JPS5989448A - Lead frame for electronic device - Google Patents

Abstract

PURPOSE:To prevent the tips of lead parts from being bent at the time of assembling by a method wherein the tips of a part among the lead parts are coupled to the frame part. CONSTITUTION:A lead frame 20 consisting of a phosphor bronze plate, etc., is formed by a punching process by press, etc. The tips of lead parts 21a are formed on the outside periphery of the position 27 where elements are attached. Each of external lead parts 21b is alternately different in length, and among the lead parts 21b are 21b1, 21b3 and 21b5 not coupling to the outer frame 20b of the frame 20, and 21b2 and 21b4 coupling to the outer frame 20b. The coupled lead parts 21b2 and 21b4 prevent the tips of the lead parts from being bent at the time of assembling.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a lead frame used in electronic devices such as semiconductor devices and integrated circuit devices, and can be effectively used in the production of power electronic devices.

Unlike electronic devices for small signals, power electronic devices generally require large heat dissipation flanges, which limits the number of external leads, making it difficult to increase the number of pins.

The present invention seeks to provide a novel lead frame particularly suitable for the assembly of power electronic devices.

Hereinafter, specific embodiments of an assembly technique for a power electronic device using the lead frame of the present invention will be described in detail. Thereby, the specific objectives, features, and effects of the present invention will be understood.

FIG. 1 shows a top view of the seven flange for attaching electronic elements, and FIG. 2 shows a longitudinal cross-sectional view thereof, which is made by punching out a plate-shaped body with a press. Industrially, for example, seven lunges for ten electronic devices are manufactured in an integrated series.

In the figure, 1 indicates a 7-lunge main body having a thickness of 1.26 mm, a width of 8 mm, and a length of 30 m per piece.
Since the heat generated in the elements connected to the flange is effectively dissipated to the outside, it is recommended to use materials such as copper, aluminum, or alloys based on these materials, which have good thermal conductivity, as well as cladding made of the above materials as the main plate. board is used. The surface of the 7 lunges mentioned above is coated for corrosion prevention and other purposes. It is advantageous to form a nickel or other plating layer, as will be explained in more detail below.

7. 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.

Hole 3 is a bolt hole through which the external heat sink and flange 7 are brought into close contact 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. The tab lead insertion part 4 is separated at the center so that the tab lead insertion part 4 is separated in the center, but in the same figure, there is an r? The tab lead holding portions 5 may be connected at the upper center of the tab 17-F insertion portion, in which case the tab lead insertion portion 4 will have a closed slit shape. Further, the tab lead insertion portion 4 is formed to be long in the same direction as the length direction of the 7 langes (left and right directions in the figure), but this is because when pressing the tab lead by caulking the protrusion 5, it is necessary to It is effective for the work if force is applied from the direction, and the reason why the tab lead insertion parts 4 are formed as a pair in the vertical direction in the figure is because of the pressure from caulking, the lead frame and the 7 langes 1
This is to avoid errors in the positional relationship with the lead frame, and to make effective use of the elasticity of the lead frame when caulking. The direction may be changed such as perpendicular to the horizontal direction, or the tab lead insertion portion may be
You can also do it.

The groove portion 7 is a groove of approximately 4.5 manφ 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. .

FIG. 3 shows that a nickel coating 9 of, for example, 5μ is formed by plating on the surface of the seven-lunge main body 1 shown in FIGS. 9 is a longitudinal cross-sectional view showing a state in which, for example, a 500 μm silver foil 10 is connected by electric welding to a surface of a 7-lunge made of copper, aluminum, etc. It is not desirable to attach the element directly to the frame.On the other hand, if silver of about 200μ to 1200μ is interposed, there will be no effect on the frame element and heat dissipation will be good.Also, since silver is a soft metal, .5
Even if a fairly large element of about +1 nm is removed, the element will not be damaged due to thermal strain, so it is extremely effective as the inclusion 10 between the element and the 7 flange. Also 1μ
The intervening nickel coating 9 of approximately 10 μm acts as a corrosion-protective coating for the 7 langes, and also acts as a resistance material in the electric welding between the 7 langes 1 and the inclusions 10, and also serves as a resistance material in the electric welding between the 7 langes 1 and the inclusions 10, and the nickel coating 9 acts as a corrosion-proofing coating for the 7 langes. Make strong connections between people. In addition to nickel, chromium, molybdenum, tungsten, alloys thereof, and alloys of these with other metals can be used as the resistive material.

In addition, 11.12 in the same figure shows a part of the electrode for electric welding.

As mentioned above, there is an inclusion 1 such as silver foil between the element and the 7-lanlay 1.
0 is required, an effective method is to first connect the opening between the inclusion 10 and the 7 flange 1 by electric welding,
It can also be used in many other cases. i.e. 7 lunges 1
Alternatively, if resistance welding is performed so that only the nickel coating on the surface and the contact surface of the inclusion 10 are melted, the other surface of the inclusion, that is, the flat surface on which the element is attached, can be maintained as it is, and the element will be attached later. This is because the attachment can be performed uniformly over the entire surface, and since electric welding is based on heat generation at the extremes, deterioration of the quality of parts other than the welded parts can be suppressed.

In addition, as an effective method, copper flange 1 element mounting position 8
There is a method of connecting the silver foil 10 by cold pressure welding (1). According to this method, the silver and the 7 lunges etc. do not change in quality, and the surface is also pressurized so that the entire surface is flat, so the flatness is not affected. Therefore, it has the same advantages as the above-mentioned resistance welding. In this case, the nickel film 9 is preferably formed 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 run 7') 1 is to use eutectic at the interface between silver and copper to connect at a relatively low temperature. There are a method of connecting through a material and a method of connecting by melting the entire inclusion, but in these cases, there is a method of connecting by heating at a temperature higher than the element mounting temperature, which is performed later. Sufficient consideration should be given to prevention.

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 semiconductor integrated circuit for power amplification having a size of 2,5+++n x 2.0111 m and having Si as a base. A device is used, the main surface of which is approximately 44 cm
It is uniformly soldered to the flat surface of the flat silver foil 10 at 0°C. In addition, as a method related to the above-mentioned soldering connection, a conductive adhesive containing conductive powder such as silver or gold can be used, and in that case, the work is easy because no heating is required, but there are problems in terms of thermal resistance and mechanical strength. Excellent soldering.

Although not shown on the other surface of the above element, 51
02 HS I 3 N 4 etc. A porous insulating film, a wiring path extending from an electronic element such as a transistor, diode, or resistor formed inside the semiconductor onto the insulating film through the hole, and a wire later connected. Therefore, electrode terminals located at the periphery of the element are formed.

The connection of the silver foil and the element to the 7 rungs does not necessarily need to be performed in the above steps, and may be performed, for example, after the lead frame is connected to the 7 rungs.

FIG. 5 is a top view showing the lead frame 20, which is made of, for example, phosphor bronze with a thickness of 0.25 m with appropriate elasticity.
+n Each electronic device consists of a strip-shaped metal plate with a length of 30+ ntn, which is photo-processed and then etched using a corrosion-resistant mask formed using the so-called photo-etching technology and press-forming processing technology. It depends on how you make it. Another method is to use press punching and press molding techniques. In any case, as in the case of the 7-run system, if, for example, 10 electronic devices are to be manufactured in series, it is necessary to manufacture such a lead frame in which 10 pieces are connected in series. When using photo-etching technology, the series of frames mentioned above can be made simultaneously in one process, and the press molding process can also be performed in one process, but in press punching and press forming technology, the press mold is Since this would be complicated, it is preferable to use multiple press dies and simultaneously punch in one press to create a series of frames by continuously punching with one set of press dies, without performing two processes.

In the figure, 21a indicates a lead part (internal lead part) located in the sealed body (the part surrounded by 2. dashed line 15 in the figure), which will be explained later, and its tip is at position 8 with the element numbering. It is preferable to form it so that it almost coincides with the outer periphery of. Reference numeral 21b indicates a lead portion (external lead portion) led out to the outside of the sealed body. What is noteworthy here is that the lengths of the external lead portions are alternately different, and that the outer frame (20b) of the frame 20
Those not connected to (2lb,, 2 lb3
．． 2 lb,) connected to (21b2.21
b4). The reason why the lengths of the external lead portions are alternately made different is to obtain an electronic device in which the leads are bent to form two rows of lead arrangement groups having approximately the same height, as will be described later. External lead part 21b2.2 lb,
The tip is connected to the outer frame 20b to prevent the tip from being bent during assembly. On the other hand, the external lead part 21+
),, 21b3. The tip of 21bs is a free end, but the lead length is short and the external lead part 2 lb2.
Since it is surrounded by 211114 etc., its tip is difficult to bend. Therefore, it becomes easier to automate the assembly of electronic devices using this lead frame.

Between the many external lead parts 21b, there is a lead frame 2.
The lead holding portion 22a constitutes a part of the lead holding portion 22a.

22b (generally referred to as 22), and the position of the lead holding part 22 is at least the outer lead part 2.
1b may be formed anywhere or in its entirety, but for the purpose of mechanically holding the internal lead portion 21a, 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. Further, in this example, the external lead portion 21b has a shape as a lead wire, and there are two lead holding portions 22&.

The lead frame 20 has different widths 22b.
This is to make the front and back sides clear at a glance, and to make the wider side 22b constitute a part of the 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. 2
0 to surround the external lead portion 21b, thereby preventing unnecessary deformation of the lead portion 21b during each process until the device is completed and during transportation between each process.

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 to form a tab lead 25, and this tab lead 25 has a constant distance between the tab lead 25a for connecting to the 7 flange 1, the main surface of the 7 flange 1, and the main surface of the lead frame. In particular, it is important to maintain a constant positional relationship between the tab lead 25a and the internal lead portion 21a in order to align the element mounting position of the 7 flange 1. As shown in FIG. 6, cut holes 24 forming the outline are formed at the same time as the photo-etching process used to form the internal lead portion 21a, and their positional relationship is defined constant, and then the portion to be made into a tab lead is formed by press molding. Just fold 25. Furthermore, as another method, the inner lead portion 21a and the tab lead 25 are simultaneously or sequentially formed by press punching and press molding techniques.
All you have to do is form. Such lead frames are plated with silver to a thickness of, for example, 1 μm or more for the purpose of increasing the sorgability of the lead wires, improving the wire bonding connection between the element lead frames described later, and preventing corrosion. . Such silver plating treatment may be performed immediately after etching when photoetching is used or after press molding, and may be performed either before or after pressing when all is performed 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 tab lead 25a (
1 and the center 27 of the internal lead portion 2ia group (coinciding with the center of the element mounting position 8).
It is important that the distance W in the length direction on the 0 plane does not change at all before and after bending the tab 25a, so that an extremely highly accurate positional relationship can be maintained. In principle, the basic purpose of the tab lead 25a can be achieved if there is only one tab lead 25a for a series of lead frames.

FIGS. 7 and 8 are enlarged perspective views showing the tab lead forming portion of the lead frame 20, and B-B thereof.
A pair of tab leads 25 that are symmetrical with respect to two base lines perpendicular to the main surface 28 of the lead frame 20 in a vertical cross-sectional view.
a to prevent positional deviation in the 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° and sufficiently smaller than 180°, and this and the elasticity of the lead frame 20 facilitate the connection with the 7 langes 1. It can be made strong. The tip of the tab lead 25a is further bent outward, but this is to further strengthen the connection with the 7 flange 1, and the tip of the tab lead 25a is inserted into the pair of tab lead insertion holes in the 7 flange 1. 1 approximately in the center of each of 4
If the lead frame 20 is placed vertically, connection of the lead frame 20 to the 7-lunge 1 becomes extremely easy. As for the material when elasticity is used as described above, in addition to phosphor bronze, Kovar, iron-nickel alloy, nickel, etc. can be used. Although the tab lead 25b does not necessarily need to be formed in the same part as the tab lead 25a, it is more effective to form the tab lead 25b in the same part in order to simplify the press molding die.
It is effective to form the tab lead 25a on both sides of the tab lead 25a integrally with it in order to reinforce the internal lead portion 21a and the like so that the stress generated when crimping the tab lead 5a to the flange 1 does not reach the internal lead portion 21a. Furthermore, as another method for controlling the distance between the lead frame 20 and the 7 langes, a jig that is placed flat under the 7 langes and in close contact with the 7 langes is placed, and the tip of the tab lead 25a is placed against the surface of the jig. There is a way to make it so that they touch each other.

The tab lead 2Sa of the lead frame 20 obtained as described above is inserted into the tab lead insertion portion 4 of the seven flange 1 to which the element 13 is attached. This time, tab lead 251
) is in contact with the upper surface of the 7 langes, and defines a constant interval between the 7 lunge lid frames. On the other hand, the tab lead 2 at the same height as the tip of the tab lead 25b of the lead frame.
The width 31 of the tab lead insertion part 4 should be approximately the same as the length 16 of the tab lead insertion part 4, and the difference should be determined within the allowable value between the tip of the internal lead part 21a of the lead frame 20 and the element mounting position 8. Therefore, it is preferable to make the width of the tip of the tab lead 25a sufficiently smaller than that width so that the tab lead 25a can be smoothly inserted into the tab lead insertion part 4. When the lead frames 20 and 7 lunges 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 alignment as described above, pressure is applied in the direction shown by arrow 6 in FIG. 1 to deform tab lead holding portion 5 and fix the tab lead within slit 4. At this time, as shown in the cross-sectional view of FIG. 9, the tab lead 25a comes into contact with the upper and lower parts of the slit due to the pressure in the direction of the arrow 6, and is further pressurized. The contact will be extremely strong.

FIG. 10 is a top view of the main parts showing the state in which the above-mentioned tab lead 25a is caulked in the slit 4. Here, it is important to pay attention to only the central part of the tab lead 2Sa, that is, the tip of the tab lead holding part 5 in this example. After sealing, the slit 4 is cut by 7 lunges only at the center of the slit 4 where the slit 4 is crimped. By reducing b, the width that can be cut can be greatly increased.

FIG. 11 shows an example of electrically connecting the electrode terminal located on the surface of the element 13 and the internal lead portion 21a by wire bonding. In the drawing, 32 is a connector wire made of gold, aluminum, etc. with a diameter of about 50 μΦ, and the material is the electrode terminal and the internal lead part 21a.
Various choices can be made depending on the tip surface material and connection technology. For example, if the electrode terminal is aluminum, the internal lead terminal 2
If the tip surface material of 1a is silver and the connection technique is thermocompression bonding, gold is suitable, and if ultrasonic welding is used, aluminum is suitable. In the above-mentioned external wire bonding, it is necessary to apply some pressure when connecting 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, it is necessary to heat the tip of the internal lead portion 21a and the element electrode to about 350°C, and it is also desirable to heat the core part to about 100°C in ultrasonic welding. For this purpose, as shown in FIGS. 11(a) and 11(b), a metal spacer 33 with good thermal conductivity such as iron or copper is inserted from a direction perpendicular to the length direction of the 7 flange, and removed after bonding. Just do it. At this time, if the metal spacer 33 is heated, the internal lead portion 21a
can also be heated directly. In addition, in Fig. 12, an insulating spacer such as a ceramic ring is positioned and interposed with a silver foil 10 before connecting the 7 langes 1 and the lead frame, and is left in place even after completion. be. In either case, the heating can be easily carried out by using the seven-lunge mounting table 34 as the heating element, so the spacer 33 is made of metal or alumina ceramics with good thermal conductivity.

An insulator with good thermal conductivity, such as beryllia porcelain, is preferred.

According to still another example, the connector wire 32 is connected to the electrode terminal by the capillary 35, and then, as shown in FIG. Connect the connector wire by bringing the tip into contact with the 7 flange 1 or silver foil to heat the core, and then use the elasticity of the internal lead part 21a to return it to the original position as shown in FIG. 13(b). This can be done by restoring it. 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 211) returns to its original position, as shown in FIG. 13(b). In this case, the connector wires 32 are provided with sufficient deflection and connected as shown in FIG. 13(a).

Alternatively, the connector wire 32 may be connected to the internal lead portion 21a first, and after the internal lead portion 21a returns to its original position, the connector wire may be connected to the electrode terminal of the element 13.

Next, the assembly completed as described above is placed in a mold, and as shown in FIGS.
Resin injection pipeline (liner) 3 with bottom 2b
6, inject a sealant such as resin, and after the resin has solidified, remove the molding jig and remove the lead holding part 2.
2 and the tip of the external lead part 21b is the lead frame 2.
If it is in contact with 0, the core part is also cut, and the structure shown in Fig. 15 is obtained by cutting the 7 langes 1 for each device as described above. As shown in the figure, it is possible to create a structure in which the lead portion 21 can be easily inserted into the hole of the printed circuit board.

That is, as shown in FIG. 16, the external lead portions 21 introduced from the sealing material (sealing body) 37 are bent in a row close to the sealing body 37. It consists of one lead group and a second lead group forming another row that is bent away from the sealing body 37 between the leads forming the first lead group. From this,
Since the lead spacing is substantially large enough and stable, mounting on a printed circuit board (not shown) is facilitated. Further, it brings about excellent effects such as being able to prevent short circuits between leads during mounting.

[Brief explanation of drawings]

Figure 1 is a top view showing the 7 langes, Figure 2 is a sectional view of the A-A section in Figure 1, and Figure 3 is a state in which a nickel coating is formed on the 7 langes in Figure 2 and silver foil is connected. Figure 4 is a vertical cross-sectional view showing the state in which electronic elements are connected to the seven lunges shown in Figure 3, Figure 5 is a top view showing the lead frame, and Figure 6 is the manufacturing of the lead frame. Enlarged view showing part of the lead frame in one process, No. 7
8 and 8 are respectively an enlarged perspective view and a vertical sectional view taken along the line B-B of the lead frame, and FIGS. 9 and 10 are sectional views showing the state of connection between the lead frame and the 7 langes, respectively. 11(,) is a plan view showing the electrical connection between the lead frame and the element, FIG. 11(1), FIG. 12, and FIG. 13() are top views.
Both a) and (b) are cross-sectional views showing the electrical connection between the lead frame and the element, and Fig. 14 (a)
, (b) are a top view and a side sectional view showing the position of the resin injection pipeline, respectively, FIG. 15 is a perspective view showing an example of a completed electronic device, and FIG. 16 is a completed electronic device. FIG. 2 is a perspective view showing an example of a pond. 1: 7 run body, 2: Notch for preventing mold material flow, 3: Bolt through hole, 4: Tab lead insertion part, 5:
Tab lead holding part, 6: Direction of pressure applied to the tab lead holding part, 7: Groove indicating the position of the element mounting, 8: Position of the element mounting, 9: Nickel coating, 10: Silver foil, 11:
Electrode for electric welding, 12: Electrode for electric welding, 13: Electronic element, 14: Gold-silicon eutectic brazing filler metal, 15: Boundary line of sealing body, 16: Length of tab insertion part, 20: Lead frame, 21: Lead wire, 21a: Internal lead part, 21b
l, 2 lb2.2 lb,, 2 lb,, 21
b5: External 1 node part, 22: Lead holding part, 22a:
Narrow lead holding part, 22b 2 Wide lead holding part, 23; Id hole, 24: Cut hole for tab formation, 2
5: Tab lead, 26: Tab lead side end, 27: Center of internal lead group, 28: Life surface of lead frame, 2
9: One base line perpendicular to the life surface of the lead frame, 30
: Angle between lead frame and tab lead, 31: Width of tab lead 25a, 32: Connector wire, 33 Varnish spacer, 34: 7 Runno mounting table, 35: Capillary, 36
: Resin injection pipeline, 37: Sealing material such as resin. Fig. 1 6 Fig. 4 Fig. 5 Fig. 7 Fig. 9 Fig. 0 Fig. 11 Fig. 12 Fig. 13 Fig. 14 Fig. 0 322- Fig. 14 (b) Fig. 15 1 3W 21

Claims (1)

[Claims] 1. A lead frame for an electronic device having a plurality of external lead parts, the lead parts having their tips connected to the frame part and the ends not connected to the frame part.