JP2008221330A - Solder alloy - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an Sn-Sb based high temperature solder alloy having excellent wettability and also having excellent mechanical properties (particularly, in ductility, and having a reduced aging change at high temperature), and in which an interfacial reaction layer grows slowly, and the reliability in the joint is excellent. <P>SOLUTION: The solder alloy has a composition comprising, by mass, 3.0 to 10.0% Sb, 0.01 to 1.0% Ni and 0.01 to 1.0% Ge, and the balance Sn with inevitable impurities. Alternatively, the solder alloy has a composition comprising 3.0 to 10.0% Sb, ≤1.0% (not including zero as the lower limit value in the range) Cu, 0.01 to 1.0% Ni and 0.01 to 1.0% Ge, and the balance Sn with inevitable impurities. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a “solder alloy”, and more particularly to a “lead-free solder alloy” that does not contain lead and is used in metal bonding in electronic equipment. This solder alloy is used in general electronic equipment. Especially in circuit boards or multi-chip modules with miniaturization and high functionality, insert mounting parts (IMD), surface mounting parts (SMD) and mixed mounting parts are used. It is used in the field of mounting directly on a printed circuit board, and is mainly applied to solder connections that require a temperature hierarchy connection on the high temperature side.

  In automotive electronic equipment and industrial electronic equipment, solder joints are exposed to high temperatures of 220 ° C. To prevent instantaneous partial melting at such high temperatures, SnSb-based lead-free solder alloys are used. By using the reaction between Sn and Cu balls and the reaction between Sn and the substrate terminal (Cu, Ni), the lower limit temperature can be raised to a level of 245 ° C. higher than Sn (232 ° C.). Thereby, even if it becomes said 220 degreeC, there is no worry of partial melting.

  By the way, when an electronic component is soldered to a printed circuit board or the like by a reflow method, soldering of the electronic component is usually performed by performing soldering twice on the high temperature side and the low temperature side using at least two types of solder having different reflow temperatures. A method, so-called temperature hierarchy connection is performed. For example, the connection of the semiconductor chip to the substrate is performed in a high-temperature process, the wiring connection to the printed circuit board is performed in a low-temperature process, and the connection portion of the semiconductor chip to the substrate cannot be melted to maintain the bonded state, or in some cases separated To prevent it from happening.

  Conventionally, when performing the above-described temperature hierarchy connection, lead-containing solder is usually used. For example, Pb-5Sn (melting point: 314 to 310 ° C.), Pb-10Sn (melting point: 302) are used as high-temperature lead-containing solder. Solder at a temperature of around 330 ° C using a soldering temperature of ~ 275 ° C), and then connect with Sn-37Pb eutectic (melting point: 183 ° C) of low-temperature lead-containing solder so as not to melt this soldered part Therefore, the temperature hierarchy connection was performed. These lead-containing solders are flexible and highly deformable, so it is possible to bond Si chips that are easy to break to substrates with different coefficients of thermal expansion, and are applied to semiconductor devices such as BGA and CSP where the chips are flip-chip connected. Has been.

  As described above, when soldering an electronic component to a printed circuit board or the like, an Sn—Pb eutectic alloy has been conventionally used as the solder alloy.

  The use of solder alloys containing this lead component is restricted from the standpoint that lead pollutes the environment, and so-called “lead-free solder” has been actively put into practical use by various companies as a countermeasure. A typical lead-free solder material is a SnAg solder material (eutectic composition 3.5% Ag), and its melting point is around 220 ° C. SnCu eutectic system (melting point: 227 ° C.) is also used.

  The Japan Electronics and Information Technology Industries Association (JEITA) is a leader in lead-free soldering in November 2001, based on data accumulated by the PG for research and development of lead-free implementation of NEDO commissioned business. Announcement roadmap was published, and Sn-3.0Ag-0.5Cu was recommended as the recommended composition of SnAgCu material. Due to the above background, Sn-3.0Ag-0.5Cu is often used in current Japanese SnAgCu-based lead-free solder.

  Patent applications relating to the above lead-free solder are also widely made by various companies (for example, see Patent Documents 1 and 2).

  Patent Document 1 relates to a SnAgCu-based lead-free solder containing Sn-3.0Ag-0.5Cu, and discloses the following. That is, when the description of the summary of Patent Document 1 is cited, “When soldering a surface-mounted component, even if it is soldered at a reflow temperature of 250 ° C. or less that does not cause thermal damage to an electronic component or a printed circuit board, For package parts, the challenge is to provide a lead-free solder paste with excellent printability that does not cause voids in the soldered parts and does not cause chip standing of chip parts. Two or more kinds of solder alloy powders having different compositions or blending ratios are composed of Ag: 0 to 8% by mass, Cu: 0 to 5% by mass, and Sn: 80 to 100% by mass. Two or more kinds of solder alloy powders are mixed to form a solder paste so that the composition after mixing and dissolution is Ag: 1-5 mass%, Cu: 0.5-3 mass%, and the balance Sn. Disclose.

  Patent Document 2 was substantially filed by the applicant of the present application. “Sn—Ag alloys are improved to have excellent strength, thermal stability, and good bondability. “Providing an Ag-based solder alloy”, and as a means for solving the problem, “mainly tin, 1.0 to 4.0% by weight of silver, 2.0% by weight or less of copper, and 0.5% of nickel Less than wt%, less than 0.2wt% phosphorus, tin as the main component, 1.0-4.0 wt% silver, less than 2.0 wt% copper, 0.5 wt% nickel The content of germanium may be 0.1% or less by weight.When Cu is added, Cu dissolves in Sn, improving the strength and heat resistance of the alloy without impairing the wettability. This increases the thermal stability of the alloy due to the high melting temperature of Ni. Ni-Sn compounds are formed and the strength and thermal fatigue properties are improved. When P and Ge are added, a thin oxide film is formed when the solder is melted, and oxidation of solder components such as Sn is suppressed. " To do.

  As mentioned above, Sn-Ag-Cu eutectic system (melting point: 221 to 217 ° C), Sn-Cu eutectic system (melting point: 227 ° C), etc. are widely used as Pb-free solder, ensuring reliability. Therefore, from the necessity of ensuring wettability, the actual mounting temperature range is, for example, about 235 to 245 ° C. in the Sn—Ag—Cu eutectic system. Therefore, the high-temperature side solder that can withstand this soldering temperature needs to have a melting point of at least 250 ° C. or higher. Moreover, since the main component of lead-free solder is Sn, it is also required to suppress oxidation during mounting.

  Sn-Sb high temperature solder alloys are known as lead-free solders on the high temperature side that satisfy the above-described conditions (see Patent Documents 3 and 4).

  Patent Document 3 states that “a high-temperature lead-free solder alloy consisting of Sb 10 to 40% by mass, Cu 1 to 9% by mass, and the balance Sn, and in order to further improve mechanical strength, Co, Fe, Mo, Cr, Ag , A solder alloy in which at least one selected from the group consisting of Bi is added or at least one selected from P, Ge, and Ga is added as an oxidation-inhibiting element is disclosed.

Patent Document 4 states that “a solder alloy for joining electronic components that contains 11 to 15% by mass of Sb and 0.01 to 1% by mass of at least one of Ni and Ge, with the balance being substantially made of Sn.” Is disclosed.
JP 2002-126893 A Japanese Patent No. 3296289 JP 2004-298931 A JP 2002-321084 A

  By the way, the Sn—Sb-based lead-free high-temperature solder alloy described in Patent Document 3 or 4 as described above has a problem that the crystal grains become coarse due to the large mass% of Sb, and the external Cracks are generated along the grain boundaries due to load stress, and there is a problem that the reliability of bonding is low.

  In addition, by improving the wettability and slowing the growth of the interface reaction layer (also referred to as the alloy layer) formed at the interface between the solder and the bonding base material when used for a long time in a high temperature environment, It is desired to further suppress the generation and propagation of cracks and further improve the reliability of bonding.

  In particular, it is desired to improve the high-temperature life by excellent ductility and less aging change at high temperature as compared with the Sn-Ag lead-free solder alloy.

  The present invention has been made in view of the situation as described above, and the object of the present invention is excellent in wettability and mechanical properties (particularly excellent in ductility and little aging change at high temperature), It is another object of the present invention to provide a Sn—Sb high temperature solder alloy having a slow interface reaction layer growth and excellent joint reliability.

  The said subject is achieved by the following solder alloys. That is, it is characterized by containing 3.0 to 10.0% by mass of Sb, 0.01 to 1.0% by mass of Ni and 0.01 to 1.0% by mass of Ge, with the balance being Sn and inevitable impurities (Claim 1).

  Also, it contains 3.0 to 10.0% by mass of Sb, 1.0% by mass or less of Cu (not including the lower limit of zero), 0.01 to 1.0% by mass of Ni, 0.01 to 1.0% by mass of Ge, and the balance is Sn and inevitable (Claim 2).

  The technical basis of each component content range and the effect of each component addition in the present invention are as follows. First, the upper limit of the Sb content will be described. When it exceeds 10.0 mass%, it will become a structure | tissue which has the coarse crystal grain (Sn-Sb type compound) which crystallizes when solidifying. Since the crystal grains are hard and brittle, cracks are generated along the crystal grain boundaries due to external load stress, resulting in a decrease in bonding reliability.

  Moreover, when it exceeds 10.0 mass%, liquidus temperature will be about 270 degreeC or more, and high joining temperature is requested | required. Note that 3.0% by mass of the lower limit of the Sb content is a content necessary for obtaining a desired melting point as a high-temperature solder.

  Next, the effect of Ni addition and its suitability range will be described. By adding Ni, it becomes possible to improve wettability and to suppress the growth of the alloy layer at the joint when used for a long time in a high temperature environment.

  In addition, the added Ni is dissolved in the solder or in the electrode of the joined body (Sn or Cu), or forms an SnNi intermetallic compound, thereby increasing the thermal stability of the solder alloy and increasing the heat resistance. Improves. However, if the SnNi intermetallic compound is excessively formed, the ductility is lowered, so that Ni cannot be added excessively. Further, there is a problem that when the amount of Ni added is increased, the liquidus line rapidly rises and the SnNi metal compound becomes excessive. In order to prevent concentration segregation of the SnNi metal alloy during solder solidification, the amount of Ni added is preferably 1.0% by mass or less.

  Further, the addition of Ni suppresses the growth of the interface reaction layer (alloy layer) formed at the interface between the solder and the bonding base material (Cu), thereby suppressing the generation (and propagation) of cracks. In addition, if the addition amount of Ni is less than 0.01%, it is difficult to impart sufficient wettability.

  Next, the effect of Ge addition and its suitable range will be described. Addition of Ge improves wettability and suppresses growth of the alloy layer when used for a long time in a high temperature environment.

  The addition amount range of Ge is 0.01 to 1.0% by mass, preferably 0.1 to 1.0% by mass. The reason is that if it is less than 0.01% by mass, it is difficult to impart sufficient wettability. This is because workability is lowered, and thin wire drawing, thin rolling, and preform punching are difficult.

  Next, the effect of adding Cu according to claim 2 will be described. By adding Cu to the Sn—Sb—Ni—Ge quaternary solder alloy, diffusion of Cu from the joining base material into the solder can be suppressed. In addition, if Cu addition amount is 1.0 mass% or less, there will be no significant rise in solidus temperature.

  According to the present invention, when applied to solder bonding in electronic equipment, it has excellent wettability and excellent mechanical properties (particularly excellent ductility and little aging change at high temperature), and further the growth of the interface reaction layer Therefore, it is possible to provide a Sn—Sb solder alloy that is slow and excellent in reliability of the joint. This solder alloy is also suitable as a solder alloy on the high temperature side in the temperature hierarchy connection.

  Next, an embodiment of the present invention will be described based on FIGS. 1 to 7 with the solder alloy according to the first aspect of the present invention as an object. Similar results can be obtained with the solder alloy according to the second aspect of the present invention.

  First, based on FIG. 1 and FIG. 7, the experimental result regarding the wettability of the solder alloy which concerns on this invention is described. In connection with the wettability experiment, using a vacuum reduction device (maximum heating temperature: about 300 ° C), solder pellets (diameter: 3.0mm) with Ni addition amount changed to Sn-5Sb solder on DBC (Direct Bond Copper) substrate X thickness 0.3 mm) was melted and solidified to form a solder fillet as shown in FIG. Based on this fillet (12 samples for each added amount), as shown in FIG. 1, with respect to the high temperature solder alloy in which the Ni added amount is changed to Sn-5Sb solder, the wetting spread rate ΔS ( %) Was calculated.

Wetting spread ratio ΔS (%) = (wetting spread area after heating−wetting spread area before heating)
÷ (wet spread area before heating) x 100
In FIG. 1, the data A on the left side is Ni addition amount 0, the center B is 0.03 mass%, and the right C is 0.15 mass%. In the above, Ge was fixed at 0.01% by mass.

According to FIG. 1, in the Sn5Sb solder material (Ni addition amount 0) A, ΔS is 10% or less, whereas Ni in B
When the addition amount is 0.03%, ΔS has a value of 10 to 13%, and when the Ni addition amount of C is 0.15%, ΔS has a value of 20 to 30%, confirming the effect of improving the wettability by adding Ni. . By the way, the variation of various solder materials in the number of samples N = 12 is represented by the standard deviation σ, and ΔS is expressed as an average value ± σ. , 24.3 ± 3.0%.

  As described above, when Ni is added, it dissolves in the solder or in the electrode of the joined body (Sn or Cu), or forms a SnNi intermetallic compound, increasing the thermal stability of the alloy, Heat resistance is improved. However, if the SnNi intermetallic compound is excessively formed, the ductility is lowered, so Ni cannot be added excessively. Further, when the amount of Ni added is increased, the liquidus line rises rapidly and the SnNi metal compound becomes excessive. In order to prevent concentration segregation of the SnNi metal compound during solidification of the solder, the amount of Ni added is preferably 1.0% by mass or less.

  Next, mechanical characteristics will be described. First, an example of an experimental result regarding the strain rate dependency of the tensile strength shown in FIG. 2 will be described. The tensile strength of a soft material such as solder is greatly affected by the tensile speed, and the tensile strength decreases when the tensile speed is lowered. This is called the strain rate dependence of tensile strength. Takemoto, A. Matsunawa, M. Takahashi: Tensile test for estimation of thermal fatigue properties of the strain rate change tensile test method has been proposed as a method for estimating thermal fatigue properties of solder. solder alloys Journal of Materials Science 32 (1997) 4077-4084).

  In FIG. 2, the vertical axis represents tensile strength (MPa), and the horizontal axis represents strain rate (% / s). The tested solder alloys are A (Sn-5Sb-0.03Ni-0.01Ge), B (Sn-5Sb-0.15Ni-0.01Ge), C (Sn-3.5Ag-0.5Cu-0.07Ni-0.01) shown in FIG. The number of samples is five. The strain rates of 0.2% / s and 0.002% / s correspond to the power cycle test (0.2% / s) and heat cycle test (0.002% / s), which are the reliability verification items of the product, respectively. For example, in a heat cycle test (-40 ° C to 125 ° C), when the magnitude of the strain component acting on the solder joint at a temperature difference ΔT = 165 ° C is 2.0%, the amount of strain in the temperature rise (or fall) process The change in ε (gradient = 0.002% / s) corresponds to the strain rate.

  As is clear from FIG. 2, the SnSb high-temperature lead-free solder according to the present invention (Ni addition amount: 0.03%, 0.15%) is SnAgCu ternary lead-free solder (Ni and Ge are added in a small amount. It can be seen that it has a large tensile strength regardless of the strain rate compared to the solder alloy.

  Next, FIG. 3 will be described. FIG. 3 is a diagram showing an example of an experimental result regarding the ductility of the solder alloy according to the present invention.

  In FIG. 3, the vertical axis represents the fracture drawing (%), and the horizontal axis represents the strain rate (% / s). The tested solder alloys are A (Sn-5Sb-0.03Ni-0.01Ge), B (Sn-5Sb-0.15Ni-0.01Ge) and C (Sn-3.5Ag-0.5Cu-0.07Ni-0.01) shown in FIG. The number of samples is five. The fracture drawing (%) is defined by the following.

Fracture drawing (%) = (S ₁ − S ₂ ) / S ₁ × 100
Where S ₁ : Original cross-sectional area of test parallel part (mm ² )
S ₂ : Minimum cross-sectional area at the fractured part after the test (mm ² )
According to FIG. 3, Sn-5Sb solder added with trace elements (Ni, Ge) has an alloy with a fracture drawing> 80% and exhibits good fracture characteristics, Sn-3.5Ag -0.5Cu-Ni- The fracture drawing value is about 20% larger than that of Ge solder alloy. That is, it can be seen that the solder alloy according to the present invention is excellent in ductility.

  Next, FIG. 4 will be described. FIG. 4 is a diagram showing an example of an experimental result regarding a change in the high temperature aging of the solder alloy according to the present invention, and the vertical axis indicates the tensile strength (MPa) of the initial product and the high temperature aging product. The tested solder alloys are A (Sn-5Sb-0.03Ni-0.01Ge), B (Sn-5Sb-0.15Ni-0.01Ge), C (Sn-3.5Ag-0.5Cu-0.07Ni) as in FIG. -0.01 Ge), and each sample number is 5.

  The tensile strengths after high temperature aging (125 ° C. × 1000 h) with respect to the initial values are decreased by 6.0%, 12.8%, and 18.1% in A, B, and C, respectively. Compared with C, the degree of decrease in each tensile strength is small. That is, it can be seen that the solder alloy according to the present invention has little aging change at high temperature.

  Next, the solder alloy of the present invention will be described in detail with reference to FIG. 5 in terms of “the effect that the growth of the interface reaction layer at the joint is slow and the reliability of the joint is excellent”. FIG. 5 is an explanatory view of the interface reaction layer of the solder alloy according to the present invention. FIG. 5 (a) shows the microstructure of the SnSb solder joint product without addition of Ni, and FIG. 5 (b) shows Ni. The structure form of the added SnSb solder joint product is schematically shown.

As shown in FIG. 5A, in the Sn—Sb solder to which Ni is not added, the reaction layer A (Cu ₆ (Sn, Sb) ₅ compound) exists in an uneven state. On the other hand, the reaction layer C ((Cu, Ni) ₆ (Sn, Sb) ₅ compound) is relatively flat in the Sn—Sb solder added with Ni shown in FIG. 5B. Further, the growth of the reaction layer D ((Cu, Ni) ₃ (Sn, Sb) compound) accompanying high temperature aging can be suppressed.

  That is, when Ni is added, the reaction layer at the solder / bonding base material interface becomes a compound containing Ni, and the growth of the reaction layer becomes slow. As shown in FIG. 5A, when the reaction layer at the solder / bonding base material interface grows, cracks are likely to occur due to external load stress, and the generated cracks are likely to propagate. On the other hand, in the case of FIG.5 (b) which concerns on this invention, generation | occurrence | production and propagation of a crack are suppressed.

  Next, in relation to the difference between the invention described in Patent Document 4 and the present invention, it is a point other than those described above, and from FIG. 6 "from the viewpoint of the difference in bonding temperature based on the difference in Sb content". Please refer to.

  One feature of the solder alloy according to the present invention is that manufacturing process management is facilitated because the difference between the liquidus temperature and the solidus temperature is smaller than that of the solder alloy described in Patent Document 4. It is. If the difference between the liquidus temperature and the solidus temperature is large, it takes time for the molten solder to solidify after soldering, and if vibration or impact is applied to the soldered part during that time, There is a risk of cracks and cracks, which is undesirable in terms of process management. This is especially true in the case of soldering electronic devices, since different heat capacities are mixed.

  FIG. 6 is a two-phase diagram of Sn-Sb, where FIG. 6 (b) shows a partially enlarged view of FIG. As shown in FIG. 6, the solder alloy has a Sb composition ratio of 11.0% by mass, a liquidus temperature of about 270 ° C. (difference from the solidus temperature: about 25 ° C.), and a Sb composition ratio of The liquidus temperature is about 295 ° C. at 15.0% by mass (difference from the solidus temperature: about 50 ° C.), and the solder alloy of Patent Document 4 requires a high bonding temperature (270 ° C. or higher). On the other hand, the liquidus temperature of the solder alloy according to the present invention (Sb: 3.0% by mass to 10.0% by mass) is about 240 ° C. to 265 ° C., and the difference between the liquidus temperature and the solidus temperature is 3 It becomes small with ℃ ~ 21 ℃. Note that the solidus temperature of the solder alloy of Patent Document 4 (Sb: 11.0% by mass to 15.0% by mass) is approximately 245 ° C., and the solder alloy according to the present invention (Sb: 3.0% by mass to 10.0% by mass). The solidus temperature is about 237 ° C. to 245 ° C., which is about 8 ° C. lower.

The figure which shows an example of the experimental result regarding the wettability of the solder alloy which concerns on this invention. The figure which shows an example of the experimental result regarding the strain rate dependence of the tensile strength of the solder alloy which concerns on this invention. The figure which shows an example of the experimental result regarding the ductility of the solder alloy which concerns on this invention. The figure which shows an example of the experimental result regarding the change of the high temperature aging of the solder alloy which concerns on this invention. Explanatory drawing about the interface reaction layer of the solder alloy which concerns on this invention. Sn-Sb binary state diagram. FIG. 2 is a solder fillet formation diagram related to the wettability experiment of FIG. 1.

Explanation of symbols

  None

Claims (2)

  A solder alloy comprising 3.0 to 10.0% by mass of Sb, 0.01 to 1.0% by mass of Ni and 0.01 to 1.0% by mass of Ge, the balance being Sn and inevitable impurities.   Contains 3.0 to 10.0 mass% of Sb, 1.0 mass% or less of Cu (excluding the lower limit of zero), 0.01 to 1.0 mass% of Ni and 0.01 to 1.0 mass% of Ge, the balance being Sn and inevitable impurities A solder alloy characterized by comprising: