JPH10163620A - Method and apparatus for soldering electronic components - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and apparatus for soldering electronic components, suited for soldering a directly bonded Cu board to a metal base. SOLUTION: A capillary diffusion type soldering zone 6 is disposed between a main chamber 7 held in a reductive and low-O concn. atmosphere inside and branch chamber 8 held in a reductive atmosphere inside. This chamber 8 is coupled just in the front of the soldering zone. The main chamber 7 has a base conveyer 7a for carrying a metal base 3 with its soldering surface up and preheating and cooling means disposed separately in an inlet, soldering zone and outlet. The branch chamber 8 has a board conveyer 8a for carrying a ceramic board 1 in this chamber 8 with the soldering surface down and overlaying it on the base 3 in the main chamber 7, and preheating means for preheating the board 1 and the base 3 being exposed to the reductive atmosphere during carrying, overlaying it on the base 3 just before the soldering zone to solder them.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor chip (IGB) for a power transistor module, for example.
T), a ceramic substrate on which electronic components such as a freewheeling diode are mounted (for example, a direct-bonded copper substrate in which copper foil is directly bonded to both sides of a ceramic plate with a metal base as a heat sink) The present invention relates to a method for soldering an electronic component, which is suitable as a soldering method in a case where the components are superposed on each other and soldered, and a soldering apparatus therefor.

[0002]

2. Description of the Related Art When a ceramic substrate on which chip elements are mounted is soldered to a metal base (copper plate),
Soldering defects in the solder layer on the joint surface (increase in heat transfer resistance)
With the aim of suppressing the generation of voids and improving product reliability and manufacturing yield, small projections are formed in advance on the periphery of the solder joint surface area on the upper side of the metal base, and solder Before stacking the substrates with the soldering surface facing down on the metal base before loading into the soldering furnace, transport the wafers into the soldering furnace with the furnace kept in a reducing gas atmosphere in this stacked state. While pre-heating the metal base and the board to the soldering temperature on the way, when soldering, press the center of the board from above to the metal base with a pressure pin from the outer peripheral side of the board through the solder supply header. The molten solder supplied on the metal base penetrates and diffuses into the gap in the joint surface area between the substrate and the metal base by capillary penetration and wettability of the solder joint surface, and soldering is performed without using flux. Is to way scheme soldering apparatus of development, the soldering method has been proposed as Japanese Patent Application No. 7-204119 of the same applicant as the present invention.

According to such a soldering method, the capillary action of the solder acts more strongly on the central portion than on the peripheral portion of the ceramic substrate, and the molten solder spreads first from the central surface area. The remaining gas or generated gas is pushed out from the central part of the substrate to the peripheral part of the substrate and is eliminated, so that the rate of voids generated in the solder layer is suppressed to a low level, and a highly reliable semiconductor device can be manufactured. It becomes possible. Moreover, there is no need for a step of applying a pre-soldering step, and the lead time of the soldering step can be shortened to obtain high productivity.

[0004]

The above-mentioned soldering method (hereinafter referred to as "capillary infiltration type soldering method") is based on the "wetting property to the molten solder in the solder joint surface area of the ceramic substrate and the metal base." It is a prerequisite that sufficient soldering is ensured. If local dirt, oxide film, etc. occur on the solder joint surface, the "wettability" with the solder is reduced in this area and the molten solder It has been found from the results of experiments and inspections (soft X-ray transmission inspection) conducted by the inventors that the capillary penetration effect of the above does not function effectively and that voids frequently occur in the solder layer. In addition, if many voids are generated in the soldering layer, the heat transfer between the substrate and the metal base is deteriorated, and this causes a significant decrease in the characteristics of the semiconductor device, such as a significant increase in the junction temperature inside the semiconductor element during energization. Becomes

[0005] In particular, the direct bonded copper substrate mentioned above is formed by reacting copper with a trace amount of oxygen.
A copper foil is bonded to a ceramics plate using a u-O eutectic liquid phase. In the bonding process, molybdenum (M
The ceramic plate and the copper foil are superimposed on the mesh plate of o), and the ceramic and the copper foil are joined by heating in a temperature range not lower than the Cu-O eutectic temperature (1065 ° C). For this reason, an oxide film is formed on the surface of the copper foil, and molybdenum remains, albeit slightly, which lowers the “wetability” with the molten solder.

In this regard, in the above-mentioned conventional soldering method, the substrate is superimposed on the metal base in the atmosphere outside the soldering furnace, and the substrate is transferred to a soldering furnace maintained in a reducing atmosphere in the superimposed state. As a result, the metal base and the soldering surface of the substrate are not sufficiently exposed to the reducing gas in the furnace. For this reason, the reducing action of the reducing gas in the furnace does not work effectively on the oxide film formed on the soldering surface before being transferred into the furnace, and the adsorbed gas on the soldering surface does not work.
Moisture is also insufficiently removed by gas replacement, and the "wetability" to the molten solder is reduced. This causes many voids to be generated at the soldered joint and deteriorates the heat transfer between the ceramic substrate and the metal base.

FIG. 3 is a schematic diagram of a power transistor module showing this state. In the figure, reference numeral 1 denotes a ceramic substrate (direct ceramic substrate) in which copper foils 1b and 1c are bonded to upper and lower surfaces of a ceramic plate 1a made of alumina or the like. Bonded copper substrate), 2 is a chip element (bare chip) such as a power transistor (IGBT), freewheeling diode mounted on a circuit pattern formed on a copper foil 1b on the upper surface side, 3 is a metal base (copper plate) for heat dissipation, Reference numeral 4 denotes a solder layer which joins between the copper foil 1c of the direct bonded copper substrate 1 and the metal base 3 by the above-mentioned capillary penetration soldering method, and has a "wetting property caused by dirt on the solder joint surface, an oxide film and the like. The voids generated locally in the solder layer 4 with the decrease in “” are indicated by reference numeral 5.

The present invention has been made in view of the above points, and has been improved based on the capillary penetration soldering method mentioned above so as to realize flux-less and void-free high-quality soldering. It is an object of the present invention to provide an electronic component soldering method and a soldering apparatus suitable for bonding a bonded copper substrate to a metal base by soldering.

[0009]

In order to achieve the above object, according to the soldering method of the present invention, an insulating substrate such as a direct bonded copper substrate on which a chip element is mounted without using a flux, and a metal base Are individually brought into a soldering furnace, preheated during the transfer while exposing the soldering surface to a reducing atmosphere, and the board is superimposed on a metal base and soldered immediately before soldering. I do.

In the soldering apparatus of the present invention used for carrying out the above-mentioned soldering method, the internal atmosphere is connected to a reducing atmosphere and a low oxygen concentration atmosphere before and after the soldering portion arranged in the center of the furnace. The main chamber has a tunnel-shaped main chamber and a tunnel-shaped branch chamber connected to the main chamber just before the soldering part while maintaining the internal atmosphere in a reducing atmosphere, with the soldering surface facing up in the main chamber. Transfer means for transferring the metal base supplied from the inlet through the soldering section to the outlet, and a section along the transfer means from the inlet of the main chamber to the soldering section and from the soldering section to the outlet. Equipped with a metal-based preheating and cooling means arranged in the main chamber, and the branch chamber receives the board supplied from the inlet with the soldering surface facing down. It shall constitute equipped substrate transfer means superposed on the metal base and transported to over, and the preheating means of the substrate.

[0011] As described above, the metal base and the substrate are individually loaded into the chamber kept in the reducing atmosphere through separate routes into the chamber for soldering and preheated, and the base and the substrate are soldered together. And soldering by capillary infiltration method just before the step, the soldering surface is sufficiently exposed to the reducing gas before the base and substrate are overlapped, reducing oxides and reducing adsorbed gas and moisture. Substitution is performed to ensure high "wetting" of the soldered surface with the molten solder. Thus, in the subsequent capillary penetration soldering step, the substrate can be soldered to the metal base without using a flux without generating voids.

The base and the substrate assembly coming out of the soldering part are cooled and solidified in the course of being conveyed to the outlet through the downstream path of the main chamber kept in a low oxygen concentration atmosphere.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION A power circuit assembly in which a chip element such as an IGBT is mounted on a ceramic substrate (direct bonded copper substrate) shown in FIG. An embodiment of the present invention will be described with reference to the drawings, taking the case of soldering as an example.

FIG. 1 shows a soldering apparatus used for carrying out the soldering method of the present invention. That is, the soldering furnace has the above-mentioned capillary-penetrating soldering portion 6 arranged at the center thereof and a tunnel-shaped main chamber 7 extending before and after the soldering portion 6.
And a tunnel-shaped branch chamber 8 branched laterally from a position immediately before the soldering portion 6.
, A reducing gas containing a mixture of nitrogen and hydrogen is supplied from the inlet (left end) to keep the section up to the soldering section 6 in a reducing atmosphere, and the solder chamber 6 exits from the main chamber 7 (right end). The section up to) is kept in a low oxygen atmosphere. Also, a reducing gas is supplied to the branch chamber 8 from the inlet side to maintain the inside of the chamber in a reducing atmosphere.

The main chamber 7 has a base transfer section 7a for transferring the metal base 3 with its soldering surface facing upward between its inlet and outlet, and inside the branch chamber 8, the soldering surface faces downward. A substrate transport unit 8a as a three-axis robot that suspends and transports the ceramic substrate 1 with a vacuum chuck or the like is installed. Furthermore, the main chamber 7
The heating path between the entrance and the soldering section 6 along the base transfer section 7a includes a hot plate type preheating section for heating and raising the temperature of the metal base 3 to the soldering temperature stepwise. A cooling path of a cold plate type is provided in a cooling path between the outlet 6 and the outlet, and an infrared ray for heating the soldering surface of the ceramic substrate 1 from below along the transfer path of the substrate transfer section 8a in the branch chamber 8. A radiant preheating source such as a lamp is provided.

On the other hand, a hot plate is disposed on the soldering portion 6 as described later, and the metal base 3 transferred thereon is soldered (for example, Sn 63% -Pb 37%, or Sn 40% -Pb 60%). 290 above melting temperature
Heat to about ° C. Further, the loader 9 picks up the metal bases 3 arranged on the tray one by one and transfers them to the transfer section 7a at the entrance side of the main chamber 7 and the base from the transfer section 7a at the exit side. Unloader 10 for removing a soldering assembly of a substrate
And a substrate loader 11 that picks up ceramic substrates (substrates on which chip elements are mounted) arranged on a tray one by one and transfers them to the substrate transfer unit 8a.

In the soldering apparatus having such a configuration, the metal base 3 is supplied to the base transfer section 7a by the loader 9 at the entrance side of the main chamber 7 with the soldering surface facing upward.
The metal base 3 is preheated while being transported through the furnace toward the soldering section 6. On the other hand, on the branch chamber 8 side, the ceramic substrate 1 is transferred to the substrate transfer section 8a with the solder joint surface facing downward by the loader 11 in accordance with the tact operation of loading the metal base 3 into the furnace, and the transfer is performed in the chamber. Preheat the soldering surface of the board with. And
The ceramic substrate 1 carried into the main chamber 7 through the branch chamber 8 is suspended from above on the metal base 1 waiting at a position immediately before the soldering section 6 from above, and is superimposed on a fixed position. 6 for soldering (detailed structure of the soldered portion will be described with reference to FIG. 2), and then cool the metal base 3 in the course of transporting to the outlet of the main chamber 7 in a low oxygen atmosphere. After the solder is solidified, the unsoldered assembly is unloaded from the transfer section 7a at the outlet side of the main chamber 7.
Take out at 0.

Next, the structure of the above-mentioned soldering section 6 is shown in FIG. 2, and a description will be given of a soldering method of the capillary diffusion method performed in the soldering section. That is, in the soldering section 6, a hot plate 13 is installed on the bottom of the chamber 12, and a molten solder supply header 14 (the header is made of ceramics having low "wettability" with molten solder,
Made of a material having a high melting point such as W or Mo, or stainless steel having a passivated surface), and a soldering pipe 15 of an elevating type, and a center of the ceramic substrate 1 on which the chip element 2 is mounted. The metal base 3 is formed from above with small protrusions 3a of 0.05 to 0.5 mm formed at several places on the periphery of the solder joint surface area of the metal base 3, and the ceramic substrate 1 is placed on the protrusions. A pressure pin 16 for pressing toward (overlapping) protrudes into the chamber. Reference numeral 17 denotes a wire solder (a thread-like solder having a diameter of about 1.2 mm) sent from outside to the solder supply pipe 15.

The superposed body of the metal base 3 and the ceramic substrate 1 in the preheated and heated state transferred by the transfer section 7a (see FIG. 1) of the main chamber 7 to the soldering section 6 having such a configuration is hot. It is transferred onto the plate 13 where it is further heated to a temperature equal to or higher than the melting point of the wire solder 17. Further, in synchronization with the transfer of the metal base 3, the solder supply pipe 15 is pulled down from above, and the molten solder discharge port 14a of the header 14 is set on the metal base plate 3 toward the periphery of the substrate 1, And wire solder 17
And press the tip thereof against the heated metal base 3, and further press the central portion of the substrate 1 from above with a pressure pin 16, and warp the ceramic substrate 1 in a concave shape with the protrusion 3 a as a fulcrum. The center area of the lever is lightly brought into contact with the metal base 3.

As a result, the resin melts inside the header 14,
The molten solder supplied from the discharge port 14a toward the gap between the substrate 1 and the metal base 3 is formed between the substrate 1 and the metal base 3 as shown by the arrow due to the wettability of the solder joint surface and the capillary penetration action. Penetrates and spreads through the joint surface area. Since slag such as oxide contained in the molten solder floats on the surface of the molten solder in the header 14, only pure solder containing no slag is supplied from the discharge port 14a. Also,
In this case, the gap between the central surface area of the ceramic substrate 1 and the metal base 3 is narrower than that of the peripheral edge portion, and the capillary phenomenon at this portion acts strongly. Therefore, the molten solder spreads from the central surface area. Go. Therefore, the gas generated or remaining in the gap between the substrate and the metal base is pushed to the periphery of the substrate 1 and is removed from the gap, so that the molten solder diffuses to all corners to suppress generation of voids. Is done.
Regarding the structure of the above-mentioned soldering portion 6 and the capillary penetration soldering method to be performed here, the one proposed in Japanese Patent Application No. 7-204119 previously applied by the same applicant as the present invention should be employed as it is. Can be.

As can be seen from the above description of the embodiment, according to the soldering method of the present invention, as shown in FIG. 1, the ceramic substrate 1 and the metal base 3 are kept in a reducing atmosphere from different routes. Into the furnace chamber,
After sufficiently exposing the soldering surface to a reducing gas while preheating during the transportation, the ceramic substrate 1 is superimposed on the metal base 3 at a position immediately before the soldering portion 6.
Subsequently, capillary penetration soldering is performed in the soldering section 6. Therefore, at the time of soldering, the solder joint surface is cleaned (reduction of oxide film, removal of adsorbed gas and moisture) by the reduction and replacement action by the reducing gas, and high "wetness" to the molten solder can be ensured, thereby making the capillary tube The features of the infiltration soldering method are fully exhibited, and the occurrence of voids in the solder joint layer can be prevented. In addition, since no flux is used, no post-treatment of flux washing and drying is required.

The application of the soldering method of the present invention is not limited to the above-described semiconductor device such as a power transistor module, but can be applied to other various electronic component soldering methods.

[0023]

As described above, according to the soldering method of the present invention, a substrate (such as a ceramic substrate on which a chip element is mounted) is placed on a metal base with the soldering surface facing down. Based on a method in which molten solder supplied onto the metal base from the outer peripheral side penetrates into the surface gap between the substrate and the metal base by capillary action to perform solder joining, the board and the metal base carried into the soldering furnace are separated from each other. By preheating individually with the soldering surface exposed to a reducing atmosphere, and superimposing the board on a metal base immediately before soldering without using flux, soldering the base and board The surface to be soldered is sufficiently exposed to the reducing gas in the furnace before the superposition, and the oxide film, adsorbed gas, and moisture on the soldering surface are exposed to the reducing gas. Reduction is almost completely removed substituted. As a result, the solder joint surface is cleaned, and high "wetness" with the molten solder can be ensured. As a result, the features of the capillary infiltration soldering method are fully exhibited, and high quality, void-free soldering is achieved. . In particular, the soldering method of the present invention is extremely effective when soldering between a direct bonded copper substrate and a metal base used in a power transistor module.

Further, by employing the soldering apparatus of the present invention, the steps from supply of a metal base and a substrate to removal of a soldered assembly through preheating, soldering and cooling steps are performed automatically. be able to.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a soldering apparatus used for implementing a soldering method of the present invention.

FIG. 2 is a cross-sectional view of a configuration of a soldering unit in FIG.

FIG. 3 is a diagram schematically illustrating a state in which voids are generated in a solder bonding layer by a conventional soldering method, taking a power transistor module as an example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ceramic substrate 2 Chip element 3 Metal base 4 Solder layer 6 Capillary penetration type soldering part 7 Main chamber 7a Base transfer part 8 Branch chamber 8a Substrate transfer part

Claims (2)

[Claims] 1. A method of soldering an electronic component, comprising joining a copper foil to both sides of a ceramic plate and soldering an insulating substrate intended for a ceramic substrate or the like having a chip element mounted on one side of the copper foil to a metal base. Yes, the board is placed on the metal base with the soldering side facing down, and the molten solder supplied to the metal base from the outer peripheral side of the board is penetrated into the surface gap between the board and the metal base by capillary action In the case of soldering by soldering, the substrate and the metal base are individually carried into a soldering furnace without using flux, and the soldering surface is exposed to a reducing atmosphere, and is preheated in the middle of the transfer, immediately before soldering. 3. A method for soldering electronic components, comprising: superposing a substrate on a metal base and performing soldering. 2. A soldering apparatus for an electronic component used for carrying out the soldering method according to claim 1, wherein an internal atmosphere is connected to a soldering portion disposed in the center of the furnace and before and after the soldering portion. And a tunnel-shaped main chamber maintained in a low oxygen concentration atmosphere and a tunnel-shaped branch chamber connected to a position immediately before a soldering portion of the main chamber while maintaining an internal atmosphere in a reducing atmosphere. Base transfer means for transferring the metal base supplied from the inlet with the mounting surface upward to the outlet via the soldering section, and a section from the inlet of the main chamber to the soldering section along the transfer means, and soldering Equipped with metal-based preheating and cooling means arranged in the section from the section to the outlet, and the branch chamber was supplied with the soldering surface facing down from the inlet. Soldering apparatus of electronic components, characterized by being configured equipped substrate transfer means superposed on the metal base and conveying the mix substrate in the main chamber, and preheating means of the substrate.