Disclosed is a component-mounted structure including a first object having a plurality of first electrodes, a second object as an electronic component having second electrodes, a joint portion joining the plurality of first electrodes and the corresponding second electrodes to each other, and a resin-reinforcing portion. The joint portion has a core including at least one of a first metal and a resin particle, and a layer of an intermetallic compound of the first metal and a second metal having a low melting point. The resin-reinforcing portion includes a particulate matter including the core and the intermetallic compound, in a portion except between the first and second electrodes. An amount of the particulate matter included in the portion is 0.1 to 10 vol %.

RELATED APPLICATIONS

This application is a national phase of International Application No. PCT/JP2013/003258, filed on May 22, 2013, which in turn claims the benefit of Japanese Application No. 2012-192246, filed on Aug. 31, 2012 the disclosures of which Applications are incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to a component-mounted structure including a first object and a second object as an electronic component.

BACKGROUND ART

Conventional component-mounted structures are composed of electronic components such as a semiconductor chip, and a substrate such as a printed circuit board. The electronic component and the circuit board are electrically and mechanically connected together by solder-joining their electrodes to each other. However, the purpose of solder joining is mainly to achieve electrical connection between the electrodes, and the mechanical connection strength therebetween is lower than that obtained by, for example, welding. Therefore, conventionally, an adhesive containing a thermosetting resin is supplied between the electronic component and the circuit board to form a resin-reinforcing portion, thereby to reinforce the solder joint portion.

In such a case, a paste prepared by mixing a solder powder with the adhesive (hereinafter referred to as “solder-resin mixture”) is sometimes supplied between the corresponding electrodes of the electronic component and the circuit board (see, e.g., Patent Literature 1). Thus, the solder-joining of the electrodes and the resin-reinforcing of the solder joint portion using the adhesive can be simultaneously performed. In Patent Literature 1, the melting temperature of the solder powder is set lower than the glass transition temperature of the thermosetting resin, thereby to suppress the thermal stress acting on the joint interface between the resin-reinforcing portion and the electronic component or the circuit board.

However, when a solder having a comparatively low melting point is used to join the electrode terminals as in Patent Literature 1, if a reheating process such as re-flowing is further performed after the electronic component is joined to the circuit board, the solder joint portion will easily melt again. This may reduce the connection reliability between the electronic component and the circuit board.

To avoid this, Patent Literature 2 proposes to add metal particles with high melting point, such as Cu particles, to the solder-resin mixture, to form an intermetallic compound of solder and Cu, and thereby to raise the re-melting temperature of the solder joint portion.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

However, in order to raise the re-melting temperature of the solder joint portion sufficiently by forming an intermetallic compound of solder and Cu, it is necessary to increase the contact area between the Cu particles and the solder, and in order to increase the contact area, it is necessary to include a comparatively large amount of Cu particles in the solder-resin mixture.

As illustrated inFIG. 17, in joining electrodes16A of an electronic component12A to corresponding electrodes18A of a circuit board14A by thermocompression bonding, the electronic component and the circuit board are pressed against each other at a specific pressure so as to bring the corresponding electrodes into contact with each other. Accordingly, in solder-joining by thermocompression bonding, the space for holding a molten solder49, i.e., a solder48melted, between the electrodes becomes small. Because of this, when Cu particles46are included in the solder-resin mixture, the molten solder49having overflowed the space between the electrodes may spread via the Cu particles46to the adjacent electrodes. As a result, if the distance between the adjacent electrodes is small, a short circuit may occur between those electrodes, and the connection reliability between the electronic component and the circuit board may be reduced.

In view of the above, an objective of the present invention is to provide a component-mounted structure having an electronic component connected to a circuit board in which their electrodes are joined to each other by thermocompression bonding using a solder having a comparatively low melting point, and yet in which a joint portion having a sufficiently high re-melting temperature can be formed, a short circuit between adjacent electrodes can be prevented, and the connection reliability between the electronic component and the circuit board can be improved.

Solution to Problem

A component-mounted structure of the present invention includes:

a first object having a plurality of first electrodes,

a second object as an electronic component, the second object having second electrodes respectively corresponding to the plurality of first electrodes,

a joint portion joining the first electrodes and the corresponding second electrodes to each other, and

a resin-reinforcing portion covering at least part of the joint portion.

The joint portion has a first core and a first intermetallic compound layer covering a surface of the first core. The first core includes at least one of a first metal and a resin particle, and the first intermetallic compound layer includes an intermetallic compound of the first metal and a second metal having a melting point lower than the first metal.

The resin-reinforcing portion has a first portion existing between the first electrodes and the second electrodes, and a second portion other than the first portion.

The second portion includes a particulate matter having a second core and a second intermetallic compound layer. The second core includes at least one of the first metal and the resin particle, and the second intermetallic compound layer includes the intermetallic compound of the first metal and the second metal.

An amount of the particulate matter included in the second portion is 0.1 to 10 vol %.

Advantageous Effects of Invention

According to the present invention, even when a component-mounted structure is produced by joining the electrodes of an electronic component and the electrodes of a circuit board to each other by thermocompression bonding using a solder having a comparatively low melting point, a joint portion having a sufficiently high re-melting temperature can be formed, and a short circuit between adjacent electrodes can be prevented, whereby the connection reliability between the electronic component and the circuit board can be improved.

DESCRIPTION OF EMBODIMENTS

The present invention relates to a component-mounted structure including: a first object having a plurality of first electrodes; a second object as an electronic component, the second object having second electrodes respectively corresponding to the plurality of first electrodes; a joint portion joining the first electrodes and the corresponding second electrodes to each other; and a resin-reinforcing portion covering at least part of the joint portion.

The joint portion has a first core and a first intermetallic compound layer covering a surface of the first core. The first core includes at least one of a first metal and a resin particle, and the first intermetallic compound layer includes an intermetallic compound of the first metal and a second metal having a melting point lower than the first metal. The resin-reinforcing portion has a first portion existing between the first electrodes and the second electrodes, and a second portion other than the first portion. The second portion includes a particulate matter having a second core and a second intermetallic compound layer. The second core includes at least one of the first metal and the resin particle, and the second intermetallic compound layer includes the intermetallic compound of the first metal and the second metal. An amount of the particulate matter included in the second portion is 0.1 to 10 vol %. More preferably, the amount is 0.1 to 5 vol %. The electronic component includes, for example, an IC chip (bare chip), a package, an electronic component module, a chip component, and other various electronic components.

The component-mounted structure configured as above can be produced by a component-mounting method as below.

For example, the method includes the steps of: (a) preparing a first object having a plurality of electrodes; (b) preparing a second object as an electronic component, the second object having second electrodes respectively corresponding to the plurality of first electrodes; (c) supplying a solder-resin mixture including a particulate matter precursor and a thermosetting resin onto the first electrodes, the particulate matter precursor having a core (third core) and a solder layer (third solder layer) covering a surface of the core, the core including a first metal or including a first metal and a resin particle, the solder layer including a second metal having a melting point lower than the first metal, the first metal being in contact with the solder layer, the first metal and the second metal being configured to form an intermetallic compound; (d) placing the second object onto the first object so that the plurality of second electrodes land on the corresponding first electrodes with the solder-resin mixture therebetween; (e) joining the plurality of second electrodes to the corresponding first electrodes by thermocompression bonding, to form a joint portion including the first metal and the second metal; and (f) heating the joint portion, thereby to accelerate the formation of the intermetallic compound through inter-diffusion of the first metal and the second metal in the joint portion, as well as to cure the thermosetting resin.

Here, the solder-resin mixture may be in the form of paste or film or in a semi-cured state (B stage). A first intermetallic compound layer and a second intermetallic compound layer are formed through heating for thermocompression bonding of the first and second electrodes and heating for accelerating the formation of the intermetallic compound in the joint portion. By allowing the solder-resin mixture to contain the particulate matter precursor in an amount of 0.1 to 10 vol %, the amount of the particulate matter included in the second portion of the resin-reinforcing portion can be 0.1 to 10 vol %. This is because the volume of the solder-resin mixture remains almost unchanged before and after joining of the first object and the second object.

The component-mounted structure configured as above can be produced by a component-mounting system as below.

An example of the system includes: a holding unit for holding a first object having a plurality of first electrodes; a mixture supply unit for supplying a solder-resin mixture including a particulate matter precursor and a thermosetting resin onto the first electrodes, the particulate matter precursor having a core (third core) and a solder layer (third solder layer) covering a surface of the core, the core including a first metal or including a first metal and a resin particle, the solder layer including a second metal having a melting point lower than the first metal, the first metal being in contact with the solder layer, the first metal and the second metal being configured to form an intermetallic compound; and a placement unit configured to hold a second object as an electronic component, the second object having a plurality of second electrodes respectively corresponding to the plurality of first electrodes, and place the second object on the first object so that the plurality of second electrodes land on the corresponding first electrodes with the solder-resin mixture therebetween. The placement unit presses the second object against the first object and heats the second object, thereby to join the second electrodes to the corresponding first electrodes by thermocompression bonding, to form a joint portion including the first metal and the second metal; and further heats the joint portion, thereby to accelerate the formation of the intermetallic compound through inter-diffusion of the first metal and the second metal in the joint portion, as well as to cure the thermosetting resin.

Another example of the system includes: a holding unit for holding a first object having a plurality of first electrodes; a mixture supply unit for supplying a solder-resin mixture including a particulate matter precursor and a thermosetting resin onto the first electrodes, the particulate matter precursor having a core (third core) and a solder layer (third solder layer) covering a surface of the core, the core including a first metal or including a first metal and a resin particle, the solder layer including a second metal having a melting point lower than the first metal, the first metal being in contact with the solder layer, the first metal and the second metal being configured to form an intermetallic compound; a placement unit configured to hold a second object as an electronic component, the second object having a plurality of second electrodes respectively corresponding to the plurality of first electrodes, place the second object on the first object so that the plurality of second electrodes land on the corresponding first electrodes with the solder-resin mixture therebetween, and press the second object against the first object and heat the second object, thereby to join the second electrodes to the corresponding first electrodes by thermocompression bonding, to form a joint portion including the first metal and the second metal; and a post-heating unit configured to enclose or hold the second object placed on the first object and further heat the joint portion, thereby to accelerate the formation of the intermetallic compound through inter-diffusion of the first metal and the second metal in the joint portion, as well as to cure the thermosetting resin.

In the component-mounting method and system as above, the particulate matter precursor contained in the solder-resin mixture includes: a core (third core) including a first metal; and a solder layer (third solder layer) including a second metal (solder or a solder alloy) and covering the surface of the core while being in contact with the first metal (seeFIGS. 4 and 11B). As a result, for example, by distributing the first metal at the surface of the core, the contact area between the first metal and the second metal can be increased, and a larger amount of intermetallic compound of the first metal having a comparatively high melting point and the second metal can be formed at the joint portion. In that way, the re-melting temperature of the joint portion can be easily raised to be higher than the melting point of the original second metal, and the connection reliability between the electronic component and the substrate can be improved.

As a result of the foregoing, as compared with when, for example, the particles (46) of the first metal are simply included in the solder-resin mixture as inFIG. 17, a sufficient amount of intermetallic compound can be formed, which can reduce the amount of the first metal particles required for raising the re-melting temperature of the joint portion to a desired temperature. Therefore, it is unlikely to happen that the molten solder (49) having overflowed the space between the corresponding electrodes spreads to the adjacent electrodes via the first metal particles (46) existing in a large amount. Thus a short circuit between adjacent electrodes can be prevented, and the connection reliability between the electronic component and the substrate can be improved.

Furthermore, the solder is included in the solder layer present on the surface of the particulate matter precursor. Therefore, the amount of solder supplied can be easily reduced to a necessary and sufficient level. Due to the inclusion of the first metal having a comparatively high melting point in the core of the particulate matter precursor, the core of the particulate matter precursor sandwiched between the corresponding electrodes may keep its original shape while those electrodes undergo thermocompression. As a result, the corresponding electrodes are joined to each other by thermocompression bonding with a certain gap ensured therebetween, and the amount of solder to overflow the space between the corresponding electrodes can be reduced. Therefore, a short circuit between adjacent electrodes can be effectively prevented.

The amount of the particulate matter included in the second portion of the resin-reinforcing portion is 0.1 to 10 vol %. By setting the lower limit of the amount to 0.1 vol %, the lower limit of the amount of the particulate matter included in the solder-resin mixture is also set to 0.1 vol %. This can suppress the occurrence of conductive failure. On the other hand, by setting the upper limit of the amount of the particulate matter precursor to 10 vol %, a short circuit between adjacent electrodes can be effectively prevented.

As described above, in the component-mounted structure of the present invention, since the joint portion includes a layer of intermetallic compound whose re-melting temperature is higher than the melting point of the original second metal, i.e., solder, the joint portion is unlikely to be broken when the component-mounted structure is further heated, and the connection reliability between the electronic component and the substrate can be improved. Moreover, since the amount of the particulate matter is set within the rage of 0.1 to 10 vol %, a conductive failure and a short circuit between adjacent electrodes can be prevented, and the connection reliability between the electronic component and the substrate can be improved.

As clear from the above, in the present invention, the core (second core) of the particulate matter has three embodiments: first, an embodiment mainly including the first metal only; secondly, including both the resin particle and the first metal; and thirdly, including the resin particle only. The core of the particulate matter of the first embodiment is formed typically when the core of the particulate matter precursor mainly includes the first metal only. The core of the particulate matter of the second and third embodiments is formed typically when the core of the particulate matter precursor includes the resin particle and a layer of the first metal covering the surface thereof. As for the core of the particulate matter of the third embodiment, all the first metal included in the core of the particulate matter precursor has been converted into an intermetallic compound, and no first metal remains in the core.

In other words, the joint portion may include a first solder layer including the second metal and covering a surface of the first intermetallic compound layer. The particulate matter may include a second solder layer including the second metal and covering a surface of the second intermetallic compound layer. The first metal may be present between the resin particle and the first solder layer. The first metal may be present between the resin particle and the second solder layer.

By including a resin particle in the core (third core) of the particulate matter precursor, the core becomes resistant to crushing when the corresponding electrodes are joined to each other by thermocompression bonding. This makes it easy to ensure a desired gap between the corresponding electrodes, and thus to ensure, for example, a signal transmission line length as designed. Furthermore, the cost can be lowered by using an inexpensive material for the resin particle. Preferably, the core of the particulate matter precursor includes a resin particle at its center, and the surface of the resin particle is entirely covered with a layer of the first metal. This can maximize the contact area between the first metal and the solder layer even though the amount of the first metal is reduced. Therefore, the re-melting temperature of the joint portion can be sufficiently raised. In the core of the particulate matter precursor, the entire surface of the resin particle may not be necessarily covered with the first metal layer, and a part of the surface of the resin particle may be directly in contact with the solder layer.

The particulate matter and the particulate matter precursor preferably have an average particle size (particle diameter at 50% cumulative volume in volumetric particle size distribution, the same is applied hereinafter) of 2 to 100 μm. The solder layer (third solder layer) of the particulate matter precursor preferably has a thickness of 0.1 to 10 μm. When the average particle size of the particulate matter precursor and the thickness of the solder layer are within the range above, almost all the solder included in the joint portion can be easily converted into an intermetallic compound because the thickness of the solder layer is comparatively thin. As a result, the re-melting temperature of the joint portion can be easily raised sufficiently. Furthermore, by setting as above, a certain gap can be easily ensured between the corresponding electrodes, and the amount of supplied solder can be reduced. Therefore, a short circuit between adjacent electrodes can be more effectively prevented.

The first metal preferably includes Cu. More specifically, the first metal may be a Cu alloy, and preferably has a melting point of 1000° C. or more. The second metal is an alloy which forms a solder, and preferably includes at least one selected from the group consisting of Sn, Pb, Ag, Zn, Bi, In, Cu, and Sb. The second metal preferably has a melting point of 110 to 240° C. A preferable heating temperature in thermocompression bonding is 60 to 250° C. A more preferable heating temperature in thermocompression bonding is 120 to 250° C.

In another embodiment of the present invention, the resin-reinforcing portion further includes an inorganic filler, such as silica (SiO2) and alumina, which is smaller in average particle size than the particulate matter. By including an inorganic filler in, for example, the solder-resin mixture, a resin-reinforcing portion including the inorganic filler can be formed. This can lower the coefficient of thermal expansion of the resin-reinforcing portion, while increasing the modulus of elasticity thereof. Therefore, the deterioration of the resin-reinforcing portion such as cracks can be suppressed even though the component-mounted structure undergoes a heat cycle in which the component-mounted structure is heated and then cooled, or even though an impact due to the drop of the electronic component is applied to the resin-reinforcing portion. As a result, the resistance against heat cycle and the impact resistance of the joint portion can be improved. Moreover, the moisture absorptivity of the resin-reinforcing portion can be lowered, and thus the corrosion of the electrodes and wires can be prevented.

In the component-mounted structure of the present invention, the first object and the second object may both include a flexible substrate; the second object may include a flexible substrate, and the first object may include a rigid substrate; the second object may include a semiconductor chip, and the first object may include a flexible substrate or a rigid substrate; and the first object and the second object may both include a semiconductor chip.

FIG. 1is a block diagram of a surface mount line, an example of a component-mounting system, for producing a component-mounted structure according to one embodiment of the present invention.FIG. 2is a cross-sectional view of a component-mounted structure according to one embodiment of the present invention.

A line10ofFIG. 1is a system for mounting an electronic component (second object) onto a substrate (example of first object), such as a circuit board of an electronic device. The substrate may be a rigid substrate or a flexible substrate. Whichever the substrate is, the substrate can be transported independently one by one, or in an integrated form of a plurality of substrates, from one unit to another on the line10. For example, when the substrate is a flexible substrate, the substrate can be transported independently one by one, for example, on a carrier board, or in the form of a tape-shaped material including a plurality of substrates, from one unit to another on the line10. A tape-shaped material including a plurality of substrates can be transported from one unit to another on the line10by using, for example, a sprocket.

The electronic component may be a semiconductor chip (bare chip), or a package or module in which a component such as a semiconductor chip is mounted on a flexible or rigid substrate. The electronic component may be a chip component such as a passive element.

The line10illustrated in the figure is a surface mount line for mounting an electronic component12, which is a module including a flexible substrate with a component such as a semiconductor chip mounted thereon, onto a rigid or flexible substrate14corresponding to a printed circuit board of an electronic device. More specifically, the line10includes a substrate supply unit1, a mixture supply unit2, a thermocompression-bonding and heating unit3including an electronic component feeder6, and a structure collecting unit4.

The substrate supply unit1supplies the substrate14onto the line. The mixture supply unit2supplies a solder-resin mixture onto land electrodes18serving as electrodes of the substrate14. The thermocompression-bonding and heating unit3forms a joint portion17so as to join a plurality of component electrodes16of the electronic component12fed by the electronic component feeder6to the corresponding plurality of land electrodes18of the substrate14by thermocompression bonding (thermocompression bonding process). In addition, the thermocompression-bonding and heating unit3heats the joint portion17for the purpose of accelerating the rise in the re-melting temperature of the joint portion17(melting point shift acceleration process). Concurrently therewith, the thermocompression-bonding and heating unit3heats the solder-resin mixture, thereby to form a resin-reinforcing portion29so as to reinforce the joint portion17(resin curing process). The structure collecting unit4collects a component-mounted structure in which the electronic component12has been mounted on the substrate14.

In a practical machine, the mixture supply unit2and the thermocompression-bonding and heating unit3can be integrated into one as a device bonder (die bonder or flip-chip bonder)5. The line10further includes a conveyor8for transporting the substrate14from one unit to another.

The line10can be a surface mount line employing a carrier transport system in which the substrate14is loaded on a carrier board, and the carrier board is transported from one unit to another by the conveyor8. The substrate14can be fixed onto the carrier board with a heat-resistant tape. Alternatively, the substrate14can be fixed by applying a low-stickiness type adhesive material onto a surface of the carrier board to face the substrate14. In the latter case, the backside of the substrate14is entirely fixed onto the carrier board. Therefore, even when the substrate14is a flexible substrate, variations in height of the substrate14due to waving or the like can be reduced. When being a rigid substrate, the substrate14can be directly loaded on the conveyor8without using a carrier board.

The substrate supply unit1can be, for example, a magazine-type substrate loader. The structure collecting unit4can be, for example, a magazine-type substrate unloader. When using a tape-shaped material including the plurality of substrates14, the substrate supply unit1can include a supply roll, and the structure collecting unit4can include a take-up roll.

When the solder-resin mixture is in the form of paste, the mixture supply unit2can include an application head (not shown) for supplying the solder-resin mixture by applying it onto the land electrodes18of the substrate14through a nozzle or the like, a dispenser (not shown) for providing the solder-resin mixture to the application head, a substrate recognition camera (not shown), and a controller (not shown). The controller controls the motion and operation of the application head, and the operation of the dispenser. The controller can include an image processor for processing images taken by the substrate recognition camera. Alternatively, the mixture supply unit2can include, in place of the application head, a printing machine such as a screen printer and an ink jet applicator. The solder-resin mixture can be supplied onto the land electrodes18of the substrate14by using these printing machines.

When the solder-resin mixture is in the form of film, the solder-resin mixture can be supplied onto the land electrodes18of the substrate14by picking up the solder-resin mixture from a separator (release paper) with a suction nozzle or the like, or transferring the solder-resin mixture from the separator onto a mounting region AR1on the substrate (seeFIG. 5) by thermocompression. When the solder-resin mixture is in the B stage described hereinlater, the solder-resin mixture dissolved in a solvent can be printed or applied onto the mounting region AR1in advance, and then heating, whereby the solder-resin mixture can be supplied onto the land electrodes18of the substrate14.

The electronic component feeder6can include various feeders such as a tape feeder, a bulk feeder, and a tray feeder. When the electronic component12is a module or a land grid array (LGA) package, a tray feeder can be used to feed the electronic component12. When the electronic component is a chip component, a tape feeder or a bulk feeder can be used.

As illustrated inFIG. 3, the thermocompression-bonding and heating unit3can include: a thermocompression head20for holding the electronic component12by, for example, suction; a press base24on which the substrate14is placed; a component recognition camera (not shown) for recognizing component electrodes16, and a controller (not shown) for controlling the motion and operation of the thermocompression head20. The thermocompression head20can include a heater22for heating the component electrodes16. The press base24also can include a heater27for heating the land electrodes18.

A description is given below of the solder-resin mixture, with reference toFIG. 3. As illustrated inFIG. 3, a solder-resin mixture26is prepared by mixing a particulate matter precursor30containing solder and an adhesive28containing a thermosetting resin together in a predetermined ratio, and dispersing them. The solder-resin mixture26may be in the form of paste or film. The solder-resin mixture26may be in the B stage. The B stage refers to an intermediate stage in the course of reaction of a thermosetting resin.

The adhesive28can be prepared by adding a curing agent, a thixotropic agent, a pigment, a coupling agent, and an activator to the thermosetting resin. The glass transition temperature of a cured product of the thermosetting resin is not particularly limited, but is preferably higher than the melting temperature of the solder contained in the particulate matter precursor30(e.g., 120 to 160° C.). The activator can be a material having an activation effect of removing oxides and other substances from the electrode surface and the bump surface in solder joining. Examples of such a material include organic acids and halogenated compounds.

Examples of the thermosetting resin to be contained in the adhesive28include, but not limited to, various resins such as epoxy resin, urethane resin, acrylic resin, polyimide resin, polyamide resin, bismaleimide, phenolic resin, polyester resin, silicone resin, and oxetane resin. One of them may be used alone, or two or more of them may be used in combination. Particularly preferred among them is epoxy resin because it is excellent in heat resistance and other properties.

The epoxy resin can be selected from the group consisting of bisphenol-type epoxy resins, multifunctional epoxy resins, flexible epoxy resins, brominated epoxy resins, glycidyl ester-type epoxy resins, and polymer-type epoxy resins. For example, bisphenol A-type epoxy resin, bisphenol F-type epoxy resin, bisphenol S-type epoxy resin, biphenyl-type epoxy resin, naphthalene-type epoxy resin, phenol novolac-type epoxy resin, and cresol novolac-type epoxy resin can be preferably used. The epoxy resin may be a modified product thereof. These may be used alone or in combination of two or more.

The curing agent to be used in combination with the thermosetting resin may be a compound selected from the group consisting of thiol compounds, modified amine compounds, multifunctional phenolic compounds, imidazole compounds, and acid anhydride compounds. These may be used alone or in combination of two or more.

Examples of the solder (second metal) to be contained in the particulate matter precursor30include, but not limited to, Sn—Bi alloy, Sn—Ag—Cu alloy, Sn—Bi—Ag alloy, Sn—Cu alloy, Sn—Sb alloy, Sn—Ag alloy, Sn—Ag—Cu—Bi alloy, Sn—Ag—Bi—In alloy, Sn—Ag—Cu—Sb alloy, Sn—Zn alloy, and Sn—Zn—Bi alloy. Examples other than the above Sn-containing solders include gold solders. In any case, the solder to be contained in the particulate matter precursor30preferably has a melting point of 110 to 240° C.

FIG. 4illustrates a cross section of an example of the particulate matter precursor. The particulate matter precursor30illustrated in the figure has a spherical core32formed of a first metal (e.g., Cu or a Cu alloy) having a comparatively high melting temperature (e.g., 1000° C. or more), and a solder layer34containing a second metal (solder or a solder alloy) and covering the surface of the core32.

A description is given below of a production method of a component-mounted structure ofFIG. 2.

First, as illustrated inFIG. 5, the solder-resin mixture26is supplied by the mixture supply unit2onto the substrate14supplied by the substrate supply unit1, at the mounting region AR1where the electronic component12is to be mounted. The mounting region AR1includes all the land electrodes18to be joined with the component electrodes16of the electronic component12.

Next, as illustrated inFIG. 3, in the thermocompression-bonding and heating unit3, the electronic component12fed by the electronic component feeder6is held by the thermocompression head20. The thermocompression head20can be provided with a plurality of suction nozzles or holes for component suction, at the area to come in contact with the electronic component12.

Then, as illustrated inFIG. 6, positioning is performed, with reference to the images taken by the component recognition camera, such that the component electrodes16of the electronic component12respectively land on the corresponding land electrodes18. Thereafter, the electronic component12is pressed against the substrate14at a predetermined pressure by the thermocompression head20, while heated to a predetermined temperature (60° C.≦Ta≦250° C.) by the heater22provided in the thermocompression head20.

In that way, as illustrated inFIG. 7, the particulate matter precursor30becomes sandwiched between each of the component electrodes16and the corresponding land electrode18. In the figure, the particulate matter precursor30is sandwiched one by one between a pair of the component electrode16and the land electrode18. This is not a limitation, and two or more particulate matter precursors30can be sandwiched between a pair of the component electrode16and the land electrode18.

Next, the state illustrated inFIG. 7is held for a predetermined period of time Ma (e.g., 5 seconds), so that the second metal (solder) contained in the solder layer34melts into a molten solder36, as illustrated inFIG. 8. Due to the oxide film removal effect of the activator contained in the adhesive28, the molten solder36spreads over the surfaces of the component electrode16and the land electrode18, and becomes elliptic in shape.

Subsequently, in the state illustrated inFIG. 8, heating is continued at a predetermined temperature Tb (300° C.≧Tb≧100° C.) for a predetermined period of time Mb (600 sec≧Mb≧1 sec) in the thermocompression-bonding and heating unit3. As a result, the first metal (Cu) contained in the core32diffuses into the molten solder36, forming an intermetallic compound layer38containing a solid-phase intermetallic compound having a melting point higher than that of the original solder, around the core32, as illustrated inFIG. 9(melting point shift acceleration process).

Concurrently therewith, the thermosetting resin contained in the adhesive28is cured by heating, forming the resin-reinforcing portion29. When the component electrode16and the land electrode18contain Cu or a Cu alloy, the Cu contained in those electrodes also diffuses into the molten solder36. Consequently, as illustrated inFIG. 9, the intermetallic compound layer38becomes thicker at portions near the component electrode16and the land electrode18than at portions away from them.

Subsequent cooling allows the molten solder36to cure into a solid solder40as illustrated in10A, completing the joint portion17. In the case where all the molten solder36is formed into an intermetallic compound with Cu, flash of solder from the joint portion17can be more effectively suppressed when the component-mounted structure is re-heated. In this case, only the intermetallic compound layer38is present around the core32, and the layer of the solid solder40is not present.

As illustrated inFIG. 10B, in a portion (second portion29a) not sandwiched between the corresponding electrodes of the resin-reinforcing portion29, a particulate matter31including the intermetallic compound layer38is formed by heating the particulate matter precursor30. On the other hand, in a first portion29bbetween the corresponding electrodes of the resin-reinforcing portion29, the joint portion17is formed. The particulate matter31includes the core32containing the first metal, the intermetallic compound layer38of the first and second metals, and the solder layer composed of the solid solder40. Note that, in the particulate matter31also, all the molten solder36may be formed into an intermetallic compound, with no solid solder40left therein.

As described above, in Embodiment 1, the solder-resin mixture26includes the adhesive28and the particulate matter precursor30having the spherical core32, most of which is composed of Cu, and the solder layer34provided on the surface of the core. The solder-resin mixture26is supplied onto the land electrodes18of the substrate14, and the component electrodes16are joined to the land electrodes18by thermocompression bonding. As a result, the contact area between the solder and the Cu is increased, which facilitates the formation of an intermetallic compound of solder and Cu. Therefore, even though the Cu content in the solder-resin mixture26is reduced, a sufficient amount of intermetallic compound can be formed, and the re-melting temperature of the joint portion17can be easily increased to a desired temperature. This enables to prevent the molten solder from spreading to the adjacent electrodes via the Cu particles contained in a large amount in the solder-resin mixture26, and thus to prevent a short circuit between the electrodes.

When the solid solder40exists as illustrated inFIGS. 10A and 10B, the joint portion17becomes multilayered, in which stress applied from outside, such as impact due to drop, tends to disperse among the layers. As a result, the joint portion17becomes hard to break. Moreover, stress applied from outside tends to disperse only within the solid solder40as the outermost layer, and even if the layer cracks, the crack is confined within the solid solder40and unlikely to reach as far as the intermetallic compound layer38. Therefore, the electrical and mechanical connection of the joint portion17can be easily ensured. On the other hand, when no solid solder40exists in the joint portion17, the joint portion17includes only the first metal core32and the intermetallic compound layer38. As a result, the re-melting temperature of the joint portion17as a whole can be raised.

In contrast, as illustrated inFIG. 18, in a conventional solder joint portion72composed of solder alone, for example, when one point of the solder joint portion72is broken due to stress applied from outside, cracks spread from the point throughout the homogeneous solder joint portion72as shown by the arrows in the figure, fracturing the solder joint portion72. In contrast, in the component-mounted structure of Embodiment 1, an excellent impact resistance can be obtained, and excellent connection reliability can be ensured. In addition, by including the particulate matter precursor30in the solder-resin mixture26in a specific amount within the range of 0.1 to 10 vol %, a short circuit between adjacent electrodes can be prevented.

Next, Embodiment 2 of the present invention is described.

FIG. 11Ais a partial cross-sectional view of a component-mounted structure according to the present embodiment.FIG. 11Bis a cross-sectional view of a particulate matter precursor used in producing the component-mounted structure according to the present embodiment

A particulate matter precursor30A illustrated in the figure is similar to the particulate matter precursor30of Embodiment 1 in that the precursor30A has a core32A and a solder layer34A covering the surface of the core32A. In the particulate matter precursor30A, the core32A includes a spherical resin particle42and a metal layer44covering the surface of the resin particle42. The material of the resin particle42is not particularly limited, but is preferably a highly heat resistant resin having high elastic modulus (e.g., divinylbenzene cross-linked polymer, a cured product of various thermosetting resins, cross-linked polyester). The metal layer44can contain the first metal similar to that of Embodiment 1 (Cu or a Cu alloy having a melting point of 1000° C. or more). The adhesive contained in the solder-resin mixture of Embodiment 2 may be the adhesive28of Embodiment 1. The amount of the particulate matter precursor30A may be set similarly to that in Embodiment 1.

The particulate matter precursor30A, like the particulate matter precursor30, preferably has a diameter of 2 to 100 μm. The solder layer34A, like the solder layer34, preferably has a thickness of 0.1 to 10 μm. The composition of the solder layer34A may be similar to that of the solder layer34. The diameter of the resin particle42may be 1 to 90 μm. The average thickness of the metal layer44may be 0.1 to 5 μm. The component mounting method and system using the solder-resin mixture including the particulate matter precursor30A for mounting the electronic component12onto the substrate14are similar to those in Embodiment 1.

In the component-mounted structure produced by using the particulate matter precursor30A, the resin-reinforcing portion29has the first portion29bin which a joint portion17A is formed between the corresponding electrodes. The joint portion17A includes the metal layer44covering the surface of the spherical resin particle42, an intermetallic compound layer38A covering the surface of the metal layer44, and a solid solder40A on the outside thereof. The thickness of the metal layer44is smaller than that of the original metal layer44in the particulate matter precursor30A. There is a case where all the first metal contained in the metal layer44in the particulate matter precursor30A has been converted into an intermetallic compound, and the joint portion17A does not include the metal layer44. In this case, the resin particle42is in direct contact with the intermetallic compound layer38A. There is another case where all the second metal contained in the solder layer34A in the particulate matter precursor30A has been converted into an intermetallic compound, and the joint portion17A does not include the solid solder40A.

In the second portion of the resin-reinforcing portion29, a particulate matter31A is formed by heating the particulate matter precursor30A. The particulate matter31A includes the resin particle42, the metal layer44containing the first metal, the intermetallic compound layer38A of the first and second metals, and a solder layer composed of the solid solder40A. There is a case where the first metal has been sufficiently diffused into the molten solder, and the metal layer44has disappeared from the particulate matter31A. Likewise, there is a case where all the second metal contained in the solder layer34A in the particulate matter precursor30A has converted into an intermetallic compound, and the particulate matter31A has no solid solder40A.

As described above, by including the resin particle42in the core32A, the first metal can be used in a smaller amount, and the cost can be easily reduced. Moreover, by composing the resin particle42of a material which is stiff to some extent, the resin particle42sandwiched between the corresponding electrodes is unlikely to be crushed when joining the electrodes to each other by thermocompression bonding. In that way, the gap between the corresponding electrodes can be easily kept as desired, and the electronic component12can be easily connected to the substrate14with an electrical transmission line length set as designed.

Next, Embodiment 3 of the present invention is described.

FIG. 12is an enlarged view of an essential part of a component-mounted structure of the present embodiment. In the component-mounted structure of Embodiment 3, the resin-reinforcing portion29includes an inorganic filler such as silica (SiO2) and alumina. The component-mounted structure of the present embodiment can be produced by using a solder-resin mixture including such an inorganic filler. Except the above, the component-mounted structure of the present embodiment can be produced by the same component mounting method and system as those in Embodiments 1 and 2.

By producing as above, the resin-reinforcing portion29can include an inorganic filler45such as silica (SiO2) and alumina as illustrated inFIG. 12. As a result, the coefficient of thermal expansion of the resin-reinforcing portion29can be lowered, while the modulus of elasticity thereof can be increased. In that way, the deterioration of the resin-reinforcing portion29such as cracks can be suppressed, even though the component-mounted structure is subjected to a heat cycle in which the component-mounted structure is heated and then cooled. Furthermore, the impact resistance of the resin-reinforcing portion29can be improved. Moreover, the moisture absorptivity of the resin-reinforcing portion29can be lowered, and thus the corrosion of the electrodes and wires can be prevented. Here, the amount of the inorganic filler45, relative to the whole solder-resin mixture including the inorganic filler45, is preferably 10 to 50 vol %.

A diameter Dk of the inorganic filler45is set smaller than a diameter Dr of the particulate matter precursor30(Dk<Dr). For example, 2 μm≧Dk≧0.1 μm. Note that if a simple solder particle48is used in place of the particulate matter precursor30or30A as shown inFIG. 13, the solder particle48, due to the absence of the core therein, will collapse boundlessly when it melts. As a result, the inorganic filler45becomes sandwiched between the component electrode16and the land electrode18, and the electrodes may fail to be wetted with the molten solder49. This is detrimental to the connection reliability. According to the component mounting method of Embodiment 3, by setting the diameter Dk of the inorganic filler45to be smaller than the diameter Dr of the particulate matter precursor30, and using a particulate matter precursor including the core32or core32A, the inorganic filler45is prevented from becoming sandwiched between the component electrode16and the land electrode18. Therefore, the above-mentioned inconvenience can be prevented.

FIG. 14is a block diagram of a surface mount line which is another example of a component-mounting system for producing a component-mounted structure of the present invention. A line10A illustrated in the figure, like the line10of Embodiment 1, is a surface mount line for mounting the electronic component12, which is a module including a flexible substrate with a component such as a semiconductor chip mounted thereon, onto the rigid or flexible substrate14corresponding to a printed circuit board of an electronic device. The line10A is similar to the line10of Embodiment 1 in that the line10A includes the substrate supply unit1for supplying the substrate14on the line, the mixture supply unit2for supplying a solder-resin mixture onto the land electrodes18serving as the electrodes of the substrate14, and the structure collecting unit4.

The line10A differs from the line10in that the line10A includes a thermocompression bonding unit3A in place of the thermocompression-bonding and heating unit3, and further includes a post-heating unit3B disposed between the thermocompression bonding unit3A and the structure collecting unit4. In the following, a description will be given with focusing on the difference.

The thermocompression bonding unit3A performs only the thermocompression bonding process as illustrated inFIGS. 7 and 8, and does not perform the melting point-shift acceleration process as illustrated inFIG. 9. Heating for the melting point-shift acceleration process is carried out in the post-heating unit3B.

FIGS. 15 and 16illustrate examples of the post-heating unit. In the example ofFIG. 15, the post-heating unit3B has an oven50. The oven50includes a container52for containing the electronic component12and the substrate14having been subjected to thermal compression bonding and joined to each other (hereinafter referred to as “structure precursor”, or simply as “precursor”). The oven50further includes a heater54for heating the joint portion of a precursor53placed in the container52, so as to facilitate inter-diffusion between the first metal included in the core32or core32A and the molten solder36. The container52is preferably capable of containing a plurality of the precursors53so that a plurality of the precursors53can be simultaneously subjected to the melting point-shift acceleration process. Therefore, when the melting point-shift acceleration process takes a longer time to complete than the thermocompression process, this will not cause the line tact time to be prolonged. Thus the production efficiency can be improved. The temperature and time of heating the joint portion17in the oven50are similar to those in Embodiments 1 to 3.

As described above, by installing the post-heating unit3B independently from the thermocompression bonding unit3A, the melting point-shift acceleration process can be performed in the post-heating unit3B, while the thermocompression bonding process is performed in the thermocompression bonding unit3A. This can shorten the line tact time, and improve the production efficiency.

In the example ofFIG. 16, the post-heating unit3B includes a press machine56. The press machine56includes a press plate58and a press base60. At least one of the press plate58and the press base60can include a heater62or64. To simultaneously subject a plurality of the precursors53to the melting point-shift acceleration process, the shape and area of the press base60are preferably such that a plurality of the precursors53can be placed thereon. Likewise, the shape and area of the press plate58are preferably such that a plurality of the electronic components12can be simultaneously pressed against the substrate14. Therefore, when the melting point-shift acceleration process takes a longer time to complete than the thermocompression process, this will not cause the line tact time to be prolonged. Thus the production efficiency can be improved.

INDUSTRIAL APPLICABILITY

According to the present invention, when a plurality of first electrodes of a first object and a plurality of second electrodes of a second object are solder-joined to each other by thermocompression bonding, and the joint portion is reinforced with resin, it is possible to sufficiently raise the re-melting temperature of the joint portion, and prevent a short circuit between adjacent electrodes. Therefore, the present invention is useful for producing a portable electronic device for which miniaturization is expected.

REFERENCE SIGNS LIST