JP7697292B2 - Solder bump forming equipment - Google Patents

Description

This disclosure relates to a solder bump forming device.

In recent years, flip-chip mounting has become known as one of the techniques for high-density mounting of electronic components. In flip-chip mounting, for example, solder bumps are formed in advance on electrodes provided on one circuit component, and the electrodes of one circuit component and the electrodes of the other circuit component are joined by melting the solder bumps. This forms a connection structure between the circuit components.

One example of a technique for forming solder bumps on electrodes is the solder bump formation method described in Patent Document 1. In this conventional solder bump formation method, a positioning plate is prepared in which multiple recesses are formed corresponding to the mutual spacing of the electrodes of the substrate, and solder particles are placed in each recess of the positioning plate. Next, a transfer roll with an adhesive outer periphery is rolled on the surface of the positioning plate to transfer the solder particles to the adhesive surface of the transfer roll. The transfer roll is then rolled over the electrodes of the substrate provided with an adhesive material, to transfer the solder particles from the transfer roll to the electrodes of the substrate.

JP 2017-157626 A

In a method such as the solder bump formation method described in Patent Document 1, it is preferable that the height of the solder balls protruding from the recesses in the positioning plate be uniform in order to ensure reliable transfer of the solder particles to the electrodes. However, when using minute solder particles, such as those used to connect electrodes spaced at intervals of several μm, it is difficult to make the solder particles uniform in shape, and there is a problem in that it is difficult to ensure reliable transfer of the solder particles to the electrodes.

This disclosure has been made to solve the above problems, and aims to provide a solder bump forming device that can ensure reliable transfer of solder particles to electrodes without the need to make the solder particles uniform in shape.

A solder bump forming apparatus according to one aspect of the present disclosure is a solder bump forming apparatus that forms solder bumps on electrodes of a circuit member, and includes a stage in which an implementation area is set for forming solder bumps on the electrodes; a first supply unit that supplies a solder bump forming member having a plurality of recesses in which solder particles are held, the recesses having deformation parts that are deformable at the melting point of the solder particles; a second supply unit that supplies the circuit member so that the solder particles held in the recesses of the solder bump forming member are arranged opposite the electrode; and a heating and pressurizing unit that heats the electrode to a temperature equal to or higher than the melting point of the solder particles in the implementation area, presses the electrode against the solder bump forming member, and deforms the deformation parts to bring the solder particles held in the recesses into contact with the electrode, transferring the solder particles to the electrode to form a solder bump.

In this solder bump forming device, solder particles are held in multiple recesses of a solder bump forming member, and by applying heat and pressure together with the electrode to be transferred, solder bumps can be formed on the electrode. In the solder bump forming member supplied to this solder bump forming device, the components of the recesses have deformation parts that can deform at the melting point of the solder particles. This causes the deformation parts to deform when the electrode is pressed against it and heat is applied, making it possible to expose the solder particles held in the recesses to the electrode side. Therefore, in this solder bump forming device, the reliability of the transfer of solder particles to the electrode can be guaranteed even if the solder particles do not have the same shape.

The first supply unit may supply a solder bump forming member in which the deformation portion is configured with a bulk modulus of 0.1 GPa or more and 5 GPa or less at the melting point of the solder particles. By making the bulk modulus of the deformation portion 5 GPa or less, when the electrode is pressed against it and heat is applied, the deformation portion is sufficiently deformed, and the solder particles held in the recess can be more reliably exposed to the electrode side. On the other hand, by making the bulk modulus of the deformation portion 0.1 GPa or more, the shape retention of the recess can be maintained, and the retention performance of the solder particles during transfer can be guaranteed. This makes it possible to precisely form the solder particles at the target position on the electrode.

The heating and pressurizing unit may heat the electrode to a temperature equal to or higher than the melting point of the solder particles while the electrode is pressed against the solder bump forming member. In this case, the solder particles are melted and the deformation portion is deformed while the solder particles are sandwiched between the electrode and the solder bump forming member, so that misalignment of the solder bump formed on the electrode can be suppressed. This makes it possible to more accurately form the solder particles at the target position on the electrode.

The first supply unit may supply a solder bump forming member in which a single solder particle is disposed in each of a plurality of recesses. In this case, solder particles with a relatively large particle size can be transferred to the electrode with a certain degree of certainty.

The first supply unit may supply a solder bump forming member having multiple solder particles arranged in each of multiple recesses. In this case, it becomes easier to adjust the volume of the solder particles held in the recesses, and it becomes easier to make the size and height of the solder bump formed on the electrode consistent within a certain range. In addition, the probability of contact between the electrode and the solder particles can be increased, and the formation of the solder bump on the electrode can be more reliably carried out.

The C.V. value of the solder particles may be 20% or less. This ensures sufficient electrical continuity and insulation reliability when connecting circuit components using solder bumps.

The average particle size of the solder particles may be 1 μm to 35 μm. When using minute solder particles in this range, it is generally difficult to make the solder particles uniform in shape, but by applying the above method, it is possible to ensure reliable transfer of the solder particles to the electrodes without making the solder particles uniform in shape.

According to this disclosure, it is possible to ensure reliable transfer of solder particles to electrodes without the need to make the solder particles uniform in shape.

1 is a schematic cross-sectional view showing a configuration of a solder bump formation member according to an embodiment of the present disclosure. 1A and 1B are diagrams illustrating an example of the configuration of a solder bump forming apparatus. FIG. 2 is a schematic cross-sectional view showing an example of the configuration of a connection structure. 1 is a flowchart illustrating an example of a method for forming solder bumps. 5A to 5C are schematic cross-sectional views showing a process of forming solder bumps. 6 is a schematic cross-sectional view showing a process subsequent to that shown in FIG. 5. 7 is a schematic cross-sectional view showing a process subsequent to that shown in FIG. 6; 8 is a schematic cross-sectional view showing a process subsequent to that shown in FIG. 7; 9 is a schematic cross-sectional view showing a process subsequent to that shown in FIG. 8. 10A to 10C are schematic cross-sectional views showing modified examples of the solder bump forming member. 13A and 13B are schematic enlarged cross-sectional views of a main part showing modified examples of solder particles.

Below, a preferred embodiment of a solder bump forming device according to one aspect of the present disclosure will be described in detail with reference to the drawings.

In this specification, a numerical range indicated using "~" includes the numerical values before and after "~" as the minimum and maximum values, respectively. The upper or lower limit of a numerical range described in stages in this specification may be replaced with the upper or lower limit of a numerical range of another stage.

[Configuration of solder bump forming member]
Fig. 1 is a schematic cross-sectional view showing a configuration of a solder bump forming member according to an embodiment of the present disclosure. The solder bump forming member 1 shown in Fig. 1 is a member used, for example, when forming a solder bump on an electrode of a circuit component. As shown in Fig. 1, the solder bump forming member 1 includes a main body 2. The main body 2 has, for example, a rectangular shape in a plan view, and has a first surface 2a and a second surface 2b opposite to the first surface 2a.

The first surface 2a of the main body 2 has a plurality of recesses 3 in which solder particles S1 are held. These recesses 3 can be formed using known methods such as imprinting, photolithography, mechanical processing, and laser processing. In particular, when using the nanoimprinting method, the recesses 3 can be formed with high precision in a relatively short process by pressing a desired mold.

The size (width, volume, depth, etc.) of the recess 3 is appropriately set according to the size of the solder particle S1. The planar shape of the recess 3 is, for example, circular. The planar shape of the recess 3 may be various shapes such as circular, elliptical, triangular, rectangular, polygonal, etc. The cross-sectional shape of the recess 3 is rectangular in the example of FIG. 1. The cross-sectional shape of the recess 3 may be tapered such that the opening area expands from the bottom surface 3b side toward the opening surface side (first surface 2a side). The bottom surface 3b of the recess 3 is not limited to a flat surface, and may be, for example, a concave curved surface.

Alignment mark 4 may also be provided on the first surface 2a of main body 2. Alignment mark 4 is formed, for example, by a concave-convex shape provided on first surface 2a of main body 2, printing with ink or pigment, printing with an inorganic material by plating or sputtering, or baking with a laser. In plan view, alignment mark 4 has, for example, a circle, double circle, multiple circles, triangle, rectangle, polygon, or any of these multiple corners. Alignment mark 4 may be made of a magnetic material or a material that absorbs, reflects, or diffracts electromagnetic waves, and in this case, the shape is not particularly limited.

By detecting the alignment marks 4 with imaging devices 15A, 15B such as cameras, it becomes easier to align the electrode to be formed with the solder particles S1 in the recess 3 when forming the solder bump. This allows the solder particles S1 to be transferred to the electrode with high precision. The alignment mark 4 may be provided in one or more locations on the first surface 2a side, but providing multiple alignment marks can further improve the precision of the alignment. Furthermore, the alignment mark 4 may also be provided on the second surface 2b side of the main body 2, for example, when the main body 2 is transparent.

The main body 2 is configured with a deformation portion 6 including the first surface 2a, and a base portion 7 that constitutes the second surface 2b side of the deformation portion 6. The deformation portion 6 is a portion that constitutes at least the first surface 2a side of the recess 3. It may be provided with a thickness of 1/3 or more, 1/2 or more, or 2/3 or more of the depth D of the recess 3 in the depth direction from the first surface 2a to the recess 3. In the example of FIG. 1, the thickness T of the deformation portion 6 is equal to the depth D of the recess 3. As a result, the entire partition portion 8 that separates the adjacent recesses 3, 3 is the deformation portion 6, and the inner wall surface 3a of the recess 3 is composed of the deformation portion 6, while the bottom surface 3b of the recess 3 is composed of the base portion 7.

The width of the partition 8 (the distance between adjacent recesses 3, 3) is not particularly limited, but may be, for example, 0.1 times or more the average particle diameter of the solder particles held in the recesses 3. The width of the partition 8 may be 0.2 times or more, or may be 0.3 times or more the average particle diameter of the solder particles held in the recesses 3. The distance between the recesses 3, 3 is determined, for example, by the shortest distance between the opening edge of one recess 3 and the opening edge of the other recess 3.

The deformation portion 6 is formed by an elastic body 9 that is deformable, for example, at the melting point of the solder particles S1 held in the recess 3. Therefore, the deformation portion 6 is elastically deformable in the compression direction when the electrode to be formed is pressed against it during solder bump formation. From the viewpoint of improving the transferability of the solder particles S1, the bulk modulus of the elastic body 9 at the melting point of the solder particles S1 may be, for example, 0.1 GPa or more and 5 GPa or less. The bulk modulus of the elastic body 9 at the melting point of the solder particles S1 may be, for example, 0.5 GPa or more and 3 GPa or less, or 0.8 GPa or more and 2 GPa or less.

The elastic body 9 constituting the deformation part 6 may be, for example, a photocurable material, a thermosetting material, or a thermoplastic material. In addition, the elastic body 9 constituting the deformation part 6 may be, for example, a resin, a polymer, a rubber, an elastomer, or a mixture thereof. When the material constituting the solder particles S1 is SnBi (melting point: 139°C), the elastic body 9 constituting the deformation part 6 may be, for example, polyethylene terephthalate (bulk modulus at melting point: 0.6 GPa), acrylic (bulk modulus at melting point: 1 GPa), or PMMA (bulk modulus at melting point: 1 GPa). When the material constituting the solder particles S1 is SnAgCu (melting point: 217°C), the elastic body 9 constituting the deformation part 6 may be, for example, polyimide (bulk modulus at melting point: 1 GPa).

The base portion 7 is a portion that constitutes the second surface 2b side of the main body portion 2. The base portion 7 is formed from a material that has a higher bulk modulus than the deformation portion 6 at the melting point of the solder particles S1. Therefore, the base portion 7 contributes to the shape retention of the solder bump forming member 1 when the solder bump is formed. The bulk modulus of the base portion 7 at the melting point of the solder particles S1 is, for example, 1 GPa or more. The bulk modulus of the base portion 7 at the melting point of the solder particles S1 may be, for example, 3 GPa or more, or 5 GPa or more.

The constituent material of the base portion 7 may be, for example, inorganic materials such as silicon, various ceramics, glass, and stainless steel, and organic materials such as various resins. The constituent material of the base portion 7 may also be a material with high optical transparency. Examples of such materials include polyethylene terephthalate, transparent (colorless) polyimide, and polyamide. The constituent material of the base portion 7 may be a heat-resistant material that does not change at the melting point of the solder particles S1. The constituent material of the base portion 7 may also be a material that does not change when alloyed or reacted with the material that constitutes the solder particles S1.

As the constituent material of the base portion 7, for example, polyethylene terephthalate, polyethylene naphthalate, vinyl chloride resin, polystyrene, polyethylene polyphenylene sulfide, polycarbonate, etc. can be used as long as it is in the form of a flexible film. In addition, from the viewpoint of improving the handleability of the base portion 7, deformation can be suppressed by increasing the thickness of the above-mentioned materials. In addition, from the viewpoint of improving the positional accuracy when transferring the solder particles S1 onto the electrodes, engineering plastics, super engineering plastics, materials in which the above-mentioned general-purpose plastics are combined with fillers or fibers, and inorganic materials can be used. For example, polyamide, polyacetal, polycarbonate, polyphenylene sulfide, polyimide, polyetherimide, polyamideimide, polysulfone, polyetheretherketone, etc. can be used.

When the material of the solder particles S1 is SnBi (melting point: 139°C), the material of the base portion 7 can be, for example, glass (bulk modulus at melting point: 40 GPa), silicon wafer (bulk modulus at melting point: 40 GPa), or stainless steel (bulk modulus at melting point: 165 GPa). When the material of the solder particles S1 is SnAgCu (melting point: 217°C), the material of the base portion 7 can be, for example, glass (bulk modulus at melting point: 40 GPa), silicon wafer (bulk modulus at melting point: 40 GPa), stainless steel (bulk modulus at melting point: 165 GPa), or aluminum (bulk modulus at melting point: 75 GPa).

As long as the base portion 7 has a higher bulk modulus than the deformation portion 6, the deformation portion 6 and the base portion 7 may be made of the same material. For example, in the case of a resin material, the bulk modulus can be adjusted by changing the degree of cross-linking, adding reinforcing materials such as fillers or fibers, or kneading with other materials. For example, the deformation portion 6 may be made of a thermosetting epoxy resin, and the base portion 7 may be made of the thermosetting epoxy resin to which glass fibers have been added to reinforce the bulk modulus.

The deformation section 6 may be made of a photocurable acrylic resin, and the base section 7 may be made of polyethylene terephthalate. In this case, uncured photocurable acrylic resin is applied to a stamper having a convex shape, and after irradiating light while pressing the polyethylene terephthalate against it, the stamper is peeled off to form recesses 3 in the photocurable acrylic resin. With this method, a main body section 2 having continuous roll-shaped recesses 3 can be obtained. In addition, the degree of crosslinking and the bulk modulus can be adjusted by adjusting the light illuminance, the curing time, and the amount of initiator of the photocurable acrylic resin.

The base portion 7 may be made of an inorganic material. For example, the deformation portion 6 may be made of a photocurable acrylic resin (volume modulus: 0.1 GPa), and the base portion 7 may be made of glass (volume modulus: 40 GPa). In this case, the volume modulus at the melting point of the base portion 7 can be sufficiently ensured, and the positional accuracy when transferring the solder particles S1 to the electrode using the alignment mark 4 can be improved. Furthermore, even if the solder particles S1 are heated above their melting point when transferring them to the electrode, the base portion 7 is unlikely to deform, so distortion and stretching of the entire main body portion 2 can be suppressed. Furthermore, it becomes possible to use the main body portion 2 repeatedly.

When the base portion 7 is made of a silicon wafer and a photosensitive material is used to form the deformation portion 6, the recess 3 can be easily formed. In this case, the photosensitive material can be, for example, an acrylic, epoxy, polyimide, or a mixture of these.

The bulk modulus K of the deformation part 6 and the base part 7 can be calculated by K = E/3 (1-2ν), where E is the Young's modulus of the material and ν is the Poisson's ratio. The bulk modulus K of the deformation part 6 and the base part 7 can be measured by, for example, mechanical testing, resonance, or ultrasonic pulse methods. For example, a nanoindenter or a surface hardness tester is used for the measurement. For example, a heating stage is attached to a surface hardness tester (manufactured by Fisher Instruments), the deformation part 6 and the base part 7 are placed on the heating stage, the stage is heated, and the deformation part 6 and the base part 7 are heated to a predetermined temperature. After that, an indenter is brought into contact with the surface of the object to be measured, and the load-displacement (Stress-Strain) curve is obtained, allowing the bulk modulus to be calculated.

In the example of FIG. 1, a single solder particle S1 is held in each of the multiple recesses 3. The solder particle S1 in the recess 3 is in contact with at least the bottom surface 3b of the recess 3. The solder particle S1 in the recess 3 may be in contact with the inner wall surface 3a of the recess 3. Also, in the example of FIG. 1, all the solder particles S1 are located in the recess 3, and the tops of the solder particles S1 do not protrude beyond the opening surface of the recess 3. In other words, when the depth of the recess 3 is D and the height of the solder particle S1 (height from the bottom surface 3b) is H, D>H is satisfied.

The ratio of the height of the solder particles S1 to the depth D of the recess 3 is not particularly limited, but may be, for example, 0.3 to 1.5, taking into consideration the amount of deformation of the deformation portion 6 in the compression direction. By making the ratio 0.3 or more, the electrode and the solder particles S1 can be more reliably contacted when the electrode is pressed against the electrode. By making the ratio 1.5 or less, the solder particles S1 can be preferably prevented from falling off the recess 3. In addition, the solder particles S1 can be prevented from protruding from the recess 3 during transfer, and the solder particles S1 can be prevented from bonding to each other between adjacent recesses 3, 3. The ratio of the height of the solder particles S1 to the depth D of the recess 3 may be 0.5 to 1.2, or may be 0.6 to 1.

The solder particles S1 are, for example, composed of tin or a tin alloy. Examples of tin alloys include In-Sn alloys, In-Sn-Ag alloys, Sn-Au alloys, Sn-Bi alloys, Sn-Bi-Ag alloys, Sn-Ag alloys, Sn-Ag alloys, Sn-Ag-Cu alloys, and Sn-Cu alloys. The solder particles S1 may include indium or an indium alloy. Examples of indium alloys include In-Bi alloys and In-Ag alloys.

The solder particles S1 may contain one or more elements selected from Ag, Cu, Ni, Bi, Zn, Pd, Pb, Au, Sb, Ge, Mn, Co, Si, Al, P, and B. From the viewpoint of obtaining good electrical conductivity reliability, the solder particles S1 may contain Ag or Cu among the above-mentioned elements. By including Ag or Cu in the solder particles S1, the melting point of the solder particles S1 can be lowered to about 220°C, and the bonding strength with the electrode can be improved.

The average particle diameter of the solder particles S1 is, for example, 35 μm or less. The average particle diameter of the solder particles S1 may be 30 μm or less, 25 μm or less, 20 μm or less, or 15 μm or less. The average particle diameter of the solder particles S1 is, for example, 1 μm or more. The average particle diameter of the solder particles S1 may be 2 μm or more, 3 μm or more, or 5 μm or more.

The average particle diameter of the solder particles S1 can be measured using various methods according to the size. Examples of the measurement methods include dynamic light scattering, laser diffraction, centrifugal sedimentation, electrical detection zone method, and resonance mass measurement method. Other measurement methods include a method of measuring the particle size based on an image obtained by an optical microscope or an electron microscope. Specific devices include a flow type particle image analyzer, a microtrack, and a Coulter counter. The average particle diameter of the solder particles S1 can be calculated based on the projected area circle equivalent diameter (the diameter of a circle having an area equal to the projected area of the particle) when the solder particles S1 are observed from a direction perpendicular to the first surface 2a of the solder bump forming member 1. When the solder particles S1 are arranged individually in each of the multiple recesses 3, the size (average particle diameter) of the solder particles S1 may be uniform.

The C.V. value of the solder particles S1 is a value calculated by dividing the standard deviation of the particle diameter measured by the above-mentioned method by the average particle diameter and multiplying the result by 100. When multiple solder particles S1 are arranged in each of multiple recesses 3, the C.V. value of the solder particles S1 may be 20% or less from the viewpoint of achieving better conductive reliability and insulating reliability. The C.V. value of the solder particles S1 may be 10% or less, or 7% or less. The lower limit of the C.V. value of the solder particles S1 is not particularly limited. For example, the C.V. value of the solder particles S1 may be 1% or more, or 2% or more.

The above describes one embodiment of the solder bump forming member, but the solder bump forming member of the present disclosure is not limited to the above embodiment.

[Solder bump forming device]
2(a) and 2(b) are schematic diagrams showing an example of the configuration of a solder bump forming apparatus. Fig. 2(a) is a side view, and Fig. 2(b) is a plan view. The solder bump forming apparatus 11 shown in the figures is an apparatus that forms a circuit member 21A with solder bumps (see Fig. 9) by transferring the solder particles S1 held in the recesses 3 of the solder bump forming member 1 described above to the electrodes 22 of the circuit member 21.

As shown in FIG. 2(a) and FIG. 2(b), the solder bump forming device 11 includes a horizontally displaceable stage 12, a first supply unit 13 for supplying the solder bump forming member 1, a second supply unit 14 for supplying the circuit member 21, imaging devices 15A and 15B, and a heating and pressing head (heating and pressing unit) 16. In this embodiment, the solder bump forming device 11 has a function of electrically connecting the circuit member 21 on which the solder bump S2 is formed to another circuit member 31 to form a connection structure 41 (see FIG. 3) as a post-process of the process of forming the solder bump S2 (see FIG. 9). The solder bump forming device 11 further includes a third supply unit 17 for supplying another circuit member 31. The operation of the solder bump forming device 11 is controlled by a control unit (not shown). The function of forming the connection structure 41 does not necessarily have to be integrated with the solder bump forming device 11, and may be configured as an independent device.

The stage 12 is provided with a placement area R1 on which the circuit member 21 supplied from the second supply unit 14 is placed, a first implementation area (implementation area) R2 in which the solder bump S2 is formed, and a second implementation area R3 in which the connection structure 41 is formed. The imaging devices 15A and 15B are parts that read the alignment marks 4 of the solder bump forming member 1 and the alignment marks (not shown) of the circuit members 21 and 31. The imaging device 15A is arranged on the front side of the stage 12 (the setting surface side of the first implementation area R2 and the second implementation area R3), and the imaging device 15B is arranged on the back side of the stage 12. The imaging device 15B may be incorporated into the stage 12. The stage 12 is displaced according to the results of reading the alignment marks by the imaging devices 15A and 15B, and performs alignment between the solder bump forming member 1 and the circuit member 21, and alignment between the circuit member 21A with solder bumps and the circuit member 31.

The heating and pressurizing head 16 is a part that applies heating and pressurizing in the first implementation area R2 and the second implementation area R3. The heating and pressurizing head 16 has an adsorption function, and performs the transfer of the circuit component 21 from the placement area R1 to the first implementation area R2, the transfer of the circuit component 21A with solder bumps from the first implementation area R2 to the second implementation area R3, and the transfer of the resulting connection structure 41. The heating and pressurizing head 16 is configured to be movable up and down relative to the stage 12, and by descending toward the stage 12, performs the heating and pressurizing when forming the solder bumps S2, and the heating and pressurizing when forming the connection structure 41.

One embodiment of the solder bump forming device has been described above, but the solder bump forming device disclosed herein is not limited to the above embodiment.

[Connection structure]
Fig. 3 is a schematic cross-sectional view showing an example of the configuration of a connection structure. As shown in Fig. 3, a connection structure 41 is configured by electrically connecting an electrode 22 of one circuit member 21 and an electrode 32 of the other circuit member 31 via a solder bump S2. In this embodiment, the space between the one circuit member 21 and the other circuit member 21 is filled with an underfill material 42 mainly composed of, for example, epoxy resin. The underfill material 42 is formed so as to cover, for example, the electrodes 22, 32 and the solder bump S2 between the electrodes 22, 32.

Specific examples of the connection structure 41 include connection parts of semiconductor memories, semiconductor logic chips, etc., connection parts of primary and secondary mounting of semiconductor packages, junctions of CMOS image elements, laser elements, LED light-emitting elements, etc., and devices using these elements, such as cameras, sensors, liquid crystal displays, personal computers, mobile phones, smartphones, tablets, etc.

Specific examples of circuit members 21, 31 include chip components such as IC chips (semiconductor chips), resistor chips, capacitor chips, driver ICs, and rigid package substrates. These circuit members have circuit electrodes, and generally have many circuit electrodes. Other examples of substrates having multiple electrodes on their surface include wiring substrates such as flexible tape substrates with metal wiring, flexible printed wiring boards, and glass substrates with vapor-deposited indium tin oxide (ITO).

Specific examples of the electrodes 22, 32 include electrodes made of copper, copper/nickel, copper/nickel/gold, copper/nickel/palladium, copper/nickel/palladium/gold, copper/nickel/gold, copper/palladium, copper/palladium/gold, copper/tin, copper/silver, and indium tin oxide. The electrodes 22, 32 can be formed using techniques such as electroless plating, electrolytic plating, sputtering, and etching of metal foil.

Although one embodiment of the connection structure has been described above, the connection structure of the present disclosure is not limited to the above embodiment.

[Solder bump formation method]
Fig. 4 is a flow chart showing an example of a solder bump forming method. The flow chart shown in the figure shows the steps of forming the solder bump S2 using the above-mentioned solder bump forming apparatus 11, and includes a step of forming the connection structure 41 following the formation of the solder bump S2. Details of each step will be described with reference to Figs. 5 to 9 as appropriate.

In this solder bump formation method, first, one circuit member 21 and solder bump formation member 1 are supplied toward the first implementation region R2 (step S01). In step S01, the solder bump formation member 1 is supplied from the first supply unit 13 to the first implementation region R2 so that the recess 3 faces upward. In addition, the circuit member 21 is supplied from the second supply unit 14 to the placement region R1 so that the electrode 22 faces downward.

Next, in the first implementation area R2, the solder particles S1 held in the recess 3 and the electrodes 22 of the circuit member 21 are arranged to face each other (step S02). In step S02, the stage 12 is displaced while the circuit member 21 is adsorbed to the heat and pressure head 16, and the circuit member 21 is transferred from the placement area R1 to the first implementation area R2 as shown in FIG. 5. At this time, for example, the position of the alignment mark 4 on the solder bump forming member 1 side is confirmed by the imaging device 15A, and the position of the alignment mark on the circuit member 21 side is confirmed by the imaging device 15B, thereby aligning the solder particles S1 held in the recess 3 with the electrodes 22 of the circuit member 21.

Next, the electrode 22 is pressed against the solder particles S1 and heated (step S03). In step S03, as shown in FIG. 6, the circuit member 21 adsorbed to the heating and pressing head 16 is lowered toward the solder bump forming member 1 on the stage 12, and the electrode 22 is pressed against the solder particles S1 and heated. Here, after the electrode 22 of the circuit member 21 is brought into contact with the first surface 2a of the solder bump forming member 1, the heating and pressing head 16 may be heated to a temperature equal to or higher than the melting point of the solder particles S1 (for example, about 130°C to 260°C) while the electrode 22 is pressed against the solder bump forming member 1 side. Alternatively, the heating and pressing head 16 may be heated to a temperature equal to or higher than the melting point of the solder particles S1 (for example, about 130°C to 260°C) and then the electrode 22 may be pressed against the solder bump forming member 1 side. By closely adhering the electrode 22 to the first surface 2a of the solder bump forming member 1, the solder bump S2 can be formed only on the electrode 22, and the formation of a solder bridge between adjacent electrodes 22, 22 can be suppressed. The pressure applied to the electrode 22 by the heating and pressing head 16 on the solder bump forming member 1 is, for example, 0.1 MPa to 600 MPa. This pressure may be 1 MPa to 300 MPa, or 10 MPa to 100 MPa.

In this embodiment, the solder particles S1 held in each of the multiple recesses 3 of the solder bump forming member 1 do not protrude beyond the opening surface of the recess 3. Therefore, when the electrode 22 is brought into contact with the first surface 2a of the solder bump forming member 1, the electrode 22 does not come into contact with the solder particles S1 in the recess 3. When the heating and pressing head 16 is heated to a temperature equal to or higher than the melting point of the solder particles S1 in this state, as shown in FIG. 6, the deformation portion 6 (the partition portion 8 between the recesses 3, 3) of the main body portion 2 of the solder bump forming member 1 is deformed in the compression direction. As a result, the electrode 22 enters the recess 3 and the solder particles S1 come into contact with the electrode 22, and the solder bump S2 is transferred onto the electrode 22 by the melting of the solder particles S1.

When the bulk modulus of elastic body 9 is small, or when the total area of electrode 22 is small and the pressing pressure is high relative to the thrust of heat and pressure head 16, elastic body 9 can be deformed even without heating heat and pressure head 16, and electrode 22 can be brought into contact with solder particles S1. After electrode 22 is brought into contact with solder particles S1, heat heat and pressure head 16 to a temperature equal to or higher than the melting point of solder particles S1, and solder bumps S2 are transferred onto electrode 22 by melting solder particles S1.

After the solder bumps S2 have been transferred onto the electrodes 22, the heating and pressure application by the heating and pressure head 16 is stopped. Then, as shown in FIG. 7, the heating and pressure head 16 is raised together with the circuit member 21, and the electrodes 22 of the circuit member 21 and the solder bumps S2 on the electrodes 22 are cooled while the circuit member 21 is separated from the solder bump forming member 1. This causes the electrodes 22 and the solder bumps S2 formed by melting the solder particles S1 to adhere to each other, and they are electrically connected. The electrical connection between the electrodes 22 and the solder bumps S2 results in a circuit member 21A with solder bumps.

When solder particles S1 are heated in the atmosphere, oxidation proceeds rapidly, and it is considered that the spreading of the solder particles onto the electrodes 22 is hindered. Therefore, the atmosphere during heating and pressurization in step S03 may be a deoxidized atmosphere. The deoxidized atmosphere may be, for example, an inert gas atmosphere using nitrogen, argon, or the like, or a vacuum atmosphere. As the furnace, a reflow furnace (under a nitrogen atmosphere) or a vacuum reflow furnace that is generally used in solder joining processes can be used. In addition, a conveyor-type reflow furnace under a nitrogen atmosphere, a batch-type (chamber-type) reflow furnace, or the like can be used. When using these reflow furnaces, air bubbles (voids) in the solder bumps S2 can be removed by performing a vacuum process after the solder has melted.

In addition, the solder particles S1 may not melt or may not spread even when heated to a temperature above the melting point due to the influence of the oxide film. Therefore, a step of exposing at least one of the solder particles S1 and the electrode 22 to a reducing atmosphere may be further provided before step S02 or between steps S02 and S03. By reducing the oxide film on the surface of the solder particles S1 or the oxide film on the surface of the electrode 22, the melting and spreading of the solder particles S1 on the electrode 22 can be efficiently promoted. The step S03 may be performed in a reducing atmosphere. For example, hydrogen gas, hydrogen radicals, formic acid gas, etc. can be used to form the reducing atmosphere. As the furnace, a hydrogen reduction furnace, a hydrogen reflow furnace, a hydrogen radical furnace, a formic acid furnace, a vacuum furnace of these, a continuous furnace, a conveyor furnace, etc. can be used.

After forming the circuit member 21A with solder bumps, the connection structure 41 is formed. First, the other circuit member 31 is supplied toward the second implementation region R3 (step S04). In step S04, the circuit member 31 is supplied from the third supply unit 17 to the second implementation region R3 so that the electrodes 32 face upward. The circuit member 31 supplied to the second implementation region R3 may have an underfill material 42 disposed thereon to cover the electrodes 32.

Next, in the second implementation area R3, the circuit member 21A with solder bumps and the circuit member 31 are arranged facing each other (step S05). In step S05, as shown in FIG. 8, the stage 12 is displaced while the circuit member 21A with solder bumps is attached to the heat and pressure head 16, and the circuit member 21A with solder bumps is arranged on the second implementation area R3. At this time, for example, the position of the alignment mark on the circuit member 31 side is confirmed by the imaging device 15A, and the position of the alignment mark on the circuit member 21A with solder bumps is confirmed by the imaging device 15B, thereby aligning the electrodes 22 of the circuit member 21A with the electrodes 32 of the circuit member 31.

Next, heat and pressure are applied to the circuit members 21 and 31 via the solder bumps S2 (step S06). In step S06, as shown in Fig. 9, the circuit member 21A with solder bumps attached to the heat and pressure head 16 is lowered toward the circuit member 31 on the stage 12, the solder bumps S2 are sandwiched between the electrodes 22 of the circuit member 21A with solder bumps and the electrodes 32 of the circuit member 31, and the heat and pressure head 16 is heated to a temperature equal to or higher than the melting point of the solder particles S1 (for example, about 130°C to 260°C), thereby melting the solder bumps S2 between the electrodes 22 and 32. Alternatively, the heating and pressure head 16 may be heated to a temperature equal to or higher than the melting point of the solder particles S1 (e.g., about 130°C to 260°C), and then the solder bumps S2 may be sandwiched between the electrodes 22 and 32 of the circuit member 21A with solder bumps and the electrodes 32 of the circuit member 31 to melt the solder bumps S2 between the electrodes 22 and 32. The pressure applied by the heating and pressure head 16 to the circuit members 21 and 31 may be the same as the pressure applied in step S03.

Then, the heating and pressure application by the heating and pressure head 16 is stopped, and the heating and pressure head 16 is raised without adsorbing the circuit member 21. In this state, the electrodes 22 of the circuit member 21, the electrodes 32 of the circuit member 31, and the solder bumps S2 between the electrodes 22, 32 are cooled. This causes the electrodes 22, 32 to adhere to the solder bumps S2, and the circuit members 21, 31 are electrically connected to each other. The electrical connection between the circuit members 21, 31 results in the connection structure 41 shown in FIG. 3. Finally, the obtained connection structure 41 is adsorbed to the heating and pressure head 16 and transferred to a specified placement area, completing the process (step S07).

Step S06 may also include a step of exposing at least one of the solder bump S2 and the electrodes 22, 32 to a reducing atmosphere. As in step S03, hydrogen gas, hydrogen radicals, formic acid gas, etc. may be used to form the reducing atmosphere. As in step S03, a hydrogen reduction furnace, hydrogen reflow furnace, hydrogen radical furnace, formic acid furnace, vacuum furnaces, continuous furnaces, conveyor furnaces, etc. may be used as the furnace.

A method of forming a reducing atmosphere can also use a material with a reducing effect. For example, a flux material or a material containing a flux component can be placed near the solder bump S2 and the electrodes 22, 32. Pastes, films, etc. containing the flux material and the material containing a flux component can be used. Pastes and films containing flux components may contain a thermosetting material. This allows the thermosetting component to harden at the same time as the solder bump S2 melts, and the circuit members 21, 31 can be fixed together. The thermosetting material may be hardened by heating again in a later process, separate from the melting and heating of the solder bump S2.

Although one embodiment of the solder bump formation method has been described above, the solder bump formation method disclosed herein is not limited to the above embodiment.

[Effects of the present disclosure]
As described above, in the solder bump forming apparatus 11, the solder particles S1 are held in the multiple recesses 3 of the solder bump forming member 1, and heat and pressure are applied together with the electrode 22 to be transferred, thereby forming the solder bumps S2 on the electrode 22. In the solder bump forming member 1 supplied to the solder bump forming apparatus 11, the components of the recesses 3 are formed by the deformation parts 6 that are deformable at the melting point of the solder particles S1. As a result, when the electrode 22 is pressed against the member 1 and heat is applied, the deformation parts 6 deform, and the solder particles S1 held in the recesses 3 can be exposed to the electrode 22. Therefore, in the solder bump forming apparatus 11, the reliability of the transfer of the solder particles S1 to the electrode 22 can be guaranteed even if the shapes of the solder particles S1 are not uniform.

In this embodiment, the first supply unit 13 supplies the solder bump forming member 1 in which the deformation portion 6 is constituted by an elastic body 9 having a bulk modulus of 0.1 GPa or more and 5 GPa or less at the melting point of the solder particles S1. By making the bulk modulus of the deformation portion 6 5 GPa or less, when the electrode 22 is pressed against the deformation portion 6 and heat is applied, the deformation portion 6 is sufficiently deformed, and the solder particles S1 held in the recess 3 can be more reliably exposed to the electrode 22 side. On the other hand, by making the bulk modulus of the deformation portion 6 0.1 GPa or more, the shape retention of the recess 3 can be maintained, and the retention performance of the solder particles S1 during transfer can be guaranteed. This makes it possible to form the solder particles S1 at the target position on the electrode 22 with good accuracy. In addition, when the deformation portion 6 is constituted by the elastic body 9, it is possible to restore the deformation portion 6 to its original shape after the transfer of the solder particles S1 to the electrode 22. This makes it possible to reuse the solder bump forming member 1.

In this embodiment, the heating and pressing head 16 heats the electrode 22 to a temperature equal to or higher than the melting point of the solder particles S1 while pressing the electrode 22 against the first surface 2a of the solder bump forming member 1. This allows the solder particles S1 to be melted and the deformation portion 6 to be deformed while the solder particles S1 are sandwiched between the electrode 22 and the solder bump forming member 1, thereby preventing the positional deviation of the solder bump S2 formed on the electrode 22. This makes it possible to more accurately form the solder particles S1 at the target position on the electrode 22.

In this embodiment, the first supply unit 13 supplies the solder bump forming member 1 in which the solder particles S1 are individually arranged in each of the multiple recesses 3. This allows the solder particles S1, which have a relatively large particle size, to be transferred to the electrode 22 with a certain degree of certainty.

In this embodiment, the average particle diameter of the solder particles S1 is 1 μm to 35 μm. When using minute solder particles S1 in this range, it is generally difficult to make the shapes of the solder particles S1 uniform, but by applying the above method, it is possible to ensure the reliability of the transfer of the solder particles S1 to the electrodes 22 even if the shapes of the solder particles S1 are not uniform.
[Modification]

The present disclosure is not limited to the above embodiment. For example, in the example of FIG. 1, the deformation portion 6 is provided with a thickness corresponding to the depth of the recess 3 from the first surface 2a toward the second surface 2b, but the thickness of the deformation portion 6 is not limited to this. For example, as in the solder bump forming member 1A shown in FIG. 10(a), the thickness T of the deformation portion 6 may be smaller than the depth D of the recess 3. In this case, only the first surface 2a side of the partition wall portion 8 separating the adjacent recesses 3, 3 is composed of the deformation portion 6. Therefore, the first surface 2a side of the inner wall surface 3a of the recess 3 is composed of the deformation portion 6, while the second surface 2b side of the inner wall surface 3a of the recess 3 and the bottom surface 3b of the recess 3 are composed of the base portion 7.

As in the example of FIG. 10(a), when the thickness T of the deformation portion 6 is made smaller than the depth D of the recess 3, the solder particles S1 held in the recess 3 may protrude toward the first surface 2a side beyond the interface between the deformation portion 6 and the base portion 7. In other words, the height H of the solder particles S1 may satisfy H>D-T, where D is the depth of the recess 3 and T is the thickness T of the deformation portion 6. This ensures reliable contact between the solder particles S1 and the electrodes 22 when the deformation portion 6 is deformed.

In addition, from the viewpoint of ensuring a sufficient amount of deformation of the deformation portion 6, even if the thickness T of the deformation portion 6 is made smaller than the depth D of the recess 3, the deformation portion 6 may be provided with a thickness of 1/2 or more of the depth D of the recess 3 in the depth direction from the first surface 2a to the recess 3. In this case, the deformation portion 6 may be provided with a thickness of 3/5 or more of the depth D of the recess 3 in the depth direction from the first surface 2a to the recess 3, or may be provided with a thickness of 4/5 or more.

Also, for example, as in the solder bump forming member 1B shown in FIG. 10(b), the thickness T of the deformation portion 6 may be greater than the depth D of the recess 3. In this case, the entire partition wall 8 separating the adjacent recesses 3, 3 becomes the deformation portion 6, and both the inner wall surface 3a and the bottom surface 3b of the recess 3 are composed of the deformation portion 6. The interface between the deformation portion 6 and the base portion 7 can be set at any position between the bottom surface 3b and the second surface 2b of the recess 3. For example, as in the solder bump forming member 1C shown in FIG. 10(c), the base portion 7 is not provided, and the entire main body portion 2 may be composed of the deformation portion 6.

In the above embodiment, none of the solder particles S1 protrude beyond the opening of the recess 3. However, the present disclosure ensures reliable transfer of the solder particles S1 to the electrode 22 without the need to align the height of the solder particles S1 in the recess 3. Therefore, some or all of the solder particles S1 may protrude beyond the opening of the recess 3. That is, as shown in FIG. 11(a), the height H of some or all of the solder particles S1 may satisfy H>D with respect to the depth D of the recess 3.

In the above embodiment, a configuration in which a single solder particle S1 is arranged in each of the multiple recesses 3 has been exemplified, but multiple solder particles S1 may be arranged in each of the multiple recesses 3. In this case, for example, as shown in FIG. 11(b), multiple solder particles S1 having a smaller average particle diameter than the example in FIG. 1 may be arranged in the recess 3. In this case, it becomes easier to adjust the volume of the solder particles S1 held in the recess 3, and it becomes easier to align the size and height of the solder bump S2 formed on the electrode 22 within a certain range. In addition, the probability of contact between the electrode 22 and the solder particles S1 can be increased, and the formation of the solder bump S2 on the electrode 22 can be more reliably performed. When multiple solder particles S1 are arranged in the recess 3, as described above, the C.V. value of the solder particles S1 may be 20% or less. This allows sufficient conductivity reliability and insulation reliability to be ensured in the connection of the circuit members 21, 31 using the solder bump S2.

Even when multiple solder particles S1 are arranged in the recess 3, the force acting between the solder particles S1 and the partition 8 (for example, intermolecular forces such as van der Waals forces) is considered to be greater than the gravity acting on the solder particles S1. Therefore, even when the recess 3 is oriented so as to face downward, the solder particles S1 can remain in the recess 3. If there is a flat portion on the outer surface of the solder particle S1 and the flat portion is in contact with the inner wall surface 3a or bottom surface 3b of the recess 3, the solder particles S1 can be more effectively prevented from falling out of the recess 3.

1, 1A to 1C...solder bump forming member, 3...recess, 6...deformation portion, 9...elastic body, 11...solder bump forming device, 12...stage, 13...first supply portion, 14...second supply portion, 16...heating and pressurizing head (heating and pressurizing portion), 21...circuit member, 22...electrode, S1...solder particle, S2...solder bump, R2...first implementation area (implementation area).

Claims (7)

A solder bump forming apparatus for forming solder bumps on electrodes of a circuit member, comprising:
a stage having an implementation area for forming the solder bumps on the electrodes;
a first supply unit that supplies a solder bump forming member having a plurality of recesses in which solder particles are held, the solder particles being accommodated in the recesses such that the top surfaces of the solder particles are positioned within the recesses, and the components of the recesses having deformation portions that are deformable at the melting point of the solder particles;
a second supply unit that supplies the circuit member so that the solder particles held in the recesses of the solder bump forming member are disposed opposite the electrodes;
a heating and pressurizing section that, in the implementation area, heats the electrode to a temperature equal to or higher than the melting point of the solder particles, presses the electrode against the solder bump forming member, and compresses and deforms the deformation section in its height direction to bring the solder particles held in the recess into contact with the electrode, and transfers the solder particles to the electrode to form a solder bump. The solder bump forming device according to claim 1, wherein the first supply unit supplies the solder bump forming member in which the deformation unit is constituted by an elastic body having a bulk modulus of 0.1 GPa or more and 5 GPa or less at the melting point of the solder particles. The solder bump forming device according to claim 1 or 2, wherein the heating and pressurizing unit heats the electrode to a temperature equal to or higher than the melting point of the solder particles while pressing the electrode against the solder bump forming member. The solder bump forming device according to any one of claims 1 to 3, wherein the first supply unit supplies the solder bump forming member in which the solder particles are individually arranged to each of the multiple recesses. The solder bump forming device according to any one of claims 1 to 3, wherein the first supply unit supplies the solder bump forming member in which a plurality of the solder particles are arranged in each of the plurality of recesses. The solder bump forming apparatus according to claim 5, wherein the C.V. value of the solder particles is 20% or less. The solder bump forming device according to any one of claims 1 to 6, wherein the average particle diameter of the solder particles is 1 μm to 35 μm.

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