 so that the housing at least partially surrounds the die 6, the die pad 4, and the clip 8. The housing 16 does not completely surround all of these components, but should at least surround the exposed surface of the die 6 (i.e., all of the components 6a, 6b of the die). Therefore, it can be said that the housing 16 surrounds the die and at least a portion of the die pad 4 and the clip 8. The extent to which the housing 16 covers the first subassembly 15 is determined by Fig. 9 In addition, the housing 16 is shown in a partially transparent view to help understand the position of the housing 16. The purpose of the housing 16 is to protect the die from moisture ingress and impact.

[0058] The housing 16 is overmolded onto the die pad 4 by injection molding a housing material that is capable of flowing. Fig. 9 1, the mold not shown in the figure defines the shape of the housing 16 once the material has solidified (e.g., hardened or cured). As discussed above, the material flows to surround the first subassembly 15. The material also flows into the groove 24. Thus, the groove 24 defines a locking feature into which the material can extend to more firmly couple the housing 16 to the die pad 4. This reduces the risk of delamination and / or cracking of the housing 16.

[0059] exist Figures 2 to 9 In a subsequent manufacturing step not shown, by cutting Figure 2 The branches 17, 19 shown separate the first subassembly 15 from the surrounding frame 18. During the cutting process, the leads 14 of the clip 8 are also cut and shaped. The assembly of the semiconductor assembly is thus completed.

[0060] In some undepicted embodiments, chemical etching can be used instead of laser ablation to remove solder. In the case of using chemical etching, the method is the same as the previous embodiment until the reflow step. After reflow, a protective layer is applied to the first subassembly 15. The protective layer is applied to the surface where chemical etching does not occur. Therefore, the protective layer can be applied to all visible surfaces of the first subassembly 15, except for the first solder layer 15 in the area between the periphery of the footprint of the tube core 6 and the periphery of the tube core seat 4. Subsequently, the first subassembly is immersed in a chemical bath. The chemical bath can contain chemicals that can dissolve solder. For example, the chemicals contained in the bath can be an aqueous solution of 0.3M fluoroboric acid and 0.2M hydrogen peroxide. The first subassembly is immersed for a predetermined amount of time. The predetermined amount of time can be, for example, at least 5 minutes and / or up to 20 minutes. After the predetermined amount of time has passed, the first subassembly 15 is removed from the chemical bath. Then the first subassembly 15 is washed. Immersed in the chemical bath removes solder from the tube core, preferably the tube core seat in the area of ​​the footprint of the tube core adjacent to the tube core, to expose the tube core seat. This allows the housing 16 to better adhere to the first subassembly 15. Then, in the same manner as above with respect to Fig. 9 The housing 16 is applied in the same manner as discussed.

[0061] Whether by laser ablation or chemical etching, removing solder from the die pad 4 advantageously improves the adhesion between the housing 16 and the first subassembly 15, in particular the adhesion between the housing 16 and the die pad 4. As described above, this is because the bonding strength between the housing 16 and the die pad 4 is greater than the bonding strength between the housing 16 and the solder material. It may be particularly desirable to increase the bonding strength between the housing 16 and the first subassembly 15, in particular the die pad 4, where the ratio of the area of ​​the footprint of the die 6 to the area of ​​the footprint of the die pad 6, also referred to as the D / P ratio, is at least 0.75. Depending on the desired function of the semiconductor device 2, a higher D / P ratio may be required. However, a higher D / P ratio reduces the area of ​​the die pad 4 to which the housing 16 can adhere, which is further reduced due to solder diffusion. Therefore, it is particularly advantageous to remove solder from the first subassembly when the D / P ratio is at least 0.75.

[0062] Although specific embodiments of the present invention have been described above, it should be understood that the present invention may be practiced in a manner other than as described. The above description is intended to be illustrative rather than restrictive. Therefore, it will be apparent to those skilled in the art that the present invention as described may be modified without departing from the scope of the claims set forth below.

Claims

1. A method for manufacturing a semiconductor device, the method comprising: securing a die to a die pad with solder and securing a clip to the die with solder to form a first subassembly; heating the first subassembly to at least a melting temperature of the solder and then subsequently removing at least some of the solder from the die paddle in an area adjacent the die to expose the die paddle in that area; as well as A housing is molded onto the first subassembly such that the housing at least partially surrounds the die, the die paddle, and the clip. 2 . The method of claim 1 , wherein the solder is removed from the die pad using laser ablation.

3. The method of claim 2, further comprising removing at least some material from the die pad to form a recess in the die pad simultaneously with removing at least some of the solder from the die pad. The method of claim 3 , wherein the groove extends around at least 50% of the circumference of the die pad.

5. A method according to claim 3 or claim 4, wherein the groove defines a plurality of sections, each section defining a continuous path or a discontinuous path.

6. A method according to any one of claims 3 to 5, wherein the groove is non-linear; optionally, wherein the groove defines a waveform.

7. The method of any one of claims 3 to 6, wherein molding the housing onto the first subassembly comprises molding the housing into the recess.

8. A method according to any one of claims 4 to 7, wherein the groove depth and / or width is at least 5 μm.

9. The method of any preceding claim, further comprising applying a protective layer to the first subassembly before removing at least some of the solder from the die pad.

10. The method of claim 1 or claim 2, further comprising applying a protective layer to the first subassembly after heating the first subassembly and before removing at least some of the solder from the die pad, and wherein the solder is removed by chemical etching.

11. A method according to any preceding claim, wherein the ratio of the area of ​​the footprint of the die to the area of ​​the footprint of the die pad is at least 0.75.

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