JP2006021205A - Lead-free solder alloy - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lead-free solder alloy capable of effectively preventing corrosion of a solder flow tank, and realizing lead-free state in a packaging process without additional equipment investment. <P>SOLUTION: The lead-free solder alloy has a composition consisting of, by weight, 0.1-3% Cu, 0.001-1% Ni, 0.001-0.05% Fe and the balance Sn, or has a composition consisting of, by weight, 0.1-3% Cu, 0.001-1% Ag, 0.001-0.05% Fe, and the balance Sn. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a lead-free solder alloy.

  Electronic components mounted on a circuit board are generally fixed to the circuit board by soldering. In addition, solder alloys having various compositions are used as solder alloys used for soldering in consideration of thermal effects on electronic components and circuit boards, workability, bonding reliability, and the like.

Conventionally used Sn-Pb eutectic solder alloys have the advantages of a low melting point and good solderability, but in recent years, the use of lead, a highly toxic heavy metal, has been used. In order to avoid this, a solder alloy called a lead-free solder alloy has been developed. As the lead-free solder alloy, Sn-Cu-Ag-based ones are mainstream, but Sn-Ag-based, Sn-Zn-based, Sn-Bi-based solder alloys are also known. Patent Document 1 below discloses a solder alloy obtained by adding Ni to a Sn-Cu-based lead-free solder alloy.
JP 2000-197988 A

  By the way, as a soldering method in electronic component mounting, a flow soldering method using a molten solder bath, a reflow method using a solder paste or a foam solder, a method combining these, and the like are known. Of these, the flow soldering method is a method of soldering by applying a flux to a circuit board on which electronic components are mounted and then immersing the board in a flow tank containing molten solder. There is a tendency to employ a method in which a jet of molten solder is formed in a tank and soldered by bringing the top of the molten solder into contact with a circuit board.

  Even in such a flow soldering method, a lead-free solder alloy can be used. However, if the lead-free solder alloy is stored and used in a solder flow bath that has been used for a conventional Sn-Pb solder alloy, It has been found that the problem arises that the wall of the solder flow bath is eroded by the solder alloy and the molten solder leaks.

  The present invention has been made in view of the above-mentioned problems of the prior art, and can effectively prevent erosion of the solder flow bath and can realize lead-free mounting processes without any new equipment investment. It aims to provide a free solder alloy.

  In order to solve the above problems, the present invention contains Cu: 0.1 to 3% by weight, Ni: 0.001 to 1% by weight, Fe: 0.001 to 0.05% by weight, with the balance being Sn. A lead-free solder alloy is provided.

  The lead-free solder alloy according to the present invention contains Cu: 0.1 to 3% by weight, Ag: 0.001 to 1% by weight, Fe: 0.001 to 0.05% by weight, with the balance being Sn. The structure characterized by comprising can also be applied.

  As described above, the lead-free solder alloy of the present invention has a great feature in that it contains 0.001 to 0.05% by weight of Fe in its composition. By adopting the above composition, the lead-free solder alloy of the present invention can reduce the erosion of the solder flow tank when stored in a molten state in the solder flow tank used in the flow soldering method, and can flow stably over a long period of time. The soldering method can be implemented.

  When the content of Fe is less than 0.001% by weight, the protective effect of the solder flow bath due to the addition of Fe can hardly be obtained. Moreover, when it adds exceeding 0.05 weight%, liquidus temperature will rise, the fluidity | liquidity of a solder will be impaired, and it will become the tendency for solderability to fall.

  In the lead-free solder alloy of the present invention, the Fe content is preferably 0.01 to 0.03% by weight, and more preferably 0.02 to 0.03% by weight. If the Fe content is within such a range, erosion of the solder flow tank can be more effectively prevented, and the flow tank can be operated stably over a long period of time.

Here, metal elements other than Fe added to the lead-free solder alloy according to the present invention will be described.
Cu has an effect of refining the crystal of the solidified structure of the solder alloy, and has an effect of improving mechanical properties such as improvement of mechanical strength. When the Cu content is less than 0.1% by weight, the effect of refining the crystal structure is insufficient. On the other hand, adding over 3% by weight is not preferable because the above effect is hardly affected and the liquidus temperature rises.
A more preferable range of the Cu content is 0.2 to 0.8% by weight, desirably 0.3 to 0.7% by weight. By setting it as these ranges, the improvement effect of sufficient mechanical characteristics can be acquired, suppressing the raise of liquidus temperature.

Ni has the effect of refining the crystal of the solidified structure of the solder alloy, and has the effect of improving mechanical properties such as improvement of mechanical strength. When the Ni content is less than 0.001% by weight, the above effects are not sufficient. On the other hand, if it exceeds 1% by weight, dross due to oxidation tends to occur and, as a result, the mechanical properties are lowered, which is not preferable.
A preferable range of the Ni content is 0.01 to 0.5% by weight, and desirably 0.05 to 0.2% by weight.

  Ag has the effect of improving the corrosion resistance of the solder alloy in addition to the effect of improving the mechanical properties such as improvement of the mechanical strength of the solder alloy. When the Ag content is less than 0.001% by weight, these effects can hardly be obtained. On the other hand, when the Ag content exceeds 1% by weight, the liquidus temperature rises and the soldering temperature increases, which is not preferable. The preferable range of the Ag content is 0.1 to 0.5% by weight, desirably 0.2 to 0.4% by weight.

  Furthermore, when the lead-free solder alloy of the present invention contains Ni, it may be a solder alloy added with 1% by weight or less of one or more metal elements selected from Co, Mn, Cr, and Mo, and does not contain Ni. If it is, a solder alloy to which 1% by weight or less of one or more metal elements selected from Ni, Co, Mn, Cr, and Mo are added may be used.

  These additive metal elements may be added according to the material of the solder flow bath used for flow soldering, and by adding, (Ni,) Co, Mn, Cr, in the molten solder stored in the solder flow bath. The concentration gradient between the content of Mo and the content of the same element in the constituent material of the solder flow bath is relaxed, and these metal elements contained in the solder flow bath are effectively prevented from eluting from the wall surface. be able to. Thereby, it is possible to effectively prevent the solder flow tank from being eroded, and it is possible to stably perform the flow soldering over a long period of time.

Next, the mounting method of the present invention is a method of mounting an element on an electronic device, wherein solder bonding is performed using a solder flow bath storing the lead-free solder alloy of the present invention described above. And
According to this mounting method, a stable mounting structure with good solderability can be easily formed.

Next, the semiconductor device of the present invention is characterized by having a mounting structure using the lead-free solder alloy of the present invention described above.
Next, the circuit board of the present invention is characterized by having a mounting structure using the lead-free solder alloy of the present invention described above.
Next, an electronic apparatus according to the present invention includes the above-described semiconductor device or circuit board according to the present invention.
If a mounting structure using the lead-free solder alloy according to the present invention is provided, a semiconductor device, a circuit board, and an electronic device having a mounting structure with good solderability and stable reliability can be realized. In addition, these are adapted to environmental problems related to lead components.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram showing a soldering apparatus used in the flow soldering method. This soldering device is mainly composed of a solder flow tank 20 and a control device 30. The solder flow tank 20 is formed in a substantially rectangular parallelepiped shape with the upper portion in the figure opened, and accommodates the molten solder 10 therein. For this solder flow tank 20, a conventional flow tank used as a flow tank for Sn-Pb solder alloy can be applied as it is, for example, made of stainless steel such as SUS304, SUS316, or iron casting. Can be used.

  The molten solder 10 is stored up to a position where the liquid level reaches the vicinity of the upper end of the solder flow tank 20, and a jet means 21 and a heating means 22 are disposed at a position where the molten solder 10 is immersed in the molten solder 10. The jet means 21 forms jets 11 and 12 on the molten solder 10 held in a molten state by the heating means 22.

  The jet means 21 may be a combination of a nozzle that ejects the molten solder 10 and a pump, or a device that stirs the molten solder 10 with a wing-shaped member. On the other hand, an electric heater or the like can be used as the heating means 22, and a method of heating the molten solder 10 from the outside of the solder flow tank 20 may be used. These jet means 21 and heating means 22 are connected to a control device 30, and the control device 30 controls the heating temperature, the molten solder ejection speed, the ejection timing, and the like.

  The molten solder 10 is a lead-free solder alloy according to the present invention, and contains Cu: 0.1 to 3 wt%, Ni: 0.001 to 1 wt%, and Fe: 0.001 to 0.05 wt%. Or a solder alloy containing the remainder of Sn, or Cu: 0.1 to 3 wt%, Ag: 0.001 to 1 wt%, Fe: 0.001 to 0.05 wt%, and the balance of Sn A solder alloy is used.

  On the circuit board 60, electronic components 61, 61 are arranged on the upper surface side in the drawing, and the terminal leads 62 extending from the electronic component 61 are connected to the circuit board through through holes provided in the circuit board 60. A tip portion projects from the back surface side (lower surface side in the drawing) of 60. The through hole into which the terminal lead 62 is inserted is formed in a land (conductive terminal) (not shown) formed on the circuit board 60, and this land and the terminal lead 62 are soldered. It has become. The circuit board 60 is supported by conveyance means (not shown) and is conveyed in the right direction (arrow F direction) in the figure.

  In order to perform soldering using the soldering apparatus having the above configuration, the circuit board 60 on which the electronic component 61 is placed is conveyed in the direction of arrow F. At this time, in the solder flow tank 20, the solder alloy is stored in a molten state at a predetermined temperature, and is jetted upward by the jet means 21 to form jet portions 11 and 12. Then, the circuit board 60 is conveyed in the direction of arrow F while being held at a predetermined distance from the liquid surface of the molten solder 10, thereby bringing the back surface of the circuit board 60 into contact with the jet portions 11 and 12 of the molten solder 10. The lands formed on the substrate 60 and the terminal leads 62 are soldered. Thereby, the electronic component 61 is mounted on the circuit board 60.

  And in the said soldering apparatus, by using the lead-free solder alloy which concerns on this invention for the molten solder 10, erosion of the solder flow tank 20 is prevented favorably, and it is the flow soldering method stably over a long period of time. It is possible to implement.

  The problem of erosion of the solder flow bath described above is remarkable in the solder flow bath storing the melt of lead-free solder alloy, and the cause of the erosion phenomenon is not clear, but the conventional Sn-Pb system It is considered that the Sn content is significantly higher than that of the solder alloy, and that the temperature of the flow tank is increased due to the high melting temperature. However, if the composition of the alloy is greatly changed, there is a possibility that the solderability and the bonding strength of soldering may be reduced. Also, a significant change in the alloy composition is necessary to lower the melting temperature.

  Therefore, the present inventor focused on the diffusion phenomenon of elements at the interface between the solder flow bath and the molten solder, and examined a lead-free solder alloy that can prevent erosion of the solder flow bath without damaging the properties such as solderability. . That is, when the erosion of the solder flow tank is regarded as a phenomenon in which the components of the solder flow tank are dissolved in the molten solder, the dissolution rate formula (the following formula A) can be applied. From Formula A, it is considered that the concentration gradient (Cs-C) of the solute (in this case, the component of the solder flow bath) in the solder flow bath and the molten solder serves as a driving force for dissolution and causes erosion of the solder flow bath. . Therefore, the present inventor has adopted the above composition in order to alleviate this concentration gradient (Cs-C).

dC / dt = K (A / V) (Cs−C) (A)
Where, in Formula A, C: solute concentration in liquid after reaction time t (s), K: constant, A: interfacial area between solid and liquid, V: volume of liquid, Cs: saturated solute concentration in liquid, It is.

  That is, in the lead-free solder alloy of the present invention, as described above, 0.001 to 0.05% by weight of Fe is contained in the solder alloy. A conventional solder flow bath using a Sn-Pb solder alloy is generally made of stainless steel, iron casting or the like, and a material mainly composed of Fe is used. Therefore, in the present invention, Fe in the above range is added to the solder alloy in order to suppress the elution of the Fe component, which is considered to be the most prominent from the solder flow tank. In this solder composition, the Fe content is preferably 0.01 to 0.03% by weight, and more preferably 0.02 to 0.03% by weight.

  In addition, the present inventor has evaluated the degree of erosion of the solder flow tank and verified the effect of the present invention for the lead-free solder alloy having such a composition. Specifically, test pieces made of stainless steel (SUS304) made of the same material as the solder flow bath were prepared and immersed in solder alloys having various compositions, and the degree of erosion (weight reduction) of the test pieces was compared. The composition of the solder alloy subjected to the test is shown in Table 1 below.

  As a result of the test by the present inventor, the samples of Examples 1 to 6 shown in Table 1 have a weight reduction of the test piece 1/2 compared to both the samples of Comparative Example 1 and Comparative Example 2. It was confirmed that the erosion of the solder flow bath can be effectively prevented by adopting the composition according to the present invention to be 10 or less. Further, in the samples of Example 2, Example 3, Example 5, and Example 6 in which Cr and Ni contained in SUS304 which is a constituent material of the solder flow tank 20 are further added, these metal elements are not added. It was confirmed that the erosion was reduced as compared with the samples of Example 1 and Example 4.

The schematic block diagram of the soldering apparatus which concerns on embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Molten solder (lead-free solder alloy), 11, 12 Jet part, 20 Solder flow tank, 21 Jet means, 22 Heating means, 30 Control apparatus, 60 Circuit board, 61 Electronic component, 62 Terminal lead

Claims (7)

  A lead-free solder alloy containing Cu: 0.1 to 3% by weight, Ni: 0.001 to 1% by weight, Fe: 0.001 to 0.05% by weight, with the balance being Sn.   A lead-free solder alloy comprising Cu: 0.1 to 3% by weight, Ag: 0.001 to 1% by weight, Fe: 0.001 to 0.05% by weight, with the balance being Sn.   The lead-free solder alloy according to claim 1, wherein the lead-free solder alloy contains 1% by weight or less of one or more metal elements selected from Co, Mn, Cr, and Mo.   The lead-free solder alloy according to claim 2, comprising 1% by weight or less of one or more metal elements selected from Ni, Co, Mn, Cr, and Mo.   The lead-free solder alloy according to any one of claims 1 to 4, wherein the Fe content is 0.01 to 0.03% by weight.   The lead-free solder alloy according to claim 5, wherein the Fe content is 0.02 to 0.03% by weight.   The lead-free solder alloy according to any one of claims 3 to 6, wherein the content of the metal element is 0.8% by weight or less.

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