Magnetic-field melting solder, and joining method in which same is used

Abstract

A magnetic-field melting solder that melts by the action of an AC magnetic field is provided. The magnetic-field melting solder includes solder material; and magnetic material composing of ferrite or Ni, a proportion of the magnetic material to the entire magnetic-field melting solder being 0.005% to 5% by weight. A joining method using the magnetic-field melting solder includes providing the magnetic-field melting solder between an electrode on a substrate and an electrode of an electronic component, and joining together the electrode on the substrate and the electrode of the electronic component by generating an AC magnetic field around the substrate and thereby melting the magnetic-field melting solder.

Claims

1-8. (canceled)

9. A Magnetic-field melting solder that melts by action of an AC magnetic field, the magnetic-field melting solder comprising: solder material; and magnetic material composing of ferrite or Ni, a proportion of the magnetic material to the entire magnetic-field melting solder being 0.005 to 5% by weight.

10. The magnetic-field melting solder according to claim 9, wherein an upper limit of the proportion is 0.9% by weight.

11. The magnetic-field melting solder according to claim 9, wherein a lower limit of the proportion is 0.1% A by weight.

12. The magnetic-field melting solder according to claim 9, further comprising: a solder layer containing the solder material; and a magnetic layer containing the magnetic material by being provided on a surface of the solder layer.

13. The magnetic-field melting solder according to claim 9, further comprising: solder particles containing the solder material; and magnetic particles containing the magnetic material by being provided inside the solder particles.

14. The magnetic-field melting solder according to claim 9, further containing flux.

15. A joining method using the magnetic-field melting solder that melts by action of an AC magnetic field, the magnetic-field melting solder comprising: solder material; and magnetic material composing of ferrite or Ni, a proportion of the magnetic material to the entire magnetic-field melting solder being 0.005 to 5% by weight, the method comprising: providing the magnetic-field melting solder between an electrode on a substrate and an electrode of an electronic component; and joining together the electrode on the substrate and the electrode of the electronic component by generating an AC magnetic field around the substrate and thereby melting the magnetic-field melting solder.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0031] FIG. 1 is a schematic sectional view of a solder preform resulting from application of a solder according to an embodiment;

[0032] FIG. 2 is a schematic sectional view of a solder ball resulting from application of a solder according to the embodiment;

[0033] FIG. 3 is a schematic sectional view of a solder paste resulting from application of a solder according to the embodiment;

[0034] FIG. 4 is a diagram showing an example of a first joining method using the solder according to the embodiment; and

[0035] FIG. 5 is a diagram showing an example of a second joining method using the solder according to the embodiment.

DESCRIPTION OF EMBODIMENTS

[0036] First, solder according to an embodiment of the present invention will be described. Note that when a numerical value range is indicated by “to,” the values at the upper and lower ends are included in the range as the lower and upper limits.

1. Magnetic-Field Melting Solder

[0037] The solder according to the present embodiment is the magnetic-field melting solder that melts by the action of an AC magnetic field. The solder according to the present embodiment contains magnetic material and solder material.

1.1 Magnetic Material

[0038] The magnetic material has the property of generating heat due to at least hysteresis losses when placed in an AC magnetic field. The reason for the reference to “at least hysteresis losses” is that eddy-current losses are conceivable. When the magnetic material is a conductor, the magnetic material generates heat due to hysteresis losses and eddy-current losses. The magnetic material is not specifically limited. For example, one metal selected from among ferromagnetic metal, paramagnetic metal, and diamagnetic metal can be used as the magnetic material.

[0039] Examples of the ferromagnetic metal include Ni, Co, Fe, Gd, and Tb. Examples of the paramagnetic metal include Y, Mo, and Sm. Examples of the diamagnetic metal include Cu, Zn, and Bi. Examples of the magnetic material include an alloy, an oxide, or a nitride containing at least one of the metals mentioned above. Examples of ferromagnetic metal oxides include Fe.sub.3O.sub.4, γ-Fe.sub.2O.sub.3, and ferrite composed principally of Fe.sub.3O.sub.4. Examples of paramagnetic metal oxides include Nd.sub.2O.sub.3, Tb.sub.3O.sub.4, and Sm.sub.2O.sub.3. Examples of diamagnetic metal oxides include CoO, NiO, α-Fe.sub.2O.sub.3, and Cr.sub.2O.sub.3. Examples of ferromagnetic metal nitrides include Fe.sub.3N.

[0040] The stronger the magnetism of the magnetic material, the larger the hysteresis losses. Increases in hysteresis losses result in an increased amount of generated heat per unit time. The increased amount of generated heat per unit time facilitates heating of the surroundings by the magnetic material. Thus, from the viewpoint of facilitating heating by the magnetic material, preferably the magnetic material has ferromagnetism. Specifically, it is preferable to select at least one magnetic material from ferromagnetic metals, oxides and nitrides of the ferromagnetic metals, ferromagnetic alloys, and oxides and nitrides of the ferromagnetic alloys.

[0041] The proportion of the magnetic material is 0.005% to 20% by weight (wt %). The proportion is calculated with reference to the entire magnetic-field melting solder. The reason why the upper limit is set to 20% by weight is that a value larger than 20% by weight will make it difficult for the solder in a molten state to cohere and will obstruct an original joining function of the solder. From the viewpoint of reducing the impact on the joining function, preferably the upper limit is 5% by weight, more preferably 0.9% by weight, and still more preferably 0.5% by weight.

1.2 Solder Material

[0042] The solder material has the property of generating heat due to at least eddy-current losses when placed in an AC magnetic field. The reason for the reference to “at least eddy-current losses” is that hysteresis losses are conceivable. When solder material has magnetism, the solder material generates heat due to eddy-current losses and hysteresis losses. When the solder material generates heat with its temperature exceeding the melting point (which refers to solidus temperature or liquidus temperature; the same applies hereinafter), the solder material melts.

[0043] The magnetic material placed in the AC magnetic field generates heat and rises in temperature more quickly than the solder material. Therefore, when the solder material is placed in the same AC magnetic field as the magnetic material, the solder material is heated by the surrounding magnetic material. That is, when the solder material and the magnetic material are placed in the same AC magnetic field, the rate of temperature rise increases compared to when the solder material is placed singly in the AC magnetic field and the melting point is exceeded in a shorter time.

[0044] The solder material is not specifically limited and any of various types of solder alloy can be used. The various types of solder alloy include binary alloys and ternary and further multi-element alloys. Examples of the binary alloys include Sn—Sb alloys, Sn—Pb alloys, Sn—Cu alloys, Sn—Ag alloys, Sn—Bi alloys, and Sn—In alloys. Examples of the multi-element alloys include alloys produced by adding one or more metals selected from the group consisting of Sb, Bi, In, Cu, Zn, As, Ag, Cd, Fe, Ni, Co, Au, Ge, and P to any of the binary alloys described above.

1.3 Flux

[0045] The solder according to the present embodiment contains flux as an optional component. The flux is not specifically limited, and a typical flux may be used. The flux includes a resin (base resin), a solvent, and various additives. Examples of the resin include rosin-based resins, acrylic resins, polyester, polyethylene, polypropylene, polyamide, epoxy resins, and phenol resins. Examples of the solvent include alcohols such as ethanol, isopropyl alcohol, and butanol; hydrocarbons such as toluene and xylene; esters such as isopropyl acetate and butyl benzoate; and glycol ethers such as ethyleneglycol and hexyl diglycol. Examples of the various additives include activators, thixotropic agents, antioxidants, surface active agents, antifoaming agents, and corrosion inhibitors.

[0046] When the solder according to the present embodiment contains a flux, there is no particular limit to the proportion of the flux to the entire magnetic-field melting solder. The proportion of the flux is, for example, 5% to 95% by weight.

2. Concrete Examples of Magnetic-Field Melting Solder

2.1 Solder Preform

[0047] The solder according to the present embodiment is applied to solder preforms. Examples of shapes of solder preforms include a ribbon shape, a disk shape, a washer shape, a chip shape, and a ring shape. FIG. 1 is a schematic sectional view of a solder preform 10 resulting from application of the solder according to the present embodiment. As shown in FIG. 1, the solder preform 10 includes a solder layer 11 and a magnetic layer 12.

[0048] The solder layer 11 contains the solder material, but does not contain the magnetic material. The solder layer 11 is a typical solder preform manufactured by a method generally known in the solder industry. The flux may be included inside the solder layer 11. The flux is not specifically limited, and any of various types of flux is used. A surface of the solder layer 11 may be coated with the flux.

[0049] The magnetic layer 12 is provided on the surface of the solder layer 11. The magnetic layer 12 contains the magnetic material and a binder, but does not contain the solder material. The magnetic layer 12 is formed by applying a mixture of magnetic material and the binder to the surface of the solder layer 11. The binder is not specifically limited as long as the binder keeps the magnetic layer 12 from separating from the solder layer 11. Examples of the binder include flux.

2.2 Solder Ball

[0050] The solder according to the present embodiment is also applied to solder balls. Solder balls are used, for example, for semiconductor packages such as BGAs (ball grid arrays). The solder balls are manufactured by a method generally known in the solder industry.

[0051] FIG. 2 is a schematic sectional view of solder balls 20 resulting from application of the solder according to the present embodiment. As shown in FIG. 2, each of the solder balls 20 contains a solder particle 21 and a magnetic particle 22. The solder particle 21 contains the solder material, but does not contain the magnetic material. The surfaces of the solder particle 21 may be coated with flux. The flux is not specifically limited, and any of various types of flux is used. The magnetic particle 22 is provided inside the solder particle 21. That is, the magnetic particle 22 makes up a core of the solder ball 20. The magnetic particle 22 contains the magnetic material, but does not contain the solder material.

2.3 Solder Paste

[0052] The solder according to the present embodiment is also applied to solder paste. FIG. 3 is a schematic sectional view of solder paste 30 resulting from application of the solder according to the present embodiment. As shown in FIG. 3, the solder paste 30 contains solder particles 31, magnetic particles 32, and flux 33. The solder particles 31 contain solder material, but do not contain magnetic material. The magnetic particles 32 contain magnetic material, but do not contain solder material. The flux 33 is added as a binder between the solder particles 31 and the magnetic particles 32. The flux 33 is not specifically limited, and any of various types of flux is used.

3. Examples of Joining Method Using Magnetic-Field Melting Solder

3.1 Joining Using Induction Heating Device

[0053] FIG. 4 is a diagram showing an example of a first joining method using the solder according to the present embodiment. An induction heating device 40 shown in FIG. 4 includes a heating coil 41, an inverter circuit 42, a control circuit 43, a conveyer 44, and a temperature sensor 45. Note that the solder according to the present embodiment is placed between an electronic component EC and a printed board PB as “solder SD” for use to join together an electrode of the electronic component EC and an electrode pattern printed on the printed board PB. Examples of the electronic component EC include an IC chip.

[0054] The heating coil 41 is provided behind the conveyer 44. The heating coil 41 heats an entire circuit board CB including the solder SD by induction heating. By being supplied with electric power from an AC power source (not shown), the inverter circuit 42 supplies high frequency current to the heating coil 41. The control circuit 43 is made up of a microcomputer. The control circuit 43 controls driving of the inverter circuit 42 based on various signals inputted to the control circuit 43. The various signals include a drive request signal and a signal that indicates the temperature around the circuit board CB. The conveyer 44 conveys the circuit board CB. The temperature sensor 45 detects the temperature around the circuit board CB. The temperature sensor 45 may generate temperature distribution information by image processing.

[0055] In the example shown in FIG. 4, as the conveyer 44 is driven, the circuit board CB is conveyed to the position of the heating coil 41. The conveyance of the circuit board CB is stopped at this position, and the inverter circuit 42 is driven based on the drive request signal. Consequently, an AC magnetic field is generated around the circuit board CB, and the magnetic material contained in the solder SD generates heat due to eddy-current losses and hysteresis losses. Besides, the solder material of the solder SD melts as a result of heat generation caused by eddy-current losses as well as heating by the magnetic material. That is, the solder SD melts. When an ending condition is satisfied, the driving of the inverter circuit 42 is stopped, or the circuit board CB is conveyed to outside the position of the heating coil 41 as the conveyer 44 resumes being driven. Subsequently, as the solder SD is cooled, the electrode of the electronic component EC and the electrode pattern are electrically connected to each other. Note that the ending condition is, for example, that a predetermined period of time elapses after the temperature around the circuit board CB reaches the melting point of the solder SD.

[0056] 3.2 Joining by Microwave Heating Device

[0057] FIG. 5 is a diagram showing an example of a second joining method using the solder according to the present embodiment. A microwave heating device 50 shown in FIG. 5 includes a cavity resonator 51, a microwave feeder 52, a conveyer 53, a controller 54, an electromagnetic wave sensor 55, and a temperature sensor 56. Note that as with the example shown in FIG. 4, the solder according to the present embodiment is placed between the electronic component EC and the printed board PB.

[0058] The cavity resonator 51 has a cylindrical interior space in which microwave irradiation is performed. The microwave feeder 52 generates a microwave as a specific standing wave in the interior space. Examples of the specific standing wave include a standing wave called TM110. The conveyer 53 conveys the circuit board CB by passing through the interior space. Based on various signals, the controller 54 adjusts the frequency of the microwave emitted from the microwave feeder 52. The various signals include a drive request signal, a signal indicating the resonance status of the standing wave generated in the interior space, and a signal indicating the temperature around the circuit board CB. The electromagnetic wave sensor 55 detects the resonance status of the standing wave. The temperature sensor 56 detects the temperature around the circuit board CB. The temperature sensor 56 may generate temperature distribution information by image processing.

[0059] In the example shown in FIG. 5, the controller 54 drives the microwave feeder 52 based on the drive request signal. The controller 54 calculates a target value (target frequency) of oscillation frequency of the microwave based on the signal indicating the resonance status of the standing wave and the controller 54 outputs the target value to the microwave feeder 52. When it is verified that a standing wave has been formed, the conveyer 53 is driven and the circuit board CB is conveyed to a specific position in the cavity resonator 51. Examples of the specific position include the position of a central axis of the interior space. The target frequency is calculated repeatedly by the controller 54 during the conveyance of the circuit board CB. As the target frequency is calculated repeatedly, a region extremely low in electric field intensity and high in magnetic field intensity is created at the specific position.

[0060] When the circuit board CB passes the specific position, an AC magnetic field being generated at this position acts on the circuit board CB. Consequently, the magnetic material contained in the solder SD generates heat due to eddy-current losses and hysteresis losses. Besides, the solder material of the solder SD melts as a result of heat generation caused by eddy-current losses as well as heating by the magnetic material. That is, the solder SD melts. When the ending condition is satisfied, the driving of the microwave feeder 52 is stopped, or the circuit board CB is conveyed to outside the microwave feeder 52 as the driving of the conveyer 53 is resumed. Subsequently, as the solder SD is cooled, the electrode of the electronic component EC and the electrode pattern are electrically connected to each other. Based on the signal indicating the temperature around the circuit board CB, the controller 54 adjusts microwave output. For example, when the temperature around the circuit board CB reaches a predetermined temperature, the controller 54 reduces output. As another example, the closer the temperature around the circuit board CB is to the melting point of the solder SD, the more greatly the controller 54 reduces output.

4. EXAMPLES

[0061] Next, the present invention will be described in detail below with reference to Examples.

4.1 Example 1

[0062] Sample paste was prepared by mixing solder paste (produced by Senju Metal Industry Co., Ltd.; composition: Sn-3.0Ag-0.5Cu; melting point: 217° C. to 220° C.) with powder of magnetic material in a mortar. Next, using a blade coating method, samples Ex.1 to Ex.6 of a predetermined size (1 cm long by 1 cm wide by 60 μm thick) were produced on a polyimide film. The compositions of samples Ex.1 to Ex.6 are shown in Table 1.

[0063] Next, the polyimide film with sample Ex.1 formed thereon was placed at the position of the central axis of the cylindrical cavity resonator. The cavity resonator is the cavity resonator 51 described in FIG. 5. Next, a standing wave was formed in the cavity resonator in TM110 mode and sample Ex.1 was heated. The output power of the microwave was 160 W. During microwave irradiation, the temperature T of sample Ex.1 was measured using a thermocamera and the time required for the temperature T to reach a melting point TM of the solder material was measured. The rate of temperature rise was calculated by dividing the difference between the initial measurement value of the temperature T and the melting point TM by measured time requirement. The rates of temperature rise of samples Ex.2 to Ex.6 were calculated using the same technique as the one used for sample Ex. 1.

[0064] Comparison sample Re.1 with a size of 1 by 1 cm.sup.3 was produced using the solder paste alone. The rate of temperature rise of sample Re.1 was calculated using the same technique as the one used for samples Ex. 1 to Ex.6.

[0065] After the rates of temperature rise of the samples were calculated, the samples were evaluated with reference to the rate of temperature rise of sample Re. 1. Any sample with a rate of temperature rise higher than that of sample Re.1 was evaluated as “A” and any sample with a rate of temperature rise lower than that of sample Re.1 was evaluated as “F.” Evaluation results are shown in Table 1.

TABLE-US-00001 TABLE 1 SOLDER MATERIAL MAGNETIC MATERIAL RATE OF HEATING (wt %) (wt %) TEMPERATURE METHOD Sn—3.0Ag—0.5Cu Ni Fe3O4 RISE Ex. 1 MW_160 W 99.9 0.1 0 A Ex. 2 MW_160 W 99.5 0.5 0 A Ex. 3 MW_160 W 99 1 0 A Ex. 4 MW_160 W 99.9 0 0.1 A Ex. 5 MW_160 W 99.5 0 0.5 A Ex. 6 MW_160 W 99 0 1 A Re. 1 MW_160 W 100 0 0 —

[0066] As shown in Table 1, the rates of temperature rise of all samples Ex.1 to Ex.6 were higher than the rate of temperature rise of sample Re.1. It can be seen from this that the addition of magnetic material makes samples of solder material higher in the rate of temperature rise than the comparison sample.

4.2 Example 2

[0067] Using the same technique as the one used for sample Ex.1, samples Ex.7 to Ex.14 were produced. The compositions of samples Ex.7 to Ex.14 are shown in Table 2. Next, using the same technique as the one used for sample Ex.1, the rates of temperature rise of samples Ex.7 to Ex.14 were calculated. Note that the output power of the microwave was 50 W. After the rates of temperature rise of the samples were calculated, the samples were evaluated with reference to the rate of temperature rise of sample Re.1. Evaluation results are shown in Table 2.

TABLE-US-00002 TABLE 2 SOLDER RATE OF MW MATERIAL (wt %) MAGNETIC MATERIAL (wt %) TEMPERATURE OUTPUT Sn—3.0Ag—0.5Cu Co Y Fe—Ni Nd2O3 Tb3O4 Sm2O3 Co3O4 Fe3N RISE Ex. 7 50 W 99.8 0.2 A Ex. 8 50 W 99.8 0.2 A Ex. 9 50 W 99.8 0.2 A Ex. 10 50 W 99.8 0.2 A Ex. 11 50 W 99.8 0.2 A Ex. 12 50 W 99.8 0.2 A Ex. 13 50 W 99.8 0.2 A Ex. 14 50 W 100 0.2 A

[0068] As shown in Table 2, the rates of temperature rise of all samples Ex.7 to Ex.14 were higher than the rate of temperature rise of sample Re.1. It can be seen from this that the effect of increasing the rate of temperature rise is obtained regardless of the type of magnetic material. When attention was paid to the type of magnetic material, it was found that magnetic materials (Co, Fe—Ni, and Fe.sub.3N) having ferromagnetism tend to be higher in the rate of temperature rise than are magnetic materials (Y, Nd.sub.2O.sub.3, Tb.sub.3O.sub.4, Sm.sub.2O.sub.3, and Co.sub.3O.sub.4) having paramagnetism or diamagnetism.

4.3 Example 3

[0069] Using low-temperature solder paste (produced by Senju Metal Industry Co., Ltd.; composition: Sn-58Bi; melting point: 139° C.), high-temperature solder paste (produced by Senju Metal Industry Co., Ltd.; composition: Sn-10Sb; melting point: 245° C. to 266° C.), and magnetic material, samples Ex.15 to Ex.36 were produced by the same technique as the one used for sample Ex.1. Comparison samples Re.2 and Re.3 were produced using the solder paste alone. The compositions of samples Ex.15 to Ex.36 and samples Re.2 and Re.3 are shown in Table 3. Next, the rates of temperature rise of the samples were calculated. After the rates of temperature rise of the samples were calculated, the samples were evaluated with reference to the rate of temperature rise of the comparison samples. Specifically, among samples Ex.15 to Ex.30, any sample with a rate of temperature rise higher than that of sample Re.2 was evaluated as “A” and any sample with a rate of temperature rise lower than that of sample Re.2 was evaluated as “F.” Samples Ex.31 to Ex.36 were evaluated in the same manner as above with reference to sample Re.3. Evaluation results are shown in Table 3.

TABLE-US-00003 TABLE 3 SOLDER MAGNETIC RATE OF MATERIAL MATERIAL TEMPER- MW (wt %) (wt %) ATURE OUTPUT Sn—58Bi Sn—10Sb Ni Fe3O4 RISE Ex. 15 50 W 99.99 0.01 A Ex. 16 50 W 99.95 0.05 A Ex. 17 50 W 99.9 0.1 A Ex. 18 50 W 99.5 0.5 A Ex. 19 50 W 99.1 0.9 A Ex. 20 50 W 99 1 A Ex. 21 50 W 90 10 A Ex. 22 50 W 80 20 A Ex. 23 50 W 99.99 0.01 A Ex. 24 50 W 99.95 0.05 A Ex. 25 50 W 99.9 0.1 A Ex. 26 50 W 99.5 0.5 A Ex. 27 50 W 99.1 0.9 A Ex. 28 50 W 99 1 A Ex. 29 50 W 90 10 A Ex. 30 50 W 80 20 A Ex. 31 160 W 99.9 0.1 A Ex. 32 160 W 99.5 0.5 A Ex. 33 160 W 99 1 A Ex. 34 160 W 99.9 0.1 A Ex. 35 160 W 99.5 0.5 A Ex. 36 160 W 99 1 A Re. 2 50 W 100 — Re. 3 160 W 100 —

[0070] As shown in Table 3, the rates of temperature rise of all samples Ex.15 to Ex.30 were higher than the rate of temperature rise of sample Re.2. The rates of temperature rise of all samples Ex.31 to Ex.36 were higher than the rate of temperature rise of sample Re.3. It can be seen from this that the effect of increasing the rate of temperature rise is obtained regardless of the type of solder material.

4.4 Example 4

[0071] Using the same material as the one used for sample Ex.3, samples Ex.37 to Ex.56 with varied proportions of the magnetic material were produced by the same technique as the one used for sample Ex.1. Next, the samples were evaluated in terms of maximum temperature and cohesiveness. The maximum temperature is a maximum value of sample temperature for a period of five seconds from the start of microwave irradiation. Any sample whose maximum temperature was equal to or higher than the melting point of the solder material was evaluated as “A” and any other sample was evaluated as “F.” The cohesiveness was evaluated by visually checking the samples after melting. Any sample whose solder material was judged to have no problem in practical use in terms of cohesion was evaluated as “A.” Any sample judged to be at or above a certain level in terms of the cohesion of solder material was evaluated as “C” and any other sample was evaluated as “F.” Evaluation results are shown in Table 4.

TABLE-US-00004 TABLE 4 SOLDER MAGNETIC MAXI- MW MATERIAL MATERIAL MUM COHE- OUT- (wt %) (wt %) TEMPER- SIVE- PUT Sn—58Bi Ni Fe3O4 ATURE NESS Ex. 37 50 W 99.995 0.005 F A Ex. 38 50 W 99.99 0.01 F A Ex. 39 50 W 99.95 0.05 F A Ex. 40 50 W 99.9 0.1 A A Ex. 41 50 W 99.5 0.5 A A Ex. 42 50 W 99.1 0.9 A A Ex. 43 50 W 99 1 A A Ex. 44 50 W 95 5 A A Ex. 45 50 W 90 10 A C Ex. 46 50 W 80 20 A C Ex. 47 50 W 99.995 0.005 F A Ex. 48 50 W 99.99 0.01 F A Ex. 49 50 W 99.95 0.05 F A Ex. 50 50 W 99.9 0.1 A A Ex. 51 50 W 99.5 0.5 A A Ex. 52 50 W 99.1 0.9 A A Ex. 53 50 W 99 1 A A Ex. 54 50 W 95 5 A A Ex. 55 50 W 90 10 A C Ex. 56 50 W 80 20 A C

[0072] As shown in Table 4, the maximum temperatures of samples Ex.40 to Ex.46 and Ex.50 to Ex.56 reached the melting point within five seconds from the start of microwave irradiation. On the other hand, the maximum temperatures of samples Ex.37 to Ex.39 and Ex.47 to Ex.49 did not reach the melting point within five seconds from the start of microwave irradiation. It can be seen from this that when the proportion of the magnetic material is small, the solder material is difficult to melt in a short time. Thus, the maximum temperature was evaluated by changing the output conditions of the microwave, and it was found that by increasing output, the maximum temperature can be adjusted to a desired value. Therefore, it was also found that it is desirable to change the microwave output according to the type and proportion of magnetic material.

[0073] As shown in Table 4, samples Ex.37 to Ex.44 and Ex.47 to Ex.54 were judged to have no problem in practical use in terms of the cohesion of solder material. On the other hand, samples Ex.45, Ex.46, Ex.55, and Ex.56 were judged to be at or above a certain level in terms of the cohesion of solder material. Thus, it was found that when the proportion of the magnetic material is 5% by mass or below, the effect of increasing the rate of temperature rise can be obtained while reducing the impact on the original joining function of the solder.

REFERENCE SIGNS LIST

[0074] 10 Solder preform [0075] 11 Solder layer [0076] 12 Magnetic layer [0077] 20 Solder ball [0078] 21 Solder particle [0079] 22 Magnetic particle [0080] 30 Solder paste [0081] 31 Solder particle [0082] 32 Magnetic particle [0083] 33 Flux [0084] 40 Induction heating device [0085] 41 Heating coil [0086] 42 Inverter circuit [0087] 43 Control circuit [0088] 44, 53 Conveyer [0089] 45, 56 Temperature sensor [0090] 50 Microwave heating device [0091] 51 Cavity resonator [0092] 52 Microwave feeder [0093] 54 Controller [0094] 55 Electromagnetic wave sensor [0095] EC Electronic component [0096] PB Printed board [0097] SD Solder