TW201403762A - Bottom source and assembly method - Google Patents

Abstract

This invention is aims to providing a bottom source power semiconductor device and the fabricating method thereof. Drop ball or bump on source and gate on wafer frontside, and mold the wafer frontside with compound, and grind wafer frontside to expose the ball or bump as desired. Then grind wafer backside to thin, and saw the molded wafer to individual die. Design leadframe with grooves on both side leads for clip alignment and position, flip die and mount to the leadframe first and then mount clip with bridge structure to the drain of die. Mold the leadframe mounted die and clip.

Description

Bottom source power device and preparation method

The present invention generally relates to a semiconductor power device and a method of fabricating the same, and more particularly to a power device having a bottom source and a method of fabricating the same.

We all know that the power consumption of power devices is very large in general. In applications similar to DC-DC power devices, based on the consideration of improving the electrical performance and heat dissipation performance of the device, it is usually a part of the metal electrode of the device. The plastic-clad material covering the wafer is exposed to the outside in order to obtain the best heat dissipation effect. A semiconductor package structure 24 in which a wafer bottom electrode is exposed and used to support surface mount technology is shown, for example, in US Patent Application No. 2003/0132531 A1. As shown in Fig. 1, a power chip is disposed in the recess of the metal can structure 12. The MOSFET 10, the drain of the MOSFET 10 side is pasted to the bottom of the recess of the can-like structure 12 by the conductive silver paste 14, so that its drain is conducted to the raised edge 22 of the can-like structure 12, and the MOSFET 10 is additionally The source contact end 18 and the gate contact end on one side are just on the same side as the raised edge 22. A low stress and high adhesion ability conductive material 16 is also filled in the void around the MOSFET 10 in the recess of the metal can structure 12. Although the package structure 24 solves the heat dissipation problem to a certain extent, it is costly to produce an object such as the metal can-like structure 12 in actual production. On the other hand, the positions of the source contact end 18 and the gate contact end are fixed, for example, the gate contact end thereof cannot be adjusted to be in the same column as the bump edge 22, so that it is difficult to fit the pad layout on the PCB. This, undoubtedly inhibits the scope of application of the package structure 24.
In addition, the substrate resistance of the wafer applied in the power device is generally large, which causes the on-state resistance RDson of the device to also increase, so how to properly reduce the substrate resistance of the wafer is a problem that needs to be solved. In the current technology, Wafer Level Wafer Size Package (WLCSP) is an alternative method. After the entire wafer is produced, the package test is performed directly on the wafer and the ball is implanted. Wafer dicing produces a single IC that is almost identical in size to the original die. Considering the advantages of miniaturization and thinning of wafers prepared by wafer-level packaging, how to use wafer-level packaging technology to provide ultra-thin wafers and apply them in power devices is still one of the problems we face.

The invention provides a bottom source power device, comprising:
a metal base unit, the metal base unit includes a first base and a second base separated from each other, and third and fourth bases respectively disposed on two sides of the first base;
a first package structure disposed on the first and second pedestals, and a plurality of solder bumps disposed on the front surface of the primary package structure are respectively soldered on the first and second pedestals;
a bridge metal piece disposed above the primary package structure, the bridge metal piece comprising a top metal piece and a side metal piece attached to both sides of the top metal piece and bent downward;
Wherein the side metal sheets on both sides of the top metal piece extend into the recesses disposed at the top of the third base and the recesses disposed at the top of the fourth base, and are located on the back of the primary package structure a bottom metal layer is soldered to the bottom surface of the top metal sheet by a conductive material;
A molded body in which the metal base unit, the primary package structure, and the bridge metal piece are covered, wherein the bottom surfaces of the first, third, and fourth bases are exposed from the bottom surface of the molded body.
In the above-mentioned bottom source power device, the primary package structure includes a wafer and a top molding layer covering the front surface of the wafer, and the plurality of solder bumps are respectively soldered to the plurality of metal pads disposed on the front surface of the wafer; And the top plastic encapsulation layer is wrapped around the sidewall of the solder bump such that any one of the solder bumps is exposed from the top mold layer; and the bottom metal layer is disposed on the wafer back.
In the above-described bottom source power device, the second pedestal is located between the third pedestal and the fourth pedestal or between an extension of the third pedestal and an extension of the fourth pedestal .
In the above-mentioned bottom source power device, the primary package structure includes a wafer, and the plurality of solder bumps are respectively soldered to a plurality of metal pads disposed on the front surface of the wafer, and at least one of the plurality of metal pads a metal pad constituting a first electrode of the wafer and a metal pad constituting a second electrode of the wafer;
Wherein the solder bumps connected to the metal pads constituting the first electrode are soldered on the top surface of the first pedestal, and the solder bumps connected to the metal pads constituting the second electrode are soldered to the second pedestal On the top.
In the power device of the bottom source described above, the bottom surface of the second base is exposed from the bottom surface of the molding body.
In the above-mentioned bottom source power device, the second pedestal comprises an extension structure having a thickness smaller than the thickness of the first pedestal and being covered in the molding body, and an external pin connected to the extension structure. The external pin is located on an extension line of the fourth base along the longitudinal direction;
Wherein, the extension structure extends laterally below the primary package structure until it overlaps a portion of the solder bumps disposed on the front side of the primary package structure in a vertical direction.
In the above-mentioned bottom source power device, the primary package structure includes a wafer, and the plurality of solder bumps are respectively soldered to a plurality of metal pads disposed on the front surface of the wafer, and the plurality of metal pads include at least a metal pad constituting a first electrode of the wafer and a metal pad constituting a second electrode of the wafer;
Wherein the solder bumps connected to the metal pads constituting the first electrodes are soldered on the top surface of the first pedestal, and the solder bumps and the extension structures connected to the metal pads constituting the second electrodes are vertically oriented Overlap and weld on the extension structure.
In the above-mentioned bottom source power device, the bottom surface of the external lead is exposed from the bottom surface of the molding body.
The power device of the bottom source described above has a width in a longitudinal direction of the side metal piece contacting the fourth base, which is smaller than a width of the top metal piece in the longitudinal direction, so as to prevent the side metal piece contacting the fourth base from contacting the second base. seat.
The above-described bottom source power device is provided with one or more through holes penetrating the thickness of the top metal piece in the top metal piece.
The bottom source power device described above is provided with one or more trench structures recessed from the bottom surface of the top metal sheet into the top metal sheet in the top metal sheet.
The bottom source power device is provided on the bottom surface of the top metal piece with a plurality of pad structures protruding from the bottom surface of the top metal piece, the pad structure being located at the bottom metal layer and the top metal Between the bottom surfaces of the sheets.
The above-mentioned bottom source power device is formed with an elongated groove recessed downward from the top surface of the top metal piece at a corner joint of the side metal piece on both sides of the top metal piece.
In the above-mentioned bottom source power device, the bottom metal layer is disposed on the back surface of the wafer and constitutes a third electrode thereof, and the wafer is a MOSFET, the first electrode is a source, the second electrode is a gate, and the third The electrode is the drain.
In the above-described bottom source power device, the molding body covers the top surface of the top metal piece.
In the above-mentioned bottom source power device, the top surface of the top metal piece is exposed from the top surface of the molding body.
The invention also provides a method for preparing a bottom source power device, which mainly comprises the following steps:
Providing a metal base unit, the metal base unit includes a first base and a second base separated from each other, and third and fourth bases respectively disposed on two sides of the first base;
Mounting a primary package structure to the first and second pedestals, wherein a plurality of solder bumps disposed on the front surface of the primary package structure are respectively soldered on the first and second pedestals;
Mounting a bridge metal piece above the primary package structure, the bridge metal piece comprising a top metal piece and a side metal piece connected to both sides of the top metal piece and bent downward;
Wherein the side metal sheets on both sides of the top metal sheet respectively extend into the recesses disposed at the top of the third base and in the recesses disposed at the top of the fourth base, and are located on the back of the primary package structure a bottom metal layer is soldered to the bottom surface of the top metal sheet by a conductive material;
Forming a plastic package, coating the metal base unit, the primary package structure, and the bridge metal piece, and each of the bottom surfaces of the first, third, and fourth bases is exposed from the bottom surface of the mold body.
In the above method, the step of forming the primary package structure includes:
Providing a wafer including a plurality of wafers, and a plurality of metal pads are disposed on a front surface of any one of the wafers;
Soldering a plurality of solder bumps correspondingly on the plurality of metal pads;
The front surface of the wafer is covered with a plastic sealing layer, and the plastic sealing layer simultaneously covers the solder bump;
Grinding and thinning the plastic sealing layer until the solder bump is exposed in the plastic sealing layer;
Grinding on the back side of the wafer to reduce the thickness of the wafer;
Depositing a metal layer on the back side of the wafer;
The wafer and the plastic sealing layer and the metal layer are diced to form a plurality of primary package structures including the wafer.
In the above method, the plastic sealing layer is cut to cover the top plastic sealing layer on the front side of the wafer, and the top plastic sealing layer is wrapped around the sidewall of the solder bump, so that any one of the solder bumps is Exposed in the top molding layer; and the metal layer is cut into a bottom metal layer on the back side of the wafer.
In the above method, the second pedestal is disposed between the third pedestal and the fourth pedestal or between the extension line of the third pedestal and the extension line of the fourth pedestal.
In the above method, the primary package structure includes a wafer, and the plurality of solder bumps are respectively soldered to the plurality of metal pads disposed on the front surface of the wafer, and the plurality of metal pads respectively comprise at least the first wafer. a metal pad of the electrode and a metal pad constituting the second electrode of the wafer;
Therefore, when the primary package structure is flip-chip mounted on the first and second pedestals, the solder bumps connected to the metal pads constituting the first electrodes are soldered to the top surface of the first pedestal, Solder bumps attached to the metal pads constituting the second electrode are soldered to the top surface of the second pedestal.
In the above method, when the molded body is formed, the bottom surface of the second pedestal is exposed from the bottom surface of the formed molded body.
In the above method, the second pedestal comprises an extension structure and an external pin connected to the extension structure, the external pin being located on an extension line of the fourth pedestal in the longitudinal direction;
Wherein the extension structure extends laterally below the primary package structure until it overlaps a portion of the solder bumps disposed on the front surface of the primary package structure in a vertical direction; and the thickness of the extension structure is less than the thickness of the first pedestal, thereby The extension structure is coated in the molding body when the molding body is formed.
In the above method, the primary package structure includes a wafer, and the plurality of solder bumps are respectively soldered to the plurality of metal pads disposed on the front surface of the wafer, and the plurality of metal pads respectively comprise at least the first wafer. a metal pad of the electrode and a metal pad constituting the second electrode of the wafer;
The extension structure extends to overlap in a vertical direction with solder bumps connected to the metal pads constituting the second electrode, thereby flip-chip mounting the primary package structure onto the first and second pedestals Solder the solder bumps connected to the metal pads constituting the first electrode to the top surface of the first pedestal, and solder the solder bumps connected to the metal pads constituting the second electrode to the extension structure .
In the above method, when the molded body is formed, the bottom surface of the outer lead is exposed from the bottom surface of the molded body.
In the above method, the width of the side metal piece contacting the fourth pedestal in the longitudinal direction is smaller than the width of the top metal piece in the longitudinal direction to prevent the side metal piece contacting the fourth pedestal from contacting the second pedestal.
In the above method, one or more through holes penetrating the thickness of the top metal piece are formed in the top metal piece.
In the above method, one or more groove structures recessed from the bottom surface of the top metal piece into the top metal piece are formed in the top metal piece.
In the above method, a plurality of pad structures protruding from the bottom surface of the top metal piece are formed on the bottom surface of the top metal piece, and the pad structure is located at the bottom metal after the bridge metal piece is mounted on the primary package structure. Between the layer and the bottom surface of the top metal sheet.
In the above method, at the corner joints of the side metal sheets on both sides of the top metal piece, an elongated groove recessed downward from the top surface of the top metal piece is formed.
In the above method, the bottom metal layer is disposed on the back surface of the wafer to constitute a third electrode thereof, and the wafer is a MOSFET, the first electrode is a source, the second electrode is a gate, and the third electrode is a drain.
In the above method, when the molding body is formed by using a molding material, the molding body covers the top surface of the top metal sheet while the molding material is further filled in the through hole.
In the above-mentioned bottom source power device, when the molded body is formed, the molding body coats the top surface of the top metal piece.
In the above-mentioned bottom source power device, when the molding body is formed, the top surface of the top metal piece is exposed from the top surface of the molding body.
These and other advantages of the present invention will no doubt become apparent to those skilled in the <RTIgt;

2A and 2B are respectively a top plan view and a bottom view of the power device 100A shown in FIG. 2C, and FIG. 2C is a magnified AA along the dotted line AA of the power device 100A shown in FIG. 2B. In the cross-sectional view in the vertical direction, the 2D-1 map is a cross-sectional view along the broken line BB. The power device 100A includes a metal base unit including at least a first base 111 and a second base 112 and a third base 113 disposed around and separated from and separated therefrom. The fourth pedestal 114 (as in Figure 2B) has substantially the same thickness and is in the same plane. The first pedestal 111 is substantially a rectangular parallelepiped or a rectangular parallelepiped, and the third pedestal 113 and the fourth pedestal 114 disposed on opposite sides of the first pedestal 111 extend longitudinally along the two longitudinal edges of the first pedestal 111, respectively. The second pedestal 112 located near the first pedestal 111 may be disposed at any position between the third pedestal 113 and the fourth pedestal 114. In one embodiment, the third pedestal 113 and the fourth pedestal 114 are symmetrical to each other with respect to a longitudinal central axis of the first pedestal 111, and the second pedestal 112 is located at the third pedestal 113 and the fourth pedestal 114. Symmetrical line. If the length of the third pedestal 113 or the fourth pedestal 114 extending in the longitudinal direction (the direction perpendicular to the plane of the drawing in FIG. 2C) is not so long, the second pedestal 112 is not located at the third pedestal 113 and fourth. Between the pedestals 114, another unillustrated embodiment is that the second pedestal 112 can be disposed between the longitudinal extension of the third pedestal 113 and the extension of the fourth pedestal 114 in the longitudinal direction. Generally, a lead frame includes a plurality of such metal base units, and the respective independent base members included in the metal base unit are connected to the lead frame through unillustrated connecting ribs, for the sake of brevity, These well-known contents in the art are not described herein again. In the present application, the terms longitudinal and lateral fingers mean a direction that is substantially parallel and substantially perpendicular to the direction in which the third pedestal 113 and the fourth pedestal 114 extend, respectively, and the vertical direction refers to the first pedestal 111 and the second pedestal 112. The common plane of the third pedestal 113 and the fourth pedestal 114 is perpendicular to the direction.
Referring to Figures 2C and 2D-1, power device 100A also includes a primary package structure 130. It is worth noting that although the primary package structure 130 is not a bare wafer but a complete, independent package structure, it is also used for the second package, so we can call it a primary package. The primary package structure 130 is flip-chip mounted on the first pedestal 111 and the second pedestal 112, and is mainly disposed on the front surface of the primary package structure 130 by using a conductive adhesive material (such as conductive silver paste, solder, etc.). The solder bumps 132a-1, 132b-1 are respectively soldered to the second pedestal 112 and the first pedestal 111. As an option, as shown, the primary package structure 130 includes a wafer 131 and a top molding layer 134 covering the front surface of the wafer 131. The front surface of the wafer 131 is provided with a plurality of metal pads, solder bumps 132a-1, 132b-1 is soldered to these metal pads, respectively, as explained in the following sections. The top molding layer 134 does not completely cover the solder bumps 132a-1, 132b-1, but only wraps around their sidewalls, so that the solder bumps 132a-1, 132b-1 are both molded from the top. The layer 134 is exposed to the outside to perform soldering with the second pedestal 112 and the first pedestal 111. The bottom metal layer 133 on the back side of the primary package structure 130 is disposed on the back surface of the wafer 131.
The power device 100A further includes a bridge-shaped metal piece 150 mounted on the primary package structure 130. The bridge-shaped metal piece 150 is bonded to the third package 113 and the fourth base, in addition to being bonded to the primary package structure 130. Block 114. Wherein, the bridge metal piece 150 includes a top metal piece 151, and includes side metal pieces 153a, 153b connected to a pair of opposite sides of the top metal piece 150, and the side metal pieces 153a, 153b are downward. Bend to an oblique downward extension. The side metal pieces 153a, 153b may be considered to expand outward in a direction away from each other such that the side metal pieces 153a, 153b are bent to a position at an obtuse angle with the top metal piece 150. In one embodiment, the side metal sheets 153a, 153b are symmetrical to each other with respect to the longitudinal central axis of the top metal sheet 151. Correspondingly, the top of the third base 113 is provided with a strip-shaped recess 113a extending in the longitudinal direction, and the top of the fourth base 114 is provided with a strip-shaped recess 114a extending in the longitudinal direction so as to be The step of adhering the bottom surface of the top metal piece 151 to the bottom metal layer 133 by the conductive material 140 while extending the side metal piece 153a attached to one side of the top metal piece 151 to be located in the groove 113a and caught therein And extending the side metal piece 153b attached to the opposite side of the top metal piece 151 to be located in the groove 114a and caught therein. The grooves 113a, 114a have various configurations, such as grooves having a V-shaped cross section, etc., so as to be engaged with the side metal pieces 153a, 153b. The side metal pieces 153a, 153b may be bonded to the third base 113 and the fourth base 114 by corresponding conductive bonding materials (not labeled) provided in the grooves 113a, 114a, respectively.
In addition, the power device 100A further includes a molding body 160 that can mold the metal base unit, the primary package structure 130, and the bridge metal piece 150. In the embodiment shown in FIG. 2B, since the power device 100A is finally used for mounting on a PCB circuit board, the first pedestal 111, the second pedestal 112, the third pedestal 113, and the fourth pedestal 114 are As the contact ends for direct soldering to the pads on the PCB, it is necessary to expose their respective bottom surfaces from the bottom surface of the molding body 160. In addition, as shown in FIG. 2B, the third pedestal 113 generally has a plurality of pins 113' which are expanded in the lateral direction to increase the volume, and the fourth pedestal 114 has a plurality of laterally increased The large-volume portion is the pin 114', so in the third pedestal 113 and the fourth pedestal 114, only the bottom surface of the pins 113', 114' may be exposed from the bottom surface of the molding body 160 as a contact. end.
In the embodiment shown in FIGS. 2C to 2D-1, one or more through holes 152 are formed in the top metal piece 151 through the thickness of the entire top metal piece 151, which are vertically from the top metal piece. The bottom surface of 151 extends to the top surface. Fig. 2E shows the top view structure of the bridge metal piece 150, and also shows a typical structure of the through hole 152, which may have a "ten" shape in cross section, or a "meter" shape or a circle or rectangle which is not illustrated. , polygon or any other suitable shape. Generally, in the process of bonding the top metal piece 151 to the bottom metal layer 133 by using the conductive material 140, the inside of the conductive material 140 usually collects some undischarged gas to form a single void (Void), which affects the power. The reliability of device 100A. The purpose of providing the through holes 152 is, on the one hand, for unblocking the gas accumulated in the conductive material 140. In addition, it is considered that the thickness of the conductive material 140 coated over the bottom metal layer 133 is not completely uniform, which may cause the top metal piece 151 pasted onto the bottom metal layer 133 to be inclined, so that the entire bridge metal piece 150 is not expected to occur. Shift. The through hole 152 is provided to introduce a portion of the conductive material 140 between the top metal piece 151 and the bottom metal layer 133 into the through hole 152, so that the final thickness of the entire conductive material 140 has uniformity.
In another embodiment shown in FIG. 2D-2, the structure of the bridge metal piece 150 can be slightly modified on the basis of the above, unlike the through hole 152. This embodiment is mainly provided in the top metal piece 151. Or a plurality of trough structures 152' that do not extend through the thickness of the entire top metal sheet 151. Instead, the trough structure 152' is only recessed from the bottom surface of the top metal sheet 151 into the top metal sheet 151. . The shape of the trough structure 152' is also variously selected, for example, its cross-sectional shape may be similar to the through hole 152. The trough structure 152' can also accommodate the gas released from the interior of the electrically conductive material 140 or introduce an excess portion of the electrically conductive material 140 into the trough structure 152' to discharge the gas accumulated in the electrically conductive material 140 and enhance the electrically conductive material 140. The effect of thickness uniformity.
Another difference between the embodiment of FIG. 2D-1 and the embodiment of FIG. 2D-2 is that the top surface of the top metal piece 151 shown in FIG. 2D-1 cannot be exposed from the outside of the molded body 160, and the second DD The top surface of the top metal piece 151 shown in Fig. 2 can be exposed from the outside of the molded body 160. The reason is that to prepare the structure as shown in FIG. 2D-2, it is necessary to cover the top surface of the top metal piece 151 with an expanded flattening film (not shown) before forming the molding body 160, and A plastic sealing material such as an epoxy resin is injected under the adhesive film to form a plastic sealing body 160 covering the metal base unit, the primary packaging structure 130, and the bridge metal piece 150 under the bonding film, in the molding material. After curing, the adhesive film is peeled off from the top surface of the top metal piece 151 and the top surface of the molding body 160, so that the top surface of the top metal piece 151 is exposed from the top surface of the molding body 160. This molding process is typically done in a mold of a molding apparatus (e.g., wafer level molding is commonly used in this technique), which is well known to those skilled in the art, and therefore will not be described in detail herein. It is obvious that if the top surface of the top metal piece 151 shown in FIG. 2D-1 is covered with an adhesive film, then the molded body 160 is prepared under the adhesive film, and if the adhesive film is directly removed, then The portion of the conductive material 140 that is poured into the through hole 152 during the bonding process of the bridge metal piece 150 will be directly exposed to the air because no molding material is filled in the through hole 152 in the molding step, and the The portion of conductive material 140 is covered. This does not meet environmental maintenance requirements because the conductive material 140 used for soldering may be a solder paste containing toxic elements such as lead. Although it is possible to fill the through holes 152 with other substances in an additional step, this will undoubtedly increase the cost.
Further, another advantage of the present invention is shown in that, at the corner joint of the top metal piece 151 and the side metal pieces 153a, 153b, a strip shape which is recessed downward from the top surface of the top metal piece 151 is formed. The grooves 154a, 154b each extend in the longitudinal direction and are respectively parallel to the respective connecting sides of the top metal piece 151 and the side metal pieces 153a, 153b. A stepped structure is formed from the bottom of the elongated grooves 154a, 154b to the top surface of the top metal piece 151. The structure of the bridge metal piece 150 is described in Figs. 2C to 2E. A currently known method for preparing the side metal sheets 153a, 153b is to bend the side metal sheets 153a, 153b which are originally in the same plane as the top metal sheet 151 downward from the plane in which the top metal sheet 151 is located. The angle (e.g., by stamping) is such that the side metal pieces 153a, 153b are respectively bent along the connecting edges of the top metal piece 151 and the side metal pieces 153a, 153b to an obtuse angle with the angle of the top metal piece 151. For example, it is shown that it extends obliquely downward. In essence, if the patterned bridge metal piece 150 is directly prepared in this manner, a disadvantage is that the resulting top metal piece 151 is an arched structure with a certain curvature, at which time the top metal piece 151 is The top surface is a circular arc-shaped convex surface (the bottom surface of which corresponds to a circular arc-shaped concave surface) rather than the intended plane. Another undesirable consequence is that at the junction of the top metal sheet 151 and the side metal sheets 153a, 153b, the top edge of the top metal sheet 151 along the longitudinal edge line will appear jagged rather than a desired straight line, which would be disadvantageous for subsequent Packaging process. In contrast, in the step of bending the side metal pieces 153a, 153b downward, the elongated grooves 154a, 154b at the junction of the top metal piece 151 and the side metal pieces 153a, 153b can cushion the blocking side. The partial metal pieces 153a, 153b exert the tensile force on the top metal piece 151 in the pressing step to ensure that the obtained top metal piece 151 is not deformed, and at this time, the longitudinal edge line 151a-1 on both sides of the top surface of the top metal piece 151, 151a-2 is also presented as a straight line such that the top surface of the top metal piece 151 is a regular rectangle. After the above bending step, in the finally obtained bridge-shaped metal piece 150 structure, the side metal pieces 153a, 153b extend along the longitudinal direction of the elongated grooves 154a, 154b, respectively, in addition to the oblique downward extension ( That is, the top metal piece 151 and the side metal pieces 153a and 153b extend in the connecting side direction.
The process flow of Figures 3A-3F discloses a method of making the primary package structure 130. The wafer 1310 shown in FIG. 3C generally includes a plurality of wafers 131 that are cast together (the enlarged schematic view of FIG. 3A), and the boundaries between adjacent wafers are defined by unillustrated cutting lines. The wafer can ultimately be diced from the wafer along the dicing line. Since these features are well known to those skilled in the art, the present invention no longer intentionally marks the wafer in the wafer. The front side of the wafer 131 is typically prepared with a plurality of metal pads 132, such as aluminum-iridium metal pads, used as electrodes for the wafer or as terminals for signal transmission to the outside world. In one embodiment, the wafer 131 is a vertical power metal oxide semiconductor field effect transistor, and the metal pads 132 include at least a metal pad 132b constituting a first electrode (such as a source) of the wafer 131, and a composition The metal pad 132a of the second electrode (such as the gate) and the drain region of the wafer 131 are located on the back side of the wafer 131. First, some solder bumps are formed on the metal pads 132 by bumping or plating, the solder bumps 132a-1 are soldered on the metal pads 132a, and the solder bumps 132b-1 are soldered on the metal pads 132b. Since the area of the metal pad 132b constituting the source is generally large, the size of the solder bump 132b-1 connected thereto is also much larger than that of the solder bump 132a-1 to carry a large current. In addition to performing electroplating on the metal pads 132a, 132b, in order to obtain such a large-sized solder bump 132b-1 as shown in FIG. 3B, it is also possible to implant some small-sized solder balls on the metal pad 132b, and The solder balls are placed close to each other, so that after the solder balls are softened and melted, they can be adsorbed and integrated with each other to form a large-sized solder bump 132b-1. As shown in FIG. 3C, a plastic encapsulation layer 1340 is formed on the front side of the wafer 1310 by a molding material, and the plastic encapsulation layer 1340 also covers all of the solder bumps 132a-1, 132b-1. The plastic seal layer 1340 is then ground to thin it until the solder bumps 132a-1, 132b-1 are exposed from the plastic seal layer 1340, as shown in FIG. 3D, the solder bumps 132a-1, 132b The top surface of each of -1 is in the same plane as the top surface of the plastic seal layer 1340. Due to the physical support of the plastic sealing layer 1340, the mechanical strength of the wafer 1310 is increased, so that when the wafer 1310 is ground and thinned, the wafer 1310 is not easily broken, so that a sufficiently thin wafer can be obtained and maximized. Reduce the substrate resistance. Further, as shown in FIG. 3E, after the back surface of the wafer 1310 is polished and thinned, it is usually necessary to implant heavily doped ions on the back surface of the thinned wafer 1310, and then after thinning the crystal. A metal layer 1330 is deposited on the back side of the circle 1310 to form an ohmic contact with the drain region on the back side of the wafer. Thereafter, wafer cutting techniques known in the art can be implemented to cut a single wafer from the wafer. That is, the wafer 1310 and the plastic sealing layer 1340 and the metal layer 1330 shown in FIG. 3E are cut to form a primary package structure 130 including the wafer 131 as shown in FIG. 3F. In this step, the plastic sealing layer 1340 is cut into a cover. At the top of the front side of the wafer 131 is a plastic encapsulation layer 134. At this time, the top molding layer 134 is only wrapped around the sidewalls of the solder bumps 132a-1, 132b-1, and all the solder bumps 132a-1, 132b-1 are The top molding layer 134 is exposed to the outside, and the exposed top surface of the solder bumps 132a-1, 132b-1 is in the same plane as the top surface of the top molding layer 134. In this step, the metal layer 1330 is simultaneously cut into a plurality of bottom metal layers 133, and the back surface of one wafer 131 is correspondingly covered with a bottom metal layer 133 which contacts the drain region on the back surface of the wafer 131 to constitute A third electrode (such as a drain) of the wafer 131.
The second package structure 130 disclosed in FIG. 3F is further described in FIGS. 2B to 2D-2. As shown in FIG. 2D-1, the solder bump 132b-1 connected to the metal pad 132b constituting the first electrode is soldered on the top surface of the first pedestal 111; and as shown in FIG. 2C, Solder bumps 132a-1 connected to metal pads 132a constituting the second electrode are soldered on the top surface of the second pedestal 112. As shown in FIG. 2B, the planar size of the first pedestal 111 constituting the source terminal tends to be larger than the planar size of the second pedestal 112 constituting the gate end, so that the exposed bottom surface area of the first pedestal 111 is generally larger than the second base. The exposed bottom surface area of the housing 112 is mainly used as a heat dissipation path in addition to carrying a large current. The third pedestal 113 and the fourth pedestal 114 electrically connected to the drain of the wafer 131 are embodied as drain terminals of the power device.
The steps shown in Figures 4A-4C disclose a method of making power device 100A. In FIG. 4A, a metal base unit is provided first, and the metal base unit includes at least a first base 111 and a second base 112 which are separated from each other, and are respectively disposed on two sides of the first base 111. The third pedestal 113 and the fourth pedestal 114 (this is described in detail in the foregoing). Then, the primary package structure 130 is flip-chip bonded to the metal base unit by using a conductive adhesive material. The primary package structure 130 is mainly the first base 111 and the second base mounted therein. 112 on. At this time, a plurality of solder bumps 132b-1, 132a-1 (refer to FIG. 3F) disposed on the front surface of the primary package structure 130 are soldered to the first pedestal 111 and the second pedestal 112, respectively. In this step, the solder bumps 132a-1 are soldered to the top surface of the second pedestal 112 by the conductive material 120a, and the solder bumps 132b-1 are soldered to the top surface of the first pedestal 111 by the conductive material 120b. In FIG. 4B, a bridge metal piece 150 is mounted over the primary package structure 130, the bridge metal piece 150 including a top metal piece 151 and a downwardly bent side portion attached to both sides of the top metal piece 151. Metal sheets 153a, 153b. In this step, the top metal piece 151 is directly pasted and mounted on the package structure 130, and the side metal pieces 153a, 153b on both sides of the top metal piece 151 are respectively aligned in the groove 113a at the top of the third base 113 and The recess 114a is provided at the top of the fourth pedestal 114 such that the side metal pieces 153a, 153b are just embedded in the recesses 113a, 114a, respectively. A conductive adhesive material may be coated in the grooves 113a, 114a to fix the bridge metal piece 150 and enhance the conductive effect between the bridge metal piece 150 and the third base 113 and the fourth base 114. The groove 113a 114a can ensure that the bridge metal piece 150 is accurately positioned and is not easily displaced. The bottom metal layer 133 at the back of the primary package structure 130 is then soldered to the bottom surface of the top metal sheet 151 by a conductive material 140. In Fig. 4C, a molding compound 160 is formed by a molding material for molding a metal base unit, a primary package structure 130, and a bridge metal piece 150, as in a molding process generally used in the art, but a metal base unit. The bottom surfaces of the first base 111, the second base 112, the third base 113, and the fourth base 144 are all exposed from the bottom surface of the molding body 160, and the top surface of the top metal piece 151 can be as needed. It is selected whether or not it is exposed from the top surface of the molded body 160. Wherein, if the top metal piece 151 is further provided with a through hole 152 penetrating the entire thickness of the top metal piece 151, a part of the molding material is filled in the through hole 152 in the molding step.
The power device 100B shown in Figs. 5A-5B is not much different from the structure of the power device 100A, and mainly the structure of the bridge metal piece 150 is changed. At this time, no through holes are provided in the top metal piece 151, and a plurality of pad structures 155 are provided on the bottom surface of the top metal piece 151. These pad structures 155 are raised structures protruding from the bottom surface of the top metal piece 151, so in the step of mounting the bridge metal piece 150 onto the primary package structure 130, the pad structure 155 is located at the bottom metal layer 133 and Between the bottom surfaces of the top metal sheets 151. After the top metal piece 151 is pasted onto the bottom metal layer 133, the height of the pad structure 155 determines the distance between the bottom surface of the top metal piece 151 and the bottom metal layer 133. Even if the thickness of the conductive material 140 just applied to the bottom metal layer 133 is not uniform, due to the presence of the spacer structure 155, it is possible to ensure uniformity of the thickness of the conductive material 140 after the completion of the pasting process. In the power device 100B, since the top metal piece 151 does not include any through holes, the top surface of the top metal piece 151 may be exposed from the top surface of the molded body 160.
The power device 100C shown in FIGS. 6A-6D is mainly in comparison with the power device 100B in that the structure and position of the second pedestal 212 are changed. The 6B and 6C are respectively a section in the vertical direction along the broken lines AA and BB in Fig. 6A. As shown in FIGS. 6A and 6B, the second pedestal 212 is no longer disposed between the third pedestal 113 and the fourth pedestal 114 or between the extension lines in the longitudinal direction. The second pedestal 212 at this time includes an extending structure 212a and an external lead 212b connected to the extending structure 212a. In the second pedestal 212, the thickness of the extending structure 212a is smaller than the thickness of the first pedestal 111 and is enclosed in the molding body 160, only the bottom surface of the external lead 212b is exposed from the bottom surface of the molding body 160, and the extending structure is extended. The bottom surface of 212a is not exposed.
In one embodiment, as shown in FIG. 6A, the length of the fourth pedestal 214 in the longitudinal direction is shorter than the length of the third pedestal 113 in the longitudinal direction, while the outer lead 212b is located in the longitudinal direction of the fourth pedestal 214. Extend the line (ie both are on the same line). Specifically, the external pin 212b is on the same line as the plurality of pins 214' included in the fourth pedestal 214. The extension structure 212a extends laterally below the primary package structure 130 until it is vertically overlapped with a portion of the solder bumps (such as the solder bumps 132a-1) disposed on the front surface of the primary package structure 130 (ie, located therein) Directly below), the solder bumps 132a-1 can be soldered to the top surface of the extension structure 212a using the conductive material 120a. Referring to FIGS. 6B-6C, the top surface of the substantially extended structure 212a is in the same plane as the top surface of the first pedestal 111, so that the primary package structure 130 is easily mounted on the first pedestal 111 and the second pedestal 212. Extending the structure 212a. The thickness of the extension structure 212a is required to be smaller than the thickness of the first pedestal 111, mainly to prevent the extension structure 212a from being exposed from the molding body 160 and not conforming to the layout of the pads on the PCB, so as to avoid the subsequent SMT process. Any unnecessary negative effects. It should be noted that since the external pin 212b and the fourth pedestal 214 are on the same line at this time, the external pin 212b cannot be in contact with the bridge metal piece 150 in order to avoid a short circuit. As shown in Fig. 6D, an effective way is to form a notch in the bridge metal piece 150, which is mainly formed on the side metal piece 153'b contacting the fourth base 214. As long as the metal sheet of the side portion 153'b width D ₁ in the longitudinal direction of the top metal plate 151 is less than the width D ₂ in the longitudinal direction, can prevent the side portion of the metal sheet to the second base 212 153'b reach, and the side portions The width of the metal piece 153a in the longitudinal direction may coincide with the width D _{2 of the} top metal piece 151 in the longitudinal direction. The power device 100D shown in FIGS. 7A-7C is mainly exposed from the outside of the molding body 160 than the power device 100C. FIG. 7C is a plan view of the power device 100D.
The exemplary embodiments of the specific structures of the specific embodiments have been described above by way of illustration and the accompanying drawings. Various changes and modifications will no doubt become apparent to those skilled in the <RTIgt; Accordingly, the appended claims are intended to cover all such modifications and Any and all equivalent ranges and contents within the scope of the claims are intended to be within the spirit and scope of the invention.

10. . . Power chip (MOSFET)

12. . . Metal can structure

14. . . Conductive silver paste

16. . . Conductive material

18. . . Source contact

twenty two. . . Raised edge

twenty four. . . Package structure

100A, 100B, 100C, 100D. . . Power device

AA, BB. . . dotted line

111, 112, 113, 114, 212, 214. . . Pedestal

113a, 114a. . . Groove

113', 114', 214'. . . Pin

120a, 120b. . . Conductive material

130. . . Primary package structure

131. . . Wafer

132, 132a, 132b. . . Metal pad

132a-1, 132b-1. . . Welding bump

133. . . Bottom metal layer

134. . . Top plastic layer

140. . . Conductive material

150. . . Bridge metal piece

151. . . Top metal sheet

151a-1, 151a-2. . . Longitudinal edge line

152. . . Through hole

152’. . . Slot structure

153a, 153b, 153'b. . . Side metal sheet

154a, 154b. . . Long groove

155. . . Pad structure

160. . . Plastic body

212a. . . Extended structure

212b. . . External pin

1310. . . Wafer

1330. . . Metal layer

1340. . . Plastic layer

D ₁ , D ₂ . . . width

Embodiments of the present invention are described more fully with reference to the accompanying drawings. However, the attached drawings are for illustration and illustration only and are not intended to limit the scope of the invention.
Fig. 1 is a schematic cross-sectional view showing a semiconductor package structure in the background art.
2A-2E is a schematic structural view of a power device shown in Embodiment 1 of the present invention.
3A-3F is a schematic flow chart for preparing the primary package structure of the present invention.
4A-4C is a schematic flow chart of the preparation of the power device of the present invention.
5A-5B is a schematic structural view of the power device in the second embodiment.
6A-6D is a schematic structural view of the power device in the third embodiment.
7A-7C is a schematic structural view of a power device in the fourth embodiment.

111, 113, 114. . . Pedestal

113a, 114a. . . Groove

120b. . . Conductive material

130. . . Primary package structure

131. . . Wafer

133. . . Bottom metal layer

132b-1. . . Welding bump

134. . . Top plastic layer

140. . . Conductive material

151. . . Top metal sheet

152. . . Through hole

153a, 153b. . . Side metal sheet

154a, 154b. . . Long groove

160. . . Plastic body

Claims (18)

A bottom source power device, comprising:
a metal base unit, the metal base unit includes a first base and a second base separated from each other, and third and fourth bases respectively disposed on two sides of the first base;
a first package structure disposed on the first and second pedestals, and a plurality of solder bumps disposed on the front surface of the primary package structure are respectively soldered on the first and second pedestals;
a bridge metal piece disposed above the primary package structure, the bridge metal piece comprising a top metal piece and a side metal piece attached to both sides of the top metal piece and bent downward;
Wherein the side metal sheets on both sides of the top metal piece extend into the recesses disposed at the top of the third base and the recesses disposed at the top of the fourth base, and are located on the back of the primary package structure a bottom metal layer is soldered to the bottom surface of the top metal sheet by a conductive material;
A molded body in which the metal base unit, the primary package structure, and the bridge metal piece are covered, wherein the bottom surfaces of the first, third, and fourth bases are exposed from the bottom surface of the molded body. The power device of the bottom source according to claim 1, wherein the primary package structure comprises a wafer and a top molding layer covering the front surface of the wafer, and the plurality of solder bumps are respectively soldered to Provided on a plurality of metal pads on the front side of the wafer; and the top plastic encapsulation layer is wrapped around the sidewalls of the solder bumps, so that any one of the solder bumps is provided from the top mold layer Exposed; and the bottom metal layer is disposed on a back side of the wafer. The bottom source power device of claim 2, wherein the second pedestal is located between the third pedestal and the fourth pedestal or at the third pedestal Between the extension cord and the extension of the fourth pedestal. The power device of the bottom source according to claim 1, wherein the second base comprises an extension structure having a thickness smaller than a thickness of the first base and being wrapped in the plastic body, and a An external pin connected to the extension structure, the external pin being located on an extension line of the fourth pedestal in the longitudinal direction;
Wherein, the extension structure extends laterally below the primary package structure until it overlaps a portion of the solder bumps disposed on the front side of the primary package structure in a vertical direction. The power device of the bottom source according to claim 4, wherein the primary package structure comprises a wafer, and the plurality of solder bumps are respectively soldered to a plurality of metals disposed on the front surface of the wafer. On the pad, at least a plurality of metal pads comprise a metal pad constituting a first electrode of the wafer and a metal pad constituting a second electrode of the wafer;
Wherein the solder bumps connected to the metal pads constituting the first electrodes are soldered on the top surface of the first pedestal, and the solder bumps and the extension structures connected to the metal pads constituting the second electrodes are vertically oriented Overlap and solder on the extension structure. The bottom source power device of claim 4, wherein the width of the side metal piece contacting the fourth base in the longitudinal direction is smaller than the width of the top metal piece in the longitudinal direction to avoid contact with the fourth The side metal piece of the base touches the second base. The bottom source power device of claim 1, wherein the top metal piece is provided with one or more groove structures recessed from a bottom surface of the top metal piece to the top metal piece. . The bottom source power device of claim 1, wherein a plurality of spacer structures protruding from a bottom surface of the top metal piece are disposed on a bottom surface of the top metal piece, the spacer A structure is between the bottom metal layer and a bottom surface of the top metal sheet. The power device of the bottom source according to claim 1, wherein a corner joint of the side metal piece on both sides of the top metal piece is formed from a top surface of the top metal piece. A long groove that is recessed. The bottom source power device of claim 5, wherein the bottom metal layer is disposed on a back surface of the wafer and constitutes a third electrode thereof, and the wafer is a MOSFET, and the first electrode thereof is The source and the second electrode are gates, and the third electrode is a drain. A method of preparing a bottom source power device, comprising the steps of:
Providing a metal base unit, the metal base unit includes a first base and a second base separated from each other, and third and fourth bases respectively disposed on two sides of the first base;
Mounting a primary package structure to the first and second pedestals, wherein a plurality of solder bumps disposed on the front surface of the primary package structure are respectively soldered on the first and second pedestals;
Mounting a bridge metal piece above the primary package structure, the bridge metal piece comprising a top metal piece and a side metal piece connected to both sides of the top metal piece and bent downward;
Wherein the side metal sheets on both sides of the top metal sheet respectively extend into the recesses disposed at the top of the third base and in the recesses disposed at the top of the fourth base, and are located on the back of the primary package structure a bottom metal layer is soldered to the bottom surface of the top metal sheet by a conductive material;
Forming a plastic package, coating the metal base unit, the primary package structure, and the bridge metal piece, and each of the bottom surfaces of the first, third, and fourth bases is exposed from the bottom surface of the mold body. The method of claim 11, wherein the step of forming the primary package structure comprises:
Providing a wafer including a plurality of wafers, and a plurality of metal pads are disposed on a front surface of any one of the wafers;
Soldering a plurality of solder bumps correspondingly on the plurality of metal pads;
The front surface of the wafer is covered with a plastic sealing layer, and the plastic sealing layer simultaneously covers the solder bump;
Grinding and thinning the plastic sealing layer until the solder bump is exposed in the plastic sealing layer;
Grinding on the back side of the wafer to reduce the thickness of the wafer;
Depositing a metal layer on the back side of the wafer;
The wafer and the plastic sealing layer and the metal layer are diced to form a plurality of primary package structures including the wafer. The method of claim 11, wherein the second pedestal is disposed between the third pedestal and the fourth pedestal or the extension line and the fourth base of the third pedestal Between the extension lines of the seat. The method of claim 13, wherein the primary package structure comprises a wafer, and the plurality of solder bumps are respectively soldered to a plurality of metal pads disposed on the front surface of the wafer, Each of the metal pads includes at least a metal pad constituting a first electrode of the wafer and a metal pad constituting a second electrode of the wafer;
Therefore, when the primary package structure is flip-chip mounted on the first and second pedestals, the solder bumps connected to the metal pads constituting the first electrodes are soldered to the top surface of the first pedestal, Solder bumps attached to the metal pads constituting the second electrode are soldered to the top surface of the second pedestal. The method of claim 13, wherein the bottom surface of the second pedestal is exposed from a bottom surface of the formed molding body when the molding body is formed. The method of claim 11, wherein the second pedestal comprises an extension structure and an external pin connected to the extension structure, the external pin being located at the fourth pedestal Longitudinal extension line;
Wherein the extension structure extends laterally below the primary package structure until it overlaps a portion of the solder bumps disposed on the front side of the primary package structure in a vertical direction; and the thickness of the extension structure is less than the thickness of the first pedestal, thereby The extension structure is coated in the molding body when the molding body is formed. The method of claim 16, wherein the primary package structure comprises a wafer, and the plurality of solder bumps are respectively soldered to the plurality of metal pads disposed on the front surface of the wafer, Each of the metal pads includes at least a metal pad constituting a first electrode of the wafer and a metal pad constituting a second electrode of the wafer;
The extension structure extends to overlap the solder bumps connected to the metal pads constituting the second electrode in a vertical direction, thereby flip-chip mounting the primary package structure onto the first and second pedestals Solder the solder bumps connected to the metal pads constituting the first electrode to the top surface of the first pedestal, and solder the solder bumps connected to the metal pads constituting the second electrode to the extension structure . The method of claim 11, wherein the top sheet metal is formed with one or more through holes extending through the thickness of the top sheet metal.