JP2007053245A - Method and device for soldering - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the occurrence of wrinkles on a solder surface. <P>SOLUTION: In a heating chamber 2 whose temperature is lower than the solder melting temperature with a pressure lower than the atmospheric pressure, an object 6 comprising a solder and a part to be soldered is irradiated with hydrogen radical. With the heating chamber 2 provided with a reducing atmosphere or inactive atmosphere at the atmospheric pressure or near it, the object is heated to the temperature of solder melting point or higher by a heating plate 4. The object 6 is cooled by a cooling device 30 in a cooling chamber 24 with the reducing atmosphere or inactive atmosphere at the atmospheric pressure or near it. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a soldering method and a soldering apparatus, and more particularly to reflow soldering.

  Examples of the reflow soldering technique include those disclosed in Patent Document 1. In this soldering technique, microwaves are generated and hydrogen radicals are generated in a state where hydrogen gas is introduced into the vacuum chamber so as to have a pressure of 133 Pa. In this state, the processing object consisting of the substrate and the solder is heated to a temperature equal to or higher than the melting point temperature of the solder, and after this heating state is continued for a predetermined time, the generation of microwaves is stopped to form a hydrogen atmosphere, and the processing object is Cooling. Heating is performed in a state in which the processing object is disposed on a support table provided with a heater, and cooling is performed by bringing a cooling device into contact with the support table.

Japanese Patent Laid-Open No. 2004-114074

  It has been found that when a solder bump is formed on a substrate by this reflow soldering technique, fine wrinkles are generated on the surface of the solder bump. This is due to the cooling rate. When solder, for example, Sn—Ag molten solder is cooled, β-Sn dendrites (dendritic crystals), which are primary crystals, are generated and grown. As this Sn dendrite grows, the silver in the molten solder is concentrated, reaches a eutectic composition, and instantly solidifies. When the Sn dendrite is formed on the surface of the bump, wrinkles are formed. In order to prevent this wrinkle, the cooling speed is set to be very high, the dendrite growth is suppressed, and the surface of the solder bump is solidified until the dendrite reaches the surface, or it is cooled at a very low speed, It is necessary to eliminate the generated primary crystal. However, cooling at a very low speed is not preferable because of the efficiency of soldering.

  An object of this invention is to provide the soldering method and apparatus which prevent that a wrinkle generate | occur | produces on the solder surface.

  In the soldering method according to the present invention, a solder and a soldered portion to which the solder is joined at a temperature lower than the solder melting temperature and a pressure lower than atmospheric pressure, for example, a pressure range of 10 to 1000 Pa. A processed product having a free radical gas is irradiated. As the solder, for example, Sn-Ag solder can be used. As the free radical gas, for example, hydrogen radical obtained by converting hydrogen gas into plasma can be used. Following this process, the treated product is heated to a temperature equal to or higher than the solder melting temperature in a reducing or inert atmosphere at or near atmospheric pressure, and then maintained at a constant temperature equal to or higher than the solder melting temperature. To do. The reducing atmosphere can be realized, for example, by filling with hydrogen gas, and the inert atmosphere can be performed by filling, for example, an inert gas such as nitrogen gas. Following this process, the workpiece is cooled under the same conditions.

  According to this soldering method, the oxide adhering to the surface of the solder or the non-soldered portion is removed by irradiation with the free radical gas, and then the temperature is raised and the temperature is maintained. This temperature rise and temperature holding is performed not only by direct conduction from the heating means to the treatment object but also by convection conduction by convection of a gas interposed between the heating means and the treatment object. Since this pressure is atmospheric pressure or a pressure close thereto, this convective conduction is performed better than when it is performed under a pressure lower than atmospheric pressure, and the temperature can be increased rapidly. If heating is performed under atmospheric pressure or a pressure in the vicinity thereof, the surface of the melted and solidified solder may not be good, but the oxide is removed by free radical gas before heating. Can be good. Further, the cooling is performed not only by direct conduction cooling but also by convection conduction. Furthermore, since the pressure during cooling is at or near atmospheric pressure, the convection conduction during cooling is performed well. As a result, the processed product can be rapidly cooled, and wrinkles can be prevented from occurring on the surface of the solidified solder.

  The temperature raising and temperature holding can be performed by bringing the heating means into direct contact with the treatment object, and the cooling process can also be carried out by bringing the cooling means into direct contact with the treatment object. If comprised in this way, direct heating and convection heating are performed simultaneously, it can be heated rapidly, direct cooling by a cooling means contacting a processed material, and cooling by convection mentioned above are performed simultaneously, The processed material can be cooled more rapidly.

  Further, the soldered portion can be a substrate having electrodes. In this case, the solder is a solder bump. This solder bump is disposed on the electrode. Further, the cooling means has a cooling block larger than the substrate, and the cooling block directly contacts a surface opposite to the surface of the substrate forming the electrode.

  If comprised in this way, cooling will be performed from the inside of the solder which is contacting the electrode on the board | substrate through a board | substrate. Therefore, before the surface of the solder is cooled, it can be cooled from the inside thereof, and the surface of the solidified solder can be prevented from wrinkling.

  The soldering apparatus according to the present invention has a heating chamber. The heating chamber has a heating means inside, and the heating means directly contacts and heats a workpiece having solder and a soldered portion to which the solder is joined. This heating is performed so as to raise the temperature of the processed material above the melting temperature of the solder and maintain the temperature above the melting temperature of the solder. The soldering device also has a cooling chamber. This cooling chamber has a cooling means inside, and this cooling means cools by contacting the said processed material directly. It is desirable to connect the heating chamber and the cooling chamber in series. Transfer means is provided so as to transfer the processed material between the heating chamber and the cooling chamber. The transfer means can also serve as a part of the cooling means. Pressure setting in which the inside of the heating chamber is set to a substantially atmospheric reducing or inert gas atmosphere during heating in the heating means, and the inside of the cooling chamber is set to a substantially atmospheric reducing or inert gas atmosphere during cooling in the cooling means. Means are provided. This pressure setting means can be provided individually in the heating chamber and the cooling chamber, or can be provided in common. The heating chamber can also be provided with a free radical gas supply means for removing oxides of the processed material before heating.

  With this configuration, the processed material is heated by direct conduction by direct contact with the heating means and by convective conduction in a reducing or inert gas atmosphere at approximately atmospheric pressure, so that rapid heating can be performed. In addition, since the processed material is cooled by direct conduction by directly contacting the cooling means and convective conduction in a reducing or inert gas atmosphere at approximately atmospheric pressure, rapid cooling can be performed. Therefore, wrinkles are not generated on the surface of the cooled solder after melting.

  As described above, according to the present invention, wrinkles can be prevented from occurring on the surface of the solidified solder.

  The soldering apparatus used for the soldering method of one embodiment of the present invention has a heating chamber 2 as shown in FIG. Inside the heating chamber 2, a heating means capable of rapidly raising and cooling temperature, for example, a flat heating plate 4 having a heater (not shown) inside is arranged. A processed product 6 is disposed on the heating plate 4. As shown in FIG. 2, the processed product 6 is, for example, a soldered portion, specifically a substrate, more specifically, a wafer 6a and solder disposed on an electrode 6b formed on the upper surface of the wafer 6a. For example, it consists of solder balls 6c. The heating plate 4 is formed in a size sufficiently larger than the processed product 6 in a state where the processed product 6 is arranged. This soldering apparatus is used to solder the solder ball 6c onto the electrode 6b. The solder ball 6c is made of, for example, Sn—Ag solder.

  As shown in FIG. 1, the wafer 6a is supported by bringing the pins 8a of the lifting device 8 provided in the heating chamber 2 into contact with the lower surface of the wafer 6a. With the pins 8a lowered, the lower surface of the wafer 6a comes into contact with the heating plate 4, and the wafer 6a is placed on the heating plate 4 and directly heated.

  In order to adjust the heating conditions in the heating chamber 2, an evacuation unit such as a vacuum pump 14 is attached to the heating chamber 2. The inside of the heating chamber 2 is exhausted by the vacuum pump 14. An inert gas supply source, for example, a nitrogen gas source 16 is also attached to the heating chamber 2 in order to fill the heating chamber 2 with a predetermined inert gas, for example, nitrogen gas. The vacuum pump 14 and the nitrogen gas source 16 constitute pressure setting means for the heating chamber.

  In order to adjust the heating conditions, the heating chamber 2 is provided with free radical gas supply means for supplying a free radical gas, for example, hydrogen radicals, into the heating chamber 2. For example, the heating chamber 2 is provided with a gas source that is a source of free radical gas, for example, a hydrogen gas source 18, and a microwave generator 20 that liberates the hydrogen gas, that is, turns it into plasma. . The microwave generator 20 is attached above the heating chamber 2 so as to face the solder balls 6c of the processed product 6, and supplies hydrogen gas so as to be exposed to the microwave from the microwave generator 20. A hydrogen gas source 18 is provided.

  In this soldering apparatus, the processed product 6 heated by the heating chamber 2 is supplied from the outlet 22 provided at the other end of the heating chamber 2 to the cooling chamber 24 provided continuously with the heating chamber 2. Is done. At the end of the cooling chamber 24 in contact with the heating chamber 2, an inlet / outlet 26 is provided opposite to the outlet 22 of the heating chamber 2, and a gate valve 28 is provided between the outlet 22 and the inlet / outlet 26. Yes. The gate valve 28 is opened when the workpiece 6 is transferred between the cooling chamber 24 and the heating chamber 2, and then closed. With the gate valve 28 closed, the heating chamber 2 is airtight.

  In the cooling chamber 24, cooling means, for example, a cooling device 30 is arranged. The cooling device 30 has transfer means, for example, an arm 32. The arm 32 is formed in a block shape, and enters the lower surface of the wafer 6a through the entrance / exit 26 and the exit 22 in a state where the workpiece 6 is lifted from the heating plate 4 by raising the pins 8a. After scooping up the processed material 6, the arm 32 retracts to the cooling chamber 24 and places it on the cooling device 30. The arm 32 itself has a function of cooling the processed product 6. The cooling device is a liquid cooling device such as a water cooling device. As shown in FIG. 2, the arm 32 is formed larger than the processing object 6 in a state where the processing object 6 is placed thereon.

  In order to adjust the cooling conditions in the cooling chamber 24, the cooling chamber 24 is provided with an exhaust means for exhausting the inside of the cooling chamber 24, for example, a vacuum pump. In order to supply an inert gas such as nitrogen gas into the cooling chamber 24 in this vacuum state, an inert gas source such as a nitrogen gas source 36 is provided in the cooling chamber 24. The vacuum pump 34 and the nitrogen gas source 36 constitute pressure setting means for the cooling chamber 24.

  Although the vacuum pump 14 is provided for the heating chamber 2 and the vacuum pump 34 is provided for the cooling chamber 24, a single vacuum pump can be commonly used for both the chambers 2 and 24. Similarly, although the nitrogen gas source 16 is provided for the heating chamber 2 and the nitrogen gas source 36 is provided for the cooling chamber 24, a single nitrogen gas source can be used in common for both the chambers 2 and 24. That is, the pressure setting means can be provided in common in the heating chamber 2 and the cooling chamber 24.

  The processed product 6 cooled in the cooling chamber 24 is taken out from an inlet / outlet 38 provided at the end of the cooling chamber 24 opposite to the heating chamber 2. A gate valve 40 is provided at the entrance / exit 38. Normally, the gate valve 40 is closed. With the gate valves 40 and 28 closed, the cooling chamber 24 is airtight. The workpiece 6 to be soldered is carried into the cooling chamber 24 through the entrance / exit 38.

  In the soldering method according to the present invention using this soldering apparatus, first, the gate valve 40 is opened, and the treatment 6 is placed on the transfer arm 32. Next, the gate valve 40 is closed, and the inside of the cooling chamber 24 is evacuated. At this time, the heating chamber 2 is also evacuated in advance. Subsequently, the gate valve 28 is opened, the transfer arm 32 is advanced into the heating chamber 2, and the processing object 6 is disposed on the raised pin 8 a in the heating chamber 2. Subsequently, after the transfer arm 32 is retracted and the gate valve 28 is closed, the pin 8a is lowered, and the treatment 6 is placed on the heating plate 4 whose temperature is controlled in advance to a temperature lower than the solder melting temperature. To do. This temperature is preferably higher than room temperature. Before and after this arrangement, hydrogen gas is supplied from the hydrogen gas source 18 into the heating chamber 2, and the pressure in the heating chamber 2 is set to 133 Pa, for example, as shown in FIG. In this state, the microwave generator 20 is operated to convert the hydrogen gas into plasma to generate free radical gas, for example, hydrogen radicals, and irradiate the processed material 6 with it. Thereby, the oxide on the surface of the solder 6c of the processed product 6 is removed.

  Next, after the supply of hydrogen gas is stopped and evacuated, nitrogen gas is introduced from the nitrogen gas source 16 into the heating chamber 2, and the pressure in the heating chamber 2 is almost atmospheric pressure. Subsequently, the temperature of the heating plate 4 is raised to the solder melting temperature or higher. Since the lower surface of the wafer 6a of the processing object 6 is in direct contact with the heating plate 4 and nitrogen gas is interposed between the processing object 6 and the heating plate 4, the processing object 6 is obtained by direct conduction and convection conduction. As shown in FIG. 3, heating is performed rapidly. This heating state is performed continuously for a predetermined time.

  On the other hand, in the cooling chamber 24, nitrogen gas is introduced from the nitrogen gas source 36, and the pressure in the cooling chamber 24 is set to substantially the same atmospheric pressure as the pressure in the heating chamber 2.

  When the solder ball 6 c is completely melted, the pins 8 a are raised by the lifting device 8, and the processed product 6 is lifted away from the heating plate 4. At this time, energization of the heater of the heating plate 4 is also terminated.

  In this state, the gate valve 28 is opened, the arm 32 advances into the heating chamber 2, comes into contact with the lower surface of the wafer 6 a of the processing object 6, moves backward while supporting the processing object 6, and enters the cooling chamber 24. The cooling device 30 is returned to. The arm 32 has already been cooled in the state in which the arm 32 is moving, and the arm 32 is in direct contact with the workpiece 6 as indicated by the solid line in FIG. Done. Moreover, since the nitrogen atmosphere is almost atmospheric pressure, this cooling is also performed by convection as shown by the broken line in FIG.

  Because of this rapid cooling, the dendrite growth in the molten solder can be suppressed, and the solder is solidified until the dendrite reaches the surface of the solder bumps, causing wrinkles on the solidified solder surface. Never do.

  When the solidification of the solder is completed, the gate valve 40 is opened and the processed product 6 is taken out from the cooling chamber 24.

  In the above embodiment, the heating chamber 2 and the cooling chamber 24 are provided separately, but heating and cooling can also be performed in one chamber. In the above embodiment, heating and cooling are performed in a nitrogen gas atmosphere. However, the heating and cooling can be performed in an inert gas atmosphere other than nitrogen gas, or in a reducing atmosphere such as a hydrogen gas atmosphere. You can also. Further, the generation of hydrogen plasma was performed under a pressure of 133 Pa, but can be performed under a pressure of 10 to 1000 Pa. In the above embodiment, when the processing object is carried into the heating chamber 2, it is carried into the heating chamber 2 through the cooling chamber. For example, an entrance is provided at the end of the heating chamber opposite to the cooling chamber 24. It is also possible to carry in the processed product 6 from the entrance.

It is the schematic of the soldering apparatus used for the soldering method by one Embodiment of this invention. It is a figure which shows the cooling process in the soldering apparatus of FIG. It is a temperature and pressure profile figure in the soldering apparatus of FIG.

Explanation of symbols

2 Heating chamber 4 Heating plate 6 Processed object 24 Cooling chamber 30 Cooling device

Claims (4)

An irradiation process of irradiating a processing object having a solder and a part to be soldered to which the solder is bonded at a temperature lower than the solder melting temperature and lower than the atmospheric pressure with a free radical gas;
Subsequent to this process, in a reducing atmosphere or an inert atmosphere at or near atmospheric pressure, a heating process for heating the treatment to a temperature equal to or higher than the solder melting temperature;
Subsequent to this process, a cooling process for cooling the treated product in a reducing atmosphere or an inert atmosphere at or near atmospheric pressure,
Soldering method provided.   The soldering method according to claim 1, wherein the heating process is performed by bringing a heating unit into direct contact with the object to be processed, and the cooling process is performed by bringing a cooling unit into direct contact with the object to be processed. Attaching method.   3. The soldering direction according to claim 2, wherein the soldered portion is a substrate having an electrode, and the solder is a solder bump, the solder bump is disposed on the electrode, and the cooling means includes: A soldering method comprising a cooling block larger than the substrate, wherein the cooling block directly contacts a surface opposite to the surface of the substrate forming the electrode. A heating chamber having inside a heating means for directly contacting and heating a workpiece having a solder and a part to be soldered to which the solder is bonded;
A cooling chamber having cooling means inside for cooling in direct contact with the workpiece,
Transfer means for transferring the workpiece between the heating chamber and the cooling chamber;
Pressure setting in which the inside of the heating chamber is set to a substantially atmospheric reducing or inert gas atmosphere during heating in the heating means, and the inside of the cooling chamber is set to a substantially atmospheric reducing or inert gas atmosphere during cooling in the cooling means. Means,
Soldering device provided.

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