JPS61259550A - Resin-sealed semiconductor device - Google Patents

Abstract

PURPOSE:To average thermal characteristics by uniformly maintaining the thickness of a sealing resin layer between a lead frame and a metal plate. CONSTITUTION:Only one surface of a metal plate 6 is bent to obtain the prescribed curvature by pressing step of differentiate the thicknesses of the center and the ends. A lead frame 1 associated with a semiconductor element 5 and a metal plate 6 finished for the bending step are integrated by a transferring step. To increase thermal conductivity, the element 5 is sealed with resin by the thermal curing reaction of the silicone resin added with a filler. In this case, the straight surface 9 of the plate 6 is bent in the same direction as the frame 1. As a result, the bent surface 8 of the plate 6 is straightened. Thus, the thickness of sealing resin 7 disposed between the frame 1 and the bent surface of the plate 6 is formed substantially the same to average the thermal characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to an isolation type resin-sealed semiconductor device having a heat sink, and is particularly suitable for a composite element made of power elements such as a power transistor.

[Technical background of the invention]

Conventionally, individual semiconductor devices, such as power transistors and other power devices, have been roughly divided into two types: those that use a common collector terminal, and those that use multiple collector terminals separately, the latter being called the isolation type. .

The cross-sectional structural diagram is shown in FIG. 4(A). After the semiconductor element (11) on which the power transistor etc. are formed is fixed to the bed part (not shown) of the lead frame (12) with Pb-5n solder, the semiconductor The electrode provided on the element (11) and the external terminal of the lead frame are made electrically conductive by a wire bonding process. These assemblies are fixed to a metal plate (13) generally called a heat sink and covered with a sealing resin layer (14). 14) to manufacture isolation type resin-sealed semiconductor devices. The wire bonding process described above is completed by bridging a conductive metal thin wire between predetermined parts, but this thin wire may be coated with a gel-like or rubber-like resin to remove contamination or distortion.

In such a structure, the metal plate (13) and the molded resin (
Warpage occurs in the product due to differences in thermal expansion coefficients (α) (1 and 4), molding shrinkage rate of the resin, etc. This amount of warpage (W) is approximately Wω(α□−α2)AT T: temperature, α
is Cu 1 for resin 20-25 x 10-'℃-1
6.5 X 10-'℃-1, Fe 11.8X10-
6°C-1123,6x io-'°C-1, and the molding shrinkage rate of the resin (14) is about 0.5-0.9%.

The metal plate (13) is usually made of 1 or 1 alloy, and the overall dimensions of the semiconductor device are 60 x 20 x 6 mm [the thickness of this white metal plate (13) is 2 mm], and the amount of warpage is approximately 0.15 m.
It becomes n. However, in the case of power transistors, the use of screws (M310 kg/an) using holes (16) for heat dissipating components caused resin cranking and peeling, and it could not be put to practical use.

Therefore, the method shown in FIG. 4(b) was devised to compensate for this drawback. That is, the metal plate (13) is curved in advance in a direction opposite to the warp direction according to the amount of warp, but according to this method, the amount of warp is at most 0.03 m.
A product which could be used for practical purposes was obtained, with n being kept in check and no resin cracks occurring.

On the other hand, a method of bending the lead frame (12) with the same curvature radius as the bending process of the metal plate (13) may be considered, but this would be difficult if carried out before the die bonding process; Both methods are impractical because they may damage the device or wire-bonded conductive thin metal wire.

[Problems with background technology]

By the way, the saturated thermal resistance [Rth
(j-c)) is a semiconductor element (11), a lead frame (
12) is the sum of the thermal resistances of each of the thermal conductive systems up to the sealing resin (14) and the metal plate (13), and the thermal conductivity (λ) is from silicon to 0.2. Solder~0.08. Cu layer 0.94
゜Resin~1~6xlO-'', AQ~0.27 (unit Ca
(1/cn-sec·'C), and the thermal resistance of the isolation type resin-sealed semiconductor device is determined by the thickness of the sealing resin located between the metal plate (13) and the lead frame (12).

As shown in FIG. 4(b), the isolation type resin-sealed semiconductor element includes a lead frame (12) and a metal plate (
13) It has been found that there are differences in heat resistance characteristics because the thickness of the resin layer (14) located between the two is partially different. In this device, the metal plate (13) is subjected to Elf lobe processing to prevent warping, and the thinner lead frame (12) is warped, and the resin layer (14) is gradually formed from the edge toward the center. becomes thinner.

[Object of the Invention] The present invention provides a novel isolation type resin-sealed semiconductor device that eliminates the above-mentioned drawbacks.

In particular, the purpose is to maintain a uniform thickness of the sealing resin layer disposed between the lead frame and the metal plate, and to maintain the flatness of the exposed surface of the metal plate to even out the thermal characteristics.

[Summary of the invention]

In order to achieve this objective, in the isolation type resin-sealed semiconductor device according to the present invention, only the resin contacting surface of the metal plate is curved with a uniform radius commensurate with the amount of warpage that occurs during resin molding, thereby making the leads thinner. A method was adopted in which the thickness of the sealing resin located between both parts was kept constant while maintaining parallel relationship with the frame surface.

[Embodiments of the invention]

The present invention will be explained in detail with reference to FIGS. 1(A) and 1(B).

A suspended frame made of Fe, FeNi alloy, Aρ, or a Cu layer as the outermost layer is prepared. As shown in FIG. 2, for example, this lead frame has a large part at the end to form terminals corresponding to the three electrodes of the transistor.
The metal strips (A) that form...■... are arranged in a regular forest, and the common terminal 0 is connected to a huge part of these ■...■...
... are arranged so as to surround them, and the metal strips (A) ... are further connected with so-called tie bars. A semiconductor element 0 such as a power transistor is fixed to this enlarged portion (1) using Pb--Sn solder. On the other hand, only one surface of the Afi metal plate 0 is curved to obtain a constant curvature through the pressing process, and the difference between the thickness of the center portion and the thickness of the end portions is approximately 0.
1 mm, and when this AQM metal plate is subjected to the resin sealing process described later, this curved surface (■) will not be in contact with the safety resin, that is, it will be on the outside, and the straight surface (0) occupying the opposite side of this will face the lead frame. .

Next, the lead frame ■ on which the semiconductor element ■ has been assembled and the metal plate 0 that has undergone this bending process are sealed with a resin in order to integrate them through a transfer process. A silicone resin to which a filler has been added is applied, and the process is carried out by employing a known transfer molding process and injecting this silicone resin melt into a mold.

This silicone resin seals the semiconductor element 0 with the resin through a thermosetting reaction, but the straight surface 0 of the metal plate 0 on the side of the semiconductor element 0 is the same as the lead frame ■, which has a thinner thickness during this resin sealing process. curve in the direction As a result, the curved surface (8) of the metal plate 0 becomes straight.

It is best to make the degree of curvature during this resin sealing process the same as the degree of curvature during the pressing process, but it is possible to make them the same, and the lead frame (■) and the metal plate (■) may be concentric circles. Finally, an arc of the shape is obtained.

As a result, the thickness of the sealing resin ω located between the curved surface of the lead frame ■ and the metal plate 0 is molded to be the same, and then screws are secured using the hole 0 with a torque of 10 kg/■. An isolation type resin-sealed semiconductor device was obtained.

〔Effect of the invention〕

The thickness of such an isolation type resin-sealed semiconductor board is 2W11), and the maximum amount of warpage is 0.03 as in the conventional example.
The thermal resistance was maintained within 100 mn, and the distribution of thermal resistance values was as shown in FIG.

In other words, the vertical axis shows the thermal resistance (°C/W), and the horizontal axis shows the 1.3
Predetermined positions ABCD of the metal plate shown in the figure were taken, and the measured value distribution state is shown. Among them, the X mark indicates a conventional isolation type resin-sealed semiconductor device, and the 0 mark indicates an isolation type resin-sealed semiconductor device according to the present invention.

As clearly seen from this figure, in the present invention, no difference is observed depending on the measurement position, whereas in the conventional example, a clear change is shown, and the results support the theoretical consideration.

[Brief explanation of drawings]

FIG. 1(A) is a sectional view of a main part of an embodiment according to the present invention;
Figure (B) is a sectional view of its main parts, Figure 2 is its top view,
FIG. 3 is a characteristic diagram showing the thermal resistance value in each part of the lead frame, and FIG. 4 is a partial sectional view of a main part 8 of the conventional device. 1: Lead frame 5: Semiconductor element 6: Metal plate
7 = Sealing resin 8: Curved surface

Claims (1)

[Claims] In a semiconductor device in which a resin layer covering the periphery of an assembly in which a semiconductor element is fixed to a plate-shaped lead frame is sealed in a metal plate thicker than the lead frame, only the surface of the metal plate on the side of the semiconductor element is curved; A resin-sealed semiconductor device characterized in that the resin thicknesses between the lead frames arranged along the lead frames are substantially the same.