JP2008087014A - Solder paste and soldered component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solder paste in which a resin layer formed to cover a solder, overflow of the molten solder and occurrence of defective short circuit can be prevented even when the thermal shock is applied in a reflow heating process after the soldering, and the solder is re-melted in a volumetric expansion, and a reliable soldered component can be efficiently manufactured, and a soldered component with high soldering reliability formed by soldering the component. <P>SOLUTION: The solder paste contains a thermosetting resin composition having the flexural modulus of ≤5 GPa after thermosetting, a flux and solder powder. As the thermosetting resin composition, the one containing rubber components or the rubber-modified thermosetting resin composition is used. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a solder paste and a joined component obtained by joining constituent members using the solder paste.

  For example, an adhesive resin and a curing agent are contained in one of the solder pastes used to mount the surface mount electronic component on the component mounting substrate on which the surface mount electronic component such as a multilayer ceramic capacitor is to be mounted. A solder paste obtained by blending and kneading a soldering flux and a solder powder is known (see Patent Document 1).

  This solder paste is used when soldering and mounting surface mount electronic components on component connection conductors (lands) for mounting on component mounting boards. It is said that it is possible to cope with downsizing of products and narrowing (higher density) of arrangement intervals of surface mount electronic components with sufficient bonding strength.

  For example, FIGS. 3A to 3C are diagrams showing a process of mounting a surface mount electronic component on a component mounting board using this solder paste.

3A to 3C, the component mounting substrate 31 has two component connecting conductors (lands) 80 formed by sequentially laminating a Cu film 51, a Ni film 61, and an Au film 71. Yes.
In mounting the surface-mounted electronic component 40 on the land 80 of the component mounting board 31, first, the solder paste 81 is applied on the land 80 (see FIG. 3A).

  Then, a surface mount electronic component 40 having a pair of external electrodes 41 is mounted on the solder paste 81 (see FIG. 3B), and the surface mount electronic component 40 is passed through a reflow furnace. Soldering is performed on the mounting substrate 31 (see FIG. 3C). In the state where the soldering is performed, the adhesive resin contained in the flux is raised on the surface of the solder 82 and the resin layer 83 is formed.

  Thus, when surface-mount type electronic components are mounted using the solder paste of Patent Document 1, the flux blended in the solder paste contains an adhesive resin and a curing agent. After soldering, the resin layer (adhesive resin) that emerges on the surface of the solder can function as an adhesive that fixes the component mounting board and the surface mount electronic component. It is said that the reliability of solder joints can be improved by preventing the peeling and dropping of the mold electronic parts.

  In addition, by using the flux as described above, it is possible to ensure a sufficient fixing strength even without a fillet portion, and a fillet is formed on a component connection conductor (land) formed on a component mounting board. It is said that it is not necessary to provide a region for generating a portion, and the mounting density can be improved.

  However, in the above solder paste, when a low-temperature solder having a low melting point is used as the solder, for example, a component mounting board joined using this solder paste is connected to a mother circuit board with a high melting point solder (high-temperature solder). When the solder is to be mounted, the solder 82 (see FIG. 3C) melts and expands in the reflow heating process for high-temperature solder, resulting in the adhesive resin contained in the flux. There is a problem that the resin layer 83 is cracked, and the molten solder 82 flows out, causing a short circuit defect. For example, the volume expansion coefficient at the time of melting Sn-based solder is about 5%, and a mounting body such as a component mounting board is covered with a resin layer derived from the flux as described above, or other thermosetting resin. Even in such a case, since the stress due to the expansion of the solder cannot be relieved, the molten solder breaks the resin and flows out.

In addition to the reflow heating process, when a thermal stress is applied, there is a problem that cracks occur in the resin layer and the solder due to the difference in linear expansion coefficient, resulting in a decrease in bonding strength.
JP 2001-170797 A

  The present invention solves the above-described problems. For example, after soldering, a thermal shock is applied in a re-flow heating process or the like, and even when the solder re-melts and expands in volume, it is formed so as to cover the solder. A solder paste that can efficiently produce a highly reliable joining component that does not cause cracks in the resin layer and that does not cause molten solder to flow out and cause short-circuit defects, and using the same It is an object of the present invention to provide a joining component formed by joining constituent members and having high soldering reliability.

  In order to solve the above problems, the solder paste of the present invention (Claim 1) contains a thermosetting resin composition having a flexural modulus of 5 GPa or less after thermosetting, a flux, and solder powder. It is characterized by.

  The solder paste of claim 2 is characterized in that, in the configuration of the invention of claim 1, the thermosetting resin composition contains a rubber component.

  The solder paste of claim 3 is characterized in that, in the structure of the invention of claim 2, the rubber component is a carboxyl group-terminated butadiene-acrylonitrile copolymer rubber.

  A solder paste according to claim 4 is characterized in that, in the configuration of the invention according to claim 1, the thermosetting resin composition is a rubber-modified thermosetting resin composition.

  Further, the joined component of claim 5 is characterized in that at least some of the constituent members are soldered by using the solder paste according to any one of claims 1 to 4.

  The solder paste of the present invention (Claim 1) contains a solder powder and a flux, and further contains a thermosetting resin composition having a flexural modulus of 5 GPa or less after thermosetting. As shown in FIG. 1, a surface mount electronic component (for example, a multilayer ceramic capacitor) 2 having external electrodes 1a and 1b at both ends is mounted on a component having mounting lands 3a and 3b using the solder paste of the present invention. When mounted on the mounting substrate 4, after soldering, the resin layer 6 derived from the thermosetting resin composition having a flexural modulus of 5 GPa or less after thermosetting (that is, after soldering) included in the solder paste, A joined component (mounting body) in which the surface of the solder 5 is covered is obtained (see FIG. 2).

Since the resin layer 6 has a low bending elastic modulus, even when a thermal stress is applied after soldering, the low elastic modulus resin layer 6 covering the surface of the solder 5 absorbs this stress. As a result, it is possible to suppress and prevent the occurrence of cracks in the resin layer 6 and the decrease in the bonding reliability of the surface mount electronic component 2 to the component mounting board 4 due to the occurrence of cracks. .
Moreover, since generation | occurrence | production of the crack to the resin layer 6 is suppressed, even when it heats after soldering and a solder fuse | melts, it can prevent that a solder flows out.

  Further, since the resin layer 6 has a low flexural modulus, for example, even when a stress is applied to the mounted surface mount electronic component, the resin layer 6 relaxes the stress, It is possible to prevent peeling at the interface of the component mounting board 4 and to ensure sufficient bonding reliability.

Therefore, when the surface-mounted electronic component 2 is mounted on the component mounting board 4 having mounting lands 3a and 3b using the solder paste of the present invention, the component mounting board 4 is mounted on the mother circuit board. When the solder is melted and volume-expanded, the resin layer 6 can be prevented from cracking and the solder can be prevented from flowing out. Bonding reliability between the electronic component 2 and the component mounting substrate 4 can be ensured.
In addition, in this invention, a thermosetting resin composition is the concept containing what mixed thermosetting resin and rubber | gum etc. like the below-mentioned Example.

  In the case of the solder paste of claim 2, the thermosetting resin composition containing a rubber component has a flexural modulus of 5 GPa or less after thermosetting, and is subject to soldering at a high temperature (for example, a component mounting board) ), The low elastic modulus resin layer 6 covering the surface of the solder 5 reliably ensures the stress applied in the re-reflow heating step as described with respect to the effect of the invention of claim 1 described above. To prevent occurrence of cracks in the resin layer 6, molten solder flowing out of the cracks, and peeling at the interface between the resin layer 6 and the component mounting board 4, and sufficient bonding reliability Can be secured.

In addition, as a rubber component, it is excellent in dispersibility, and since the interface strength of a thermosetting resin and rubber | gum becomes strong by carrying out a chemical bond with a thermosetting resin, it is like the solder paste of Claim 3. It is particularly preferable to use carboxyl group-terminated butadiene-acrylonitrile copolymer rubber (CTBN).
In the present invention, the thermosetting resin composition containing a rubber component means that the rubber component is dispersed in the thermosetting resin composition without being incorporated into the molecular structure of the thermosetting resin. It is a composition contained in a state.

In the case of the solder paste of claim 4, the rubber-modified thermosetting resin composition has a flexural modulus of 5 GPa or less after thermosetting, and is to be soldered at a high temperature (for example, a component mounting board). Because of its excellent adhesion to the resin, the low elastic modulus resin layer covering the surface of the solder reliably absorbs the stress applied in the reflow heating process as described with respect to the effect of the invention of claim 1 above. This prevents cracks in the resin layer, molten solder from flowing out of the cracks, and peeling at the interface between the resin layer and the component mounting board, thereby ensuring sufficient bonding reliability. .
In the present invention, the rubber-modified thermosetting resin composition refers to a composition in which a rubber component is incorporated in the molecular structure of the thermosetting resin.

  Moreover, in the joining component of Claim 5, at least one part structural member is soldered using the solder paste in any one of Claims 1-4, The above-mentioned invention of Claim 1 is carried out. As described with respect to the effect, since the solder is covered with a resin layer having a flexural modulus of 5 GPa or less after thermosetting, for example, when the solder is subjected to a re-reflow heating process as described above, stress is applied. It is possible to prevent the resin layer 6 from absorbing and generating cracks in the resin layer 6 or peeling at the interface between the resin layer 6 and the component mounting board 4, and the constituent members are reliably connected. A bonded joint component with high reliability can be provided.

  The features of the present invention will be described in more detail below with reference to examples of the present invention.

[Thermosetting resin composition]
First, as a thermosetting resin composition, a bisphenol A type epoxy resin at a ratio shown in composition numbers 1 to 7 in Table 1 and a carboxyl group-terminated butadiene-acrylonitrile copolymer rubber (Table 1 as a rubber component) are used. Then, a thermosetting resin composition containing “CTBN” was prepared (however, the thermosetting resin composition of composition number 7 was made of carboxyl group-terminated butadiene-acrylonitrile copolymer rubber (CTBN)). Not included (content: 0% by weight)).

  Moreover, the silicon modified epoxy resin of composition number 8 was prepared as a rubber-modified thermosetting resin composition.

[Preparation of solder paste]
The solder powder, the thermosetting resin composition of composition numbers 1 to 8 in Table 1 above, the imidazole curing agent, and the flux are blended in the proportions shown in Table 2, kneaded, and paste number 1 to 8 solder pastes were prepared.
As the solder powder, a solder powder whose composition is an alloy having Sn of 96.5% by weight, Ag of 3% by weight, and Cu of 0.5% by weight was used.
Moreover, as a flux, what contains a rosin-type component, a thixotropy imparting agent, an activator (organic acid), and a solvent was used.

  In addition, in the solder paste of paste numbers 1-8, the thermosetting resin composition of the same number (composition number) in Table 1 is used as a thermosetting resin composition.

  Among the solder pastes of paste numbers 1 to 8 in Table 2, in the pastes of paste numbers 1 to 3, the flexural modulus of the cured resin of composition numbers 1 to 3 in Table 1 is 5.0 GPa or less. Thus, a thermosetting resin composition in which a carboxyl group-terminated butadiene-acrylonitrile copolymer rubber (CTBN) is blended as a rubber component with an epoxy resin is used, and the solder paste satisfies the requirements of the present invention. .

  Further, in the solder paste of paste number 8 in Table 2, a silicon-modified epoxy resin having a flexural modulus of 5.0 GPa or less after curing is used as a rubber-modified thermosetting resin composition. The solder paste meets the requirements.

  On the other hand, in the solder pastes with paste numbers 4 to 7 in Table 2, a thermosetting resin composition having a flexural modulus after curing exceeding 5.0 GPa is used, and the solder paste does not satisfy the requirements of the present invention. It has become.

[Production of mounting body]
Twenty lots of each of the solder pastes with paste numbers 1 to 8 in Table 2 were prepared and used for the following mountings.

  Here, referring to FIG. 1 and FIG. 2, a multilayer ceramic capacitor is mounted as a surface mount electronic component on a component connecting conductor (land made of Cu foil) disposed on a component mounting board. A method for manufacturing the mounting body will be described.

  First, using a metal mask having a thickness of 100 μm, as shown in FIG. 1, the solder paste 15 having paste numbers 1 to 8 in Table 2 was printed on the lands (Cu foil portions) 3 a and 3 b of the component mounting substrate 4. .

  Then, as a surface mount electronic component, a multilayer ceramic capacitor (length: 1 mm, width: 0.5 mm, thickness: 0.5 mm) 2 is used, and a land 3a on which the solder paste 15 of the component mounting board 4 is printed. , 3b and heating with a reflow profile having a peak temperature of 250 ° C., the multilayer ceramic capacitor 2 is mounted on the component mounting board 4, and a mounting body as shown in FIG. The mounted bodies (joint parts) A of Nos. 1 to 8 were produced.

  In each mounting body (mounting bodies with mounting body numbers 1 to 8) A of this embodiment, each solder of Table 2 having the same paste number as the mounting body number of Table 3 is used as the solder paste 15 (FIG. 1). Paste is used.

  In this mounting body, as shown in FIG. 2, the external electrodes 1a, 1b of the multilayer ceramic capacitor 2 are placed on the lands 3a, 3b of the component mounting board 4 with the solder 5 derived from the solder paste 15 (FIG. 1). The surface of the solder 5 and a part of the component mounting board 4 are covered with the resin layer 6 (FIG. 2) derived from the thermosetting resin composition contained in the solder paste 15 (FIG. 1). ing.

[Bending elastic modulus of resin layer after curing]
About each mounting body of the mounting body numbers 1-8, the bending elastic modulus of the resin layer 6 (FIG. 2) derived from the thermosetting resin composition contained in the said solder paste is measured by the method prescribed | regulated to JISK7171. evaluated. The results are shown in Table 3.

  As shown in Table 3, in the mounting bodies of mounting body numbers 1 to 7, the flexural modulus increases as the blending ratio of the rubber component, that is, the carboxyl group-terminated butadiene-acrylonitrile copolymer rubber (CTBN) increases. It decreased, and it was confirmed that the bending elastic modulus of the resin layer is 5 GPa or less in the mounting body of mounting body numbers 1 to 3 manufactured using the solder paste of paste numbers 1 to 3 (Table 2).

  Moreover, the mounting body of the mounting body number 8 produced using the solder paste of the paste number 8 (Table 2) containing the silicon | silicone modified epoxy resin which is a thermosetting resin composition modified | denatured as rubber | gum as a thermosetting resin composition. Also in this case, it was confirmed that the flexural modulus of the resin layer was 0.7 GPa and lower than 5 GPa.

[Measurement of bonding strength before and after thermal shock test and number of cracks after thermal shock test]
The manufactured mounting body was examined for bonding strength before and after the thermal shock test, and the number of occurrences of cracks was examined for the mounting body after the thermal shock test.

  The thermal shock test is performed by performing 1000 cycles of maintaining the mounted body at −55 ° C. and 125 ° C. for 30 minutes, respectively, and mounting the multilayer ceramic capacitor and the component before the thermal shock test and after the 1000 cycle thermal shock test. The bonding strength of the substrate was examined. The bonding strength was measured as the maximum strength when the mounted multilayer ceramic capacitor was laterally pressed with a bonding tester. The results are shown in Table 4.

  In addition, the number of occurrences of cracks was determined by observing the cross section of the mounting body with a metal microscope to check the bonding state. Counted the number. The results are also shown in Table 4.

In addition, the mounting body of the mounting body numbers 1-8 of Table 4 is the same mounting body as the mounting body of the mounting body numbers 1-8 of Table 3.
As shown in Table 4, paste number 1 including a thermosetting resin composition having a high content of carboxyl group-terminated butadiene-acrylonitrile copolymer rubber (CTBN) as in the mounting bodies of mounting body numbers 1 to 3 In the mounting body in which the bending elastic modulus of the cured resin layer is 5 GPa or less, which is mounted using the solder paste of -3 (Table 2), the bonding strength is reduced even after the thermal shock test described above. Not much was recognized.

  Moreover, after the hardening which mounted using the solder paste of paste number 8 (Table 2) whose thermosetting resin composition which comprises a solder paste is a silicone modified epoxy resin like the mounting body of the mounting body number 8 Even in the case of a mounting body having a bending elastic modulus of 5 GPa or less of the resin layer, a decrease in the bonding strength after the thermal shock test was not recognized.

  In addition, in the mounting bodies having the mounting body numbers 1 to 3 and the mounting body number 8, no cracks were observed in the resin layer after the thermal shock test.

  On the other hand, the solder of paste numbers 4 to 7 (Table 2) containing a thermosetting resin composition containing little or no carboxyl group-terminated butadiene-acrylonitrile copolymer rubber (CTBN) In the case of the mounting bodies of mounting body numbers 4 to 7 produced using the paste, as shown in Table 4, after the thermal shock test, a decrease in bonding strength was observed, and the occurrence of cracks in the resin layer was observed. .

  From these results, even when subjected to thermal shock by using a solder paste satisfying the requirements of the present invention, containing a thermosetting resin composition having a flexural modulus of 5 GPa or less after thermosetting, the bonding strength It was confirmed that a mounting body in which there was no decrease in the thickness and cracks were not generated in the resin layer was obtained.

[Evaluation of bonding strength at high temperature]
With respect to the mounting bodies of mounting body numbers 1 to 8, the surface mounting type electronic component (multilayer ceramic capacitor) mounted on the component mounting board is laterally pressed with a bonding tester under the temperature condition of 260 ° C. assuming reflow soldering. The occurrence mode of fracture (peeling) at the interface between the resin layer and the component mounting board was investigated.

  As a result, mounting of mounting body numbers 1 to 3 in Table 4 mounted using the solder paste of paste numbers 1 to 3 (Table 2) having a high content of carboxyl group-terminated butadiene-acrylonitrile copolymer rubber (CTBN). In the case of the body and the mounting body mounted using the solder paste of paste number 8 (Table 2) whose thermosetting resin composition is a silicon-modified epoxy resin, the surface mounting type electronic component is pressed. However, the adhesion at the interface between the resin layer and the component mounting substrate was maintained, and no occurrence of breakage (peeling) at the interface was observed.

  On the other hand, in the case of the mounting body of mounting body numbers 4 to 7 containing little or no carboxyl group-terminated butadiene-acrylonitrile copolymer rubber (CTBN), the interface between the resin layer and the component mounting board The occurrence of fracture (peeling) was observed, and it was confirmed that sufficient bonding strength could not be obtained at high temperatures.

  From this result, in the mounting body produced using the solder paste satisfying the requirements of the present invention, containing a thermosetting resin composition having a flexural modulus of 5 GPa or less after thermosetting, the resin layer and the component mounting board It was confirmed that there was little fracture at the interface and sufficient bonding strength was obtained even at high temperatures.

[Solder flow-out test]
The mounting bodies of mounting body numbers 1 to 8 were reflow-heated again at a peak temperature of 260 ° C., and the number of cracks generated in the resin layer and the number of solder flow-outs were evaluated.
The results are shown in Table 5.

  As shown in Table 5, the mounting bodies of mounting body numbers 1 to 3 mounted using a solder paste with a high content of carboxyl group-terminated butadiene-acrylonitrile copolymer rubber (CTBN), and mounting body number 8 In the case of a mounting body mounted using a solder paste in which the thermosetting resin composition constituting the solder paste is a silicon-modified epoxy resin, no crack was generated in the resin layer, and no solder flow was observed.

  On the other hand, in the case of mounting bodies with mounting body numbers 4 to 7 that are mounted using a solder paste that contains little or no carboxyl group-terminated butadiene-acrylonitrile copolymer rubber (CTBN) Cracks were generated in the layer, and the occurrence of short-circuit defects due to the flow of solder was also observed.

  From this result, in a mounting body using a solder paste that contains a thermosetting resin composition having a bending elastic modulus of 5 GPa or less after thermosetting and satisfies the requirements of the present invention, reflow is performed at a high temperature (260 ° C.). Even when heated, it was confirmed that cracks were not generated in the resin layer, and solder flow-out could be suppressed and prevented.

  In the above examples, bisphenol A type epoxy resin was used as the resin component constituting the thermosetting resin composition, but the resin component is not limited to this, and other than bisphenol A type, Different types of epoxy resins (for example, bisphenol type, novolak type, cycloaliphatic type, long chain aliphatic type, glycidyl ester type, glycidylamine type, silane modification, urethane modification, rubber modification, chelate modification, water-based, polyfunctional epoxy resin ), Polyurethane resin, phenol resin, urea resin, melamine resin, guanamine resin, unsaturated polyester resin, vinyl ester resin, diallyl phthalate resin, silicon resin (silicone resin), polyimide resin, alkyd resin, dicyclopentadiene resin, acrylic Resin, diethylene glycol bis (allyl carbonate) Boneto) resin, it is possible to use a rubber-modified resin, it is possible to use a combination of these resins alone, or two or more kinds.

  Further, in the above examples, carboxyl group-terminated butadiene-acrylonitrile copolymer rubber (CTBN) was used as the rubber component, but the rubber component is not limited to this, and a styrenic block copolymer, amino group, It is possible to use terminal butadiene-acrylonitrile copolymer rubber (ATBN), fine particle acrylic rubber, carboxyl group-terminated polybutyl acrylate, and the like.

  In addition, although a silicone-modified epoxy resin was used as the rubber-modified thermosetting resin composition, the means for rubber modification is not limited to silicon modification, and various rubbers such as urethane modification, acrylic modification, CTBN modification, etc. A modified thermosetting resin composition can be used.

  There is no particular restriction on the composition of the solder. For example, it is possible to use solders having various compositions such as Sn—Ag, Sn—Cu, Sn—Bi, Sn—Sb, and Sn—Zn. Is possible.

  In the above embodiment, the joining component is a mounting board (component mounting circuit board) in which a surface mounting type electronic component (multilayer ceramic capacitor) is soldered and mounted on the component mounting board using the solder paste of the present invention. However, the joining parts in the present invention are not limited to this example, and at least some of the constituent members should be various parts to be soldered by the solder paste of the present invention. Can do.

  In addition, the invention of the present application is not limited to the above examples in other points as well, and relates to the type of curing agent and the type of flux for curing the thermosetting resin composition, and within the scope of the invention. Various applications and modifications can be added.

According to the present invention, for example, when a mounting board on which a surface-mounted electronic component is soldered and mounted using a solder paste is subjected to a high-temperature re-reflow heating process, solder remelting or volume expansion is caused. Even in such a case, it is possible to efficiently produce a highly reliable joint component that does not cause cracks in the resin layer covering the solder and does not cause the molten solder to flow out and cause a short circuit failure. It becomes possible.
Therefore, the present invention can be widely applied to the field of manufacturing circuit boards and multilayer circuit boards manufactured through the process of mounting the surface mount type electronic component using the solder paste, and the field of solder paste used therefor. Is possible.

It is a figure explaining the method of mounting a surface mount type electronic component on a component mounting board using the solder paste concerning the Example of this invention. It is a figure which shows the structure of the joining component (component mounting circuit board) concerning the Example of this invention which mounted the surface mounting type electronic component on the component mounting board using the solder paste of this invention. (a), (b), (c) is a figure which shows the process of mounting a surface mounting type electronic component on a component mounting board using the conventional solder paste.

Explanation of symbols

1a, 1b External electrode 2 Surface mount electronic component (multilayer ceramic capacitor)
3a, 3b Mounting land 4 Component mounting substrate 5 Solder 6 Resin layer 15 Solder paste A Mounted body (joint component)

Claims (5)

A thermosetting resin composition having a flexural modulus of 5 GPa or less after thermosetting;
With flux,
A solder paste containing solder powder.   The solder paste according to claim 1, wherein the thermosetting resin composition contains a rubber component.   The solder paste according to claim 2, wherein the rubber component is a carboxyl group-terminated butadiene-acrylonitrile copolymer rubber.   The solder paste according to claim 1, wherein the thermosetting resin composition is a rubber-modified thermosetting resin composition.   At least a part of constituent members are soldered by using the solder paste according to any one of claims 1 to 4.

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