JPH07161909A - Resin-sealed type semiconductor device - Google Patents

Abstract

PURPOSE:To prevent a resin or a semiconductor element from being cracked even when heat stress is applied there as in the case of reflow-soldering. CONSTITUTION:A resin-sealed type semiconductor device in which a semiconductor element 9, an island with the semiconductor element mounted on and a plurality of leads 1 to be electrically connected with the semiconductor element 9 are sealed with a resin, comprises an opening part formed in the rear surface of the semiconductor element 9 substantially at the center of the island to have a smaller diameter than the outer diameter of the semiconductor element 9 and a metal part 7 engaged with the rear surface of the semiconductor element 9 at predetermined intervals to have a smaller outer diameter than that of the opening part and sealed with a resin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin-encapsulated semiconductor device, and more particularly to a resin-encapsulated semiconductor device having improved resistance to cracks in an encapsulating resin or a semiconductor element.

[0002]

2. Description of the Related Art In recent years, with the miniaturization and high performance of electronic equipment, the miniaturization and thinning of the entire mounting circuit has been advanced. Along with this, the surface mount type semiconductor package has been widely used instead of the conventional lead insertion type. Generally, the method of mounting the surface mount type component on the printed wiring board is to supply cream solder to the component mounting land of the printed wiring board by printing etc., align the lead of the component and mount it. So-called reflow soldering is employed in which solder is melted and attached by heating with far infrared rays or hot air from above and below the plate.

In reflow soldering, compared with flow soldering which has been conventionally used for soldering lead insertion type parts, the mounted parts are heated directly, so that the temperature of the parts themselves rises, and therefore various kinds of parts are used. There is a problem with. For example, in the case of a resin-encapsulated semiconductor device, if the encapsulating resin absorbs moisture, the absorbed moisture may vaporize, and cracks may occur in the encapsulating resin. In addition, stress may occur due to the difference in the coefficient of thermal expansion of the component parts, which may cause the package to warp. The situation during this time will be described with reference to FIGS.

FIG. 5 is a sectional view schematically showing the structure of a general resin-sealed semiconductor device. Reference numeral 21 is a lead, and a semiconductor element 24 is mounted on the island 22 via a conductive adhesive 23. A lead wire 25 such as a bonding wire is connected between the lead 21 and an electrode portion (not shown) of the semiconductor element 24, and the entire sealing resin 2 is formed.
It is molded (sealed) by 6.

FIG. 6 is a cross-sectional view illustrating the mechanism of cracks in the sealing resin. The water vapor that has entered the sealing resin 26 from the outside air is condensed and liquefied by capillaries in the minute gaps existing at the interface between the sealing resin 26 and the island 22. This liquefied water explosively expands at high temperature during reflow.
Therefore, a large water vapor pressure is applied to the interface between the sealing resin 26 and the island 22, and the interface is peeled off to generate the gap 27. If the amount of moisture absorption of the sealing resin 26 is large, the interface peeling leads to the crack 28 of the resin.

On the other hand, with the demand for thinner semiconductor packages, the thickness of the resin covering the semiconductor element or the lead frame is inevitably thinner. Therefore, the stress due to the difference in thermal expansion coefficient between the semiconductor element or the island and the mold resin cannot be endured, and the semiconductor element or the mold resin may be cracked. FIG. 7 illustrates a state in which the package is warped due to the difference in the coefficient of thermal expansion and cracks 29 are generated in the semiconductor element.

Therefore, for the purpose of minimizing the stress generation, the thickness of the resin on the upper part of the semiconductor element and the thickness of the resin on the lower part of the island on which the semiconductor element is mounted are made equal and balanced. There is.

[0008]

As described above, the resin-encapsulated semiconductor device has a problem that cracks occur in the semiconductor element or the encapsulating resin during reflow soldering. The present invention has been made in view of such circumstances,
An object of the present invention is to provide a resin-sealed type semiconductor device in which cracks do not occur in a sealing resin or a semiconductor element even when a thermal stress such as reflow soldering is applied.

[0009]

In order to achieve the above object, according to the present invention, a semiconductor element, an island on which the semiconductor element is mounted, and a plurality of leads electrically connected to an electrode portion of the semiconductor element are provided. A resin-sealed semiconductor device obtained by resin-sealing a semiconductor element, the opening having a diameter smaller than the outer diameter of the semiconductor element and formed outside the rear surface of the semiconductor element at substantially the center of the island. And a metal plate which has a small diameter and is retained at a predetermined distance below the back surface of the semiconductor element and is included in the resin encapsulation.

[0010]

As described above, according to the present invention, an opening having a diameter smaller than the outer diameter of the semiconductor element is provided below the back surface of the semiconductor element at approximately the center of the island, and the opening is provided with a predetermined distance from the back surface of the semiconductor element. Since the metal plate smaller than the outer diameter of the opening is locked, the resin enters between the metal plate and the back surface of the semiconductor element at the time of resin sealing, and at the same time, the entire metal plate is sealed with resin. Contained within. Since the adhesive strength between the semiconductor element and the resin is stronger than the adhesive strength between the metal plate and the resin,
Water does not accumulate at the interface between the semiconductor element and the resin. Water may accumulate between the edge of the island and the resin, but since the central area of the island is open and the area of the edge is small, cracking does not occur.

There is a possibility that water may be accumulated on the bonding surface between the resin and the outward main surface of the metal plate to cause resin cracks.
Since the area of the metal plate is smaller than the area of the conventional island, the generated stress is small.

On the other hand, when the stress applied to the back surface of the semiconductor element is simulated by considering the five-layer structure of resin-semiconductor element-resin-metal plate-resin as a beam structure, the results shown in FIG. 3 are obtained. In the figure, the horizontal axis represents the distance between the back surface of the semiconductor element and the metal plate, and the vertical axis represents the relative value when the stress when there is no metal plate under the semiconductor element is 100. This is a simulation when the metal plate is an Fe-Ni alloy and the resin is an epoxy resin. By placing the metal plate about 0.1 mm away from the back surface of the semiconductor element, the stress on the back surface of the semiconductor element is reduced by about 40%. be able to. The above two effects work together to prevent cracks in the sealing resin and cracks in the semiconductor element.

[0013]

Embodiments of the present invention will now be described with reference to the drawings. 1 is a plan view of a lead frame according to an embodiment of the present invention, and FIG. 2 is a sectional view of a semiconductor device using the same.
In FIG. 1, 1 is a dam bar 2 which is cut later by a lead.
Is connected to the other lead and the frame portion 3.
Reference numeral 4 denotes an island on which a semiconductor element is to be mounted later. The island is connected to the frame portion 3 by the hanging pin 5 and the island is depressed so as to deform the hanging pin 5. A metal plate 7 hung by a hanging pin 6 is formed substantially in the center of the iron and wire 4, and the metal plate 7 is depressed so as to deform the hanging pin 6. That is, as shown in the sectional view of the semiconductor device of FIG. 2 (corresponding to the sectional view taken along the line AA of FIG. 1), the lead 1
On the other hand, the island 4 is lowered by one step, and the metal plate 7 is formed in a shape lower than the island 4 by one step.

Using this lead frame, the semiconductor device shown in FIG. 2 can be manufactured as follows. That is, the conductive adhesive 8 is supplied to the periphery of the opening of the island 4 of the lead frame shown in FIG. 1 by a dispenser or the like. Then, the semiconductor element 9
The conductive adhesive 8 is hardened by placing the peripheral edge of the conductive adhesive 8 so as to overlap the peripheral edge of the opening and heating.

Next, the electrode pad (not shown) of the semiconductor element and the lead 1 are connected by a well-known wire bonding method. 10 is a conducting wire (bonding wire). Then, the bonded lead frame is loaded into a molding die, and the heated and melted resin is fed under high pressure to perform so-called transfer molding. At this time, the molten resin fills the periphery of the metal plate 7 and also enters between the semiconductor element 9 and the metal plate 7. After the sealing resin 11 is cured,
The tip of the dam bar 2 and the lead 1 is taken out from the mold and the lead is formed. Next, the hanging pins 5 are cut to complete the semiconductor device shown in FIG.

The semiconductor device thus formed is
The center of the back surface of the semiconductor element 9 is in close contact with the sealing resin 11, and moisture does not collect at this interface. Further, since the metal plate 7 is interposed between the back surface of the semiconductor element 9 and the back surface of the package, thermal stress generated on the back surface of the semiconductor element 9 is also reduced.

As a specific example, the lead frame shown in FIG. 1 was prepared using a Fe-Ni alloy having a thickness of 0.15 mm. Island 4
The metal plate 7 is also formed of the same material and the same thickness. An opening of 7 × 5 mm is provided in the center of the island 4 of 10 × 8 mm, and a metal plate 7 of 5 × 3 mm hung from the hanging pins 6 at the four corners is further formed in the center. To 0.1
mm depressed. 9.4 x 7.4 mm, thickness 0.35
A mm semiconductor element was mounted using a silver-based conductive adhesive 8. The thickness of the conductive adhesive 8 after curing was 0.03 mm. Next, after wire bonding was performed, transfer molding was performed using epoxy resin as the sealing resin 11 to produce a semiconductor device as shown in FIG.

In the above specific example, the dimension in the thickness direction in FIG. 2 is as follows. That is, the resin thickness on the semiconductor element 9 is
0.235 mm, the thickness of the semiconductor element 9 is 0.35 mm, the distance between the semiconductor element 9 and the metal plate 7 is 0.13 mm, and the thickness of the metal plate 7 is
0.15 mm, the resin thickness under the metal plate 7 was 0.135 mm, and a semiconductor device with a total thickness of 1.0 mm was realized.

The semiconductor device thus produced was subjected to IR (infrared) reflow (maximum temperature 240 ° C.) known as the most severe reflow method, but no resin cracks or semiconductor element cracks occurred.

Although the embodiments of the present invention have been described above, it is needless to say that the present invention is not limited to the above embodiments and various modifications can be made without departing from the spirit of the invention. For example, in the above-mentioned embodiment, the example of the bonding wire is explained as the conductive wire 10, but TAB (Tape Automated B
It may be a foil conductor such as an onding type.

[0021]

As described above, according to the present invention, the opening is provided in the substantially central portion of the island so that the central portion of the back surface of the semiconductor element is in close contact with the resin. You can Therefore, it is possible to prevent resin cracks due to vaporization and expansion of water due to heating during reflow.

In addition, since the metal plate is locked under the opening at a predetermined distance, the stress on the back surface of the semiconductor element can be reduced by about 40% as compared with the case without the metal plate. It is also possible to prevent cracks in the device. As described above, the structure of the present invention is extremely effective in improving crack resistance during reflow.

[Brief description of drawings]

FIG. 1 is a plan view of a main part of one element of a lead frame according to an embodiment of the present invention.

FIG. 2 is a sectional view of a semiconductor device according to an embodiment of the invention.

FIG. 3 is a diagram showing the relationship between the distance between the back surface of the semiconductor element and the metal plate and the relative stress on the back surface of the semiconductor element in the structure of the present invention.

FIG. 4 is a plan view of an essential part of one element of a lead frame according to a conventional technique.

FIG. 5 is a cross-sectional view of a semiconductor device according to a conventional technique.

FIG. 6 is a cross-sectional view illustrating a mechanism of resin crack generation in a semiconductor device according to a conventional technique.

FIG. 7 is a cross-sectional view illustrating a mechanism of a semiconductor element crack of a semiconductor device according to a conventional technique.

[Explanation of symbols]

 1 ... Lead 2 ... Dam bar 3 ... Frame part 4 ... Hanging pin 5 ... Island 6 ... Hanging pin 7 ... Metal plate 8 ... Conductive adhesive 9 ... Semiconductor element 10 ... Conducting wire (bonding wire) 11 ... Sealing resin

Claims (1)

[Claims] 1. A resin-sealed semiconductor device comprising a semiconductor element, an island on which the semiconductor element is mounted, and a plurality of leads electrically connected to an electrode portion of the semiconductor element, which are resin-sealed. An opening smaller than the outer diameter of the semiconductor element formed under the back surface of the semiconductor element at approximately the center of the island, and a predetermined distance under the back surface of the semiconductor element having an outer diameter smaller than the opening. And a metal plate included in the resin encapsulation, the resin-encapsulated semiconductor device.