JP2004130351A - Soldering method requiring no flux - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a soldering method requiring no flux. <P>SOLUTION: Solder 6 is arranged on the soldering face 2a of one of the two objects 2, 4 to be soldered. While a free radical gas is supplied to this soldering face 2a and the soldering face 4a of the other object 4, the two objects 2, 4 are heated to a temperature at which the solder 6 is melted and are then cooled. The soldering face 2a on which the solder 6 is melted is superposed on the soldering face 4a of the other object 4, heated at the melting temperature of the solder 6, and subsequently cooled. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for soldering, and more particularly, to a method for soldering two objects to be joined.
[0002]
[Prior art]
Solder bonding may be used, for example, when bonding a semiconductor device to a heat sink or the like. Usually, when soldering is performed, a flux is used to form an interface between the solder and the object to be bonded and to perform bonding. This flux is removed by washing after forming the bond.
[0003]
[Problems to be solved by the invention]
However, this flux is not completely removed in the washing step, and the remaining flux becomes a residue. For example, in the case of bonding the semiconductor device to the heat sink as described above, this residue prevents the formation of terminals by wire bonding performed in the next step, or short-circuit of the circuit due to ions precipitated from solder called ion migration. Problems.
[0004]
An object of the present invention is to provide a method for performing solder joining without using a flux that causes such a problem.
[0005]
[Means for Solving the Problems]
The solder joining method according to the present invention includes two steps. In the first step, the solder is arranged on the joining surface of one of the two joining objects to be soldered to each joining surface by solder. These joining objects include, for example, a semiconductor device and a base for the semiconductor device, for example, a heat sink. As the solder, a lead-free solder, for example, SnAgCu, SnAg, or a lead solder, for example, SnPb can be used. The two joining objects are heated at a temperature at which the solder melts while supplying free radical gas to the joining surface of the solder placement and the joining surface of the other joining object. The free radical gas may be any gas having a reducing property, and for example, a hydrogen radical can be used. In the second step, the bonding surface of the other object to be bonded is overlapped on the bonding surface where the solder has been melted, heated at a temperature at which the solder melts, and then cooled.
[0006]
In this bonding method, in the first step, the solder is melted in a state where the free radical gas is supplied, so that the oxide contained in the solder is reduced. At the same time, the bonding surface of the bonding target is also reduced, and cleaning is performed. As a result, the wettability of the solder to the joining surface of the joining object on which the solder is placed is also improved. Thereafter, in a second step, the two joining objects can be joined by soldering by heating, melting and cooling the solder in a state where the joining surfaces of the two joining objects are overlapped. By soldering in this manner, two objects to be joined can be soldered without using a flux.
[0007]
The solder may have a shape having a gap between a part of the solder and a joining surface of one of the joining objects. For example, thread solder can be used. By forming the gaps in this manner, the cleaning of the bonding surface on which the solder is placed and the reduction of the solder are favorably performed by the hydrogen free radical gas, and the wettability of the solder can be improved.
[0008]
Also in the second step, a free radical gas can be supplied to the two joining surfaces. In this case, the reduction by the free radical gas is performed also at the time of joining the joining objects.
[0009]
In a solder bonding method according to another aspect of the present invention, first, two objects to be soldered, each of which is to be soldered to each bonding surface, are arranged so that their bonding surfaces are opposed to each other, and solder is applied between these bonding surfaces. It is interposed so as to form a gap between the two joining surfaces. The two objects to be joined are heated in a free radical gas atmosphere at a temperature at which the solder melts, and then cooled.
[0010]
Also in this solder joining method, when the solder is melted, the oxide contained in the solder is reduced by the free radical gas, and the cleaning is performed by reducing both joint surfaces, so that the object to be joined can be satisfactorily soldered without using flux. Can be joined.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
In the first embodiment of the present invention, as shown in FIG. 1C, two joining objects 2 and 4 are joined by solder. As the joining objects 2 and 4, for example, a semiconductor device and a base for the semiconductor device, for example, a heat sink can be used. The joining objects 2 and 4 have joining surfaces 2a and 4a as shown in FIG.
[0012]
On the joining surface 2a of the joining object 2, solder, for example, thread solder 6 is arranged. The thread solder 6 is, for example, U-shaped and has a gap between the joint surface 2a and a part of the thread solder 6. The joining object 2 placed on the joining surface 2a of the thread solder 6 and another joining object 4 are accommodated in a soldering device 8 shown in FIG.
[0013]
This soldering device 8 has a vacuum chamber 10. The vacuum chamber 10 has a chamber 12, and the chamber 12 includes a lower chamber 12a and an upper chamber 12b. The lower chamber 12a has a box shape having an opening at an upper edge, and the upper chamber 12b is connected by a hinge so as to cover the opening. When the lower chamber 12a is covered by the upper chamber 12b, the insides of the two chambers are airtight. By operating the vacuum pump 14 in the covered state, the inside of the vacuum chamber 10 can be brought into a vacuum state.
[0014]
A heating means, for example, a heating device 16 is provided on the lower chamber 12a side. The heating device 16 has a flat support 18 capable of supporting the above-described objects 2 and 4, and a heater 20 is embedded inside the support 18. Although not shown, a cooling device large enough to contact the entire back surface of the support base 18 is provided in the vacuum chamber 10 so as to be able to contact and non-contact the back surface of the support base 18.
[0015]
In the upper chamber 12b of the chamber 12, a free radical gas generating means, for example, a hydrogen radical generator 22 is provided. The hydrogen radical generator 22 is a device for generating hydrogen radicals by converting hydrogen gas into plasma by plasma generating means. The hydrogen radical generator 22 has a microwave generator 24 outside the upper chamber 12b, and has a waveguide 26 for transmitting microwaves generated in the microwave generator 24 in the upper chamber 12b. The waveguide 26 has a microwave introduction window 28 formed so as to face the support 18 and to cover the entire surface of the support 18 so as to be larger than the large support. Therefore, the microwave enters the upper chamber 12b over a wide area covering the entire surface of the support base 18. A hydrogen gas supply pipe 30 is provided in the upper chamber 12b so as to be located near the introduction window 28. The supply pipe 30 is for supplying hydrogen gas into the upper chamber 12b from a hydrogen gas supply source 32 outside the vacuum device 8. The supplied hydrogen gas is converted into plasma by the microwave introduced through the microwave introduction window 28 to generate hydrogen radicals. The hydrogen radicals are directed to the entire region of the bonding objects 2 and 4 via the wire net 34 for collecting unnecessary charged particles such as ions inside the upper chamber 12b.
[0016]
The objects 2 and 4 to be joined are placed on the support base 18 of the soldering device 8. The objects 2 and 4 to be joined are arranged so that the joining surfaces 2 a and 4 a face the microwave introduction window 28 side. ing.
[0017]
In the processing by the soldering device 8, the vacuum pump 14 is operated to make a vacuum state until the pressure in the vacuum chamber 10 becomes, for example, 1 Pa or less, and then hydrogen gas is supplied from the hydrogen gas supply source 32 to the vacuum chamber 10. Then, the pressure is adjusted to, for example, 133 Pa. When this state is reached, heating by the heater 20 and supply of hydrogen radicals by microwave generation are started. The heating temperature is set to be higher than the melting point of the thread solder 6, for example, 275 degrees Celsius. The state in which the solder is melted is maintained for about one minute or more after the thread solder 6 starts to melt. During this time, cleaning is performed by reducing the oxide of the thread solder 6 and reducing the bonding surfaces 2a and 4a. At this time, since the thread solder 6 is formed in a U-shape so as to form a partial gap without contacting the entire surface of the joining surface 2a, hydrogen radicals are applied to the thread solder 6 and the joining surface 2a. It is supplied efficiently, and cleaning by reduction of the oxide of the thread solder 6 and reduction of the joint surface 2a is performed efficiently. FIG. 1B shows a state in which the thread solder 6 is melted. In this state, the solder 6 has good wettability and little voids. After the elapse of one minute, the heating is stopped, and cooling is performed in a hydrogen atmosphere at a pressure of 133 Pa until the temperature of the joining objects 2 and 4 becomes about 100 degrees Celsius or less. FIG. 3 shows how the temperature and pressure of the vacuum chamber 10 change during this time.
[0018]
Thereafter, as shown in FIG. 1C, the joining surfaces 2a and 4a of the joining objects 2 and 4 are overlapped, and heating and cooling as shown in FIG. 3 are performed again. Hydrogen radicals can also be supplied during the second heating and cooling. During the second heating, the supply of the hydrogen radicals further promotes the reducing action. In this way, the soldering of the objects 2 and 4 is performed.
[0019]
As described above, under the supply of hydrogen radicals, the thread solder 6 is melted, the oxide of the thread solder 6 is reduced, and the bonding surfaces 2a and 4a are cleaned. Therefore, soldering can be performed without using flux. Is possible.
[0020]
FIG. 4 shows a second embodiment of the present invention. In this embodiment, soldering is performed by one-time heating and cooling. The joining surface 2a of the joining object 2 and the joining surface 4a of the joining object 4 are opposed to each other, and the solder 6a is arranged therebetween. It is. As shown in FIG. 4, the solder 6a is, for example, corrugated so as to have a gap between the solder surfaces 6a and 4a. This is to ensure that the bonding surfaces 2a, 4a and the solder 6a are sufficiently exposed to hydrogen radicals. In this state, the joining objects 2 and 4 and the solder 6a are accommodated in the vacuum chamber 10, and the hydrogen radicals are supplied while changing the pressure and temperature as shown in FIG. 3, for example. By doing so, the joining objects 2 and 4 can be satisfactorily soldered. In this embodiment, bonding can be performed by one process.
[0021]
In the above-described first embodiment, the thread solder 6 is used. However, the present invention is not limited to this. Any shape may be used so that a gap is formed between the joint surface 2a and a part of the solder. For example, various types can be used. Further, in each of the above-described embodiments, the soldering apparatus as shown in FIG. 2 is used. However, the present invention is not limited to this, and it is an apparatus which can supply a free radical gas and can melt the solder. If so, various things can be used. In addition, a hydrogen radical is used as a free radical gas. However, the present invention is not limited to this, and another free radical gas can be used.
[0022]
【The invention's effect】
As described above, according to the present invention, the two objects to be joined can be joined by soldering without using a flux, since the reduction and cleaning actions by the free radical gas are used. In addition, since a free radical gas is efficiently supplied by forming a gap between the solder and the object to be joined, reduction and cleaning are performed efficiently.
[Brief description of the drawings]
FIG. 1 is a process chart of a solder bonding method according to a first embodiment of the present invention.
FIG. 2 is a longitudinal sectional view of a soldering apparatus used in the solder joining method of FIG.
FIG. 3 is a diagram showing changes in temperature and pressure in the solder bonding method of FIG. 1;
FIG. 4 is a schematic view of a solder bonding method according to a second embodiment of the present invention.
[Explanation of symbols]
24 Joining object 2a 4a Joining surface 6 6a Solder

Claims (4)

Solder is placed on the joining surface of one of the two joining objects to which the respective joining surfaces are soldered with solder, and the joining surface of this solder mounting and the joining surface of the other joining object are A first step of heating the two objects to be joined at a temperature at which the solder melts while supplying free radical gas;
A second step of superimposing the joining surface of the other object to be joined on the joining surface where the solder is melted, heating at a temperature at which the solder melts, and then cooling.
A soldering method that does not use the provided flux. 2. The soldering method according to claim 1, wherein the solder has a gap between a part of the solder and a joining surface of the one joining object. 2. The soldering method according to claim 1, wherein a free radical gas is supplied to the two joining surfaces also in the second step. Two joining objects for soldering the respective joining surfaces with solder are arranged such that the joining surfaces face each other, and solder is interposed between these joining surfaces so as to form a gap between the two joining surfaces. The step of causing
Heating the two objects to be joined, under an atmosphere of free radical gas, at a temperature at which the solder melts, and then cooling.
A soldering method that does not use the provided flux.

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