WO2009104294A1

WO2009104294A1 - Lead-free solder alloy and semiconductor device

Info

Publication number: WO2009104294A1
Application number: PCT/JP2008/066018
Authority: WO
Inventors: 石川　久雄
Original assignee: 日本ジョイント株式会社; ホライゾン技術研究所株式会社
Priority date: 2008-02-22
Filing date: 2008-08-29
Publication date: 2009-08-27
Also published as: JP4375485B2; JP2009197315A; WO2009104338A1

Abstract

A molten lead-free solder alloy comprising tin as a main component and at least one metal selected from silver, copper, zinc, bismuth, antimony, nickel, and germanium added to the tin is immersed in a solution of an oil containing 5 to 80% by weight of an organic fatty acid having 13 to 20 carbon atoms at a solution temperature of 180 to 300°C. The solution is stirred to remove oxides and impurities contained in the lead-free solder. According to the above constitution, the treated lead-free solder alloy is advantageous in that the lead-free solder alloy is flexible and has excellent elongation and toughness and, as compared with the conventional lead-free solder alloy, the treated lead-free solder alloy has lower viscosity in a molten state, possesses better solder wet spreading properties, and can realize solder jointing which provides a solder joint, particularly a microjoint, having high joint reliability unattainable by the prior art technique.

Description

Specification

Lead-free solder alloy oppi semiconductor device

Technical field

[0001] The present invention relates to circuit formation of a mounting member such as a semiconductor package or an electronic element on a printed circuit board.

A lead-free solder alloy that is soldered via solder between the copper land of the printed circuit board and the lead terminals of semiconductor packages, electronic devices, etc. More specifically, it relates to semiconductor devices that are soldered using the solder. More specifically, it is much more flexible and stretchable than the current lead-free solder alloy. Solder joints with low viscosity in the state, good wetting and spreadability, less likely to become a per volume, difficult to leak into adjacent leads at narrow intervals, and high joint reliability of soldered micro joints In addition, the present invention relates to a lead-free solder alloy that can be used, a semiconductor device soldered using the lead-free solder alloy of the present invention, and a technology.

Background art

[0002] In recent years, electronic devices are increasingly required to have higher reliability and smaller size and weight, and electronic components such as transistors, diodes, ICs, resistors, capacitors, and electronic components such as connectors are soldered to printed circuit boards. Bonded and mounted to form an electronic circuit, it is widely used as a semiconductor device and electronic device, but with the miniaturization of these electronic elements and electronic components, the solder joints are also miniaturized and increasingly higher Quality reliability is required. In particular, extremely strict reliability is required for the quality of fine solder joints between printed circuit boards and electronic component parts. For this reason, the solder alloy side used for solder joints is also required to have high solder joint strength, in particular, high reliability of the solder joints as the electronic element and electronic component lead joint area and pitch become smaller. .

[0003] On the other hand, in recent years, the use of lead has been banned or regulated due to environmental pollution and harmfulness to the human body, and so-called "lead-free solder alloys" that do not contain lead have been developed especially in the field of electronic components. It is widely used for soldering processing. Especially, it is possible to use tin or silver solder alloy, and solder alloy with antimony added (Patent Document 1), or tin or silver solder alloy. Solder alloys with added germanium (Patent Document 2) etc. have been proposed It has become. In addition, a number of various solder alloys have been proposed, such as a tin 'zinc' nickel-based solder alloy and a solder alloy further added with silver, copper, bismuth, etc. (Patent Document 3).

However, since these lead-free solder alloys do not have good wettability at the time of melting, when the solder joint area becomes finer, the solder rises in the joint at a capacity higher than necessary. In circuits where the volume j and the pitch between leads are narrow, there is a difficulty that bridges over adjacent leads and leaks easily, and the elongation, which is one of the physical and mechanical characteristics of the solder during solidification, occurs. Because of its small size, it tends to cause poor continuity due to fatigue fracture of solder joints due to repeated heat cycles when energization is turned on and off, and often impairs the connection reliability of miniaturized electronic devices.

Patent Document 1: Japanese Patent Laid-Open No. 5-0 2 8 6 (Patent 3 0 2 7 4 4 1)

Patent Document 2: JP-A-11 1 7 7 3 6 6 (Patent 3 2 9 6 2 8 9)

Patent Document 3: Japanese Patent Laid-Open No. 9-9 4 6 8 8 (Patent 3 2 9 9 0 9 1)

Disclosure of the invention

Problems to be solved by the invention

[0005] The present invention relates to the problem of the above-mentioned overvolume, which is a difficulty in soldering a small part of a lead-free solder alloy that is currently in practical use, and a small part of a very narrow lead-pitch circuit. In order to solve the problem of leakage with leads and the problem of poor continuity due to poor fatigue over time due to repeated heat cycles of the solder joints, the reliability of the joints of micro electronic parts is improved. The present invention provides a lead-free solder alloy that dramatically improves, and a semiconductor device in which the solder joint reliability of minute parts is dramatically improved by using the lead-free solder alloy.

Means for solving the problem

[0006] The present invention is currently widely used in a solution having a liquid temperature of 180 to 30 consisting of an oil containing 5 to 80% by weight of an organic fatty acid having 13 to 20 carbon atoms. A normal lead-free solder alloy, that is, a molten lead-free solder alloy containing tin as the main component and one or more metals selected from silver, copper, zinc, bismuth, antimony, nickel and germanium added thereto. By immersing and stirring, and removing oxides and impurities in the lead-free solder, unprecedented physical properties Solder joints that have good wetting and spreading properties, are flexible and stretchable as the physical and mechanical properties of solder, have excellent toughness, and have high joint reliability, especially for micro-joints. The present invention relates to a solder alloy that can be used, a semiconductor device in which the reliability of solder joints in a minute part is dramatically improved by using the solder alloy, and a technology for the semiconductor device.

More specifically, although the organic fatty acid used in the present invention can be used even with a carbon number of 12 or less, it has a water absorption property, which is not preferable because it is used at a high temperature. In addition, organic fatty acids having 21 or more carbon atoms have a high melting point and poor permeability and are difficult to handle, and the lead-free solder alloy after the treatment has an insufficient antifungal effect. Desirably, palmitic acid having 16 carbon atoms and stearic acid having 18 carbon atoms are optimal, and one of them is 10 to 70% by weight, and the liquid temperature is composed of the remaining ester synthetic oil 1 80 to 30 By using a solution at 0, the oxides and impure metals present inside the lead-free solder alloy are removed, and unprecedented physical, mechanical and chemical properties, especially flexible, stretchable, tough, and melted. It has a low viscosity at the time (the apparent sensation is clearly “smooth” compared to conventional lead pre-solder) and provides a clean, lead-free solder alloy with good solder wettability.

[0008] The organic fatty acid concentration is effective even if it is 10% by weight or less, but complicated, such as replenishment management, and if it is 70% by weight or more, the liquid viscosity increases, and the stirring resistance with the lead-free solder alloy In order to cause a problem in the mixed permeability, it is preferably 10 to 70% by weight. The liquid temperature is determined by the melting point of the lead-free solder alloy to be used, and it is necessary to vigorously stir and contact the organic fatty acid solution and the molten lead-free solder at least in a temperature range above the melting point.

[0009] Further, the upper limit temperature is about 300 ° from the viewpoint of smoke generation and energy saving, and is desirably a temperature not lower than the melting point of the lead-free solder to be used up to 27 ° C. The reason for mixing the ester synthetic oil is to reduce the viscosity of the liquid and perform uniform processing and to suppress high-temperature smoke generation of organic fatty acids. The concentration is determined by the concentration of organic fatty acids.

[0010] The stirring method is a method in which the above-mentioned organic fatty acid and ester synthetic oil are put in a stainless steel container equipped with a heating device and heated to a predetermined temperature while stirring using a normal patch-type stainless steel impeller stirrer. The lead-free solder alloy solution, which has been made into a solution and previously melted in a separate tank, is poured into the solution with vigorous stirring little by little. Stirring can efficiently remove oxides and impurities in the sharp free solder in a short time by using a static mixer. [0011] The types of lead-free solder alloys are actually tin 'silver' copper-based and commercial alloys with nickel and germanium added, and tin 'zinc-based alloys with nickel and silver added. The effects of the immersion stirring treatment were conducted with the above-described organic fatty acid and ester synthetic oil of the present invention centering on the alloy, and the effect was verified. It can be inferred that

The invention's effect

[0012] 5 to 80% by weight of the organic fatty acid having 13 to 20 carbon atoms and the remaining ester synthesis liquid temperature 1 80 (temperature higher than the melting point of the lead solder alloy material to be used) In general, a lead-free solder alloy that is widely used at present, that is, tin as a main component, and silver, copper, zinc, bismuth, antimony, nickel, germanium, or more When molten lead-free solder alloy added with metal is injected and immersed and stirred, oxidation of tin oxide, copper oxide, silver oxide, or other added metals present in the molten lead-free solder alloy is performed. Oxidized impurities such as iron, lead, silicon, potassium, etc. that are mixed in the product and react with organic fatty acid ruponyl groups to be saponified and separated and removed from the lead-free solder alloy.

The stirring time depends on the amount of the lead-free solder alloy used, the structure of the stirrer, and the stirring conditions, but generally strong stirring for about 10 to 60 minutes is sufficient. Then, using the difference in specific gravity, the lead oxide solder alloy, which has been separated and removed from the bottom of the reaction vessel by the specific gravity difference, has been cleaned and taken out in a molten form, solidified, and solidified. It can be put into a normal soldering device and soldered.

[0013] When the physical mechanical and chemical properties of the lead-free solder alloy of the present invention manufactured under the above conditions were examined, as shown in the following examples (1 to 3), it is currently widely used. Compared to lead-free solder alloys (Comparative Examples 1 to 3), the elongation and breaking elongation are significantly improved, the solder wettability during soldering is much better, and the viscosity during melting It was confirmed that the lead-free solder alloy is optimal for soldering small parts. In other words, even at an extremely narrow pitch with a lead area of 0.08 ιηπι and an adjacent lead spacing of 0.08 mm, there is no over-volume or bridge over and leakage to the adjacent leads, and there is a small amount associated with low temperature heat cycles. There is no electrical circuit continuity failure due to fatigue fracture of solder joints, It was found that the long-term connection reliability of the joint by using the re-solder is excellent.

[0014] <Example Oppi Comparison>

First, as Comparative Example 1, a commercially available lead-free solder alloy consisting of 2.5% by weight of silver, 0.5% by weight of copper, and the balance tin was used.

[0015] On the other hand, as Example 1 of the present invention, a lead-free solder alloy composed of 2.5% by weight of silver, 0.5% by weight of copper, and the remaining tin having the same composition as Comparative Example 1 was previously melted. Stir vigorously with a rotary stirrer with a stainless impeller installed in two stages while dripping a small amount into a solution at a liquid temperature of 260% consisting of 50% by weight of stearic acid and the remaining ester synthesis. However, after 30 minutes, the cleaned lead-free solder was taken out from the lowermost part of the treatment tank and subjected to an evaluation test.

[0016] Furthermore, as Comparative Example 2, a lead-free solder alloy comprising 2.5% by weight of silver, 0.5% by weight of copper, 0.1% by weight of nickel, 0.05% by weight of germanium, and the balance tin used.

On the other hand, in Example 2, 2.5% by weight of silver and 0.5% of copper having the same composition as Comparative Example 2 were used.

5 weight ^_0/0, nickel 0.0 1 wt%, germanium 0 0 5 wt%, allowed to advance melted lead-free solder alloy and the balance tin, palmitic acid 4 0% by weight and liquid balance consisting ester synthesis Purify from the bottom of the treatment tank after 60 minutes while stirring vigorously with a rotary stirrer with stainless steel impeller installed in two stages while dripping a small amount into the solution at a temperature of 255 ° C. The lead-free solder thus taken out was subjected to an evaluation test.

[0018] Furthermore, as Comparative Example 3, a lead-free solder alloy consisting of 8.0 wt% zinc, 0.05 wt% nickel, 1.0 wt% silver and the balance tin was used.

On the other hand, as Example 3, lead having the same composition as Comparative Example 3 above, consisting of 8.0% by weight of zinc, 0.05% by weight of nickel, 1.0% by weight of silver, and the balance tin Free solder alloy is melted in advance and palmitic acid is 40 weight. Stir vigorously with a rotary stirrer with stainless steel impeller installed in two stages while dripping a small amount into the solution at a liquid temperature of 2 80, consisting of / ₀ , stearic acid, 20% by weight and the remaining ester synthesis. However, after 20 minutes, the cleaned lead-free solder was taken out from the lowermost part of the treatment tank and subjected to an evaluation test.

[0020] The physical-mechanical evaluation method is based on the lead-free solder joints of Comparative Examples 1 to 3 and Examples 1 to 3. Using a stainless steel (SUS 304) forged mold (JIS No. 6), make a test piece with a distance between grades of L = 50mm, a diameter of 8κιιηφ, a length of the chucking section of L = 20mm, and a diameter of 1Οπιιιιφ, JISZ 4421 ) Tensile tester made by Shimadzu Corporation

(AG 100 type) was used and tested at room temperature 25, repeatedly at '3 (n = 3), at a load rate of 5 mm / min.

In addition, the chemical property evaluation method was repeated for each lead-free solder alloy of Comparative Examples 1 to 3 and Examples 1 to 3 according to a meniscograph solder wettability test method.

The zero crossing time was measured in 5). At that time, a pure copper wire of 0.4 mm ψ was used as the measurement pin.

[0021] The results are as shown in [Table 1] below. The cleaned lead-free solder alloy of the example has an especially large elongation of 1.5 times or more compared to the comparative example, and hardly breaks. This suggests. In addition, it is overwhelmingly easy to wet even with solder wettability, and has a low viscosity that is not found in conventional solder alloys. This is because, in the case of the lead-free solder alloy of the present invention (Example 1), the crystal grain boundary is small ([Fig. 1]). In the case of the lead-free solder alloy not subjected to the inventive treatment (Comparative Example 2), it was found that the length of the columnar crystal was long ([Fig. 2]). In addition, the tensile strength of the examples was not much different from that of the comparative example with respect to the magnitude of the elongation, and therefore it was confirmed that the toughness was strong and fatigue failure due to expansion and contraction in the long-term heat cycle test did not easily occur.

Brief Description of Drawings

FIG. 1 is an example of a cross-sectional crystal structure of a lead-free solder alloy (Example 2) according to the present invention.

[Fig. 2] This is an example of the internal cross-sectional crystal structure of a conventional lead-free solder alloy (Comparative Example 2).

[0023] [Table 1〗 Evaluation results of Examples and Comparative Examples

As described above, the technology of the present invention clearly has high elongation and toughness not found in conventional lead-free solder alloys, especially electronic devices that have small joint breakage risk due to repeated heat cycle fatigue of small area joints, and are therefore miniaturized. This is a technology that is industrially valuable as a lead-free solder alloy that can ensure long-term high-reliability solder joints.

Claims

The scope of the claims

[1] The printed circuit board is mainly composed of tin in a solution composed of oil containing 5 to 80% by weight of an organic fatty acid having 13 to 20 carbon atoms and having a temperature of 180 to 300 ° C. Molten lead free solder alloy with one or more metals of silver, copper, zinc, bismuth, antimony, nickel, germanium added as an ingredient in this lead free solder is immersed in the solder. Lead-free solder alloy for electronic parts from which oxides and impurities are removed.

[2] In the solution at a liquid temperature of 180 to 300, comprising 10 to 70% by weight of any one of palmitic acid and stearic acid as the organic fatty acid in claim 1 and the remaining ester synthetic oil, By immersing and stirring a molten lead-free solder alloy containing tin as a main component and adding at least one of silver, copper, zinc, bismuth, antimony, nickel, and germanium to the lead-free solder alloy. A lead-free solder alloy for electronic parts from which oxidants and impurities in the solder are removed.

[3] The main component of tin in a printed circuit board is a solution composed of an oil containing 5 to 80% by weight of an organic fatty acid having 13 to 20 carbon atoms at a liquid temperature of 180 to 300. Molten lead to which one or more metals of silver, copper, zinc, bismuth, antimony, nickel, and germanium are added. Semiconductor devices soldered using lead-free solder alloys for electronic components from which oxides and impurities have been removed.

[4] The organic fatty acid according to claim 3 is a solution having 10 to 70% by weight of any one of panolemitic acid and stearic acid, and a liquid temperature of 180 to 300 ° C. comprising the remaining ester synthetic oil. By immersing and stirring the molten lead-free solder alloy containing tin as a main component and adding at least one of silver, copper, zinc, bismuth, antimony, nickel, and germanium, the lead A semiconductor device soldered using a lead-free solder alloy for electronic parts from which oxides and impurities in the free solder have been removed.