JPH0870087A - Lead frame - Google Patents

Abstract

PURPOSE: To restrain failure generation of a plastic molded semiconductor device, by preventing a lead frame from warping at the time of resin molding. CONSTITUTION: A tab 20 whose plane form is square is arranged in the central part, and tip parts of inner leads 22 are arranged on the periphery of the tab 20. Tab leads 26 stretching outward in the directions of the diagonal lines of the tab are formed in the four corners of the tab 20. Holes 28 penetrating the tab in the plane thickness direction are formed in the four corners of the tab 20. The hole 28 is formed so as to be bent outward along the two sides of each corner. Holes 30 penetrating the tab in the plate thickness direction are formed. The form of the hole 30 constitutes a rectangle stretching along the side of the tab 20. Two holes 30 are arranged along each side between the holes 28.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin-sealed lead frame for connecting semiconductor chips by a wire bonding method and sealing with a molding resin.

[0002]

2. Description of the Related Art Generally, a resin-sealed lead frame has a shape in which a tab is provided in the center and a plurality of leads are arranged around the tab. A semiconductor chip is fixed on the tab, and a pad of the semiconductor chip After the leads are electrically connected by wires, a part of the leads, the semiconductor chip and the tab are used so as to be sealed with a molding resin. As the lead frame is highly integrated, the power consumption of the semiconductor chip tends to increase, and the chip size tends to increase. Therefore, as a material of the lead frame, a transition to a copper-based material, which has a better heat dissipation characteristic than an iron-based material, is being promoted. Copper-based materials have about 10 times better thermal conductivity than iron-based materials, but have a thermal expansion coefficient of about 4
It has the characteristic of being twice as large.

[0003]

A semiconductor chip is fixed to a tab of a lead frame, an electrode pad of the semiconductor chip and an inner lead of the lead frame are electrically connected by a gold wire, and then a semiconductor chip is molded by a mold resin. The tab and the inner lead portion are sealed. The resin sealing step is performed by inserting a lead frame having a semiconductor chip mounted therein into a molding die and injecting a molding resin into the die.

FIG. 1 schematically shows the resin sealing process. As shown in (A), the lead frame 6 on which the semiconductor chip 4 is mounted is placed on the lower mold 2 of the molding die. At this time, the frame portion 6a of the lead frame 6 comes into contact with the mold 2,
The tab portion 6b to which the chip 4 is fixed is located in the space of the mold. Since the mold die is heated to about 180 ° C., the frame portion 6a is heated by the die 2 and its temperature rises, and a temperature difference occurs between the tab portion 6b and the frame portion 6a in the lead frame, and the lead frame 6 warps.

Thereafter, as shown in (B), when the upper die 8 of the molding die is pressed from above the lead frame 6 so as to cover the lower die 2, and the die is tightened, warping due to the temperature distribution in the lead frame 6 causes The tab portion 6b is warped in the direction opposite to (A). In that state, when the mold resin 10 is injected into the spaces of the molds 2 and 8 as in (C), the flow balance of the mold resin 10 is disturbed by the lead frame in which the tab portion 6b is raised or lowered, and the tab portion 6b is raised or lowered. Will be even larger. In particular, in the case of a package having a thin mold resin layer, there is a problem that a semiconductor chip is exposed from the package surface or a tab back surface is exposed on the back surface side of the package. In particular, such a problem tends to occur when a copper-based material having a large thermal expansion coefficient is used as the material of the lead frame.

It is an object of the present invention to prevent the lead frame from warping when a semiconductor chip mounted on a lead frame is resin-sealed, and to suppress the occurrence of defects in the resin-sealed semiconductor device.

[0007]

The lead frame of the present invention is made of a copper material, has tabs of rectangular shape, and has four corners bent outwardly at right angles along two sides of each corner.
A hole is formed through the tab in the plate thickness direction. Further, it is preferable that one or more holes are formed along each side of the tab and between the holes at the corners and parallel to the side. In another aspect, the tab is provided with a plurality of outwardly extending tab leads, and a connecting portion between the tab lead and the tab is bifurcated so as to expand outward and form a hole inside.

In still another aspect, the tab is divided into four parts by cross-shaped grooves, and each divided part is provided with a tab lead extending outward. It is preferable that the divided four portions are connected by a connecting portion having a bent shape. Various copper-based lead frame materials are commercially available. For example, T
CZ (product of Toshiba Corporation), KLF-125 (product of Kobe Steel, Ltd.), MF202 (product of Mitsubishi Electric Corporation), EFTEC64T (product of Furukawa Electric Co., Ltd.), CDA7025 (product of Yamaha OLIN Corporation) Products), TAMAC15 (product of Mitsubishi Shindoh Co., Ltd.) and the like. All of these are alloys containing copper as a main component and containing Ti, Cr, Zr, Sn, Ni, P, Mg and the like.

[0009]

Embodiment 1 FIG. 2A shows an embodiment 1 corresponding to claim 1.
It shows a portion related to two semiconductor chips. A tab 20 having a square planar shape is arranged in the center, and the tip portions of the inner leads 22 are arranged around the tab 20. Tab leads 26 are provided at four corners of the tab 20 and extend outward in a diagonal direction of the tab. The inner leads 22 and the tab leads 26 are integrally connected by dams 24.

Holes 28 penetrating in the plate thickness direction are formed at four corners of the tab 20, and the holes 28 are formed in a shape bent outward along two sides of each corner. Due to the holes 28, when the lead frame is mounted in the molding die as shown in FIG. 1, the uneven heat of the tab 20 and the tab lead 26 due to the uneven temperature in the lead frame is caused. The hole 28 absorbs the expansion,
Prevents tabs from floating and sinking when molding resin is injected into the mold.

When the semiconductor chip 4 is mounted using this lead frame, the semiconductor chip 4 is die-bonded to the central portion of the tab 20 and the electrode pad of the semiconductor chip 4 and the inner lead 22 are connected by a gold wire. To be done. After that, the lead frame on which the semiconductor chip is mounted is put into a molding die, and a molding resin is injected into the die, whereby a part of the lead 22 and the semiconductor chip 4 are inserted.
Also, the tab 20 is sealed with the mold resin. After that, the lead 22 and the tab lead 26 are separated so as to be independent from each other.

FIG. 2 (B) shows an embodiment corresponding to claim 2. As compared with the embodiment of FIG. 2A, in the tab 20, the hole 3 further penetrating in the plate thickness direction.
0, the shape of the hole 30 is a rectangle extending in the direction along the side of the tab 20, and the hole 28 is formed along each side.
And 28 are arranged between the two. By increasing the holes around the tab as shown in (B), it becomes possible to more effectively absorb the uneven thermal expansion of the tab 20 and the tab lead 26 during molding.

FIG. 3 shows an embodiment corresponding to claim 3. The connecting portion between the tab 20 and the tab lead 26 extending from the four corners of the tab 20 outward in the diagonal direction of the tab is bifurcated so as to spread outward by the branch portions 26a and 26b to form a hole inside. Tab lead 26
Because the connection part with the tab 20 of is bifurcated,
The uneven thermal expansion of the tab 20 and the tab lead 26 at the time of molding can be absorbed. The tab 20 is shown in FIG.
Alternatively, holes 28, 30 as shown in (B) may be drilled. In that case, non-uniform thermal expansion during molding can be more effectively absorbed.

FIG. 4 (A) shows an embodiment corresponding to claim 4. The tab is divided into four parts 20-1 to 20-4 by a groove 32 intersecting in a cross shape, and each divided part 20-1 to 20-4 has a tab lead 26 extending outward in the diagonal direction of the tab. Each is provided. In this way, by dividing the tab into a plurality of parts, it is possible to absorb uneven thermal expansion during molding.

Further, by dividing the tabs, the area of each tab is reduced, and package cracks are less likely to occur when the tabs are mounted on the substrate by solder reflow after molding. Package cracks are more likely to occur as the tab area is larger, and in the structure of FIG. 4A, the area of each of the divided tab portions 20-1 to 20-4 is reduced to 1/4 of the original tab 20. As a result, the resistance to package cracks increases. Further, by dividing the tab, it is possible to absorb the difference in thermal expansion between the tab and the semiconductor chip, and it is possible to suppress the occurrence of cracking of the semiconductor chip when the semiconductor chip is mounted on the tab.

FIG. 4B shows an embodiment corresponding to claim 5, and a bar shape in which each tab portion 20-1 to 20-4 of the embodiment of FIG. 4A is bent. Connection part 3
It has a structure that is connected by 4. In addition to the effect of the embodiment of FIG. 4 (A) due to the division of the tabs, the tab portions 20-1 to 20-2 each divided by the bent connecting portion 34.
The effect that the stability of 0-4 is ensured can be achieved.

In the diagram showing the process of FIG. 1, the lead frame 6 having the IC chip 4 mounted thereon is placed on the lower die 2 of the molding die, and then the standing time until the upper die 8 of the molding die is covered, The relationship with the floating amount of the tab is shown in FIG. In the case of a conventional copper alloy lead frame in which a tab is not provided with a means for absorbing thermal expansion as a lead frame, FIG.
The case b of the lead frame according to the embodiment of the present invention shown in FIG. In either case, after placing the lead frame 6 on the lower mold 2 as shown in FIG.
The longer it takes to place, the smaller the temperature nonuniformity in the lead frame and the less the floating amount. Further, it can be seen that the crack floating amount becomes smaller over the entire leaving time on the lower mold 2 of the molding die according to the present invention. Similar results could be obtained with lead frames of other examples.

[0018]

According to the present invention, the tab is provided with means such as forming holes through the four corners of the tab in the plate thickness direction, dividing the tab, and bifurcating the connecting portion between the tab lead and the tab. This makes it possible to absorb uneven thermal expansion of the tabs and tab leads due to heat applied from the mold to the lead frame during molding, and suppress the amount of tab ups and downs during molding. In addition, the holes provided in the peripheral portion of the tab have the effect of improving the adhesion between the mold resin and the tab, and preventing separation of the tab and resin after molding. Further, the present invention in which the tab is divided into several parts also has an effect of preventing cracks or breakage of the semiconductor chip due to a difference in thermal expansion between the tab and the LSI chip when the semiconductor chip is mounted on the tab. When the tab is divided, there is also an effect that the strength of the tab can be improved by connecting the divided tab portions with a bent connecting portion. Further, when the tabs are divided, the area of the tabs becomes small, and it is also effective in suppressing the occurrence of package cracks in the hand reflow process when mounting the molded semiconductor device on the printed circuit board.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a molding process.

FIGS. 2A and 2B are plan views showing one chip of a lead frame in each example.

FIG. 3 is a plan view showing one chip of a lead frame in another embodiment.

4A and 4B are plan views showing one chip of a lead frame in still another embodiment, respectively.

FIG. 5 is a diagram showing the relationship between the tab floating amount and the time from placing the lead frame on the lower die of the molding die to covering the upper die during molding.

[Explanation of symbols]

20 tabs 20-1 to 20-4 divided tab portion 22 inner lead 24 dam 26 tab lead 28, 30 hole formed in tab 26a, 26b bifurcated portion for connecting the connecting portion between the tab lead and the tab 32 tab divided Groove 34 Connecting part for connecting divided tab parts

Claims (5)

[Claims] 1. A tab is provided at the center, and a plurality of leads are arranged around the tab. A semiconductor chip is fixed on the tab, and a wire is electrically connected between the pad and the lead of the semiconductor chip. In the lead frame in which a part of the lead, the semiconductor chip and the tab are sealed by the molding resin after being connected, the material is copper, the tab is rectangular, and the four corners are along two sides of each corner. A lead frame having a shape bent at a right angle to the outside and having a hole penetrating in the plate thickness direction of the tab. 2. The lead frame according to claim 1, wherein the tab has one or more holes extending along each side and between the holes and parallel to the side. 3. The tab is provided with a plurality of outwardly extending tab leads, and a connecting portion between the tab leads and the tab is bifurcated so as to extend outward and form a hole inward. Item 1 The lead frame described in item 2. 4. A tab is formed in the center, and a plurality of leads are arranged around the tab. A semiconductor chip is fixed on the tab, and a wire is electrically connected between the pad and the lead of the semiconductor chip. In the lead frame in which a part of the lead, the semiconductor chip and the tab are sealed by the molding resin after being connected, the tab is divided into four parts by the grooves intersecting in a cross shape, and each part is divided into external parts. A lead frame having tab leads extending in the direction. 5. The lead frame according to claim 4, wherein the four divided portions are connected by a connecting portion having a bent shape.