JP5667467B2 - Alloy material, circuit board, electronic device and manufacturing method thereof - Google Patents

Description

  The present invention relates to an alloy material for filling a fine space, a circuit board having an electric conductor made of the alloy material, an electronic device using the circuit board, and a method for manufacturing the same.

  As a technique for realizing a three-dimensional structure such as a three-dimensional system package (3D-SiP) in an electronic device such as an integrated circuit of various scales, various semiconductor elements or chips thereof, a large number of through electrodes are provided on a circuit board. A TSV (Through-Silicon-Via) technique for laminating these circuit boards has been proposed. If an electronic device having a three-dimensional structure is realized by applying the TSV technology, a large amount of functions can be packed in a small occupied area. In addition, important electrical paths between elements can be dramatically shortened, leading to faster processing. In Patent Document 1, as a very effective means for realizing an electronic device having a three-dimensional structure using the TSV technology, a through electrode is formed by filling a molten metal into a fine through hole by a molten metal filling method. Techniques to do this are disclosed.

  However, when a through electrode is formed on a semiconductor chip or wafer on which a semiconductor element is already formed by a molten metal filling method, the semiconductor element may be thermally damaged by the heat of the molten metal. From the viewpoint of avoiding deterioration of the semiconductor element due to the heat of fusion, a metal bonding material having a low melting point may be used. However, in this case, heat resistance as an electronic device is lowered.

Japanese Patent No. 4278007

  An object of the present invention is to provide an alloy material for an electric conductor that has a high melting point after solidification and has a high heat resistance while being capable of low-temperature melting operation, a circuit board having an electric conductor made of this alloy material, and this circuit board. It is to provide an electronic device used and a manufacturing method thereof.

  In order to achieve the above-described problems, the alloy material according to the present invention fills a fine space, contains Bi, Sn, and Ag, has a melting point of 257 ° C. or higher, and a freezing point of 240 ° C. It is as follows.

  The alloy material having the above-described freezing point and melting point can ensure a temperature hierarchy (temperature hierarchy) of 20 ° C. or more and around 65 ° C., for example. For this reason, according to the present invention, it is possible to provide an alloy material having a low freezing point and a low-temperature melting operation and a high melting point after solidification and high heat resistance. This is because, for example, when filling a liquefied alloy material into a fine space by a molten metal filling method, a low-temperature working environment of 240 ° C. or lower is maintained, and the heat of the molten liquid metal heats the semiconductor element. This means that, after solidification, a melting point of 257 ° C. or higher is secured, and a highly heat-resistant electrical conductor, for example, a circuit board having a through electrode and an electronic device can be realized.

  When the freezing point exceeds 240 ° C., the semiconductor chip or wafer on which the semiconductor element is formed may be thermally damaged. When the melting point is lower than 257 ° C., it is difficult to secure heat resistance at a freezing point of 240 ° C. or higher in the Bi—Sn—Ag system of the present invention.

  Since the alloy material according to the present invention is a Bi—Sn—Ag alloy containing Bi, Sn, and Ag, the above-described freezing point and melting point can be realized by controlling the composition ratio.

  The alloy material according to the present invention can be used for forming an electric conductor in a fine space in various electronic circuit boards and electronic devices. An example of such an electrical conductor is a through electrode that is essential for realizing TSV technology. The electronic elements constituting the electronic device can include a light emitting element, a memory, a logic IC, a digital circuit element, an analog circuit element, or a combination thereof.

  In the above-described circuit board and electronic device, as a method of forming an electrical conductor such as a through electrode, a metal filling method in which a liquid metal is filled into the inside from an opening of a minute space provided in the structure and solidified. Can be applied.

  In the metal filling method described above, nucleation / growth generally occurs randomly in the liquid metal injected into the fine space, so that when solidified, cavities and fine voids are generated with a certain probability. This degrades the electrical characteristics and quality of the electrical conductor formed in the fine space.

  Therefore, the present invention discloses a metal filling method effective for solving such a problem. In the metal filling method disclosed in the present invention, the fine space is provided with a temperature gradient in which the temperature decreases from the opening toward the bottom, and the liquid metal is moved from the bottom toward the opening in the fine space. Solidify in one direction.

  According to this method, since solidification can be started from the bottom in the fine space and solidification can proceed in one direction from the bottom to the opening, it is possible to suppress the generation of cavities and fine voids. Can do.

  The liquid metal used in the above-described metal filling method is preferably an alloy material according to the present invention. As a result, a low-temperature working environment of 240 ° C. or lower is maintained, the semiconductor element is prevented from being thermally damaged, heat resistance of 240 ° C. or higher is ensured after solidification, and cavities and fine voids are prevented. Excellent electrical conductors can be formed.

  Other objects, configurations and advantages of the present invention will be described in more detail with reference to the accompanying drawings. However, the attached drawings are merely examples.

It is a ternary diagram of the alloy material concerning the present invention. It is sectional drawing which expands and shows a part of ternary figure shown in FIG. It is a figure which shows the thermal characteristic and temperature characteristic of the alloy material which concern on this invention. 1 is a cross-sectional view schematically showing a circuit board according to the present invention. It is sectional drawing which shows another example of the circuit board which concerns on this invention typically. It is sectional drawing which shows the device based on this invention typically. It is a figure which shows the metal filling method which concerns on this invention. It is a figure which shows the step after the step of FIG.

  The alloy material according to the present invention is an alloy material that fills a fine space, contains Bi, Sn, and Ag, and has a melting point of 257 ° C. or higher and a freezing point of 240 ° C. or lower. This alloy material may be in an alloyed state (ingot), or may be one in which each component is mixed in a powder state.

  As described above, since the alloy material according to the present invention is a Bi—Sn—Ag ternary alloy containing Bi, Sn, and Ag, depending on the composition ratio, the melting point is 257 ° C. or more and the freezing point is 240. It can set so that it may be below ° C. This point will be described later with data.

Therefore, for example, when filling a liquefied alloy material into a fine space by a molten metal filling method, a low-temperature working environment of 240 ° C. or lower is maintained, and the semiconductor element is thermally heated by the heat of the molten liquid metal. In addition to avoiding damage, a melting point of 257 ° C. or higher can be secured after solidification, and a highly heat-resistant electric conductor, for example, a circuit board or an electronic device having a through electrode can be realized. Bi contributes to filling the micropores without generating voids or gaps due to the volume expansion characteristics during solidification. Sn and Ag, in particular Ag, contribute to the improvement of conductivity due to their high conductivity (63 × 10 ⁶ m ⁻¹ Ω ⁻¹ ).

  When the freezing point exceeds 240 ° C., when a through electrode or the like is formed on the semiconductor chip or wafer on which the semiconductor element is formed by a molten metal filling method, the semiconductor element is thermally damaged by the heat of the molten metal. Sometimes. On the other hand, when the melting point is lower than 257 ° C., it is difficult to ensure heat resistance at a freezing point of 240 ° C. or higher in the Bi—Sn—Ag system.

  The composition of the alloy material suitable for realizing the melting point and freezing point in the present invention includes Bi in the range of 92 to 98% by mass, Sn in the range of 0.5 to 7.5% by mass, and 0.5 to It is a composition containing 4 mass% Ag. In the ternary composition diagram of FIG. 1 and a partially enlarged view of FIG. 2, the composition region of the alloy material according to the present invention is shown as a hatched region S1. According to this composition, the melting point can be set to 257 ° C. or higher and the freezing point can be 240 ° C. or lower. Moreover, a temperature hierarchy key of 35 ° C. or higher can be secured.

  In the alloy material according to the present invention, the freezing point is preferably 220 ° C. or lower, more preferably 210 ° C. or lower. Such a low-temperature freezing point can be realized by controlling the composition ratio in the Bi-Sn-Ag system of the present invention. A preferred example of the composition ratio is a composition containing Bi in the range of 95 to 98% by mass, Sn in the range of 1.0 to 2% by mass, and Ag in the range of 1.9 to 2.7% by mass. Or Bi in the range of 93 to 95% by mass, Sn in the range of more than 3.0% by mass and 4.0% by mass or less, and Ag in the range of 2.0 to 3.0% by mass. Composition. If it is these composition ranges, the effect of the raise of a melting point and the expansion of a temperature hierarchy will be acquired with the fall of a freezing point.

  The alloy material according to the present invention can further contain Ga. Addition of Ga tends to lower the freezing point. Ga is in the range of 0.01 to 4% by mass, more preferably in the range of 0.01 to 0.8% by mass, with the total amount of Bi, Sn and Ag as 100 parts by mass. Next, further details will be described with reference to the data shown in Table 1.

  In Table 1, the temperature hierarchy (temperature hierarchy) is represented by a temperature difference ΔT (° C.) between the melting point (° C.) and the freezing point (° C.). When it is in the range of ΔT <35 ° C., Δ is marked, and when ΔT <33 ° C., it is marked with ×. The column for low temperature filling is divided into three columns of freezing point 210 ° C. or lower, 220 ° C. or lower, and 240 ° C. or lower.

  In Table 1, Sample No. 1 is a case where Bi is 100 mass%, and is outside the present invention in that it does not contain Sn, Ag, and Ga. Sample No. In the case of 1, the effect by containing Sn, Ag, and Ga cannot be obtained. Sample No. 2 is outside the present invention in that it does not contain Sn.

  Sample No. 3-No. 23 is a composition containing Bi in the range of 92 to 98% by mass, Sn in the range of 0.5 to 7.5% by mass, and Ag in the range of 0.5 to 4% by mass. In this composition, the freezing point is in the range of 202.9 ° C to 233.5 ° C. Therefore, low temperature filling at 240 ° C. or lower is possible. In addition, the alloy material having the composition range described above has a melting point in the range of 257.6 ° C. to 278 ° C., and can reliably ensure heat resistance of 240 ° C. or higher.

  Sample No. 3-No. No. 23 satisfies the temperature hierarchy ΔT ≧ 35. As an example of the temperature hierarchy, FIG. 3 shows a sample No. by DSC (Differential Scanning Calorimetry). 5 shows a thermal analysis diagram. In the temperature characteristic of temperature increase / decrease indicated by a dotted line, a melting point appears at 268 ° C. during the temperature increase process, and a freezing point appears at 209 ° C. during the temperature decrease process. In the illustrated case, a temperature hierarchy of about 50 ° C. is secured. Therefore, for example, when filling a liquefied alloy material into a fine space by a molten metal filling method, a low-temperature working environment of 210 ° C. or lower is maintained, and the semiconductor element is thermally heated by the heat of the molten liquid metal. In addition to avoiding damage, a melting point of 268 ° C. or higher can be secured after solidification, and a highly heat-resistant electric conductor, for example, a circuit board or an electronic device having a through electrode can be realized.

  When the freezing point exceeds 240 ° C., when a through electrode or the like is formed on the semiconductor chip or wafer on which the semiconductor element is formed by the molten metal filling method, the temperature of the molten metal exceeds 240 ° C. The semiconductor element may be thermally damaged by heat.

  Assuming that the alloy material according to the present invention is applied to a semiconductor chip or a wafer, the freezing point is preferably 220 ° C. or lower, more preferably 210 ° C. or lower. In consideration of workability, it is desired to secure a temperature hierarchy ΔT ≧ 35 ° C. Such a low temperature freezing point and a temperature hierarchy are realizable by controlling the composition ratio in the Bi-Sn-Ag system of this invention.

  A sample having a freezing point of 220 ° C. or lower is designated as Sample No. 5-8, 15-17, 20, 23. Among these, sample no. 5 to 8 is a composition containing Bi in the range of 95 to 98 mass%, Sn in the range of 1.0 to 2.0 mass%, and Ag in the range of 1.9 to 2.7 mass%. is there. Sample No. 15 to 17, Bi in the range of 93 to 95 mass%, Sn in the range of more than 3.0 mass% and 4.0 mass% or less, and Ag in the range of 2.0 to 3.0 mass% It is a composition to contain.

  Among these, sample no. 5, 6, 16 and 20 have a freezing point of 210 ° C. or lower and can be filled at a low temperature of 210 ° C. or lower.

  First, sample no. 5 contains 96.66 mass% Bi, 1.00 mass% Sn, 2.20 mass% Ag, and 0.41 mass% Ga, and has a freezing point of 209 ° C. The melting point is 268 ° C. and the temperature hierarchy is 59 ° C.

  Sample No. 6 contains 96.48 mass% Bi, 1.00 mass% Sn, 2.37 mass% Ag, and 0.41 mass% Ga, and has a freezing point of 209.5 ° C. . The melting point is 274 ° C., and the temperature hierarchy reaches 64.5 ° C.

  Sample No. 16 contains 93.74 mass% Bi, 3.38 mass% Sn, 2.73 mass% Ag, and 0.41 mass% Ga, and has a freezing point of 202.9 ° C. Moreover, the melting point is 264.1 ° C., and the temperature hierarchy is 61 ° C.

  Sample No. 20 contains 93.23 mass% Bi, 3.91 mass% Sn, 2.72 mass% Ag, and 0.41 mass% Ga, and the freezing point is 207.1 ° C. . The melting point is 263.8 ° C. and the temperature hierarchy is 56 ° C.

  A sample having a freezing point exceeding 210 ° C. and not more than 220 ° C. is designated as Sample No. 7, 8, 15, 17, 23. First, sample no. 7 contains 96.23 mass% Bi, 1.70 mass% Sn, 1.93 mass% Ag, and 0.41 mass% Ga, the freezing point is 218.8 ° C. . The melting point is 275.7 ° C., showing the highest heat resistance. The temperature hierarchy is 57 ° C.

  Next, sample No. 8 contains 95.17 mass% Bi, 2.00 mass% Sn, 2.69 mass% Ag, and 0.41 mass% Ga, and has a freezing point of 219.2 ° C. . The melting point is 267.3 ° C. and the temperature hierarchy is 48 ° C.

  Sample No. 15 contains 94.57% by mass of Bi, 3.27% by mass of Sn, 2.05% by mass of Ag, and 0.41% by mass of Ga, and the freezing point is 216.3 ° C. . The melting point is 264.4 ° C. and the temperature hierarchy is 48 ° C.

  Sample No. 17 contains 93.77 mass% Bi, 3.88 mass% Sn, 2.21 mass% Ag, and 0.41 mass% Ga, and has a freezing point of 221.2 ° C. . The melting point is 259.7 ° C. and the temperature hierarchy is 38 ° C.

  Furthermore, sample no. 23 contains 94.21 mass% Bi, 4.30 mass% Sn, 1.35 mass% Ag, and 0.41 mass% Ga, and has a freezing point of 217.9 ° C. . The melting point is as low as 257.6 ° C, but the temperature hierarchy is 40 ° C.

In the alloy material according to the present invention, Bi contributes to filling the micropores without generating voids or gaps due to the volume expansion characteristics during solidification. Ag contributes to the improvement of conductivity due to its high conductivity (63 × 10 ⁶ m ⁻¹ Ω ⁻¹ ). Further, the inclusion of low melting point Sn (melting point: 231.97 ° C.) and Bi (melting point: 271.5 ° C.) causes Sn and Bi to melt at a low temperature in the melting and filling operation into a fine space, and the heat of fusion causes Ag to melt. (Melting point 961.78 ° C.) contributes to melting at a temperature lower than its melting point.

  The alloy material according to the present invention can further contain Ga. Addition of Ga tends to lower the freezing point. In Table 1, Ga is 0.41% by mass, but Ga is in the range of 0.01 to 4% by mass, more preferably 0.00%, with the total amount of Bi, Sn and Ag as 100 parts by mass. It is the range of 01-0.8 mass%.

  In sample Nos. 24-34, the freezing point is 240 ° C. or lower, but the melting point is 254.5 ° C. or lower, which is lower than 257 ° C. When the melting point is lower than 257 ° C, it is difficult to ensure heat resistance of 240 ° C or higher in the Bi-Sn-Ag system. Therefore, sample no. 24 to 34 are outside the scope of the present invention.

  The alloy material according to the present invention can be used to form an electrical conductor in a fine space in various electronic circuit boards. An example of such an electrical conductor is a through electrode that is essential for realizing TSV technology. Referring to FIG. 4, an example of such a circuit board is illustrated. The illustrated circuit board may be a single layer substrate or an interposer formed of a laminated body, or may be a semiconductor substrate on which a semiconductor element, a semiconductor circuit, or the like is formed. In this circuit board, a large number of columnar electric conductors 2 serving as through electrodes are arranged on a substrate 1 in, for example, a matrix. The electric conductor 2 can be formed by a metal filling method in which a molten metal obtained by liquefying the alloy material according to the present invention is filled inside the opening of a fine space provided in the substrate 1 and solidified.

  The circuit board obtained in this way can be used as an electronic device as it is, or can be used to form an electronic device in combination with the electronic element 3 as shown in FIG. The electronic element 3 is supported by the substrate 1. When the substrate 1 is a semiconductor substrate, the electronic element 3 may be formed inside the substrate 1 as a semiconductor element.

  Furthermore, as shown in FIG. 6, a laminated electronic device may be used. In this case, the circuit board 4 is disposed between the two chip-shaped electronic elements 5 and 6 as an interposer. Thereby, a three-dimensionally arranged electronic device is realized.

  The electronic elements 5 and 6 constituting the electronic device can include a light emitting element, a memory, a logic IC, a digital circuit element, an analog circuit element, or a combination thereof.

  In the above-described circuit board and electronic device, as a method for forming the columnar electric conductor 2, a metal filling method is applied in which liquid metal is filled into the interior from the opening of a minute space provided in the structure and solidified. can do.

  In the metal filling method described above, nucleation / growth generally occurs randomly in the liquid metal injected into the fine space, so that when solidified, cavities and fine voids are generated with a certain probability. This degrades the electrical characteristics and quality of the electrical conductor formed in the fine space.

  The present invention discloses a metal filling method effective as a means for solving such problems in FIGS.

  First, as shown in FIG. 7, when applying the metal filling method, the substrate 1 provided with a large number of fine spaces 10 having fine pore diameters at predetermined intervals is placed on a support base 11 or the like. Preferably, the support base 11 and the substrate 1 are arranged in a vacuum chamber capable of controlling the internal pressure so that the liquid metal can be filled with a differential pressure. A heating / cooling device 71 is thermally coupled to the support base 11. Further, temperature detectors 72 and 73 are disposed on both surfaces of the substrate 1 in the thickness direction. The temperature detection signals of the temperature detectors 72 and 73 are supplied to the temperature control device 74. Based on the temperature detection signals supplied from the temperature detectors 72 and 73, the temperature control device 74 controls the heating / cooling device 71 so that a temperature gradient is generated in which the temperature decreases from the opening to the bottom of the fine space 10. Control. Thus, a temperature gradient can be provided between the surface temperature T1 of the substrate 1 and the surface temperature T2 of the bottom. However, the temperature control system is not limited to that shown in the drawing because a temperature gradient in which the temperature decreases as it goes from the opening to the bottom of the fine space 10 may be generated.

  By the temperature control system described above, the fine space 10 is given a temperature gradient in which the temperature decreases from the opening toward the bottom. In this state, as shown in FIG. 8, when the liquid metal 2 is filled into the fine space 10, the liquid metal 2 is solidified in one direction from the bottom of the fine space 10 toward the opening in the fine space 10. To do.

  According to this method, solidification can be started from the bottom of the fine space 10 and solidification can proceed in one direction from the bottom toward the opening, thereby suppressing the generation of cavities and fine voids. Can do. The temperature gradient may be about 10 ° C./mm. However, this temperature difference (temperature gradient) needs to be larger than the maximum temperature difference on the opening surface of the substrate 1.

  Further, according to the above method, the liquid metal filled in the fine space 10 solidifies and precipitates from the high melting point phase, and therefore, by selecting the composition, the liquid metal is reduced to the upper part (opening side) of the fine space 10. The melting point phase solidifies and precipitates. Due to this phenomenon, the bonding bumps are formed in a self-aligned manner, so that the bonding bumps can be directly applied to the bonding process without passing through the bonding bump forming process.

  In addition, according to the above method, since the high melting point phase can be preferentially precipitated in the Sn-based alloy having a low resistance, the low resistance and the expansion of the temperature hierarchy can be realized at the same time.

  Therefore, the metal filling method disclosed here contributes to the expansion of the application range and the ultimate cost performance.

  When the liquid metal 2 filled in the fine space 10 is cooled, a pressing pressure, injection pressure, rolling pressure, or the like using a pressing plate is applied to the liquid metal 2 inside the fine space 10 from the opening surface side. It is preferable to cool and cure while applying.

  The liquid metal used in the metal filling method described above is an alloy material according to the present invention. As a result, a low-temperature working environment of 240 ° C. or lower is maintained, the semiconductor element is prevented from being thermally damaged, heat resistance of 240 ° C. or higher is ensured after solidification, and cavities and fine voids are prevented. Excellent electrical conductors can be formed.

  The present invention has been described in detail with reference to the preferred embodiments. However, the present invention is not limited to these embodiments, and various modifications can be made by those skilled in the art based on the basic technical idea and teachings. It is self-evident that

Claims (2)

An alloy material that fills a fine space,
A quaternary system comprising Bi in the range of 92 to 98% by mass, Sn in the range of 0.5 to 7.5% by mass, Ag in the range of 0.5 to 4% by mass, and Ga;
The addition of Ga is in the range of 0.01 to 0.8% by mass, with the total amount of Bi, Sn and Ag being 100 parts by mass.
Alloy material. An electronic device in which a plurality of substrates are stacked,
Each of the substrates has an electrical conductor provided in the thickness direction,
The electrical conductor is made of an alloy material according to claim 1,
Electronic devices.

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