JPH10340914A - Manufacture of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To dispense with an independent cleaning step by performing a conductive paste hardening step for fixing a semiconductor device onto the die pad of a leadframe and a cleaning step for irradiating the semiconductor device with ultraviolet rays simultaneously. SOLUTION: A semiconductor device is fixed onto the die pad of a leadframe using conductive paste during a die bonding step. Successively, both the obverse and reverse surfaces of the semiconductor device are cleaned by irradiation with ultraviolet rays and the conductive paste is hardened by heating the semiconductor device to about 150 to 180 deg.C. During the cleaning, exposed surfaces such as those of the die pads and the leadframe are cleaned by the ultraviolet irradiation. Thereafter, a wire bonding step is performed so that the leadframe is connected to aluminum electrodes. Then, a resin sealing step is performed. Thus, by irradiating the semiconductor device with ultraviolet rays, the conductive paste hardening step and the semiconductor device cleaning step are preformed simultaneously. Hence, the number of process steps can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device, and more particularly, to a method for manufacturing a semiconductor device in a resin-sealed package using a conductive paste.

[0002]

2. Description of the Related Art In a conventional surface mount type package, a semiconductor element is mounted on a die pad of a lead frame by bonding the back surface of the semiconductor element to a die pad of a lead frame using a conductive paste. The structure is such that the die pad is sealed with resin. Hereinafter, up to a resin sealing step in a general semiconductor package assembling step will be described with reference to FIG.

[0003] As shown in FIG. 9, a wafer that has completed the "wafer process" is cut into semiconductor elements in a "dicing process". Next, the cut semiconductor element is fixed to a die pad of a lead frame using a conductive paste in a “die bonding step”. Subsequently, in a “conductive paste curing step”, the conductive paste is cured by heating to about 150 ° C. to 180 ° C. This curing step may be performed by a method of processing all at once in a constant temperature bath, or may be performed by a method of passing through a furnace. Thereafter, wire bonding for connecting the aluminum electrode and the lead frame is performed in a “wire bonding step”. Then, in a “resin sealing step”, the semiconductor element, the die pad, and the like are sealed with resin.

[0004] In a semiconductor package manufactured by the above-described manufacturing method, a package crack may occur due to thermal stress when the semiconductor package is mounted on a circuit board. The cause of the occurrence of the package crack is that the semiconductor element is contaminated with organic matter. Therefore, in order to prevent the front and back surfaces of the semiconductor element from being contaminated with organic substances and thereby reducing the adhesive force with the sealing resin, as shown in the manufacturing process diagram of FIG. After the completion of the process and before the "wire bonding step", a "semiconductor element cleaning step" for cleaning the front or back surface of the semiconductor element by irradiation of ultraviolet rays, plasma, or the like is added. Alternatively, as shown in the manufacturing process diagram of FIG. 11, after the “wire bonding step” is completed and before the “resin sealing step”, the front surface or the back surface of the semiconductor element is cleaned by irradiation with ultraviolet light, plasma, or the like. An additional "cleaning step" has been performed.

[0005]

However, adding a "semiconductor element cleaning step" causes an increase in manufacturing cost and an increase in manufacturing time.

[0006]

SUMMARY OF THE INVENTION The present invention is a method for manufacturing a semiconductor device which has been made to solve the above problems,
That is, in a method of manufacturing a semiconductor device including a step of fixing a semiconductor element to a die pad of a lead frame using a conductive paste, the step of curing the conductive paste and the step of cleaning the semiconductor element are performed simultaneously. The step of curing the conductive paste and the step of cleaning the semiconductor element are performed by, for example, a process of irradiating ultraviolet rays.

In the method of manufacturing a semiconductor device, the step of curing the conductive paste is performed simultaneously with the step of cleaning the semiconductor element, so that it is not necessary to perform the step of curing the conductive paste and the step of cleaning the semiconductor element in separate steps. . Therefore,
The semiconductor element can be cleaned without increasing the number of steps. In addition, since the conductive paste curing step and the semiconductor element cleaning step are performed by treatment with ultraviolet irradiation, the semiconductor element surface and the back surface are cleaned by the ultraviolet light applied to the semiconductor element. The conductive paste is cured.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention is shown in FIG.
This will be described with reference to a manufacturing process diagram of FIG.

As shown in FIG. 1, the wafer which has completed the "wafer process" S1 is cut into semiconductor elements in a "dicing process" S2. Next, the cut out semiconductor element is
In a “die bonding step” S3, the semiconductor chip is fixed to a die pad of a lead frame using a conductive paste. Subsequently, in a “conductive paste curing / semiconductor element cleaning step” S4, the front and back surfaces of the semiconductor element are cleaned by irradiating ultraviolet rays, and the semiconductor element is heated to about 150 ° C. to 180 ° C. to cure the conductive paste. Let it. At this time, the exposed surfaces such as the die pad and the lead frame are also cleaned by the above-described ultraviolet irradiation. Thereafter, wire bonding for connecting the aluminum electrode and the lead frame is performed in a “wire bonding step” S5. Then, in a “resin sealing step” S6, the semiconductor element, the die pad, and the like are sealed with resin. As described above, the “conductive paste curing step” and the “semiconductor element cleaning step” are simultaneously performed by irradiating the semiconductor element with ultraviolet rays.

[0010] The cleaning effect by the above-mentioned ultraviolet irradiation increases as the distance to the object to be cleaned is shorter and the irradiation time is longer. And the effect becomes large, so that the output of an ultraviolet lamp is large.

Next, an example of an ultraviolet irradiation apparatus used in the above-described manufacturing method will be described with reference to the schematic configuration diagram of FIG.

As shown in FIG. 2, the ultraviolet irradiation device 10 is provided with a transport means for transporting the lead frame 21, for example, a transport belt 11 which is moved by a driving device (not shown). Ultraviolet lamps 12 and 13 are provided above and below the conveyor belt 11 so as to face each other.

In the ultraviolet irradiation apparatus 10, the lead frame 21 to which the semiconductor element 22 is die-bonded is placed on the conveyor belt 11, and the conveyor belt 11 is moved in the direction of arrow A to move the lead frame 21 below the ultraviolet lamp 12. (Above the UV lamp 13) and stop. Next, the ultraviolet lamps 12 and 13
Is turned on to irradiate the semiconductor element 22 with the ultraviolet light Lv, thereby cleaning the semiconductor element 22 and curing the conductive paste (not shown). For example, the semiconductor element 22 is heated to about 150 ° C. to 180 ° C., for example, for 2 to 3 minutes by irradiating the ultraviolet light Lv to cure a conductive paste (not shown) for bonding the semiconductor element 22 to the die pad of the lead frame 21. Let it. Normally, the semiconductor element 22 is irradiated with ultraviolet light Lv.
It is sufficient to irradiate the substrate to such an extent that it is heated to a temperature of about 50 ° C. to 80 ° C.
(About 0 ° C.) so that the semiconductor element 2 is decomposed by ultraviolet rays to decompose organic substances.
The front and back surfaces of 2 are thoroughly cleaned. The irradiation time of the ultraviolet light Lv is appropriately determined depending on the intensity of the ultraviolet light Lv.

The amount of heat generated from the ultraviolet lamps 12 and 13 per unit area increases as the lamp output increases and increases as the distance from the ultraviolet lamps 12 and 13 increases. Therefore, it is preferable that the ultraviolet lamps 12 and 13 and the lead frame 21 are brought as close as possible (for example, within 10 mm) to irradiate the ultraviolet light Lv to cure the conductive paste and clean the semiconductor element 22. At that time, for example, the temperature is measured at the position of the lead frame 21, and based on the measured temperature, the outputs of the ultraviolet lamps 12 and 13 are determined.
It is desirable to set the distance between the ultraviolet lamps 12 and 13 and the lead frame 21. Further, from the cleaning state of the semiconductor element 22 and the cured state of the conductive paste, the ultraviolet light Lv
The irradiation time is preferably set.

In the method of manufacturing a semiconductor device, the “conductive paste curing / semiconductor element cleaning step” is performed so that the “conductive paste curing step” and the “semiconductor element cleaning step” are simultaneously performed by ultraviolet irradiation. In addition, it is not necessary to perform the “conductive paste curing step” and the “semiconductor element cleaning step” in separate steps. Therefore, the semiconductor element can be cleaned without increasing the number of steps.
In addition, since the “conductive paste curing / semiconductor element cleaning step” is performed by a process of irradiating ultraviolet rays, the semiconductor element front and back surfaces are cleaned by the ultraviolet rays radiated to the semiconductor elements, and the heat generated at that time causes conduction. The conductive paste is cured.

Further, according to the above-described manufacturing method, the adhesive force between the front and back surfaces of the semiconductor element and the sealing resin can be improved, as in the conventional manufacturing method in which a semiconductor element cleaning step is added. The interface between the semiconductor element, the die pad, and the sealing resin does not peel off due to the thermal stress sometimes generated, so that the occurrence of package cracks can be suppressed and the quality of the package can be improved.

Next, the cause of the occurrence of the package crack will be described, and subsequently, the reason why the package crack can be suppressed will be described.

In a semiconductor package formed by a conventional manufacturing method without performing the semiconductor element cleaning step, a package crack may occur due to thermal stress when the semiconductor package is mounted on a circuit board. The following is known about the mechanism of occurrence of this package crack. As shown in FIGS. 3A and 3B, first, moisture (not shown) diffuses from the surface of the sealing resin 23 constituting the package into the inside thereof. Die pad 24 which is a constituent material,
Since the semiconductor element 22 and the sealing resin 23 have different coefficients of thermal expansion, the interface having the smallest adhesive force peels off due to heat at the time of solder reflow to form a gap 41, and at the same time, moisture enters the gap 41. Spread. The gap 41 expands due to the vaporization and expansion of the moisture, and a package crack 42 occurs.

On the other hand, the conductive paste 25 used to fix the semiconductor element 22 to the die pad 24 is generally made of a thermosetting resin, and this thermosetting resin removes a solvent or unreacted organic matter during the curing process. Generating the semiconductor element 22
To contaminate. On the back surface of the semiconductor element 22,
Transfer of an adhesive material from an adhesive sheet (not shown) used for fixing a wafer in a dicing process is a contamination source. Due to these contaminations, the bonding between the front and back surfaces of the semiconductor element 22 and the sealing resin 23 is prevented, and as a result, the adhesive strength is reduced. This causes separation at the time of solder reflow, causing a gap 41 at the interface with the sealing resin 23, and further causing a package crack 42.

In the manufacturing method of the present invention, the “conductive paste curing / semiconductor element cleaning step” is performed simultaneously with the “conductive paste curing step” and the “semiconductor element cleaning step”. The front and back surfaces of the semiconductor element 22 are cleaned. Therefore, since the front and back surfaces of the semiconductor element 22 are in a cleaned state during the resin sealing, the bonding between the front and back surfaces of the semiconductor element 22 and the sealing resin 23 is sufficiently performed. Therefore, peeling does not occur between the semiconductor element and the sealing resin, and as a result, a package crack due to the peeling does not occur.

The die pad 24 may be a flat plate for bonding the entire back surface of the semiconductor element 22. Generally, the interface having low adhesive strength is the interface between the sealing resin and the lead frame material. Then, the interface between the conductive paste and the die pad, or the interface between the front and back surfaces of the semiconductor element and the sealing resin. Therefore, a semiconductor package having a structure in which the back surface of the semiconductor element is exposed from the die pad may be used by utilizing the fact that the back surface of the semiconductor element has a relatively high adhesive force with the sealing resin to the lead frame material.

An example of such a die pad will be described with reference to FIGS.

As shown in FIG. 4, an opening 24A is formed in the center of the die pad 24 of the lead frame 21, and the back surface of the semiconductor element 22 is formed on the die pad 24 around the opening 24A by a conductive paste ( (Not shown). Therefore, a part of the back surface of the semiconductor element 22 is exposed from the opening 24A.
4A is a diagram viewed from the front surface side of the semiconductor device 22, FIG. 4B is a diagram viewed from the back surface side of the semiconductor device 22, and FIG. FIG. 4 is a cross-sectional view taken along a line A.

Alternatively, as shown in FIG.
May be provided with a plurality of openings 24A to 24D. In FIG. 5, (1) is a view as viewed from the front side of the semiconductor element 22, and (2) is a view as viewed from the back side of the semiconductor element 22.

Further, as shown in FIG.
Is formed in a so-called X-shape linear shape substantially in line with the diagonal line of the semiconductor element 22 to be mounted. As shown in FIG.
The semiconductor element 22 may be formed linearly from the outside of the side of the semiconductor element 22 toward the semiconductor element 22 so as to support the corners of the semiconductor element 22. 6 and 7, (1) is a view as viewed from the front side of the semiconductor element 22, and (2) is a view as viewed from the back side of the semiconductor element 22.

Even when the semiconductor element 22 is bonded to the die pad 24 described with reference to FIGS. 4 to 7, it is effective to apply the manufacturing method of the present invention.

[0027]

As described above, according to the present invention,
By simultaneously performing the conductive paste curing step and the semiconductor element cleaning step, the number of steps can be reduced. Moreover, as in the case where the conventional semiconductor element cleaning step is performed, the adhesive strength between the front and back surfaces of the semiconductor element and the sealing resin can be improved. Therefore, the interface does not peel off due to the thermal stress generated at the time of solder reflow, the generation of package cracks can be suppressed, and the quality can be improved.

[Brief description of the drawings]

FIG. 1 is a manufacturing process diagram of an embodiment according to the present invention.

FIG. 2 is a schematic configuration diagram of an example of an ultraviolet irradiation device.

FIG. 3 is an explanatory diagram of a package crack.

FIG. 4 is an explanatory diagram of a die pad.

FIG. 5 is an explanatory diagram of a die pad.

FIG. 6 is an explanatory diagram of a die pad.

FIG. 7 is an explanatory diagram of a die pad.

FIG. 8 is a manufacturing process diagram relating to a conventional manufacturing method.

FIG. 9 is a manufacturing process diagram related to a conventional manufacturing method.

FIG. 10 is a manufacturing process diagram related to a conventional manufacturing method.

[Explanation of symbols]

 S4: Conductive paste curing / semiconductor element cleaning process

Claims (2)

[Claims] 1. A method for manufacturing a semiconductor device comprising a step of fixing a semiconductor element to a die pad of a lead frame using a conductive paste, wherein the step of curing the conductive paste and the step of cleaning the semiconductor element are performed simultaneously. A method for manufacturing a semiconductor device. 2. The method of manufacturing a semiconductor device according to claim 1, wherein the step of curing the conductive paste and the step of cleaning the semiconductor element are performed by irradiation with ultraviolet light.