JPH0629448A - Lead frame and semiconductor device - Google Patents

Abstract

(57) [Summary] [Structure] A through hole 2 is formed in the tab 1. The through hole 2 is formed such that the thinned portion 17 of the tab is formed on the element mounting surface side, and this serves as a locking portion within the thickness of the sealing resin. An element is mounted on the upper surface of this tab and sealed with a resin portion 5. [Effect] Since the distance for restraining the resin portion 5 below the tab 1 when the tab 1 and the resin portion 5 are peeled off is reduced, the stress of the resin portion 5 due to the pressure of water vapor is reduced, and reflow cracks are prevented. You can

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lead frame and a semiconductor device, and more particularly to a lead frame and a semiconductor device suitable for preventing resin cracks due to heating during reflow soldering.

[0002]

2. Description of the Related Art In a resin-sealed type semiconductor device, a surface mounting type in which a lead is directly soldered to a substrate is becoming the mainstream instead of the conventional pin insertion type. In such a package, when stored in a high temperature and high humidity environment, the resin absorbs moisture, and when the solder is heated (during reflow), the moisture is a tab (an element mounting portion; the same applies to the present application hereinafter) and a resin. Vapor is generated at the interface with the part, and cracks are likely to occur in the corners on the lower surface of the tab. This crack is commonly called a reflow crack because it occurs during solder reflow.

As a conventional technique for preventing such reflow cracks, there is a method of making holes on the back surface of the package and allowing the generated vapor to escape, as described in JP-A-60-208847.

As a technique for improving the adhesive strength at the interface between the resin portion and the tab and preventing the clearance, the anti-element mounting surface of the tab (the surface that contacts the back surface of the element mounting side surface; the same applies hereinafter) is uneven. As a method for providing, Japanese Patent Laid-Open No. 58-1995
No. 48, No. 60-186044, the same as the technique shown in FIGS.
There are techniques described in Japanese Patent No. 16357 and Japanese Utility Model Laid-Open No. 60-118252.

[0005]

Of the above-mentioned conventional techniques,
The method of making holes in the lower surface of the package prevents reflow cracks, but creates moisture passages inside and outside the package, which may lead to corrosion of the chip electrodes.

Further, although the method of providing a simple unevenness on the anti-element mounting surface of the tab has the effect of restraining the displacement in the bonding surface between the tab and the resin portion, the displacement in the direction of separating the tab and The resin part that entered can be easily removed, so no effect can be expected.

When the resin-sealed semiconductor is reflow-soldered, the water contained in the resin is vaporized, and this vapor pressure acts as a void in the tab-resin interface or a non-bonded portion. , The tab-resin interface is peeled off. Even if the pores become large due to the progress of peeling, the surrounding moisture is supplied by diffusion, as a result, the pressure in the pores is not relaxed, the resin part deforms, and cracks start from the point where the maximum stress occurs at the tab end. (See crack 10 in FIG. 6).

The above-mentioned Japanese Patent Laid-Open No. 59-16357 discloses a technique of removing a part of the tab and filling the part with resin. By using this technique to prevent peeling due to thermal stress and equivalently increase the thickness of the resin portion, the moisture resistance can be improved to some extent. But,
Due to the vapor pressure generated during reflow soldering, the resin part is deformed when it is separated from the tab, and the stress at the point of maximum stress is not much different from when the tab is partially removed. The effect of cracking the resin portion during soldering is not sufficient.

The technique disclosed in Japanese Utility Model Laid-Open No. 60-118252 discloses a structure in which the through hole for locking the sealing resin widens from the back surface side to the front surface side. However, in such a simple structure. It is difficult to securely lock the resin within the plate thickness of the through hole.

An object of the present invention is to prevent reflow cracks caused by vapor pressure.

[0011]

The above object is to provide a through hole having a special shape in the tab, and the resin portion is constrained to the tab by this hole so that the resin portion of the lower corner portion of the tab where reflow crack occurs This is achieved by reducing the stress generated.

In order to prevent resin cracks during reflow soldering, it is necessary to prevent a large stress from being generated at the maximum stress generating portion at the tab end even if the resin portion and the tab are separated. This requirement can be achieved by a structure that can prevent the deformation of the resin portion even when the adhesive force between the resin portion and the tab is lost, that is, a locking structure in which the resin portion does not come out of the tab due to vapor pressure.

The invention of the first lead frame of the present application is as follows.
In a lead frame including a tab on which a semiconductor element is mounted and a lead group integrally connected to the tab around the tab, a through hole is formed at least just under the portion where the semiconductor element is mounted on the entire tab surface. And the through hole is formed with a constricted portion or a stepped portion so that the sealing resin does not escape within the thickness of the tab.

A second semiconductor device invention of the present application is to provide a semiconductor element, a tab for mounting the semiconductor element, a lead group arranged around the tab, and an inner lead of the lead group. In a semiconductor device including a portion, a tab, and a resin portion that seals the semiconductor element, a through hole is formed at least immediately below a portion where the semiconductor element is mounted on the entire tab surface, and the through hole is within the tab thickness. So that the sealing resin does not come out,
Alternatively, it is characterized in that a stepped locking portion is formed.

A third semiconductor device invention of the present application is a semiconductor device, a tab on which the semiconductor device is mounted, a lead group arranged around the tab, and an inner lead of the lead group. In a semiconductor device including a portion, a tab, and a resin portion that seals the semiconductor element, a through hole is formed at least immediately below a portion where the semiconductor element is mounted on the entire tab surface, and the through hole is within the tab thickness. The locking portion is formed so that the sealing resin does not come out, and the outer lead end portion is a surface mounting type in which the outer lead end surface is mounted on the substrate.

The through hole may be, for example, a mode in which the tab is entirely inclined with respect to the plate thickness direction (having a taper part), a mode in which a constricted part is formed within the plate thickness of the tab, and the like. . Further, the opening area on the element mounting surface side is not limited to at least one portion of the tab that is larger than the opening area on the back side surface of the element mounting surface. It is effective if locked.

The area of the through hole on the element mounting surface side is preferably in the range of 24% or more of the area on the element mounting surface side of the tab to 80% or less of the bonding area of the tab and the element. It is preferable to provide a groove around the through hole.

[0018]

In order to roughly determine the stress in the resin portion of the bottom corner portion of the tab where reflow cracks occur, the resin portion under the tab is surrounded by a rectangular flat plate to which uniform pressure is applied as shown in FIG. It can be modeled as At this time, the maximum stress occurs in the center of the long side, and the value is given by the following equation (Equation 1).

[0019]

[Equation 1]

Here, β is a stress coefficient determined by the ratio of the length of the long side to the length of the short side, a is the length of the short side, h is the plate thickness, and p is the pressure of water vapor. As is clear from the equation (1), the generated stress increases with the square of the tab size a. Therefore, when the element size becomes large, solder reflow crack (10 in FIG. 6)
Is likely to occur. Therefore, in order to reduce the stress, the length of the short side may be shortened or the plate thickness may be increased.

However, increasing the plate thickness means that
This makes the package thicker, and cannot be applied to a thin package such as a flat package. In addition, the size of the tab cannot be made smaller than the size of the chip, and thus is determined by the chip size.

Therefore, in the present invention, a resin restraining portion is provided on a part of the tab and the peeled portion of the tab is divided. As a result, the effective tab size a is reduced, so that the stress in the resin portion is reduced and reflow cracking of the resin portion can be prevented.

[0023]

Embodiments of the lead frame and semiconductor device of the present invention will now be described with reference to the drawings along with their principles and comparative examples.

FIG. 1 is a perspective view of a simple lead frame having a taper-like through hole, and FIG. 2 is a sectional view of a surface-mounting type semiconductor device using the same.

Both ends of the tab 1 are suspended by tab suspension leads 3 and a through hole 2 is formed substantially at the center. As is clear from the cross section of FIG. 2, the through hole 2 gradually expands in the direction of the element 4 and gradually narrows on the side opposite to the element 4. In FIG. 2, reference numeral 5 is a resin portion, 6 is water vapor, and 7
Is a lead, 8 is a solder, and 9 is a substrate.

Water vapor 6 is generated at the interface between the tab 1 and the resin portion 5, and the pressure causes the resin portion 5 to swell. At this time, stress is generated in the resin portion 5 of the corner portion of the tab lower surface,
Since the through hole 2 of the tab 1 according to this example restrains the resin portion 5, as shown in a comparison between FIG. 2 and FIG. 6 (conventional view), a
The size is less than half that of conventional tabs. Therefore, the stress generated by the equation (1) can be reduced to a quarter or less, and reflow cracks can be prevented. However, in this example, it is difficult to securely lock and restrain the resin in the through hole, and the tape
Depending on the angle of the pad, there is a risk of contraction and the like, and there is a risk that it will come out. Therefore, the present invention has been devised as follows.

The first and second embodiments of the present invention are shown in FIG.
As shown in FIG. In the first embodiment, a portion having an area smaller than the area of the anti-element mounting surface of the through hole 2 is provided inside the through hole 2. Further, in the second embodiment, the through hole 2 is formed obliquely with respect to the tab 1. The inclination angle of the through hole with respect to the tab may be about 10 °. In both of the embodiments, the resin portion enters the through hole 2 and is restrained by the tab 1, so that the reflow crack can be surely prevented.

The planar shape of the through hole of the present invention does not have to be circular as shown in FIGS. 1 to 3, but may be elliptical, rectangular,
The cross shape has the same effect. Further, by providing a plurality of through holes so that the tab 1 does not impair the required rigidity, the effect can be further enhanced.

Stress σ generated in the resin portion that has entered the through hole
_h is represented by the equation (2).

[0030]

[Equation 2]

Here, A _t is the area of the tab and A _h is the minimum value of the area inside the hole. This stress is the fracture stress σ of the resin part
_If it exceeds _B , the resin portion will be destroyed, and therefore the equation (3) and therefore the equation (4) must be established.

[0032]

[Equation 3]

[0033]

[Equation 4]

Normally, during solder reflow, the package is heated to about 220 ° C., and the saturated vapor pressure of water at this temperature is 0.24 kgf / mm ² . Further, since the fracture stress of the resin portion at this temperature is about 1 kgf / mm ² , substituting these values into the equation (4) gives the equation (5).

[0035]

[Equation 5]

That is, it is desirable that the minimum area of the holes is 24% or more of the area of the tab. Further, if the through hole is excessively large, the rigidity of the tab is reduced, so that the chip mounting surface becomes uneven, and it becomes difficult to bond the chip and the tab. Further, during wire bonding, the heat applied from the surface of the tab opposite to the element mounting becomes difficult to be transferred to the chip. Therefore, there is an upper limit to the optimum size of the through hole, and according to the experiments and confirmation by the present inventors, the area of the through hole is preferably 80% or less of the mounted chip. The range of holes described above can be applied to each through hole as well as to the total number of through holes.

Next, a method of manufacturing a through hole according to the present invention will be described.

FIG. 7 shows a method of forming a through hole in a tab by a conventional etching technique. Etching patterns 14a and 14b of the same shape are adhered to both sides of the tab, and the etching solution 1
Immerse in 5. Since the etching proceeds from both sides of the tab, a hole having a slightly narrow central portion is formed as shown in FIG. However, in the conventional method, since the area inside the hole is almost uniform, even if the resin enters, it cannot be restricted. If the etching from both sides is stopped in the middle as in the process of FIG. 8, it is possible to form the constricted portion within the plate thickness depending on the degree of the treatment (concentration and time of the treatment liquid for etching). Lead frame according to example
It can also be used for the production of aluminum.

FIG. 9 shows a method of forming a through hole according to the first embodiment of the present invention. Etching pattern 14c on top of tab
The holes are larger than the holes in the etching pattern 14d on the lower surface. When immersed in the etching solution 15 in such a state,
Since the holes shown in FIG. 10 are formed, the first embodiment can be realized.

FIG. 11 shows a method of forming a through hole according to the second embodiment of the present invention. Etching patterns 14e, 14f
The holes have the same size but are out of position. Therefore,
As shown in FIG. 12, it is possible to realize a hole that is oblique to the tab, that is, the second embodiment.

FIG. 13 shows a method of realizing the present invention by pressing. First, according to a conventional technique, a through hole is formed in the tab, and a convex press die 16a is pressed on this portion. By this method, as shown in FIG. 14, a portion having an area larger than the area inside the hole on the anti-element mounting surface can be provided.

Next, a third embodiment of the present invention will be described with reference to FIGS.
6 will be described. The through hole of the tab is not a taper, but the element mounting surface has a larger hole diameter than the non-element mounting surface. Further, in the present embodiment, the thinned portion 17 is formed, and this becomes a stepped portion within the plate thickness to securely lock the sealing resin. Further, a plurality of holes are provided. Reference numeral 18 is a die bonding material.

FIG. 15 shows that the tab 1 is provided with a through hole 2 and
The reduced thickness portion 17 is provided on the upper portion of the tab 1 to form a stepped portion. According to this structure, the die bonding material 18
Although the space between the element 4 and the tab 1 is completely filled with, the resin portion 5 is filled in the upper portion of the tab. Reflow-tab 1 for soldering
Even if the resin part 5 is peeled off, the resin part 5 does not come out of the tab 1 because it is the resin part filled in the upper part of the tab, and the deformation due to the vapor pressure is as shown in FIG. Here, if the maximum width d of the tab remaining portion is set to be equal to or less than the value given by the following equation, no crack is generated in the resin portion.

[0044]

[Equation 6]

Here, K _IC is the fracture toughness value of the resin at the reflow temperature, and p is the vapor pressure generated during the reflow.

FIG. 17 shows another embodiment in which a plurality of through holes 2 are formed so as to spread upward and the same effect as above can be obtained. The through holes 2 may be circular, but the reinforcing effect is larger when the shape is close to a rectangle or an ellipse as shown in FIG.

Finally, a problem in implementing the present invention and a method for solving the problem will be described. FIG. 19 shows a state in which the adhesive 18 is applied to bond the element to the tab 1 of the present invention. FIG. 20 shows a state in which the element 4 is mounted and joined after the state of FIG. As shown in the figure, when the amount of the adhesive 18 is excessive, the adhesive 18 may flow out to the side surface of the through hole 2. In the state of FIG. 20,
If the resin part is molded after the adhesive is cured, peeling between the resin part and the adhesive is likely to occur, and the effect of the present invention may be lost.

To solve such a problem, FIG.
As shown in FIG. 5, an outflow prevention groove 19 for the adhesive 17 may be provided around the through hole on the element mounting surface of the tab 1. FIG. 22
Shows a state in which the element 4 is mounted on the tab 1 provided with the adhesive outflow prevention groove 19. As shown in the figure, the extra adhesive
Since it is retained in the groove 18, it does not flow out into the through hole.

[0049]

According to the present invention, when the tab and the resin portion are separated, the distance for restraining the resin portion under the tab is shortened, so that the stress of the resin portion due to the pressure of water vapor is reduced and reflow cracks are prevented. Can be prevented.

[Brief description of drawings]

FIG. 1 is a perspective view of a lead frame having a simple taper-shaped through hole.

FIG. 2 is a cross-sectional view of an imposition mounting type semiconductor device using the lead frame of FIG.

FIG. 3 is a cross-sectional view of a lead frame according to an embodiment of the present invention.

FIG. 4 is a sectional view of a lead frame according to an embodiment of the present invention.

FIG. 5 is a perspective view of a calculation model used for the stress calculation of the lead frame.

FIG. 6 is a sectional view of a semiconductor device according to a conventional example.

FIG. 7 is a partial cross-sectional view showing a step of forming a through hole of a lead frame according to a conventional example.

FIG. 8 is a partial cross-sectional view showing a step of forming a through hole of a lead frame according to a conventional example or when a constricted portion is formed in the plate thickness.

FIG. 9 is a partial cross-sectional view showing a step of forming a through hole in a lead frame according to an embodiment of the present invention.

10 is a partial cross-sectional view of a lead frame obtained through the through hole forming step of FIG.

FIG. 11 is a partial cross-sectional view showing a step of forming a through hole in a lead frame according to an embodiment of the present invention.

12 is a reel obtained through the through hole forming process of FIG.
It is a fragmentary sectional view of a dframe.

FIG. 13 is a partial cross-sectional view showing a through-hole forming process of the lead frame according to the embodiment of the present invention together with a press die.

14 is a reel obtained through the through hole forming process of FIG.
It is a fragmentary sectional view of a dframe.

FIG. 15 is a sectional view of a semiconductor device according to an example of the present invention.

FIG. 16 is a sectional view of a semiconductor device according to an example of the present invention.

FIG. 17 is a sectional view of a semiconductor device according to an example of the present invention.

FIG. 18 is a perspective view of a lead frame according to an embodiment of the present invention.

FIG. 19 is a partial cross-sectional view showing a step of forming a through hole in a lead frame according to an embodiment of the present invention.

20 is a cross-sectional view showing a state in which an element is mounted on the lead frame according to the embodiment of FIG.

FIG. 21 is a partial cross-sectional view showing a step of forming a through hole in a lead frame according to an embodiment of the present invention.

22 is a cross-sectional view showing a state in which an element is mounted on the lead frame according to the embodiment of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Tab, 2 ... Through hole, 3 ... Tab suspension lead, 4 ... Element, 5 ... Resin part, 6 ... Water vapor, 7 ... Lead, 8 ... Solder,
9 ... Substrate, 18 ... Die bonding material, 19 ... Adhesive outflow prevention groove.

Front page continuation (72) Inventor Hideo Miura 502 Jinritsu-cho Machinery Research Center, Tsuchiura-shi, Ibaraki Machinery Research Laboratories, Ltd. (72) Inventor Akihiro Tachimichi 502 Jinre-machi, Tsuchiura-shi, Ibaraki Machinery Research Laboratories, Hiritsu Manufacturing Co., Ltd. (72) Inventor Chikako Kitabayashi 502 Jinritsucho, Tsuchiura-shi, Ibaraki Machinery Research Laboratory, Hiritsu Manufacturing Co., Ltd. (72) Inventor Kazuo Shimizu 111 Nishiyote-cho, Takasaki-shi, Gunma Hitachi Ltd. Takasaki Plant (72) Invention Toshio Hatsuda, 502 Jinritsucho, Tsuchiura-shi, Ibaraki Machinery Research Laboratory, Hiritsu Manufacturing Co., Ltd. (72) Inventor, Toshinori Ozaki 502, Jinritsucho, Tsuchiura-shi, Ibaraki Machinery Research Laboratory, Hiritsu Manufacturing Co., Ltd. (72) Inventor, Toshio Hattori 502 Jinritsu-cho, Tsuchiura-shi, Ibaraki Machinery Research Laboratory, Hiritsu Seisakusho Co., Ltd. (72) Inventor, Shoji Sakata, 502, Jinre-machi, Tsuchiura-shi, Ibaraki Machinery Research Center, Hiritsu Seisakusho, Ltd.

Claims (3)

[Claims] 1. A lead comprising a tab on which a semiconductor element is mounted and a lead group integrally connected to the tab around the tab.
In the dframe, a through hole is formed at least just under the portion where the semiconductor element is mounted, on the entire surface of the tab,
Further, the lead frame is characterized in that the through hole is formed with a constricted portion or a stepped portion so that the sealing resin does not come out within the thickness of the tab. 2. A semiconductor element, a tab on which the semiconductor element is mounted, a lead group arranged around the tab, an inner lead portion and a tab of the lead group, and the semiconductor. In a semiconductor device having a resin portion for encapsulating an element, a through hole is formed at least directly under the portion where the semiconductor element is mounted in the entire tab surface, and the through hole is sealed within the tab thickness. A semiconductor device, characterized in that a locking portion having a constriction or a step is formed so that the stop resin does not come out. 3. A semiconductor element, a tab on which the semiconductor element is mounted, a lead group arranged around the tab, an inner lead portion and a tab of the lead group, and the semiconductor. In a semiconductor device having a resin portion for encapsulating an element, a through hole is formed at least directly under the portion where the semiconductor element is mounted in the entire tab surface, and the through hole is sealed within the tab thickness. A semiconductor device characterized in that an engaging portion is formed so that the stop resin does not come out, and an outer lead end portion is an imposition mounting type in which the outer lead end is impositioned on a substrate.