JPH0964266A - Lead frame - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide a novel lead frame capable of mounting a large semiconductor chip without causing stress due to thermal history even if there is a large difference in thermal expansion coefficient from the semiconductor chip. provide. SOLUTION: Each die pad 4 is divided into a plurality of parts (4a, 4b, 4c, 4d) integrated with a hanging part, and each hanging part 3a, 3b, 3c, 3d relieves stress such as S-shape. Make it possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is a lead that can be mounted so that a large stress does not occur in the semiconductor chip even if there is a large difference in coefficient of thermal expansion between the die pad and the semiconductor chip mounted thereon. Regarding the frame.

[0002]

2. Description of the Related Art As the scale of ICs increases year by year, IC products with large chip size and large power consumption are being introduced. In the past, such IC products were usually mounted in a ceramic package, but even as consumer products, ICs with large chip size and large power consumption tend to be used, and lead frames are used. A mounting method of resin sealing has come to be adopted. This is because the ceramic package is very expensive, whereas the resin-sealed package is inexpensive, and consumer products are required to be inexpensive.

As shown in FIG. 4 (A), the lead frame generally has a die pad b on which the semiconductor chip a is mounted and a plurality of suspension parts c, c, c, c and the semiconductor chip a for supporting the die pad b. What is composed of a plurality of leads d, d, ... Connected to the electrodes through wires,
A plurality of semiconductor chips are integrated, and a copper-based material having a large thermal conductivity is often used. And
As shown in (B), the semiconductor chip a is bonded to the die pad b via the adhesive agent e.

[0004]

By the way, when a semiconductor chip having a large size is mounted by resin encapsulation using a lead frame, stress may remain inside the semiconductor chip at the product completion stage due to heat history in the assembly process. There was a problem. This is because the thermal expansion coefficient of the copper forming the lead frame is 17 × 10 ⁻⁶ / K, while the silicon forming the semiconductor chip that is chip-bonded to the die pad of the lead frame made of copper is 1 ×.
It is 10 ⁻⁶ / K, and the coefficient of thermal expansion of the semiconductor chip and the die pad bonded to each other is very different.

Then, for example, in the die-bonding process of the semiconductor chip, the curing of the adhesive is performed by 150 to 2
In order to apply a temperature of about 00 ° C., when the temperature returns to room temperature after curing, a dimensional difference of 20 μm per 1 cm of the chip size tends to occur between the semiconductor chip and the die pad, and the die pad contracts. Stress is applied. This stress increases as the size of the semiconductor chip increases. In addition to the die bonding process, the process in which such stress occurs includes a molding process and a reflow process.

When such a stress is generated in the semiconductor chip, there is a problem that the characteristics of the IC change due to the piezo effect. In addition, such a thermal history that causes stress in the semiconductor chip causes cracks in the semiconductor chip itself, peeling of the adhesive, package cracks, and the like.

The present invention has been made to solve such a problem, so that even if there is a large difference in the coefficient of thermal expansion between the semiconductor chip and the semiconductor chip, the stress due to the thermal history does not occur in the large semiconductor chip. It is intended to provide a novel lead frame that can be mounted on the.

[0008]

A lead frame according to a first aspect of the present invention is characterized in that each die pad is divided into a plurality of portions integrated with a suspension portion, and each suspension portion has a stress relaxation shape. Therefore, according to the lead frame of the first aspect, although the lead frame largely contracts with respect to the semiconductor chip each time the heating process is performed, the stress can be relieved by the respective hanging portions, so that a large stress is applied to the semiconductor chip. It can be prevented from occurring.

According to a second aspect of the lead frame, each die pad is shaped so that the rigidity in the surface direction is equal to or less than the adhesive strength in the surface direction of the semiconductor chip bonding adhesive. Therefore, according to the lead frame of the second aspect, since the rigidity of the die pad is smaller than the rigidity of the adhesive, the stress caused by the difference in the coefficient of thermal expansion between the die pad and the semiconductor chip after the thermal process is caused by the adhesive. It affects the die pad and does not affect the semiconductor chip itself. Therefore, it is possible to prevent stress from being generated in the semiconductor chip.

A lead frame according to a third aspect is the lead frame according to the second aspect, characterized in that the die pad is formed in a mesh shape. Therefore, according to the lead frame of claim 3, since the die pad has a mesh shape, the rigidity in the surface direction of the die pad can be weakened,
Further, the rigidity of the adhesive in the surface direction can be made weaker.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments. 1A and 1B show an embodiment of a lead frame of the present invention.
Is a plan view showing an outline of a main part, and FIG. 6B is a plan view showing an enlarged part B of FIG. In the drawing, 1 is a tie bar, which is used for the leads 2, 2, ...
Connect c and 3d.

The suspension portions 3a, 3a, 3c, 3d support a die pad for one semiconductor chip, and the die pad is divided into four portions 4a, 4b, 4c, 4d, and each divided portion 4a. 4b, 4c, and 4d support the corners of one semiconductor chip 5. And the hanging parts 3a, 3
Each of b, 3c, and 3d is formed in an S shape so as to relieve stress.

Therefore, according to such a lead frame, although the lead frame largely contracts with respect to the semiconductor chip 5 after the heating process, the hanging portions 3a, 3b, 3c,
Since the stress can be relieved by 3d, it is possible to prevent a large stress from being generated in the semiconductor chip 5. Therefore, there is no fear that the characteristics of the IC will change due to the piezo effect, cracks in the semiconductor chip itself, peeling of the adhesive, package cracks, and the like.

FIG. 2 is a perspective view showing a modification of the suspension portion of the embodiment shown in FIG. The suspension portions 3a, 3b, 3c, and 3d (only 3a is shown in the drawing) in the present modification are designed to relieve stress by depressing. Thus, stress relief can be achieved in various ways.

[0015]

FIG. 3 is a plan view showing one die pad which is a main part of another embodiment of the lead frame of the present invention. By forming each die pad 4 of the lead frame in a mesh shape as shown in FIG. 3, the rigidity of the die pad 4 in the plane direction is weakened.
In the above, the part where the line is present is the part made of the copper-based member of the lead frame, and the part where the line is not present is the hole part. Since the die pad 4 is formed in a mesh shape with thin lines in this manner, the rigidity can be weakened, and the rigidity can be made equal to or less than the rigidity of the adhesive (the adhesive that bonds the semiconductor chip to the die pad 4). . By reducing the rigidity of the die pad 4 as described above, the stress due to heat can be absorbed by the deformation caused by the weak rigidity of the die pad 4 itself, and a large stress can be prevented from occurring in the semiconductor chip.

That is, the residual stress is generated in the semiconductor chip because both the semiconductor chip and the die pad connected to each other have strong rigidity. However, when the rigidity is weakened as in the present lead frame, the stress caused by the difference in thermal expansion coefficient when the semiconductor chip is bonded to the die pad by the adhesive is applied to the adhesive and the die pad, and is not applied to the semiconductor chip. Therefore,
No heat stress is generated in the semiconductor chip. Such a stress relaxation effect can be sufficiently obtained by making the rigidity of the die pad in the plane direction equal to or less than that of the adhesive.

[0017]

According to the lead frame of the first aspect of the present invention, even though the lead frame contracts greatly with respect to the semiconductor chip each time the heating process is performed, the stress can be relieved by the respective hanging portions. It is possible to prevent a large stress from being generated. According to the lead frame of the second aspect, since the rigidity of the die pad is smaller than the rigidity of the adhesive agent, the stress caused by the difference in the thermal expansion coefficient between the die pad and the semiconductor chip after the thermal process is caused by the adhesive agent and the die pad. It does not affect the semiconductor chip itself. Therefore, it is possible to prevent stress from being generated in the semiconductor chip. According to the lead frame of the third aspect, since the die pad has a mesh shape, the rigidity in the surface direction of the die pad can be weakened, and further, the rigidity in the surface direction of the adhesive can be weakened.

[Brief description of drawings]

1A and 1B show one embodiment of a lead frame of the present invention, where FIG. 1A is a schematic plan view of a main part, and FIG. 1B is an enlarged view of part B of FIG. 1A. FIG.

FIG. 2 is a perspective view showing a modified example of the suspension unit of the one embodiment.

FIG. 3 is a plan view showing a main part of another embodiment of the lead frame of the present invention.

4A and 4B show a conventional example, and FIG.
Is a perspective view, and (B) is a sectional view.

[Explanation of symbols]

 2 Leads 3a to 3d Hanging part 4a to 4d Divided part of die pad 5 Semiconductor chip

Claims (3)

[Claims] 1. A lead frame, wherein each die pad on which one semiconductor chip is mounted is divided into a plurality of parts integrated with a hanging part, and each hanging part has a stress relaxation shape. 2. A lead frame, wherein each die pad on which one semiconductor chip is mounted is shaped so that the rigidity in the surface direction is equal to or less than the adhesive strength in the surface direction of the semiconductor chip adhesive. 3. The lead frame according to claim 2, wherein the die pad is formed in a mesh shape.