JP2005103554A - Soldering paste, manufacturing method of soldering paste and mounting structure of electronic component, and mounting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a soldering paste for internal bonding which can endure a reheat treatment and maintain a reliable bonding state though it is Pb-free. <P>SOLUTION: The soldering paste contains Sn or Sn-based alloy(a first bonding element) and a metal or an alloy(a second bonding element) having a higher melting point than the Sn or Sn-based alloy and having an oxide film formed on the surface, which are dispersed in a flux. The metal of the second bonding element is Ni or Cu. When an electronic component is mounted by using the soldering paste, a bonded part comprising a first bonded part made of the first bonding element and a second bonded part which is made of the second bonding element consisting of the metal or the alloy and covers the first bonded part is formed. The second bonded part functions as a protective layer of the first bonded part and prevents the electronic component from falling off and the solder from flowing away during the reheat treatment. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a solder paste and a method for producing the same, and more particularly to an improvement in a solder paste for internal bonding that can be reheated. Furthermore, the present invention relates to a mounting structure and mounting method for an electronic component using the solder paste.

  In recent years, from the viewpoint of global environmental conservation, reduction of the use amount of environmental pollutants such as Pb, and further prohibition of use have been demanded. Therefore, Sn—Pb eutectic alloy solder used for soldering electronic components is shifting to Sn—Ag solder and the like.

  However, as for the solder for internal joining for internally joining electronic parts, the actual situation is that no alternative solder has been developed at present. For example, when various electronic circuit boards such as an electronic circuit module are manufactured, a molded part obtained by previously joining and molding electronic parts with joining solder may be further mounted on a printed board and soldered for external connection. In this case, the electronic component joined in the molded component is reheated when soldering the external connection solder.

  Therefore, it is necessary to use a solder having a melting point higher than that of the external connection solder as the joining solder. For example, Sn-10Sb which is a joining solder not containing Pb has a melting point of about 245 ° C. When considering heat treatment, it is not enough. When Sn-10Sb is used for external bonding and Sn-Ag solder (for example, Sn-Ag-Cu) is used for external connection, the reflow temperature is as high as about 260 ° C during soldering for external connection. Due to the atmosphere, there is a possibility that the joint part of the electronic component soldered to the substrate melts and the electronic component that is internally joined falls off. Moreover, when the solder for internal joining is joined to parts other than the joining location of an electronic component, there exists a possibility that the solder for joining will melt and flow out by reheat processing, and may contact and short-circuit with another wiring. As a solder having a high melting point, for example, a Sn—Au-based alloy is also known. However, since it contains Au, the manufacturing cost is increased, which is not practical for general-purpose use.

Under such circumstances, the applicant of the present application has already proposed a soldering composition that is Pb-free and can withstand reheating at a high temperature (see Patent Document 1). The composition for soldering described in Patent Document 1 is composed of a metal component that melts at a reflow soldering temperature and a metal component that does not melt, and is alloyed during reflow soldering to form an alloy having a higher melting point than that of the composition. As a result, when further soldering is performed on a soldered substrate or the like, soldering can be performed under substantially the same temperature condition.
JP 2002-254195 A

  However, for example, when Sn—Sb solder and a refractory metal are alloyed during reflow soldering, the melting point is certainly increased and it can withstand re-heat treatment, but it becomes brittle and decreases the bonding reliability. I know that there is.

  The present invention has been proposed in view of such a conventional situation, and a solder paste that can withstand re-heat treatment while being Pb-free and that can maintain a highly reliable joining state is provided. It aims at providing, Furthermore, it aims at providing the manufacturing method. In addition, the present invention provides a mounting structure and mounting method for an electronic component that can prevent the electronic component from falling off even under a high-temperature atmosphere such as a reflow and a reflow process, or has a low risk of short-circuit due to melting. The purpose is to provide.

  In order to achieve the above-mentioned object, the solder paste of the present invention includes Sn or a Sn-based alloy and a metal or alloy having a melting point higher than that of the Sn or Sn-based alloy and having an oxide film formed on the surface thereof. It is characterized by being dispersed in the flux. In the method for producing a solder paste according to the present invention, at least one of Ni and Cu is heat-treated in an atmosphere containing oxygen to form an oxide film on the surface and then dispersed in the flux together with Sn or an Sn-based alloy. It is characterized by.

  When soldering is performed using the solder paste of the present invention, the surface of the Sn or Sn-based alloy is coated to form a metal or alloy film having a melting point higher than that of the Sn or Sn-based alloy. The formed metal (or alloy) film has a high melting point and does not melt when reheated. In addition, this film reacts with Sn or the Sn-based alloy at the interface to be in a strongly bonded state. Therefore, even if Sn or the Sn-based alloy is melted during the reheat treatment, the bonding state is maintained by the high melting point film. Further, most of the internal Sn or Sn-based alloy is not alloyed, and therefore, deterioration of the bonding reliability due to the brittleness of this portion is avoided.

  On the other hand, the electronic component mounting structure of the present invention is an electronic component mounting structure in which the electronic component is mounted by soldering, and the soldered joint portion is made of Sn or Sn-based alloy. And a second joint formed by covering the first joint with a metal or alloy having a melting point higher than that of the Sn or Sn-based alloy. The mounting method of the present invention is characterized in that an electronic component is soldered with the solder paste to form the mounting structure.

  In the mounting structure, a good bonding state is ensured by the first bonding portion formed of Sn or an Sn-based alloy. At the same time, since the first joint portion is covered with the second joint portion made of a metal or alloy having a higher melting point than Sn or an Sn-based alloy, the first joint portion is formed in a high temperature atmosphere such as a reflow and reflow process. Even if one joining portion is in a molten state, the entire joining portion does not melt and the electronic component does not fall off. Further, the covering by the second joint portion functions as a protective layer of the solder that melts the second joint portion, and the first joint portion does not flow out during the reheat treatment.

  ADVANTAGE OF THE INVENTION According to this invention, it is possible to provide the solder paste which can endure reheat processing while being Pb free, and can maintain a highly reliable joining state, and its manufacturing method. In addition, according to the present invention, an electronic component mounting structure and a mounting method that can prevent the electronic component from falling off even under a high-temperature atmosphere such as a reflow process and a reflow process, and are less likely to cause a short circuit due to melting of the solder. Can be realized.

  Hereinafter, a solder paste to which the present invention is applied, a manufacturing method thereof, a mounting structure of an electronic component, and a mounting method will be described with reference to the drawings.

  The solder paste of the present invention includes Sn or an Sn-based alloy (hereinafter referred to as a first bonding component) and a metal or alloy (hereinafter referred to as a first alloy) having a melting point higher than that of the Sn or Sn-based alloy and having an oxide film formed on the surface. 2) and these are dispersed in the flux.

  First, as the first bonding component, Sn powder or Sn-based alloy powder is used as the first bonding component. The Sn-based alloy includes at least one selected from Ag, Cu, Zn, Bi, In, Ni, and Sb, and is a so-called Sn-based solder. Although there is no restriction | limiting in particular in the addition amount of the metal selected, It is preferable to set it as the composition which has sufficient wettability on mounting.

  On the other hand, as the second bonding component, metal powder or alloy powder having a melting point higher than that of the first bonding component is used. Specifically, it is Ni powder or Cu powder. The Ni powder or Cu powder used as the second bonding component is required to have a surface covered with an oxide film. When the oxide film is not formed, Ni or Cu reacts with Sn as the first bonding component and, for example, is alloyed during reflow soldering, and the object cannot be achieved. However, when a perfect oxide is used as the second bonding component, the second bonding component does not react at all with the first bonding component, and bonding at the interface between the first bonding component and the second bonding component can be realized. Can not.

  Although there is no restriction | limiting in the thickness of the said oxide film, From the above viewpoints, it is preferable that the thickness of the oxide film in a 2nd joining component shall be 0.01-1 micrometer. If the thickness of the oxide film is less than 0.01 μm, it is difficult to control the thickness, and as a result, alloying may occur. Conversely, if the thickness of the oxide film exceeds 1 μm, the oxide film may not be completely decomposed by the flux and may remain on the surface. If the oxide film remains on the surface of the Ni powder or Cu powder, the reaction between the second bonding component and the first bonding component becomes insufficient, and the adhesion between the coating film made of the second bonding component and the first bonding component is sufficient. It becomes difficult to secure. If the adhesion is ensured, there is no problem even if oxide remains in the second bonding component.

  The mixing ratio of the first bonding component and the second bonding component in the solder paste is not particularly limited. For example, the ratio of the first bonding component is about 95 to 60% by weight, and the ratio of the second bonding component is 5 to 40%. % Is preferable. If the ratio of the first bonding component is too large, the thickness of the coating formed by the second bonding component becomes thin, and there is a possibility that the function may not be sufficiently exhibited. Conversely, if the proportion of the second bonding component is too large, the volume of the portion that functions as solder becomes too small, and it may be difficult to maintain a good soldered state.

  The first joining component and the second joining component described above are dispersed in the flux and prepared as a solder paste. At this time, the flux to be used is arbitrary, but it is preferable to use a flux containing a specific activator as the activator in consideration of the reducing property to the oxide film. The flux usually includes rosin and an activator. The activator includes a chlorine (Cl) system, a fluorine (F) system, a bromine (Br) system, and the like, but considering the reducibility, a chlorine system or a bromine system is preferable. Specifically, ethylamine HCl, aminodiethylaniline HCl, N hexyl HBr, isopropyl HBr and the like are preferable.

  The solder paste of this invention should just disperse | distribute a 1st joining component and a 2nd joining component in a flux similarly to a normal solder paste. However, for the second bonding component, it is necessary to form an oxide film in advance. For example, after Ni powder or Cu powder is heat-treated in an atmosphere containing oxygen to form an oxide film on the surface, Sn or Disperses in the flux together with the Sn-based alloy. The thickness of the oxide film can be controlled by controlling the temperature, processing time, oxygen concentration, and the like during the heat treatment. Note that the method for forming the oxide film is not limited to this, and is not particularly limited as long as the method can form the oxide film.

  When soldering using the solder paste of the present invention, the Sn or Sn alloy (first bonding component) is first melted, and the metal or alloy having a melting point higher than that of the Sn or Sn alloy and having an oxide film formed on the surface (Second bonding component) floats on the surface. In the floated metal or alloy, the oxide film is reduced by the reducing action of the flux, and a film of metal or alloy is formed to cover the surface of the Sn or Sn-based alloy. The metal or alloy film covering the surface reacts with the surface of the Sn or Sn-based alloy to form a reaction phase. As a result, the first bonding component and the second bonding component are firmly bonded.

   FIG. 1 shows a mounting structure of an electronic component soldered using the solder paste of the present invention. In this mounting structure, an electronic component (for example, a ceramic capacitor) 2 is mounted on the substrate 1 by soldering using the above-described solder paste. The electronic component 2 has terminal electrodes 3 and 4 at both ends, which are soldered and electrically connected to connection electrodes 5 and 6 provided on the substrate 1.

  The joint portion 7 is formed by soldering with a solder paste. The joint portion 7 includes a first joint portion 7a formed of Sn or an Sn-based alloy (first joint component) and a first surface covering the surface. 2 joints 7b. The second bonding portion 7b is formed of a metal (second bonding component) having a higher melting point than Sn or an Sn-based alloy, for example, Ni or Cu. As described above, a reaction phase is formed at the interface between the first bonding portion 7a and the second bonding portion 7b, and the reaction phase is firmly bonded. The formation of a reaction phase at the interface can be easily confirmed by a change in color tone. Layers with different color tones are formed at the interface, which corresponds to the reaction phase.

  The electronic component 2 is soldered by the joint portion 7 and mounted on the substrate 1. At this time, the first joint portion 7a mainly functions as solder. That is, the 1st junction part 7a is contacting with the terminal electrodes 3 and 4 of the electronic component 2, and the terminal electrodes 3 and 4 and the connection electrodes 5 and 6 are soldered.

  On the other hand, the second joint portion 7b is formed so as to cover the surface of the first joint portion 7a, and prevents the electronic component 2 from falling off during re-heat treatment, and prevents the first joint portion 7a from flowing out. It has a function. That is, even if the temperature rises during reheat treatment and the first joint 7a is melted, the second joint 7b keeps the first joint 7a in contact with the terminal electrodes 3 and 4, and the electronic component 2 Dropping is prevented. For example, when the joining part 7 is formed in parts other than the terminal electrodes 3 and 4 of the electronic component 2, even if the 1st joining part 7a melts, the 2nd joining part 7b works as a defense wall, and the 1st joining The part 7a does not flow out and cause a short circuit or the like.

  As described above, it is effective to use the solder paste of the present invention for reheat treatment, that is, for soldering for internal joining. Hereinafter, a mounting method when the solder paste of the present invention is used for internal bonding will be described.

  When the electronic component is internally bonded to the substrate and further externally connected, the electronic component is first mounted using the solder paste of the present invention. The mounting structure of the electronic component using this solder paste is as shown in FIG. When re-heat treatment is necessary, mold the electronic component attached to the substrate and mount the electronic component mounted on another substrate as a molded component, or mount the electronic component on one side of the substrate Then, the case where solder reflow is performed with respect to the other surface of a board | substrate is mentioned.

  Next, reflow for external connection, which is re-heat treatment, is performed on the mold component and the substrate. At this time, the mold component or the substrate in which the electronic component is internally bonded is exposed to a high temperature atmosphere in a reflow process or the like. In the case where Sn—Ag solder, for example, Sn—Ag—Cu, is used for external connection, it is exposed to a high temperature of about 260 ° C. in the reflow process.

  Here, if the solder paste of the present invention is used for internal joining of electronic parts and the mounting structure shown in FIG. 1 is used, the electronic parts will not fall off in the reflow process for external connection that is reheat treatment. No short circuit occurs due to the flow of solder for joining.

  Hereinafter, specific examples to which the present invention is applied will be described based on experimental results.

(Example 1)
Formation of oxide film on metal powder Cu powder having an average particle diameter of 12 μm was prepared and heat-treated at 400 ° C. for 1 hour. At this time, the oxide film thickness was controlled by changing the amount of oxygen. The thicknesses of the formed oxide films were 0.05 μm, 0.1 μm, 0.5 μm, 1.0 μm, and 2.0 μm. The thickness of the oxide film was determined by burying and polishing Cu powder in a resin and observing with a scanning electron microscope (SEM).

Preparation of solder paste Sn powder having an average particle size of 12 μm, Cu powder with an oxide film formed thereon, and Cu powder not subjected to oxidation treatment were mixed at a weight ratio of 80:20 and mixed in the flux. The solder paste was obtained by dispersing.

Mounting of electronic components and test solder paste is applied to a paper phenol substrate on which a land pattern made of test Cu is formed, and a capacitor element having a C5750 (length 5.7 mm × width 5.0 mm × thickness 4 mm) shape thereon The capacitor element was mounted on a paper phenol substrate at a reflow temperature of 260 ° C.

  Then, the drop test by a load was done in the temperature environment of 260 degreeC by the method shown in FIG. In FIG. 2, the mounting structure of the capacitor element corresponding to the electronic component 2 is the same as that shown in FIG. 1, and the description thereof is omitted here. A substrate on which this capacitor element was mounted was tilted by 90 °, and a weight test was carried on the electronic component 2 to perform a drop test. The load was 5 g, 10 g, 15 g, and 20 g. 30 test samples were tested under each load condition. The results are shown in Table 1. The numbers in the table indicate the number of drops.

  Further, using the pattern shown in FIG. 3, a solder film was formed, and the substrate was held sideways at 260 ° to examine whether the solder melted and a bridge was formed. As shown in FIG. 3, the pattern 12 is formed on the substrate 11. The width W of each pattern 12 is 2 mm and the interval p is 1 mm. 30 test samples were prepared and the number of bridges was examined. The results are also shown in Table 1.

  As is apparent from Table 1, in mounting with solder paste using Cu powder on which an oxide film having a thickness of 0.05 to 1 μm is formed, the capacitor element does not fall off and a bridge is generated between the wiring patterns. There is nothing. On the other hand, when the thickness of the oxide film was zero, the solder became brittle due to alloying, and the capacitor element was dropped. In addition, if the thickness of the oxide film becomes too thick, the first joint portion and the second joint portion are not joined, and the result rapidly deteriorates.

(Example 2)
In this example, Ni powder was used instead of Cu powder, the same test sample as in Example 1 was prepared, and a drop test and a bridge formation test were performed. The results are shown in Table 2.

  Even when Ni powder is used, as in the case of Cu powder, by forming an oxide film with a thickness of 0.05 to 1 μm, the capacitor element does not fall off and a bridge is generated between the wiring patterns. It was confirmed that there was not.

It is sectional drawing which shows an example of the mounting structure of the electronic component to which this invention is applied. It is a schematic perspective view which shows the method of a drop test. It is a top view of the board | substrate used for the bridge formation test.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Board | substrate, 2 Electronic components, 3, 4 Terminal electrode, 5, 6 Connection electrode, 7 Junction part, 7a 1st junction part, 7b 2nd junction part, 8 weight, 11 Board | substrate, 12 pattern

Claims (18)

  A solder paste comprising Sn or an Sn-based alloy and a metal or alloy having a melting point higher than that of the Sn or Sn-based alloy and having an oxide film formed on the surface thereof, which are dispersed in a flux.   2. The solder paste according to claim 1, wherein the metal or alloy having a melting point higher than that of the Sn or Sn-based alloy is at least one of Ni and Cu.   The solder paste according to claim 1, wherein the Sn-based alloy is a solder containing at least one selected from Ag, Cu, Zn, Bi, In, Ni, and Sb.   The solder paste according to claim 1, wherein the oxide film has a thickness of 0.05 to 1 μm.   The solder paste according to claim 1, wherein the flux includes rosin and an activator, and the activator is a chlorine activator or a bromine activator.   6. The solder paste according to claim 5, wherein the activator is at least one selected from ethylamine HCl, aminodiethylaniline HCl, N-hexyl HBr, and isopropyl HBr.   The solder paste according to claim 1, wherein the solder paste is used for an internal bonding application to be reheat-treated.   A method for producing a solder paste, comprising: heat-treating at least one of Ni or Cu in an atmosphere containing oxygen, forming an oxide film on the surface, and then dispersing the resultant together with Sn or an Sn-based alloy in a flux. An electronic component mounting structure in which the electronic component is mounted by soldering,
The joint by soldering is composed of a first joint composed of Sn or a Sn-based alloy and a metal or alloy having a melting point higher than that of the Sn or Sn-based alloy, and covers the first joint. A mounting structure for an electronic component, comprising: a second joint portion formed as described above.   The mounting structure for an electronic component according to claim 9, wherein a reaction phase is formed at an interface between the first joint and the second joint and is joined to each other.   10. The electronic component mounting structure according to claim 9, wherein the metal or alloy having a melting point higher than that of the Sn or Sn-based alloy is at least one of Ni and Cu.   The electronic component mounting structure according to claim 9, wherein the Sn-based alloy is a solder including at least one selected from Ag, Cu, Zn, Bi, In, Ni, and Sb.   The electronic component mounting structure according to claim 9, wherein the electronic component is internally bonded and reheated after mounting.   A method for mounting an electronic component, wherein the electronic component is soldered with the solder paste according to claim 1 to obtain a mounting structure according to claim 9.   15. The electronic component mounting method according to claim 14, wherein re-heat treatment is performed after the soldering.   16. The electronic component mounting method according to claim 15, wherein the reheat treatment is a reflow for external connection.   17. The electronic component mounting method according to claim 16, wherein Sn or a Sn-based alloy is used for the external connection.   18. The electronic component mounting method according to claim 17, wherein the Sn-based alloy is a solder containing at least one selected from Ag, Cu, Zn, Bi, In, Ni, and Sb.

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