JP2006289474A - Brazing filler metal sheet, its manufacturing method, and electronic component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Pb-free brazing filler metal sheet which solves the problem of degradation in bonding reliability caused by voids in a brazing filler metal and a compound phase formed between particles. <P>SOLUTION: The brazing filler metal sheet is composed of 70-90 mass% of Ag and the balance Sn, and has such a structure that a particle size of Ag is &le;300 &mu;m and a particle size of Sn is &le;100 &mu;m. A void ratio is &le;30%. Preferably, an aspect ratio of Ag particles is &ge;1.2 on average. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

  The present invention relates to a brazing material sheet used for joining electronic components, a manufacturing method thereof, and an electronic component.

  In recent electronic equipment industries, wire bonding using Au wire is widely used as a method for electrically connecting a semiconductor element made of Si or the like to a wiring board. In order to perform wire bonding, it is necessary to bond and fix a semiconductor element to a wiring board. Various materials have been proposed as bonding members for fixing the semiconductor element. Among them, a Pb—Sn alloy containing 90% or more by weight of Pb has a melting point of about 300 ° C. and is superior in heat resistance as compared with a resin-based bonding material. It is often used when bonding an element to a wiring board. Pb—Sn alloys are also used as structural materials for electronic components in applications other than fixing semiconductor elements. This is because when an electronic component is mounted on a wiring board, a solder alloy having a melting point of approximately 200 ° C. is generally used. However, since a Pb—Sn alloy has a higher melting point, it does not remelt during soldering. It is.

On the other hand, in recent years, there has been a so-called Pb-free movement to reduce Pb in solder and brazing material in consideration of the natural environment, and various alternative materials for Pb—Sn alloys have been studied.
For example, Patent Literature 1 and Patent Literature 2 propose a joining member in which Cu and Sn particles are mixed with a reducing flux to form a paste. In this joining member, only Sn particles having a low melting point are melted and reacted with Cu particles at the time of brazing, and a Cu—Sn compound having a melting point higher than that of the Sn particles is formed as a diffusion phase between the Cu particles and joined. This proposal is excellent in that it is a brazing material containing no Pb and maintains the strength as a structural material even when reheated to the melting point of Sn.
JP 2002-254194 A JP 2003-211289 A

The bonding materials disclosed in Patent Document 1 and Patent Document 2 described above are advantageous in that they do not contain Pb and ensure bonding even in a high-temperature environment, but only Sn particles and Cu particles are kneaded with flux. Since it is a material, there are many gaps between the particles, and the voids tend to remain after brazing. Further, since the contact between the Sn particles and the Cu particles is basically a point contact, there is a problem that the reactivity between the particles is poor. Further, the Cu—Sn diffusion phase formed between the Cu particles when the Sn particles melt is not only a very brittle intermetallic compound, but also when exposed to high temperatures due to heat generation of the semiconductor element during actual use. In addition, the diffusion of Sn atoms is activated and remarkably grows, causing a decrease in strength. These problems are serious problems in terms of reducing the reliability of electronic components and electronic devices.
An object of the present invention is to provide a brazing material sheet containing no Pb, which solves the problem of reduction in bonding reliability caused by a compound phase formed between voids and particles in the brazing material.

  The present inventor has found that the use of a specific green compact can suppress the generation of voids even after brazing, and has reached the present invention.

That is, the present invention is a brazing material sheet composed of 70% to 90% Ag and the remaining Sn in mass%, wherein the particle size of Ag is 300 μm or less, the particle size of Sn is 100 μm or less, and the porosity is 30% or less. This is a brazing material sheet.
Preferably, the aspect ratio of Ag particles in the brazing material sheet is 1.2 or more on average.

  Further, the present invention is a method for producing a brazing material sheet consisting of 70 to 90% Ag in mass% and the balance Sn, Ag particles having a particle size of 300 μm or less, and Sn particles having a particle size of 100 μm or less. This is a method for producing a brazing material sheet which is mixed to form a mixture, and the mixture is pressed to form a green compact having a porosity of 30% or less.

Further, the present invention is a structure composed of 70% to 90% Ag and the remaining Sn in mass%, and a structure in which the thickness of the Ag—Sn diffusion phase formed around Ag particles of 300 μm or less is 10 μm or less. It is an electronic component which comprises the junction part which has.
Preferably, the electronic component has an area ratio of 20% or less of the metal Sn phase remaining in the joint structure.

  According to the present invention, it is possible to drastically improve the problem of strength reduction at a joint portion of an electronic component or the like, and this is an indispensable technique for practical use of a brazing material not containing Pb.

  As described above, the important feature of the present invention is a mixture of Ag particles and Sn particles, the particle size of Ag is 300 μm or less, the particle size of Sn is 100 μm or less, and the porosity is 30% or less. That is. This is because when the Ag particles are larger than 300 μm, the specific surface area is small, so the contact ratio with the Sn particles is low and the reactivity is lowered. In addition, there are many portions where no Ag—Sn compound is formed around the Ag particles. As a result, the bonding strength between particles is insufficient. Also, when the Sn particles are larger than 100 μm, the contact ratio with the Ag particles is low, and even if Sn melts during brazing, the Ag—Sn compound is formed only locally around the Ag particles. As a result, the joint strength is insufficient. On the other hand, when the porosity of the mixture is larger than 30%, a large number of voids remain in the joint after brazing, and the strength is not sufficient.

  Moreover, it is preferable that the content rate of Ag in the brazing material sheet | seat of this invention is 70 to 90% by mass%. This is because when the amount is less than 70 mass%, unreacted Sn remains in the joint even after brazing, and the joint may be melted again when exposed to a high temperature environment, resulting in a decrease in strength. It is. Moreover, when larger than 90 mass%, it is the quantity of Sn particle | grains inadequate to form an Ag-Sn compound as a diffused phase, and it is because joining between Ag particle | grains is not fully performed.

  Further, the aspect ratio of Ag particles in the brazing material sheet of the present invention is preferably 1.2 or more on average. This is because if the average aspect ratio is 1.2 or more, the specific surface area of the Ag particles is large when contacting with the molten Sn during brazing, and the reaction with Sn is promoted.

Furthermore, the Ag particles in the brazing material sheet of the present invention need not be pure Ag. For example, an Ag alloy containing Ag as a main component and containing one or more of Sn and Cu may be used. Even if these elements are added to Ag, there is no problem in bondability, and it is possible to provide a cheaper brazing material sheet.
Furthermore, the Sn particles in the brazing material sheet of the present invention need not be pure Sn. For example, a Sn alloy mainly containing Sn and containing any one or more of Ag, Cu, Bi, and Zn may be used. When these elements are added to Sn, there is an effect of lowering the melting point of Sn, and bonding at a lower brazing temperature becomes possible.

  Further, the brazing material sheet of the present invention uses, for example, Ag having a particle size of 300 μm or less and Sn having a particle size of 100 μm or less, and mixes 70% to 90% Ag in mass% and the remaining Sn to form a mixture. To obtain a green compact having a porosity of 30% or less. In the production method of the present invention, the Ag particles and the Sn particles are mixed to form a mixture, whereby the Sn particles are uniformly dispersed between the Ag particles, and the Sn particles and the Ag particles react with each other in the entire joint portion during brazing. It becomes possible. Further, in the state of the mixture, there are many voids between the particles, but in addition to being able to reduce the porosity of the mixture by pressing, the particles are deformed so that the particles come into surface contact with each other. The reactivity between the Sn particles is improved. Furthermore, in this invention, it can also extend after pressing. The porosity can be reduced sufficiently by pressing, but the porosity can be further reduced by applying a stretching process, and in addition, a thin solder sheet suitable for joining electronic components that are becoming smaller and thinner is manufactured. It is also easy to do.

Moreover, it is preferable that the junction part of the electronic component brazed using the brazing material sheet of the present invention has a structure in which a diffusion phase of 10 μm or less is formed around Ag particles of 300 μm or less.
Particles are joined together by forming an Ag—Sn diffusion phase around the particles, but since this diffusion phase is more brittle than Ag particles and Sn particles, if a diffusion phase larger than 10 μm is formed, This is because the ductility of the portion is lowered and the bonding strength of the electronic component is lowered.
Furthermore, in the plane cross section of the joint portion of the electronic component brazed using the brazing material sheet, the metal Sn layer remaining in the joint portion is preferably 20% or less in area ratio. Even if it is larger than 20%, it has a function as a joint part. However, when it is exposed again to a high temperature due to heat generation of electronic parts, the metal Sn in the joint part is remelted and the joint strength is increased. It is because it falls.

Ag particles of 300 μm or less and Sn particles of 60 μm or less were mixed at a weight ratio of 95: 5, 90:10, 80:20 and 60:40 to prepare a mixture. Next, a pressure of 525 MPa or 700 MPa was applied by a pressure press to produce a brazing material sheet having a length of 70 mm and a width of 8 mm. For comparison, an unpressurized mixture was also prepared. The aspect ratio of Ag particle | grains was calculated | required with respect to each non-pressurized mixture and a press-molded body. Here, the aspect ratio is defined as the ratio of the maximum length of Ag particles and the length in the direction perpendicular to the maximum length in the plane cross section of the mixture or molded body, and the average value of Ag particles per 1 mm ^{2 of} the plane cross section. Asked. The porosity of the mixture and the molded body is 100 (1 when the apparent density T is obtained by measuring the weight and volume of the mixture or the molded body and the theoretical density T ₁₀₀ is 100% when the filling rate is 100%. -T _{/ T 100)} was determined as. The measurement results are shown in Table 1. From Example 1 to Example 4, the porosity of the mixture could be significantly reduced by pressurization, and the aspect ratio of Ag particles in the sheet could be 1.2 or more.

Next, the Ag-Sn mixture is placed on the base material on which the non-pressurized mixture and the pressure-formed body are subjected to electroless Ni / Au plating imitating the terminals of the electronic component, and the mixture is heated up to 280 ° C in a nitrogen atmosphere. Warm and braze. In the joint portion after brazing, an Ag—Sn compound is formed by the reaction of Ag particles and Sn particles, and the density changes. Therefore, the void ratio of the joint after brazing was obtained as the area ratio of the void in the plane cross section of 1 mm ² of the joint. Similarly, the metal Sn remaining in the joint after brazing was defined and measured as the area ratio of the Sn phase occupying 1 mm ² in the plane cross section in the joint after brazing. In addition, the base material was peeled off after brazing in order to evaluate the degree of joining at the joint. The degree of joining was determined as unjoined when peeled with a bare hand, and joined when not peeled at all with a bare hand. The evaluation results are shown in Table 2, the structure photograph of the pressure-formed body before brazing is shown in FIG. 1, the structure photograph of the joint after brazing is shown in FIG. 2, and the structure of the diffusion phase formed around the Ag particles. A photograph is shown in FIG. From Table 2, in Comparative Example 2 and Comparative Example 3 brazed using an unpressurized mixture, the porosity of the joint after brazing exceeded 30%, and when peeled, the strength of the joint was obtained. Was missing and destroyed. Further, since there are many voids, a large amount of metal Sn oozes out from the joint, and the area ratio of metal Sn remaining in the joint cannot be measured. On the other hand, when the void ratio in the brazing material sheet is reduced by pressure forming, the void ratio in the joint after brazing is less than 10%, and it can be seen that the pressure can be greatly reduced by pressing. However, in Comparative Example 1 in which the mixing ratio of Sn particles is low, the diffusion phase necessary for bonding was not sufficiently formed even when pressed, so that the base material was incompletely bonded so that it could be peeled off by hand. The function of was not satisfied. On the contrary, in Comparative Example 4 where the mixing ratio of Sn particles was high, the area ratio of the metal Sn phase remaining in the joint portion was almost half although it was sufficiently joined.

The effect of the thickness of the diffusion phase formed around the Ag particles during brazing on the bonding reliability of the joint was evaluated by a three-point bending test. The result of the three-point bending test depends greatly on the base material to which the brazing material is joined, and the characteristics of the joint cannot be accurately grasped. For this reason, the bulk material which simulated the junction part was produced by heating only a brazing material sheet to 280 degreeC, without joining to a base material. The bulk material had a width of 8 mm, a length of 60 mm, and a thickness of 1 mm. The thickness of the diffusion phase formed around the Ag particles was determined by using a metal microscope as the average thickness of the diffusion phase formed around the Ag particles in a plane cross section of 1 mm ² after brazing.
The fulcrum interval in the three-point bending test was 50 mm, and the bending strength and the amount of deflection at break were measured. These measurement results are shown in Table 3. In Comparative Example 4 in which the diffusion phase was thick, the bending strength was low and the amount of deflection was small, but in the examples of the present invention, both the strength and the amount of deflection were greatly improved. Observation of the fracture surface after the test revealed that a large amount of the diffuse phase was exposed, indicating that the fracture mainly occurred in the diffuse phase. Therefore, it was found that the brazing material sheet of the present invention, which can provide a joint having a thin diffusion phase, is superior in joining reliability.

2 is a cross-sectional structure photograph of a brazing material sheet of Example 1. FIG. 2 is a cross-sectional structure photograph of a joint after brazing in Example 1. FIG. 2 is a structure photograph of a diffusion phase formed around Ag particles after brazing in Example 1. FIG.

Claims (5)

A brazing material sheet consisting of 70 to 90% Ag and the rest Sn in mass%, wherein the Ag particle size is 300 μm or less, the Sn particle size is 100 μm or less, and the porosity is 30% or less. A brazing material sheet. The brazing material sheet according to claim 1, wherein an average aspect ratio of the Ag particles is 1.2 or more. A method for producing a brazing material sheet comprising 70% to 90% Ag in mass% and the remaining Sn, wherein Ag particles having a particle size of 300 μm or less and Sn particles having a particle size of 100 μm or less are mixed to form a mixture. A method for producing a brazing material sheet, wherein the mixture is pressed into a green compact having a porosity of 30% or less. It is composed of 70% to 90% Ag in mass% and the remaining Sn, and has a junction having a structure in which the thickness of the Ag-Sn diffusion phase formed around Ag particles of 300 μm or less is 10 μm or less. Electronic parts. The electronic component according to claim 4, wherein the metal Sn phase remaining in the joint structure is 20% or less in terms of area ratio.