JPH07226414A - Method of sealing semiconductor device, and resin-sealed semiconductor device - Google Patents

Abstract

PURPOSE:To provide a method of reliable resin sealing of a semiconductor chip placed in a given position on a circuit board. CONSTITUTION:A method of sealing a semiconductor chip 1 on a circuit board 3 with resin comprises the steps of placing a solid piece of resin 9, and heating and compressing the solid piece of resin. Since the semiconductor chip is placed face down, its face with electrodes is not covered with resin. Further, the whole semiconductor chip on the circuit board, except the chip surface with electrodes, is molded with resin.

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 semiconductor element and a resin encapsulation type semiconductor device, and more particularly to a resin encapsulation method for a semiconductor element mounted on a circuit board and a resin encapsulation type semiconductor device.

[0002]

2. Description of the Related Art Various methods have been conventionally used for mounting a semiconductor device on a circuit board. As the most reliable and easy method, there is a method of connecting the external lead-out of a semiconductor package in which a semiconductor element is sealed by resin compression molding (transfer molding) to a circuit board by soldering. However, this method has a drawback that the packaging density is not very high.

Therefore, a bare semiconductor element not resin-sealed is fixedly connected to a predetermined position on the circuit board with a conductive paste,
A resin encapsulation method by non-compression in which an electrode of a semiconductor element and a circuit pattern of a circuit board are connected by a thin metal wire and a liquid resin is dropped and covered is also used. In this method, since a bare semiconductor element is used, the packaging density can be increased.

Further, instead of the above method of dropping and coating the liquid resin, a circuit board on which a semiconductor element is mounted is sandwiched in a transfer molding die, and the molten plasticized resin is pressed to apply the semiconductor element portion. There is also used a method of injecting into and compressing.

[0005]

The method of soldering the resin-encapsulated semiconductor device having the external leads to the circuit board as described above has a limit in reducing the size and thickness of the package. It is an obstacle to improvement. As a soldering method, an infrared reflow method in which the entire semiconductor device is heated at a high temperature has become the mainstream, and cracking of the resin package during heating has become a serious problem. From the viewpoint of improving the mounting density, a method of directly mounting and sealing the semiconductor element on the circuit board is preferable.

At present, as a method for sealing a semiconductor element directly attached to a circuit board, (1) a liquid resin is dropped onto the surface of the semiconductor element and a bonding portion to be cured, and (2) a sheet-like solid resin. Is placed on a semiconductor element to be heated and melted for coating, and (3) resin sealing by transfer molding is available. In the case of (1) and (2), the adhesion between the circuit board and the resin is inferior to that of the compression molding due to non-compression molding, and the resin cannot be contained in a large amount because the fluidity of the resin is deteriorated. There is a problem that there is a limit to reducing the stress on the semiconductor element due to the contraction.

On the other hand, in the transfer molding of (3), since the mold is used, the size of the circuit board and the position of the semiconductor element on the circuit board are restricted, and it is necessary to consider the fluidity of the resin for the transfer molding. Therefore, in order to achieve both high filler filling for reducing molding shrinkage and fluidity, special fillers such as spherical fillers and fine fillers have to be used, which causes a problem that the resin price increases.

The present invention has been made in view of the above circumstances, and is a means for easily forming a resin encapsulation having good adhesion and high reliability with respect to a semiconductor element mounted at an arbitrary position on a circuit board. And a new resin-encapsulated semiconductor device based on it.

[0009]

In order to achieve the above object, in the resin sealing method of the present invention, in the resin sealing method for a semiconductor element mounted on a circuit board, a solid resin is mounted on the semiconductor element. It is characterized by comprising a step of placing and a step of heat compression molding the solid resin.

Another feature is that the semiconductor element is mounted face down and its electrode surface is not covered with the solid resin. Further, in the resin-sealed semiconductor device of the present invention, a circuit board on which a wiring circuit is formed, a semiconductor element mounted face down on the circuit board, and a sealing for covering the semiconductor element except its electrode surface And a resin.

[0011]

In the resin sealing method of the present invention, the solid resin is heated and compression-molded by using a simple mold. Therefore, the resin whose viscosity is temporarily lowered by heating and becomes fluidized is sufficiently compressed with the circuit board. In close contact. FIG. 8 compares the conventional potting sealing and compression molding sealing in terms of cumulative defective rate in a pressure cooker test (2 atm, 121 ° C.). Sealing by potting is non-compression molding and has poor adhesion and causes defects early, whereas sealing by compression molding has excellent adhesion and dramatically improves reliability.

Since the mold may be simpler than the transfer molding mold, the semiconductor element can be resin-sealed at almost any position on the circuit board by compression molding. When a thermoplastic resin or a semi-cured thermosetting resin is used as the solid resin, it can be handled as a film, so that workability is improved.

If the semiconductor element is mounted face down on the circuit board and the solid resin is compression-molded in a state in which an air escape path is not formed between the two, a gap between the circuit board and the electrode surface of the semiconductor element is formed. The resin can be prevented from entering. As a result, when the semiconductor element has a fine electrode surface which is weak against mechanical stress, the electrode surface is not damaged by the resin, and the reliability is improved.

[0014]

Embodiments of the present invention will now be described with reference to the drawings. 1 to 3 are sectional views schematically showing the manufacturing process of the first embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a semiconductor element, on the surface of which a bump electrode 2 of Au is formed. The bump electrode 2 can be formed by a transfer bump method or a plating method. Reference numeral 3 is a circuit board of a glass epoxy base material on which wiring circuits are formed of copper foil on both sides. As the circuit board, it is also possible to use a thick film board having a circuit formed by printing a conductive paste on a ceramic substrate or a thin film board having a circuit formed by vapor deposition or the like.

A lead electrode 4 corresponding to the bump electrode 2 is formed at a position where the semiconductor element 1 is mounted on one main surface of the circuit board 3, and the surface is plated with Au. Further, the portion excluding the connecting portion of the lead electrode 4 is covered with the solder resist 5. Also, the circuit board 3
A vent hole 6 for venting gas is provided immediately below the semiconductor element 1. The bump electrodes 2 and the lead electrodes 4 are brought into contact with each other after alignment and joined by thermocompression bonding.

Next, FIG. 2 is a cross-sectional view schematically showing the resin sealing process, in which the circuit board 3 on which the semiconductor element 1 is mounted is placed on the hot plate 7. A fixed die 8 surrounding the semiconductor element 1 is placed around the semiconductor element 1 and fixed by a fixture (not shown). Since the fixed mold 8 is placed on the solder resist 5 having a cushioning property, good adhesion with the circuit board 3 is maintained.

Next, the solid sealing resin 9 is put into the opening of the fixed mold 8. As the solid sealing resin 9, a thermoplastic resin or a thermosetting resin in a semi-cured state (B stage) can be used, and polyphenylene sulfide resin, polysulfone resin, polyimide resin, silicone resin, epoxy resin or the like is preferable.

In the case of the epoxy resin in the B stage, if the temperature of the hot plate 7 is set to 170 to 190 ° C., the epoxy resin is heated and melted. A movable mold 10 that fits into the opening of the fixed mold 8 is set on the upper part of the sealing resin 9, and the sealing resin 9 is pressed with a predetermined pressure (8 to 10 MPa in the case of an epoxy resin). . As a result, the molten sealing resin 9 enters the gap between the semiconductor element 1 and the circuit board 3. Since the circuit board 3 has the vent hole 6, air is discharged from the vent hole 6 and escapes into the gap between the hot plate 7 and the circuit board 3. As a result, as shown in a sectional view in FIG. 3, the resin 9 fills the gap and the resin sealing is completed.

The size of the fixed mold 8 used for this resin encapsulation is such that the chip size of the semiconductor element 1 is 15 × 15 mm.
In the case of about 40 x 40 mm outer diameter, 20 x 20 mm inner diameter
Although the surface mounting components other than the semiconductor element 1 are prohibited to be mounted in this region, the area is relatively small and the compression sealing effect is larger than the mounting restriction.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 3 is a cross-sectional view for explaining the resin sealing method, but since the basic structure is the same as that of FIG. 2, the same parts are designated by the same reference numerals and the description thereof is partially omitted. In this embodiment, a vent hole is not formed in the circuit board 3 ', and the surface (electrode forming surface) of the semiconductor element 1 can be formed in a hollow mold in which it is not covered with the sealing resin 9'. This is an effective configuration when the semiconductor element 1 has a fine electrode surface and damage to the semiconductor element 1 due to direct contact with the sealing resin is expected.

The height of the bumps 2 of the connected semiconductor element 1 is 10 μm, and the height of the plated terminal wiring 4 is 32.
The gap of 42 μm in total is the semiconductor element 1 and the circuit board 3.
However, if the compression molding of the present invention is performed, the sealing resin 9'flows evenly from each side of the semiconductor element 1 and stays on the surface side of the semiconductor element to enable hollow molding. The concave portion 11 provided on the surface of the circuit board 3 is provided as a reservoir for the accumulated air and is not always necessary.

Further, by adjusting the maximum particle size and particle size distribution of the resin filler, it is possible to prevent the resin from flowing through the above-mentioned gap. FIG. 5 shows the relationship between the maximum particle size of silica and the minimum value of flowable clearance when silica is used as the filler. In the case of the gap of 42 μm in the above example, the filler contains 55 μm or more. I understand that I should do it.

FIG. 6 shows the relationship between the silica volume fraction (Vol%) and the molding shrinkage or the spiral flow. In the case of transfer molding, a spiral flow of 80 cm or more is required, so the silica content is 65 V
Although the limit is ol%, in the case of the compression molding of the present invention, sealing is possible even with a spiral flow of 80 cm or less, and silica can be contained in an amount of 65 Vol% or more to reduce molding shrinkage as compared with transfer molding.

Next, a third embodiment of the present invention is shown in FIG. FIG. 7 is a cross-sectional view showing a state where the resin sealing is completed, which is an example using a semiconductor element connected to a tape carrier. In the figure, the leads 23 connected to the semiconductor element 21 and held by the support ring 22 are connected to the terminal wirings 25 formed on one main surface of the circuit board 24. Two
6 is a solder resist. Reference numeral 27 denotes a sealing resin, which is compression molded by the same method as in the first embodiment. Reference numeral 28 is a vent hole, and in this case, since the lower surface of the semiconductor element 21 cannot be used because it is a die mount, it is provided at a place avoiding the die pad 29. In this way, the sealing method of the present invention can be applied even when the semiconductor element is mounted face up. This is an effective mounting method when it is desired to sufficiently carry out burn-in or characteristic inspection of the semiconductor element 21 before mounting the semiconductor element 21 on the circuit board 24. It goes without saying that the semiconductor element 21 may be attached face down or may be formed by hollow molding.

[0025]

As described above, the resin encapsulation method of the present invention is excellent in adhesion to the circuit board because it is resin-encapsulated by compression molding, and is superior to conventional potting encapsulation with liquid resin. Moisture resistance can be obtained. Further, since a simple mold is used, resin molding by compression molding can be performed at almost any position on the circuit board.

Further, as miniaturization of the semiconductor element progresses, the semiconductor element may be damaged by the stress generated by the molding shrinkage of the resin or the thermal stress such as the cooling / heating cycle.
These can be avoided by using the hollow mold of the present invention.

The encapsulating material used for hollow molding does not need to take fluidity into consideration as compared with the material used for transfer molding, and the amount of the filler can be easily increased. Therefore, molding shrinkage can be reduced and heat dissipation can be improved, so that deterioration of the semiconductor element due to heat generation can be reduced.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a connection state of a semiconductor device according to a first embodiment of the present invention with a circuit board.

FIG. 2 is a sectional view showing a compression molding step according to the first embodiment of the present invention.

FIG. 3 is a cross-sectional view showing a state where resin sealing according to the first embodiment of the present invention is completed.

FIG. 4 is a sectional view showing an embodiment of a compression molding process according to the second embodiment of the present invention and a state in which the compression molding is completed and a hollow mold is formed.

FIG. 5 is a graph showing the relationship between the maximum particle size of the filler and the clearance through which resin can flow (enter) according to the second embodiment of the present invention.

FIG. 6 is a graph showing the relationship between the filler volume fraction and the molding shrinkage rate according to the second example of the present invention.

FIG. 7 is a sectional view showing a state in which resin sealing according to a third embodiment of the present invention is completed.

FIG. 8 is a graph comparing the cumulative defective rate in the pressure cooker test of non-compression molding (potting) and compression molding.

[Explanation of symbols]

 1 ... Semiconductor element 2 ... Bump electrode 3 ... Circuit board 4 ... Terminal wiring 5 ... Solder resist 6 ... Vent hole 7 ... Hot plate 8 ... Fixed mold 9 ... Solid resin 10 ... Movable mold

Claims (3)

[Claims] 1. A resin sealing method for a semiconductor element mounted on a circuit board, comprising: a step of placing a solid resin on the semiconductor element; and a step of heat compression molding the solid resin. A resin encapsulation method for a semiconductor element, comprising: 2. The resin encapsulating method for a semiconductor element according to claim 1, wherein the semiconductor element is mounted face down and the electrode surface thereof is not covered with the solid resin. 3. A circuit board on which a wiring circuit is formed, and a semiconductor element mounted face down on the circuit board,
A resin-encapsulated semiconductor device, comprising: a sealing resin that covers the semiconductor element excluding its electrode surface.