JP6543890B2 - High temperature solder alloy - Google Patents

Description

  The present invention relates to high temperature solder alloys. In particular, the present invention relates to a lead-free high-temperature solder alloy used in the field of lead-free solder mounting technology used for wiring connection of parts such as electric devices, electronic devices, communication devices, etc.

  The use of Sn-Pb eutectic or Pb-based solder alloy with 90% by mass or more of Pb, which is conventionally used, contains toxic lead, and its use is being restricted. In recent years, as an alternative to Sn-Pb eutectic solder, Sn-Ag eutectic or Sn-Ag-Cu-based solder containing no lead has been widely spread, and is used to connect electronic parts and printed circuit boards. However, if lead-free solder containing Sn as the main component is used, the soldered part will be exposed to a high temperature of, for example, 260 ° C., and in the case of connection inside the electronic component, so-called heat resistance such as melting or disconnection of the electrode. Sexual problems may occur.

  Moreover, in the power device field, the demand for high temperature use has been increasing in recent years, and from the one that had been good at the operating temperature specification of about 150 ° C of self-heating level conventionally, 175 ° C, 200 ° C and its power device products are required Operating temperature specifications are rising. Therefore, heat resistance improvement is calculated | required also about the connection part of a power device. In JEITA (Electronic Information Technology Industries Association) Environmentally Conscious Advanced Mounting Technology Results Report 2011 (July 2011), Pb-based (as a main component of lead, for example, materials with a melting point of 290 ° C or higher) as the technology so far The heat resistance is secured by the composition. Further, there is also a report that the heat resistance required temperature of the die bond joint used for the internal connection of electronic parts needs to be 260 ° C. or more. In the case of Sn—Ag—Cu-based solder widely used as a conductive adhesive and Pb-free solder, the solidus temperature is around 220 ° C., and it melts at the above-mentioned heat request temperature 260 ° C. Therefore, heat resistance defects such as melting and disconnection of the electrodes described above may occur.

  A through type ceramic characterized in that a crack is not generated in the interface between the inner electrode and the inner wall of the hole of the structure or the inside of the structure using Bi-based solder used as a high temperature solder alloy and having sufficient inner electrode strength. A capacitor is known (see Patent Document 1). Insertion mounting parts such as ceramic capacitors are additionally flow soldered via leads. However, when the Bi-based solder of Patent Document 1 is applied to a surface-mounted component such as a semiconductor element requiring two-level reflow, bonding defects (for example, generation / growth of interface reaction layer, etc.) (3), and there is a concern that bonding reliability may be reduced due to poor resistance to reflow. In addition, the invention disclosed in Patent Document 1 is directed to an insertion mounting component, and the characteristic required for the solder is that there is no volume contraction at the time of solidification, and the solder for bonding the surface mounting component is used. It is different from the required characteristics.

  In addition, lead-free solder containing Bi as a main component is known (see Patent Document 2). However, the solder alloy disclosed in Patent Document 2 contains a relatively large amount of Sn at 1 to 5% by mass, so the proportion of the low melting point layer (Sn layer: melting point 232 ° C.) in the joint is large. Repeating the reflow process at a high temperature is a problem in that there is a concern of remelting in the low melting point layer.

JP 2007-181880 A International Publication No. 2012/002173

  In order to secure the joint reliability of the surface mounted parts requiring the two-layer reflow, in particular, the initial characteristics and the reflow resistance, while suppressing the formation of intermetallic compounds in the vicinity of the interface between the object to be joined and the solder joint What is needed is a high temperature solder alloy having a composition that does not remelt the solder joints during reflow.

  In order to solve the above problems, the present inventors have found that a desired characteristic can be obtained by using a Bi-Sn alloy to which a very small amount of Sn is added based on Bi having a relatively high melting point. The present invention has been completed.

  The invention, according to one embodiment, is a high temperature solder alloy, comprising 0.05% to 0.3% by weight tin, the balance being bismuth and unavoidable impurities.

  In the high temperature solder alloy, the tin content is more preferably 0.1% by mass to 0.3% by mass.

  The high temperature solder alloy preferably further contains silver in an amount of 0.5% by mass to 11% by mass.

  More preferably, the silver is contained in an amount of 0.5% by mass to 2.5% by mass in the high temperature solder alloy.

  Moreover, it is preferable to use the said high temperature solder alloy for joining of surface mounting components.

  According to another embodiment, the present invention is a semiconductor device comprising a joined body formed by joining a metal substrate and a Si chip or a SiC chip with the high temperature solder alloy described above.

  The high temperature solder alloy according to the present invention suppresses the formation of an intermetallic compound including Bi near the bonding object and the solder bonding interface and secures the reflow resistance without remelting the solder bonding portion in the reflow process. Is possible. In the present specification, the fact that the solder joint does not remelt in the reflow process at a temperature of 260 ° C. is defined as “with reflow resistance to solder”. In particular, by adding Sn to a Bi-based solder, a surface treatment component of the body to be joined, for example, an intermetallic compound of Ni, P, Au, Ti, etc., and Sn is formed in the vicinity of the bonding interface to form a barrier layer. By doing this, it is possible to suppress the diffusion of the surface treatment component into the solder. Further, by setting the addition amount of Sn in a predetermined range, it is possible to reduce Sn having a low melting point, and to secure a joint portion in which the solder does not remelt during two-level reflow. This makes it possible to ensure bonding reliability.

FIG. 1 is a conceptual view for explaining a surface mounting component in which a high temperature solder alloy according to the present invention is preferably used, and a two-level reflow process. FIG. 2 is a schematic view showing a cross section of a joined body in which a chip and a substrate are joined using the high temperature solder alloy according to the present invention. FIG. 3 is a schematic view showing a cross section of a joined body in which a chip and a substrate are joined using a Sn-free Bi solder alloy. FIG. 4 is a conceptual view showing a bonding sample used in Example 1. FIG. 5 is a graph showing the temperature profile of the reflow process in Example 1. FIG. 6 shows an observation result of a fractured surface by a shear test of the joined body shown in FIG. 4 using the high temperature solder alloy according to the present invention. FIG. 7 shows an observation result of a fractured surface by shear test of a joined body using a Bi solder alloy to which Sn is not added. FIG. 8 shows an observation result of a cross section perpendicular to the bonding surface of the joined body shown in FIG. 2 using the high temperature solder alloy according to the present invention. FIG. 9 shows an observation result of a cross section perpendicular to the bonding surface of the joined body shown in FIG. 3 using a Bi solder alloy to which Sn is not added. FIG. 10 shows a Bi-Sn binary alloy phase diagram. FIG. 11 is a photomicrograph showing changes in voids of the high temperature solder alloy according to the present invention and the solder alloy of the comparative example after the reflow process. FIG. 12 is a graph showing the temperature profile of the reflow process in Example 2. FIG. 13 is a view schematically showing a measurement outline of the wetting spread area and the contact angle of the solder alloy to the substrate. FIG. 14 is a graph showing changes in the wetting spread area and the contact angle when the amount of Ag added to Bi is changed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited by the embodiments described below.

First Embodiment Bi--Sn Binary High-Temperature Solder Alloy
The present invention, according to a first embodiment, is a high temperature solder alloy containing 0.05% by mass to 0.3% by mass of tin (Sn), and the balance from bismuth (Bi) and unavoidable impurities Become. Inevitable impurities mainly include copper (Cu), nickel (Ni), zinc (Zn), iron (Fe), aluminum (Al), arsenic (As), cadmium (Cd), silver (Ag), gold (Au) ), Indium (In), phosphorus (P), lead (Pb) and the like. Also, the high temperature solder alloy according to the present invention is a Pb-free lead-free high temperature solder alloy.

  In the Bi-Sn binary high-temperature solder alloy, by containing 0.05% by mass to 0.3% by mass of Sn, the solder joint portion is formed in the second and subsequent reflow steps of the two-layer reflow step described in detail later. An effect of preventing deterioration of bonding characteristics due to the formation of voids can be expected without remelting. Further, an intermetallic compound of a surface treatment component of the object to be joined and Sn is formed in the vicinity of the joint interface between the object to be joined and the solder, and the surface treatment component diffuses into the solder material to promote brittle fracture. To prevent. In addition, the addition of a small amount of Sn to Bi can be expected to have the effect of slightly improving the ductility of Bi.

  The addition amount of Sn is preferably 0.1 to 0.3% by mass. When it is assumed that Sn is not formed in part due to the segregation of Sn in the solder layer, the amount of Sn added is in the above range, It is possible to ensure the formation of the surface treatment component of and the intermetallic compound of Sn.

  The high temperature solder alloy according to the present embodiment can be prepared by melting the raw materials of Bi and Sn in an electric furnace according to a conventional method. In addition, the high temperature solder alloy according to the present embodiment can be processed as a plate solder, a thread solder, or a powder of the alloy to be combined with a flux as a cream solder.

  When a high temperature solder alloy is processed into powder and combined with a flux to form a cream solder, the particle size of the solder powder preferably has a particle size distribution in the range of 10 to 100 μm, and in the range of 20 to 50 μm More preferably, The average particle size can be, for example, 25 to 50 μm as measured using a general laser diffraction / scattering type particle size distribution measuring device. Although any flux can be used as the flux, it is particularly preferable to use a flux having a composition capable of suppressing the oxidation of Bi. For example, although halogen activated rosin flux etc. can be mentioned, it is not limited to this.

  The high temperature solder alloy according to the present embodiment is preferably used to join surface mounted components that require a two-level reflow process. The conceptual diagram which manufactures an electronic member by a two-levels reflow process in FIG. 1 is shown. Here, in the two-layer reflow process, after the first reflow process is performed to manufacture a predetermined electronic member, the electronic member manufactured further is electrically connected to another member in general. In other words, applying a solder material different from the first reflow process to a different bonding site to carry out the second reflow process. At this time, there is a problem that the solder alloy used in the first reflow process is remelted and a void is generated, so that a bonding failure or the like is easily generated. In addition, the number of times of the reflow process in two-level reflow is not limited to two.

  More specifically, the method includes a first reflow step of mounting the high temperature solder alloy 1 on the metal substrate 3 and further mounting the Si chip or the SiC chip 2 and heating with a predetermined temperature profile, A process of manufacturing a semiconductor device 100 such as a power module formed by bonding 4 and sealing with a sealing material 5 and heating the semiconductor device 100 with a predetermined temperature profile using another solder material (not shown) Then, it is used for the manufacture of an electronic member including a second reflow process of bonding to the printed circuit board 400. Similarly, surface-mounted components such as Small Outline Package (SOP) 200 and Quad Flat Package (QFP) 300 are soldered to the printed circuit board 400. The high temperature solder alloy according to the present invention is advantageously used in that it is difficult to be remelted in the second and subsequent reflow processes after the joint is formed in the first reflow process.

  Here, the predetermined temperature profile in the first reflow step is preferably heated to a solidus temperature of Bi of 270 ° C. or higher, and the heating peak temperature is set to about the liquidus temperature of the alloy + 30 ° C. Good wettability can be obtained by maintaining the heating time for at least 60 seconds or more. The heating peak temperature does not necessarily need to be heated above the liquidus temperature, and in the case of a component closer to pure Bi, it is good by heating at around 270 ° C. + 30 ° C., which is the solidus temperature of pure Bi. Connection can be secured. As an example, although the heating temperature profile shown in FIG. 5 used in Example 1 can be used, it is not limited to this.

  FIG. 2 is a view schematically showing a cross section perpendicular to the bonding surface of the bonded body after bonding the Si chip 2 to the copper substrate 3 using the high temperature solder alloy 1 according to the present invention. In FIG. 2, a copper substrate 3, a high temperature solder alloy 1, and a Si chip 2 are sequentially stacked. The Si chip 2 has a structure in which an Au plating film 23, an Ni—P film 22, an Al—Si film 21, and a Si layer 20 are sequentially stacked in order from the bonding surface of the high temperature solder alloy 1. The high temperature solder alloy according to the present invention is also preferably used for bonding the back surface electrode of the SiC chip to the metal substrate, and the back surface structure of the SiC chip is, for example, Au plated film in order from the bonding surface of the high temperature solder alloy Ni-P plating film, Al-Si film, and Ti film.

When the first reflow process is performed with the temperature profile as described above, the Sn—Ni compound layer 1 b is formed at the interface with the Si chip 2 in the high temperature solder alloy 1 layer. The Sn-Ni compound layer 1 b is mainly composed of Ni ₃ Sn ₄ , Ni ₃ Sn ₂ , or NiSn, and tends to be generated in the order described. It is considered that this Sn-Ni compound layer 1b can prevent the diffusion of Ni into the high temperature solder alloy layer 1a and can suppress the formation of a Bi-Ni compound. Bi-Ni compounds are known to shorten the fracture life of the bonding layer because they are hard and brittle. In order to form the Sn—Ni compound layer 1 b to a thickness that prevents the diffusion of Ni, it is necessary to include at least 0.05 mass% of Sn in the Bi—Sn binary high-temperature solder alloy. If the content of Sn is less than 0.05% by mass, the Sn-Ni compound layer 1b becomes thin, and the barrier effect on Ni diffusion is reduced. When an external force is applied to the joined body shown in FIG. 2, the fracture surface is typically more brittle than the Sn-Ni compound layer 1b, and in the high temperature solder alloy layer 1a, for example, a cross section A-A in the figure. It is formed. Incidentally, the back surface processing components other than Ni, for example, P, Au, for the barrier layer composed of a Ti or the like and Sn, Ni-SnP intermetallic compound _{(Ni 2 SnP, Ni 10 Sn} 5 P 3), AuSn intermetallic compound _{(AuSn 4, AuSn 2, AuSn} ), Ti-Sn intermetallic compound _{(Ti 6 Sn 5, Ti 5} Sn 3) and the like.

FIG. 3 is a view schematically showing a cross section perpendicular to the bonding surface after the Si or SiC chip 2 is bonded to the copper substrate 3 using the Sn-free Bi—Ge solder alloy 9. The layer configuration of the Si chip 2 is the same as that of the joined body shown in FIG. When the first reflow process is performed using the Bi-Ge solder alloy 9 with the temperature profile as described above, the interface between the Bi-Ge solder alloy 9 layer and the Si chip 2 in the solder layer is relatively large. The Bi-Ni compound 9b is formed in a wide range. Bi-Ni compound is typically a _Bi 3 Ni, a layer of Bi-Ni compound 9b, rather than Bi alloy, further brittle, a short rupture life. Therefore, when an external force is applied to the joined body shown in FIG. 3, typically, the Bi-Ni compound 9b layer is more brittle than the Bi alloy layer 9a, for example, the AA cross section in the figure is a fracture surface Become.

  According to the Bi-Sn binary high-temperature solder alloy according to the first embodiment of the present invention, a junction with high junction reliability, in which diffusion of Ni, which is a component of an object to be joined, into the solder alloy layer is suppressed after joining Can be formed. In addition, when the second and subsequent reflow processes are performed in the two-level reflow process, the solder is not remelted, and therefore, it can be preferably used in soldering of surface-mounted components.

[Second embodiment: Bi-Sn-Ag ternary high-temperature solder alloy]
The present invention, according to a second embodiment, is a high temperature solder alloy containing 0.05% by mass to 0.3% by mass of Sn and 0.5% by mass to 11.0% by mass of Ag. And the balance is composed of Bi and unavoidable impurities. The high temperature solder alloy according to the second embodiment is also a lead-free high temperature solder alloy containing no Pb except for inevitable impurities. Since Ag can improve the wettability of Bi, the characteristics of the Bi—Sn binary solder according to the first embodiment can be further improved.

  More preferably, the high temperature solder alloy according to the present embodiment contains 0.5% by mass to 2.5% by mass of Ag. With the above preferable addition range, the liquidus temperature is in the range of 262 ° C. to 269 ° C., and the bonding process temperature can be reduced (for example, when the amount of Ag is 11%, the liquidus temperature 360 ° C.) Is obtained.

  The high temperature solder alloy according to the present embodiment can also be prepared by melting the raw materials of Bi, Sn and Ag in an electric furnace according to a conventional method. In addition, the high temperature solder alloy according to the present embodiment can also be processed as a plate solder, as a thread solder, or as a powder solder which is combined with a flux to form a cream solder. The characteristics of the flux are as described in the first embodiment.

  The high temperature solder alloy according to the present embodiment is also used to join surface mounted components that require a two-level reflow process. Therefore, a member to which the ternary high-temperature solder alloy according to the second embodiment is applied, an object to be joined, a bonding profile, and the like can be substantially the same as those described in the first embodiment.

  Furthermore, also in the ternary high-temperature solder alloy according to the second embodiment, after bonding, a Sn—Ni compound layer is formed in the high-temperature solder alloy layer at the bonding interface with the Si chip, and a barrier effect against Ni diffusion is obtained. The same effects as those of the first embodiment can be obtained.

  The Bi-Sn-Ag ternary high-temperature solder alloy according to the second embodiment of the present invention has all the advantages of the first embodiment, and further has improved wettability and reflow resistance.

  In the following, the invention will be described in more detail with reference to examples. However, the following examples do not limit the present invention.

[1. Characteristic evaluation of Bi-Sn binary high temperature solder alloy]
The bonding characteristics were evaluated using the Bi-Sn binary high-temperature solder alloy according to the example of the present invention and the Bi-Ge-based solder of the comparative example.

  (1) A bondability evaluation sample was prepared. A fixed amount of three Bi-based solders shown in Table 1 was placed on a bonding surface of a copper plate with a diameter of 10 mm using a metal mask (opening: 5 mm, plate thickness: 150 μm). Here, the solder used was a cream solder containing a halogen activated rosin flux in the range of 10% by mass to 15% by mass. Thereafter, the Si chip 2 was stacked. As the Si chip, one having a layer configuration as shown in FIG. 2 was used. A bonding evaluation sample is shown in FIG. Next, heating and melting were performed in a two-step temperature profile shown in FIG. 5 to bond the Si chip and the Cu plate to obtain a bonded body (initial product, first reflow process).

  (2) The shear strength of each of the three Si-Cu bonded bodies obtained in (1) was measured using a joint strength tester (manufactured by RHESCA, model: STR-1001). The shear rate was 1 mm / min. From the measurement results of shear strength, the Sn-added Bi-based solder (B2S) according to the present invention exhibited high strength of 25 MPa or more. On the other hand, Bi-based solder (BG, B10AG) to which Sn was not added had a bonding strength of about 11 MPa.

  (3) The appearance and cross-sectional analysis of the fractured sample after the shear test were performed. FIG. 6 (a) is a photomicrograph of a fractured surface of a fractured sample using B2S solder. In FIG. 6 (a), a dimple-like pattern can be confirmed, and it is inferred that fracture has occurred in the Bi high-temperature solder alloy layer. Referring to FIG. 2 described in the embodiment of the present invention, it is inferred that it is broken at the AA cross section of FIG. FIG.6 (b)-(i) shows the EDX cross-section analysis result about the element considered to be added to the conjugate | zygote. FIG. 6 (b) shows that a large amount of Bi exists in the fracture surface, and (d) shows that a large amount of fracture surface Sn exists. On the other hand, FIG. 6 (f) shows that the fracture surface contains less Ni.

  FIG. 7 (a) is a photomicrograph of a fractured surface of a fractured sample using BG solder. The porous structure of the Ni—P layer is reflected in FIG. 7A, and it is inferred that the fracture surface is not the Bi high temperature solder alloy layer. Referring to FIG. 3 described in the embodiment of the present invention, it is inferred that it is broken at the A-A cross section of FIG. FIG.7 (b)-(i) shows the EDX analysis result about the element considered to be added to the conjugate. FIG. 7 (b) shows that the amount of Bi in the fracture surface is smaller than that in FIG. 6 (b). On the other hand, FIG. 7 (e) shows that P is more present in the fracture surface than in FIG. 6 (e), and (f) shows that Ni is more present in the fracture surface. Moreover, FIG.7 (c) shows that many Ge which is a component of BG solder exists.

  From these fracture surface observation results and EDX analysis results, it can be explained that the reason for the difference in bonding strength is that the failure mode differs between the Sn-containing Bi solder according to the present invention and the solder not containing Sn. .

  (4) The observation and EDX analysis of the cross section perpendicular to the bonding surface of the Si-Cu bonded body before the shear test were performed. FIG. 8A is a photomicrograph of a cross section of a joined body using B2S solder. In FIG. 8A, a high temperature solder alloy 1 layer, an Au plating film, a Ni-P film, and an Al-Si film are formed in that order. In addition, since the Au plating film thickness is less than 0.1 μm, it can not be distinguished by the cross-sectional image of FIG. FIG.8 (b)-(i) shows the EDX analysis result about the element considered to be added to the conjugate | zygote. It can be seen from FIG. 8 (d) that Ni has not diffused to the high temperature solder alloy layer. In addition to the fact that Sn is located between the high temperature solder alloy 1 layer and the Si chip 2, the presence of Sn in the high temperature solder alloy layer can also be confirmed from FIG. 8 (i). In the B2S solder joint, the diffusion of Ni was suppressed, and the Bi—Ni-based compound was not formed. For this reason, it can be inferred that the fractured sample after the shear test is broken in the solder layer. This is because the formation of the Sn-Ni-based compound at the interface between the Si chip and the solder suppresses the diffusion of Ni. That is, it can be said that the joining property is improved by the Sn addition effect (suppressing the formation of the Bi-Ni-based intermetallic compound in the vicinity of the interface between the joined body and the solder joint).

  FIG. 9A is a photomicrograph of a cross section of a bonded body using BG solder. In FIG. 9A, a high temperature solder alloy 1 layer, an Au plating film, an Ni-P film, and an Al-Si film are formed in that order. In addition, since the Au plating film thickness is less than 0.1 μm, it can not be distinguished by the cross-sectional image of the magnification of FIG. FIG.9 (b)-(i) shows the EDX analysis result about the element considered to be added to the conjugate | zygote. It can be seen from FIG. 9 (d) that Ni is widely diffused into the high temperature solder alloy layer. Thus, in the joint of a joined body using BG solder to which Sn is not added, Ni, which is a component of the surface film of the Si chip, diffuses into the solder (diffusion length: about 53 μm at maximum), and Bi-Ni-based Formed a compound. From this, it can be determined that the fractured sample after the shear test was broken at the interface between the Bi-Ni compound layer formed in the solder alloy layer or the Bi-Ni compound layer and the Ni-P film.

  (5) It is assumed that a low melting point layer is generated in the solder joint when adding Sn excessively, and the solder joint remelts in the two-level reflow. Therefore, the formation of the Bi-Ni-based intermetallic compound in the vicinity of the interface between the body to be joined and the solder joint was suppressed, and the determination of the amount of Sn addition which does not remelt the solder joint during two-level reflow was examined.

  According to the Bi-Sn alloy phase diagram in FIG. 10, the solidus temperature rises from 247 ° C. to 260 ° C. when the Sn content is reduced from 0.3% by mass to 0.14% by mass. Therefore, in the equilibrium state, it can be said that when the amount of added Sn is 0.14 mass% or less, it has a reflow resistance at a temperature of 260 ° C. However, it is a non-equilibrium state at the time of mounting, and a phenomenon in which the composition becomes locally nonuniform occurs due to composition variation of the alloy resulting from diffusion of the substance from the object to be joined and segregation in the solder joint. The amount of Sn added was set in the range of 0.05% by mass to 2.0% by mass.

  (6) Using a Bi-Sn binary high-temperature solder alloy having a different Sn content, heating was performed along the temperature profile of FIG. 5 in the same process as (1) above to obtain a Si-Cu bonded body (Early goods). With respect to this Si-Cu bonded initial product, the reflow resistance (temperature: 260 ° C., holding time: 3 min) was measured three times, and the resistance to reflow was examined by X-ray observation. If expansion of the void or movement of the void is observed, it can be determined that remelting has occurred.

  FIG. 11 shows the result of the X-ray observation. In the X-ray photograph, the black part shows the high temperature solder alloy 1 and the whitish part shows the Cu substrate 3 which is a bonded body. Also, the white portion in the high temperature solder alloy 1 is a void 50. From FIG. 11, re-melting (void expansion) of the solder joint was confirmed in the samples to which 1% by mass and 2% by mass of Sn were added. From these results, it has been found that a Bi—Sn binary high-temperature solder alloy in which the amount of Sn is 0.3 mass% or less is useful because it does not cause remelting of the solder joint. It was found from FIG. 11 that there was no change in void expansion, movement, etc. between the case where the reflow process was performed once and the case where it was performed three times. Although not shown, the same applies to the case where the reflow process is performed twice.

  The high temperature solder alloy according to the present invention, in which a predetermined amount of Sn is added to a Bi based solder, forms an intermetallic compound of Ni and Sn which is a surface treatment component of the joined body in the vicinity of the bonding interface to form a barrier layer. Thus, it is possible to suppress the diffusion of the surface treatment component into the solder and to secure a joint where the solder does not remelt at the time of the two-level reflow.

[2. Characteristic Evaluation of Bi-Ag Solder Alloy]
In this experimental example, in place of the characteristic evaluation of the Bi-Sn-Ag ternary high-temperature solder alloy, the addition effect of Ag for improving the characteristics of the Bi solder was investigated. When the Ag ₃ Sn intermetallic compound is formed by the addition of Ag, the low melting point layer (Sn layer) decreases, and the improvement of the reflow resistance is predicted, and the addition of Ag demonstrates the Bi-Sn high temperature solder alloy demonstrated in the previous example. It can be reasonably inferred that the advantageous properties are not impaired.

  (1) The wettability evaluation sample was produced. Solder pieces (weight: about 100 mg) of 2.5 mm × 3 mm × 1.5 mm were mounted on the bonding surface of a 20 mm ×× 1.6 mm copper-clad double-sided board (copper foil thickness: 50 μm). Solder pieces were coated with JEITA standard flux (halogen activated rosin) and heated and melted with a two-step temperature profile shown in FIG. 12 to obtain a sample. The composition of the solder was four types consisting of no Ag, 2.5% by mass of Ag, 7% by mass of Ag, 11% by mass of Ag, with the balance being Bi.

  (2) The wettability was evaluated by measuring the wetting spread area and the contact angle (N = 3) on the copper-clad double-sided substrate after the sample prepared above was melted and solidified. FIG. 13A schematically shows a plan view in a state in which the high temperature solder alloy 1 is spread on the copper-clad double-sided substrate 3. The wet spread area S in this case was measured. The measurement was performed using a reflow soldering observation apparatus SMT Scope SK-5000 (model number) (manufactured by Sanyo Seiko Co., Ltd. (manufacturer name)). FIG. 13 (b) similarly schematically shows a cross-sectional view in a direction perpendicular to the bonding surface in a state in which the high temperature solder alloy 1 is spread on the copper-clad double-sided substrate 3. FIG. The contact angle between the substrate 3 and the high temperature solder alloy 1 represented by θ in the figure was measured. The measurement was performed using a shape measuring laser microscope VK-8700 (manufactured by KEYENCE (manufacturer name)).

  (3) FIG. 14 is a graph showing changes in the wetting spread area and the contact angle when the amount of Ag added to Bi is changed. It can be seen that the wettability of the Bi alloy is improved by adding about 2.5 to about 11% by mass of Ag to Bi. Especially with the increase of Ag content. The tendency to improve the wettability became clear. Therefore, in addition to the characteristics possessed by the above-mentioned Bi-Sn binary system, in the Bi-Sn-Ag ternary high-temperature solder alloy, the effect of improving the wettability by the addition of Ag is expected.

  The high temperature solder alloy according to the invention is used in the joints of surface mounted components. In particular, it is suitably used for package parts, such as IC. Further, it is suitably used for internal connection junctions such as IC devices in general electronic components mounted on components with large heat generation, for example, LED devices, power semiconductor devices such as power diodes, and printed wiring boards. The applied products include the above-described illumination components using the LED elements, a drive circuit of an inverter, and a power converter called a power module.

1 High temperature solder alloy 1a High temperature solder alloy layer 1b Ni-Sn compound layer 2 Si chip (SiC chip)
DESCRIPTION OF SYMBOLS 20 Si layer 21 Al-Si film 22 Ni-P film 23 Au plating film 3 board | substrate 4 wire bonding 5 sealing material 9 Sn-free solder alloy 9a solder alloy layer 9b Bi-Ni intermetallic compound layer 50 void 100 semiconductor device 200 SOP
300 QFP
400 printed circuit board

Claims (5)

And the metal substrate, the back electrode a high temperature solder alloy for use in bonding between Si chip or SiC chip including Ni,
A high temperature solder alloy containing 0.2% by mass to 0.3% by mass of tin, with the balance being bismuth and unavoidable impurities, or
A high temperature solder alloy comprising 0.2% by mass to 0.3% by mass of tin and 0.5% by mass to 11% by mass of silver, with the balance being bismuth and unavoidable impurities.   Solder containing a metal substrate and a Si electrode or SiC chip with a back electrode containing 0.05% by mass to 0.3% by mass of tin, with the balance being a high-temperature solder alloy consisting of bismuth and unavoidable impurities A semiconductor device comprising a bonded body formed by bonding with an alloy layer. The semiconductor device according to claim 2 , wherein the high temperature solder alloy further contains 0.5 mass% to 11 mass% of silver. The semiconductor device according to claim 2 , wherein the back electrode further contains Au, Ti, and P. The semiconductor device according to any one of claims 1 to 4 , wherein an interface between a Ni-containing Si chip or a SiC chip and the solder alloy layer comprises a Sn-Ni compound layer.