Solder bump formation method

Abstract

This solder bump formation method comprises: a step for preparing a solder bump formation member 1 having a plurality of recesses 3 and having deformation parts 6 at which constituent portions of the recesses 3 are deformable at the melting point of solder particles S1; a step for arranging the solder particles S1 held in the recesses 3 of the solder bump formation member 1 so as to oppose an electrode 22; a step for heating the electrode 22 to a temperature equal to or higher than the melting point of the solder particles S1; and a step for pressing the electrode 22 against the bump formation member 1. The solder particles S1 held in the recesses 3 are brought into contact with the electrode 22 by deforming the deformation parts 6, the solder particles S1 are transferred to the electrode 22, and a solder bump S2 is formed.

Description

Technical Field

[0001] The present disclosure relates to a method for forming solder bumps.

Background Art

[0002] In recent years, flip chip mounting is known as one of the methods for mounting electronic components with high density. In flip chip mounting, for example, solder bumps are previously formed on electrodes provided on one circuit member, and the electrodes of one circuit member and the electrodes of the other circuit member are joined by melting the solder bumps. Thereby, a connection structure between circuit members is formed.

[0003] As a technique for forming solder bumps on electrodes, for example, there is a solder bump forming method described in Patent Document 1. In this conventional solder bump forming method, a positioning plate having a plurality of recesses formed corresponding to the mutual intervals of the electrodes of the substrate is prepared, and solder particles are respectively arranged in each recess of the positioning plate. Next, by rolling a transfer roll whose outer peripheral surface is an adhesive surface on the surface of the positioning plate, the solder particles are transferred to the adhesive surface of the transfer roll. Then, by rolling the transfer roll on the electrodes of the substrate provided with the adhesive material, the solder particles are transferred from the transfer roll to the electrodes of the substrate.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In methods such as the solder bump formation method described in Patent Document 1, it is preferable that the heights of the solder balls protruding from the recesses of the positioning plate are uniform, from the viewpoint of ensuring the reliability of the transfer of solder particles to the electrodes. However, when using minute solder particles, such as those used for connecting electrodes at micro-level intervals, it is difficult to uniformize the shape of the solder particles, which presents a problem in ensuring the reliability of the transfer of solder particles to the electrodes.

[0006] This disclosure was made to solve the above-mentioned problems and aims to provide a solder bump formation method that can ensure the reliability of solder particle transfer to electrodes even without standardizing the shape of the solder particles. [Means for solving the problem]

[0007] A solder bump formation method relating to one aspect of the present disclosure is a solder bump formation method for forming solder bumps on electrodes of a circuit member, comprising the steps of: preparing a solder bump forming member having a plurality of recesses, wherein the components of the recesses have deformable parts that can be deformed at the melting point of solder particles; arranging solder particles held in the recesses of the solder bump forming member opposite to the electrodes; heating the electrodes to a temperature above the melting point of the solder particles; and pressing the electrodes against the solder bump forming member, wherein the components of the recesses are deformed to bring the solder particles held in the recesses into contact with the electrodes, thereby transferring the solder particles to the electrodes and forming solder bumps.

[0008] In this solder bump formation method, solder particles are held in multiple recesses of a solder bump forming member, and solder bumps can be formed on the electrode by applying heat and pressure together with the electrode to be transferred. In this solder bump formation method, the recessed parts of the solder bump forming member have deformable parts that can be deformed at the melting point of the solder particles. As a result, when the electrode is pressed and heat is applied, the deformable parts deform, exposing the solder particles held in the recesses to the electrode side. Therefore, in this solder bump formation method, the reliability of transferring solder particles to the electrode can be ensured even if the shape of the solder particles is not uniform.

[0009] The electrode may be heated to a temperature above the melting point of the solder particles while pressed against the solder bump forming member. In this case, since the solder particles are sandwiched between the electrode and the solder bump forming member, the melting of the solder particles and the deformation of the deformation portion are carried out, so that misalignment of the solder bumps formed on the electrode can be suppressed. Therefore, it becomes possible to form solder particles at the target position on the electrode with greater precision.

[0010] Solder particles may be placed individually in each of the multiple recesses. In this case, solder particles with a relatively large particle size can be transferred to the electrode with a certain degree of reliability.

[0011] Multiple solder particles may be placed in each of the multiple recesses. In this case, it becomes easier to adjust the volume of solder particles held within the recesses, and it becomes easier to standardize the size and height of the solder bumps formed on the electrodes to a certain range. Furthermore, the probability of contact between the electrodes and solder particles can be increased, and the formation of solder bumps on the electrodes can be carried out more reliably.

[0012] The CV value of the solder particles may be 20% or less. This ensures sufficient conductivity and insulation reliability when connecting circuit components using solder bumps.

[0013] The average particle size of the solder particles may be between 1 μm and 35 μm. When using such minute solder particles, it is generally difficult to standardize the shape of the solder particles. However, by applying the above method, the reliability of transferring the solder particles to the electrodes can be ensured even without standardizing the shape of the solder particles. [Effects of the Invention]

[0014] According to this disclosure, the reliability of transferring solder particles to electrodes can be ensured even without standardizing the shape of the solder particles. [Brief explanation of the drawing]

[0015] [Figure 1]It is a schematic cross-sectional view showing the configuration of a solder bump forming member according to an embodiment of the present disclosure. [Figure 2] (a) and (b) are diagrams schematically showing an example of the configuration of a solder bump forming apparatus. [Figure 3] It is a schematic cross-sectional view showing an example of the configuration of a connection structure. [Figure 4] It is a flowchart showing an example of a solder bump forming method. [Figure 5] It is a schematic cross-sectional view showing the process of solder bump formation. [Figure 6] It is a schematic cross-sectional view showing the subsequent process of FIG. 5. [Figure 7] It is a schematic cross-sectional view showing the subsequent process of FIG. 6. [Figure 8] It is a schematic cross-sectional view showing the subsequent process of FIG. 7. [Figure 9] It is a schematic cross-sectional view showing the subsequent process of FIG. 8. [Figure 10] (a) to (c) are schematic cross-sectional views showing modified examples of the solder bump forming member. [Figure 11] (a) and (b) are schematic enlarged cross-sectional views of main parts showing modified examples of solder particles. [Embodiments for Carrying Out the Invention]

[0016] Hereinafter, with reference to the drawings, a preferred embodiment of a solder bump forming method according to one aspect of the present disclosure will be described in detail.

[0017] In this specification, a numerical range indicated by using "~" includes the numerical values described before and after "~" as the minimum value and the maximum value, respectively. The upper limit value or the lower limit value of the numerical range described stepwise in this specification may be replaced with the upper limit value or the lower limit value of the numerical range of other steps. [Configuration of Solder Bump Forming Member]

[0018] Figure 1 is a schematic cross-sectional view showing the configuration of a solder bump forming member according to one embodiment of the present disclosure. The solder bump forming member 1 shown in Figure 1 is a member used, for example, when forming solder bumps on the electrodes of a circuit member. As shown in Figure 1, the solder bump forming member 1 comprises a main body portion 2. The main body portion 2 has, for example, a rectangular shape in plan view and has a first surface 2a and a second surface 2b opposite to the first surface 2a.

[0019] Multiple recesses 3 are provided on the first surface 2a side of the main body 2, which hold solder particles S1. These recesses 3 can be formed using known methods such as imprinting, photolithography, machining, and laser processing. In particular, when using nanoimprinting, the recesses 3 can be formed accurately in a relatively short process by pressing a desired mold.

[0020] The size (width, volume, depth, etc.) of the recess 3 is set appropriately according to the size of the solder particles S1. The planar shape of the recess 3 is, for example, circular. The planar shape of the recess 3 may be various shapes other than circular, such as elliptical, triangular, quadrilateral, or polygonal. In the example in Figure 1, the cross-sectional shape of the recess 3 is rectangular. The cross-sectional shape of the recess 3 may be tapered, with the opening area expanding from the bottom surface 3b side to the opening surface side (first surface 2a side). The bottom surface 3b of the recess 3 is not limited to a flat surface, but may be, for example, a concave curved surface.

[0021] Furthermore, alignment marks 4 may be provided on the first surface 2a of the main body 2. The alignment marks 4 are formed, for example, by creating an uneven shape on the first surface 2a of the main body 2, printing with ink or pigment, printing with inorganic material by plating or sputtering, or burning with a laser. In a plan view, the alignment marks 4 may be, for example, a circle, a double circle, a multi-circle, a triangle, a rectangle, a polygon, or a multi-sided polygon thereof. The alignment marks 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.

[0022] By detecting the alignment marks 4 with imaging devices 15A and 15B such as cameras, the alignment of the electrode to be formed and the solder particles S1 in the recess 3 becomes easier during solder bump formation. This allows for accurate transfer of the solder particles S1 to the electrode. One or more alignment marks 4 are sufficient on the first surface 2a side, but providing multiple marks can further improve the accuracy of the alignment. In addition, if the main body 2 is transparent, for example, additional alignment marks 4 may be provided on the second surface 2b side of the main body 2.

[0023] The main body 2 may be composed of a deformable portion 6 that includes the first surface 2a and a base portion 7 that constitutes the second surface 2b side. The deformable portion 6 is a part that constitutes at least the first surface 2a side of the recess 3, and may be provided in the depth direction of the recess 3 from the first surface 2a with a thickness of 1 / 3 or more of the depth D of the recess 3, or with a thickness of 1 / 2 or more of the depth D. In the example of Figure 1, the thickness T of the deformable portion 6 is equal to the depth D of the recess 3. As a result, the entire partition wall portion 8 separating adjacent recesses 3, 3 is the deformable portion 6, the inner wall surface 3a of the recess 3 is composed of the deformable portion 6, while the bottom surface 3b of the recess 3 is composed of the base portion 7.

[0024] There are no particular restrictions on the width of the partition wall 8 (the distance between adjacent recesses 3, 3), but it can be, for example, 0.1 times or more the average particle diameter of the solder particles held in the recess 3. The width of the partition wall 8 may also be 0.2 times or more the average particle diameter of the solder particles held in the recess 3, or 0.3 times or more. The distance between the recesses 3, 3 is defined, for example, by the shortest distance between the opening edge of one recess 3 and the opening edge of the other recess 3.

[0025] The deformable portion 6 is formed by an elastic body 9 that is deformable at the melting point of the solder particles S1 held in the recess 3, for example. Therefore, the deformable portion 6 can be elastically deformed in the compression direction when the electrode to be formed is pressed against it during solder bump formation. The melting point of the solder particles S1 here is the temperature at which the first endothermic peak occurs when a DSC (Differential Scanning Calorimeter) measurement is performed in a He gas flow at a heating rate of 10°C / min. 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, 0.5 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.

[0026] Examples of elastic materials 9 constituting the deformable portion 6 include photocurable materials, thermosetting materials, and thermoplastics. Examples of elastic materials 9 constituting the deformable portion 6 include resins, polymers, rubbers, elastomers, and mixtures thereof. When the constituent material of the solder particle S1 is SnBi (melting point: 139°C), examples of elastic materials 9 constituting the deformable portion 6 include polyethylene terephthalate (bulk modulus at melting point: 0.6 GPa), acrylic (bulk modulus at melting point: 1 GPa), and PMMA (bulk modulus at melting point: 1 GPa). When the constituent material of the solder particle S1 is SnAgCu (melting point: 217°C), examples of elastic materials 9 constituting the deformable portion 6 include polyimide (bulk modulus at melting point: 1 GPa).

[0027] The base portion 7 is the part that constitutes the second surface 2b side of the main body portion 2. The base portion 7 is made of 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 during solder bump formation. 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.

[0028] Examples of materials that can be used to construct the base portion 7 include inorganic materials such as silicon, various ceramics, glass, and stainless steel, and organic materials such as various resins. The base portion 7 may also be made of a material with high light transmittance. Examples of such materials include polyethylene terephthalate, transparent (colorless) polyimide, and polyamide. The base portion 7 may also be made of a heat-resistant material that does not change at the melting point of the solder particles S1. The base portion 7 may also be made of a material that does not alloy with or react with the materials constituting the solder particles S1.

[0029] As the constituent material of the base portion 7, for example, if it is a flexible film, polyethylene terephthalate, polyethylene naphthalate, polyvinyl chloride resin, polystyrene, polyethylene polyphenylene sulfide, polycarbonate, etc. can be used. Furthermore, from the viewpoint of improving the handling of the base portion 7, deformation can be suppressed by increasing the thickness of the aforementioned materials. In addition, from the viewpoint of improving the positional accuracy when transferring solder particles S1 onto the electrode, engineering plastics, super engineering plastics, materials compounded with fillers or fibers into the aforementioned general-purpose plastics, and inorganic materials can be used. For example, polyamide, polyacetal, polycarbonate, polyphenylene sulfide, polyimide, polyetherimide, polyamideimide, polysulfone, polyetheretherketone, etc. can be used.

[0030] If the constituent material of the solder particle S1 is SnBi (melting point: 139°C), the constituent 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). If the constituent material of the solder particle S1 is SnAgCu (melting point: 217°C), the constituent 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).

[0031] The deformable part 6 and the base part 7 may be made of the same material system, provided that the base part 7 has a higher bulk modulus than the deformable part 6. For example, in the case of resin materials, the bulk modulus can be adjusted by changing the degree of crosslinking, adding reinforcing materials such as fillers or fibers, or mixing in other materials. For example, the deformable part 6 may be made of a thermosetting epoxy resin, and the base part 7 may be made of the thermosetting epoxy resin with glass fibers added to reinforce its bulk modulus.

[0032] The deformable portion 6 may be made of a photocurable acrylic resin, and the base portion 7 may be made of polyethylene terephthalate. In this case, the photocurable acrylic resin can be formed by applying uncured photocurable acrylic resin to a stamper having a convex shape, irradiating it with light while pressing polyethylene terephthalate against it, and then peeling off the stamper. This method allows for the formation of a main body portion 2 having continuously roll-shaped recesses 3. Furthermore, the degree of crosslinking and the bulk modulus can be adjusted by adjusting the light intensity, curing time, and the amount of initiator in the photocurable acrylic resin.

[0033] The base portion 7 may be made of an inorganic material. For example, the deformable portion 6 may be made of a photocurable acrylic resin (bulk modulus: 0.1 GPa) and the base portion 7 may be made of glass (bulk modulus: 40 GPa). In this case, the bulk modulus at the melting point of the base portion 7 can be sufficiently secured, and the positional accuracy when transferring 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 transferred to the electrode, the base portion 7 is less likely to deform, thus suppressing distortion and elongation of the entire main body portion 2. In addition, the main body portion 2 can be reused repeatedly.

[0034] If the base portion 7 is made of a silicon wafer and a photosensitive material is used to form the deformable portion 6, the formation of the recess 3 becomes easier. In this case, as the photosensitive material, for example, acrylic, epoxy, polyimide, or mixtures thereof can be used.

[0035] The bulk modulus K of the deformable part 6 and the base part 7 can be determined by the formula K = E / 3(1-2ν), where E is the Young's modulus of the material and ν is Poisson's ratio. The bulk modulus K of the deformable part 6 and the base part 7 can be measured by, for example, mechanical testing, resonance testing, or ultrasonic pulse testing. For measurement, for example, a nanoindenter or surface hardness tester can be used. For example, a heating stage can be attached to a surface hardness tester (manufactured by Fischer Instruments), the deformable part 6 and the base part 7 can be placed on the heating stage and the stage can be heated to raise the temperature of the deformable part 6 and the base part 7 to a predetermined temperature. Then, an indenter can be brought into contact with the surface of the object to be measured, and the bulk modulus can be calculated by obtaining a load-displacement (Stress-Stren) curve.

[0036] In the example shown in Figure 1, each of the multiple recesses 3 individually holds a solder particle S1. The solder particles S1 within each recess 3 are in contact with at least the bottom surface 3b of the recess 3. The solder particles S1 within each recess 3 may also be in contact with the inner wall surface 3a of the recess 3. Furthermore, in the example shown in Figure 1, all the solder particles S1 are located within the recesses 3, and the tops of the solder particles S1 do not protrude beyond the opening surface of the recess 3. That is, if the depth of the recess 3 is D and the height of the solder particles S1 (height from the bottom surface 3b) is H, then D > H is satisfied.

[0037] The ratio of the height of the solder particles S1 to the depth D of the recess 3 is not particularly limited, but considering the amount of deformation in the compression direction of the deformable portion 6, it may be, for example, 0.3 to 1.5. By setting the ratio to 0.3 or higher, the electrode and the solder particles S1 can be made to come into contact more reliably when the electrode is pressed against the surface. By setting the ratio to 1.5 or lower, the detachment of the solder particles S1 from the recess 3 can be suitably suppressed. Furthermore, the solder particles S1 can be prevented from overflowing from the recess 3 during transfer, and the solder particles S1 can be prevented from bonding with 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 0.6 to 1.

[0038] Solder particles S1 are composed of, for example, tin or a tin alloy. Examples of tin alloys include In-Sn alloy, In-Sn-Ag alloy, Sn-Au alloy, Sn-Bi alloy, Sn-Bi-Ag alloy, Sn-Ag alloy, Sn-Ag-Cu alloy, and Sn-Cu alloy. Solder particles S1 may also contain indium or an indium alloy. Examples of indium alloys include In-Bi alloy and In-Ag alloy.

[0039] 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 conductivity reliability, the solder particles S1 may also contain Ag or Cu from the aforementioned elements. By containing 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.

[0040] 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.

[0041] The average particle diameter of solder particles S1 can be measured using various methods appropriate to the size. Measurement methods include, for example, dynamic light scattering, laser diffraction, centrifugal sedimentation, electrical detection band method, and resonant mass measurement. Other measurement methods include measuring particle size based on images obtained from optical microscopes or electron microscopes. Specific devices include flow-type particle image analyzers, microtrac, and Coulter counters. The average particle diameter of solder particles S1 can be calculated based on the projected area circle equivalent diameter (the diameter of a circle with an area equal to the projected area of ​​the particle) when observing the solder particles S1 from a direction perpendicular to the first surface 2a of the solder bump forming member 1. When solder particles S1 are individually placed in each of the multiple recesses 3, the size (average particle diameter) of the solder particles S1 may be uniform.

[0042] The CV value of the solder particles S1 is calculated by multiplying the value obtained by dividing the standard deviation of the particle diameter measured by the method described above by the average particle diameter by 100. When multiple solder particles S1 are placed in each of the multiple recesses 3, the CV value of the solder particles S1 may be 20% or less from the viewpoint of achieving better conductivity and insulation reliability. The CV value of the solder particles S1 may be 10% or less, or 7% or less. The lower limit of the CV value of the solder particles S1 is not particularly limited. For example, the CV value of the solder particles S1 may be 1% or more, or 2% or more.

[0043] Although one embodiment of a solder bump forming member has been described above, the solder bump forming member of this disclosure is not limited to the above embodiment. [Solder bump forming machine]

[0044] Figures 2(a) and 2(b) are schematic diagrams showing an example of the configuration of a solder bump forming apparatus. Figure 2(a) is a side view, and Figure 2(b) is a top view. The solder bump forming apparatus 11 shown in the figures is a device that forms a circuit member 21A with solder bumps (see Figure 9) by transferring solder particles S1 held in the recess 3 of the solder bump forming member 1 described above to the electrodes 22 of the circuit member 21.

[0045] As shown in Figures 2(a) and 2(b), the solder bump forming apparatus 11 includes a horizontally displaceable stage 12, a first supply unit 13 for supplying solder bump forming material 1, a second supply unit 14 for supplying circuit material 21, imaging devices 15A and 15B, and a heating and pressing head 16. In this embodiment, the solder bump forming apparatus 11 has the function of electrically connecting the circuit material 21 on which the solder bump S2 (see Figure 9) has been formed to another circuit material 31 to form a connection structure 41 (see Figure 3) as a post-process of the solder bump forming process. The solder bump forming apparatus 11 further includes a third supply unit 17 for supplying another circuit material 31. The operation of the solder bump forming apparatus 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 apparatus 11 and may be configured as an independent device.

[0046] Stage 12 is provided with a mounting area R1 on which the circuit member 21 supplied from the second supply unit 14 is placed, a first implementation area (implementation area) R2 on which solder bumps S2 are formed, and a second implementation area R3 on which the connecting structure 41 is formed. The imaging devices 15A and 15B are responsible for reading 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 positioned on the front side of Stage 12 (the setting surface side of the first implementation area R2 and the second implementation area R3), and the imaging device 15B is positioned on the back side of Stage 12. The imaging device 15B may be incorporated into Stage 12. Stage 12 is displaced according to the reading results of the alignment marks by the imaging devices 15A and 15B to align the solder bump forming member 1 and the circuit member 21, and to align the circuit member 21A with solder bumps and the circuit member 31.

[0047] The heating and pressing head 16 is the part that performs heating and pressing in the first implementation area R2 and the second implementation area R3. The heating and pressing head 16 has a suction function and performs the transfer of the circuit member 21 from the mounting area R1 to the first implementation area R2, the transfer of the circuit member 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 pressing head 16 is configured to move up and down relative to the stage 12, and by descending toward the stage 12, it performs heating and pressing when forming the solder bumps S2 and when forming the connection structure 41.

[0048] Although one embodiment of a solder bump forming apparatus has been described above, the solder bump forming apparatus of this disclosure is not limited to the above embodiment. [Connection structure]

[0049] Figure 3 is a schematic cross-sectional view showing an example of the configuration of a connecting structure. As shown in Figure 3, the connecting structure 41 is configured such that the electrode 22 of one circuit member 21 and the electrode 32 of the other circuit member 31 are electrically connected via solder bumps S2. In this embodiment, the space between one circuit member 21 and the other circuit member 21 is filled with an underfill material 42, for example, mainly composed of epoxy resin. The underfill material 42 is formed to cover, for example, the electrodes 22, 32 and the solder bumps S2 between the electrodes 22, 32.

[0050] Specific examples of the connection structure 41 include connection parts for semiconductor memory and semiconductor logic chips, connection parts for primary and secondary mounting of semiconductor packages, junctions for CMOS image elements, laser elements, LED light-emitting elements, and devices such as cameras, sensors, liquid crystal displays, personal computers, mobile phones, smartphones, and tablets that use these.

[0051] Specific examples of circuit components 21 and 31 include IC chips (semiconductor chips), resistor chips, capacitor chips, driver ICs and other chip components, and rigid package substrates. These circuit components are equipped with circuit electrodes, and generally have a large number of circuit electrodes. Other examples of substrates having multiple electrodes on their surface include flexible tape substrates with metal wiring, flexible printed circuit boards, and wiring substrates such as glass substrates with indium tin oxide (ITO) deposited on them.

[0052] Specific examples of electrodes 22 and 32 include 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. Electrodes 22 and 32 can be formed using methods such as electroless plating, electrolytic plating, sputtering, and etching of metal foil.

[0053] Although one embodiment of the connection structure has been described above, the connection structure of this disclosure is not limited to the above embodiment. [Method for forming solder bumps]

[0054] Figure 4 is a flowchart illustrating an example of a solder bump formation method. The flowchart in this figure shows the steps involved in forming solder bumps S2 using the solder bump formation apparatus 11 described above, and also includes the step of forming the connecting structure 41 following the formation of the solder bumps S2. Details of each step will be explained with reference to Figures 5 to 9 as appropriate.

[0055] In this solder bump formation method, first, one circuit member 21 and the solder bump forming member 1 are supplied to the first implementation area R2 (step S01). In step S01, the solder bump forming member 1 is supplied from the first supply unit 13 to the first implementation area R2 so that the recess 3 faces upward. Also, the circuit member 21 is supplied from the second supply unit 14 to the mounting area R1 so that the electrode 22 faces downward.

[0056] 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 positioned opposite each other (step S02). In step S02, with the circuit member 21 adsorbed to the heating and pressing head 16, the stage 12 is displaced to transfer the circuit member 21 from the mounting area R1 to the first implementation area R2, as shown in Figure 5. At this time, for example, the position of the alignment mark 4 on the solder bump forming member 1 side is confirmed with the imaging device 15A, and the position of the alignment mark on the circuit member 21 side is confirmed with the imaging device 15B, thereby aligning the solder particles S1 held in the recess 3 and the electrodes 22 of the circuit member 21.

[0057] Next, the electrodes 22 are pressed against the solder particles S1 and heated (step S03). In step S03, as shown in Figure 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 electrodes 22 are pressed against the solder particles S1 and heated. Here, after the electrodes 22 of the circuit member 21 are brought into contact with the first surface 2a of the solder bump forming member 1, the electrodes 22 are pressed toward the solder bump forming member 1, and the heating and pressing head 16 may be heated to a temperature above the melting point of the solder particles S1 (for example, about 130°C to 260°C), or to a temperature below the melting point of the solder particles S1. Alternatively, the heating and pressing head 16 may be heated to a temperature above the melting point of the solder particles S1 (for example, about 130°C to 260°C) before pressing the electrodes 22 toward the solder bump forming member 1. By bringing the electrode 22 into close contact with the first surface 2a of the solder bump forming member 1, solder bumps S2 can be formed only on the electrode 22, thereby suppressing the formation of solder bridges between adjacent electrodes 22, 22.

[0058] The pressure applied by the electrode 22 to the solder bump forming member 1 by the heating and pressing head 16 is, for example, 0.1 MPa to 600 MPa. This pressure may also be 1 MPa to 300 MPa, or 10 MPa to 100 MPa.

[0059] In this embodiment, the solder particles S1 held in each of the multiple recesses 3 of the solder bump forming member 1 may 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 recesses 3 that do not protrude beyond the opening surface of the recesses 3. When the heating and pressing head 16 is heated to a temperature above the melting point of the solder particles S1 in this state, as shown in Figure 6, the deformable portion 6 (partition wall portion 8 between the recesses 3, 3) of the main body portion 2 of the solder bump forming member 1 deforms 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 a solder bump S2 is transferred onto the electrode 22 by the melting of the solder particles S1.

[0060] Furthermore, if the bulk modulus of the elastic body 9 is small, or if the total area of ​​the electrodes 22 is small and the pressing pressure is high relative to the thrust of the heating and pressing head 16, the elastic body 9 can deform even without heating the heating and pressing head 16, allowing the electrodes 22 and solder particles S1 to come into contact. After bringing the electrodes 22 and solder particles S1 into contact, heating the heating and pressing head 16 to a temperature above the melting point of the solder particles S1 transfers solder bumps S2 onto the electrodes 22 by melting the solder particles S1.

[0061] After transferring the solder bump S2 onto the electrode 22, heating and pressurizing by the heating and pressurizing head 16 are stopped. Then, as shown in Figure 7, the heating and pressurizing head 16 is raised together with the circuit member 21, and the electrode 22 of the circuit member 21 and the solder bump S2 on the electrode 22 are cooled while the circuit member 21 is separated from the solder bump forming member 1. As a result, the electrode 22 and the solder bump S2 formed by the melting of solder particles S1 are fixed together and electrically connected. The electrical connection between the electrode 22 and the solder bump S2 gives rise to the circuit member 21A with solder bumps.

[0062] As described above, this solder bump formation method comprises the steps of: preparing a solder bump forming member having a plurality of recesses, the components of which the recesses have deformable parts that can be deformed at the melting point of the solder particles; arranging the solder particles held in the recesses of the solder bump forming member opposite an electrode; heating the electrode to a temperature above the melting point of the solder particles; and pressing the electrode against the solder bump forming member. In this solder bump formation method, when heat is applied by pressing the electrode, the deformable parts deform, and the solder particles held in the recesses can be exposed to the electrode side. Therefore, the reliability of transferring solder particles to the electrode can be ensured even without aligning the shape of the solder particles.

[0063] Solder particles S1 may undergo rapid oxidation upon heating in the atmosphere, which could inhibit their wetting and spreading onto the electrode 22. Therefore, the atmosphere during heating and pressurizing in step S03 may be a deoxygenated atmosphere. The deoxygenated atmosphere may be an inert gas atmosphere using nitrogen, argon, etc., or a vacuum atmosphere. As the furnace, a reflow oven (under nitrogen atmosphere) or a vacuum reflow oven, which are commonly used in solder joining processes, can be used. Alternatively, a conveyor-type reflow oven or a batch-type (chamber-type) reflow oven under nitrogen atmosphere can be used. When using these reflow ovens, performing a vacuum step after the solder has melted can remove air bubbles (voids) in the solder bump S2.

[0064] Furthermore, due to the influence of the oxide film, solder particles S1 may not melt even when heated to a temperature above their melting point, or wetting may not occur. Therefore, the process may further include a step before step S02 or between step S02 and step S03 in which at least one of the solder particles S1 and the electrode 22 is exposed to a reducing atmosphere. 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 wetting of the solder particles S1 on the electrode 22 can be efficiently promoted. The process in step S03 may also be carried out under a reducing atmosphere. For example, hydrogen gas, hydrogen radicals, formic acid gas, etc., can be used to form the reducing atmosphere. As for the furnace, a hydrogen reduction furnace, hydrogen reflow furnace, hydrogen radical furnace, formic acid furnace, vacuum furnaces of these, continuous furnaces, conveyor furnaces, etc., can be used.

[0065] After forming the solder bump-equipped circuit member 21A, the connecting structure 41 is formed. First, the other circuit member 31 is supplied toward the second implementation area R3 (step S04). In step S04, the circuit member 31 is supplied from the third supply unit 17 to the second implementation area R3 so that the electrodes 32 face upward. The circuit member 31 supplied to the second implementation area R3 may have an underfill material 42 placed so as to cover the electrodes 32.

[0066] Next, in the second implementation area R3, the solder bump-equipped circuit member 21A and the circuit member 31 are placed facing each other (step S05). In step S05, as shown in Figure 8, the stage 12 is displaced while the solder bump-equipped circuit member 21A is held in suction to the heating and pressing head 16, and the solder bump-equipped circuit member 21A is placed 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 with the imaging device 15A, and the position of the alignment mark on the solder bump-equipped circuit member 21A side is confirmed with the imaging device 15B, thereby aligning the electrode 22 of the solder bump-equipped circuit member 21A with the electrode 32 of the circuit member 31.

[0067] Next, heating and pressurizing are performed on the circuit members 21 and 31 via the solder bump S2 (step S06). In step S06, as shown in Figure 9, the circuit member 21A with the solder bump, which is adsorbed onto the heating and pressurizing head 16, is lowered toward the circuit member 31 on the stage 12, the solder bump S2 is sandwiched between the electrode 22 of the circuit member 21A and the electrode 32 of the circuit member 31, and the heating and pressurizing head 16 is heated to a temperature above the melting point of the solder particles S1 (for example, around 130°C to 260°C), thereby melting the solder bump S2 between the electrodes 22 and 32. Alternatively, the heating and pressing head 16 may be heated to a temperature above the melting point of the solder particles S1 (for example, around 130°C to 260°C), and then the solder bump S2 may be sandwiched between the electrode 22 of the circuit member 21A with solder bumps and the electrode 32 of the circuit member 31, thereby melting the solder bump S2 between the electrodes 22 and 32. The pressure applied to the circuit members 21 and 31 by the heating and pressing head 16 can be the same as the pressure used in step S03.

[0068] Subsequently, heating and pressurizing by the heating and pressurizing head 16 are stopped, and the heating and pressurizing 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 electrodes 22 and 32 are cooled. As a result, electrodes 22 and 32 and the solder bumps S2 are fixed together, and the circuit members 21 and 31 are electrically connected to each other. The electrical connection between the circuit members 21 and 31 results in the connection structure 41 shown in Figure 3. Finally, the obtained connection structure 41 is adsorbed onto the heating and pressurizing head 16 and transferred to a predetermined mounting area, completing the process (step S07).

[0069] Step S06 may further include a step of exposing the solder bump S2 and at least one of the electrodes 22, 32 to a reducing atmosphere. Similar to step S03, hydrogen gas, hydrogen radicals, formic acid gas, etc., can be used to form the reducing atmosphere. As for the furnace, similar to step S03, a hydrogen reduction furnace, hydrogen reflow furnace, hydrogen radical furnace, formic acid furnace, vacuum furnaces of these, continuous furnaces, conveyor furnaces, etc., can be used.

[0070] As a method for creating a reducing atmosphere, materials with reducing properties can be used. For example, a flux material or a material containing flux components can be placed near the solder bumps S2 and electrodes 22 and 32. The flux material and materials containing flux components can be pastes, films, etc., containing these materials. Pastes and films containing flux components may also contain thermosetting materials. This allows the thermosetting components to harden simultaneously with the melting of the solder bumps S2, fixing the circuit members 21 and 31 together. The hardening of the thermosetting material may be carried out separately from the melting and heating of the solder bumps S2 by reheating in a later process. [Effects of this disclosure]

[0071] As explained above, in this solder bump formation method, solder particles S1 are held in multiple recesses 3 of the solder bump formation member 1, and solder bumps S2 can be formed on the electrode 22 by applying heat and pressure together with the electrode 22 to be transferred. In this solder bump formation method, the components of the recesses 3 in the solder bump formation member 1 are formed by deformable parts 6 that can be deformed at the melting point of the solder particles S1. As a result, when the electrode 22 is pressed and heat is applied, the deformable parts 6 deform, and the solder particles S1 held in the recesses 3 can be exposed to the electrode 22. Therefore, in this solder bump formation method, the reliability of transferring solder particles S1 to the electrode 22 can be ensured even if the shape of the solder particles S1 is not uniform.

[0072] In this embodiment, the deformable portion 6 is composed of an elastic body 9 having a bulk modulus of 0.5 GPa or more and 5 GPa or less at the melting point of the solder particles S1. By setting the bulk modulus of the deformable portion 6 to 5 GPa or less, when the electrode 22 is pressed against the first surface 2a and heat is applied, the deformable portion 6 deforms sufficiently, allowing the solder particles S1 held in the recess 3 to be more reliably exposed to the electrode side. On the other hand, by setting the bulk modulus of the deformable portion 6 to 0.5 GPa or more, the shape retention of the recess 3 can be maintained, ensuring the holding performance of the solder particles S1 during transfer. This makes it possible to accurately form the solder particles S1 at the target position on the electrode 22. Furthermore, when the deformable portion 6 is composed of an elastic body 9, it is possible to return the deformable portion 6 to its original shape after transferring the solder particles S1 to the electrode 22. This allows the solder bump forming member 1 to be reused.

[0073] In this embodiment, the electrode 22 is heated to a temperature above the melting point of the solder particles S1 while pressed against the first surface 2a of the solder bump forming member 1. As a result, the solder particles S1 are sandwiched between the electrode 22 and the solder bump forming member 1, and the melting of the solder particles S1 and the deformation of the deformation portion 6 occur, thereby suppressing misalignment of the solder bumps S2 formed on the electrode 22. Therefore, it becomes possible to form solder particles S1 at the target position on the electrode 22 with greater precision.

[0074] In this embodiment, solder particles S1 are individually placed in each of the multiple recesses 3. This allows solder particles S1 with a relatively large particle size to be transferred to the electrode 22 with a certain degree of reliability.

[0075] In this embodiment, the average particle diameter of the solder particles S1 is 1 μm to 35 μm. When using minute solder particles S1 within this range, it is generally difficult to standardize the shape of the solder particles S1. However, by applying the above method, the reliability of transferring the solder particles S1 to the electrode 22 can be ensured even without standardizing the shape of the solder particles S1. [Differentiation]

[0076] This disclosure is not limited to the embodiments described above. For example, in the example shown in Figure 1, the deformable portion 6 is provided with a thickness corresponding to the depth of the recess 3, extending from the first surface 2a to the second surface 2b, but the thickness of the deformable portion 6 is not limited to this. For example, as shown in the solder bump forming member 1A in Figure 10(a), the thickness T of the deformable 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 adjacent recesses 3, 3 is composed of the deformable portion 6. Therefore, the first surface 2a side of the inner wall surface 3a of the recess 3 is composed of the deformable 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.

[0077] As shown in the example in Figure 10(a), when the thickness T of the deformed portion 6 is smaller than the depth D of the recess 3, the solder particles S1 held in the recess 3 may protrude towards the first surface 2a side beyond the interface between the deformed portion 6 and the base portion 7. That is, the height H of the solder particles S1 may satisfy H > DT with respect to the depth D of the recess 3 and the thickness T of the deformed portion 6. This ensures reliable contact between the solder particles S1 and the electrode 22 when the deformed portion 6 is deformed.

[0078] Furthermore, from the viewpoint of ensuring sufficient deformation of the deformable portion 6, even if the thickness T of the deformable portion 6 is smaller than the depth D of the recess 3, the deformable 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 deformable 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 it may be provided with a thickness of 4 / 5 or more of the depth D of the recess 3.

[0079] Furthermore, as shown in Figure 10(b), for example, the solder bump forming member 1B, the thickness T of the deformed portion 6 may be greater than the depth D of the recess 3. In this case, the entire partition wall portion 8 separating adjacent recesses 3, 3 becomes the deformed portion 6, and both the inner wall surface 3a and the bottom surface 3b of the recess 3 are composed of the deformed portion 6. The interface between the deformed 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 shown in Figure 10(c), the solder bump forming member 1C may not have a base portion 7, and the entire main body portion 2 may be composed of the deformed portion 6.

[0080] In the above embodiment, all solder particles S1 do not protrude beyond the opening surface of the recess 3. However, this disclosure ensures reliable transfer of solder particles S1 to the electrode 22 even if the height of the solder particles S1 in the recess 3 is not uniform. Therefore, some or all of the solder particles S1 may protrude beyond the opening surface of the recess 3. That is, as shown in Figure 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.

[0081] In the above embodiment, a configuration in which a single solder particle S1 is placed in each of the multiple recesses 3 was illustrated, but multiple solder particles S1 may be placed in each of the multiple recesses 3. In this case, for example, as shown in Figure 11(b), multiple solder particles S1 with a smaller average particle diameter than those in the example of Figure 1 may be placed in the recesses 3. In this case, it becomes easier to adjust the volume of solder particles S1 held in the recesses 3, and it becomes easier to make the size and height of the solder bumps S2 formed on the electrodes 22 within a certain range. In addition, the probability of contact between the electrodes 22 and the solder particles S1 can be increased, and the formation of solder bumps S2 on the electrodes 22 can be carried out more reliably. When multiple solder particles S1 are placed in the recesses 3, as described above, the CV value of the solder particles S1 may be 20% or less. This ensures sufficient continuity reliability and insulation reliability when connecting circuit members 21 and 31 using solder bumps S2.

[0082] Even when multiple solder particles S1 are placed within the recess 3, the force acting between the solder particles S1 and the partition wall 8 (for example, intermolecular forces such as van der Waals forces) is considered to be greater than the gravitational force acting on the solder particles S1. Therefore, even when the recess 3 is oriented downwards, the solder particles S1 can remain within the recess 3. If the outer surface of the solder particles S1 has a flat portion, and this flat portion is in contact with the inner wall surface 3a or the bottom surface 3b of the recess 3, the detachment of the solder particles S1 from the recess 3 can be more effectively prevented. [Explanation of Symbols]

[0083] 1, 1A~1C... Solder bump forming member, 3... Recess, 6... Deformed part, 9... Elastic body, 21... Circuit member, 22... Electrode, S1... Solder particle, S2... Solder bump.

Claims

1. A solder bump formation method for forming solder bumps on electrodes of circuit components, A step of preparing a solder bump forming member having multiple recesses, wherein the components of the recesses have deformable parts that can be deformed at the melting point of the solder particles, A step of arranging the solder particles held in the recess of the solder bump forming member opposite the electrode, A step of heating the electrode to a temperature above the melting point of the solder particles, The process includes pressing the electrode against the solder bump forming member, A solder bump forming method comprising deforming the deformable portion to bring the solder particles held in the recess into contact with the electrode, thereby transferring the solder particles to the electrode and forming a solder bump.

2. The solder bump forming method according to claim 1, wherein the electrode is pressed against the solder bump forming member and heated to a temperature above the melting point of the solder particles.

3. The solder bump forming method according to claim 1, wherein the solder particles are individually placed in each of the plurality of recesses.

4. The solder bump forming method according to claim 1, wherein a plurality of solder particles are arranged in each of the plurality of recesses.

5. The solder bump formation method according to claim 4, wherein the C.V. value of the solder particles is 20% or less.

6. The solder bump formation method according to any one of claims 1 to 5, wherein the average particle size of the solder particles is 1 μm to 35 μm.

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