JP6136853B2 - Bi-based solder alloy, method for manufacturing the same, electronic component bonding method using the same, and electronic component mounting board - Google Patents

Description

  The present invention relates to a Bi-based solder alloy, an electronic component bonding method using the Bi-based solder alloy, and an electronic component mounting substrate, and more specifically, substantially free of Pb, having a solidus temperature of 265 ° C. or higher, and a liquidus wire Bi solder alloy having a temperature of 390 ° C. or less and excellent in machinability, mechanical strength, and bonding reliability, and a bonding method to a bare Cu frame electronic component using the bonding surface of which is a Cu surface And an electronic component mounting board.

  When joining electronic components, the electronic components such as semiconductor element chips are first joined to the lead frame with solder (die bonding), and then the solder is remelted (reflowed) and mounted on a printed circuit board such as a semiconductor package. Is generally done.

  Conventionally, Sn / 37 mass% Pb eutectic solder (melting point: 183 ° C.) is widely used for mounting electronic components on a substrate, and reflow is performed at 220 to 230 ° C. during mounting. It was. On the other hand, for bonding inside the electronic component, in order to prevent connection failure due to remelting at the reflow temperature (220 to 230 ° C.) at the time of mounting, for high temperature having a solidus temperature higher than the reflow temperature at the time of mounting. Solder, Pb / 5 mass% Sn (solidus temperature 305 ° C), Pb / 3 mass% Sn (solidus temperature 315 ° C) have been used.

  However, products that use lead (Pb) -containing solder have been pointed out that after disposal, Pb flows out of the product, penetrates into the soil, accumulates in crops, etc., and can cause health damage to humans. In recent years, lead-free solders containing no Pb have been actively developed because it has been pointed out that the outflow of Pb from products discarded due to acid rain has been pointed out.

As an alternative to Pb-containing solder for medium and low temperatures, lead-free solder containing no Pb such as Sn—Ag—Cu has been put into practical use.
However, the melting point of lead-free solder such as Sn—Ag—Cu is higher than that of the conventional Sn / Pb eutectic solder and is about 220 ° C., and the reflow temperature during mounting is around 250 to 260 ° C. For this reason, a lead-free solder for high temperature that does not cause a problem in the bonding reliability inside the electronic component even after the cycle of holding for 10 seconds at a reflow temperature of 260 ° C. is required (Patent Document 1). .

  That is, lead-free solders for high temperature use remelting at the reflow temperature during mounting (ie 250 to 260 ° C.) in addition to the characteristics such as heat dissipation, stress relaxation, heat fatigue resistance, and electrical conductivity. In order to prevent poor connection, it is necessary to have a solidus line of at least 260 ° C. or higher, and a solidus temperature of 265 ° C. or higher is required in consideration of temperature variations during reflow (about 5 ° C.).

  In addition, when the liquidus temperature of lead-free solder is 400 ° C. or higher, it is necessary to increase the working temperature during die bonding to 400 ° C. or higher, which may cause adverse effects such as changes in chip characteristics and promotion of member oxidation. . Accordingly, the liquidus temperature needs to be lower than 400 ° C., and is preferably 390 ° C. or lower, more preferably 350 ° C. or lower in consideration of an actual production process.

  As lead-free solder having a melting point of 260 ° C. to 350 ° C., Au—Sn solder, Bi—Ag solder and the like have been proposed. This Au—Sn solder has a melting point of 280 ° C., and there is no problem of re-melting at the time of mounting, but it is expensive and impractical in terms of cost, so many Bi—Ag solders have been proposed.

  The Bi / 2.5 mass% Ag eutectic solder (melting point 262 ° C.) is a typical Bi-Ag solder, but the solidus temperature is less than 265 ° C., so there is a problem of remelting during mounting. May occur. Moreover, it has the weak mechanical characteristic peculiar to Bi solder, and when it is applied as it is, it will have a bad influence on joining reliability, machinability, and the continuous supply property by an apparatus.

  Patent Document 2 discloses Bi / Ag solder of Bi to 80% by mass, but the solidus is 262 ° C., and there is a possibility of remelting. In addition, since the liquidus temperature is as high as 400 to 700 ° C., adverse effects such as changes in chip characteristics and promotion of member oxidation may occur.

  Patent Document 3 discloses a method for producing a multi-component solder containing Bi, which describes that variation in liquidus temperature is reduced and the melting point is 250 to 300 ° C. However, it does not describe improvement of fragile mechanical characteristics unique to Bi-based solder.

  Patent Document 4 proposes a solder alloy containing Al and Cu in Bi and further containing Sn. However, by adding Sn, a low melting point layer of 139 ° C. appears depending on the alloy composition, and remelting may occur during reflow at 260 ° C.

  Furthermore, for lead-free solders for high temperatures, sufficient reliability against thermal stress on solder joints due to large currents and large amounts of heat generated in power devices, etc., and to preform-shaped solder such as solder wires (preform solder) However, the conventional Bi-Ag solder can be supplied only in paste form due to its weak mechanical properties. However, there were many aspects that were insufficient as a substitute for preform solder.

  In addition, the lead frame island portion to which the solder alloy is applied may be pre-plated with Ag, but may be Ni-plated instead of Ag, and has been frequently used in in-vehicle devices in recent years. Yes. This is because the growth of the bonding interface reaction layer may be suppressed in a temperature cycle test or the like in the reliability test, and the plating has high long-term reliability. On the other hand, in order to reduce the cost, there is a case where such processing as Ag plating or Ni plating is not performed, and it is called a bare Cu frame. Although this bare Cu frame is frequently used in general-purpose devices such as transistors, wetting and spreading in this bare Cu frame is important.

  However, when the solder alloy is applied to the lead frame island part, Cu starts to react preferentially with a specific element in the solder, for example Sn, but there is an oxide film on the surface, which affects the reduction of wetting spread. Easy to affect. In addition, since Cu hardly dissolves in Bi-based solder alloys and Pb-based solder alloys, wetting spread tends to be lower than that of Ag plating. That is, in the bare Cu frame, there is a problem that the surface oxidation is likely to proceed, and the solder wetting spread is likely to deteriorate due to the influence of the surface roughness. Thus, the solder alloy has been required to be improved so as not to reduce the wetting spread during bonding to the bare Cu frame.

JP 2002-321084 A JP 2002-160089 A JP 2006-167790 A JP 2012-066270 A

  In view of the problems of the prior art, an object of the present invention is substantially free of Pb, has a solidus temperature of 265 ° C. or higher, and a liquidus temperature of 390 ° C. or lower, and has machinability and mechanical strength. It is another object of the present invention to provide a Bi solder alloy having excellent bonding reliability, a bonding method to a bare Cu frame electronic component using the Cu solder surface, and an electronic component mounting substrate.

  As a result of intensive research in order to solve the above problems, the present inventor has mixed and alloyed a specific amount of Al in the conventional Bi-Ag solder, and an intermetallic compound of Ag and Al in the solder alloy. If the particles containing bismuth are dispersed, there is no deterioration or damage of electronic parts due to heat during bonding, and there is no problem of remelting due to heat during solder reflow. A base solder alloy was obtained, and when P or Ge was further added to this alloy, it was found that electronic components could be joined without lowering the wetting spread during bonding to the bare Cu frame, and the present invention was completed. .

That is, according to the first invention of the present invention, a Bi-based solder alloy having a melting point of a solidus of 265 ° C. or higher and a liquidus of 390 ° C. or lower, with an Ag content of 0.6 to 18 mass. %, Al content is 0.1 to 3% by mass, one or more of P and Ge are 0.001 to 0.3% by mass, and Cu content is 0 to 1% by mass The balance is made of Bi and inevitable impurities, the Al content is 1/20 to 1/2 of the Ag content, and particles containing an intermetallic compound of Ag and Al are dispersed in the solder alloy. Thus, a Bi-based solder alloy is provided in which 97% by volume or more of the particles have a particle size of less than 50 μm with respect to the total volume of the particles.

According to the second invention of the present invention, in the first or second invention, the Al content is 1/15 to 1/4 of the Ag content. A Bi-based solder alloy is provided.
According to a third invention of the present invention, there is provided a Bi-based solder alloy characterized in that, in the first to third inventions, 0.01 to 1% by mass of Cu is contained.

According to a fourth aspect of the present invention, there is provided a Bi-based solder alloy manufacturing method according to the first to third aspects of the present invention , which is a molten solder alloy containing, as a raw material, each component constituting the Bi-based solder alloy. the after flushing the mold, by rapidly cooled and solidified at 3 ° C. / sec or more cooling rate until 260 ° C., the particles comprising an intermetallic compound of Ag and Al and wherein Rukoto dispersed in the alloy A method for manufacturing a Bi-based solder alloy is provided.

According to a fifth aspect of the present invention, an electronic component is bonded to a substrate or frame whose surface is formed of a Cu material using the Bi-based solder alloy according to any one of the first to third aspects. An electronic component bonding method is provided.

The sixth aspect of the present invention, an electronic component mounting board of the electronic component using a Bi based solder alloy according to any one of aspects 1-3 therein is mounted is provided.

The Bi-based solder alloy of the present invention does not substantially contain Pb, has a solidus temperature of 265 ° C. or higher and a liquidus temperature of 390 ° C. or lower. An intermetallic compound of Ag and Al is contained in the solder alloy. Since the fine particles that are contained are dispersed, there is no deterioration or damage of electronic parts due to heat during bonding, and there is no problem of remelting due to heat during solder reflow. A Bi-based solder alloy can be provided, and can be suitably used for die bonding or the like, which is bonding inside an electronic component. Further, the improvement in mechanical strength and machinability enables the formation and winding of wire-shaped preform solder, which is particularly suitable as a preform material for high-temperature solder alloys for die bonding.
In addition to the above Ag and Al as additive elements, any one or more of P or Ge is included, so that the wettability of the solder can be improved and the generation of voids during bonding can be reduced. The bonding strength with respect to is not reduced.
Furthermore, an electronic component mounting substrate having high mechanical strength is provided by the electronic component using the Bi-based solder alloy of the present invention and the bonding method of the electronic component to the substrate without causing any change in chip characteristics or member oxidation. be able to.

It is sectional drawing which shows an example of the semiconductor package using the Bi group solder alloy of this invention. It is a chart which shows the melting | fusing point measurement result of the conventional Bi group solder alloy (Bi / 2.5Ag). It is a chart which shows the melting | fusing point measurement result of Bi base solder alloy (Bi / 5Ag / 1Al) used as the base of this invention. It is a chart which shows the tension test result of the conventional Bi group solder alloy (Bi / 2.5Ag). It is a chart which shows the tension test result of Bi base solder alloy (Bi / 5Ag / 1Al) used as the base of the present invention.

  The present invention relates to a Bi-based solder alloy in which a specific amount of Al is contained in Bi-Ag and particles containing an intermetallic compound of Ag and Al are dispersed in the solder alloy, and an electronic component using the same The present invention relates to a bonding method to a Cu frame and an electronic component mounting substrate.

1. Bi-Ag
The Bi-based solder alloy of the present invention is mainly composed of Bi, which belongs to the group Va element of the periodic table, and has a trigonal crystal (rhombohedral crystal) with very low crystal structure and is very fragile.

  As described above, the conventional Bi-Ag solder is known as a high-temperature solder that does not contain lead and has a solidus line higher than the upper limit of 260 ° C. when the electronic component is mounted on the substrate. For example, Bi-2.5 mass% Ag solder is a eutectic type alloy having a solidus temperature of 262 ° C., which is about 9 ° C. lower than the melting point 271 ° C. of pure Bi.

  Further, as is apparent from FIG. 5, the conventional Bi—Ag solder shows only about 8% elongation even in a Bi / 2.5 Ag Ag eutectic solder alloy. Due to this fragility, conventional Bi-Ag solder is prone to defects during bonding and subsequent reliability tests, and it can be machined into preform solder and continuously supplied by electronic component assembly equipment such as die bonders. Could not be secured.

  Therefore, the present applicant, as a result of paying attention to the elemental Al, which has a lower melting point drop or no lowering than Bi-Ag eutectic when combined with Bi in order to increase the solidus temperature of Bi-Ag solder, By containing Al at a specific ratio with respect to Ag, it has a high solidus temperature and an appropriate liquidus temperature, and can improve mechanical strength, machinability, and the like.

That is, in the present invention, a Bi-Ag solder is used as a base, and the solidus temperature of 265 ° C. or higher is obtained by setting the ratio of Ag and Al within a specific range. Further, the Bi-based solder alloy of the present invention can maintain the initial state of the solder inside the electronic component without being remelted after being mounted on the substrate, and is excellent in mechanical strength, machinability and the like. is there.
Hereinafter, each component used for the Bi-based solder alloy of the present invention, an electronic component bonding method using the obtained solder alloy, a mounting substrate, and the like will be described in detail.

  In the present invention, the Bi content is determined according to the addition amount of other essential additive elements such as Ag and Al, but must be 80% by mass or more based on the total amount of the solder alloy. When the Bi content is less than 80% by mass, the liquidus increases greatly, which may cause adverse effects such as changes in chip characteristics and promotion of member oxidation.

In the solder alloy of the present invention, Ag forms an Ag-Al intermetallic compound described later together with Al, and the particles are dispersed in Bi, thereby improving the brittleness of the Bi matrix as dispersion strengthening.
The content of Ag is 0.6 to 18% by mass. If the Ag content is less than 0.6% by mass, the Ag-Al compound is not sufficiently generated, and the brittle mechanical characteristics of the Bi matrix become dominant, and the elongation is not sufficiently improved. It is not possible to ensure the machinability and continuous supply by assembly equipment. Further, when the Ag content exceeds 18% by mass, the liquidus increases and the solder spread becomes poor at the time of assembly at 390 ° C., so that the bonding reliability is lowered.

2. Al
In the Bi-based solder alloy of the present invention, Al increases the solidus temperature of Bi-Ag solder and further improves the fragile mechanical properties unique to Bi-based solder.

The Al content is 0.1% by mass or more and 3% by mass or less. If the Al content is less than 0.1% by mass, the Bi-Ag solidus temperature rise is insufficient and does not exceed 265 ° C., which may cause poor bonding reliability due to remelting. If it exceeds 3%, the liquidus temperature rises, and a wetting defect appears at a joining operation temperature of 390 ° C. or lower.
The amount of Al is determined according to the content of Ag. That is, in the Ag-Al phase diagram, the Ag ₂ Al intermetallic compound in the intermediate layer ζ phase and the Ag in the intermediate layer μ phase at a ratio of 5 to 33 wt% Al. _{Since 3} Al intermetallic compound exists, the content of Ag is set to 1/20 to 1/2. Outside this range, solder wettability is poor and joint reliability is lost. A preferable amount of Al is 1/15 to 1/4 of the content of Ag.

  In the Bi—Ag—Al alloy of the present invention, the Ag—Al intermetallic compound is present in the form of particles in the solder alloy. By disperse | distributing this Ag-Al intermetallic compound particle | grain in Bi, the brittleness of Bi matrix can be disperse-strengthened and improved. Here, the Ag-Al intermetallic compound refers to an intermetallic compound containing Ag and Al, but also includes a compound in which the amount of either Ag or Al metal is extremely small, or the essential element P or Ge, A compound with an optional component Cu metal described later is also included.

  The particle containing the Ag—Al intermetallic compound preferably has a particle size of less than 50 μm. Further, those having a particle size of less than 50 μm are preferably 97% by volume or more, more preferably 98% by volume or more, and particularly preferably 99% by volume or more based on the total volume of the particles. If particles with a particle size of 50 μm or more are 3% by volume or more, the dispersion by the compound is not locally strengthened, and the Bi matrix remains fragile, and there is a possibility that the fragility may occur from that part and the fragility may not be improved as a whole. . In this case, it becomes a cause of insufficient bonding reliability and poor handling. The particle size of the particles containing the Ag—Al intermetallic compound is more preferably smaller than 40 μm, and particularly preferably smaller than 30 μm.

  In addition, as for the particle | grains containing an Ag-Al intermetallic compound, the magnitude | size and distribution state of precipitation particle | grains can be easily discriminate | determined by optical microscope observation. The particle size was measured by observing each specimen with a 200 × optical microscope, counting the number of particles containing all intermetallic compounds in the field of view, and measuring the cross-sectional diameter of the particles. Obtained by multiplying by 12. Based on this particle size, the volume of each intermetallic compound particle is calculated using all intermetallic compound particles as true spheres, and the proportion of particles having a particle size of less than 50 μm in all particles is calculated in volume%.

3. P, Ge
In addition to the above, the Bi-based solder alloy of the present invention further contains at least one of P and Ge. P or Ge is added to improve the wettability of the solder and reduce the generation of voids during bonding. When P and Ge are added, P and Ge are preferentially oxidized, and the oxidation of the solder surface is suppressed. Therefore, the wettability of the solder can be improved and the generation of voids during bonding can be reduced.

  The addition amount of P and Ge is 0.001 to 0.3 mass%. When the addition amount of P and Ge exceeds 0.3 mass%, P and Ge will form many oxides, which will adversely affect wettability. Moreover, when the addition amount of P and Ge is less than 0.001 mass%, the effect of addition becomes insufficient. The content of P or Ge is preferably 0.003 to 0.08% by mass, and more preferably 0.005 to 0.05% by mass.

4). Cu
The Bi-based solder alloy of the present invention can contain Cu as an optional component in addition to the above as an additive element. Cu has the effect of promoting the reaction with the bare Cu frame and improving the wetting and spreading.
Al often preferentially moves and reacts as a diffusion element to the bare Cu frame in the solder, but when Cu added in the solder is present, the Cu atoms are in contact with each other between the surfaces of the bare Cu frame. Diffusion movement occurs, and as a result, the effect of improving the wetting spread is obtained.
Cu is an element that precipitates at a temperature higher than the liquidus temperature of the Bi-Ag-Al alloy, so that it becomes an initial crystal component that precipitates first, and finely precipitates Ag-Al compounds and matrix crystals that are precipitated later. There is an effect, and the coarsening of the solidified structure can be suppressed as a whole. As a result, the solder structure becomes a fine solidified structure compared to the case where Cu is not added, and cracks are less likely to occur.
The addition amount of Cu is 0 to 1% by mass. When the added amount of Cu exceeds 1% by mass, it may be produced as a coarse primary crystal component. Further, if the amount of Cu added is less than 0.01% by mass, it may not sufficiently contribute to the refinement of the solidified structure. Therefore, the content of Cu is more preferably 0.01 to 1% by mass. 0.03 to 0.8 mass% is more preferable.

The solder alloy of the present invention does not substantially contain Pb, and in addition to Bi, Ag, and Al, P or Ge can be included as an essential additive component, and Cu can be included as an optional additive component. Here, “substantially” means that it can be contained as an inevitable impurity. In the solder alloy, inevitable impurities such as Pb, Sb, and Te can be included within a range that does not affect the properties of the solder alloy of the present invention.
When inevitable impurities are included, the total amount is preferably less than 100 ppm in consideration of the influence on the solidus temperature, wettability, and bonding reliability.

4). Production of Bi-based solder alloy The production method of the Bi-based solder alloy of the present invention is not particularly limited, and can be produced by a conventionally known method using each of the components described above.
As a raw material, in order to form particles (intermetallic compound of Ag and Al) having a particle size of less than 50 μm in the solder alloy, a shot shape or a piece processed product having a diameter of 5 mm or less, particularly 3 mm or less Is preferably used.

  This raw material is put into a melting furnace, and in order to suppress oxidation of the raw material, an atmosphere of nitrogen or an inert gas is used and heated and melted at 500 to 600 ° C., preferably 500 to 550 ° C. At this time, when casting a molten metal having a melting temperature of 500 ° C. or higher, for example, a cylindrical graphite mold having an inner diameter of 30 mm or less and a thickness of about 10 mm can be used. When the metal starts to melt, stir well, and continue stirring sufficiently to prevent local compositional variations. The stirring time varies depending on the apparatus and the amount of raw materials, but is preferably 1 to 5 minutes.

After that, a chill metal made of a material having good thermal conductivity, such as Cu, is brought into close contact with the outside of the mold, or a chill metal made by passing cooling water as a hollow structure is preferably adhered, and the molten metal is poured into the mold. Depending on the composition, it is desirable to rapidly solidify by cooling at a cooling rate of 3 ° C./sec or more, more preferably 20 ° C./sec or more, up to about 260 ° C. By such a method, an ingot of a solder material in which the particle size of most of the precipitated particles is less than 50 μm can be reliably and stably produced.
Moreover, when using a continuous casting method in consideration of productivity, it is preferable to make it the shape where the cross-sectional area of the ingot formed by continuous casting becomes small. For example, in order to use a die having an inner diameter of 30 mm or less and cool and solidify the molten metal in a short time, the die is preferably covered with a water cooling jacket and cooled at a cooling rate of 50 ° C./sec or more.

The Bi-based solder alloy of the present invention thus obtained is substantially free of Pb, has a solidus temperature of 265 ° C. or higher and a liquidus temperature of 390 ° C. or lower, so that it does not remelt even after mounting on the substrate. The initial shape of the solder inside the electronic component can be maintained.
The solidus temperature is measured using a differential scanning calorimeter (DSC), and is preferably 265 ° C. or higher, more preferably 267 ° C. or higher. Moreover, liquidus temperature is confirmed using a differential scanning calorimeter (DSC) measurement and a melting test, and is preferably 390 ° C. or less, more preferably 380 ° C. or less.

Further, the Bi-based solder alloy of the present invention is excellent in mechanical strength, machinability and joining reliability.
The elongation rate of the Bi-based solder alloy of the present invention is preferably 15 to 50%, more preferably 20 to 45%. The elongation and the tensile strength are measured by a tensile tester (Tensilon universal tester) after extrusion processing to, for example, 0.75 mmφ to produce a wire-shaped preform solder.

5). Electronic component bonding method and electronic component mounting substrate The Bi-based solder alloy of the present invention is used in an electronic component bonding method, and an electronic component mounting substrate can be easily manufactured.

  As an example, FIG. 1 shows a cross-sectional view of a semiconductor package of an electronic component using the Bi-based solder alloy of the present invention. In this semiconductor package, the Bi-based solder alloy 3 of the present invention is applied to the center surface of the lead frame island 4 and the semiconductor chip 1 is mounted and soldered (die bonding), and then the electrode 2 on the semiconductor chip 1 is bonded. They are connected to the lead frame 5 via the wires 6, and all of them are covered with the mold resin 7 except for the outer periphery of the lead frame 5.

  The lead frame island portion 4 to which the solder alloy 3 of the present invention is applied may be pre-plated with Ag plating or Ni plating instead of Ag. As described above, in order to reduce the cost, In some cases, such treatment as Ag plating or Ni plating is not performed, and this is referred to as a bare Cu frame. In the bare Cu frame, wetting and spreading in the bare Cu frame is important. However, when the solder alloy 3 is applied to the lead frame island part 4, Cu is preferentially given to a specific element in the solder, for example, Sn. Although the reaction starts, the oxide film on the surface tends to affect the decrease in wetting spread. Moreover, since Cu hardly dissolves in Bi or Pb, wetting spread tends to be lower than that of Ag plating. That is, in the bare Cu frame, there is a problem that the surface oxidation is likely to proceed, and the solder wetting spread is likely to deteriorate due to the influence of the surface roughness.

However, in the present invention, since P or Ge is added to the solder alloy, a decrease in wettability is suppressed. In other words, Ag undergoes a metal reaction while forming an intermetallic compound with Al, and further, melted Bi has a eutectic composition and dissolves in the solder. At this time, the structure of the intermetallic compound becomes fine due to P and Ge in the solder alloy, and the wetting spread in the bare Cu frame is further improved. In addition, P and Ge are preferentially oxidized, and the oxidation of the solder surface is suppressed, so that the wettability of the solder is improved and the generation of voids during bonding is reduced.
That is, in the electronic component bonding method of the present invention, it is preferable to use a Bi-based solder alloy and bond the electronic component to a mounting substrate of a bare Cu frame in which no Ag layer or Ni layer is formed on the surface of the Cu material. .
The soldered (die-bonded) semiconductor chip 1 is heated to a reflow temperature around 260 ° C. when mounted on the substrate, but the solidus temperature of the Bi-based solder alloy of the present invention is 265 ° C. or higher. The electronic component can maintain mechanical strength without any change in chip characteristics or member oxidation.

  That is, the electronic component mounting board of the present invention is obtained by mounting an electronic component using the Bi-based solder alloy at a reflow work peak temperature of 260 to 265 ° C. In addition, as a board | substrate for electronic component mounting, a conventionally well-known board | substrate can be used and although a ceramic is common, a printed circuit board and Si board | substrate can also be used.

  EXAMPLES The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. The measurement methods and evaluation methods used in the examples are as follows.

1. Measurement method, evaluation method (1) Solidus temperature, liquidus temperature This was confirmed by performing differential scanning calorimetry (DSC) measurement and melting test.
(2) Tensile strength, elongation rate First, Bi alloys of each component composition shown in Table 1 are melted using an atmospheric melting furnace by the method described later, extruded to 0.75 mmφ, and a wire-shaped preform. A solder sample was prepared.
The obtained solder wire 0.75 mmφ was cut into a predetermined length to obtain a test sample for measuring the tensile strength. This was set in a tensile tester (device name: Tensilon universal tester), and the tensile strength and elongation were measured by automatic measurement.

(3) Observation of Ag-Al intermetallic compound and particle size First, Bi alloys having respective component compositions shown in Table 1 are prepared, melted using an atmospheric melting furnace, extruded to 0.75 mmφ, and wire Shaped preform solder samples were prepared.
The obtained 0.75 mmφ wire was embedded in a resin and subjected to cross-sectional polishing. This was immersed in an aqueous nitric acid solution at normal temperature (nitric acid concentration 20%) for 5 seconds to be etched, thereby obtaining a specimen for observation of the alloy structure of the cross section.
In this specimen, the Bi matrix of the main element looks corroded and black, while the precipitated particles such as intermetallic compounds appear white. Therefore, the size and distribution of the precipitated particles can be easily determined by observation with an optical microscope. Can do. Each specimen was observed with a 200 × optical microscope, the number of particles containing all intermetallic compounds in the field of view was counted, the cross-sectional diameter of the particles was measured, and the measured value was multiplied by 1.12. The diameter. Based on this particle size, the volume of each intermetallic compound particle was calculated using all intermetallic compound particles as true spheres, and the proportion of particles having a particle size of less than 50 μm in all particles was calculated in volume%.

(4) Wettability Set the die bonder (manufactured by NEC Machinery, CPS-400) at 350 ° C or 390 ° C in a nitrogen atmosphere, set the 0.75mmφ sample obtained in (2) above, and place it on the Cu lead frame Supplied. Thereafter, a dummy chip prepared by vapor-depositing Au on the die bonding surface of the silicon chip was die-bonded to a Cu lead frame.
At that time, as evaluation of solder wettability, the case where the solder did not protrude from the chip side was evaluated as “bad”, and the case where the solder protruded was evaluated as “good”.

(5) Bonding reliability A sample obtained by die bonding the above-mentioned dummy chip to a Cu lead frame was further molded with an epoxy resin. The molded product was first subjected to a 260 ° C. reflow test, and then a temperature cycle test of −50 ° C./150° C. was performed 500 cycles (or 700 cycles). Thereafter, the resin was opened, and the bonded portion was observed by die bonding.
As a reliability evaluation, the number of cycles was shown as “good” when no crack occurred in the chip and the joint, and “bad” when the joint failure or crack occurred.

(Examples 1 to 13)
(1) Production of Solder Alloy (Preform Solder) First, Bi, Ag, Al, P, Ge, and Cu (purity of each element: 99.99% by weight or more) were prepared as raw materials. The raw material used is a shot-shaped raw material of 3 mmφ or less, and when the raw material is large flakes or bulk, cut, pulverize, etc. while keeping in mind that there is no variation in composition due to the sampling location in the alloy after melting, The size was reduced to 3 mm or less. Next, a predetermined amount of these raw materials was weighed into a graphite crucible for a high frequency melting furnace.
Next, the crucible containing the raw material was put into a high-frequency melting furnace, and nitrogen was flowed at a flow rate of 0.7 L / min or more per 1 kg of the raw material in order to suppress oxidation. In this state, the inside of the melting furnace was heated to 500 ° C. at a rate of 5 ° C./sec to heat and melt the raw material. When the metal began to melt, it was stirred well with a stirring rod and stirred for 3 minutes so as not to cause local compositional variations. After confirming sufficient melting, the high frequency power supply was turned off, the crucible was quickly taken out, and the molten metal in the crucible was poured into the mold of the solder mother alloy.
As the mold, a cylindrical graphite mold having an inner diameter of 30 mm or less and a wall thickness of about 10 mm was used, and a material having good heat conductivity (made of Cu, cooling water was passed as a hollow structure outside the mold. (Cold metal) was in close contact, and the molten metal was poured into the mold, and then rapidly solidified by cooling at a cooling rate of 5 ° C./sec to about 260 ° C., depending on the composition.
A part of the obtained solidified product was used as a sample, and the amount of particles (intermetallic compound of Ag and Al) formed in the solder alloy and having a particle size of less than 50 μm was measured by the method described above.
Thereafter, the remaining solidified product was transferred to an atmospheric melting furnace and extruded to a diameter of 0.75 mm under the following conditions to produce a wire-shaped preform solder. In all of the examples, processing and winding into a wire shape were possible.

(2) Physical properties and performance test Using the wire-shaped preform solder sample obtained by the above method, measurement of solidus temperature and liquidus temperature, and observation of particle diameter including Ag-Al intermetallic compound And measurements were taken.
Further, the preform solder sample was further die-bonded to a Cu lead frame, and the wettability was evaluated. After molding with an epoxy resin, a temperature cycle test and a reflow test were performed to evaluate the bonding reliability. These results are shown in Table 1.

(Comparative Examples 1-12)
A solder alloy was produced in the same manner as in Example 1 except that the raw materials were mixed so as to have the composition shown in Table 1. A part of the obtained solidified product was used as a sample, and the amount of particles (intermetallic compound of Ag and Al) formed in the solder alloy and having a particle size of less than 50 μm was measured by the method described above. A wire-shaped preform solder was produced. In all comparative examples, processing and winding into a wire shape were possible.
Moreover, using the obtained wire-shaped preform solder sample, the measurement of the solidus temperature and the liquidus temperature, and the observation and measurement of the particle diameter including the Ag-Al intermetallic compound were performed.
Further, the preform solder sample was further die-bonded to a lead frame, and the wettability was evaluated. After molding with an epoxy resin, a temperature cycle test and a reflow test were performed to evaluate the bonding reliability. These results are shown in Table 1.

3. Evaluation In Examples 1 to 13, Al is 0.1 to 3% by mass, and the Al content ratio (X) with respect to Ag is in the range of 1/20 ≦ X ≦ 1/2. In the case of FIG. As represented, a solidus temperature of 265 ° C. or higher was confirmed. Moreover, about Examples 1-8, it was confirmed by cross-sectional observation that 97% or more of the additive and the intermetallic compound particles in the solder wire had a particle diameter of less than 50 μm. Further, in Examples 1 to 8, as represented by the case of FIG. 5 of Example 3, it was confirmed that the elongation was 15% or more and the vulnerability was improved. Cracks did not occur in the chip and the joint at 500 cycles with a small number of cycles, and the evaluation result of the joint reliability was “good”. This is considered to be due to the fact that wetting and spreading were ensured because P and Ge were included, and the reliability was improved.
In Examples 7 to 8 and Examples 10 to 11, since Cu is contained in addition to P or Ge, wetting and spreading are further secured, and even in a temperature cycle test of 700 cycles with a large number of cycles, the chip and the joint are cracked. As a result, the evaluation result of the bonding reliability was “good”.
Next, a part of the molded product was mounted on the substrate five times at 260 ° C., and as a result of examining the presence or absence of abnormality of the chip and the joint after mounting, no abnormality was found, and no conspicuous voids could be confirmed. . Therefore, it was confirmed that the part joined by the solder according to the present invention was maintained without melting even after being held at a reflow temperature of 260 ° C. for 10 seconds about 5 times.

In addition, Comparative Examples 1 to 5 deviating from the scope of the present invention do not contain P or Ge, or the content is outside the upper and lower limits of the required content, and the bare Cu frame in the wettability test at 390 ° C. As a result, wetting spread was insufficient, and the evaluation results of the wettability test / reliability test were “bad”. The solid / liquid phase line of the conventional Bi / 2.5Ag eutectic solder alloy is 262 ° C. as shown in the state diagram, which decreases from the melting point 271 ° C. of Bi alone, as shown in FIG. Even if it was “good”, it did not contain Al, and therefore, as shown in FIG. 4, it showed only an elongation of about 8%, and because of its brittle characteristics, the bonding reliability was “bad”.
In Comparative Examples 6 to 7, the wettability was improved by adding Ge within the scope of the present invention, but Ag or Al was outside the scope of the present invention, and cracked in the solder layer during the reliability test. Was generated and failed in the evaluation of 500 cycles.
In Comparative Examples 8 to 9, Bi, Ag, Al, and P or Ge were blended within the scope of the present invention, but in Comparative Example 8, the blending amount of Al with respect to Ag is less than 1/20, and reliability Since cracks occurred in the solder layer during the test, the evaluation failed for 500 cycles, and in Comparative Example 9, since the blending amount of Al with respect to Ag exceeded 1/2, wetting failure due to segregation of Al It occurred in part and cracks occurred from the insufficiently bonded part, and the evaluation was rejected for 500 cycles.
In Comparative Example 10, Cu was added to the solder alloy of Comparative Example 6 within the scope of the present invention, but cracking of the solder layer was not improved, and the evaluation was rejected after 500 cycles. In Comparative Example 11, Cu was added to the solder alloy of Comparative Example 9 within the scope of the present invention, but the wetting failure was not improved and the evaluation failed for 500 cycles. In Comparative Example 12, the liquidus was 400 ° C., and a part of the liquidus remained undissolved at a bonding temperature of 390 ° C., resulting in insufficient wetting and spreading. Moreover, there was a surface that was not partly joined, and the evaluation was rejected after 500 cycles.

  As described above, peeling and voids do not occur at the portion joined with the Bi-based solder alloy of the present invention even during reflow for mounting the electronic component on the substrate, and there is no problem in the characteristics of the electronic component. It can be said.

  The Bi-based solder alloy of the present invention can be suitably used as a preform solder or a paste solder for a bare Cu frame substrate as a substitute for a high-temperature solder such as Pb / 5Sn, and can be used for semiconductor packages such as power devices and power modules. It can be particularly suitably used for chip bonding and the like.

1 Chip 2 Electrode 3 Solder 4 Lead Frame Island 5 Lead Frame 6 Bonding Wire 7 Mold Resin

Claims (6)

A Bi-based solder alloy having a melting point of 265 ° C. or higher and a liquidus of 390 ° C. or lower,
Ag content is 0.6-18% by mass,
Al content is 0.1 to 3 mass%,
The content of one or more of P and Ge is 0.001 to 0.3 mass%, and the content of Cu is 0 to 1 mass%,
The balance consists of Bi and inevitable impurities,
The Al content is 1/20 to 1/2 of the Ag content,
Dispersing particles containing an intermetallic compound of Ag and Al in the solder alloy,
A Bi-based solder alloy, wherein 97% by volume or more of the particles have a particle size of less than 50 μm with respect to the total volume of the whole particles.   The Bi-based solder alloy according to claim 1, wherein the Al content is 1/15 to 1/4 of the Ag content.   The Bi-based solder alloy according to claim 1 or 2, containing 0.01 to 1% by mass of Cu. A method for producing a Bi-based solder alloy according to any one of claims 1 to 3,
After pouring a molten solder alloy containing each component constituting the Bi-based solder alloy as a raw material into a mold, the alloy is rapidly cooled and solidified to 260 ° C. at a cooling rate of 3 ° C./sec or more. A method for producing a Bi-based solder alloy, wherein particles containing an intermetallic compound are dispersed in an alloy.   A bonding method for an electronic component, wherein the electronic component is bonded to a substrate or a frame having a surface formed of a Cu material using the Bi-based solder alloy according to claim 1. An electronic component mounting board on which an electronic component using the Bi-based solder alloy according to claim 1 is mounted.

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