JPH11289041A - Manufacture of multilayer lead frame - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify a manufacturing process of a multilayer lead frame and remarkably reduce the manufacturing cost. SOLUTION: In this manufacturing method, a second lead frame 2b is laminated on a first lead frame 2a, and four portions of a linked strip belt 7 is compressed and worked to be 50%, thereby bonding them. In the first frame 2a, a die pad 3 is formed in a region surrounded by the linked strip belt 7 via a suspension lead 6. In the second frame 2b, an inner lead 4 and an outer lead 5 are formed in the region surrounded by the linked strip belt 7. The two frames are composed of copper material, and nickel, palladium and a very thin gold plating film are previously formed in order.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a multilayer lead frame in which a plurality of lead frames are overlapped and bonded.

[0002]

2. Description of the Related Art Usually, a lead frame for a semiconductor device is manufactured by punching a single metal plate into a predetermined shape by press working. FIG. 3 is a plan view of a general lead frame. A die pad 3 on which a semiconductor element (not shown) is mounted in a region surrounded by a connecting strip 7, and a suspension lead 6 for connecting the die pad 3 to the connecting strip 7. And an inner lead 4 extending near the die pad 3 and connected to the semiconductor element, and an outer lead 5 connected to the inner lead 4 and mounted on a printed circuit board or the like.

[0003] In recent years, various multilayer lead frames in which a plurality of lead frames are stacked have been used. FIG. 4 (a)
(D) is an explanatory view showing an example of a conventional multilayer lead frame. FIG. 4A is a plan view of the multilayer lead frame, which has the same configuration as the lead frame 1 made of a single metal plate described with reference to FIG. 4, outer leads 5 and the like. This multilayer lead frame 2 has a first frame 2 a in which a die pad 3 is formed via a suspension lead 6 in a region surrounded by a connecting strip 7 shown in FIG.
And a second frame 2b provided with an inner lead 4 and an outer lead 5 in a region surrounded by a connecting strip 7 shown in FIG. 4D, the second frame 2b is superimposed on the first frame 2a, and the adhesive 11
, And the two are joined together.

One of the reasons for using such a multilayer lead frame is to increase the number of pins in the lead. In forming a lead frame by stamping a metal veneer by pressing, the pitch between inner leads is narrowed by the space required for punching the suspension leads, and the number of pins cannot be increased. Therefore, the above problem can be solved by forming the die pad and the inner lead in separate frames and using a multilayer lead frame in which both are joined.

[0005] In addition, as lead frames have become smaller and more diversified, each time various lead frames having different numbers or arrangements of leads are formed, expensive large precision dies must be newly prepared. The cost of the frame increases. For this reason, it is possible to reduce the cost of the lead frame by preparing frames with various numbers and arrangements of leads and selecting these appropriately and combining them with another frame on which a die pad is formed.

[0006]

As the adhesive for joining the two lead frames described above, a film having an adhesive layer on both surfaces is used. However, such a film is expensive in itself, and also requires a step of attaching the film to a lead frame, so that there is a problem that the cost of the multilayer lead frame is increased.

[0007] In addition, a method of joining two lead frames by welding is sometimes used. However, in the case of a material having a high conductivity such as a copper-based material, a splash occurs during welding and a lead frame is formed. There are problems such as lower quality.

An object of the present invention is to solve the above-mentioned problem and to provide a method for manufacturing a multilayer lead frame which can easily and inexpensively join a plurality of lead frames without using an adhesive. And

[0009]

SUMMARY OF THE INVENTION The present invention is a method for manufacturing a multi-layer lead frame in which a plurality of lead frames are overlapped, a predetermined area is joined by compression working, and the plurality of lead frames are integrated.

[0010] A metal joining method called a cold pressure welding method in which the overlap of ductile metal materials is compressed at room temperature and the boundary surface is locally plastically deformed to join the metal materials together is called a cold welding method.
It is based on the principle that the free electrons of a metal atom become common and metal bonding is performed when the distance is approached. In order to perform a good cold pressure welding, two factors are important: a pressure for increasing the contact area, and two pure metals having no formed film on the surface.

According to the present invention, the compression processing is performed to 30% to 60% of the superposed thickness of the lead frame, and a sufficient pressure is applied to the cold welding to obtain good metal bonding.

According to the present invention, a metal plating film is formed on a plurality of lead frames in advance. When the compression processing is performed with the surfaces on which the metal plating films are formed facing each other, the metal plating film breaks and a clean new surface without an oxide film appears, so that good cold welding can be performed.
The metal plating film preferably has less ductility than the material metal. For example, when the material metal is a copper material, nickel, gold, silver, palladium, or the like may be plated.

Further, in the present invention, it is desirable that the region to be subjected to the compression working includes a side surface of the metal material or a region whose cross section is exposed. When the two lead frames are overlapped and the side or cross-section exposed area is compressed, the upper lead frame digs into the lower lead frame, and the metal is integrated at that part, thus making the two lead frames more Can be firmly joined. For this reason, the larger the compression area, the higher the bonding strength. If the surface area is constant, the larger the cross-sectional area, the higher the bonding strength. By providing a through-hole in the portion to expose the cross section and compressing this portion, the joining strength can be further increased.

More specifically, the present invention provides a first lead frame having a die pad and a suspension lead for supporting the die pad, and a second lead frame having an inner lead and an outer lead. The lead frames are overlapped at a predetermined position, and a part of the connecting strip that is cut off in a later step is compressed in the overlapped area, so that the two lead frames are integrated in the compressed area. It becomes something.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIGS. 1A to 1E are explanatory views showing a method for manufacturing a multilayer lead frame according to the present embodiment. First, a first frame 2a in which a die pad 3 is formed via a suspension lead 6 in a region surrounded by a connecting strip 7 shown in FIG. 1A and a connecting strip 7 shown in FIG. A second frame 2b in which the inner lead 4 and the outer lead 5 are formed in the set area is prepared. These two frames are formed by punching a copper material having a thickness of 0.25 mm by press working, and nickel, palladium, and a very thin gold plating film are sequentially formed on the surfaces thereof.

Next, as shown in FIG. 1C, the second frame 2b is overlaid on the first frame 2a and set in a mold (not shown). In this state, connecting strip 7
Are compressed by the punch 31 at four locations (only two locations shown). The compression ratio is desirably 30% to 60%, and in this embodiment, the compression processing is performed to 50%.

FIG. 1D is a plan view of the multilayer lead frame manufactured as described above. The connecting strip 7 has four compression regions 12 at which the first frame and the second frame are joined.

Thereafter, as shown in FIG. 1E, the semiconductor element 21 is mounted on the die pad 3 of the multilayer lead frame 2, and the semiconductor element 21 and the inner lead 4 are connected by bonding wires 22. After these are sealed with the resin 23, unnecessary portions of the multilayer lead frame 2, that is, the connecting strips 7 are cut off, and the semiconductor device is completed.

In the present embodiment, a two-layer lead frame in which the first and second frames are joined has been described. However, the present invention can be applied to joining of three or more layers.

Although the lead frame is made of a copper material, the invention is not limited to this, and other metals such as an iron-nickel alloy and aluminum can be manufactured in the same manner. The same applies to the case where the first and second frames are made of different metal materials.

(Embodiment 2) As shown in FIG. 2A, a connecting strip 7 of a first frame 2a having a die pad 3 and a suspension lead 6 has a pair of semicircular through holes in advance. A joining auxiliary bar 14a is formed between 13 and 13 so as to be parallel to the longitudinal direction of the frame.
As in the case of the compression region 12 described in the first embodiment, the joining auxiliary bar 14a is formed at four locations on the connecting strip 7;
The illustration is omitted at the places.

On the other hand, as shown in FIG. 2 (b), the connecting strip 7 of the second frame 2b provided with the inner lead 4 and the outer lead 5 has a pair of halves at the same place as the first frame 2a. A joining auxiliary bar 14b was formed between the circular through holes 13 and 13. However, in the second frame 2b, the joining auxiliary bar 14b was formed so as to be perpendicular to the longitudinal direction of the frame.

As a result, when the first frame 2a and the second frame 2b are superimposed, as shown in the enlarged view of FIG.
a and 2b are overlapped so that the joining auxiliary bars 14a and 14b cross each other, and by compressing this portion, the second
Of the first joining auxiliary bar 14a can be sunk into the first joining auxiliary bar 14a, and a larger joining strength can be obtained.

[0025]

As described above, according to the present invention, 2
Two or more lead frames can be joined only by overlapping and compressing. Therefore, it is not necessary to use an adhesive, and the cost of the multilayer lead frame can be significantly reduced. In addition, the quality of the multilayer lead frame is stable because splash such as welding does not occur even in a metal such as copper.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a method for manufacturing a multilayer lead frame according to the present invention.

FIG. 2 is an explanatory view showing a method for manufacturing a multilayer lead frame according to another embodiment of the present invention.

FIG. 3 is a plan view of a general lead frame.

FIG. 4 is an explanatory view showing an example of a conventional multilayer lead frame.

[Description of Signs] 2 Multilayer lead frame 2a First frame 2b Second frame 3 Die pad 4 Inner lead 5 Outer lead 6 Suspended lead 7 Connecting strip 12 Compression region 13 Through hole 14a Joining assist bar 14b Join assist bar 31 Punch

Claims (6)

[Claims] 1. A method of manufacturing a multi-layer lead frame, comprising: stacking a plurality of lead frames; compressing a predetermined area of the lead frame; and joining the plurality of lead frames in the compressed area. Method. 2. The method for manufacturing a multilayer lead frame according to claim 1, wherein the region to be compressed is a region where the lead frame is separated after being assembled as a semiconductor device. 3. The method according to claim 1, wherein the region to be compressed is a region including a side surface or a cross section of the plurality of lead frames. 4. The method for manufacturing a multilayer lead frame according to claim 1, wherein said plurality of lead frames are compression-processed to 30% to 60% of a superposed thickness. 5. The method according to claim 1, wherein a metal plating film is formed on the plurality of lead frames in advance. 6. A first pad having a die pad and a suspension lead for supporting the die pad in a region surrounded by the connecting strip.
And a second frame provided with an inner lead and an outer lead in a region surrounded by the connecting strip, and the first frame and the second frame are overlapped with each other. A method for manufacturing a multilayer lead frame, comprising compressing a predetermined area to join the first frame and the second frame in the compressed area.