Molded interconnect bumps in semiconductor devices

Abstract

In one example, a semiconductor package (100) includes a lead frame (102) and a semiconductor die (104) attached to the lead frame (102) via shaped or tapered bumps (106). Each of the bumps (106) includes a first end (108) connected to the semiconductor die (104) and an opposite second end (110) connected to the lead frame (102). The first end (108) has a first end surface area. The second end (110) has a second end surface area. The first end surface area is smaller than the second end surface area.

Description

[Technical field]

[0001] This application relates generally to semiconductor devices, and more particularly to molded interconnect bumps in semiconductor devices. [Background technology]

[0002] In some types of semiconductor packages, a semiconductor die is attached directly to a leadframe via interconnect bumps or posts. The interconnect bumps electrically connect the semiconductor die to the leadframe. The interconnect bumps may include both signal bumps and power bumps. Signal bumps may generally be primarily focused on transmitting electrical signals between the semiconductor die and the leadframe. Power bumps may generally be primarily focused on transmitting the bulk of power between the leadframe and the semiconductor die. As the density of connections increases, interconnectivity becomes more challenging. Summary of the Invention

[0003] In one embodiment, a semiconductor package includes a leadframe and a semiconductor die attached to the leadframe via a plurality of bumps. Each of the plurality of bumps includes a first end connected to the semiconductor die and an opposing second end connected to the leadframe. The first end has an end surface area A1. The second end has an end surface area A2. The end surface area A1 of the first end is smaller than the end surface area A2 of the second end.

[0004] In one aspect, a semiconductor package includes a leadframe, a semiconductor die attached to the leadframe, and a plurality of bumps electrically connecting the semiconductor die and the leadframe. The bumps have a longitudinal length extending from a first end to an opposing second end. The first end is connected to the semiconductor die and the second end is connected to the leadframe. The first end has a lateral width W1 perpendicular to the longitudinal length that is less than a lateral width W2 of the second end.

[0005] According to one aspect, a method of forming a plurality of tapered bumps on a die for attaching the die to a leadframe in a semiconductor package includes depositing a seed material on a wafer, depositing photoresist on the seed material, masking the photoresist according to a pattern having bump sites, and overexposing the masked photoresist to form a plurality of tapered sites therein. Each of the tapered sites has a first end closest to the wafer and a second end furthest from the wafer. The method further includes depositing one or more metals at the plurality of tapered sites and removing the photoresist to form a plurality of tapered bumps. Each of the tapered bumps of the plurality of tapered bumps has a first surface area A1 at the first end closest to the wafer and a second end surface area A2 at the second end furthest from the wafer. The first end of the tapered bump abuts the wafer, and the first surface area A1 is less than the second surface area A2.

[0006] According to one embodiment, a method of electrically coupling a semiconductor die to a leadframe includes forming a plurality of tapered bumps on the die, such that each of the plurality of tapered bumps has a first end surface area A1 at a first end closest to the die and a second end surface area A2 at an opposite second end. The first end has an end surface area A1 that is less than the second end surface area A2. The first end is attached to the die. The method further includes soldering the second ends of the plurality of tapered bumps to the leadframe. Other embodiments are disclosed herein. [Brief description of the drawings]

[0007] [Figure 1] 1 is a schematic perspective view of a portion of an example semiconductor package.

[0008] [Figure 2A] 2 is a schematic front view of the example semiconductor package of FIG. 1.

[0009] [Figure 2B] 2B is a schematic detail view of a portion of the example semiconductor package of FIG. 2A.

[0010] [Figure 3A] 2 is a schematic diagram of one end of an exemplary shape of an interconnect bump.

[0011] [Figure 3B] FIG. 3B is a schematic perspective view of the molded interconnect bump of FIG. 3A.

[0012] [Figure 4] 4 is a schematic diagram of an interconnect bump of another exemplary shape.

[0013] [Diagram 5] 1 is a schematic plan view of a portion of an example semiconductor package.

[0014] [Figure 6] 1 is a schematic plan view of a portion of an example semiconductor package.

[0015] [Figure 7A] 1A-1D are schematic diagrams, in cross section, illustrating process steps for forming shaped interconnect bumps on a semiconductor wafer. [Figure 7B] 1A-1D are schematic diagrams, in cross section, illustrating process steps for forming shaped interconnect bumps on a semiconductor wafer. [Figure 7C] 1A-1D are schematic diagrams, in cross section, illustrating process steps for forming shaped interconnect bumps on a semiconductor wafer. [Figure 7D] 1A-1D are schematic diagrams, in cross section, illustrating process steps for forming shaped interconnect bumps on a semiconductor wafer. [Figure 7E] 1A-1D are schematic diagrams, in cross section, illustrating process steps for forming shaped interconnect bumps on a semiconductor wafer. [Figure 7F]1A-1D are schematic diagrams, in cross section, illustrating process steps for forming shaped interconnect bumps on a semiconductor wafer. [Figure 7G] 1A-1D are schematic diagrams, in cross section, illustrating process steps for forming shaped interconnect bumps on a semiconductor wafer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Some semiconductor packages are configured so that the semiconductor die is attached directly to a leadframe via a number of interconnect bumps (sometimes referred to as posts or pillars). This type of packaging may provide improved electrical and thermal performance over other types of leaded packages that use wirebonding. Additionally, by eliminating the wirebonds connecting the semiconductor die to the leadframe, package parasitics may be reduced.

[0017] However, semiconductor dies generally have smaller interconnect bumps or available surface area for connecting to the bumps compared to lead frames. Also, with the increasing popularity and functionality of electronic devices, it is desirable to further reduce the dimensions of semiconductor dies. As a result, as semiconductor dies shrink, the surface area available for interconnect bump connections also decreases. The surface area available on a semiconductor die for interconnect bumps may no longer be a limiting factor in some circumstances.

[0018] Typically, the interconnect bumps have a uniform cylindrical shape. For example, the diameter of the interconnect bump is uniform between the die side and the leadframe side of the interconnect bump. Therefore, the contact surface area of ​​the interconnect bump on its die-attached side is the same as its contact surface area on its leadframe-attached side. Reducing the diameter of the interconnect bump reduces the contact surface area of ​​the interconnect bump on the leadframe as well as the semiconductor die.

[0019] A reduction in the contact surface area of ​​the interconnect bumps on the leadframe tends to increase the power and current density at the joint between the interconnect bumps and the leadframe. Increased power and current density can result in higher temperatures and premature failure due to electromigration at the joint between the interconnect bumps and the leadframe. The solder material used to attach the interconnect bumps to the leadframe can further contribute to electromigration problems due to the properties of the solder material used in attaching the interconnect bumps to the leadframe.

[0020] Smaller packages, such as WCSP and QFN, may have more limited electromigration due to their smaller dimensions, i.e., the power and current density at the junction between the interconnect bump and the lead frame may be greater due to the smaller dimensions of the smaller packages.

[0021] The interconnect bumps and methods herein address at least some of the above limitations. In one arrangement, the interconnect bumps herein have a narrower first end (e.g., smaller diameter) on the die end and a wider first end (e.g., larger diameter) at the leadframe. The interconnect bumps reduce the size of the bump on the die side and increase the area on the solder or leadframe side.

[0022] 1-2B, a semiconductor package 100 is presented. Semiconductor package 100 includes a leadframe 102, a semiconductor die 104 (which may be singulated or still be part of a semiconductor wafer), and a number of interconnect bumps 106 or bumps that electrically couple semiconductor die 104 to leadframe 102. Portions of die 104 and molding compound 114 have been removed in FIG. 1 to better show bumps 106.

[0023] In some embodiments, the leadframe 102 is formed of metal. The plurality of bumps 106 include a first end 108 or die end that is connected to the semiconductor die 104 and an opposing second end 110 or leadframe end that is connected to the leadframe 102. The bumps 106 are coupled at one end to a plurality of copper on anything (COA) elements 105.

[0024] Although some other bumps may be present, the bumps 106 have an angled shape such that the second ends 110 of the bumps 106 are larger than the first ends 108 of the bumps 106. The bumps 106 are not cylindrical members. Thus, the transverse cross section or end at the first ends 108 is smaller than the transverse cross section or end at the second ends 112. Shaping the bumps 106 such that the second ends 110 of the bumps 106 are larger than the first ends 108 of the bumps 106 allows the second ends 110 to utilize a larger end surface area available on the lead frame 102 while keeping the first ends 108 small enough to fit on the semiconductor die 104. Increasing the dimensions of the second ends 110 of the bumps 106 can help reduce the current and power density flowing between the second ends 110 of the bumps 106 and the lead frame 102. Aspects of the plurality of bumps 106 are described in more detail below.

[0025] The semiconductor package 100 further includes a solder material 112, such as SnAg, disposed between the plurality of bumps 106 and the lead frame 102. The solder material 112 is used to attach the second ends 110 of the plurality of bumps 106 to the lead frame 102. In some embodiments, the solder material 112 may be formed of a tin-silver (SnAg) alloy. Other types of solders may also be used. In some embodiments, the solder material 112 may have a height H1 (FIG. 2B) of about 20-30 μm.

[0026] A solder bump interface 126 is formed between the second ends 110 of the plurality of bumps 106 and the solder material 116. The solder bump interface 126 may suffer from electromigration problems, including void propagation. An increase in current density may contribute to the destruction of the solder bump interface 126, which may cause reliability problems and may prevent some types of active circuitry in the semiconductor die 104 from being placed in close proximity to the plurality of bumps 106. By increasing the dimensions of the second ends 110 of the plurality of bumps 106, the current density through the solder bump interface 126 may be reduced, thereby increasing the life of the solder bump interface 126. Similarly, increasing the dimensions of the second ends 110 of the plurality of bumps 106 may increase the efficiency of current exchange, which may result in a decrease in heat output at the solder bump interface 126.

[0027] In some embodiments, the semiconductor package 100 further includes a molding compound 114 (FIGS. 2A and 2B) to protect the components of the semiconductor package 100. The molding compound 114 can provide structural support to the semiconductor package 100 and can cover at least a portion of the lead frame 102, the semiconductor die 104, the bumps 106, or any combination thereof. In some embodiments, the molding compound 114 can also fill gaps between the components of the semiconductor package 100, such as between the bumps 106. Additionally, in some embodiments, the molding compound 114 is an epoxy, polymer, or other insulating material.

[0028] 1-2B, the plurality of interconnect bumps 106 extend between the semiconductor die 104 on a first end and the lead frame 102 on a second end along a longitudinal axis 116 (FIGS. 2A and 2B) or centerline. The plurality of interconnect bumps 106 are also referred to as pillars or bumps. Each of the plurality of interconnect bumps 106 has an angled shape on a sidewall in the direction of the longitudinal axis 116. A first end 108 of each of the plurality of interconnect bumps 106 has a width or diameter D1 that is smaller than a width or diameter D2 of a second end 110. The first end 108 of each of the plurality of interconnect bumps 106 also has an end surface area A1 that is smaller than an end surface area A2 of the second end 110 of the plurality of interconnect bumps 106. In other words, the first end 108 of the plurality of interconnect bumps 106 is smaller than the second end 110 of the plurality of interconnect bumps 106. In one example, A1 is at least 10 percent smaller than A2. In one example, A2 is at least twice as large as A1.

[0029] In some embodiments, each of the plurality of interconnect bumps 106 is tapered from the second end 110 to the first end 108 such that each of the plurality of interconnect bumps 106 decreases in dimension from the second end 110 to the first end 108. In some embodiments, the end surface area A2 of the second end 110 may be one to up to three times larger than the dimension of the end surface area A1 of the first end 108. Further, in some embodiments, the end surface area A2 of the second end 110 may be approximately twice the dimension of the end surface area A1 of the first end 108. The ratio between the end surface area A2 of the second end 110 and the end surface area A1 of the first end 108 may be modified based on the available surface area on the semiconductor die 104 and the leadframe 102 for interconnect bump connection.

[0030] 1-2B show the second ends 110 of the plurality of interconnect bumps 106 being larger than the first ends 108 of the plurality of interconnect bumps 106, in some instances it may be beneficial for the second ends 110 of the plurality of interconnect bumps 106 to be smaller than the first ends 108 of the plurality of interconnect bumps 106. Thus, in some embodiments, the surface area A2 of the second ends 110 of the plurality of interconnect bumps 106 may be less than 1 times the dimension of the surface area A1 of the first ends 108. Additionally, in some embodiments, the surface area A2 of the second ends 110 of the plurality of interconnect bumps 106 may be approximately 0.75 times the dimension of the surface area A1 of the first ends 108.

[0031] In some embodiments, the plurality of interconnect bumps 106 have a circular cross-sectional shape or other curvilinear shape transverse to or perpendicular to the longitudinal axis 116 to have a truncated cone or frustum shape along the longitudinal axis 116. Additionally, in some embodiments, the plurality of interconnect bumps 106 have an oval cross-sectional shape transverse to or transverse to the longitudinal axis 116 to have an angled shape along the longitudinal axis 116. The plurality of interconnect bumps 106 can have several angled shapes along the longitudinal axis 116 so long as the surface area A2 of the second end 110 is different from the surface area A1 of the first end 108.

[0032] In some embodiments, the plurality of interconnect bumps 106 have sidewalls with a slope θ of about 70 degrees or less relative to the surface 117 of the semiconductor die 104. In one arrangement, the slope θ is between 45° and 90°. The plurality of interconnect bumps 106 have a height H2 ( FIG. 2B ), or longitudinal dimension. In some embodiments, the height H2 of the plurality of interconnect bumps 106 is between about 35 and 75 μm. In some embodiments, the height H2 of the plurality of interconnect bumps 106 is about 50 μm. The plurality of interconnect bumps 106 are formed of a conductive material. In some embodiments, the plurality of interconnect bumps 106 are formed of copper (Cu) or a copper alloy.

[0033] The angle θ may be selected to achieve a desired end surface area relationship. In one exemplary arrangement, the end surface area A2 is desirably twice the end surface area A1. Assuming the bump is circular in lateral cross section, has a height of h along the centerline 116, has a lateral width or diameter of b at a first end, and a diameter at a second end given by b+2a, the following may be used to find the angle θ: Tan(90-θ)=a / h Tan(θ)=h / a a=h / Tan(θ) Again, assuming a circular cross section, we double the area, giving: b+2a=(2) 1 / 2 ×b b + 2(h / Tan(θ)) = (2) 1 / 2 ×b h / Tan(θ)=1 / 2b((2) 1 / 2 -1) = 0.2071 × b Tan(θ)=h / (0.2071×b) θ=aTan(h / 0.2071b) Thus, if h=50 microns and b=100 microns, then θ is 67° and a=20.7 microns.

[0034] Still referring primarily to FIGS. 1-2B , in some embodiments, the plurality of interconnect bumps 106 may include a plurality of power bumps 122 and a plurality of signal bumps 124. The plurality of power bumps 122 are configured to carry at least a majority of the power transmission between the semiconductor die 104 and the leadframe 102. The plurality of signal bumps 124 are configured to transmit electrical signals between the semiconductor die 104 and the leadframe 102. In some embodiments, the plurality of power bumps 122 are larger in terms of average cross-sectional area (lateral cross-section) than the plurality of signal bumps 124. The plurality of power bumps 122 may be larger than the plurality of signal bumps 124 because the current exchanged through the plurality of power bumps 122 tends to be larger than the current exchanged through the plurality of signal bumps 124.

[0035] In some aspects, at least a portion of the plurality of power bumps 122 are tapered or otherwise have an angled shape in longitudinal cross section. Additionally, in some aspects, at least some of the plurality of power bumps 122 and at least some of the plurality of signal bumps 124 are tapered or otherwise have an angled shape. The plurality of signal bumps 124 and the power bumps 122 are formed as described above.

[0036] Referring primarily to Figures 3A and 3B, an interconnect bump 206 is presented according to some embodiments. The interconnect bump 206 can be one of the interconnect bumps 106 of Figure 1. Figure 3A is a schematic end view (second end with reference to Figure 1) of the interconnect bump 206, with a first end of the interconnect bump 206 shown through hidden lines. Figure 3B is a schematic perspective view of the interconnect bump 206 of Figure 3A. In some embodiments, the interconnect bump 206 may be referred to as having a truncated cone shape or a truncated cone or a truncated cone shape. The interconnect bump 206 has a circular cross-sectional shape, i.e., transverse cross-section, transverse to the longitudinal axis 216 (or centerline), although other shapes (e.g., elliptical, square, polygonal, etc.) may also be used. In some arrangements, the transverse cross-section is curvilinear.

[0037] The interconnect bump 206 has a first end 208 and an opposite second end 210. The first end 208 of the interconnect bump 206 is for attachment to a semiconductor die, such as the semiconductor die 104 shown in FIG. 1. The second end 210 of the interconnect bump 206 is for attachment to a lead frame, such as the lead frame 102 shown in FIG. 1, or other conductive material. The interconnect bump 206 has a tapered shape that is best seen in longitudinal cross section, such that the interconnect bump 206 decreases in dimension from the second end 210 to the first end 208. As best seen in FIG. 3B, the first end 208 of the interconnect bump 206 has a diameter D1 that is smaller than the diameter D2 of the second end 210 of the interconnect bump 206. The first end 208 of the interconnect bump 206 also has a second surface area A2 (π×(D2 / 2) 2 ) smaller than the first end surface area A1(π×(D1 / 2) 2 ) Both the first end 208 and the second end 210 of the interconnect bump 206 have a circular cross-sectional shape in one arrangement.

[0038] Referring primarily to FIG. 4, a schematic diagram of a second end of an interconnect bump 306 is shown, in which a first end (narrower end) of the interconnect bump 306 is shown via hidden lines, according to some embodiments. The interconnect bump 306 differs from the interconnect bump 206 of FIGS. 3A-3B in that the interconnect bump 306 has an oval cross-sectional shape that is transverse or perpendicular to a longitudinal axis (similar to axes 116, 216) that extends into the page. The interconnect bump 306 has a first end 308 and an opposite second end 310. The first end 308 of the interconnect bump 306 is for attachment to a semiconductor die, such as the semiconductor die 104 shown in FIG. 1. The second end 310 of the interconnect bump 306 is for attachment to a lead frame, such as the lead frame 102 shown in FIG. 1.

[0039] The interconnect bump 306 has a tapered shape along its longitudinal dimension such that the interconnect bump 306 decreases in dimension from the second end 310 to the first end 308. The first end 308 of the interconnect bump 306 has a width (longer dimension in a transverse cross-section) Dl that is smaller than the width (longer dimension in a transverse cross-section) of the second end 310 of the interconnect bump 306. The first end 308 of the interconnect bump 306 also has a first surface area A1 that is smaller than the second surface area A2 of the second end 310 of the interconnect bump 306. In one example, A1 is less than 10% of A2. In one arrangement, A2 is at least twice as large as A1. While FIG. 4 shows an oval transverse cross-section, it is understood that other cross-sectional shapes may be used, such as, for example, curvilinear, circular, polygonal, square, circular, oval, rectangular, and polygonal with rounded corners.

[0040] Referring primarily to FIG. 5, a schematic plan view of a portion of a semiconductor package 400 according to an exemplary arrangement is shown. The semiconductor package 400 includes a lead frame 402 connected to a semiconductor die 404 via a plurality of shaped angled interconnect bumps 406. The semiconductor package 400 provides an example of how interconnect bumps, such as the plurality of shaped angled interconnect bumps 406 shown herein, may be configured based on the dimensions or arrangement of components within the semiconductor package 400, such as the semiconductor die 404 and the lead frame 402. The semiconductor die 404 may be, for example, a 250-100 nanometer process. The semiconductor die 404 has a landing site 450 for connection to the interconnect bumps 406. In some embodiments, the landing site 450 on the semiconductor die 404 may have a width or diameter of about 25-400 microns. The lead frame 402 may have a landing site 452 or element having a cross-sectional width W1 of about 35-600 microns, for example.

[0041] A first end 408 of the interconnect bump 406 is connected to the semiconductor die 404, and a second end 410 of the interconnect bump 406 is connected to the lead frame 402. The first end 408 has a surface area A1 with a length L1, and the second end 410 has a surface area A2 and a length L2. The surface area A1 and width W1 of the first end 408 of the interconnect bump 406 are typically limited, at least in part, by the dimensions of a landing site 450 on the semiconductor die 404. The landing site 450 is an area on the die for receiving at least a portion of the interconnect bump 406. However, the landing site 452 on the lead frame 402 is typically larger than the landing site 450 on the semiconductor die 404 and therefore may accommodate a larger interconnect bump or a portion of the interconnect bump 406. As such, the plurality of interconnect bumps 406 are shaped such that the surface area A2 and width W2 of the second end 410 connected to the lead frame 402 is greater than the surface area A1 and width W1 of the first end 408 connected to the semiconductor die 404. In this manner, the plurality of interconnect bumps 406 can utilize the greater available surface area on the lead frame 402. The shape of the plurality of shaped angled interconnect bumps 406, e.g., the dimensions of the first end 408 and second end 410 of the plurality of interconnect bumps 406, can be modified based on the available dimensions of the landing site 450 on the semiconductor die 404 and the landing site 452 on the lead frame 402. The plurality of shaped interconnect bumps 406 are angled or otherwise non-uniform such that the end configured to be connected to the semiconductor die 404 (first end 408) has a smaller surface area than the end configured to be connected to the lead frame 402 (second end 410).

[0042] Referring primarily to FIG. 6, a schematic diagram of a portion of a semiconductor package 500 according to an exemplary arrangement is presented. The semiconductor package 500 includes a lead frame 502 connected to a semiconductor die 504 via a plurality of shaped angled interconnect bumps 506. The semiconductor package 500 is similar to the semiconductor package 400 illustrated in FIG. 5, except that the semiconductor die 504 is smaller than the semiconductor die 404 illustrated in FIG. 5 and, as a result, has a smaller landing site 550. The plurality of shaped angled interconnect bumps 506 are configured at least in part based on the dimensions of the landing site 550 on the semiconductor die 504. The semiconductor die 504 can be, for example, a process-produced die that is less than 100 nanometers. In some embodiments, the landing site 550 on the semiconductor die 504 can have a width of about 0.3×0.3 mm to 10×10 mm. In some embodiments, the landing site 552 on the leadframe 502 has a width W1 that can be similar to or the same as the width W1 of the landing site 452 on the leadframe 402 of Figure 5. As such, the landing site 552 on the leadframe 502 can be the same dimensions as the landing site 452 on the leadframe 402 of Figure 5. The shape of the plurality of shaped angled interconnect bumps 506, e.g., the dimensions of the first ends 508 (die side) and second ends 510 (leadframe side) of the plurality of interconnect bumps 506, can be modified based on the available dimensions of the landing site 550 on the semiconductor die 504 and the landing site 552 on the leadframe 502.

[0043] Referring primarily to FIGS. 7A-7G, schematic diagrams depicting process steps for forming a portion of a semiconductor package 600 (similar in most respects to semiconductor packages 100, 400, 500) are presented. Referring first to FIGS. 7A-7B, a seed layer 640 (FIG. 7B) is disposed on a semiconductor wafer 604, or what will become a die after singulation, via a suitable formation process. The wafer 604 has a number of copper on anything (COA) elements 605. In some embodiments, the seed layer 640 may be disposed on the semiconductor die 604 or wafer by chemical vapor deposition (CVD) or sputter deposition. In some arrangements, the seed layer 640 may include titanium (Ti) and titanium tungsten (TiW).

[0044] 7C, photoresist 642 is deposited on seed layer 640 overlying COA 605. A mask (not explicitly shown) is placed on photoresist 642 according to the photoresist pattern. The photoresist pattern identifies the locations of sites for interconnect bumps.

[0045] Comparing Figures 5 and 6, it should be understood that the taper of bumps 406, 506 can be used to keep the lead frame 402 the same dimensions but reduce the edge surface area on the first side (Figure 5) to then use a smaller area on the wafer / die 504, or bumps 406 can be used to keep the edge surface area the same at a first end on the die / wafer (Figure 6) but increase the edge surface area at a second end, or some combination thereof.

[0046] Referring primarily to FIG. 7D , the photoresist 642 is exposed to light to form a plurality of openings 644 in the photoresist 642 according to a photoresist pattern. The plurality of openings 644 extend all the way to the seed layer 640. Each of the plurality of openings 644 is defined by a sloped sidewall 646. In some embodiments, the sidewall 646 is sloped at an angle α (θ=180−α in FIG. 2B ) of about 110 degrees or more. The sloped sidewall 646 may be achieved by overexposing the photoresist 642. In some embodiments, the angle α of the sidewall 646 may vary based on the amount of light exposure to the photoresist 642. The angle α of the sidewall 646 may be altered based on the desired size or shape of the plurality of interconnect bumps 606.

[0047] Each of the plurality of openings has a width W3 ( FIG. 7D ) along a lowest (relative to the illustrated orientation) portion of the opening 644 proximate the seed layer 640. The width W3 of the plurality of openings 644 corresponds to a width W1 ( FIG. 7E ) of a first end 608 of the plurality of interconnect bumps 606. In some embodiments, some of the plurality of openings 644 have different dimensions than others of the plurality of openings 644. For example, the width along the lowest portion of the opening 644 may be different for a signal bump opening than for a power bump opening.

[0048] Referring primarily to Figure 7E, metal is deposited in the plurality of openings 644. The metal may be deposited as copper and solder plate bumps. The photoresist is then stripped, resulting in the stage shown in Figure 7G.

[0049] 7G, a plurality of interconnect bumps 606 are formed on a seed layer 640 on the wafer in each of a plurality of openings 644. The plurality of interconnect bumps 606 take the shape of the plurality of openings 644 as defined at least in part by sloped or angled sidewalls 646 and width W3 (FIG. 7D) along a lowest portion of the plurality of openings 644.

[0050] The plurality of interconnect bumps 606 may be formed by a process such as plating. The material used to form the plurality of interconnect bumps 606 may be plated to a desired height. In one example, the height H2 (FIG. 7E) of the plurality of bumps 606 is about 35-75 μm. In some embodiments, the plurality of interconnect bumps 606 are formed of copper. In some embodiments, a solder material 612 is disposed on the second ends 110 of the plurality of interconnect bumps 106 before the photoresist 142 is removed. In some embodiments, the height H1 (FIG. 7E) of the solder material 112 may be about 20-30 μm.

[0051] After the interconnect bumps 606 are formed in the openings 644, the photoresist 642 is removed or stripped by a suitable removal process, such as ashing. Also, after removing the photoresist 642, the portions of the seed layer 640 that are not directly under the interconnect bumps 606 may be removed by a suitable removal process, such as etching.

[0052] 7G, the semiconductor die 604 may then be attached to the leadframe 602 by soldering a solder material 612 to the leadframe 602. In some embodiments, the solder material 612 is disposed on the second ends 610 of the plurality of interconnect bumps 606 after the photoresist 642 is removed from the semiconductor die 604. The process of attaching the semiconductor die 604 to the leadframe 602 may be referred to as flipping the semiconductor die 604.

[0053] There are many possible advantages to having shaped bumps as described herein. Shaped or non-cylindrical bumps provide a smaller landing area on the wafer / die side and a larger area on the leadframe side. This allows for more interconnects on the wafer / die while also allowing for larger connections on the leadframe to gain efficiency. An optional polyamide (PI) or metal layer (usually copper) on the top of the die after the final fab process step ("METTOP") can also be used between the bump and the wafer. Solder interface can be reduced and current ratings can be increased. No additional masks are required. Overall package size can be reduced. These are just some of the possible advantages.

[0054] Modifications may be made to the exemplary embodiments described, and other embodiments are possible, within the scope of the invention.

Claims

1. 1. A semiconductor package comprising: a lead frame including a plurality of first landing sites and a plurality of second landing sites, the first landing sites being larger than the second landing sites; a semiconductor die including a plurality of linearly arranged first landing sites and a plurality of linearly arranged second landing sites, the first landing sites being larger than the second landing sites; A plurality of power bumps configured to transmit a power signal, each of the plurality of power bumps comprising: a first end connected to a first landing site of the semiconductor die, the first end having an end surface area A1 corresponding to the first landing site of the semiconductor die; an opposite second end connected to the first landing site of the lead frame, the second end having an end surface area A2 corresponding to the first landing site of the lead frame and greater than the end surface area A1; the plurality of power bumps including: A plurality of signal bumps configured to transmit electrical signals, each of the plurality of signal bumps comprising: a first end connected to a second landing site of the semiconductor die, the first end having an end surface area A3 corresponding to the second landing site of the semiconductor die; an opposite second end connected to a second landing site of the lead frame, the second end having an end surface area A4 corresponding to the second landing site of the lead frame and greater than the end surface area A3; the plurality of signal bumps including:

2. A semiconductor package comprising:

2. 2. The semiconductor package of claim 1, A semiconductor package, wherein an end surface area A2 of the second end of the power bump is at least 10 percent greater than an end surface area A1 of the first end of the power bump.

3. 2. The semiconductor package of claim 1, A package, wherein an end surface area A2 of the second end of the power bump is at least twice an end surface area A1 of the first end of the power bump.

4. 2. The semiconductor package of claim 1, a semiconductor package, wherein each of the plurality of power bumps is shaped as a truncated cone, a larger end of the truncated cone defining A2 and a narrower end of the truncated cone defining A1.

5. 2. The semiconductor package of claim 1, The package, wherein each of the plurality of power bumps has an oval or circular cross section taken perpendicular to a line extending from the first end to the second end.

6. 2. The semiconductor package of claim 1, A semiconductor package, wherein the lead frame is made of metal, and the plurality of power bumps and the plurality of signal bumps are composed of copper.

7. 2. The semiconductor package of claim 1, a solder material associated with each of the plurality of power bumps and the plurality of signal bumps, the solder material being disposed between a second end of the bump and the lead frame to attach the second end of the bump to the package.

8. 2. The semiconductor package of claim 1, The semiconductor package further includes a molding compound at least partially covering the leadframe, the semiconductor die, the plurality of power bumps, and the plurality of signal bumps.

9. 1. A semiconductor package comprising: a lead frame including a first lead and a second lead, the first and second leads being linear and arranged in parallel; a semiconductor die attached to the leadframe; a plurality of bumps including power bumps configured to transmit a power signal and signal bumps configured to transmit an electrical signal, the power bumps electrically connecting the semiconductor die to a first lead of the lead frame and the signal bumps electrically connecting the semiconductor die to a second lead of the lead frame, each of the bumps having a longitudinal length extending from a first end to an opposite second end; Including, the first end is connected to the semiconductor die and the second end is connected to the lead frame; the first end has a lateral width W1 perpendicular to the longitudinal length that is less than a lateral width W2 of the second end.

10. 10. The semiconductor package of claim 9, Each of the plurality of bumps is tapered between the first end and the second end.

11. 10. The semiconductor package of claim 9, 11. A semiconductor package, comprising: said first end having an end surface area A1; said second end having an end surface area A2; said end surface area A1 being at least half the dimension of said end surface area A2.

12. 10. The semiconductor package of claim 9, A semiconductor package, wherein each of the plurality of bump cross sections taken perpendicular to a line extending from the first end to the second end is oval or circular.

13. 10. The semiconductor package of claim 9, A semiconductor package, wherein the signal bumps have an average lateral width that is less than an average lateral width of the power bumps.

14. 14. The semiconductor package of claim 13, a solder material disposed between second ends of the plurality of bumps and the lead frame; a molding compound at least partially covering the first and second leads of the leadframe, the semiconductor die, and the plurality of bumps; The semiconductor package further comprises:

15. 10. The semiconductor package of claim 9, The semiconductor package, wherein the lead frame is made of metal.

16. 1. A method for forming a plurality of tapered bumps on a die for attaching the die to a lead frame in a semiconductor package, comprising: depositing a seed material on the wafer; depositing a photoresist over the seed material; masking the photoresist according to a pattern comprising bump sites; overexposing the masked photoresist to form a plurality of tapered sites therein, each tapered site having a first end closest to the wafer and a second end furthest from the wafer; disposing one or more metals at the plurality of tapered sites; removing the photoresist to form a plurality of tapered bumps, each tapered bump of the plurality of tapered bumps having a first surface area A1 at a first end closest to the wafer and a second end surface area A2 at a second end furthest from the wafer, a first end of the tapered bump abutting the wafer and the first surface area A1 being less than the second surface area A2; Singulating the wafer into a plurality of dies; Including, the plurality of tapered bumps including a plurality of power bumps configured to transmit power signals and a plurality of signal bumps configured to transmit electrical signals; the plurality of power bumps are arranged in a linear fashion, and the plurality of signal bumps are arranged in a linear fashion; The method, wherein the plurality of power bumps and the plurality of signal bumps are arranged in parallel.

17. 17. The method of claim 16, wherein the second end surface area A2 is 10 percent greater than the first surface area A1.

18. 17. The method of claim 16, The method, wherein the second surface area A2 is at least twice the first surface area A1.

19. 17. The method of claim 16, wherein each of the plurality of tapered sites is formed with a sidewall slope of about 70 degrees or less relative to a surface of the die that faces the leadframe.

20. 17. The method of claim 16, The method, wherein each of the plurality of tapered bumps has a transverse cross-section having a curvilinear shape.

21. 21. The method of claim 20, The method, wherein each of the plurality of tapered bumps has a transverse cross-section that is circular or oval shaped.

22. 1. A method of electrically coupling a semiconductor die to a leadframe, comprising the steps of: forming a plurality of tapered bumps, including power bumps and signal bumps, on the semiconductor die, each of the plurality of tapered bumps having a first end surface area A1 at a first end closest to the semiconductor die and a second end surface area A2 at an opposing second end, the first end surface area A1 being smaller than the second end surface area A2, the first ends being attached to the semiconductor die; soldering second ends of the power bumps to first leads of the lead frame and soldering second ends of the signal bumps to second leads of the lead frame, the first and second leads being linear and arranged parallel; Including, The method, wherein the power bump is configured to carry a power signal and the signal bump is configured to carry an electrical signal.

23. 23. The method of claim 22, The method of claim 1, wherein the second end surface area A2 is at least twice the first end surface area A1.

24. 23. The method of claim 22, The method, wherein the plurality of tapered bumps have a sidewall slope of about 70 degrees or less relative to a centerline of the tapered bump.

25. 23. The method of claim 22, wherein each of the plurality of tapered bumps has an oval shape in a transverse cross section perpendicular to a centerline of the tapered bump.

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