JPH0745765A - Resin sealing method for semiconductor device - Google Patents

Abstract

PURPOSE:To provide a method of sealing a semiconductor device with resin high in productivity at a low molding temperature at which eutectic solder used for the inner connection of a circuit assembly is not melted again. CONSTITUTION:A semiconductor device is sealed with resin through such a method that a circuit assembly which includes a semiconductor chip 3 formed on a lead frame 2 is mounted on a heat dissipating metal insulating board 1 and jointed together with eutectic solder 7, and the periphery of the circuit assembly is sealed with resin making the underside of the metal insulating board 1 exposed for the formation of a resin-sealed semiconductor device, wherein mold releasing agent is previously applied onto the underside of the metal insulating board 1. The circuit assembly mounted on the metal insulating board is inserted into an injection molding die 8, and liquid epoxy resin is filled into the cavity of the die 8 at molding temperatures of 140 deg.C to 180 deg.C to form a sealing resin layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin encapsulation method for a resin encapsulation type semiconductor device intended for power semiconductor devices and the like.

[0002]

2. Description of the Related Art In recent years, downsizing of semiconductor devices has progressed, and from the viewpoint of mass productivity and manufacturing cost, power semiconductor devices having a resin-encapsulated package have been widely used. In addition, in order to secure the heat dissipation and electrical insulation properties required for a power semiconductor device, a circuit assembly composed of a lead frame is provided on a metal insulating substrate (a conductor on an insulating layer bonded to a metal plate to be a heat sink). A eutectic solder having a low melting point (melting point 183) is mounted between the lead frame and the metal insulating substrate by being mounted on a patterned substrate.
There is known a structure in which the circuit assembly is packaged by being sealed with a resin while sealing the periphery of the metal insulating substrate while exposing the bottom surface of the metal plate as a heat dissipation surface.

FIG. 7 shows a typical conventional assembly structure of the resin-sealed semiconductor device described above. In the figure, 1 is a metal insulating substrate including a metal plate 1a, an insulating layer 1b, and a conductor pattern 1c, 2 is a lead frame, 3 is a semiconductor chip mounted on the die pad 2a of the lead frame 2, and 4 is an external lead of the lead frame 2. Bonding wires connecting between 2b and the semiconductor chip 3 are a resin case bonded to the metal insulating substrate 1, and a sealing resin 6 is filled inside the resin case 5. The thickness of the insulating layer 1b in the metal insulating substrate 1 is selected in accordance with the trade-off characteristic between heat transfer resistance and electrical insulation strength.

Here, the lead frame 2 is soldered onto the conductor pattern 1c of the metal insulating substrate 1 by using the eutectic solder 7. The sealing resin 6 is filled in the resin case 5 by the potting method. The molding temperature condition by this potting method is that the resin temperature is about 130 ° C.,
The eutectic solder 7 described above is safe because there is no risk of remelting.

[0005]

By the way, in the structure shown in FIG. 6 in which the potting method is used to mold the sealing resin layer 6 as described above, the resin case 5 is required to prevent the flow of the fluid resin. However, the resin case 5 becomes functionally unnecessary after the encapsulating resin layer 6 is cured, and the presence of the resin case 5 increases the outer size of the semiconductor device. Therefore, it is desired to promote the miniaturization of the external dimensions of the semiconductor device by resin-sealing without using the resin case 5.

On the other hand, as a resin encapsulation method for a semiconductor device that does not use a resin case, a transfer molding method is known in addition to the potting method described above. In this molding method, a solid epoxy resin tabletized is used as a molding material. Since this is plasticized by heating and filled in the cavity of the mold, the molding temperature condition is 180 ° C. or higher. For this reason, as described above, in the case where the lead frame 2 and the metal insulating substrate 1 are solder-joined with the eutectic solder (melting point 183 ° C.), the solder may be remelted by heating during molding, It cannot be put to practical use as it is.

The present invention has been made in view of the above points, and it is intended to solve the above-mentioned problems in the resin-encapsulated semiconductor device described above and to re-solder the solder joint between the lead frame and the metal insulating substrate. It is an object of the present invention to provide a resin-encapsulating method for a resin-encapsulated semiconductor device with high productivity, which enables resin encapsulation under a low molding temperature condition without the risk of melting.

[0008]

According to the present invention, the above-mentioned object is to insert a circuit assembly mounted on a metal insulating substrate into an injection molding die, and to form a liquid in the cavity under a molding temperature condition of 140 ° C to 180 ° C. It is achieved by injecting the thermosetting resin of to mold the sealing resin layer. Further, there is the following method as a specific means for preventing the bottom surface of the metal insulating substrate from being covered with the resin when the above method is carried out.

(1) A mold release agent is applied to the bottom surface of the metal insulating substrate in advance to mold the sealing resin layer. (2) A sealing resin layer is formed by arranging a packing that abuts the peripheral area of the bottom surface of the metal insulating substrate at the bottom of the cavity of the mold. (3) A stepped portion is formed in advance on the bottom surface side of the metal plate of the metal insulating substrate, and a stepped recess is formed in the cavity of the mold so as to be closely fitted to the stepped portion and sealed. The resin layer is molded.

Further, as a means for preventing burrs from being generated in the peripheral region of the sealing resin layer due to mold formation, a dam bar surrounding the outer periphery of the sealing resin layer molding region is previously formed on the lead frame to seal it. There is a method of molding the stop resin layer.

[0011]

According to the above resin sealing method, the molding temperature condition is set to 1
Since the encapsulating resin layer is injection-molded using a liquid resin in the range of 40 to 180 ° C., a low melting point eutectic solder (melting point 183 ° C.) that joins the lead frame and the metal insulating substrate is used. While preventing re-melting during injection molding, internal stress and cracks in the encapsulating resin layer during the cooling process after molding, and preventing the bottom surface of the metal insulating substrate from being covered with resin, In the molding process performed through the molding operation, the liquid resin can be gelled within a short time from the start of injection. As a result, it is possible to improve the product quality and shorten the molding cycle time to improve the productivity.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. In the drawings of the embodiments, the same members corresponding to FIG. 7 are denoted by the same reference numerals. Example 1 FIG. 1 is a process diagram for inserting a semiconductor device assembly (see FIG. 7 for each part of the semiconductor device) into an injection molding die 8 to injection-mold a sealing resin layer.
Here, the mold 8 comprises an upper mold 8a and a lower mold 8b.
Metal insulating substrate 1 inserted in the cavity in a
Is provided with a pressing piece 8c for holding the mold 8 in a fixed position in a clamped state, and a gate 8d for injecting a liquid resin forming material into the cavity is opened in the lower mold 8b.

Before the semiconductor device assembly is inserted into the mold 8, a mold release agent 9 (for example, a product of Shin-Etsu Silicone Co., Ltd .: spray) is preliminarily formed on the entire bottom surface of the metal insulating substrate 1 which functions as a heat dissipation surface. Mold release agent SEPA-COA
TII) is applied. The release agent 9 serves to prevent the sealing resin from adhering to the heat dissipation surface of the metal insulating substrate 1 during molding.

Then, in the state shown in the drawing, the mold 8 is inserted from the injection nozzle.
Molding is performed by injecting the following molding material into the cavity at a predetermined injection pressure through the gate 8d. In this case, the molding material is a two-part liquid epoxy resin in which a main agent and a curing agent are mixed in advance in an appropriate ratio (for example, products of Nagase Ciba Co., Ltd .: XNR8205 (main agent), XNH820).
5 (curing agent)) and the molding temperature condition is 140 to 1
After setting the temperature in the range of 80 ° C., a series of molding operations are performed to seal the periphery of the circuit assembly with resin.

Here, the upper limit of the molding temperature condition is set to 180 ° C. because the eutectic solder (melting point 1 which joins the metal insulating substrate 1 and the lead frame 2 in the assembly of the semiconductor device is joined.
This is to suppress the occurrence of internal stress in the resin layer and cracks caused by internal stress in the process of remelting (83 ° C.) during molding or cooling to room temperature after molding. Further, the lower limit of the molding temperature condition was set to 140 ° C. in order to accelerate the gelation time of the liquid epoxy resin injected into the mold during the series of molding processes, and thereby the mold was injected from the start of injection of the liquid resin. The molding cycle time can be shortened because the time required for opening can be shortened. The liquid epoxy resin described above can be molded even at a low temperature of 130 ° C. However, when the molding temperature is lowered to 140 ° C. or lower, the gelling time of the liquid epoxy resin is significantly increased. It takes a long time.

Next, FIGS. 4 and 5 show a resin-sealed semiconductor device manufactured through the above-mentioned injection molding process. In the illustrated configuration, the peripheral area of the circuit assembly including the semiconductor chip 4 assembled on the lead frame 2 except for the bottom area (the heat radiation surface of the heat sink) of the metal plate 1a of the metal insulating substrate 1 is the sealing resin layer 6. It is sealed by. It should be noted that the resin can be prevented from adhering to the bottom surface of the metal insulating substrate 1 by applying the release agent 9 as described in FIG.

Example 2 In the above-described Example 1, the release agent 9 was applied to prevent the sealing resin from adhering to the back surface of the metal insulating substrate 1. However, in this example, the release agent is not used. Instead, measures are taken to prevent the resin from adhering to the bottom surface of the metal insulating substrate. That is, in this embodiment,
On the bottom side of the cavity of the lower die 8a of the die 8, a ring-shaped packing 10 is provided in the inner peripheral region of the recess outside the central pedestal portion 8e on which the metal insulating substrate 1 is placed. This packing 10 is in close contact with the peripheral portion of the bottom surface of the metal insulating substrate 1 inserted in the mold, and serves to prevent the molding resin injected into the mold 8 from wrapping around to the bottom surface side of the metal insulating substrate 1. Therefore, a packing made of a material having high heat resistance (for example, silicone resin) that sufficiently withstands the molding temperature is used. As a result, the resin does not wrap around on the bottom surface side of the metal insulating substrate 1, and it is not necessary to apply the release agent as described in the first embodiment.

Embodiment 3: FIG. 3 shows an application embodiment for preventing resin from adhering to the bottom surface of a metal insulating substrate. In this embodiment, the stepped portion 1d is formed on the bottom surface side of the metal insulating substrate 1 in advance, and on the other hand, the stepped portion 1d is fitted on the bottom side of the lower die 8b of the die 8 by a stop fit. A stepped recess 8f is formed so as to fit together.

As a result, in the metal insulating substrate 1 inserted in the mold 8, the peripheral edge of the stepped portion 1d is abutted against the peripheral edge of the recessed portion of the lower mold 8b, so that the resin injected into the mold 8 is metal-insulated. It does not go around to the bottom side of the substrate 1. That is, the stepped recess 8f formed in the mold plays the same role as the packing 10 described in the second embodiment. Example 4: Next, an example will be described with reference to FIG. 6 in which measures are taken to prevent burrs from being produced in the peripheral region of the resin encapsulation layer during resin encapsulation molding.

The liquid epoxy resin, which is a molding material for the sealing resin layer 6, has a low viscosity, and the mold 8 described in each of the above-mentioned embodiments is used.
When a liquid epoxy resin is injected by applying a predetermined injection pressure to, a part of the resin is extruded into the gap between the mating surfaces (parting surfaces) between the upper mold 8a and the lower mold 8b, which solidifies to form burrs. . Therefore, as a means for preventing the formation of burrs, in FIG. 6, a dam bar 2c is formed in advance on the lead frame 2 so as to surround the outer periphery of the molding region in accordance with the outer shape of the sealing resin layer 6. Molding is performed with the dam bar sandwiched between the mating surfaces of the mold. As a result, the peripheral area of the mating surface of the mold is closed by the dam bar, so that burr formation can be prevented.

The dam bar 2c is ideally formed so that its inner peripheral edge matches the outer contour of the resin sealing layer 6, but the dam bar 2c is resin-sealed as shown in the figure due to restrictions such as mold structure. When it is necessary to separate from the outer periphery of the stopper layer 6, a sheet-like spacer made of a material having releasability is formed in this portion so as to fill the space between the dam bar 2c and the sealing resin layer 6. By applying (the same thickness as the lead frame 2) and sandwiching it between the mating surfaces of the molds, it is possible to prevent the occurrence of burrs.

[0022]

As described above, according to the resin encapsulation method of the present invention, the circuit assembly is inserted into the injection molding die as in the resin encapsulation method by the transfer molding, and the liquid is injected into the die. Since the thermosetting resin is injected and the encapsulating resin layer is injection-molded in the peripheral area of the circuit assembly, a resin case such as the potting method is not required. Downsizing can be promoted.

In this case, the injection molding temperature condition is set to 1
By setting the temperature in the range of 40 to 180 ° C., there is no fear that the low melting point eutectic solder used for joining the circuit assembly will be remelted during the molding of the sealing resin layer, and even during the cooling process after molding. A resin-encapsulated semiconductor with stable quality, such as suppressing internal stress and cracks in the encapsulating resin layer and shortening the time required for the molding cycle by speeding the gelation time of the liquid resin injected into the mold. The device can be manufactured with high productivity.

[Brief description of drawings]

FIG. 1 is a molding process diagram of a sealing resin layer of a semiconductor device corresponding to a first embodiment of the present invention.

FIG. 2 is a molding process diagram of a sealing resin layer of a semiconductor device corresponding to Example 2 of the invention.

FIG. 3 is a molding process diagram of a sealing resin layer of a semiconductor device corresponding to Example 3 of the invention.

FIG. 4 is a structural cross-sectional view of a resin-sealed semiconductor device manufactured through a molding process of a sealing resin layer.

5 is a plan view of FIG.

FIG. 6 is a plan view of a lead frame with a dam bar used in Embodiment 4 of the present invention.

FIG. 7 is an assembly configuration diagram of a conventional resin-encapsulated semiconductor device manufactured by a potting method.

[Explanation of symbols]

 1 Metal Insulation Substrate 1a Metal Plate 1d Stepped Part 2 Lead Frame 3 Semiconductor Chip 6 Encapsulation Resin Layer 7 Eutectic Solder 8 Injection Mold 8a Upper Mold 8b Lower Mold 8f Stepped Recess 9 Release Agent 10 Packing

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Claims (5)

[Claims] 1. A circuit assembly formed by using a lead frame is mounted on a metal insulating substrate, the lead frame and the metal insulating substrate are solder-joined with a low melting point eutectic solder, and heat dissipation of the metal insulating substrate is performed. A resin encapsulation method for a resin-encapsulated semiconductor device in which the peripheral area of the circuit assembly is resin-encapsulated while exposing the bottom surface, which is a surface, for injection molding of the circuit assembly mounted on a metal insulating substrate. Insert into the mold, 140 ℃ ~ 180
A resin encapsulation method for a resin-encapsulated semiconductor device, which comprises filling a cavity with a liquid thermosetting resin under a molding temperature condition of ° C to form an encapsulation resin layer. 2. The resin encapsulation type semiconductor device according to claim 1, wherein a mold release agent is applied to the bottom surface of the metal insulating substrate in advance to form the encapsulation resin layer. Resin encapsulation method. 3. The resin encapsulation method according to claim 1, wherein a packing which is in contact with the bottom surface peripheral region of the metal insulating substrate is arranged at the bottom of the cavity of the mold to mold the encapsulating resin layer. A resin encapsulation method for a resin encapsulation type semiconductor device. 4. The resin encapsulation method according to claim 1, wherein a stepped portion is formed in advance on the bottom surface side of the metal plate of the metal insulating substrate, and the cavity of the mold is in close contact with the stepped portion. A resin encapsulation method for a resin encapsulation type semiconductor device, which comprises forming a stepped recess to be fitted with each other to form an encapsulation resin layer. 5. The resin encapsulation method according to claim 1, wherein a dam bar surrounding the outer periphery of the encapsulation resin layer molding region is previously formed on the lead frame to mold the encapsulation resin layer. A resin encapsulation method for a resin encapsulation type semiconductor device.