JP2009253157A - Soldering method and method of manufacturing semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a soldering method by which soldering using lead-free solder can be performed while preventing the generation of voids and making wettability of the solder favorable without using flux, and to provide a method of manufacturing a semiconductor device. <P>SOLUTION: For soldering a circuit board and a semiconductor device, the inside of a container is pressurized by a first atmosphere gas up to a primary pressurization pressure higher than the atmospheric pressure, then solder is heated up to a high melting temperature higher than its melting temperature with maintaining the pressurization by the primary pressurization pressure and is melted. Then the temperature of the solder is maintained at the high melting temperature for a predetermined time with the pressure of the inside of the container being maintained at the primary pressurization pressure and the inside of the container is turned into a vacuum state with the temperature of the solder being maintained at the high melting temperature. The inside of the container is pressurized by a second atmosphere gas from the vacuum state up to a secondary pressurization pressure higher than the primary pressurization pressure with the temperature of the solder being at its melting temperature or higher. After that, the temperature of the solder is lowered to a temperature lower than its melting temperature and the circuit board and the semiconductor device are soldered. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a soldering method for soldering a semiconductor element to a circuit board with lead-free solder, and a method for manufacturing a semiconductor device.

  Conventionally, a semiconductor device using a circuit board in which a wiring layer is formed on one surface of a ceramic substrate and a metal layer is formed on the other surface is known. This semiconductor device is manufactured, for example, by soldering a semiconductor element such as MOSFET or IGBT on a wiring layer of a circuit board.

  By the way, in the soldering of the semiconductor element, a void may be generated in the solder layer in the process from melting and solidifying the solder. If many voids are generated in the solder layer that joins the circuit board and the semiconductor element, the presence of voids increases the electrical and thermal resistance of the solder layer. Furthermore, if one void is large, electricity or heat generated by the semiconductor element flows around the large void and flows to the circuit board side. There is a possibility that a high temperature region (hot spot) is generated and the semiconductor element is destroyed.

Therefore, proposals have been made to suppress the generation of voids in the solder layer (see, for example, Patent Document 1). In Patent Document 1, a solderable object in which lead-free solder is interposed between a circuit board and a semiconductor element is housed in a sealable container, and a reducing gas is supplied into the container. It has been proposed to perform soldering in a state where the pressure is increased to a pressure equal to or higher than atmospheric pressure (normal pressure). In this soldering method, the pressurized state is maintained in a solder melting region from the start of solder melting to the solidification of the solder.
JP 2007-180447 A

However, it has been confirmed by experiments of the present inventor that voids are generated in the solder layer even in the soldering method of Patent Document 1.
In recent years, lead-free solder is often used for soldering semiconductor elements in order to cope with the environment. Lead-free solder is a material having characteristics that the melting temperature is higher than that of normal solder and that wettability during soldering is poor. If the wettability at the time of soldering is poor, the solder does not spread over the entire bonding area of the semiconductor element, and a solder non-adhered portion where no solder exists between the bonding area of the semiconductor element and the circuit board occurs. Become. When a relatively large semiconductor element such as MOSEFT or IGBT is used, the loss due to the unattached portion of solder becomes a big problem.

  It is conceivable to use flux as a method for improving the wettability of lead-free solder. However, when flux is used, after soldering, a flux cleaning step is required, which causes a new problem that the number of soldering steps increases.

  The present invention has been made paying attention to such problems existing in the prior art, and the object thereof is to use a flux while suppressing the generation of voids in soldering using lead-free solder. It is an object of the present invention to provide a soldering method and a semiconductor device manufacturing method capable of performing soldering with good solder wettability.

  In order to solve the above-mentioned problems, the soldering method according to claim 1, a soldering object in which lead-free solder is interposed between a circuit board and a semiconductor element is contained in a container, and the inside of the container is accommodated. After filling with a first atmospheric gas containing a reducing gas, the inside of the container is pressurized to a primary pressurizing pressure greater than atmospheric pressure by the first atmospheric gas, and the pressure in the container is maintained at the primary pressurizing pressure. In this state, the solder is heated to a high melting temperature equal to or higher than the melting temperature of the solder to melt the solder, and the temperature of the solder is set to the high melting temperature in a state where the pressure in the container is maintained at the primary pressurizing pressure. In a state where the temperature of the solder is maintained at the high melting temperature, the inside of the container is depressurized to be in a vacuum state, and an inert gas is contained in a state where the temperature of the solder is equal to or higher than the melting temperature. The container by the second atmosphere gas From the vacuum state to a secondary pressurization pressure greater than the primary pressurization pressure, and then the temperature of the solder is less than the melting temperature in a state where the pressure in the container is maintained at the secondary pressurization pressure. The gist is to lower the temperature to solidify the solder and to solder the circuit board and the semiconductor element.

  The invention according to claim 5 is a method of manufacturing a semiconductor device in which a semiconductor element is soldered to a circuit board with lead-free solder, wherein lead-free solder is interposed between the circuit board and the semiconductor element. And filling the container containing the soldering object with a first atmosphere gas containing a reducing gas, then pressurizing the container to a primary pressurization pressure greater than atmospheric pressure with the first atmosphere gas, With the internal pressure maintained at the primary pressure, the solder is heated to a high melting temperature equal to or higher than the melting temperature of the solder to melt the solder, and the pressure in the container is maintained at the primary pressure. In this state, the temperature of the solder is maintained at the high melting temperature for a certain period of time, and the container is depressurized and vacuumed while the temperature of the solder is maintained at the high melting temperature, and the temperature of the solder is melted. More than temperature Then, the inside of the container is pressurized from the vacuum state to a secondary pressurizing pressure larger than the primary pressurizing pressure by the second atmospheric gas containing an inert gas, and then the pressure in the container is changed to the secondary pressurizing pressure. In this state, the temperature of the solder is lowered to a temperature lower than the melting temperature to solidify the solder, and the circuit board and the semiconductor element are soldered.

  According to the first and fifth aspects of the invention, since the solder is melted in a state where the inside of the container is pressurized to a primary pressurizing pressure larger than the atmospheric pressure, the area around the interface of the molten solder is larger than the atmospheric pressure. There will be a first ambient gas at the primary pressurization pressure. Also, the solder is heated to a high melting temperature, which is higher than its melting temperature, and the molten state is maintained. For this reason, the wettability of solder can be made favorable. This is thought to be due to the fact that the interface of the molten solder, which is heated to a temperature higher than the melting temperature and has a reduced surface tension, is strongly pulled outward by the surrounding first ambient gas. It is done. Furthermore, in the present invention, by evacuating the container while maintaining the solder temperature at a high melting temperature, relatively large voids existing in the molten solder layer can be extracted from the molten solder layer to the outside. it can. Then, by pressurizing the inside of the container to a secondary pressurizing pressure larger than the primary pressurizing pressure continuously after evacuation, the fine voids in the molten solder layer that could not be extracted by evacuation can be crushed. As a result, even when lead-free solder is used, the generation of voids can be effectively suppressed, and the wettability of the solder can be improved without using a flux.

  Further, the pressurization for changing the pressure in the container from the vacuum state to the secondary pressurization pressure may be performed while the heating of the solder is stopped and the solder is in a temperature-decreasing state. According to this, since the heating of the solder is stopped while the inside of the container is evacuated and the inside of the container is pressurized to a secondary pressurizing pressure in a state where the temperature of the solder starts to drop, Time can be shortened.

  The high melting temperature may be 50 ° C. or more higher than the melting temperature of the solder. The first atmosphere gas may be a mixed gas of nitrogen as an inert gas and hydrogen as a reducing gas, and the proportion of the hydrogen in the first atmosphere gas may be less than the nitrogen.

  According to the present invention, in soldering using lead-free solder, it is possible to perform soldering with good solder wettability without using flux while suppressing generation of voids.

Hereinafter, an embodiment embodying the present invention will be described with reference to FIGS.
1 and 2 show a semiconductor module 10 as a semiconductor device. The semiconductor module 10 includes a circuit board 11 having a square plate shape, a square plate-like semiconductor element 12 to be soldered to the circuit board 11, and a square plate-like base 13. The circuit board 11 is configured by joining metal plates 15 and 16 to both surfaces of a ceramic substrate 14. The ceramic substrate 14 is made of, for example, aluminum nitride, alumina, silicon nitride, or the like. The metal plate 15 functions as a wiring layer, and is formed of, for example, aluminum (pure aluminum and aluminum alloy), copper, or the like. The semiconductor element 12 is soldered to the metal plate 15. The symbol “H” in FIG. 2 indicates a solder layer. The solder layer H is formed by a square sheet-like solder sheet 33 (see FIG. 3), and the solder sheet 33 is formed by lead-free solder made of an alloy with a metal other than lead containing tin as a main component.

  The semiconductor element 12 is composed of an IGBT (Insulated Gate Bipolar Transistor) or a diode, and a plurality (four in this embodiment) of semiconductor elements 12 are soldered to the circuit board 11 (metal plate 15). The metal plate 16 functions as a bonding layer for bonding the ceramic substrate 14 and the base 13 and is made of, for example, aluminum or copper. The base 13 is a cooler (heat sink) that cools the semiconductor element.

  FIG. 3 schematically shows the configuration of a soldering apparatus HK used for soldering. The soldering apparatus HK is configured as an apparatus for soldering the semiconductor element 12 to the circuit board 11 (metal plate 15). Further, as shown in FIG. 5, the soldering apparatus HK of the present embodiment is configured as an apparatus for soldering a semiconductor module (semiconductor device) 100 including six circuit boards 11. For this reason, 24 semiconductor elements 12 are soldered to the semiconductor module 100.

  The soldering apparatus HK includes a container (chamber) 17 that can be sealed. The container 17 has a box-shaped main body member 18 having an opening 18a, and a lid member 19 that opens and closes the opening 18a of the main body member 18. It consists of and. A support base 20 that positions and supports the semiconductor module 100 is installed in the main body member 18. Further, a packing 21 is disposed on the body member 18 at a portion where the lid member 19 is mounted.

  The lid member 19 is formed to have a size capable of closing the opening 18 a of the main body member 18, and the sealed space S is formed in the container 17 by attaching the lid member 19 to the main body member 18. It has become. Further, the portion of the lid member 19 that faces the sealed space S is formed of a nonmagnetic and electrically insulating material. In the present embodiment, glass is used as an electrical insulating material, and a glass plate 22 is assembled to the lid member 19.

The main body member 18 is connected to a reducing gas supply unit 23 for supplying a reducing gas (hydrogen (H ₂ ) in the present embodiment) into the container 17. The reducing gas supply unit 23 includes a pipe 23a, an opening / closing valve 23b of the pipe 23a, a pressure reducing valve 23c, and a hydrogen tank 23d. The pressure reducing valve 23c is configured so that the pressure of the hydrogen gas from the hydrogen tank 23d introduced through the opening / closing valve 23b is kept constant and is supplied into the container 17.

The main body member 18 is connected to an inert gas supply unit 24 for supplying an inert gas (nitrogen (N ₂ ) in the present embodiment) into the container 17. The inert gas supply unit 24 includes a pipe 24a, an opening / closing valve 24b of the pipe 24a, and a nitrogen tank 24c.

  The main body member 18 is connected to a vacuum unit 25 for evacuating the inside of the container 17. The vacuum unit 25 includes a pipe 25a, an opening / closing valve 25b of the pipe 25a, and a vacuum pump 25c. The main body member 18 is connected to a gas discharge portion 26 for discharging the gas filled in the container 17 to the outside. The gas discharge unit 26 includes a pipe 26a, an opening / closing valve 26b of the pipe 26a, and a throttle valve 26c.

  The amount of gas in the container 17 is adjusted by the throttle valve 26c and discharged to the outside. The soldering apparatus HK includes a reducing gas supply unit 23, an inert gas supply unit 24, a vacuum unit 25, and a gas discharge unit 26 so that the pressure in the sealed space S can be adjusted. 17 is pressurized or depressurized by adjusting the pressure.

  The main body member 18 is provided with a temperature sensor (for example, a thermocouple) 27 for measuring the temperature in the container 17. In the present embodiment, the temperature sensor 27 is installed in the container 17 so as to measure the temperature of the joint part (part where soldering is performed) between the semiconductor element 12 and the metal plate 15.

  A high-frequency heating coil 28 is installed on the upper part of the soldering apparatus HK (upper part of the lid member 19). In the present embodiment, as shown in FIG. 5, the six high frequency heating coils 28 are arranged on the upper side of each circuit board 11 so as to correspond to the six circuit boards 11. The high-frequency heating coil 28 of the present embodiment is formed in a size that covers one circuit board 11. Further, as shown in FIG. 3, each high-frequency heating coil 28 is formed in a spiral shape (square spiral shape) and is developed in a plane. Moreover, each high frequency heating coil 28 is arrange | positioned so that the cover member 19 (attachment part of the glass plate 22) may be opposed. Each high-frequency heating coil 28 is electrically connected to a high-frequency generator 29 provided in the soldering apparatus HK, and is controlled to a predetermined temperature based on the measurement result of the temperature sensor 27 installed in the container 17. It has come to be. Each high-frequency heating coil 28 is formed with a cooling path 30 for passing cooling water through the coil, and is connected to a cooling water tank 31 provided in the soldering apparatus HK.

  FIG. 4 shows a jig 32 used for soldering. The jig 32 is formed in a flat plate shape having the same size as the ceramic substrate 14 constituting the circuit board 11. The jig 32 is formed of a material such as graphite or ceramics, for example. As shown in FIG. 3, the jig 32 is used to position the solder sheet 33 and the semiconductor element 12 on the circuit board 11 during soldering. Therefore, a positioning through-hole 34 is formed in the jig 32 at a portion corresponding to the bonding portion of the semiconductor element 12 in the circuit board 11. The through hole 34 is formed in a size corresponding to the size of the semiconductor element 12 and the solder sheet 33. In the present embodiment, a plurality (four) of the semiconductor elements 12 are bonded onto the circuit board 11, so that a plurality (four) of through holes 34 are formed in the jig 32.

  Next, a method for soldering the semiconductor element 12 using the above-described soldering apparatus HK will be described. When soldering is performed using the soldering apparatus HK illustrated in FIG. 3, the base 13 is bonded to the circuit board 11 in advance.

  When performing soldering, first, the lid member 19 is removed from the main body member 18, and the opening 18a is opened. Then, as shown in FIG. 3, the base 13 to which the circuit board 11 is bonded is placed on the support base 20 of the main body member 18, and the base 13 is positioned. Next, a jig 32 is placed on each circuit board 11 (ceramic substrate 14), and a solder sheet 33 made of lead-free solder and the semiconductor element 12 are placed in each through hole 34 of the jig 32. That is, a soldering target portion in which the solder sheet 33 is interposed between the circuit board 11 and the semiconductor element 12 is accommodated in the container 17.

  Next, the lid member 19 is attached to the main body member 18, the opening 18 a is closed, and the sealed space S is formed in the container 17. In a state where the soldering object is accommodated in the sealed space S (shown in FIG. 3), each high-frequency heating coil 28 is disposed above the soldering object, and each high-frequency heating coil 28 and the soldering object. A glass plate 22 assembled to the lid member 19 is disposed between the two.

  Next, gas replacement in the container 17 is performed. First, the inside of the container 17 is evacuated by operating the vacuum unit 25, and nitrogen is supplied into the container 17 by operating the inert gas supply unit 24, and the inside of the sealed space S is filled with the inert gas. This evacuation and supply of nitrogen are repeated several times.

  Next, the inert gas supply unit 24 and the reducing gas supply unit 23 are operated to supply nitrogen and hydrogen into the container 17, and a mixed gas of hydrogen (reducing gas) and nitrogen (inert gas) That is, the first atmospheric gas is used to pressurize the interior of the container 17 to a primary pressure higher than the atmospheric pressure and maintain the primary pressure (primary pressure process). In addition, it is preferable that 1st atmosphere gas contains hydrogen which is reducing gas in the ratio of 5 to 10% with respect to the whole capacity | capacitance of 1st atmosphere gas. That is, the ratio of hydrogen in the first atmosphere gas is less than that of nitrogen. Further, the primary pressurizing pressure may be set to a pressure higher than atmospheric pressure in order to improve the wettability of the solder, and is set to 0.16 Mpa, for example.

  Next, in a state where the inside of the container 17 is pressurized to the primary pressurizing pressure by the first atmospheric gas containing the reducing gas, the high-frequency generator 29 is operated, and a high-frequency current is caused to flow through each high-frequency heating coil 28. The solder sheet 33 is heated by the high-frequency heating coil 28 (heating process). Then, the solder sheet 33 is melted when the temperature becomes higher than the melting temperature of the solder in the pressurized state. Then, based on the measurement result of the temperature sensor 27, the solder sheet 33 is heated to a high melting temperature that is higher than the melting temperature (eg, 221 ° C.) of the solder sheet 33. The high melting temperature is preferably set to a temperature that is 50 ° C. or more higher than the melting temperature of the solder, and is particularly preferably set to a temperature that is 50 to 80 ° C. higher. In this embodiment, in order to improve the wettability of the solder, the high melting temperature is set to 60 ° C. or higher than the melting temperature of the solder.

  Next, based on the measurement result of the temperature sensor 27, the high frequency heating coil 28 is controlled by the high frequency generator 29, the temperature of the solder is kept at a high melting temperature for a certain period of time, and the vacuum portion 25 is melted. To evacuate the inside of the container 17 to reduce the pressure, and the inside of the container 17 is evacuated (vacuum process). This evacuation is preferably performed until the pressure in the container 17 is 0.0005 to 0.01 MPa (low vacuum) or less.

  Then, after the inside of the container 17 becomes a pressure equal to or lower than the low vacuum, the high frequency generator 29 is stopped to stop the heating of the solder. Then, the temperature of the solder at the high melting temperature gradually decreases, and the temperature of the solder starts to fall.

  Then, while the solder in the lowered temperature is above the melting temperature, the inert gas supply unit 24 is operated to supply the second atmosphere gas (including the inert gas) made of nitrogen (including the inert gas) into the container 17. The pressure in the container 17 is increased from the vacuum state to a secondary pressure higher than the primary pressure by the atmospheric gas. This secondary pressurizing pressure is maintained until the molten solder is solidified (secondary pressurizing step). Therefore, the solidification of the solder is performed in a state where the solder is pressurized at the secondary pressurizing pressure by the second atmospheric gas containing the inert gas.

  The melted solder is solidified by being cooled below the melting temperature, and joins the metal plate 15 and the semiconductor element 12. The semiconductor module 100 is completed by joining the metal plate 15 and the semiconductor element 12. Then, the lid member 19 is taken out from the main body member 18, and after removing the jig 32, the semiconductor module 100 is taken out from the container 17. When the semiconductor module 100 is taken out from the container 17, the gas in the container 17 is released to the atmosphere via the gas discharge unit 26.

Hereinafter, an aspect of adjusting the internal atmosphere in the container 17 during heating and cooling in the soldering of the present embodiment will be described using an experimental example shown in FIG.
Each dimension of the semiconductor module 10 used in the experimental example is as follows.

  The ceramic substrate 14 is made of aluminum nitride, is a 30 mm × 30 mm square, and has a thickness of 0.635 mm. The metal plates 15 and 16 are made of pure aluminum (for example, 1000 series aluminum, which is industrial pure aluminum), are a square of 27 mm × 27 mm, and have a thickness of 0.4 mm. The semiconductor element 12 has a thickness of 0.35 mm. The solder sheet 33 is made of Sn (tin) -Cu (copper) -Ni (nickel) -P (phosphorus) lead-free solder, and has a square shape and a thickness of 0.1 mm to 0.2 mm.

  In the experimental example, as shown in the graph of FIG. 6, the pressure and temperature in the container 17 are changed (adjusted). In addition, the change of the pressure in the container 17 is shown by the solid line in the graph of FIG. 6, and the change of the temperature of the solder is shown by the broken line.

  First, the evacuation in the container 17 and the supply of nitrogen are repeated several times, and the gas in the container 17 is replaced. Next, a primary pressurization step is performed, and the inside of the container 17 is pressurized to a primary pressurization pressure (0.16 MPa) larger than the atmospheric pressure by the first atmospheric gas (nitrogen + hydrogen), and the primary pressurization pressure is increased. Maintain the state.

  Next, a heating process is performed in a state where the inside of the container 17 is maintained at a constant primary pressurizing pressure, and the solder sheet 33 is heated to a high melting temperature (301 ° C.) higher than the melting temperature. Is maintained at a high melting temperature. Next, a vacuum process is performed in a state where the temperature of the melted solder is maintained at a high melting temperature, and the pressure in the container 17 is reduced to 0.0005 MPa (low vacuum) or less.

  Heating by the high frequency generator 29 is stopped while the pressure in the container 17 is maintained at a low vacuum or lower. Then, the solder temperature starts to decrease. Then, the secondary pressurization step is started in a state where the solder temperature is equal to or higher than the melting temperature, and the secondary pressurization pressure (0.2 MPa) larger than the primary pressurization pressure in the container 17 by the second atmospheric gas (nitrogen). Until the pressure is maintained. Then, the solder is solidified while maintaining the pressurized state. An X-ray photograph showing the back surface side (joint surface side) of the semiconductor element 12 when soldered in the experimental example is placed beside the graph of FIG. In the X-ray photograph, the darkest part is the solder layer H. According to the X-ray photograph, the solder layer H extends to the four corners of the solder layer H, and almost no voids can be confirmed.

According to the above embodiment, the following effects can be obtained.
(1) In the soldering method of the present embodiment, in a state where the inside of the container 17 is pressurized to a primary pressure higher than atmospheric pressure, the solder sheet 33 is heated and melted to a high melting temperature equal to or higher than the melting temperature. Therefore, the solder wettability can be improved. This is considered to be due to the fact that the interface of the molten solder, which is heated to a temperature higher than the melting temperature and has a reduced surface tension, is strongly pulled outward by the first ambient gas present around it. It is done. Therefore, the solder layer H extends to the four corners of the semiconductor element 12, that is, the solder wets and spreads over the entire bonding area of the semiconductor element 12, and the solder layer H is between the bonding area of the semiconductor element 12 and the circuit board 11. It is possible to prevent the occurrence of a solder non-adhered portion where the solder layer H is not present.

  Further, the container 17 is evacuated while the solder temperature is maintained at a high melting temperature. For this reason, the comparatively big void which exists in a molten solder layer can be pulled out from a molten solder layer. Then, the minute voids remaining in the molten solder layer can be crushed by pressurizing the inside of the container 17 to a secondary pressurizing pressure larger than the primary pressurizing pressure continuously after evacuation. As a result, generation of voids can be suppressed even when lead-free solder is used, and solder wettability can be improved without using flux. Since no flux is used, a flux cleaning step is not required, and the soldering operation can be easily performed.

  (2) The pressurization to change the pressure in the container 17 from the vacuum state to the secondary pressurization pressure is performed while the heating of the solder is stopped and the solder is in the temperature lowered state. For this reason, heating of the solder is stopped while the inside of the container 17 is evacuated, and pressurization is performed so that the inside of the container 17 becomes a secondary pressurizing pressure in a state where the temperature of the solder starts to decrease. Time can be shortened.

  (3) When performing the process of pressurizing the inside of the container 17 to the primary pressurizing pressure, the value of the primary pressurizing pressure is kept constant. For this reason, for example, the secondary pressurization pressure can be lowered in the step of pressurizing to the secondary pressurization pressure as compared with the case where pressurization is performed by gradually increasing the primary pressurization pressure.

  (4) Since the first atmosphere gas for pressurizing the inside of the container 17 to the primary pressurizing pressure is a mixed gas of nitrogen and hydrogen, it is possible to prevent the molten solder from being oxidized by hydrogen which is a reducing gas. Can contribute to improvement of wettability. Furthermore, since the proportion of hydrogen in the first atmosphere gas is less than that of nitrogen, the cost associated with the first atmosphere gas can be reduced as compared with the case where the proportion of hydrogen is greater than that of nitrogen.

  (5) The process of pressurizing the inside of the container 17 to the primary pressurizing pressure is started before the solder sheet 33 is heated. For this reason, before the solder reaches the melting temperature, the inside of the container 17 can be brought into a pressurized state up to the primary pressurizing pressure.

(6) Since the high melting temperature is set to a temperature higher by 50 ° C. or more than the melting temperature of lead-free solder, the solder wettability can be improved.
In addition, you may change the said embodiment as follows.

In the embodiment, in the primary pressurizing step, the first atmosphere gas is a mixed gas of nitrogen and hydrogen, but the first atmosphere gas may be only hydrogen.
In the embodiment, in the secondary pressurizing step, the second atmosphere gas is nitrogen, but the second atmosphere gas may be a mixed gas of nitrogen and hydrogen.

In the embodiment, the primary pressurization pressure in the container is kept constant in the primary pressurization step, but the primary pressurization pressure may be gradually increased.
○ In the embodiment, the pressurization by the secondary pressurization pressure is started while the temperature of the melted solder is lowered, but the pressurization by the secondary pressurization pressure is started while the melted solder temperature is at the high melting temperature. May start.

The reducing gas is not limited to a gas containing hydrogen, but may be a gas having another composition such as containing formaldehyde.
In the embodiment, heating is performed by high-frequency induction heating by the high-frequency heating coil 28, but the heating method may be changed. For example, a heater may be provided in the container 17 for heating.

  As a soldering object to be soldered, the circuit board 11 in a state where the base 13 is not joined may be used. In this case, a semiconductor device composed of the circuit board 11 and the semiconductor element 12 is accommodated and soldered in the container 17 of the present embodiment. Moreover, although the soldering object (semiconductor module 100) is composed of six circuit boards 11, the number of circuit boards 11 may be changed.

Next, the technical idea that can be grasped from the above embodiment and other examples will be described below.
(1) The soldering method according to claim 3, wherein the high melting temperature is 50 to 80 ° C higher than the melting temperature of the solder.

The top view of a semiconductor module. AA sectional view taken on the line AA of FIG. The longitudinal cross-sectional view of a soldering apparatus. The top view of a jig | tool. The schematic diagram which shows arrangement | positioning of a semiconductor module and a high frequency heating coil. The graph and X-ray photograph which show the change of the pressure and temperature in an experiment example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10,100 ... Semiconductor module as a semiconductor device, 11 ... Circuit board, 12 ... Semiconductor element, 17 ... Container, 33 ... Solder sheet as lead-free solder.

Claims (5)

A soldering object in which lead-free solder is interposed between the circuit board and the semiconductor element is accommodated in a container, and the container is filled with a first atmosphere gas containing a reducing gas, and then the first atmosphere gas is contained. By pressurizing the inside of the container to a primary pressurizing pressure greater than atmospheric pressure,
The solder is melted by heating the solder to a high melting temperature equal to or higher than the melting temperature of the solder while maintaining the pressure in the container at the primary pressure.
Maintaining the temperature of the solder at the high melting temperature for a certain period of time while maintaining the pressure in the container at the primary pressure.
In a state where the temperature of the solder is maintained at the high melting temperature, the inside of the container is reduced to a vacuum state,
In a state where the temperature of the solder is equal to or higher than the melting temperature, the inside of the container is pressurized from the vacuum state to a secondary pressurization pressure larger than the primary pressurization pressure by a second atmosphere gas containing an inert gas,
Thereafter, the solder is solidified by lowering the temperature of the solder to a temperature lower than the melting temperature while maintaining the pressure in the container at the secondary pressurizing pressure, and soldering the circuit board and the semiconductor element. Soldering method characterized by performing.   2. The soldering method according to claim 1, wherein the pressure in the container from the vacuum state to the secondary pressurizing pressure is performed while heating of the solder is stopped and the solder is in a temperature lowered state. .   The soldering method according to claim 1, wherein the high melting temperature is a temperature that is 50 ° C. or more higher than the melting temperature of the solder.   The first atmosphere gas is a mixed gas of nitrogen, which is an inert gas, and hydrogen, which is a reducing gas, and the proportion of the hydrogen in the first atmosphere gas is less than that of the nitrogen. The soldering method as described in any one of these. A method of manufacturing a semiconductor device in which a semiconductor element is soldered to a circuit board with lead-free solder,
After filling the inside of the container containing the soldering target object in which lead-free solder is interposed between the circuit board and the semiconductor element with the first atmosphere gas containing the reducing gas, the container is filled with the first atmosphere gas. Is heated to a primary pressurizing pressure greater than atmospheric pressure, and the solder is melted by heating the solder to a high melting temperature equal to or higher than the melting temperature of the solder while maintaining the pressure in the container at the primary pressurizing pressure. And maintaining the solder temperature at the high melting temperature for a certain time while maintaining the pressure in the container at the primary pressurizing pressure, and maintaining the solder temperature at the high melting temperature in the container. In a state where the pressure is reduced to a vacuum state and the temperature of the solder is equal to or higher than the melting temperature, a secondary atmosphere larger than the primary pressurization pressure is applied from the vacuum state to the inside of the container by a second atmospheric gas containing an inert gas. Pressurization up to pressure Thereafter, the solder is solidified by lowering the temperature of the solder to a temperature lower than the melting temperature while maintaining the pressure in the container at the secondary pressurizing pressure, and soldering the circuit board and the semiconductor element. A method for manufacturing a semiconductor device, characterized by comprising: