JPH11154785A - Manufacture of electronic component - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for efficiently forming an electronic component with a highly reliable solder junction. SOLUTION: Solder set between two components is melted in a chamber 8 that is filled with a gas having a lower oxygen concentration and a higher thermal conductivity than those of the normal atmosphere under a pressure low enough to obtain the same temperature profile as under a normal pressure. Then, while the soldering temperature is maintained, the pressure inside the chamber 8 is rapidly increased immediately before the molten solder is solidified so that voids in the molten solder 3 are compressed. Consequently, the solder volume is 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 an electronic component, and more particularly, to a method for manufacturing an electronic component in which the reliability of bonding by soldering or the like, which is indispensable for the technology for manufacturing an electronic component, is improved.

[0002]

2. Description of the Related Art The most important manufacturing technology in the electronics field is bonding of a substrate to an electronic element such as an LSI, soldering used for hermetically sealing a package, or bonding a cooling fin or the like to the electronic element. It is positioned as. For this reason, the establishment of the reliability of the joint such as soldering is a very important issue in the electronics field.

[0003] One of the factors that are considered to be particularly problematic as a factor that lowers the reliability of a joint such as soldering and, consequently, the performance of an electronic device itself, is that a solder joint and a base material (component mounting on a substrate). Voids (bubbles) formed in the interface with the solder pattern and the solder joint.

FIG. 3 is a view showing a state of a void formed in the above-mentioned joint. This type of void will be described below with reference to FIG. In FIG. 3, 1
Is a substrate, 2 is an electronic element, 4 is a component mounting pattern, 5 is a terminal pattern, 6 is a solder joint, and 7 is a void.

In general, an electronic component is formed by forming a solder joint 6 between a component mounting pattern 4 on a substrate 1 which is two base materials and a terminal pattern 5 of an electronic element 2. Then, the bonding of the electronic element 2 onto the substrate 1 is usually performed.
A solder material is sandwiched between the component mounting pattern 4 on the substrate 1 and the terminal pattern 5 of the electronic element 2, and the whole is heated to melt the solder material and then cooled to form a solder joint portion 6. This is done by: In this joining process, as shown in FIG. 3, voids are formed in the solder joint 6 or at the interface between the component mounting pattern 4 on the substrate 1 and the terminal pattern 5 of the electronic element 2 in the solder joint 6. 7
May be formed.

Therefore, when joining electronic elements and the like by soldering, generally, various measures are taken to suppress the formation of voids as described above. For example, as one of the prior arts that have made such a contrivance, there is known a method of performing a pre-treatment called "older soldering".

FIG. 4 is a cross-sectional view for explaining the procedure of a conventional soldering method for performing a pre-treatment of performing pre-soldering. The conventional soldering method will be described below with reference to FIG. In FIG. 4, 3 is solder, 9 is a heater, and other reference numerals are the same as those in FIG.

In the method shown in FIG. 4, first, as shown in FIG. 4 (a), the solder 3 is placed on the component mounting pattern 4 on the substrate 1, and as shown in FIG. These are placed on the heater 9 and the solder 3 is once heated and melted. As a result, impurities and the like taken into the solder 3 are vaporized, and the voids 7 are formed in the molten solder in which the solder 3 is heated and melted.
Generate. Since the void 7 does not obstruct defoaming on the molten solder, the void 7 can quickly escape from the state shown in FIG. 4B.

Thereafter, as shown in FIG. 4C, the electronic element 2 having the terminal pattern 5 is placed on the solder 3 having no void 7, and the solder
Is heated and melted again and cooled to obtain FIG.
As shown in (d), an electronic component in which the component mounting pattern 4 on the substrate 1 and the terminal pattern 5 of the electronic element 2 are joined by the solder joint 6 can be obtained. In this case, it is possible to eliminate voids in the solder joint 6, and to increase the reliability of the electronic component.

[0010] As a conventional technique relating to the above-mentioned cross soldering, a technique described in, for example, JP-A-3-202787 is known.

In addition, as a conventional soldering method for suppressing the formation of voids other than the above-mentioned method using the conventional soldering, a technique described in, for example, Japanese Patent Application Laid-Open No. 5-291314 is known. This method is a method of performing soldering using a vacuum heat treatment furnace (hereinafter, referred to as a vacuum heating type soldering method). By performing soldering in a vacuum, it is included in molten solder during soldering. This is a method of forcibly removing bubbles that are present.

Further, as another conventional technique, for example, a technique described in Japanese Patent Application Laid-Open No. 63-22603 is known. In this method according to the prior art, solder is supplied in a state where a space area for soldering is created in advance,
A method in which the space is heated in a vacuum to melt the solder in a vacuum state, the pressure of the atmosphere in the space is increased at the time of melting the solder, and voids generated inside the melted solder are crushed (hereinafter, referred to as a method). Vacuum space method).

[0013]

According to the above-described method of performing the soldering, the voids can be removed by once melting the solder in advance, and the reliability of the solder joint can be improved. Extra time is required for the time required for the process of melting the solder in advance, and a new problem occurs in that the efficiency of the entire process for solder joining is reduced.

The soldering method of the vacuum heating method is as follows.
It is necessary to raise the temperature of the work from room temperature to the soldering temperature in a vacuum heat treatment furnace in a vacuum state, and the time required for this is about twice as long as heating at normal pressure, which is not efficient. There is a problem that.
Such efficiency problems can be easily solved by operating multiple soldering apparatuses simultaneously, but this method requires a considerable amount of new equipment in connection with the introduction of multiple soldering apparatuses. There is a problem that it is not a reasonable solution to the current situation where investment has to be made and the demand for suppressing the production cost is increasing.

Further, since the above-mentioned soldering method using the vacuum space method requires heating in a vacuum as in the above-described vacuum heating method, it takes a considerable time to raise the temperature to the soldering temperature. There is a problem that solder must be supplied in a state where a space region has been created in advance, which causes a problem such as poor workability.

In any of the above-mentioned soldering method, vacuum heating method, and vacuum space method, the substrate is made of a porous material such as ceramics, and a pretreatment (plating) prior to soldering is performed. Etc.), the substrate immersed in the liquid is not completely dried,
During the heating and melting of the solder, gas is constantly generated from the inside of the board, so the entrainment and generation of gas into the molten solder cannot be completely suppressed. There is a problem that voids are formed.

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a method of manufacturing an electronic component by a soldering method capable of efficiently forming a more reliable solder joint. Another object of the present invention is to provide a method of manufacturing an electronic component by a soldering method which can easily secure the reliability of a defective solder joint formed by a conventional soldering method.

[0018]

According to the present invention, an object of the present invention is to heat and melt a solder or a solder paste interposed between two base materials in an atmosphere formed in a sealed container.
Alternatively, in the method for manufacturing an electronic component that forms a solder joint by re-melting the solder between two base materials that have already been solder-joined, the atmosphere is formed with a gas having a higher thermal conductivity than the atmosphere as the atmosphere. An atmosphere is prepared, and the solder is melted in a state where the pressure of the atmosphere is reduced prior to the heating and melting of the solder, and the pressure of the atmosphere is higher than the pressure before the heating and melting before the molten solder is solidified. This is achieved by:

[0019] The object of the present invention is to provide a gas atmosphere having a higher thermal conductivity than the atmosphere, the atmosphere having a lower oxygen concentration than the air, and to reduce the pressure prior to the heating and melting of the solder. This can be achieved by setting the pressure of the atmosphere in a range in which the temperature of the two base materials for performing the solder joining rises substantially at the same level as at normal pressure.

The above-mentioned atmosphere formed by a gas having a higher thermal conductivity than that of the atmosphere and below normal pressure can be quickly heated from normal temperature to the soldering temperature by externally applied heat. Therefore, the solder can be melted in a short preheating time. For example, as this gas, helium (He) gas having a thermal conductivity of 1.4 × 10 ^-1 w / mK is used, and ^１ ／ of normal pressure (760 Torr) (about 150
rr), even if a heater having the same performance as that used in the vacuum heating type soldering method described in the section of the prior art is used, the solder can be heated in less than half the time of the conventional method. It can be heated and melted, and the same temperature profile can be obtained as when the solder is heated and melted at normal pressure.

As a gas having a higher thermal conductivity than the atmosphere, there is a hydrogen (H ₂ ) gas in addition to the above-mentioned He gas, which has a higher thermal conductivity than the He gas, but the H ₂ gas is mixed with the atmosphere. Sometimes explodes easily and is difficult to handle. But,
By mixing about 4% of H ₂ gas into He gas, it can be used safely, and in the present invention, even better results can be obtained by using such a mixed gas.

Before the heat-melted solder solidifies (preferably at a timing immediately before the heat-melted solder completely solidifies), the pressure of the atmosphere is rapidly returned to normal pressure (increased). Thereby, the bubbles formed during the heating and melting are compressed to such an extent that the bubbles hardly remain. Therefore, the finally formed solder joints
A state in which almost no void remains can be obtained. At this time, if the difference between the pressure before the heat melting and the pressure returned immediately before the solder being solidified during the heat melting is large, the void is compressed in proportion to the pressure ratio.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a method for manufacturing an electronic component according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a flowchart for explaining the processing operation of the electronic component manufacturing method according to one embodiment of the present invention, and FIG.
FIG. 3 is a cross-sectional view showing a state of a workpiece during processing. In FIG. 2, reference numeral 8 denotes a chamber, and other reference numerals are the same as those in FIGS.

In one embodiment of the present invention described below, a component mounting pattern 4 (surface area of about 40 cm ² ) on a substrate 1 as two base materials and a terminal pattern 5 (surface area of 50 cm ² ) of the electronic element 2 are used. ² )) to manufacture electronic components by soldering. In addition, it does not matter whether or not the through hole is formed in the substrate 1 as a matter of course. Also, the size relationship between the component mounting pattern 4 of the substrate 1 and the terminal pattern 5 of the electronic element 2 does not matter.

(1) First, an operator sets the solder 3 on the component mounting pattern 4 of the board 1 as shown in FIG. At this time, a solder paste or the like may be applied on the component mounting pattern 4 of the substrate 1. After that, the electronic element 2 is mounted thereon so that the solder 3 is sandwiched between the component mounting pattern 4 of the substrate 1 and the terminal pattern 5 of the electronic element 2. Then, the work thus configured is arranged on the heater 9 inside the chamber 8 as shown in FIG. In this case, the work is placed on the heater 9 such that the surface of the substrate 1 opposite to the component mounting pattern 4 contacts the heater 9 (step 100).

(2) After the above setting is completed, the inside of the chamber 8, which is a processing chamber constituted by a sealed container, is depressurized by a vacuum pump, and a gas having a high thermal conductivity (for example, He gas, He and H _{2) is used.} Etc.). At this time, this operation is repeated until the atmosphere formed by the introduced gas reaches a certain oxygen concentration (step 101).

(3) Thereafter, the pressure is further reduced again by the vacuum pump, and the gas having a high thermal conductivity is introduced into the chamber 8 while the atmosphere in the chamber 8 is controlled by the pressure controller so as to have a predetermined pressure. To a predetermined pressure. Note that this process is performed once by using a high-performance vacuum pump to supply high-vacuum gas and then supplying the gas, so that the process is performed once together with the process in step 101. Can also. At this time, the pressure in the chamber due to gas introduction needs to obtain the same temperature profile as when heating is performed by introducing gas to normal pressure. The pressure in the atmosphere at this time differs depending on the thermal conductivity of the gas to be introduced, the substrate size and the material. In the described embodiment, when He gas is used as the gas having a high thermal conductivity and the substrate 1 having the component mounting pattern 4 having the above-described size is processed, the atmospheric pressure is set to 1 at normal pressure. Even if the pressure before heating and melting was reduced to about / 5, the same temperature profile (time-to-temperature rise characteristic) as that when the gas was introduced to room temperature could be obtained (step 102).

(4) Thereafter, the heater 9 is operated to start heating so as to heat the inside of the chamber 8 at a stretch.
In the processing described above, the inside of the chamber 8 is depressurized, but the inside of the chamber 8 is filled with an atmosphere gas having a higher thermal conductivity than the atmosphere, and the temperature profile is the same as that at normal temperature. Therefore, even if a heater having the same performance as the heater used in the vacuum heating type soldering method is used, the chamber 8 can be heated in less than half the time of this method. Can be quickly raised from the normal temperature to the soldering temperature. Here, the soldering temperature is a temperature set according to the type of the solder 3 used, for example, a eutectic solder (Sn-37P
b: 183 ° C.) is usually set at a temperature of about 200 ° C., which is slightly higher than the melting point (step 103).

(5) After the internal temperature of the chamber 8 has been raised to the soldering temperature, the internal temperature of the chamber 8 (to be precise, the substrate 1 (Temperature) is maintained so that the heater 9 is maintained. During this time, the solder 3 sandwiched between the component mounting pattern 4 of the substrate 1 and the terminal pattern 5 of the electronic element 2 is heated and melted, as shown in FIG.
It spreads sufficiently on the component mounting pattern 4 on the substrate 1 and the terminal pattern 5 of the electronic element 2. In an atmosphere having an oxygen concentration lower than that of the atmosphere, an oxide film that hinders the spread of the molten solder 3 is hardly formed on the surface of the molten solder 3. You don't have to. Therefore, a cleaning step using an organic solvent or the like is not required (step 104).

(6) Thereafter, a gas is introduced into the chamber 8 before, if possible, immediately before the molten solder solidifies, and the internal pressure of the chamber 8 is adjusted to an appropriate pressure (a constant pressure of 7).
(About 60 Torr). Then, while maintaining the pressure state inside the chamber 8, the chamber 8 is left for an appropriate time (usually about 30 seconds). As a result, the voids 7 contained in the molten solder 3 are forcibly compressed by the rapid rise of the pressure, and are reduced to such a degree that almost no trace is left, and as shown in FIG. The voids 7 hardly remain in the solder joints 6 to be formed. That is, this makes it possible to almost completely remove the voids that could not be removed conventionally. Since the internal pressure and the standing time of the chamber 8 in this process are not uniquely determined, it is desirable to appropriately adjust the composition and volume of the solder 3 to be used and the volume of the chamber 8 (step 105). .

(7) After that, the driving of the heater is stopped, and the inside of the chamber 8 is cooled by driving the cooling device, and the molten solder 3 is gradually solidified.
After cooling itself to room temperature, the substrate 1
Is taken out (steps 106 and 107).

According to the method according to the embodiment of the present invention described above, a better solder joint can be formed without performing any pretreatment such as soldering and without extending the heating time at all. And an efficient electronic component can be manufactured.

In the above-described embodiment of the present invention, a case where an electronic component is manufactured by soldering the component mounting pattern 4 on the substrate 1 and the terminal pattern 5 of the electronic element 2 will be described as an example. However, the present invention does not require any operation when soldering other components to each other, for example, when soldering a heat sink on a substrate, or when sealing a package. It can be applied without any special changes.

In the above-described embodiment of the present invention, the internal temperature of the chamber 8 and the like are measured in-process by a sensor, and the pressure is controlled based on the measurement result. For example, a time chart of the soldering process may be prepared in advance based on past experience, and the pressure may be controlled based on the elapsed time from the soldering process start time measured by the timer. .

Further, the above-described embodiment of the present invention
The reliability of the defective solder joint formed by the conventional soldering method can be easily restored, and the electronic component having the defective solder joint can be restored to a normal and highly reliable one. In this case, the process described with reference to FIG. 1 may be performed after an electronic component having a defective solder joint is set in the chamber 8.

[0037]

As described above, according to the present invention, a solder joint having higher reliability than before can be formed efficiently without the need for special jigs and tools. Electronic components can be manufactured efficiently. In addition, the reliability of the defective solder joint formed by the conventional soldering method can be easily recovered. Furthermore, since there is no need to use a flux, an effect of not adversely affecting the environment can be obtained.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating a processing operation of an electronic component manufacturing method according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a state of a workpiece during processing.

FIG. 3 is a diagram showing a state of a void formed in a solder joint.

FIG. 4 is a cross-sectional view for explaining a procedure of a soldering method according to a conventional technique for performing pre-soldering as preprocessing.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Electronic element 3 Solder 4 Component mounting pattern of substrate 1 5 Terminal pattern of electronic element 6 Solder joint 7 Void 8 Chamber 9 Heater

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Kaoru Katayama 1st Horiyamashita, Hadano-shi, Kanagawa Prefecture General-purpose Computer Division, Hitachi, Ltd. (72) Inventor Ken Ken Mitsui 1st Horiyamashita, Hadano-shi, Kanagawa Japan Inside the General-purpose Computer Division of Ritsu Works

Claims (3)

[Claims] In an atmosphere formed in a sealed container, 2
In a method for manufacturing an electronic component that forms a solder joint by heating and melting a solder or a solder paste interposed between two base materials, or by remelting a solder between two base materials that have already been soldered, An atmosphere formed of a gas having a higher thermal conductivity than the atmosphere is prepared as the atmosphere, and the solder is melted in a state where the pressure of the atmosphere is reduced prior to the heating and melting of the solder, and the molten solder is solidified. A method of manufacturing the electronic component, wherein the pressure of the atmosphere is made higher than the pressure before the heating and melting. 2. The method for manufacturing an electronic component according to claim 1, wherein the atmosphere of the gas having a higher thermal conductivity than the atmosphere is an atmosphere having a lower oxygen concentration than the atmosphere. 3. The pressure of the atmosphere in which the pressure is reduced prior to the heating and melting of the solder is a pressure within a range in which a rise in the temperature of two base materials for performing the solder joining is substantially the same as that at normal pressure. The method for manufacturing an electronic component according to claim 1, wherein: