JP5699897B2 - Pb-free solder alloy based on Zn - Google Patents

Description

  The present invention relates to a so-called Pb-free solder alloy containing no Pb, and more particularly to a Pb-free solder alloy mainly composed of Zn suitable for high temperatures.

  Starting with die bonding of power transistor elements, high temperature soldering is performed in soldering in the assembly process of various electronic components, and a solder alloy having a relatively high melting point of about 300 to 400 ° C. (hereinafter referred to as “high temperature”). Also referred to as “solder alloy for use”). As such a high temperature solder alloy, a Pb solder alloy represented by a Pb-5 mass% Sn alloy has been mainly used conventionally.

  However, in recent years, there has been a strong movement to limit the use of Pb due to consideration for environmental pollution. For example, Pb is a regulated substance in the RoHS directive. Corresponding to such a movement, in the field of assembling electronic components and the like, it is required to provide a Pb-free (lead-free) solder alloy, that is, a Pb-free solder alloy.

  As for a solder alloy for medium and low temperatures (about 140 to 230 ° C.), a Pb-free solder alloy containing Sn as a main component has already been put into practical use. For example, in Patent Document 1, Sn is the main component, Ag is 1.0 to 4.0 mass%, Cu is 2.0 mass% or less, Ni is 0.5 mass% or less, and P is 0.2 mass%. Pb-free solder alloys containing up to 10% are described. Patent Document 2 describes a Pb-free solder alloy containing 0.5 to 3.5% by mass of Ag, 0.5 to 2.0% by mass of Cu, and the balance being Sn.

  On the other hand, Bi-based solder alloys, Zn-based solder alloys, and the like have been developed by various organizations in order to realize Pb-free soldering alloys for high temperatures. For example, for a Bi-based solder alloy, Patent Document 3 discloses a Bi / Ag-based brazing material containing 30 to 80% by mass of Bi and having a melting temperature of 350 to 500 ° C. Patent Document 4 discloses a production method in which a binary eutectic alloy is added to a Bi-containing eutectic alloy and an additive element is further added to adjust the liquidus temperature and reduce variations. Yes.

  As for a Zn-based solder alloy, for example, Patent Document 5 describes a high-temperature Zn-based solder alloy based on a Zn—Al alloy in which Al is added to lower the melting point of Zn, and Ge or Mg is added thereto. ing. Patent Document 5 also describes that there is an effect of further lowering the melting point by further adding Sn or In.

  Specifically, in Patent Document 5, a Zn alloy containing 1 to 9% by mass of Al and 0.05 to 1% by mass of Ge, with the balance being Zn and inevitable impurities; 5 to 9% by mass of Al, Mg Zn alloy composed of 0.01 to 0.5% by mass with the balance being Zn and inevitable impurities; Al is 1 to 9% by mass, Ge is 0.05 to 1% by mass, Mg is 0.01 to 0.5% Zn alloy containing Zn and the balance consisting of Zn and unavoidable impurities; Al containing 1 to 9% by mass; Ge containing 0.05 to 1% by mass; Sn and / or In containing 0.1 to 25% by mass and the balance being Zn alloy composed of Zn and inevitable impurities; Al 1-9 mass%, Mg 0.01-0.5 mass%, Sn and / or In 0.1-25 mass%, the balance Zn and inevitable impurities Zn alloy comprising: Al 1-9 mass%, Ge 0.05-1 mass%, Mg 0.01-0.5 The amount%, Sn and / or In includes 0.1 to 25 wt%, and the balance are described Zn alloy consisting of Zn and unavoidable impurities.

Japanese Patent Laid-Open No. 1999-077366 JP-A-8-215880 JP 2002-160089 A JP 2006-167790 A Patent No. 3850135

  Thermoplastic resins and thermosetting resins are often used as materials for general electronic components and substrates, and therefore, the working temperature during bonding is preferably less than 400 ° C., more preferably 370 ° C. or less. However, since the Bi / Ag brazing material of Patent Document 3 has a liquidus temperature as high as 400 to 700 ° C., it is presumed that the working temperature at the time of joining is 400 to 700 ° C. or more, and the electronic parts and substrates to be joined It is considered that the temperature exceeds the allowable temperature. In addition, the method of Patent Document 4 becomes a quaternary or higher multi-component solder alloy only by adjusting the temperature of the liquidus, and the fragile mechanical characteristics of Bi are not effectively improved.

  Furthermore, the Zn-based solder alloy disclosed in Patent Document 5 often has insufficient wettability within the composition range. That is, Zn, which is the main component, has a strong reducibility, so that it is easily oxidized by itself, and as a result, the wettability is extremely deteriorated. Furthermore, since Al is more reducible than Zn, for example, when it is added by 1% by weight or more, wettability may be lowered.

  And it is considered that these oxidized Zn and Al cannot be reduced even if Ge or Sn is added in terms of thermodynamic equilibrium, and the wettability cannot be improved. However, when melting and solidifying in a very short time, such as soldering, the metal reaction is often a non-equilibrium reaction, and not all can be explained by equilibrium theory.

  In addition to the problem of wettability, the Zn-based solder alloy disclosed in Patent Document 5 has problems with workability and stress relaxation. That is, Zn and Al are eutectic alloys and are soft alloys with a certain degree of flexibility. However, since the bonding temperature is relatively high (eutectic temperature of Zn—Al alloy: 381 ° C.), after bonding, an electronic component mainly composed of Si or a substrate mainly composed of Cu is cooled to room temperature. The temperature difference becomes large and is greatly affected by the stress due to shrinkage. Therefore, even more excellent stress relaxation properties are required as compared with the solder for medium and low temperatures.

  Patent Document 5 discloses a Zn alloy containing 1 to 9% by mass of Al and 0.05 to 1% by mass of Ge, with the balance being Zn and inevitable impurities. Since Ge forms a eutectic alloy with Zn or Al, it seems that the Zn-Al-Ge alloy is softer than the Zn-Al alloy. However, since Ge is a brittle metal with poor ductility, even if Ge is added as a eutectic alloy, the effect is not great. In other words, the improvement in flexibility due to the eutectic alloy and the embrittlement due to the inclusion of brittle Ge are offset.

  Further, when Mg or the like is added to the Zn—Al alloy, an intermetallic compound is generated and becomes extremely hard, and there may be a case where good workability and stress relaxation properties cannot be obtained. For example, when Mg is contained in an amount of 5% by mass or more, it is practically impossible to process into a wire shape or a sheet shape that is difficult to process. As described above, although the Zn—Al-based alloy has a melting point in a preferable range of about 300 to 400 ° C., it is not always an optimum alloy from the viewpoint of wettability, stress relaxation, workability, and the like.

  As described above, high-temperature Pb-free solder alloys, especially Pb-free solder alloys mainly composed of Zn, should be made of a material that balances various characteristics such as wettability, stress relaxation, and workability. However, this problem has not been solved yet. As described above, in reality, a high-temperature solder alloy that can replace a Pb-based solder alloy typified by a conventional Pb-5 mass% Sn alloy has not yet been put into practical use.

  The present invention has been made in view of such circumstances, has a melting point of about 300 to 400 ° C. suitable for use in assembling electronic components, and has excellent wettability, stress relaxation properties and workability. An object of the present invention is to provide a high-temperature Zn-based solder alloy that does not contain copper.

In order to achieve the above object, the Pb-free solder alloy containing Zn as a main component provided by the present invention contains Al in an amount of 1.0 to 9.0% by mass and Ge in an amount of 0.001 to 0% by mass. containing less than .050 wt%, the Mg containing 4.0 wt% or less than 0.01 mass% (excluding 0.5 wt% or less), Ag is contained exceeding 4.0% by mass P is not contained in excess of 0.500% by mass, and the balance is made of Zn except for elements that are inevitably contained in the production.

Furthermore, Pb-free solder alloy mainly containing Zn of the present invention, further the A g may contain more than 0.1 mass%. Furthermore, the Pb-free solder alloy containing Zn as a main component of the present invention contains Al in an amount of 3.0% by mass or more and 7.0% by mass or less, Ge is contained in an amount of 0.003% by mass or more, and Ag is 3. It is preferable that it does not contain more than 0% by mass, and P does not contain more than 0.300% by mass.

  According to the present invention, in particular, it has excellent wettability, stress relaxation and workability, and at the same time can sufficiently withstand a reflow temperature of about 300 ° C. Therefore, in the assembly process of various electronic components such as die bonding of power transistor elements. A high-temperature Pb-free solder alloy suitable for soldering and excellent in bondability and reliability can be provided.

  The Pb-free solder alloy containing Zn as a main component according to the present invention does not contain Pb, contains Al and Ge, and the balance is made of Zn except for elements that are inevitably contained in production. Zn has a disadvantage that its melting point is 419 ° C., which is too high for 300 to 400 ° C., which is the bonding temperature of electronic components and the like. In order to cope with such defects of Zn, in the present invention, by incorporating Al, the melting point is lowered to a temperature that is easy to use as solder, and the workability and the like are improved to some extent. Further, by containing a small amount of Ge, it has good wettability and high stress relaxation properties that are particularly strongly required for high-temperature solder.

  By containing Al, an eutectic alloy with Zn can be formed to lower the melting point to about 400 ° C. or less, and at the same time, the effect of improving the workability by refining the crystal can be obtained. However, Zn-Al alloys used as high-temperature solders are required to have higher stress relaxation properties than medium- and low-temperature solders, but it is not always possible to have sufficient stress relaxation. Therefore, Ge is added to the Zn—Al alloy in order to improve stress relaxation and workability and to improve wettability.

  That is, by containing a small amount of Ge, Ge having a specific gravity smaller than that of Zn (Zn specific gravity: 7.1, Ge specific gravity: 5.4) is easily exposed on the surface of the molten solder after the solder is melted. As a result, Ge present in the vicinity of the surface is oxidized to suppress oxidation of Zn as a main component and improve wettability. In addition, since a very small amount of Ge present in the molten solder has a high melting point (Ge melting point: 938 ° C.), Ge is first precipitated at the time of solidification of the solder, and this serves as a nucleus to refine the crystal. This increases the flexibility of the solder alloy and improves the workability and stress relaxation properties.

  Further, the Pb-free solder alloy containing Zn as a main component further contains at least one of P, Mg, and Ag, so that the melting point, wettability, bonding strength, reliability, and the like are adjusted according to the purpose. It becomes possible to adjust appropriately. Each element added to the Zn-based solder alloy of the present invention will be described in detail below.

<Al>
Al is an essential element that plays an important role in the Pb-free solder alloy containing Zn as a main component of the present invention, and its content is 1.0 mass% or more and 9.0 mass% or less. When the Al content is less than 1.0% by mass, even if other elements are added, the melting point is not sufficiently lowered, so that the bondability is lowered. On the other hand, if the Al content exceeds 9.0% by mass, the liquidus temperature of the Zn-Al alloy becomes too high, and it does not melt sufficiently at the actual bonding temperature of electronic parts and the void ratio increases. Since it is too much or alloying of the joint portion becomes insufficient, joining that can withstand practical use cannot be performed.

  The Al content is more preferably 3.0% by mass or more and 7.0% by mass or less. Because, if the Al content is within this range, the eutectic composition of the Zn—Al binary alloy (Zn = 95 mass%, Al = 5 mass%) becomes close to the liquidus temperature, This is because the crystal is also refined to improve the workability and closer to the easy-to-use solder.

  The effect of including Al is to first adjust the melting point, that is, to lower the melting point to a solidus temperature of 381 ° C. as a Zn—Al alloy. Naturally, since it is a eutectic alloy, the metal becomes soft and the workability and stress relaxation properties are improved. However, since high temperature solder is required to have high stress relaxation properties, it is essential to contain Ge described below. Furthermore, when the Al content exceeds a certain level, the wettability decreases due to the increase in Al that is more easily oxidized than Zn. In order to improve the wettability, it is an indispensable condition to contain a small amount of Ge.

<Ge>
Ge is an essential element that plays an important role in improving workability and stress relaxation properties in addition to wettability in the Pb-free solder alloy of the present invention containing Zn as a main component. Ge has a higher melting point than Zn or Al (Zn melting point: 419 ° C., Al melting point: 660 ° C., Ge melting point: 938 ° C.), and when the solder alloy of the present invention is solidified in the cooling process after melting, The Ge having a high melting point first precipitates and forms crystals as nuclei, so that the solder alloy is microcrystallized.

  The Pb-free solder alloy of the present invention is essentially different from the Zn alloy containing Ge disclosed in Patent Document 5. This is because the Zn alloy of Patent Document 5 has a Ge content of 0.05 to 1% by mass, and the purpose of containing Ge is to lower the melting point or to form a Zn—Al—Ge ternary eutectic. This is because the processability is improved. On the other hand, in the present invention, the Ge content is extremely small as 0.001% by mass or more and less than 0.050% by mass as described later. When Ge is contained, the effect that can be obtained with such a small amount is large.

  Further, unlike Patent Document 5, the addition of Ge provides two effects of improving wettability and stress relaxation. More specifically, when a small amount of Ge is contained in a Zn—Al alloy, Ge having a small specific gravity floats during solder melting and is preferentially oxidized over Zn. In the thermodynamic equilibrium theory, Zn and Al are more likely to be oxidized. However, since Ge is present in a relatively large amount on the surface of the solder due to the specific gravity, the rate at which Ge is oxidized increases. Oxidation of the main component Zn is suppressed and wettability is improved.

  Further, Ge present in the molten solder is first precipitated at the time of solidification of the solder, and a crystal grows using this as a nucleus, so that the solder alloy is microcrystallized, and workability and stress relaxation are improved. By containing a small amount of Ge as described above, wettability and stress relaxation properties can be improved.

  Specifically, the Ge content is 0.001% by mass or more and less than 0.050% by mass, and more preferably 0.003% by mass or more and less than 0.050% by mass. Even if this amount is 0.050% by mass or more, there is an effect of adding Ge, but the effect of adding Ge decreases because the oxide layer of Ge becomes thick or crystal grains grow greatly. There are many cases. On the other hand, if it is less than 0.001% by mass, the content is too small and the effect does not appear.

<P>
P is an element that is added as appropriate when adjusting various characteristics of the Pb-free solder alloy containing Zn as a main component of the present invention in accordance with the purpose, and its effect is in improving wettability. The mechanism by which P improves wettability is as follows. P is highly reducing and suppresses oxidation of the solder alloy surface by being oxidized by itself. In particular, in the present invention, Zn that is easily oxidized is a main component, and Al that is more easily oxidized than Zn is contained. Therefore, when wettability is insufficient, the role of improving wettability by containing P is significant.

  Moreover, the effect of reducing the generation | occurrence | production of a void at the time of joining by containing P is also acquired. That is, as already described, since P is easily oxidized by itself, oxidation proceeds preferentially over Zn and Al, which are the main components of the solder alloy, at the time of joining. As a result, it is possible to prevent the solder mother phase from being oxidized and reduce the joint surface of the electronic component or the like to ensure wettability. At the time of joining, since solder and oxides on the surface of the joining surface disappear, gaps (voids) formed by the oxide film are less likely to be generated, and the joining property and reliability are improved. Note that P is vaporized when the solder alloy or the substrate is reduced to become an oxide, and flows into the atmospheric gas, and does not remain on the solder or the substrate. For this reason, there is no possibility that the residue of P adversely affects reliability and the like, and it can be said that this is an excellent element.

  When it contains P, it is preferable that the content is 0.500 mass% or less. This is because, as described above, P has a very strong reducibility, and if a trace amount is contained, an effect of improving wettability can be obtained. Even if the content exceeds 0.50% by mass, the effect of improving the wettability does not change much, and excessive inclusion may generate a large amount of P or P oxide gas and increase the void ratio. There is a possibility that a fragile phase is formed and segregates, and the solder joint is embrittled to reduce reliability. In particular, it has been confirmed that wire breakage is likely to be caused when processing into a wire shape or the like. If the content of P is not more than 0.300% by weight, it is more preferable since it exhibits a reducing effect and does not produce a brittle P compound.

<Mg>
Mg is an element added as appropriate when adjusting the various characteristics of the Pb-free solder alloy containing Zn as a main component of the present invention in accordance with the purpose. The effects obtained by containing Mg are as follows. Mg makes a eutectic alloy with Zn with two compositions, and their eutectic temperatures are 341 ° C. and 364 ° C. Thus, since it has two eutectic temperatures lower than those of the Zn—Al alloy, it is added when it is desired to further lower the melting point of the solder alloy.

  Furthermore, since Mg is more easily oxidized than Zn and Al, it has an effect of improving wettability with a small amount. However, if Mg is contained in a large amount, a strong oxide film is formed on the surface of the solder. Although the bonding conditions are various, the content is preferably 0.01% by mass or more and 4.0% by mass or less in consideration of the melting point lowering effect and the wettability improving effect described above. If the content is less than 0.01% by mass, the content of Mg is too small to sufficiently exhibit the effect of Mg. On the other hand, if it exceeds 4.0% by mass, the wettability is lowered or the liquidus temperature is excessively increased.

<Ag>
Ag, like Mg, is an element that is added as appropriate when adjusting various properties of the Pb-free solder alloy of the present invention containing Zn as a main component in accordance with the purpose. The Ag content is preferably 0.1% by mass or more and 4.0% by mass or less. If the Ag content is less than 0.1% by mass, the effect of improving wettability and bondability cannot be obtained. Conversely, if it exceeds 4.0% by mass, the melting point becomes too high, which is not preferable.

  That is, in the Zn—Ag alloy, the liquidus temperature increases monotonously as the Ag content increases on the Zn-rich side. Therefore, it is better that Ag is less in view of the melting point. On the other hand, from the standpoint of improving wettability, it is better that there is more Ag. In other words, as can be seen from the fact that Ag is used in the uppermost layer of the metallization of substrates and electronic parts, the wettability improvement effect is large, which is due to the property that Ag is not easily oxidized.

  Thus, although considering the balance of the melting point and wettability, Ag will be appropriately contained, but when Ag exceeds 4.0% by mass, the liquidus temperature becomes too high even if Al is contained, It becomes difficult to obtain good bonding. Therefore, the upper limit of the Ag content is 4.0% by mass. When a large amount of Mg or Ge having a high melting point is contained, the melting point of the solder alloy becomes high. Therefore, the Ag content is preferably 3.0% by mass or less. Further, if there is no problem in terms of characteristics even from the viewpoint of cost, it is preferable to reduce the Ag content.

  As raw materials, Zn, Al, Ge, P, Mg and Ag having a purity of 99.9% by mass or more were prepared. Large flakes and bulk-shaped raw materials were reduced to a size of 3 mm or less by cutting and crushing while paying attention to ensure that the alloy after melting did not vary in composition depending on the sampling location. Next, a predetermined amount of these raw materials was weighed and put into a graphite crucible for a high-frequency melting furnace.

  The crucible containing the raw materials was placed in a high-frequency melting furnace, and nitrogen was flowed at a flow rate of 0.7 liter / min or more per kg of the raw materials in order to suppress oxidation. In this state, the melting furnace was turned on to heat and melt the raw material. When the metal began to melt, it was stirred well with a mixing rod and mixed uniformly 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. A mold having the same shape as that generally used in the production of a solder mother alloy was used.

  Thus, the Zn type solder mother alloy of samples 1-23 was produced by changing the mixing ratio of each above-mentioned raw material. The composition of each solder mother alloy of the obtained samples 1 to 23 was analyzed using an ICP emission spectroscopic analyzer (SHIMAZU S-8100). The analysis results of the obtained solder composition are shown in Table 1 below.

  Next, each solder mother alloy of Samples 1 to 23 was processed into a sheet shape with a rolling mill as described below, and the workability of the Pb-free solder alloy containing Zn as a main component was evaluated. Moreover, about each solder alloy processed into the sheet form, the wettability (joinability) evaluation and the reliability evaluation by the heat cycle test were performed by the following method. The evaluation of solder wettability or bondability does not depend on the shape of the solder, and may be evaluated by the shape of a wire, a ball, a paste, or the like, but in this example, it was evaluated by the shape of a sheet.

<Evaluation of workability>
Each solder mother alloy (plate-shaped ingot having a thickness of 5 mm) of Samples 1 to 23 shown in Table 1 was rolled to a thickness of 0.05 mm using a rolling mill. At that time, rolling was performed while adjusting the feed speed of the ingot, and then it was cut into a width of 25 mm by slitting. After processing each sample into a sheet having a length of about 120 m in this way, the obtained sheet-like Zn-based solder alloy was observed, and the case where there were no scratches or cracks was “、”, and the sheet length was 50 m. The case where there were 1 to 2 hit cracks or cracks was indicated as “◯”, the case where 3 to 9 locations were present, “Δ”, and the case where there were 10 or more locations as “X”.

<Evaluation of wettability (bondability)>
Each solder alloy processed into a sheet shape as described above was evaluated using a wettability tester (device name: atmosphere control type wettability tester). In other words, a double cover is applied to the heater section of the wettability tester, and the heater set temperature is about 10 ° C. higher than the melting point of each sample while flowing nitrogen from four locations around the heater section at a flow rate of 12 liters / minute. Heated to set temperature. After the set heater temperature was stabilized, a Cu substrate (plate thickness: about 0.70 mm) was set in the heater section and heated for 25 seconds.

  Next, the solder alloy of each sample was placed on a Cu substrate and heated for 25 seconds. After the heating was completed, the Cu substrate was taken up from the heater part, and once installed in a place where the nitrogen atmosphere next to it was kept, it was cooled. After sufficiently cooling, it was taken out into the atmosphere and a joint portion was confirmed. The joint between the solder alloy of each sample and the Cu substrate was visually confirmed, and “X” indicates that the joint could not be joined, and “△” indicates that the joint was joined but the wetting spread was poor (the solder did not spread and swelled). ”, The case where bonding was possible and the sample spread and was wet was evaluated as“ ◯ ”, and the case where the solder was thinly spread and wet was evaluated as“ ◎ ”.

<Heat cycle test>
A heat cycle test was conducted to evaluate the reliability of solder joints. In this test, two samples each having a solder alloy bonded to the Cu substrate in the above-described wettability evaluation (samples having a wettability evaluation of “◎”, “◯”, or “Δ”) were used. went. That is, for one of the two Cu substrates to which the solder alloy of each sample is bonded, 300 cycles are required for confirming the heat cycle test in which one cycle includes cooling at −40 ° C. and heating at + 150 ° C. The same heat cycle test was repeated up to 500 cycles for the remaining one.

  Then, about each sample which performed the heat cycle test of 300 cycles and 500 cycles, Cu board | substrate with which the solder alloy was joined was embedded in resin, cross-sectional grinding | polishing was performed, and SEM (device name: HITACHI S-4800) performed the joining surface. Observations were made. As a result of this observation, the case where the joint surface peeled or the solder cracked was indicated as “X”, and the case where there was no such defect and the same joint surface as in the initial state was indicated as “◯”. . The evaluation results are shown in Table 2 below.

  As can be seen from Tables 1 and 2 above, the solder alloys of Samples 1 to 16 that satisfy the requirements of the present invention exhibit good characteristics in all evaluation items. That is, even when processed into a sheet shape, no scratches or cracks were generated, and wettability and reliability were very good. It is considered that a good result in workability is due to the fact that since a small amount of Ge is added to the Zn—Al alloy, the flexibility of the solder alloy is increased and no cracks or the like are generated even when rolled.

  Furthermore, even in the heat cycle test, cracks and the like did not occur up to 500 times, and good bondability and reliability were shown. This is because the wettability is improved by containing a small amount of Ge, and the bond strength and the like are increased. This is considered to be caused by this. Naturally, the increased stress relaxation due to the refinement effect of Ge is considered to contribute to the improvement of reliability.

  On the other hand, the solder alloys of Samples 17 to 23 that do not satisfy the requirements of the present invention are not preferable except for Sample 19 because the content of any one of Al, Ge, P, Mg, and Ag is not appropriate. Evaluation results were obtained. Specifically, in the evaluation of workability, scratches and cracks occurred in all samples except the sample 19, and four samples out of the six samples except the sample 19 were bad in terms of wettability. In the test, defects occurred up to 300 times in all samples except sample 19 (excluding samples 17, 18, 21, and 23 that could not be joined).

  Regarding sample 19, although it was somewhat inferior as compared with samples 1 to 16 that satisfy the requirements of the present invention, a result of “good (◯)” was obtained in all evaluations. The reason why the sample 19 was inferior to the samples 1 to 16 is that the Ge content is large, so that the oxide of Ge is increased on the solder surface or the crystal refinement obtained when a small amount of Ge is added. It is mentioned that the effect of was small.

Claims (3)

The Al containing 1.0 wt% to 9.0 wt% or less, a Ge containing less than 0.001 mass% or more 0.050 mass%, the Mg containing less 4.0 wt% 0.01 wt% (However, excluding 0.5% by mass or less) , Ag does not contain more than 4.0% by mass, P does not contain more than 0.50 % by mass, and the balance is manufactured. A Pb-free solder alloy containing Zn as a main component, characterized by being composed of Zn excluding elements inevitably contained. 2. The Pb-free solder alloy containing Zn as a main component according to claim 1, wherein Ag is contained in an amount of 0.1% by mass or more.   Al is contained in an amount of 3.0% by mass or more and 7.0% by mass or less, Ge is contained in an amount of 0.003% by mass or more, Ag is not contained more than 3.0% by mass, and P is 0.30% by mass. The Pb-free solder alloy containing Zn as a main component according to claim 1 or 2, wherein the Pb-free solder alloy is not contained in excess of%.