JPH081371A - Joining method by applying magnetic field - Google Patents

Abstract

PURPOSE:To easily array the reinforcing members to improve the fatigue life of the joined part in the prescribed direction by feeding the material for joining provided with the non-magnetic material and a long magnetic body between the members to be joined, heating the non-magnetic material to be melted, and applying the magnetic field thereto. CONSTITUTION:In the feeding process of the solder, the non-magnetic material 15 and a long magnetic body 16 of the ball-shaped soldering material are mixed together, and fed to the part to be joined in the paste-like condition with the flux 17. In the following heating process, the space between the members 13, 14 to be joined is filled with the melted non-magnetic material 20, and the long magnetic body 16 is in the random floating condition in the melted solder, i.e., the non-magnetic material 20. In the process to apply the magnetic field, if the magnetic field where the direction or the intensity is fluctuated when the non-magnetic material 15 is in the molten condition is applied, the non- magnetic material 20 in the molten condition is stirred by the movement of the long magnetic body 16 inside, and the contained gas is easily discharged outside and the defects such as voids can be prevented, which is effective for the fine structure and for the improvement of the quality of the joined part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a means for joining electronic parts and semiconductor parts to a substrate, and more particularly to a magnetic field applying joining method using a joining material capable of greatly improving the fatigue life of the joining part.

[0002]

2. Description of the Related Art Recent electronic devices have been mounted in higher densities with the increase in system size and performance, and the packages mounted on a printed circuit board have changed from the conventional dual in-line insertion type to flat packages and chip carriers. It is changing to the mold surface mounting method. Also, in ultra-high-performance devices such as electronic computers, the conventional 1-chip package system is changing to a multi-chip module system in which a plurality of bare LSI chips are mounted on a single multilayer wiring board.
Furthermore, the LSI chip itself is becoming larger. Therefore, in the solder joint between the package or the LSI chip and the printed circuit board or the multilayer wiring board, there is an increase in the rate of joint failure due to poor wettability during solder joint and an increase in thermal fatigue fracture due to thermal cycles during operation of the device. It's a big problem. With respect to the former defect, it is possible to reduce the defect rate to some extent by controlling the parts and the soldering process. However, although the idea described below has been devised for the latter disconnection failure due to thermal fatigue failure, the fact is that no definitive countermeasure has been found yet. The conventional measures will be described below.

FIG. 10 shows a soldering structure of a flat package. In the figure, 1 is a semiconductor chip and 2 is Au.
Wire, 3 Al electrode, 4 lead, 5 package,
6 is a printed circuit board, 7 is a wiring pattern, and 8 is a solder joint. The joining method is as follows. A solder paste in which Pb-Sn based preform solder and flux are mixed is printed on the wiring pattern 7, and the flat package 5 is aligned and mounted on the wiring pattern 7 and passed through the vapor of the hydrocarbon based system. The latent heat of vaporization is used to melt and join the solder. The leads 4 of the flat package 5 need to have a certain degree of rigidity in order to prevent deformation during handling, and Fe—Ni alloys and recently Cu alloys are used.

FIG. 11 shows another example of the structure for soldering a semiconductor chip. In the figure, 1 is a semiconductor chip, 9 is a Cr-Ni-Au electrode, 8 is a solder joint portion, 6
Is a multilayer wiring board, and 10 is a wiring electrode. The joining method is
A film having a predetermined composition of Pb and Sn is formed on the electrode 10 of the semiconductor chip 1 and the multilayer wiring substrate 6 by a mask vapor deposition method,
Next, this film is heated and melted once to form hemispherical solder bumps, and finally the bumps of the semiconductor chip 1 and the bumps of the multilayer wiring board 6 are opposed to each other, and the solder is melted by heating in a furnace in an inert atmosphere. The semiconductor chip 1 is mechanically pulled up and joined before the solder is solidified. This is based on the idea that the fatigue life is extended when the solder column is formed in a continuous shape as compared with the case where the solder column is formed in a barrel shape.

[0005]

In the conventional method shown in FIG. 10, the elasticity of the leads 4 is lowered and softened in consideration of the retroactive processability of the leads 4 and the handling property of the package 5 during the joining process. I can't. When softened, the leads 4 are likely to be deformed, so that insufficient assembly is likely to occur. In addition, the method of increasing the height of the legs as the shape of the leads 4 and relaxing the stress due to the difference in thermal expansion is difficult to adopt because the volume occupied by the package 5 increases and the mounting density cannot be increased. Therefore, the method shown in FIG. 10 cannot sufficiently improve the fatigue life of the solder joint portion 8.

Next, in the conventional method shown in FIG. 11, the fatigue life can be improved by several times by changing the solder shape from the barrel shape to the stagnation type. Is a material hand when the number of chips 1 and chip carriers is large because the individual LSI chips 1 and chip carriers must be pulled up from the surface of the substrate 6 to a certain height when the solder is melted during the joining process. The technique is difficult, or it is difficult to mass-produce it because it needs to be held at a certain height until it solidifies.
There is a problem that the height of the chip 1 or the chip carrier with respect to the surface of the substrate 6 varies due to warpage or the like, and the quality or reliability of the solder joint 8 deteriorates.

A fracture mechanism of the solder joint portion 8 in the electronic device and a measure for improving the fatigue life will be described with reference to FIGS. 12 and 13. Flat package, chip carrier or L
The coefficient of thermal expansion of the semiconductor component such as the SI chip 1 is different from the coefficient of thermal expansion of the wiring board 6 made of an organic or ceramic multilayer plate, and it is practically impossible to match them. Therefore, the thermal stress F due to shearing is generated in the solder joint portion 8 due to the heat generated during the operation of the semiconductor component. By repeating this thermal stress F, a crack 11 is generated from the stress concentrated portion of the solder joint portion 8 which is weakest in strength, and the crack 11 propagates in a form crossing the solder joint portion 8. If the crack 11 propagates to the other end, the electrical connection here will be broken and the device will cease to function. When the fibers 12 having higher strength than the solder material are mixed in the solder joint portion 8, the fibers 1
If 2 exists in parallel to the propagation direction of the crack 11, the crack 11 receives no obstacle and the solder joint 8
When the fiber 12 is present in the direction perpendicular to the direction of propagation of the crack 11, the fiber 12 stops the propagation of the crack 11 and either breaks the fiber 12 or As long as the interface between the matrix and the solder is not separated, the crack 11 does not further propagate (FIG. 13). That is, if the fibers 12 having high strength and excellent wettability with the solder are oriented in the direction perpendicular to the joint surface, the thermal fatigue life of the solder joint portion 8 can be dramatically improved.

Usually, the solder joint portion 8 of an electronic component is extremely fine with a joint area of several mm ² or less and a joint gap of several hundred μm or less. Therefore, the high-strength fiber 12
Even if mixed, it is difficult to control the distribution and direction.

An object of the present invention is to use a joining material capable of improving the fatigue life of the joint, and a reinforcing material for improving the fatigue life of the joint can be easily arranged in a certain direction. It is intended to provide a voltage bonding method.

[0010]

According to the present invention, a joining material having a non-magnetic material and a magnetic elongated body is supplied into a gap between members to be joined and heated to melt the non-magnetic material, and a magnetic field is applied. This is a magnetic field application joining method in which a magnetic long body is applied and arranged in a direction substantially orthogonal to both joining members, and then cooled to solidify the non-magnetic material.

[0011]

According to the present invention, the magnetic elongated bodies can be easily arranged in a certain direction by applying a magnetic field.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram for explaining the process of a magnetic application bonding method according to the present invention which was made to solve the above problems. In the figure, 13 and 14 are members to be joined, and 15
Is a non-magnetic material made of a solder material, 16 is a magnetic long body serving as a reinforcing material, 17 is flux, 18 and 19 are heaters, 20
Is a melted non-magnetic material, 21 and 22 are magnets, 23 is a solidified non-magnetic material, and 24 is a magnetic field line. Also, FIG.
(B) and (c) show the time course of the joining process. In the solder supply step (a), the non-magnetic material 15 which is a ball-shaped solder material and the magnetic elongated body 16 are mixed and made into a paste with the flux 17 and supplied to the joint portion. Method or forming soldering method. The magnetic elongated body 16 used here is made of an alloy or a composite material containing at least one or more of Fe, Ni, and Co, and its shape may be a directional shape such as a fibrous shape or a long piece shape. . As the elongated body, a flexible one is preferable to a rigid one as a reinforcing material. In addition, the magnetic long body 16
In order to improve the wettability with the solder, it is preferable to coat a metal having a good wettability with the solder such as Cu or Au, or to pre-coat the solder in advance. The length of the magnetic elongated body 16 is shorter than the gap of the joint. In the next heating step (b), the gap between the members to be joined 13 and 14 is filled with the melted non-magnetic material 20, but the magnetic elongated body 16 is in a state of floating at random in the melted solder, that is, the non-magnetic material 20. Becomes In the present invention, after this, a magnetic field applying step (c) is further provided to orient the freely floating magnetic elongated body 16 in a certain direction by a magnetic force, and in this state, the non-magnetic material is solidified by cooling. 23. The magnetic elongated body 16 receives a rotational force directed in a direction parallel to the magnetic field lines in a magnetic field, and also receives an attractive force in a dense direction from a portion having a low magnetic field line density. This force is used to control the distribution state and direction of the magnetic elongated body 16.

Further, in the magnetic field applying step (c) of FIG. 1, if a magnetic field whose direction or magnetic field strength fluctuates when the non-magnetic material 15 is in a molten state is applied, the magnetic elongated body 16 moves by Since the non-magnetic material 20 in the molten state is agitated, the built-in gas can be easily discharged to the outside to prevent defects such as voids, which is effective for making the structure fine and improving the quality of the joint.

FIG. 2 shows a schematic structure of an apparatus for performing magnetic field application solder joining. Further, FIG. 3 shows a cross-sectional view seen from the III-III cross-sectional direction of FIG. In the figure, 25 is an electronic component to be joined, and 6 is a wiring board. Heating is performed by blowing an inert hot gas 26. The magnetic field applied to the joint is performed by permanent magnets 21 and 22. The magnets 21 and 22 are rotatable cylinders 2 made of a ferromagnetic material.
It is attached inside 7 at a position facing each other.
The cylinder 27 is rotatable by a motor 28, and monitors the temperature of the wiring board 6 during joining and controls the timing of rotation. The joining is performed in the case 29 with non-magnetic properties and a high heat insulating effect, and the magnetic lines of force 26 penetrate the joining part and the permanent magnets 21 and 22 have a structure and a material structure which are not heated by the heat during the joining.

Next, the procedure of the magnetic field application solder joining using this apparatus and the joining material will be described. As the solder material, that is, a non-magnetic material, a powdery material having a diameter of 10 μm or less is used, and as the magnetic long body, a Ni whisker having a length of several tens of μm and a diameter of several μm grown by a hydrogen reduction method is used. As a supply method, both are adhered in a paste form with a rosin-based binder, and the pad of the wiring board 6 is patterned by an application method. The electronic component 25 is placed on the wiring board 6 so that the electrode pads to be joined are located on the solder paste, and set in the center of the case 29. Hot gas 2 at this time
The thermocouple 31 is attached to the wiring board 6 on the leeward side of 6. After the setting of the bonded sample is completed, the N ₂ hot gas 26 heated to 300 ° C. is passed through the supply duct 30. When the temperature reaches 240 ° C. at which the Pb—Sn eutectic solder, which is the non-magnetic material used, is completely melted, the cylinder 27 is rotated several times to stop the magnetic field lines 24 in the vertical direction. After stopping the rotation of the cylinder 27, the blowing of the hot gas 26 is stopped and the air is blown to cool the joint.

4 and 5 show how electronic components are joined by the joining method according to the present invention. 4 shows the case of a flat package, and FIG. 5 shows the case of an LSI chip.
In the case of a flat package, the bonding gap is distributed in the range of several tens to several hundreds of μm due to variations in molding the leads 4. Even if the distance of the bonding gap is several times or more wider than the length of the magnetic elongated body 16, the magnetic elongated body 16 can be used as the lead 4 and the wiring pattern 7 by using the magnetic lead 4 and the wiring pattern 7. Since the magnetic force acts so as to be linearly arranged so as to connect the gaps, the magnetic elongated members 16 are appropriately distributed to the center, the upper part, and the lower part of the solder joint 8. In the case of an LSI chip, the joint gap is determined in proportion to the amount of the solder material supplied, and is adjusted to be about 50 μm.

According to the joining method of the present embodiment, the inside of the solder joint portion 8 of the electronic component 25 and the wiring board 6 can be soldered only by providing a step of applying a short-time magnetic field to the conventional solder joining step. Since the magnetic long body 16 made of metal fiber or the like having a higher strength can be made into a composite material by orienting it in the direction perpendicular to the joint surface, the fatigue life of the solder joint portion 8 can be remarkably improved at the same manufacturing cost as the conventional one. You can Further, since the magnetic elongated body 16 can be moved and the molten solder can be stirred by rotating the magnet, it is possible to remarkably reduce the residue of the flux inside the solder and the generation of voids, and to improve the reliability of the solder joint portion 8. In addition, the reliability of the electronic device can be improved.

In this embodiment, hot gas 2 is used for heating.
6 is used, the soldering method may be any of the conventionally used heat sources such as infrared light beam, laser, latent heat of vaporization, and heater. Further, the method of supplying the solder material is not limited to the solder paste.

FIG. 6 shows an example of a magnetic elongated body 16 mixed in a non-magnetic material. FIG. 6 (a) is a longitudinal section and FIG. 6 (b) is a transverse section. In the figure, numeral 32 is a magnetic core material made of a ferromagnetic material such as Fe, Co, Fe-Ni alloy, Fe-Ni-Co alloy, etc., and has a needle-like or fibrous shape with an aspect ratio of 2 times or more. ing. The manufacturing method is hydrogen reduction method,
A metal whisker crystal growth method such as a vapor deposition method may be used, a method of thinning a wire by drawing and cutting it, or a chattering method of cutting a metal surface in cross section to form a short fiber. Three
Reference numeral 3 is a surface layer of Cu, Au, Ni, Ag or the like, which has good wettability with the non-magnetic material and is excellent in adhesion or bondability with the magnetic core material 32. The coating method of the surface layer 33 is
The sputter magnetic deposition method is preferable, but a CVD method or a chemical plating method may be used. In the case of the sputter-magnetization method, if a fibrous sample is placed underneath and a method of sputter-magnetism is applied from above while vibrating the sample to stir the sample, a uniform film can be formed on the entire circumference. After forming the film, heat treatment is performed in vacuum to improve the adhesion between the film and the core. According to the above-mentioned magnetic elongated body, since wetting easily occurs even if the magnetic core material 32 of a ferromagnetic material having poor wettability with the solder, that is, the non-magnetic material is used, the orientation when the magnetic field is applied can be more reliably performed. Moreover, since the joint strength between the solder and the magnetic elongated body is increased, the fatigue life of the solder joint portion 8 can be further improved.

FIG. 7 shows another example of the magnetic elongated body 16.
The magnetic core material 32 is replaced with a non-magnetic inorganic material 34 such as SiC, C, or B.
Even when using, a ferromagnetic magnetic coating material 35 is formed on the surface.
And a surface layer 33 having excellent wettability with solder can be used as the magnetic elongated body 16 for magnetic field application bonding. According to the elongated magnetic body of FIG. 7, the core material can be freely selected, so that it is possible to adjust the characteristics of the joint portion by using a composite material. The use of a Cu core can improve conductivity, and the use of a C core has an effect of reducing the coefficient of thermal expansion in the arrangement direction of the magnetic elongated bodies.
Moreover, an inexpensive magnetic long body can be used, and the material cost can be reduced.

8 and 9 show an embodiment in which the magnetic field applying device is an electromagnet in the device for carrying out the magnetic field applying solder joining method. FIG. 8 is a schematic configuration diagram of the apparatus seen from the lateral direction, and FIG. 9 is a schematic configuration diagram of the apparatus seen from a cross-sectional direction along the line IX-IX in FIG. In the figure, reference numeral 36 denotes a ferromagnetic housing that supports an electromagnet composed of a coil 37 and a magnetic core 38. Cooling holes 39 are provided in the housing 36 to prevent the electromagnet from overheating, and the inside is water-cooled. A total of four electromagnets are provided on the left, right, top and bottom of the wiring board 6 (FIG. 9). The upper and lower electromagnets and the left and right electromagnets work in pairs, and when it is necessary to apply rotational magnetic field fluctuations, the electromagnets in each pair are driven in a time-divisional manner and the current directions are alternately reversed. Keep the upper and lower electromagnets in a driven state during solidification of the solder. 40, 4 in the figure
Reference numeral 1 is a power source capable of reversing the current direction, and 42 and 43 are switching circuits. According to the present embodiment, since the magnetic field strength can be adjusted by the electric current, the applied magnetic field can be set to the optimum strength without changing the device according to the size and shape of the parts to be joined. Further, since the rotation of the magnetic field can be performed only by electric operation without moving the device, the device can be downsized, and there is an advantage that it has a long life because there is no consumable part.

[0022]

According to the magnetic field applying method of the present invention, when electronic components or semiconductor components are mounted on wiring boards having different coefficients of thermal expansion, a non-magnetic material is formed by a joining process similar to the conventional solder joining process. It is possible to easily disperse the magnetic elongated bodies arranged in a certain direction in the solder joint portion made of. Therefore, it is possible to easily manufacture an electronic device in which the long magnetic body serves as a reinforcing material and the fatigue life of the solder joint is significantly improved.

[Brief description of drawings]

FIG. 1 shows a method of applying a magnetic field of the present invention, (a) to (c).
FIG. 6 is a diagram showing a process of a magnetic field application bonding method.

FIG. 2 is a configuration diagram of a magnetic field applying / bonding apparatus for carrying out the magnetic field applying method of the present invention.

3 is a sectional view taken along line III-III in FIG.

FIG. 4 is a cross-sectional view of a magnetic field applying solder joint portion of a flat package.

FIG. 5 is a sectional view of a magnetic field applying solder joint portion of an LSI chip.

FIG. 6 shows an example of a magnetic elongated body, (a) is a longitudinal sectional view,
(B) is a cross-sectional view.

7A and 7B show another example of a magnetic elongated body, in which FIG. 7A is a longitudinal sectional view and FIG. 7B is a transverse sectional view.

FIG. 8 is a configuration diagram of a different magnetic field application bonding apparatus for carrying out the magnetic field application method of the present invention.

9 is a sectional view taken along line IX-IX in FIG.

FIG. 10 is a cross-sectional view of a conventional flat package joint.

FIG. 11 is a cross-sectional view of a conventional LSI chip joint portion.

FIG. 12 is an explanatory diagram of occurrence and progress of fatigue.

FIG. 13 is an explanatory diagram of fatigue occurrence and progress.

[Explanation of symbols]

 13 Member to be bonded 14 Member to be bonded 15 Non-magnetic material 16 Long magnetic body 32 Magnetic core material 33 Surface layer 34 Non-magnetic inorganic material 35 Magnetic coating material

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Asahiko Shida 4026 Kuji Town, Hitachi City, Hitachi, Ibaraki Pref., Hitachi Research Laboratory Ltd. Hitachi Research Laboratory

Claims (5)

[Claims] 1. A bonding material comprising a non-magnetic material and a magnetic elongated body is supplied to a gap between the non-bonded members, heated to melt the non-magnetic material, and a magnetic field is applied to form the magnetic elongated body. A magnetic field applying joining method in which the non-magnetic material is solidified by cooling after being arranged in a direction substantially orthogonal to both joining members. 2. The supply of the bonding material into the gap of the members to be bonded according to claim 1, wherein the granular non-magnetic material and the magnetic elongated body are mixed and supplied in the form of a paste with a flux. Magnetic field application bonding method. 3. The non-magnetic material according to claim 1,
A magnetic field application joining method of supplying to a joint by a plating method or a forming solder method. 4. The magnetic field application joining method according to claim 1, wherein the magnetic field application direction is varied before the magnetic elongated bodies are arranged in a direction substantially orthogonal to the joining members. 5. The magnetic field application bonding method according to claim 1, wherein the applied magnetic field strength is variable.