JP5643972B2 - Metal filler, low-temperature connection lead-free solder, and connection structure - Google Patents

Description

  The present invention relates to a metal filler that can be used for connecting various electronic components, filling vias, and the like, and a lead-free solder containing the metal filler, particularly a low-temperature lead-free solder. The present invention also relates to a connection structure obtained by using the lead-free solder, and a component mounting board having the connection structure and the substrate.

  Conventionally, Sn-37Pb eutectic solder having a melting point of 183 ° C. has generally been used as a solder material used in reflow heat treatment. In addition, as a high-temperature solder used in an electronic component or the like that requires high heat resistance, Sn-90Pb high-temperature solder having a solidus wire of 270 ° C. and a liquidus wire of 305 ° C. has been widely used.

  However, in recent years, the harmfulness of Pb has become a problem, as indicated by EU environmental regulations (WEEE, RoHS directive). Therefore, from the viewpoint of preventing environmental pollution, the lead-free solder is rapidly progressing. Under such circumstances, as a substitute for Sn-37Pb eutectic solder, lead-free solder composed of Sn-3.0Ag-0.5Cu having a melting point of about 220 ° C. is typical. As a reflow heat treatment condition for the lead-free solder, a temperature range in which a peak temperature is about 240 ° C. to 260 ° C. is becoming common.

  The above-described lead-free solder composed of Sn-3.0Ag-0.5Cu having a melting point of about 220 ° C. has a higher melting point of the alloy than Sn-37Pb eutectic solder, and therefore the reflow heat treatment conditions also become higher. In recent years, there are concerns about depletion of fossil fuels, global warming, and the like, and it is eager to establish an energy saving process and a low carbon dioxide emission process by lowering the reflow heat treatment temperature. Further, the lowering of the reflow heat treatment temperature is expected from the fact that it is possible to suppress the thermal damage of the electric / electronic equipment and the substrate material, and the range of selection of the usable substrate material is expanded. Currently, typical examples of Pb-free solder materials that can be melt-bonded at low temperatures include Sn-58Bi eutectic solder (melting point 138 ° C.), In (melting point 157 ° C.), Sn-52In alloy solder (melting point 118 ° C.), and the like. (See Patent Documents 1 and 2). However, all of these solder materials have a low melting point, and have a problem that they are remelted when the temperature again becomes higher than the melting point after soldering.

  By the way, the trend of downsizing, weight reduction and higher functionality of electronic devices typified by mobile phones is remarkable, and following this, high-density mounting technology continues to make rapid progress. Various mounting techniques have been developed to effectively use a limited volume, such as incorporating components in a substrate or packaging a plurality of LSIs into one package. However, on the other hand, as the density increases, the number of times that the solder connection portion of the component incorporated in the substrate or the package is subjected to heat treatment in a subsequent process increases. As a result, the problem that the solder is remelted in a later process, the solder flows out from the gap between the component and the sealing resin, and a short circuit occurs between the component electrodes and the like has become apparent.

  Therefore, there is a demand for the development of a lead-free solder material that does not remelt even when subjected to a plurality of heat treatments in the subsequent process for connecting components incorporated in the substrate or package.

  The present inventors have proposed a highly heat-resistant solder material that can be melt-bonded under reflow heat treatment conditions of lead-free solder, for example, a peak temperature of 246 ° C., and does not melt under the same heat-treatment conditions after joining (Patent Document 3). . The metal particles contained in the solder material are a mixture of first metal particles and second metal particles having a lower melting point than the first metal particles. In the technique of Patent Document 3, Sn is used as the second metal particles. When the solder material is subjected to a reflow heat treatment at, for example, 246 ° C. which is equal to or higher than the melting point of Sn (232 ° C.), The metal diffuses between the first metal particles, and a joint having excellent heat resistance is formed. However, considering the need for energy saving and low carbon dioxide emission, and application to substrate materials and electronic equipment with low heat resistance, bonding can be performed at a lower temperature, and after bonding, re-melting is not performed under reflow heat treatment conditions of lead-free solder. Material is desired.

  In view of this, the present inventors have proposed a solder material capable of low-temperature melt bonding at a peak temperature of 149 ° C. or higher and having heat resistance under a heat treatment condition of 260 ° C. after the bonding (Patent Document 4). The conductive filler contained in the solder material is a mixture of first metal particles and second metal particles having a melting point higher than that of the first metal particles.

  Apart from this, a solder paste using a mixture of Cu powder and Sn-Bi based powder alloy has been proposed as a solder paste that includes a plurality of types of metal particles and can be bonded at a low temperature. (See Patent Document 5).

JP 2001-334386 A JP-A-11-239866 International Publication No. 2006/109573 Pamphlet JP 2008-183582 A JP 2008-200788 A

  However, in the technique described in Patent Document 4, there is room for improvement in the bonding strength after bonding, particularly at room temperature. Further, in the technique described in Patent Document 4, since expensive metals such as In and Ag are used for the first metal particles, the raw material cost is high, and the manufacturing cost is high because the alloy composition is complicated. There was a problem. On the other hand, in the technique described in Patent Document 5, Cu powder easily oxidizes and aggregates, and when it absorbs moisture, it aggregates more firmly, which causes a problem in storage stability. Moreover, in the techniques described in Patent Documents 4 and 5, there is room for improvement in the bonding strength after bonding, particularly at room temperature.

  The present invention has been made in view of the above problems, and can be melt-bonded at a temperature lower than the reflow heat treatment conditions of Sn-37Pb eutectic solder (for example, a peak temperature of 160 ° C.), and good bonding at room temperature after bonding. It aims at providing the metal filler which can give intensity | strength. Another object of the present invention is to provide a lead-free solder containing the metal filler, a connection structure obtained by using the lead-free solder, and a component mounting board having the connection structure and the substrate.

[1] A metal filler comprising a mixture of first metal particles and second metal particles,
The first metal particles are Cu alloy particles containing Cu as a main component which is an element present in the highest mass ratio, and further containing In and Sn,
The second metal particles are Bi alloy particles composed of Bi40 to 70% by mass and one or more metals selected from the group consisting of Ag, Cu, In and Sn, and 30 to 60% by mass, and
The metal filler whose quantity of this 2nd metal particle with respect to 100 mass parts of this 1st metal particle is 40-300 mass parts.
[2] The metal filler according to [1], wherein the second metal particle contains Sn.
[3] The metal filler according to [1] or [2], wherein the average particle diameters of the first metal particles and the second metal particles are both in the range of 5 to 25 μm.
[4] The metal filler according to any one of [1] to [3], wherein the first metal particles further contain one or more metals selected from Ag and Bi.
[5] The first metal particles are composed of Ag 5 to 15% by mass, Bi 2 to 8% by mass, Cu 49 to 81% by mass, In 2 to 8% by mass, and Sn 10 to 20% by mass,
In the differential scanning calorimetry (DSC), the first metal particles have at least one exothermic peak observed in the range of 230 to 300 ° C. and at least one endothermic peak observed in the range of 480 to 530 ° C. The metal filler according to any one of the above [1] to [4].
[6] A lead-free solder containing the metal filler according to any one of [1] to [5].
[7] A first electronic component, a second electronic component, and a solder joint that joins the first electronic component and the second electronic component, wherein the solder joint is the above [6] A connection structure formed by reflow heat-treating the lead-free solder described in 1.
[8] A component mounting board having a substrate and the connection structure according to [7] mounted on the substrate.

  The metal filler of the present invention and the lead-free solder containing the metal filler can be melt-bonded under conditions lower than the reflow heat treatment conditions of, for example, Sn-37Pb eutectic solder (for example, a peak temperature of 160 ° C. or higher). The solder joint does not remelt even after multiple heat treatments. Therefore, according to the present invention, an effect of preventing a short circuit due to remelting of solder that occurs between component electrodes and the like can be obtained. Moreover, the metal filler of this invention and the lead-free solder containing this metal filler can give the favorable joint strength at room temperature after joining.

<Metal filler>
The metal filler of the present invention is a metal filler composed of a mixture of first metal particles and second metal particles, and the first metal particles are Cu (copper) as a main component which is an element present in the highest mass ratio. ) And further containing In (indium) and Sn (tin), the second metal particles are Bi (bismuth) 40 to 70% by mass, and Ag (silver), Cu (Bi) alloy particles composed of 30 to 60% by mass of one or more metals selected from the group consisting of (copper), In (indium), and Sn (tin), and second relative to 100 parts by mass of the first metal particles. The amount of metal particles is 40 to 300 parts by mass.

  In the present invention, the melting point of the first metal particles is set higher than the melting point of the second metal particles by the combination of the first metal particles and the second metal particles having the above composition. Thereby, in the reflow heat treatment, the second metal particles having a melting point lower than that of the first metal particles are melted, and an alloying reaction due to thermal diffusion occurs between the first metal particles and the melted second metal particles, A stable alloy phase having a melting point higher than that of the second metal particles is formed. In a typical embodiment, the first metal particles do not melt at the reflow heat treatment temperature when using the lead-free solder according to the present invention. As a result, the lead-free solder containing the metal filler of the present invention can be melt-bonded at a low temperature condition (typically, a temperature lower than the reflow heat treatment condition of Sn-37Pb eutectic solder) and melt-bonded. Later, it has the effect of not being remelted by heat treatment. The possibility of low-temperature melt bonding is advantageous in that it can be used in an energy saving process and a low carbon dioxide emission process, and heat damage of applied electric / electronic devices and substrate materials can be suppressed.

  In the present invention, the combination of the first metal particles and the second metal particles having the above composition can avoid the problem of agglomeration due to moisture absorption that occurs when, for example, Cu powder is used. In the present invention, the first metal particles have a composition containing Cu as a main component and the second metal particles contain a large amount of Bi. As a result, it is possible to provide a metal filler that can be melt-bonded at a low temperature, has a good bonding strength at room temperature after bonding, and reduces the amount of expensive metals such as In and Ag.

[First metal particles]
The first metal particles have Cu as a main component. That is, the mass ratio of Cu is the largest among the elements constituting the first metal particles. The first metal particles further contain In and Sn in addition to Cu. Thereby, the first metal particles can form a metastable alloy phase. The formation of the metastable alloy phase contributes to the promotion of alloying between the first metal particles and the second metal particles, and therefore contributes to the provision of a good bonding strength at the time of fusion bonding at a low temperature.

  The first metal particles further contain one or more metals selected from Ag and Bi, in addition to Cu, In and Sn, from the viewpoint of favorably realizing alloying by thermal diffusion with the second metal particles. Is preferred.

  In a preferred embodiment, the first metal particles are composed of Ag 5 to 15% by mass, Bi 2 to 8% by mass, Cu 49 to 81% by mass, In 2 to 8% by mass, and Sn 10 to 20% by mass. In this case, inevitable impurities may be included.

  In a preferred embodiment, the first metal particles have at least one exothermic peak observed in the range of 230 to 300 ° C. and at least one observed in the range of 480 to 530 ° C. in differential scanning calorimetry (DSC). With two endothermic peaks. The exothermic peak observed within the range of 230 to 300 ° C. indicates that the first metal particles form a metastable alloy phase, and the endothermic peak observed within the range of 480 to 530 ° C. is the first The melting point of the metal particles is shown. In addition, melting | fusing point described in this specification shows the solidus temperature analyzed by differential scanning calorimetry (DSC). The differential scanning calorimetry is typically performed in a measurement range of 40 to 580 ° C. under a nitrogen atmosphere under a temperature increase rate of 10 ° C./min.

  In a more preferred embodiment, the first metal particles are composed of Ag 5 to 15% by mass, Bi 2 to 8% by mass, Cu 49 to 81% by mass, In 2 to 8% by mass, and Sn 10 to 20% by mass, and the first metal The particles have at least one exothermic peak observed in the range of 230-300 ° C. and at least one endothermic peak observed in the range of 480-530 ° C. in differential scanning calorimetry (DSC).

  The average particle size of the first metal particles is preferably in the range of 2 to 30 μm. When the average particle diameter of the first metal particles is 2 μm or more, the specific surface area of the particles becomes small. Therefore, when forming a solder paste from the metal filler of the present invention using, for example, a flux described later, there is an advantage that the contact area between the first metal particles and the flux is reduced and the life of the solder paste is increased. . Furthermore, when the average particle diameter of the first metal particles is 2 μm or more, outgas generated by the reduction reaction of the metal filler by the flux (that is, removal of the oxide film of the metal filler particles) can be reduced in the reflow heat treatment. Voids generated inside the solder connection can be reduced. The average particle diameter of the first metal particles is preferably 30 μm or less from the viewpoint of the adhesive strength of the solder paste. If the particle size becomes too large, the gaps between the particles become large, so the adhesive strength of the solder paste is likely to be impaired, and the component is likely to come off from the mounting of the component to be soldered to the end of the reflow heat treatment. . The average particle diameter of the first metal particles is more preferably in the range of 5 to 25 μm.

  In addition, the average particle diameter in this specification is a value measured with a laser diffraction type particle size distribution measuring apparatus.

[Second metal particles]
A 2nd metal particle consists of 30-60 mass% of 1 or more types of metals chosen from Bi40-70 mass% and Ag, Cu, In, and Sn. In this case, inevitable impurities may be contained. With the above composition, the second metal particles can be melted in the reflow heat treatment, and the alloying by thermal diffusion is favorably realized between the first metal particles and the melted second metal particles.

  The content of Bi in the second metal particles is 40% by mass or more and 70% by mass or less from the viewpoint of enabling fusion bonding at low temperature and obtaining good bonding strength at room temperature after bonding. The content is preferably 50 to 60% by mass.

  The content of one or more metals selected from Ag, Cu, In and Sn in the second metal particles is 30% by mass from the viewpoint of favorably realizing alloying of the first metal particles and the second metal particles. From the viewpoint of allowing a sufficient amount of Bi to be contained in the second metal particles and enabling fusion bonding at a low temperature, it is 60% by mass or less. The content is preferably 40 to 50% by mass.

The second metal particles you contain Sn. In this case, it is possible to provide a metal filler that has good low-temperature meltability and bondability of the metal filler and that provides good bonding strength even by low-temperature melt bonding. The Sn content in the second metal particles is preferably 40 to 50% by mass.

  When the second metal particles contain one or more metals selected from Ag, Cu and In, it is possible to improve ductility, lower melting point, mechanical strength and the like.

  Further, from the viewpoint of low-temperature meltability and bondability, the second metal particles are more preferably Sn—Bi alloy particles, and more preferably a eutectic composition (typically Sn that hardly causes solidification defects and segregation). Sn-Bi alloy particles having -58Bi). Typically, Sn—Bi alloy particles contain only Sn and Bi as constituent elements (however, they may contain inevitable impurities), but they have improved ductility, lower melting point, mechanical strength, etc. For the purpose of improvement, a trace amount of one or more metals selected from Ag, Cu and In may be added.

  The average particle diameter of the second metal particles is preferably in the range of 5 to 40 μm from the same reason as the average particle diameter of the first metal particles, that is, from the viewpoint of the reactivity with the flux and the adhesive strength of the paste. The average particle diameter of the first metal particles is more preferably in the range of 5 to 25 μm.

[Mixture of first metal particles and second metal particles]
The metal filler of the present invention comprises a mixture of first metal particles and second metal particles. In the metal filler which is the mixture, the amount of the second metal particles with respect to 100 parts by mass of the first metal particles (hereinafter also referred to as “mixing ratio of the second metal particles”) is in the range of 40 to 300 parts by mass. When the mixing ratio of the second metal particles is 40 parts by mass or more, the presence of the component that melts during the reflow heat treatment in the metal filler is large, so that fusion bonding at a low temperature can be carried out satisfactorily. Good physical strength is imparted after being joined. When the mixing ratio of the second metal particles is 100 parts by mass or more, better physical strength can be obtained. On the other hand, when the mixing ratio of the second metal particles exceeds 300 parts by mass, the existence ratio of the high melting point stable alloy phase formed by the reaction of the molten second metal particles with the first metal particles is small. Heat resistance cannot be obtained. From the viewpoint of physical strength and heat resistance of the solder joint, the mixing ratio of the second metal particles is preferably in the range of 100 to 300 parts by mass.

  The particle size distribution of the first metal particles and the second metal particles can be determined according to the solder paste application. For example, in screen printing applications, emphasis is placed on plate spillability, and it is preferable to make the particle size distribution broad. In dispensing applications and via filling applications, emphasis is placed on discharge fluidity and hole filling properties, and the particle size distribution is sharp. It is preferable to do this.

  As described above, the average particle diameters of the first metal particles and the second metal particles are preferably in the range of 2 to 30 μm and 5 to 40 μm, respectively, from the viewpoint of the reactivity with the flux and the paste characteristics. Preferably, the average particle diameters of the first metal particles and the second metal particles are both in the range of 5 to 25 μm. As described later, the metal filler of the present invention can form a paste-like lead-free solder, for example, by being combined with a flux. When component mounting is performed using this solder paste, a thin flux layer may be formed on the surface of the solder joint, particularly the fillet portion, formed by reflow heat treatment. If the average particle size of the metal filler is small, the metal particles are likely to be entrained in a state where the fine particles of the metal filler are suspended in the flux layer (that is, the metal particles are separated from each other), and the solder-joined parts are subsequently subjected to a flux cleaning process. In the case of being used, there may be a disadvantage that the metal filler particles flow out into the cleaning liquid and adhere to the parts. When the average particle diameter of the first metal particles and the second metal particles is 5 μm or more, the fine particles of the metal filler are less likely to be entrained in the flux layer during component mounting, and the generation of floating particles in the flux layer can be suppressed. The number of particles flowing out can be reduced. On the other hand, when the average particle diameters of the first metal particles and the second metal particles are both 25 μm or less, the adhesive strength of the solder paste is hardly damaged.

  Melting | fusing point of a 2nd metal particle becomes like this. Preferably it is the range of 80-160 degreeC, More preferably, it is the range of 100-150 degreeC. In an exemplary embodiment, the second metal particles melt at the reflow heat treatment temperature when using the lead-free solder according to the present invention.

  The elemental composition of the first metal particles and the second metal particles defined in this specification can be confirmed by, for example, inductively coupled plasma (ICP) emission analysis. Further, the elemental composition of the particle cross section can be analyzed by using SEM-EDX (characteristic X-ray analyzer).

  As a method for producing each of the first metal particles and the second metal particles, a known method can be adopted as a method for producing fine powder, but a rapid solidification method is preferred. Examples of the method for producing fine powder by the rapid solidification method include a water spray method, a gas spray method, and a centrifugal spray method. Among these, the gas spraying method and the centrifugal spraying method are more preferable because the oxygen content of the particles can be suppressed.

  In the gas spraying method, an inert gas such as nitrogen gas, argon gas, or helium gas can be usually used. Among these, it is preferable to use helium gas having a low specific gravity in that the linear velocity during gas spraying can be increased and the cooling rate can be increased. The cooling rate is preferably in the range of 500 to 5000 ° C./second. In the centrifugal spray method, from the viewpoint of forming a uniform molten film on the upper surface of the rotating disk, the material is preferably sialon, and the disk rotation speed is preferably in the range of 60,000 to 120,000 rpm.

<Lead-free solder>
The present invention also provides a lead-free solder containing the metal filler of the present invention described above. In this specification, “lead-free” means that the lead content is 0.1% by mass or less in accordance with EU environmental regulations. The lead-free solder of the present invention is preferably a solder paste containing a metal filler component and a flux component. The lead-free solder of the present invention more typically comprises a metal filler component and a flux component. The metal filler component may be composed of the metal filler of the present invention described above, or may contain a small amount of other metal fillers as long as the effects of the present invention are not impaired. As a content rate of the metal filler component in the said solder paste, the range of 84-94 mass% is preferable among 100 mass% of solder paste from a viewpoint of paste characteristics. A more preferable range of the content can be determined according to the paste application. For example, in screen printing applications, emphasis is placed on plate slippage, and the content is preferably in the range of 87 to 91% by mass, and more preferably in the range of 88 to 90% by mass. In dispensing applications, the content is preferably in the range of 85 to 89% by mass, more preferably in the range of 86 to 88% by mass, with emphasis on discharge fluidity.

  The flux component preferably includes rosin, solvent, activator, and thixotropic agent. The above flux components are suitable for the surface treatment of the metal filler. That is, by removing the oxide film of the metal filler component in the solder paste during reflow heat treatment and suppressing reoxidation, alloying by melting and thermal diffusion of the metal is promoted. A known material can be used as the flux component.

<Connection structure>
The present invention includes a first electronic component, a second electronic component, and a solder joint that joins the first electronic component and the second electronic component, the solder joint being the book described above. There is also provided a connection structure formed by subjecting the inventive lead-free solder to reflow heat treatment. Examples of the combination of the first electronic component and the second electronic component include a combination of a substrate electrode and a mounted component electrode. As a method for joining the first electronic component and the second electronic component for forming the connection structure of the present invention, a method of joining a mounting component electrode after applying a solder paste to a substrate electrode and joining them by reflow heat treatment For example, a solder paste is applied to the mounting component electrode or the substrate electrode, bumps are formed by reflow heat treatment, and then the mounting component electrode and the substrate electrode are overlapped and joined again by reflow heat treatment. In the above case, the electrodes can be connected by solder bonding between the electrodes.

  The reflow heat treatment temperature is preferably in the range of 100 to 200 ° C, more preferably in the range of 120 to 190 ° C. The reflow heat treatment temperature is typically set below the melting point of the first metal particles and above the melting point of the second metal particles. In the case where a mounting component electrode such as an electronic device and a substrate electrode are connected using the lead-free solder according to the present invention, the second metal particles are melted when a thermal history equal to or higher than the melting point of the second metal particles is given. 1 Metal particle and mounting component electrode and substrate electrode are joined. At this time, the thermal diffusion reaction proceeds at an accelerated rate between the first metal particles and the second metal particles, and a new stable alloy phase having a melting point higher than the melting point of the second metal particles is formed. A connection structure for connecting the particles and the mounted component electrodes and the substrate electrode is formed. The melting point of this new stable alloy phase is higher than the reflow heat treatment temperature (for example, about 260 ° C.) of the lead-free solder made of Sn-3.0Ag-0.5Cu. Does not melt. Therefore, according to the present invention, it is possible to prevent a short circuit that occurs between the component electrodes due to remelting of the solder.

<Component mounting board>
The present invention also provides a component mounting board having a board and the above-described connection structure of the present invention mounted on the board.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to this.

[Example 1]
(1) Production of first metal particles Cu 6.5 kg (purity 99 mass% or more), Sn 1.5 kg (purity 99 mass% or more), Ag 1.0 kg (purity 99 mass% or more), Bi 0.5 kg (purity 99 mass%) Above, and In 0.5 kg (purity 99 mass% or more) (that is, the target element composition is Cu: 65 mass%, Sn: 15 mass%, Ag: 10 mass%, Bi: 5 mass%, and In: 5 mass) %) Was placed in a graphite crucible and heated and melted to 1400 ° C. with a high-frequency induction heating device in a helium atmosphere of 99% by volume or more. Next, this molten metal is introduced into the spray tank in the helium gas atmosphere from the tip of the crucible, and then helium gas (purity 99 volume% or more, oxygen concentration 0.1 volume) from a gas nozzle provided in the vicinity of the crucible tip. The first metal particles were produced by atomizing by spraying (less than%, pressure 2.5 MPa). The cooling rate at this time was 2600 ° C./second.

  The first metal particles were classified using an airflow classifier (Nisshin Engineering: TC-15N) at a setting of 20 μm, and after collecting the large particles, they were classified again at a setting of 30 μm, and the small particles were collected. When the collected alloy particles were measured with a laser diffraction particle size distribution analyzer (HELOS & RODOS), the average particle size was 15.1 μm. The first metal particles were measured with a differential scanning calorimeter (Shimadzu Corporation: DSC-50) in the range of 40 to 580 ° C. under a nitrogen atmosphere under a temperature rising rate of 10 ° C./min. An endothermic peak was detected at 521 ° C., and the presence of a plurality of alloy phases could be confirmed from the plurality of melting points indicated by these. Further, exothermic peaks were detected at 258 ° C. and 282 ° C., and the presence of a metastable alloy phase could be confirmed. The first metal particles obtained here are hereinafter referred to as first metal particles A.

  Similarly, the first metal particles obtained by atomization were classified at a setting of 10 μm, the large particles were collected, and then classified again at a setting of 20 μm, and the small particles were collected. The collected alloy particles were measured with a laser diffraction particle size distribution analyzer (HELOS & RODOS), and the average particle size was 8.1 μm. The obtained first metal particles are hereinafter referred to as first metal particles B.

  Similarly, the first metal particles obtained by atomization were classified at a setting of 1.6 μm, the large particle side was collected, and then classified again at a setting of 10 μm, and the small particle side was collected. When the collected alloy particles were measured with a laser diffraction particle size distribution analyzer (HELOS & RODOS), the average particle size was 2.7 μm. The obtained first metal particles are hereinafter referred to as first metal particles C.

  Similarly, the 1st metal particle obtained by atomization was classified by 30 micrometers setting, and the large particle side was collect | recovered. The collected alloy particles were measured with a laser diffraction particle size distribution analyzer (HELOS & RODOS), and the average particle size was 30.2 μm. The obtained first metal particles are hereinafter referred to as first metal particles D.

(2) Production of second metal particles The second metal particles include a solder powder Bi-42Sn having a particle size of 25 μm to 45 μm manufactured by Yamaishi Metal Co., Ltd. (element composition is Bi: 58 mass%, Sn: 42 mass%). (Hereinafter referred to as second metal particles A) or Yamaishi Metal Co., Ltd. solder powder Bi-42Sn having a particle size of 10 μm to 25 μm (element composition is Bi: 58 mass%, Sn: 42 mass%) ( Hereinafter, the second metal particles B are used). The melting point measured by a differential scanning calorimeter (Shimadzu Corporation: DSC-50) under the same measurement conditions as described above was 138 ° C. for both the second metal particles A and the second metal particles B. In addition, when the 2nd metal particle A and the 2nd metal particle B were measured with the laser diffraction type particle diameter distribution measuring apparatus (HELOS & RODOS), the average particle diameter was 35 micrometers and 20.4 micrometers, respectively.

(3) Preparation of lead-free solder paste Said 1st metal particle A and 2nd metal particle A were mixed by mass ratio 100: 300, and it was set as the metal filler component. Next, 89.5 mass% of the metal filler component and 10.5 mass% of the flux (A) are mixed, and the solder softener (Malcom: SPS-1) and the defoaming kneader (Matsuo Sangyo: SNB-350) are mixed. Solder paste was produced in sequence.

(4) Measurement of bonding strength (shear strength) The solder paste is printed on a Cu substrate having a size of 25 mm × 25 mm and a thickness of 0.25 mm, and a Cu chip having a size of 2 mm × 2 mm and a thickness of 0.5 mm is mounted, and then nitrogen is added. A sample was prepared by reflow heat treatment at a peak temperature of 160 ° C. in an atmosphere. A reflow simulator (Malcom: SRS-1C) was used as the heat treatment apparatus. The temperature profile increased from 1.5 ° C / second to 120 ° C from the start of heat treatment (normal temperature), gradually increased from 120 ° C to 135 ° C over 110 seconds, and then increased at 2.0 ° C / second. The conditions of heating and holding at a peak temperature of 160 ° C. for 15 seconds were employed. A screen printer (Microtech: MT-320TV) was used for forming the print pattern. The printing mask is made of metal and the squeegee is made of urethane. The mask has an opening size of 2 mm × 3.5 mm and a thickness of 0.1 mm. The printing conditions were a speed of 50 mm / second, a printing pressure of 0.1 MPa, a squeegee pressure of 0.2 MPa, a back pressure of 0.1 MPa, an attack angle of 20 °, a clearance of 0 mm, and a printing frequency of once.

  Next, at normal temperature (25 ° C.), the chip bonding strength in the shear direction of the sample prepared above was measured at a pushing speed of 10 mm / min with a push-pull gauge and converted to a value per unit area of 15.4 MPa. Met. Further, after heating the sample prepared above to 260 ° C. on a hot plate and holding it for 3 minutes, the chip bonding strength in the shear direction was measured by the same method as described above, and converted to a value per unit area. .35 MPa. Therefore, it was confirmed that the sample had heat resistance capable of maintaining the bonding strength even when heated at 260 ° C. In addition, being able to hold | maintain joining strength means showing the joining strength of 0.20 Mpa or more.

[Examples 2 to 10, Comparative Examples 1 and 2]
Using a metal filler component in which the mixing ratio of the first metal particle A and the second metal particle A is changed, a solder paste is prepared in the same manner as in Example 1, and the chip bonding strength is measured in the same manner as in Example 1. did. The results are shown in Examples 2 to 5 in Table 1 and Comparative Example 1. Moreover, using each of the metal filler components having the same mixing ratio as in Examples 1 to 5, the temperature profile at the time of joining the Cu chips was increased from the start of heat treatment (normal temperature) to 120 ° C. at 1.5 ° C./second. Table 6 shows the results obtained by gradually increasing the temperature from 120 ° C. to 135 ° C. over 110 seconds, then increasing the temperature at 2.0 ° C./second, and maintaining the peak temperature at 180 ° C. for 15 seconds. -10 and Comparative Example 2. As is apparent from the results of Comparative Examples 1 and 2 in Table 1, when the first metal particles are not included, the solder joint portion (connection portion) melts when heated to 260 ° C., and thus the shear strength is 0 MPa. . On the other hand, in Examples 1-10 containing 1st metal particle, even when it heats to 260 degreeC, it turns out that joining strength is 0.2 Mpa or more and the solder is not remelted. In the present specification, that the solder is not remelted means that the bonding strength is 0.20 MPa or more.

[Comparative Example 3]
Using a conventional representative lead-free solder (Sn-3.0Ag-0.5Cu) paste, the bonding strength of the Cu chip was measured in the same manner as in Example 1 (4). The results are shown in Table 1. However, the reflow temperature profile when the Cu chip is joined using the solder material is as follows: from the start of heat treatment (room temperature) to 140 ° C. at a rate of 1.5 ° C./second and from 140 ° C. to 170 ° C. for 110 seconds. The temperature was gradually increased over a period of 170 ° C. to 250 ° C. at a rate of 2.0 ° C./second, and a condition was maintained at a peak temperature of 250 ° C. for 15 seconds. From the result of Comparative Example 3, it can be seen that when a typical lead-free solder Sn-3.0Ag-0.5Cu is used, the solder joint is melted and heated to 0 MPa when heated to 260 ° C.

[Examples 11 to 20]
Using a metal filler component in which the mixing ratio of the first metal particle B and the second metal particle B is changed, a solder paste is produced in the same manner as in Example 1, and at a peak temperature of 160 ° C. or 180 ° C. Reflow heat treatment (similar to Examples 1 to 10) was performed, and the bonding strength was measured in the same manner. The results are shown in Examples 11 to 20 in Table 2. From Table 2, it can be seen that Examples 11 to 20 containing the first metal particles B exhibit a bonding strength of 0.20 MPa or more even when heated to 260 ° C., and exhibit heat resistance that maintains the bonded state.

[Example 21]
A lead-free solder produced in Example 2 was printed on a Cu electrode of a printed circuit board made of a high heat-resistant epoxy resin glass cloth, and 0603 size multilayer ceramic chip capacitor (hereinafter abbreviated as 0603C, or simply referred to as a mounted component). ) Was then subjected to reflow heat treatment under the conditions described in Example 1 to prepare a sample.

  Next, the sample produced above was heated to 105 ° C. on a hot plate, the underfill was applied so as not to cover the upper part of the mounted component, and cured in an oven at 165 ° C. for 2 hours. Next, a transparent mold resin was applied to the upper part and the periphery of the mounted component and cured in an oven at 150 ° C. for 4 hours.

  Next, after moisture absorption at 60 ° C. and 60% RH for 40 hours, reflow heat treatment at a peak temperature of 260 ° C. was performed in a nitrogen atmosphere. A reflow simulator (Malcom: SRS-1C) was used as the heat treatment apparatus. The temperature profile was as follows: from heat treatment start (room temperature) to 150 ° C. at a rate of 1.5 ° C./second, gradually increasing from 150 ° C. to 210 ° C. over 100 seconds, then from 210 ° C. to 260 ° C. The temperature was raised at a rate of 0.0 ° C./second, and the conditions were maintained at a peak temperature of 260 ° C. for 15 seconds. Next, it was visually observed whether the solder was melted by reflow heat treatment and shorted between the component electrodes. The results are shown in Table 3. In Example 21, no short-circuit between the component electrodes was observed, and it was confirmed that the solder material exhibited heat resistance that did not flow even at 260 ° C.

[Comparative Example 4]
A conventional representative lead-free solder Sn-3.0Ag-0.5Cu was evaluated in the same manner as in Example 21. However, only the temperature profile when mounting 0603C is different, the temperature is increased from the start of heat treatment (room temperature) to 140 ° C at 1.5 ° C / second, and gradually from 140 ° C to 170 ° C over 100 seconds. The temperature was raised from 170 ° C. to 250 ° C. at a rate of 2.0 ° C./second and maintained at a peak temperature of 250 ° C. for 15 seconds. The results are shown in Table 3.

  As is clear from the results in Table 3, it was found that in Comparative Example 4, the solder melted and a short circuit occurred between the component electrodes with a very high probability. On the other hand, in Example 21, although the melting point of the second metal particles is 138 ° C., no short circuit occurs between the component electrodes. From the above results, the lead-free solder using the metal filler of the present invention is capable of joining parts at low temperatures, and does not melt and flow out even in subsequent reflow, and is a material with excellent heat resistance. Recognize.

[Example 22]
The 1st metal particle A and the 2nd metal particle A were mixed by mass ratio 100: 186, and it was set as the metal filler component. Next, 90% by mass of the metal filler component and 10% by mass of the flux (B) were mixed, and a solder paste was produced in the same procedure as in Example 1. The solder paste is printed and applied onto a Cu electrode of a printed circuit board made of high heat-resistant epoxy resin glass cloth, and after mounting a 1005 size resistor chip (hereinafter referred to as 1005R, or simply referred to as a mounted component), the peak temperature in a nitrogen atmosphere Reflow heat treatment was performed at 160 ° C. to prepare a sample. The obtained sample is embedded in epoxy resin, and the cross-section of the mounted component is observed by polishing the cross-section, and the suspended state (that is, the metal particles are separated from each other) in the flux layer existing on the solder upper layer of the mounted component joint. Counts the number of metal particles (floating particles) present. The results are shown in Table 4. In addition, the number of suspended particles shown in Table 4 is an average of values obtained by counting suspended particles at six joint portions of 1005R.

[Examples 23 to 24]
The same evaluation was performed using the first metal particle B or the first metal particle C instead of the first metal particle A in Example 22. The results are shown in Table 4. As can be seen from the results in Table 4, when the first metal particles C having an average particle diameter of 2.7 μm are used, many suspended particles are observed in the flux layer of the solder upper layer of the joint. On the other hand, when the first metal particles B having an average particle diameter of 8.1 μm or the first metal particles A having an average particle diameter of 15.1 μm are used, there are few floating particles generated in the flux layer. I understand. Thus, compared with the case where the average particle diameter of the metal particles used is small (for example, 2.7 μm), when the average particle diameter is, for example, 8.1 μm and 15.1 μm, floating particles are generated in the flux layer. It turns out that the advantage that it is hard to do is acquired.

[Examples 25 to 27]
The first metal particles A and the second metal particles B were mixed at a mass ratio of 100: 186 to obtain a metal filler component. Next, 89.5 mass% of the metal filler component and 10.5 mass% of the flux (B) were mixed, and a solder paste was produced in the same procedure as in Example 1. The obtained solder paste was printed and applied onto an alumina substrate, and the adhesive strength was measured using a tackiness tester (manufactured by Malcolm) TK-1. The results are shown in Example 25 in Table 5. The adhesive strength was measured at 5 points, and the average value is shown in Table 5. Moreover, using the 1st metal particle B or the 1st metal particle D instead of the 1st metal particle A, the solder paste was produced in the procedure similar to Example 1, and adhesive force was measured similarly. The results are shown in Examples 26 and 27 in Table 5, respectively. Accordingly, when the average particle size is 8.1 μm and 15.1 μm, for example, compared to the case where the average particle size of the metal particles used is as large as the metal particle D (average particle size: 30.2 μm). It can be seen that the advantage that the adhesive strength is high and the adhesive strength as a paste is strong can be obtained.

[Examples 28 and 29]
The 1st metal particle A and the 2nd metal particle A were mixed by mass ratio 100: 186, and it was set as the metal filler component. Next, 90% by mass of the metal filler component and 10% by mass of the flux (B) were mixed, and a solder paste was produced in the same procedure as in Example 1. Using the obtained paste, similarly to Example 1 (4), a reflow heat treatment was performed at a peak temperature of 160 ° C. in a nitrogen atmosphere to prepare a Cu chip bonded substrate, and the bonding strength at room temperature and 260 ° C. heating was obtained. It was measured. The results are shown in Example 28 of Table 6.

  Moreover, the 1st metal particle A and the 2nd metal particle B were mixed by mass ratio 100: 186, and it was set as the metal filler component. Next, 89.5 mass% of the metal filler component and 10.5 mass% of the flux (B) were mixed, and a solder paste was produced in the same procedure as in Example 1. Similarly to Example 1 (4), a reflow heat treatment was performed at a peak temperature of 160 ° C. in a nitrogen atmosphere to prepare a Cu chip bonded substrate, and the bonding strength when heated at normal temperature and 260 ° C. was measured. The results are shown in Example 29 of Table 6.

[Comparative Examples 5 and 6]
Cu powder (manufactured by Fukuda Metal Foil Powder Industry Co., Ltd., Cu-HWQ average particle size 15 μm) and second metal particles A were mixed at a mass ratio of 100: 186 to obtain a metal filler component. Next, 90% by mass of the metal filler component and 10% by mass of the flux (B) were mixed, and a solder paste was produced in the same procedure as in Example 1. Using the obtained paste, similarly to Example 1 (4), a reflow heat treatment was performed at a peak temperature of 160 ° C. in a nitrogen atmosphere to prepare a Cu chip bonded substrate, and the bonding strength at room temperature and 260 ° C. heating was obtained. It was measured. The results are shown in Comparative Example 5 in Table 6.

  Moreover, Cu powder (Fukuda metal foil powder industry company make, Cu-HWQ 15micrometer) and the 2nd metal particle B were mixed by mass ratio 100: 186, and it was set as the metal filler component. Next, 89.5 mass% of the metal filler component and 10.5 mass% of the flux (B) were mixed, and a solder paste was produced in the same procedure as in Example 1. Using the obtained paste, similarly to Example 1 (4), a reflow heat treatment was performed at a peak temperature of 160 ° C. in a nitrogen atmosphere to prepare a Cu chip bonded substrate, and the bonding strength at room temperature and 260 ° C. heating was obtained. It was measured. The results are shown in Comparative Example 6 in Table 6.

  When Example 28 of Table 6 and Comparative Example 5 or Example 29 and Comparative Example 6 are compared, it is 2nd metal particle compared with the combination of Bi-42Sn which is 2nd metal particle, and Cu powder | flour. It can be seen that the bonding strength at room temperature is significantly better when the combination of Bi-42Sn and the first metal particles A is used.

[Comparative Examples 7 and 8]
The following evaluation was performed for comparison with the prior art of the present inventors (Japanese Patent Laid-Open No. 2008-183582).

Production of third metal particles 1.0 kg of Ag particles (purity 99% by mass or more), 2.0 kg of Bi particles (purity 99% by mass or more), 1.5 kg of Cu particles (purity 99% by mass or more), 2.0 kg of In particles (Purity 99% by mass or more), Sn particles 3.5 kg (Purity 99% by mass or more) (namely, the target element composition is Ag: 10% by mass, Bi: 20% by mass, Cu: 15% by mass, In: 20% by mass) , And Sn: 35% by mass) were put into a graphite crucible and heated to 1400 ° C. with a high-frequency induction heating apparatus in a helium atmosphere of 99% by volume or more to melt. Next, this molten metal is introduced into the spray tank in the helium gas atmosphere from the tip of the crucible, and then helium gas (purity 99 volume% or more, oxygen concentration 0.1 volume) from a gas nozzle provided in the vicinity of the crucible tip. Atomization was performed by ejecting less than% and a pressure of 2.5 MPa to produce third metal particles. The cooling rate at this time was 2600 ° C./second. The obtained third metal particles were spherical when observed with a scanning electron microscope (manufactured by Hitachi, Ltd .: S-2700). The metal particles are classified using an airflow classifier (Nisshin Engineering Co., Ltd .: TC-15N) at a setting of 5 μm, and after collecting the large particles, the particles are classified again at a setting of 15 μm. Was recovered. When the recovered third metal particles were measured with a laser diffraction particle size distribution analyzer (HELOS & RODOS), the average particle size was 5.5 μm. Differential scanning calorimetry was performed using the third metal particles thus obtained as a sample. As a result, endothermic peaks at 66 ° C., 87 ° C., and 380 ° C. were present, and it was confirmed that the films had a plurality of melting points in the low melting points of 66 ° C. and 87 ° C.

  Next, the 1st metal particle A and the 3rd metal particle were mixed by mass ratio 100: 186, and it was set as the metal filler component. Next, 88.4% by mass of the metal filler component and 11.6% by mass of the flux (B) were mixed, and a solder paste was produced in the same procedure as in Example 1. Using the obtained paste, similarly to Example 1 (4), a reflow heat treatment was performed at a peak temperature of 160 ° C. in a nitrogen atmosphere to prepare a Cu chip bonded substrate, and the bonding strength at room temperature and 260 ° C. heating was obtained. It was measured. The results are shown in Comparative Example 7 in Table 7.

  Moreover, Cu powder (the Fukuda metal foil powder industry company make, Cu-HWQ 15micrometer) and 3rd metal particle were mixed by mass ratio 100: 186, and it was set as the metal filler component. Next, 88.7 mass% of the metal filler component and 11.3 mass% of the flux (B) were mixed, and a solder paste was produced in the same procedure as in Example 1. Similarly to Example 1 (4), a reflow heat treatment was performed at a peak temperature of 160 ° C. in a nitrogen atmosphere to prepare a Cu chip bonded substrate, and the bonding strength when heated at normal temperature and 260 ° C. was measured. The results are shown in Comparative Example 8 in Table 7.

  From Examples 28 and 29 and Comparative Example 7, when a metal filler in which the third metal particles are mixed instead of the second metal particles is used for the first metal particles, the bonding strength at room temperature is low. It turns out that it becomes. Further, when Comparative Example 7 and Comparative Example 8 are compared, it can be seen that the bonding strength is a relatively low value, and both have substantially the same bonding strength. That is, when the third metal particles were used, it was confirmed that both the combination with the first metal particles A and the combination with the Cu powder showed low bonding strength.

  The metal filler of the present invention and the lead-free solder containing the metal filler are used for a plurality of heat treatments in a subsequent process (for example, a solder material used for an electronic device such as a component-embedded substrate and a package, and further, for example, a conductive adhesive). And can be mounted at low temperature.

Claims (6)

A metal filler comprising a mixture of first metal particles and second metal particles,
The first metal particles are Cu alloy particles composed of Ag 5 to 15% by mass, Bi 2 to 8% by mass, Cu 49 to 81% by mass, In 2 to 8% by mass, and Sn 10 to 20% by mass,
The second metal particles are Bi alloy particles composed of Bi 40 to 70% by mass and Sn 30 to 60% by mass , and
The metal filler whose quantity of the said 2nd metal particle with respect to 100 mass parts of said 1st metal particles is the range of 40-300 mass parts. 2. The metal filler according to claim 1, wherein the first metal particles and the second metal particles both have an average particle diameter in the range of 5 to 25 μm. Before Symbol first metal particles in differential scanning calorimetry (DSC), at least one exothermic peak is observed in the range of 230 to 300 ° C., at least one endotherm observed in the range of four hundred eighty to five hundred and thirty ° C. The metal filler according to claim 1 or 2 , which has a peak. The lead-free solder containing the metal filler as described in any one of Claims 1 thru | or 3 . The lead according to claim 4 , further comprising a first electronic component, a second electronic component, and a solder joint that joins the first electronic component and the second electronic component. A connection structure formed by reflow heat treatment of free solder. A component mounting board comprising: a board; and the connection structure according to claim 5 mounted on the board.