JP2003209347A - Method and apparatus for reflow soldering - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for reflow soldering in which, even when a soldering material without flux is used, a sufficient connectibility can be assured and which largely contributes to a short circuit prevention and a void occurrence suppression. <P>SOLUTION: The method for reflow soldering comprises the steps of setting a board 1 having a conductor pattern 2 to a jig 10 (1), supplying a solder foil 14 without flux onto the conductor pattern 2, further supplying a ceramic capacitor 4 and a power semiconductor element 5, and supporting the capacitor 4 to a receiving member 17 (2). The method further comprises the steps of thereafter moving the jig 10 to a reflow furnace of a hydrogen reducing atmosphere (3), sliding the member 17 to meet melting of the foil 4, and dropping the capacitor 4 on the molten solder 14' (4). Thus, the molten solder 14' does not have a time allowance of leaking to a periphery, and its wettability is not so large due to the foil without flux, and the solder is solidified without shortening. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflow soldering method for manufacturing an electronic device, and more particularly to a reflow soldering method and apparatus suitable for mounting a chip component.

[0002]

2. Description of the Related Art As an electronic device, for example, as shown in FIGS. 5 and 6, on a conductor pattern 2 provided on a substrate 1,
There is one in which a ceramic capacitor 4 as a chip component and a power semiconductor element 5 are joined via a solder 3,
Conventionally, reflow soldering has been generally adopted as a method for mounting such chip components.

FIG. 7 shows a conventional reflow soldering method for mounting the above-mentioned ceramic capacitor 4 and power semiconductor element 5, and a mask for screen printing is provided on a substrate 1 on which a conductor pattern 2 is provided in advance. 6 (), then a squeegee 7 is used to print a flux-cored cream solder material 8 on the mask 6 (), and then the ceramic capacitor 4 is placed on the solder material 8.
And the power semiconductor element 5 (), and then the substrate 1
Is carried into a reflow furnace (not shown) to melt the solder material 8 (), and finally cleaning water is sprayed onto the substrate 1 to remove the flux residue ().

[0004]

By the way, since the ceramic capacitor 4 has electrodes on both sides thereof, it is joined to the conductor pattern 2 in a state of straddling the cut. However, according to the above-described conventional reflow soldering method, since the solder material 8 contains flux and has a high wettability, the molten solder material is not melted in the ceramic capacitor 4 during heating in the reflow furnace. A phenomenon often occurs in which a short circuit is caused by penetrating into the gap between the lower surface and the substrate 1, and there is a problem that a reduction in manufacturing yield cannot be avoided. In addition, since the flux-containing cream solder material 8 is used, the solder material 8 is activated by the flux during the reflow process, and voids are likely to occur in the solder 3 (FIG. 5) after joining, which is of a surface-joint type. There is a problem that the electric connection and the bonding strength on the power semiconductor element 5 side are adversely affected. Furthermore, a cleaning process for finally removing the flux residue is required, which causes a rise in manufacturing cost. As a countermeasure against the void, for example, Japanese Patent Laid-Open No. 5-291314 describes a method of remelting the solder in a vacuum heat treatment furnace after soldering or a method of reflowing the solder in a vacuum heat treatment furnace. However, since the flux is used in this method as well, the above-mentioned cleaning step still remains and does not contribute at all to the solution of the above-mentioned short circuit problem. Further, by using a fluxless solder material containing no flux, various problems due to the use of the flux described above are solved, but in this case, the wettability of the solder material deteriorates due to the influence of the oxide film, Since sufficient bondability was not obtained, in reality, there was no choice but to abandon its use.

The present invention has been made in view of the above-mentioned conventional problems, and it is a matter of course that sufficient bondability can be ensured even if a fluxless solder material is used. It is an object of the present invention to provide a reflow soldering method which greatly contributes to prevention of short circuit and suppression of void generation, and also to provide an apparatus for efficiently carrying out this method.

[0006]

In order to solve the above-mentioned problems, a reflow soldering method according to the present invention is a reflow furnace in which a fluxless solder material is placed on one of two members to be joined to create a reducing atmosphere. After melting the solder material inside, the other member is brought into contact with the melted solder material. In the reflow soldering method performed in this way, the solder material is melted in the reflow furnace in a reducing atmosphere, so that even if a fluxless solder material is used, the necessary wettability can be secured and sufficient bondability can be obtained. Is obtained. Further, since the fluxless structure suppresses the activation of the solder material, the generation of voids is suppressed, and the subsequent cleaning step is also unnecessary. Moreover, since the solder material is melted and the other member is brought into contact with it, there is no time margin for the melted solder material to leak to the surroundings, and the flux wetness may not be so great. Therefore, the occurrence of short circuit is prevented in advance. In the method of the present invention, in order to bring the other member into contact with the molten solder material, the other member is positioned and arranged above the solder material in advance, and the other member is dropped onto the molten solder material in the reflow furnace. The method of making it possible can be adopted. In the method of the present invention, the types of the two members to be joined are not particularly limited, but one member is a conductor pattern on a substrate and the other member is a chip component having a plurality of electrodes, for example, It can be a ceramic capacitor. In the method of the present invention, a surface-bonding type chip component such as a power semiconductor element may be further mounted on the fluxless solder material mounted on the conductor pattern on the substrate, whereby different types of chips can be mounted. Chip components can be mixed effectively.

A reflow soldering apparatus according to the present invention for solving the above-mentioned problems includes a jig for holding one of two members to be joined, a reflow furnace in a hydrogen reducing atmosphere, and the jig in the reflow furnace. In a reflow soldering apparatus equipped with a conveyer for transporting at the same time, a receiving member for supporting the other of the two members to be joined is slidably disposed on the jig, and the conveyor is provided in the reflow furnace. It is characterized in that an actuating member is arranged to advance and retreat on the carrying line of the jig, slide the receiving member, and drop the other member onto the molten solder material on the one member. In the reflow soldering device configured as described above, the fluxless solder material should be bonded onto the solder material at a timing when the fluxless solder material is melted by operating the operating member in accordance with the movement of the jig by the conveyor. The other member can be contacted easily and surely.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. 1 and 2 show an embodiment of a reflow soldering method according to the present invention and an apparatus used for carrying out the method. The present reflow soldering method is applied to the manufacture of the electronic device shown in FIGS. 5 and 6, and there is no change in the structure of the electronic device. is doing.

When performing the reflow soldering method,
A jig 10 for holding the substrate 1 provided with the conductor pattern 2 in advance.
To prepare. The jig 10 comprises a jig body 12 having a storage recess 11 for the substrate 1 and a cover 13 which is covered by the jig main body 12. The cover 13 stores the jig in the storage recess 11. On the conductor pattern 2 of the substrate 1, two inlets 15 and 16 for inserting the solder foil 14 and for inserting the ceramic capacitor 4 and the power semiconductor element 5 are provided. The jig main body 12 and the cover 13 constituting the jig 10 are made of carbon, which is excellent in thermal conductivity and emissivity, on the other hand,
The solder foil 14 is made of a so-called fluxless solder material containing no flux.

As shown in FIG. 2, the jig 10 is provided with a flat bar-shaped receiving member 17 for supporting the ceramic capacitor 4. This receiving member 17
Is inserted into a guide hole 18 provided in the cover 13, and can be arbitrarily slid in a reflow furnace 20 described later in a direction along a carrying direction F of a jig 10 carried by a conveyor 21. The receiving member 17 has the other end (rear end) outside the jig 10 in a state where one end (front end) is provided under the ceramic capacitor 4 insertion opening 15 provided in the cover 13. It has a sufficient length to allow it to project. An arm piece 19 is fixed to the rear end portion of the receiving member 17 extending outside the jig 10 so as to extend in a direction orthogonal to the transport direction F. This arm piece 19
The length is set so that both ends of the conveyor 21 project laterally from both sides of the conveyor 21.

The reflow furnace 20 is constructed as a continuous furnace and a hydrogen reducing atmosphere furnace. Meanwhile, conveyor 2
1 comprises a belt conveyor made of metal (for example, stainless steel), and a jig 10 mounted on the belt conveyor is
The reflow furnace 20 is conveyed at a constant speed from an inlet (not shown) on one end side to an outlet (not shown) on the other end side.
In the reflow furnace 20, a pair of lifting members (operating members) 22 are provided so that they face each other with a conveyor 21 in between.
Is provided. The pair of elevating / lowering bodies 22 are adapted to move up and down in synchronization between a position where they interfere with both ends of the arm piece 19 integral with the receiving member 17 and a non-interference position with respect to the arm piece 19. The elevating member 22 is appropriately timing according to the conveyance of the jig 10 by the conveyor 21.
Is raised, the elevating body 22 interferes with the arm piece 19 and the receiving member 17 moves (retracts) relative to the jig 10. Then, the pair of lifting bodies 22 are
Solder foil 1 put on the substrate 1 held by the jig 10.
4 is set so that the ceramic capacitor 4 rises at the timing when it begins to melt, and the rising and lowering timing is set, whereby the ceramic capacitor 4 supported on the receiving member 17 is provided.
Will fall onto this molten solder material.

Hereinafter, the reflow soldering method using the above apparatus will be described more specifically with reference to FIG.
At the time of reflow soldering, the substrate 1 provided with the conductor pattern 2 is set in the storage recess 11 of the jig body 12, and the jig body 12 is covered with the cover 13 to form the integrated jig 10 (). Next, the solder foil 14 is supplied onto the conductor pattern 2 (one member) of the substrate 1 through the inlets 15 and 16 provided in the cover 13, and the ceramic capacitor 4 and the power semiconductor element are further provided through the inlets 15 and 16. Put 5 and (). At this time, the tip of the receiving member 17 is positioned below the one inlet 15, and the ceramic capacitor 4 as the other member is supported on the receiving member 17. On the other hand, the bottom of the other charging port 16 is open, and therefore, the power semiconductor element 5 has the solder foil 1
Placed directly on top of 4 ().

Thereafter, the jig 1 which has been prepared as described above
0 is supplied on the conveyor 21 at a predetermined pitch, and is sequentially conveyed in the reflow furnace 20. The jig 10 is moved at a constant speed in the reflow furnace 20 by the conveyor 21, and the solder foil 14 on the conductor pattern 2 of the substrate 1 is gradually heated in accordance with this movement and finally melted. At this time, since the power semiconductor element 5 is directly placed on the conductor pattern 2 via the solder foil 14, it adheres to the conductor pattern 2 via the molten solder material 14 '(). On the other hand, as the solder foil 14 is melted, the pair of elevating bodies 22 (FIG. 2) arranged in the reflow furnace 20 ascend, and the forward movement of the receiving member 17 is stopped via the arm piece 19. Then, the receiving member 17
Moves backward with respect to the jig 10, and the ceramic capacitor 4 supported on the jig 10 falls onto the molten solder material 14 ′. As a result, the ceramic capacitor 4 also passes through the molten solder material 14 ′. Adhere to the conductor pattern 2 (). In addition, the lifting body 22 is the ceramic capacitor 4
Descends when it falls onto the melted solder material 14 ', and thereafter, the lifting operation is repeated for the subsequent jig 10.

In the present embodiment, the lifting / lowering body 22 is used.
Is arranged near the outlet of the reflow furnace 20, and the jig 10 is
It is carried out of the reflow furnace 20 in a relatively short time, and the molten solder material 14 'is rapidly solidified by this, and the reflow soldering of the ceramic capacitor 4 and the power semiconductor element 5 to the substrate 1 is completed. That is,
As shown in FIGS. 5 and 6, the electronic device in which the ceramic capacitor 4 and the power semiconductor element 5 are mounted (mixed) is completed.

In the reflow soldering described above, the solder material (solder foil 14) is melted in the reflow furnace 20 in a reducing atmosphere, so that the necessary wettability can be secured even if a fluxless solder material is used. It is possible to obtain sufficient bondability. Further, since the activation of the solder material is suppressed by the fluxless, void generation in the solder material 3 not only under the ceramic capacitor 4 but also under the surface-bonding type power semiconductor element 5 is significantly suppressed, and their electrical connection is achieved. Also, the bonding strength is sufficient. By the way, the void ratio in the solder material 3 under the power semiconductor element 5 decreases to 2% or less. Further, since the fluxless solder material does not require a subsequent cleaning step, it is very advantageous in terms of cost. Further, when a flux-containing solder material is used, the electrical components are positioned by self-alignment, so the degree of freedom in designing the conductor pattern 2 is small. However, according to the present reflow soldering method, flux-less solder material self-alignment is performed. As a result, the degree of freedom in designing the conductor pattern is increased. Further, since the ceramic capacitor 4 is brought into contact with the solder material after it is melted, the molten solder material 14
There is not enough time to penetrate into the gap between the ceramic capacitor 4 and the substrate 1 to be joined, and the solder material wettability is not so great due to the fluxless, so that a short circuit between the electrodes of the ceramic capacitor 4 occurs. Prevented in advance. Although the solder foil 14 is used as the solder material in the above-described embodiment, the type of the solder material is arbitrary, and instead of the solder foil 14, granular solder,
Thread solder or the like can be used.

By the way, as an electronic device, for example, FIG.
As shown in FIG. 4 and FIG.
1. Two semiconductor elements, such as IGBT
There is one in which an upper electrode 35 is joined by using solder 34 on (insulated gate bipolar transistor) 32 and FW diode (free wheel diode) 33. The present invention is also applicable to such reflow soldering of the upper electrode 35. In this case, after the substrate 30 is held by a jig similar to the jig 10 including the receiving member 17 described above, A fluxless solder foil (solder material) is placed on the IGBT 32 and the FW diode 33, and the upper electrode 35 is supported by the receiving member. And
After this preparation is completed, the jig is moved in the reflow furnace 20 in the hydrogen reducing atmosphere by the conveyor 21 in the mode shown in FIG. 2, and the elevating body 22 is raised at the timing when the solder material is melted. Then, the receiving member retracts and the upper electrode 35 supported by the receiving member falls onto the molten solder material, and the upper electrode 35 is joined to the IGBT 32 and the FW diode 33. In this case, the molten solder material is I
There is no time to leak to the back side of the GBT 32 and the FW diode 33, and the wettability of the solder material is not so great due to the fluxless, so that there is no risk of short circuit between the front and back of these semiconductor elements. Further, by using the fluxless solder material, void generation is suppressed as in the above-described embodiment.

[0017]

As described above, according to the reflow soldering method of the present invention, the reflow treatment is performed in the reducing atmosphere, so that sufficient bondability can be secured even if a fluxless solder material is used. In addition, the generation of voids can be suppressed, and the reliability of the obtained electronic device is significantly improved. Further, the use of the fluxless solder material also eliminates the need for a cleaning step, thus reducing the manufacturing cost of the electronic device. Moreover, since the other material to be joined is brought into contact with the solder material after it is melted, there is no time margin for the melted solder material to diffuse to the surroundings,
Due to the fluxlessness, the wettability of the solder material is not so great, so that the occurrence of a short circuit is prevented.
In addition, because fluxless solder suppresses self-alignment of the solder material, the degree of freedom in the design of the conductor pattern is increased, and in combination with the suppression of void generation described above, it is extremely useful when mounting surface-bonding type chip components together. It will be useful. Further, according to the reflow soldering apparatus according to the present invention, the fluxless solder material is joined onto the solder material at the timing when the fluxless solder material is melted by operating the operating member in accordance with the movement of the jig by the conveyor. The other member to be made can be brought into contact with each other easily and surely.

[Brief description of drawings]

FIG. 1 is a process drawing showing one embodiment of a reflow soldering method according to the present invention.

FIG. 2 is a plan view showing, as a partial cross-section, a device configuration for carrying out the present reflow soldering method and a mode of use thereof.

FIG. 3 is a plan view showing a structure of a different type of electronic device to which the present reflow soldering method is applied.

FIG. 4 is a cross-sectional view of the electric device shown in FIG.

FIG. 5 is a plan view showing the structure of an electronic device to which the present reflow soldering method is applied.

6 is a cross-sectional view of the electric device shown in FIG.

FIG. 7 is a process drawing showing an embodiment of a conventional reflow soldering method.

[Explanation of symbols]

1 Board 2 Conductor Pattern (One Member) 3 Solder 4 Ceramic Capacitor (Chip Component: Other Member) 5 Power Semiconductor Device (Surface Bonding Type Chip Component) 10 Jig 14 Solder Foil (Solder Material) 14 'Melted Solder Material 17 Receiving member 20 Reflow oven 21 Conveyor 22 Elevating body (operating member) 30 Substrate 32 IGBT (one member) 33 FW diode 33 (one member) 34 Solder 35 Upper electrode (other member)

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B23K 31/02 310 B23K 31/02 310B

Claims (7)

[Claims] 1. A fluxless solder material is placed on one of two members to be joined, the solder material is melted in a reflow furnace in a reducing atmosphere, and then the other member is attached to the melted solder material. A reflow soldering method characterized by contacting. 2. The reflow soldering according to claim 1, wherein the other member is positioned and arranged in advance above the solder material, and the other member is dropped onto the melted solder material in a reflow furnace. Method. 3. One of the two members to be joined is a conductor pattern on a substrate, and the other member is a chip component having a plurality of electrodes. Reflow soldering method. 4. The reflow soldering method according to claim 3, wherein the chip component is a ceramic capacitor. 5. The reflow soldering method according to claim 3, wherein a surface-bonding type chip component is further mounted on the fluxless solder material mounted on the conductor pattern on the substrate. 6. The reflow soldering method according to claim 5, wherein the surface-bonding type chip component is a power semiconductor element. 7. A reflow soldering apparatus comprising a jig for holding one of two members to be joined, a reflow furnace in a hydrogen reducing atmosphere, and a conveyor for transporting the jig in the reflow furnace. A receiving member that supports the other of the two members to be joined is slidably arranged in the jig, and is moved forward and backward on the jig conveying line by the conveyor in the reflow furnace to move the receiving member. A reflow soldering device, wherein an operating member is provided which slides and drops the other member onto the molten solder material on the one member.