KR19980024344A - Pressable beads on the side of the lead finger to improve moldability - Google Patents

Abstract

Surface-mount semiconductor packages use a locking element for securing a plastic housing to a metal pad on which a semiconductor device is mounted. The package includes a terminal with elongate pressable beads on its side adjacent to the portion of the terminal just outside the plastic housing. The beads are pushed inwards by the molding tool when the mold is closed, providing a seal that the molding plastic overflows over the sidewall of the terminal extending beyond the housing, preventing the soldered connection to the terminal from interfering.

Description

Pressable beads on the side of the lead finger to improve moldability

1 is a top view of a package of a preferred embodiment of the present invention.

2 is a bottom view of a package of the preferred embodiment of the present invention.

3 is a side view of a package of a preferred embodiment of the present invention.

4 is a cross-sectional view of an end portion of a main power supply terminal of a package of a preferred embodiment of the present invention;

Fig. 5 is a sectional view of the IMS support plate on which the package of Figs. 1 to 4 can be mounted.

6 is a top view of a lead frame used in the package of FIGS. 1 to 4;

FIG. 7 is a cross-sectional view of FIG. 6 taken along line 7-7 of FIG. 6;

8 is a bottom view of the lead frame shown in FIG. 6, FIG.

9 is an enlarged view of the original zone A of FIG.

10 is an enlarged view of the original zone B of FIG. 3, in which the control terminal is locked in the plastic housing and a detailed view of the new cleaning groove structure;

FIG. 11 shows a portion of the planar single gauge lead frame without terminal lead offset in the preferred embodiment of the present invention. FIG.

FIG. 12 is a lead frame shown in FIG. 11 and illustrates a lead frame after a terminal lead is offset;

FIG. 13 shows a cornered section C in FIG. 12 in which stepped corners are formed to prevent plastic from overflowing the bottom of the terminal during molding; FIG.

FIG. 14 is an enlargement of the circular zone D of FIG. 6, showing a plastic lock groove extending from the plastic lock slot into the lead frame, FIG.

FIG. 15 is a cross-sectional view of FIG. 14 taken along line 15-15 of FIG. 14;

16 is a top of one separate lead frame terminal, provided that a sacrificial vertical indentable bump or bead is provided on the terminal side that seals the forming tool and prevents plastic from overflowing to the exposed solderable surface of the terminal. Figure,

17 is a side view of FIG. 16;

FIG. 18 shows a method of finishing and finishing a lead frame after forming a lead frame and a molding housing (not shown) of FIG. 6 provided with a bonding wire connecting a semiconductor soldered to a pad and a die to an external terminal. ,

19 is a circuit diagram of FIG. 18;

20 is a view showing a structure according to the prior art in which no sacrificial beads are provided in a terminal extending through a plastic housing;

FIG. 21 is a view showing the terminal of FIG. 20 provided with a sacrificial protrusion;

22 is a view showing a sacrificial protrusion after molding;

23 shows a mold and a terminal before molding;

24 shows a mold and a terminal after molding;

The present invention relates to a semiconductor device package and a lead frame therefor, in particular a high power semiconductor device suitable for surface mounting.

Packages for high power semiconductor devices capable of surface mounting on insulating metal substrates (IMS) or other planar support plate surfaces are well known. One such package is described in US patent application Ser. No. 08 / 583,219, entitled Surface Mount Semiconductor Package, filed Jan. 4, 1996, which is incorporated herein by reference. Such devices are well suited for surface mounting on conductive patterns of planar support plates such as IMS structures (thick copper or aluminum substrates covered by thin insulating films with copper or other conductive solderable top surfaces that can be patterned thinly). Do.

The present invention is intended to improve such devices, making them more efficient and easier to manufacture.

According to the present invention, a new lead frame capable of receiving one or more semiconductor dies, such as a power supply IGBT die, an IGBT die, a Schottky diode die, and mixtures thereof, on a central planar pad section. ) Is provided. These dies are connected to each other by pads on their bottoms and by suitable wire bonds on their tops. The lead frame has two power terminals that can be connected to each other in two adjacent corners of the square package. The power terminal makes it easy to externally connect the flat plastic housing that surrounds the top and side of the center lead frame pad. Initially a portion of the lead frame, or after the housing is molded, a plurality of control pins or terminals isolated from the heat sink pads extend from the side of the housing facing the side containing the power terminals.

Within the housing there are at least two control terminals close together which can be wired to the gate and the cathode or current sensing terminals of the die. The third terminal, which is remote from the first and second control terminals, which are located close to each other, may also be used for connection to other terminals, such as the gate terminal of such a diester die, when the thyristor die is in the housing. It is available.

The lead frame is a single gauge conductor. Terminals extending through the border of the molding housing may be partially vertically offset to provide an improved plastic lock for the lead frame. The bottom of the terminal and the lead frame are in a common plane. The main heatsink pad may be provided with parallel slots through the opposite sides of the die on the pad to provide additional plastic locks to the molding housing. Shallow dovetail grooves may extend from the medial ends of these slots to provide improved plastic locking.

The surface of the pad may be provided with a waffle or dimpled surface to facilitate soldering the bottom die surface electrode to the pad. According to the present invention, the bottom of the pad to be surface-mounted on the conductive pattern of the heat sink or IMS plate facilitates the soldering of the pad to the heat sink, and avoids solder voids due to the convexities occurring at the bottom of the lead frame. It can be patterned in grid shape.

The bottom of the insulated housing may also be provided with a cleaning groove, which extends across the width of the package and is parallel to the side containing the input and output terminals and lies between the terminal and the pad. These grooves increase the surface tracking distance between the terminal and the pad and allow the solder flux to be cleaned while soldering down.

According to another feature of the invention, a short, shallow shelf extends across the width of the housing bottom from the bottom of the groove to enhance the flux cleaning function.

As mentioned above, the various terminal pins are partially cut off or offset in order to enhance the plastic lock. According to another feature of the invention, the partially rounded edge of the offset zone is provided with a small rectangular notch or in order to provide an edge that can prevent the plastic from overflowing the bottom of the terminal during molding. Stepped corners are provided.

As another feature of the invention, an elongate crushable bead is formed on the side of the terminal adjacent to the portion of the terminal just outside the plastic housing. Such beads, when closed, may be provided by a molding tool to provide a seal that prevents the molding plastic from spilling over the sides of the terminal that extends beyond the housing, thereby preventing the solder connection to the terminal. Is pushed inward.

As a further feature of the invention, one integrated lead frame bar connects the input terminal with two corners of the housing therein. The combination of the housing and this single bar contained therein is made by wire. The bar also improves the wire bond connection, while also acting as a plastic lock to the housing.

Other features and advantages of the invention will be apparent from the following description of the invention by the accompanying drawings.

1 to 4 show a surface mount package according to a preferred embodiment of the present invention, which has an elongated quadrangular shape and has a top surface and an end portion of a flat single gauge lead frame made of a conventional copper alloy having a thickness of about 1.27 mm. The exterior of a surface mount package consisting of one molded insulated plastic housing is incorporated. In a preferred embodiment, the housing 30 is about 29 mm long, about 14.2 mm wide and about 4.27 mm rusted. The lead frame will be described in more detail with reference to FIGS. 6, 7 and 8 as follows. The lead frame elements shown in Figs. 1 to 4 are provided along the lead frame heat sink pad 31, the power supply terminals 32 and 33 with the quadrilateral housing 30 at the edges of one end and the opposite side of the housing. Control terminals or pins 34, 35, 36. The terminals 32 to 36 protrude about 1 mm beyond the ends of the housing. Terminals 34 and 35 are spaced at a close spacing of about 2.5 mm from center to center, for example, while terminals 35 and 36 are spaced wider by about 6.0 mm.

As shown in Fig. 3, the bottom surface of the pad 31 and the terminals 32 to 36 are coplanar, and the pattern of the heat sink support such as the IMS plate can be connected to the colored surface. have. FIG. 5 is a cross-sectional view of a typical IMS plate composed of a thick thermally conductive (copper or aluminum alloy) substrate 40 covered with a very thin insulating polymer 41. On this insulator 41, a thin conductive solderable layer 42, which can be a color pattern, is arranged. Any desired pattern can be formed in this layer 42, but in FIG. 5, the layer 42 is divided into one segment 42a and a plurality of segments, which are arranged in line with the terminals 32 to 36. FIG. . In FIG. 5, for example, only segments 42b and 42c are arranged in line with the terminals 32 and 34. Therefore, it is convenient to solder the bottom of the package shown in Figs. 1 to 4 to the IMS plate shown in Fig. 5 using a standard soldering method.

Flux cleaning grooves 50, 51 (FIGS. 2 and 3) assist the soldering operation and, in order to facilitate this, the plastic housing 30 crosses the bottom, so that the opposite ends of the pad 31 and the terminals 32-33, 34-36), parallel to the pad end. The grooves 50, 51 are provided with a curved cross section and a radius of about 0.4 mm. These grooves are useful to help flush out the solder flux after the soldering operation is finished, increasing the tracking distance to the plastic surface between the pad 31 and the terminals 32 to 36.

In order to improve the flux cleaning function, it has been found useful to provide a shallow and short shelf, which is shown as a shelf 60, 61 in FIG. 10. These shelves 60 and 61 have a depth of about 0.1 mm, and the cleaning grooves 50 and 51 are spaced apart from each other at regular intervals, and are opened onto the substrate to which the package is soldered.

6, 7 and 8 show the lead frame itself before receiving the die or housing. The pad 31 and the terminals 32 to 36 are integral parts of the lead frame and are joined by segments, and after such segment over-molding, the contacts 34 to 36 are connected to the contacts 32 and 33. And cut to isolate the pad 31 from each other. One heavy cross bar 70 (FIGS. 6-8, 18) which connects the power terminals 32, 33 to the lead frame together and helps to fix the lead frame in the plastic housing 30 as a plastic lock. Also heard. This bar 70 is also used as a joining surface for wire bonding, as described with reference to FIGS. 18 and 19.

The pad section 31 is provided with two thin parallel slots 71, 72 (FIGS. 6 to 8, 14 and 15), which slots are filled with plastic during the molding operation and the pad 31 is housed. Create a plastic lock to help lock it in motion relative to (30). Intentionally shortened barbs 73 and 74 extend from the inner walls of slots 71 and 72, creating another plastic lock that further secures lead frame pad 31 to the plastic housing.

Dovetail grooves 80-83 (FIGS. 6, 14, 15) are pads from the ends of slots 71, 72 on the top of the pad 31 to provide support as plastic locks. Stretched to the end of the. This groove is filled with plastic during the molding operation and further secures the pad 31 to the housing.

The upper center surface of the pad 31 is provided with a waffle surface 85. The top surface of the pad 31 can be plated with nickle, and the top surface is provided with a shallow (preferably about 0.05 mm) face, preferably a dot-shaped face with a center of about 0.6 mm and a diameter of about 0.25 mm. . Such waffle patterns are known to facilitate the soldering of dies and waffle surfaces. According to another aspect of the preferred embodiment of the present invention, one waffle pattern 86 (FIG. 8) is provided on the opposite side of the pad 31. Such a surface was originally flat and smooth, but it has been found that if this surface is slightly concave, undesirable solder voids may form during the soldering process. By the present invention, the waffle pattern on the bottom of the concave lead frame surface increases the wetness of the solder and the flow of solder therebetween, thereby enhancing its ability to be soldered to the flat heat sink surface.

11 is a cross-sectional view showing a portion of the lead frame containing the pad 31 and the bottom point 36. This frame is originally a completely flat frame with a flat top and bottom. By moving the terminal section of the leadframe slightly by partial stamping as shown in Fig. 12, it was found that the terminal was locked more firmly in the plastic housing. For a 1.27 mm thick lead frame, the actual travel distance is about 0.5 mm. It has been found that during the molding operation (after this offset process), it is likely to flow past the slightly rounded podium at position C and beyond the bottom of terminal 36 and other offset terminals 32 to 35. It has also been found that stamping the square notch 95 (FIGS. 9 and 13) at the corner C of each terminal prevents such plastic overflow. This notch 95 is such that cutting rather than bending the material does not require additional space in the transverse direction.

The notch 95 has a depth of about 0.2 mm and a depth of about 0.3 mm. 6 and 7, notches 95 are shown for each of the offset terminals 32 to 36.

One or more small beads are provided that extend from the thick portion of the new package. The thickness of the beads (100, 101) is varied depending on the thickness of the lead frame. In general, the beads 100 and 101 have a thickness of 0.05 to 0.5 mm. Thus, as shown in Figs. 16 and 17, for example, two pressable beads 100, 101 having a radius of about 0.2 mm (for a lead frame of 1.2 mm) are pushed by a forming tool, or Partially flattened, it is used to prevent the plastic from overflowing beyond the bounds bounded by the beads 100,101. 6 and 7 the indentable beads are shown in all the necessary positions on the lead frame.

16, 17 and 20-24 are detailed views of the pressable beads 100, 101 on the illustrated terminals. According to FIG. 20, during molding of the housing 30, it was found that thin plastics 120 and 121 flowed out from the side surfaces of the terminals such as the terminals 36 on the outside of the molding housing 30. This plastic must be removed because it interferes with the soldering with the terminal 36.

This problem is solved by the press-fit beads 100 and 101 on the side of the terminal 36 shown in Figs. 16, 17 and 21. Beads 100 and 101 are pushed by the mold during molding and act as dams to prevent plastic from leaking out or overflowing, as shown in FIG. A trapezoidal flat is pushed into the beads 100, 101. As shown in FIGS. 23 and 24, the mold is provided with a tapered channel portion 141 for receiving the terminal 36. As the mold is closed in the position of FIG. 23, the terminal 36 is pushed into the tapered channel 141, which flattens the beads 100, 101 by flats 150, 151. The pushed in bead seals the channel 141, thereby preventing plastic from overflowing past the indentation zones of the beads 100, 101. Terminal 36 (and all terminals 32-36) can be easily released by the divergent angle of channel 141 after shaping is complete, as in FIG.

FIG. 18 shows a lead frame pad 31 after two semiconductor device dies 110 and 111 are soldered to a pad 31 called a copack. Copac dies 110 and 111 may be of any type, but are shown as power IGBTs and fast recovery diodes (FRED) in FIGS. 18 and 19.

In FIG. 19, all the electrodes are soldered and connected to the conductive pads, so that the collector of the IGBT 100 is connected to the cathode of the FRED diode 111. As such, the conductive pad 31 provides a means for electrically interconnecting the nose pack with an external circuit. The top emitter electrode of the IGBT 110 is wire coupled to the anode of the FRED diode 111 by a wire 112. Wire bonds are then connected to cross bars 70 and terminals 32 and 33.

In addition, the wire bond 15 consists of the gate pad of the IGBT 110 to the gate terminal 35, and as shown in FIG. 18, the emitter Kelvin connection 116 can also be provided at the terminal 34. have.

The above description of the preferred embodiment of the present invention has the purpose of illustration. Accordingly, the description is not intended to limit the invention to the form disclosed.

In the light of the above description, any modifications and variations are possible. The scope of the invention is not limited by this detailed description, but only by the appended claims.

Claims (7)

As a surface mount semiconductor device package, One semiconductor device, A metal pad on which the semiconductor element is mounted, A housing coupled to the metal pad and formed of a flowable material surrounding the semiconductor device when it is cured, At least one terminal spaced apart from the metal pad and coplanar with the metal pad, At least one pressable bead arranged on the side of the terminal, in order to prevent the flowable material of the housing from overflowing the forming tool used to form the housing, Surface-mounted semiconductor device package including back. The method of claim 1, A surface mount semiconductor device package, wherein the package includes a plurality of terminals having one pushable bead on each side. The method of claim 2, A surface mount semiconductor device package in which at least one of the pressable beads in one of the terminals is axially aligned with at least one of the pressable beads on the other terminal located on one side of the package. The method of claim 3, A surface mount semiconductor device package having a thickness of about 0.05 to 0.5 mm of pressable beads. The method of claim 1, Surface-mounted semiconductor device package with indentable beads having a radius of approximately 0.2 mm. The method of claim 1, Ladders formed by forming apparatus, in which pressable beads can push in beads The method of claim 6, A surface mount semiconductor device package in which a molding device is provided with a tapered channel portion for receiving terminals and beads and for leveling the beads when the mold is closed.