JPS6242390B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to electronic devices such as semiconductor devices and integrated circuit devices, and particularly to assembly techniques thereof, and can be effectively utilized in the production of power electronic devices.

Unlike electronic devices for small signals, power electronic devices generally require large heat dissipation flanges, which makes assembly between elements, flanges, and lead wires complicated. The mold used for sealing is also complicated, which has delayed its industrialization compared to small-signal electronic devices.

Therefore, the present application seeks to provide a new technique that is effective for industrializing power electronic devices.

FIG. 1 shows a top view of a flange for mounting an electronic element, and FIG. 2 shows a longitudinal cross-sectional view thereof, which is made by punching out a plate-shaped body using a press. Industrially, for example, flanges for 10 electronic devices are manufactured in an integrated series.

In the figure, 1 indicates a flange body with a thickness of 1.26 mm and a width of 8 mm and a length of 30 mm per piece, and the heat generated in the elements connected to the flange is effectively dissipated to the outside. Copper, aluminum, or an alloy mainly composed of these materials, which have good conductivity, or a clad plate made of the above-mentioned materials as a main plate are used. It is effective to form a plating layer of nickel or other material on the surface of the flange for corrosion prevention or other purposes, and this will be explained in detail later.

The notch 2 formed in the flange 1 is a mold material flow prevention notch formed to prevent the molten mold material from flowing out to unnecessary portions in the mold sealing process to be performed later.

The holes 3 are bolt holes for tightly fitting the external heat sink and the flange when the electronic device is completed, thereby making it possible to significantly increase heat dissipation.

Reference numeral 4 designates an open slit tab lead insertion portion formed for inserting a tab lead of a lead frame, which will be explained later.

The narrow protrusion 5 forming the outer circumference of the tab lead insertion part 4 is a tab lead holding part formed to swage the tab lead located inside the tab lead insertion part 4, and in the figure, it is swaged with a small pressure. Although the tab lead insertion part is separated at the upper center as shown in FIG. In that case, the tab lead insertion portion 4 has a closed slit shape. Furthermore, the tab lead insertion portion 4 is formed to be long in the same direction as the length direction of the flange (left and right directions in the figure). It is effective for the work if force is applied from the direction shown in FIG. This is to prevent the lead frame from becoming loose and to make effective use of the elasticity of the lead frame when caulking.If these purposes are not taken into consideration, it is not possible to set the length direction of the tab lead insertion part in a direction perpendicular to the length direction of the flange. The number of tab lead insertion parts may be changed or the number of tab lead insertion parts may be changed to one.

The groove portion 7 is a groove having a diameter of approximately 4.5 mm and is formed to define a position 8 where an element is to be attached.

As described above, the flange main body can be manufactured by one press process, and it is desirable that at least the groove 7 is constructed integrally with the press mold for forming the tab lead insertion part 4. That is, the element mounting position 8 and the tab lead insertion part 4 are defined in a fixed positional relationship, and therefore the positional relationship between the lead frame held by the tab lead insertion part 4 and the element mounting position 8 is accurately defined. It is from.

In FIG. 3, a nickel coating 9 of, for example, 5 μm is formed by plating on the surface of the flange main body 1 shown in FIGS.
FIG. 2 is a longitudinal cross-sectional view showing a state in which silver foils 10 of FIG. 1 are connected by electric welding. Particularly when the above-mentioned element is a semiconductor element such as a transistor or a semiconductor integrated circuit element, it is not desirable to attach the element directly to the surface of a flange made of copper, aluminum, etc.
If silver of about 200μ to 1200μ is inserted, there will be no effect on the frame elements, and heat dissipation will be extremely good.Also, since silver is a soft metal, 4.5mm
Even if a fairly large element of about 4.5 mm is attached, the element will not be damaged due to thermal strain, so it is extremely useful as the inclusion 10 between the element and the flange. Also, a nickel coating 9 of about 1μ to 10μ
The intervening material acts as a corrosion-proofing coating for the flange, and also acts as a resistance material in the electric welding between the flange 1 and the inclusion 10, thereby providing a strong connection between the inclusion 10 and the flange body. In addition to nickel, chromium,
Molybdenum, tungsten, alloys thereof, alloys of them with other metals, and the like can be used in the same manner. In addition, 11 and 12 in the same figure show a part of the electrode for electric welding.

As mentioned above, when the inclusion 10 such as silver foil is required between the element and the flange 1, an effective method is to first connect the inclusion 10 and the flange 1 by electric welding, and there are many other methods. It can also be used in the case of That is, if resistance welding is performed so that only the contact surface of the flange 1 or the nickel coating on its surface and the inclusion 10 is melted, the other surface of the inclusion, that is, the flat surface to which the element is to be attached, can be maintained as is, which will be carried out later. This is because the element can be attached uniformly over the entire surface, and since electric welding is based on heat generation at the extreme part, deterioration of the quality of parts other than the welded part can be suppressed.

Another effective method is to connect the silver foil 10 to the copper flange 1 element mounting position 8 by cold pressure welding. According to this method, the silver and the flange etc. do not change in quality and the entire surface is pressed flat. Since the flatness is not impaired, the welding has the same advantages as the resistance welding described above. In this case, the formation of the nickel film 9 is preferably performed by plating after cold pressure welding, with the silver foil protected by a corrosion-resistant material such as resin.

Another effective method for connecting the silver foil 10 and the copper flange 1 is to use eutectic at the interface between silver and copper to connect at a relatively low temperature. There are two methods: one method is to connect by melting the entire inclusion, and the other is to connect by melting the entire inclusion. However, in these cases, it is necessary to heat the connection at a temperature higher than the element mounting temperature that will be performed later, and the temperature is sufficient to prevent deterioration of the flange 1 and the inclusion 10. consideration should be given.

FIG. 4 shows a vertical cross-sectional view of the element 13 mounted on the silver foil 10 by soldering, and the element 13 is a power amplifier with a size of 2.5 mm x 2.0 mm having Si as a base. Semiconductor integrated circuit elements are used,
One main surface thereof is uniformly soldered to the flat surface of the flat silver foil 10 at about 440° C. by a gold-silicon eutectic solder 14. Further, as an alternative to the above-mentioned soldering connection, the present invention utilizes a conductive adhesive containing conductive powder such as silver-gold, and in this case, the work is easy because no heating is required. Therefore, it is extremely beneficial for industrialization. Although not shown on the other main surface of the above element, SiO ₂ , Si ₃ N ₄
A wiring path extends from an electronic element such as a transistor, diode, or resistor formed inside the semiconductor onto the insulating film through the hole, and a wiring path extends to the periphery of the element to connect a wire later. electrode terminals are formed.

The connection of the silver foil and the element to the flange does not necessarily have to be carried out in the above process, and may be carried out, for example, after the lead frame is connected to the flange.

FIG. 5 is a top view showing the lead frame 20, which is made of a band-shaped metal plate made of, for example, phosphor bronze, which has a suitable elasticity, has a thickness of 0.25 mm, and has a length of 30 mm per electronic device. It can be manufactured using a so-called photo-etching technique and a press molding technique in which a corrosion-resistant mask is formed by etching. Alternatively, it can be made using press stamping and press molding techniques. In any case, as in the case of the flange, if, for example, 10 electronic devices are to be manufactured in a series, it is necessary to manufacture a lead frame in which 10 pieces are connected in series. When using this technology, the above series of frames can be made simultaneously in one process, and the press forming process can also be done in one process.
However, in press punching and press forming technology, the press mold is complicated, so multiple press molds are used to process the process simultaneously in one press, and one set of press molds is used. It is preferable to punch out continuously to create a series of frames.

21a in the figure is a sealed body (21a in the figure) which will be explained later.
A lead portion (internal lead portion) located in a portion surrounded by a dashed dotted line 15 is shown, and its tip is preferably formed so as to substantially coincide with the outer periphery of the element mounting position 8. Reference numeral 21b indicates a lead portion (external lead portion) led out to the outside of the sealing body, and although it is shown in the shape of a lead in the figure, it does not necessarily have to have such a shape, and it may be made into a flat plate shape. It may also be formed into a lead shape by punching. Above lead parts 21a, 21
b constitutes the lead wire 21 that is integrated in the finished product.

Between the many external lead parts 21b is a lead holding part 22 that constitutes a part of the lead frame 20.
a, 22b (generally referred to as 22), and the lead holding portion 22 may be located anywhere at least on the outer lead portion 21b, and may be located on all of the outer lead portions 21b. For the purpose of retention, it is desirable to form at least a portion of it as close as possible to the boundary line 15 of the sealing portion.
This is particularly important when sealing by transfer molding (injection molding) of resin or the like is used because it serves the purpose of stopping the flow of the sealing material. In addition, in this example where the external lead portion 21b is shaped as a lead wire, the widths of the two lead holding portions 22a and 22b are different from each other so that the front and back sides of the lead frame 20 can be clearly seen at a glance, and the width is wide. The end 22b is for forming a part of a molding material injection pipe (runner). In addition, in this example, the tip of the lead portion 21b is tapered to facilitate insertion into a printed circuit board, etc., so that the lead portion 21b is easily subjected to unnecessary mechanical action from the outside world. 20 so as to surround the external lead portion 21b, thereby preventing unnecessary deformation of the lead portion 21b during each step until the device is completed and during transportation between the steps.

The hole 23 formed in the lead frame 20 is a guide hole used as a positioning guide during later assembly, cutting of the lead holder, and molding.

The hole 24 is a tab lead hole formed for forming a tab lead 25.
is a tab lead 25a for connecting to flange 1
and a tab lead 25b for maintaining a constant distance between the main surface of the flange 1 and the main surface of the lead frame.
It is important to maintain a constant positional relationship with the element mounting position of the flange 1. Therefore, the notch hole 24 that forms the outline of the tab lead 25 is inserted into the internal lead part as shown in FIG. 21
It is sufficient to form the tab lead at the same time as the photo-etching process used to form the tab lead a, and to prescribe the positional relationship to be constant. As another method, the inner lead portion 21a and the tab lead 25 may be formed simultaneously or sequentially by press punching and press molding techniques. Such a lead frame increases the solderability of the lead wires, improves the wire bonding connection between the element lead frames described later, and is used for corrosion prevention purposes, such as 1.
Silver plating with a thickness of μ or more is applied. Such silver plating treatment may be carried out immediately after etching when photoetching is used or after press molding, or may be carried out either before or after pressing when all is carried out by press. Further, although gold is a material for achieving the above object, it is expensive, and silver is preferable from an industrial standpoint.

In any of the above methods, when the tab lead 25a is bent in the same direction as the length direction of the lead frame 20 (the left and right direction in the figure), the one side end 20 of the tab lead 25a and the internal lead portion It is important that the distance W in the length direction on the plane of the lead frame 20 from the center 27 of the group 21a (coinciding with the center of the element mounting position 8) does not change at all before and after bending the tab 25a. This allows extremely accurate positional relationships to be maintained. And that tab lead 2
5a is 1 for a series of lead frames in principle.
If there is a certain point, the basic purpose can be achieved.

7 and 8 show the lead frame 20
FIG. 2 is an enlarged perspective view and a BB longitudinal cross-sectional view of the tab lead forming portion of the lead frame 20, and includes a pair of tab leads 25a that are symmetrical with respect to a base line 29 perpendicular to the main surface 28 of the lead frame 20; This is to prevent positional displacement in a direction perpendicular to the length direction of the lead frame 20. In this case, if the tab leads 25a are provided as a pair for a series of lead frames, the basic purpose can be achieved in principle. Furthermore, the angle 30 formed by the tab lead 25 and the main surface portion 28 of the lead frame 20 connected thereto is formed to be slightly larger than 90 degrees and sufficiently smaller than 180 degrees, and the connection with the flange 1 is made possible by this and the elasticity of the lead frame 20. can be made stronger. The tip of the tab lead 25a is further bent outward, but this is to further strengthen the connection with the flange 1. If they are located approximately at the center, the lead frame 20 can be connected to the flange 1 very easily. In addition to phosphor bronze, Kovar, iron-nickel alloy, nickel, and the like can be used as the material when elasticity is utilized as described above. Also tab lead 2
5b does not necessarily have to be formed in the same part as the tab lead 25a, but it is more effective to form the same part in order to simplify the press molding die, and the stress when caulking the tab lead 25a to the flange 1 is reduced to the internal lead part. It is effective to form them on both sides of the tab lead 25a integrally with the tab lead 25a in order to reinforce the tab leads 25a and the like so that they do not reach there. Furthermore, another method for controlling the distance between the lead frame 20 and the flange is to place a jig under the flange that is flattened and brought into close contact with the flange, and set the tip of the tab lead 25a in contact with the surface of the jig. There is a way to do it.

Lead frame 20 obtained as described above
The tab lead 25a is inserted into the tab lead insertion portion 4 of the flange 1 to which the element 13 is attached. At this time, the tab lead 25b is in contact with the upper surface of the flange, and defines a constant interval between the flange lead frames. On the other hand, the tab lead 25b of the lead frame
Tab lead 25a width 3 at the same height as the tip of
1 should be approximately the same as the length 16 of the tab lead insertion portion 4, and the difference should be determined within an allowable value between the tip of the internal lead portion 21a of the lead frame 20 and the element mounting position 8. It is preferable that the width of the distal end of the tab lead 25a is made sufficiently smaller than that to allow smooth insertion into the tab lead insertion portion 4. When the lead frame 20 and flange are used, which are made with consideration as described above, the positional relationship between the internal lead portion 21a and the element mounting portion 8 is uniquely determined only by the insertion of the tab lead 25a.

After being aligned as described above, pressure is applied in the direction shown by arrow 6 in FIG. At this time, as shown in the cross-sectional view in FIG.
The tab lead 25a comes into contact with the upper and lower parts of the slit due to the pressure in the direction, and since the lead frame is further pressurized and has a certain degree of elasticity, the contact between the two is extremely strong.

FIG. 10 is a top view of the main part showing the state in which the tab lead 25a described above is caulked in the slit 4. Here, it is important to pay attention to only the central part of the tab lead 25a, that is, the tip of the tab lead holding part 5 in this example. After sealing, the flange is cut only at the center of the slit 4 where the slit 4 is crimped. , the caulking pressure can be reduced, and the width that can be cut can be increased.

FIG. 11 shows an example in which the electrode terminal located on one main surface of the element 13 and the internal lead portion 21a are electrically connected by wire bonding. In the drawing, reference numeral 32 denotes a connector wire made of gold, aluminum, or the like with a diameter of about 50 μΦ, and its material can be selected from various types depending on the tip surface material and connection technology of the electrode terminal and internal lead portion 21a. For example, if the electrode terminal is aluminum, the internal lead terminal 21
If the tip surface material of a is silver and the connection technique is thermocompression bonding, gold is suitable, and if ultrasonic welding is used, aluminum is suitable. In wire bonding as described above, it is necessary to apply some pressure to connect the internal lead part 21a and the connector wire 32, so that the internal lead part 21a is bent. On the other hand, in the case of thermocompression bonding, the tip of the internal lead part 21a and the element electrode
It is necessary to heat the part to about 350°C, and it is desirable to heat the part to about 100°C even in ultrasonic welding. For this purpose, as shown in FIGS. 11a and 11b, a metal spacer 33 having good thermal conductivity such as iron or copper may be inserted from a direction perpendicular to the length direction of the flange and removed after bonding. At this time, if the metal spacer 33 is heated, the internal lead portion 21a can be directly heated. Furthermore, in Fig. 12, an insulating spacer such as a ceramic ring is positioned and interposed with a silver foil 10 before connecting the flange 1 and the lead frame, and is left in place even after completion. It is. In either case, it is easy to heat the flange by using the flange mounting table 34 as the heating element, so the spacer 33 is made of a metal with good heat conduction or an insulator with good heat conduction such as alumina ceramics or beryllia porcelain. Something is preferred.

According to yet another example, the capillary 35
Connect the connector wire 32 to the electrode terminal, and then use the elasticity of the internal lead part 21a to bring the tip of the internal lead part 21a into contact with the flange 1 or the silver foil at the time of connection, as shown in FIG. 13a. This can be carried out by heating the connector wire to connect the connector wire, and then using the elasticity of the internal lead portion 21a to return it to its original position as shown in FIG. 13b. In this case, if the connection to the element 13 is made first, there is a problem that the connector wire 32 is pulled upward when the internal lead part 21b returns to its original position, as shown in FIG. 13b. With sufficient sag in the wire 32, connect the connector wires as shown in FIG. 13a. Alternatively, first connect the connector wire 32 to the internal lead part 21a,
The connector wire may be connected to the electrode terminal of the element 13 after the internal lead 21a returns to its original position.

Next, the assembly completed as described above is placed in a mold, and as shown in FIGS. 14a and 14b, a resin injection pipeline (runner ) 36, inject an encapsulant such as resin, and after solidifying the resin, remove the molding jig, and if the tips of the lead holding part 22 and external lead part 21b are in contact with the lead frame 20, cut those parts as well. Then, as mentioned above, flange 1
If the is cut for each device, a structure as shown in FIG. 15 will be obtained, and if this is further folded appropriately, a structure will be obtained in which the lead part 21 can be easily inserted into the hole in the printed circuit board, as shown in FIG. 16. can do.

[Brief explanation of the drawing]

Figure 1 is a top view showing the flange, Figure 2 is the top view of the flange.
3 is a vertical sectional view showing the state in which a nickel coating is formed on the flange in FIG. 2 and silver foil is connected; FIG.
5 is a top view showing the lead frame; FIG. 6 is an enlarged view showing a part of the lead frame in one step of manufacturing the lead frame; 7th
FIG. 8 is a perspective view and a vertical cross-sectional view taken along the line B-B, respectively, showing an enlarged part of the lead frame.
9 and 10 are a cross-sectional view and a top view showing the state of connection between the lead frame and the flange, respectively, FIG. 11a is a plan view showing the state of electrical connection between the lead frame and the element, and FIG. Figures 11b, 12 and 13a and 13a and 13a and 13b are all cross-sectional views showing the state of electrical connection between the lead frame and the element, and Figures 14a and b are the positions of the resin injection pipeline, respectively. 15 is a perspective view showing an example of a completed electronic device, and FIG. 16 is a perspective view showing another example of a completed electronic device. 1 is the flange body, 2 is the notch for preventing mold material flow, 3 is the bolt through hole, 4 is the tab lead insertion part, 5 is the tab lead holding part, 6 is the direction of pressure to be applied to the tab lead holding part, and 7 is the element mounting position. The groove shown, 8 is the element mounting position, 9 is the nickel coating, 10 is the silver foil, 11 is the electric welding electrode, 12 is the electric welding electrode, 13 is the electronic element, 1
4 is a gold-silicon eutectic brazing material, 15 is a boundary line of a sealing body, 16 is a length of a tab insertion part, 20 is a lead frame, 21 is a lead wire, 21a is an internal lead part, 21b is an external lead part, 22 is a lead holding part, 22a is a narrow lead holding part, 22b is a wide lead holding part, 23 is a guide hole, 24 is a notch hole for forming a tab, 25 is a tab lead, 26 is a tab lead side end, 27 is an inside Center of lead group,
28 is one main surface of the lead frame, 29 is a base line perpendicular to the one main surface of the lead frame, 30 is the angle formed by the lead frame and the tab lead, 31 is the width of the tab lead 25a, 32 is the connector wire, 33 is the spacer, 34 is a flange mounting table, 35 is a capillary, 36 is a resin injection pipeline, and 37 is a sealing material such as resin.

Claims (1)

[Claims] 1. A metal plate with good thermal conductivity, a semiconductor element attached to the metal plate, a plate-shaped lead placed close to the semiconductor element, and an electrode terminal provided on the main surface of the semiconductor element. 1. An electronic device comprising a connector wire for electrically connecting a plate-shaped lead, the semiconductor element being fixed to a metal plate with a conductive adhesive containing silver.