JPH05283570A - Method and apparatus for soldering - Google Patents

Abstract

PURPOSE:To eliminate bubbles generated in molten solder by introducing gas for preventing oxidation, corrosion of nitrogen gas, etc., into an airtight vessel in a state that the solder is heated to be melted, and raising gas pressure in a state that invasion of the air is prevented. CONSTITUTION:Vacuum evacuation means 9, 9a in an airtight vessel 10 which has a semiconductor element 6 and a heat sink 4 so arranged that connecting surfaces are opposed and solder 6 so arranged as to be interposed between opposed connecting surfaces of the element 6 and the heat sink 4 are vacuum- evacuated. Then, heating means 8 heats to melt solder 5 in the vessel 10. Further, gas supply means 17, 17a, 17b in the vessel 10 which contains the element 6, the heat sink 4 and the melted solder 5 introduce gas for preventing oxidation or corrosion such as nitrogen gas, etc., and raise gas pressure in the vessel 10. Thus, generation of bubbles in a connected part of the element 6 and the heat sink 4 is prevented, and they are connected in a satisfactory state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a soldering method and device for soldering a semiconductor chip to a heat dissipation board or the like.

[0002]

2. Description of the Related Art As one method for increasing the mounting density of electronic parts, a semiconductor element such as a bare power semiconductor chip, for example, a semiconductor chip is joined and fixed to a metal heat radiator, for example, a heat dissipation substrate, and electric A mounting method in which a physical connection is performed by wire bonding has become widespread. According to this method, the semiconductor chip is bonded to the heat dissipation substrate, so that if the bonding is completed, predetermined heat dissipation characteristics can be secured. In this connection, a method of soldering without using flux in a clean room is usually adopted.

FIG. 3 is a sectional view of a conventional soldering apparatus used when soldering a bare semiconductor chip (hereinafter referred to as a bare chip) and a heat dissipation board. In the case of the conventional apparatus shown in FIG. 3, since no flux is used, soldering is performed in a hydrogen atmosphere which is a reducing atmosphere. In the figure, 1 is an airtight container, for example, a sealed container. Further, 2a is a hydrogen gas inlet for introducing hydrogen gas into the sealed container 1, 2b is a nitrogen gas inlet for introducing nitrogen gas into the sealed container 1, and 3 is a gas for discharging hydrogen gas and nitrogen gas in the sealed container 1. It is an outlet. A safety device (not shown) is provided to prevent air from entering the gas outlet 3 and exploding.

Reference numeral 4 is a heat dissipation board, and 5 is solder. Further, 6 is a bare chip, and 7 is a weight. The solder 5 has a plate shape. The heat dissipation board 4, the solder 5, the bare chip 6, and the weight 7 have the solder 5 placed on the heat dissipation board 4, the bare chip 6 placed on the solder 5, and the weight 7 placed on the bare chip 6. It is placed in the sealed container 1 in a closed state. 8 is a sealed container 1
It is a heating means provided inside, for example, an infrared heater. Further, the hermetically sealed container 1 is provided with a door (not shown) so that an operator can put in and take out the heat dissipation substrate 4, the solder 5, the bare chip 6, the weight 7, etc. in the hermetically sealed container 1. ..

Next, the procedure of soldering by the conventional soldering device shown in FIG. 3 will be described. First, outside the hermetically sealed container 1, the heat dissipation substrate 4, the plate-shaped solder 5, the bare chip 6, and the weight 7 are stacked. At this time, the heat dissipation board 4
A positioning jig (not shown) is used so that the bare chip 6 is positioned at a predetermined position. The heat dissipating substrate 4, the solder 5, the bare chip 6, and the weight 7 set in this way are put into a sealed container 1 as shown in FIG.
Close the door of and seal it.

Then, nitrogen gas is introduced into the sealed container 1 through the nitrogen gas inlet 2b to replace the air in the sealed container 1 with nitrogen gas. After that, hydrogen gas is introduced through the hydrogen gas introduction port 2a to make the sealed container 1 have a hydrogen atmosphere. Next, the infrared heater 8 is turned on to melt the solder 5. Then, the infrared heater 8 is turned off while the sealed container 1 is kept in a hydrogen atmosphere, the sealed container 1 is cooled to solidify the solder 5, and the heat dissipation substrate 4 and the bare chip 6 are bonded. in this case,
Since the sealed container 1 has a reducing hydrogen atmosphere, soldering can be performed without flux.

However, in order to prevent bubbles from being generated at the joint between the heat sink 4 and the bare chip 6, it is necessary to melt the solder 5 with the weight 7 placed on the bare chip 6 as described above. is there. For this reason, the surface of the bare chip 6 may be soiled or damaged, resulting in malfunction or deterioration of reliability. Further, even if the weight 7 is placed, it is difficult to completely prevent the generation of bubbles. Also, since hydrogen gas is used at high temperature, it was necessary to give due consideration to the danger of explosion.

As another method for soldering without flux, there is a method described in Japanese Patent Laid-Open No. 2-137393, in which the sealed container 1 is evacuated without hydrogen atmosphere and soldered in vacuum. is there. FIG. 4 is a sectional view of the soldering device shown in the above publication.

Next, this method will be described with reference to FIG. First, in a sealed container 31 of 0.001 atm or less,
The printed board 41, the solder (not shown), and the semiconductor device 61 are set and heated in advance by the heater 81 at 50 ° C. or higher and 150 ° C. or lower to remove moisture from the object to be bonded.
Next, the infrared heater 8 heats and melts the solder. Then, after that, the printed circuit board 41 and the semiconductor device 6 are cooled.
The joining with 1 is completed. In this case, since hydrogen gas is not used, there is no danger of explosion. Note that the above publication does not describe a cooling method. Although the problem of surface oxidation of the semiconductor device 61 does not occur if the semiconductor device 61 is cooled in a vacuum state, the method of cooling by introducing air is particularly suitable for the semiconductor device 61.
In the case of a bare chip, it cannot be used because it causes a problem of surface oxidation.

[0010]

When the conventional apparatus shown in FIG. 3 is used for joining in a hydrogen atmosphere, soldering is possible without flux, but the weight 7 is placed on the bare chip 6.
It is difficult to completely prevent the generation of bubbles even if the solder 5 is melted in the state where the solder is placed. Therefore, there is a problem that the thermal conductivity, electrical conductivity, and mechanical strength between the bare chip 6 and the heat dissipation substrate are impaired.

Further, even when the conventional apparatus shown in FIG. 4 is used for joining in a vacuum, since cooling is performed in the vacuum state, bubbles are likely to be formed in the joining section as in the case of the conventional apparatus shown in FIG. Therefore, this case also has the same problems as those of the conventional apparatus shown in FIG.

The present invention has been made in order to solve the above problems, and prevents bubbles from being generated at the joint between the semiconductor element and the heat radiator, thereby allowing heat conduction between the semiconductor element and the heat radiator. It is an object of the present invention to obtain a soldering method and a device capable of joining in a state of good electrical conductivity, electrical conductivity and mechanical strength.

[0013]

In the soldering method according to the present invention, a semiconductor element and a heat dissipating member arranged so that the joint surfaces face each other are sandwiched between the semiconductor element and the heat dissipating member. Or a solder arranged so that the molten solder flows between the opposing joint surfaces of the semiconductor element and the radiator when heated, and a vacuum exhaust means is provided inside the airtight container. The step of evacuating, the step of heating and melting the solder in the airtight container by the heating means, the gas supply means in the airtight container in which the semiconductor element and the radiator and the solder in the molten state are stored, such as nitrogen gas A step of introducing a gas that inhibits oxidation or corrosion to raise the atmospheric pressure in the airtight container.

Further, the soldering device according to the present invention is arranged so as to be sandwiched between the semiconductor element and the heat dissipating body which are disposed so that the joint surfaces face each other, and the opposing joint surface of the semiconductor element and the heat dissipating body. Or a vacuum that evacuates the inside of the airtight container and an airtight container that contains the solder that is arranged so that the molten solder flows between the facing surfaces of the semiconductor element and the heat radiator when heated. Exhaust means, vacuum detection means for detecting that the inside of the airtight container is in a predetermined vacuum state, heating means for heating and melting the solder in the airtight container, and temperature detection for detecting that the solder is in a predetermined molten state Means and the vacuum detection means to detect that the inside of the airtight container is in a predetermined vacuum state and the temperature detection means to detect that the solder is in a predetermined molten state. Are those as provided with gas supply means for introducing a gas to prevent corrosion, the.

[0015]

The soldering method and apparatus according to the present invention are
The semiconductor element and the heat sink are arranged so that the joint surfaces face each other, and the semiconductor element and the heat sink are placed so as to be sandwiched between the facing joint surfaces of the semiconductor element and the heat sink, or when heated. After evacuating the inside of the airtight container containing the solder arranged so that the molten solder flows between the facing joint surfaces of the body, and then heating the solder, the solder is heated and melted. A gas such as nitrogen gas that prevents oxidation or corrosion is introduced into the container, and the air pressure inside the airtight container is raised with the invasion of air blocked, so that the bubbles generated in the molten solder disappear. ..

[0016]

EXAMPLES Example 1. 1 is a block diagram of a soldering device according to an embodiment of the present invention. In the figure,
4, 5, 6, and 8 are the same as those in the conventional device shown in FIG. 20 is a programmable controller (hereinafter P
(Abbreviated as C). Reference numeral 9 is a vacuum evacuation means, for example, a vacuum pump. A vacuum pump power ON / OFF drive unit 9a drives the power of the vacuum pump 9 ON / OFF based on a command given by the PC 20. 10 is a hermetic container, 10a is a nitrogen gas inlet provided in the hermetic container 10, 10b is a nitrogen gas outlet provided in the hermetic container 10, and 10c is provided in the hermetic container 10. This is a vacuum exhaust port that discharges gas to evacuate the inside of the sealed container 10. Further, 11 is a vacuum detecting means for measuring the degree of vacuum in the sealed container 10, for example, a vacuum detector. The vacuum detector 11 is called a Pirani vacuum gauge, and its life is shortened when it is energized in the atmosphere, so the power is turned off in the atmosphere.

Reference numeral 12 is a pressure detector for detecting the pressure of nitrogen gas in the hermetically sealed container 10, reference numeral 13 is a thermocouple having a temperature detecting portion attached to the heat dissipation board 4, and reference numeral 13a is a temperature signal detected by the thermocouple 13. This is a temperature signal amplifier for sending to the PC 20. The thermocouple 13 and the temperature signal amplifier 13
The temperature detecting means is constituted by a. Also, 14 is a PC
It is an infrared heater driving unit that supplies the infrared heater 8 with electric power based on the command of 20. In addition, the PC 20 receives the temperature signal sent from the temperature signal amplifier 13a and the solder 5
A command is given to the infrared heater driving unit 14 so as to eliminate the difference from the required heating temperature.

An infrared heater switch 15 connects or disconnects the infrared heater 8 and the output of the infrared heater driving section 14. Further, 15a is an infrared heater switch ON for driving the infrared heater switch 15 ON / OFF.
・ OFF drive unit. In addition, infrared heater switch O
The N / OFF drive unit 15a operates based on a command from the PC 20. Reference numeral 16 denotes a vacuum detector power supply ON / OFF drive unit for turning on / off the power supply of the vacuum detector 11. In addition,
This vacuum detector power ON / OFF drive unit 16 is a PC 20
It operates based on the command.

Reference numeral 17 is a nitrogen cylinder storing compressed nitrogen gas, 17a is a nitrogen valve for opening and closing a gas passage connecting the nitrogen cylinder 17 and the nitrogen gas inlet 10a of the hermetically sealed container 10, and 17b is a command of the PC 20. It is a nitrogen valve drive unit that drives the nitrogen valve 17a to open and close based on the above. When the nitrogen valve 17a is opened, nitrogen gas is introduced into the sealed container 10 from the nitrogen cylinder 17. The nitrogen cylinder 17, the nitrogen valve 17a, and the nitrogen valve drive unit 1
Gas supply means is constituted by 7b.

Reference numeral 18 denotes a gate valve that opens and closes a gas passage that connects between the vacuum exhaust port 10c of the sealed container 10 and the vacuum pump 9, and 18a denotes a gate valve drive unit that drives the gate valve 18 to open and close based on a command from the PC 20. .. Reference numeral 19 is a leak valve that opens and closes a gas passage that connects the nitrogen gas outlet 10b of the sealed container 10 and the outside of the sealed container 10, and 19a is a leak valve drive unit that opens and closes the leak valve 19 in response to a command from the PC 20. When the leak valve 19 is opened, the gas such as nitrogen gas stored in the sealed container 10 is released to the outside of the sealed container 10.

Next, the procedure of soldering using the soldering apparatus according to the present invention will be described with reference to FIG. Prior to the operation, the solder 5 is placed on the heat dissipation substrate 4 in advance, and the bare chip 6 placed on the solder 5 is put in the sealed container 10 and the door is closed. Then, in step 1 of FIG. 2, the state of each part is set to the initial state.

That is, the vacuum pump 9 is turned off, the leak valve 19 is closed, the gate valve 18 is closed, the vacuum detector 11 is turned off, the infrared heater switch 15 is turned off, and the output of the temperature signal amplifier 13a is turned off. The temperature in the sealed container 10 is lowered so that the temperature is 130 ° C. or less, the electromagnetic valve 17a is closed, and the atmospheric pressure in the sealed container 10 is set to the atmospheric pressure in advance. When the operator inputs an operation start command from the PC 20 in this state, the process proceeds to the next step 2,
Start operation.

In step 2, the PC 20 gives a command to the vacuum pump power supply ON / OFF drive unit 9a to turn on the power supply of the vacuum pump 9 and also gives a command to the gate valve drive unit 18a to open the gate valve 18. Then, evacuation of the sealed container 10 is started and the next step 3
Proceed to. In step 3, the PC 20 gives a command to the vacuum detector power ON / OFF drive unit 16, and the vacuum detector 1
Turn on the power source of No. 1 and proceed to Step 4.

In step 4, the process waits until the vacuum detection output of the vacuum detector 11 reaches a predetermined degree of vacuum of 10 ^-3 Torr, and then proceeds to step 5. In step 5, PC2
0 gives a command to the infrared heater switch ON / OFF drive unit 15a to enable the infrared heater 8 to be energized,
Go to step 6. In step 6, the temperature of the heat dissipation board 4 rises, the temperature signal amplifier 13a stays in this step until the temperature signal sent from the temperature signal amplifier 13a indicates 350 ° C., and proceeds to the next step 7.

In step 7, the PC 20 gives a command to the vacuum detector power ON / OFF drive unit 16 to cause the vacuum detector 1 to operate.
1 is turned off, a command is given to the gate valve driving unit 18a, the gate valve 18 is closed, and a command is given to the vacuum pump power ON / OFF driving unit 9a to turn off the power of the vacuum pump 9, and the process goes to Step 8. move on. Step 8
Then, the PC 20 gives a command to the nitrogen valve drive unit 17b, opens the nitrogen valve 17a, introduces nitrogen gas into the sealed container 10, and proceeds to step 9.

In step 9, the process waits until the detection output of the pressure detector 12 reaches a value 0.5 Kg / cm ² higher than the atmospheric pressure, and the process proceeds to step 10. In step 10, PC2
0 gives an instruction to the infrared heater switch ON / OFF drive section 15a to turn off the infrared heater switch 15 and also gives an instruction to the leak valve drive section 19a to open the leak valve 19 and proceed to step 11.

When the leak valve 19 and the nitrogen valve 17a are open, new nitrogen gas is introduced into the sealed container 10 from the nitrogen cylinder 17 and the already introduced nitrogen gas is discharged from the leak valve 19 to the outside. Since it is discharged to, the cooling is performed promptly. At this time, the pressure inside the sealed container 10 is controlled by the PC 20 so as to be maintained at a value higher than the atmospheric pressure by 0.5 Kg / cm ^2, so that the outside air does not enter through the leak valve 19.

In step 11, the PC 20 waits until the output of the temperature signal amplifier 13a shows a temperature of 130 ° C. or less, and proceeds to step 12. In step 12, the PC 20 gives a command to the nitrogen valve drive unit 17b,
The nitrogen valve 17a is closed, and the introduction of nitrogen gas from the nitrogen cylinder 17 into the sealed container 10 is stopped. At this time, since the leak valve 19 is in the open state, the inside of the sealed container 10 quickly returns to atmospheric pressure. After that, the door of the hermetically sealed container 10 may be opened, and the heat dissipation substrate 4 and the bare chip 6 that have been joined may be taken out.

Next, the result of solder joining when the samples shown below are soldered by the procedure shown in FIG. 2 will be described. The bare chip 6 of the sample is gold vapor-deposited on the bonding surface and has a size of 4 mm × 4.5 mm and a thickness of 0.4 mm. The heat dissipation board 4 of the sample has a size of 6 mm × 8 mm and a thickness of 2 mm in which copper is plated with nickel.
The melting range of the solder 5 is 270 to 312 ° C, and the composition is 5% Sn-Pb.

A sample in which the heat dissipation substrate 4, the plate-shaped solder 5 and the bare chip 6 were stacked was placed in the sealed container 10 without the weight 7 placed thereon, and solder bonding was performed in the procedure shown in FIG. As a result, although the weight 7 was not used, the solder 5 was well fit to the heat dissipation substrate 4 and the bare chip 6 in the sample that had been joined, and the soldering was performed in a good state. Further, since the heat dissipation board 4, the solder 5 and the bare chip 6 are not exposed to the outside air in a high temperature state, their surfaces are hardly affected by oxidation.

Further, according to the procedure shown in FIG. 2, nitrogen gas is introduced into the sealed container 10 in a state where the solder 5 is melted in the vacuum sealed container 10, and the sealed container is sealed by the introduced nitrogen gas. Since the cooling is performed after the atmospheric pressure in 10 rises, as shown in FIG. 4, the air bubbles in the solder 5 are remarkably increased as compared with the case where the weight 7 is used to melt the solder in a vacuum and the solder is cooled in the vacuum as it is. It was found to be low by an X-ray transmission test. Further, the gas introduced into the sealed container 10 in a state where the solder 5 is melted in the vacuum sealed container 10 is not limited to nitrogen gas, and may be any gas as long as it does not cause oxidation and corrosion.

Further, the heat dissipation substrate 4, the solder 5 and the bare chip 6 are not vertically stacked, but are stacked horizontally, and the heat dissipation substrate 4, the solder 5 and the bare chip 6 are pressed so that the solder 5 is pressed by the heat dissipation substrate 4 and the bare chip 6. It may be supported. In addition, the solder 5 is not sandwiched between the heat dissipation substrate 4 and the bare chip 6, but the solder 5 is arranged so that the molten solder flows between the facing joint surfaces of the heat dissipation substrate 4 and the bare chip 6 when heated. May be. In this case,
The shape of the solder 5 may not be a plate shape.

[0033]

As described above, the semiconductor element and the heat dissipating body are disposed so that the joint surfaces face each other, and the semiconductor element and the heat dissipating body are disposed so as to be sandwiched between the opposing joint surfaces. Or, after evacuating the inside of an airtight container containing the solder arranged so that the molten solder flows between the facing joint surfaces of the semiconductor element and the radiator when heated, the solder is heated to In the melted state, a gas such as nitrogen gas that prevents oxidation or corrosion is introduced into this airtight container, and the air pressure inside the airtight container is raised with the invasion of air blocked. Since the air bubbles generated in the semiconductor element and the heat sink can be eliminated, the surfaces of the semiconductor element and the heat sink can be prevented from being oxidized, and the generation of the air bubble in the solder joint can be prevented. Target It is possible to improve the degree, there is a good solder joint can be effectively heat dissipation characteristics can significantly improve the thermal conductivity between the semiconductor element and heat radiator.

[Brief description of drawings]

FIG. 1 is a block diagram of a soldering device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a procedure of soldering by the soldering device shown in FIG.

FIG. 3 is a cross-sectional view of a conventional soldering device (in a hydrogen atmosphere).

FIG. 4 is a sectional view of a conventional soldering device (in a vacuum atmosphere).

[Explanation of symbols]

 4 Heat dissipation board 5 Solder 6 Bare chip 8 Infrared heater 9 Vacuum pump 9a Vacuum pump power ON / OFF drive unit 10 Sealed container 10a Nitrogen gas inlet 10b Nitrogen gas outlet 10c Vacuum exhaust port 11 Vacuum detector 12 Pressure detector 13 Thermocouple 13a Temperature signal amplifier 14 Infrared heater driving unit 15 Infrared heater switch 15a Infrared heater switch ON / OFF driving unit 16 Vacuum detector power ON / OFF driving unit 17 Nitrogen gas cylinder 17a Nitrogen valve 17b Nitrogen valve driving unit 18 Gate valve 18a Gate valve driving Section 19 leak valve 19a leak valve drive section 20 programmable controller

Claims (2)

[Claims] 1. A semiconductor element and a heat radiator arranged such that their joint surfaces face each other, and a semiconductor element and a heat radiator disposed so as to be sandwiched between the joint surfaces of the semiconductor element and the heat radiator facing each other, or heated. When the semiconductor element and the heat radiator are arranged so that molten solder flows between the facing joint surfaces of the semiconductor element and the heat-dissipating body, the step of evacuating the inside of the airtight container by the vacuum evacuation means, A step of heating and melting the solder in a container, a gas for preventing oxidation or corrosion of nitrogen gas by the gas supply means in the airtight container in which the semiconductor element and the radiator and the solder in a molten state are stored And a step of increasing the atmospheric pressure in the airtight container, the soldering method comprising: 2. A semiconductor element and a heat radiator arranged such that their joint surfaces face each other, and a semiconductor element and a heat radiator disposed so as to be sandwiched between the joint surfaces of the semiconductor element and the heat radiator facing each other, or heated. An airtight container for containing molten solder so that the molten solder flows between the facing surfaces of the semiconductor element and the radiator, a vacuum evacuation unit for evacuating the airtight container, and the airtight container Vacuum detecting means for detecting that the inside is in a predetermined vacuum state, heating means for heating and melting the solder in the airtight container, temperature detecting means for detecting that the solder is in a predetermined molten state, the vacuum detection Oxidation of nitrogen gas or the like in the airtight container based on the detection of the predetermined vacuum state in the airtight container by the means and the detection of the solder in the predetermined molten state by the temperature detection means. Alternatively, a soldering device including a gas supply unit that introduces a gas that prevents corrosion.