JP2012228729A - Pb FREE SOLDER ALLOY MAKING Zn PRINCIPAL INGREDIENT AND METHOD OF MANUFACTURING THE SAME - Google Patents

Abstract

PROBLEM TO BE SOLVED: To have a melting point of about 300 ° C. to 400 ° C. suitable for use in assembling electronic parts, etc., excellent wettability, bondability, workability and reliability, does not contain Pb, and contains Zn as a main component A high temperature solder alloy is provided.
SOLUTION: Al is contained in an amount of 0.01% by mass to 9.0% by mass, Ge is 0.01% by mass to 8.0% by mass, Mg is 0.01% by mass to 5.0% by mass. %, Ag is 0.1 mass% or more and 4.0 mass% or less, P is in the range of 0.5 mass% or less, and contains at least one of Ge, Mg, Ag, and P, and the balance Zn And a Zn-based Pb-free solder alloy characterized in that the oxide layer on the alloy surface made of unavoidable impurities is 120 nm or less and the surface roughness Ra is 0.60 μm or less.
[Selection figure] None

Description

  The present invention relates to a solder alloy mainly composed of Zn not containing Pb and a method for producing the same.

In soldering used in the assembly process of various electronic components including die bonding of power transistor elements, high temperature soldering is performed, and a solder alloy having a relatively high melting point of about 300 ° C. (high temperature solder alloy) is obtained. It is used. As such a high-temperature solder alloy, a Pb-based 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 restrict the use of Pb due to consideration for environmental pollution, and it has become a regulated substance in the RoHS directive, for example. Therefore, in the field of assembling electronic parts and the like, a Pb-free (lead-free) solder alloy, that is, a Pb-free solder alloy is required.

As for a solder alloy for medium and low temperatures (about 140 ° C. 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% by mass, Cu is 2.0% by mass or less, Ni is 0.5% by mass or less, and P is 0.2% by mass. The following Pb-free solder alloys are described. Patent Document 2 describes a Pb-free solder alloy containing 0.5 to 3.5% by mass of Ag and 0.5 to 2.0% by mass of Cu, with the balance being Sn.

On the other hand, various developments have been made for solder alloys for high temperatures in order to realize Pb-free.
However, a high temperature solder alloy that can replace a Pb solder alloy represented by a conventional Pb-5 mass% Sn alloy has not yet been proposed.
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. However, since the liquidus temperature of this Bi / Ag brazing material is as high as 400 to 700 ° C., it is presumed that the working temperature at the time of joining is also 400 to 700 ° C. or higher. The working temperature of thermoplastic resins and thermosetting resins that are widely used as materials for general electronic components and substrates is less than 400 ° C., preferably 370 ° C. or less. The temperature exceeds that the component or board can withstand.

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.
However, in this method, a quaternary or higher multi-component solder is obtained only by adjusting the temperature of the liquidus, and Bi's brittle mechanical properties are not effectively improved.

Similarly, no practical high-temperature Pb-free solder alloy is provided for Zn-based solder alloys. For example, Patent Document 5 describes a high-temperature Zn-based solder alloy based on a Zn—Al alloy whose melting point has been lowered by adding Al to Zn, to which Ge or Mg is added, and Sn or In. It is described that there is an effect of further lowering the melting point by the addition of.
However, since Zn solder alloys are highly reducible by themselves and oxidize themselves, a major problem is that the wettability is very poor.

  Specifically, Patent Document 5 includes a Zn alloy containing 1 to 9% by mass of Al, 0.05 to 1% by mass of Ge, the balance being Zn and inevitable impurities, 5 to 9% by mass of Al, and Mg. Zn alloy containing 0.01 to 0.5% by mass, the balance being Zn and inevitable impurities, Al 1 to 9% by mass, Ge 0.05 to 1% by mass, Mg 0.01 to 0.5% A Zn alloy composed of Zn and unavoidable impurities, and 1 to 9% by mass of Al, 0.05 to 1% by mass of Ge, 0.1 to 25% by mass of Sn and / or In, and the balance Zn alloy consisting of Zn and inevitable impurities, Al 1-9 mass%, Mg 0.01-0.5 mass%, In and / or n 0.1-25 mass%, the balance is Zn and Zn alloy composed of inevitable impurities, Al 1-9% by mass, Ge 0.05-1% by mass, g 0.01 to 0.5 mass%, Sn and / or In includes 0.1 to 25 wt%, Zn alloy and the balance being Zn and unavoidable impurities is described.

However, the Zn-based solder alloy described here cannot be said to have sufficient workability of the alloy within the range of the composition, and it is often difficult to process the wire that requires the highest workability. Moreover, as described above, Zn is easily oxidized and has poor wettability, so that it cannot be easily joined to Cu, Ni, or the like.
For example, when it is joined to a Cu substrate or a Cu substrate having Ni as the uppermost layer, it is difficult to continue to use in a severe environment such as in-vehicle use. Even if Ge or Sn is added, oxidized Zn cannot be reduced, and wettability cannot be improved.

  In Patent Document 6, the main component is a metal whose oxide is more easily reduced than the oxide film after the oxide film on the surface of the material containing Zn as a main component is removed or in the absence of the oxide film. It describes a solder material mainly composed of Zn and having a coating layer on the surface. That is, it has been shown that by providing a coating metal layer on a material mainly composed of Zn in the absence of an oxide film, a solder material having high heat resistance and capable of bonding a bonded body densely is obtained.

  However, Cu specifically mentioned as a coating material is generally considered to have poor wettability. That is, in most cases, the substrate to which electronic parts are joined is Cu, but when trying to join electronic parts such as Si chips and SiC chips to Cu, wettability and bondability may not be sufficient. In order to improve wettability and the like, it is a common practice to provide a metallized layer of Ag or Au.

  In other words, in order to compensate for the wettability of Cu, etc., the number of manufacturing steps has been increased on the Cu substrate, and the fact is that an expensive metallization layer of Ag or Au is provided. Is inferior in wettability. Therefore, it is difficult to think that the wettability or bondability of Zn-based solder having poor wettability or bondability is improved when a coating layer such as Cu is provided on the solder containing Zn as a main component. Is also difficult. In addition, an oxide film removing process and a coating forming process are added, and the manufacturing process becomes long, resulting in poor productivity and a large cost increase.

  As described above, Pb-free solder alloys for high temperatures, particularly Pb-free solder alloys mainly composed of Zn, have many problems to be improved including wettability, and are not yet put into practical use. It is.

Japanese Patent Laid-Open No. 1999-077366 Japanese Patent Laid-Open No. 08-215880 JP 2002-160089 A JP 2006-167790 A Japanese Patent No. 3850135 JP 2009-125753 A

  The present invention has a melting point of about 300 ° C. to 400 ° C. suitable for use in assembling electronic components, etc., is excellent in wettability, bondability, workability, and reliability, does not contain Pb, and contains Zn as a main component. An object of the present invention is to provide a high temperature solder alloy.

  A first invention of the present invention is a Pb-free solder alloy containing Zn as a main component, characterized in that the oxide layer on the surface of the solder alloy is 120 nm or less and the surface roughness Ra is 0.60 μm or less. .

  According to a second aspect of the present invention, the solder alloy according to the first aspect of the invention includes Al in an amount of 0.01% by mass to 9.0% by mass, Ge is 0.01% by mass to 8.0% by mass, Mg, 0.01 mass% or more, 5.0 mass% or less, Ag in the range of 0.1 mass% or more and 4.0 mass% or less, P in the range of 0.5 mass% or less, Ge, Mg, Ag, It is a Pb-free solder alloy containing Zn as a main component, containing any one or more of P, and remaining Zn and inevitable impurities.

  According to a third aspect of the present invention, the solder alloy according to the first aspect of the present invention includes Al in a range of 3.0% by mass to 7.0% by mass, and Ge in a range of 0.1% by mass to 3.0% by mass. The main component is Zn, characterized in that it contains at least one of Ge and Mg in the range of 0.01% by mass or more and 3.0% by mass or less of Mg, and consists of the balance Zn and inevitable impurities. Pb-free solder alloy.

  A fourth invention of the present invention is a Pb containing Zn as a main component, characterized in that the surface of the solder alloy is polished so that the thickness of the oxide layer on the surface is 120 nm or less and the surface roughness Ra is 0.60 μm or less. This is a method for producing a free solder alloy.

  According to a fifth aspect of the present invention, there is provided a method for producing a Pb-free solder alloy containing Zn as a main component, characterized in that the surface of the solder alloy is subjected to acid cleaning so that the thickness of the oxide layer on the surface is 120 nm or less.

  A sixth aspect of the present invention is characterized in that a rolling roll having a surface roughness Ra of 0.3 μm or less is used to roll a solder alloy so that the surface roughness Ra of the solder alloy is 0.60 μm or less. This is a method for producing a Pb-free solder alloy containing Zn as a main component.

  According to a seventh aspect of the present invention, the solder alloy according to the fourth to sixth aspects includes 0.01 mass% or more and 9.0 mass% or less of Al, 0.01 mass% or more of Ge, and 8.0 mass%. Mass% or less, Mg 0.01 mass% or more, 5.0 mass% or less, Ag 0.1 mass% or more and 4.0 mass% or less, P in a range of 0.5 mass% or less, Ge, This is a method for producing a Pb-free solder alloy containing Zn as a main component, which contains at least one of Mg, Ag, and P, and consists of the balance Zn and inevitable impurities.

  According to an eighth aspect of the present invention, the solder alloy according to the fourth to sixth aspects of the invention contains Al in an amount of 3.0% by mass or more and 7.0% by mass or less, and Ge in an amount of 0.1% by mass or more and 3.0% by mass. Mainly composed of Zn, characterized in that it contains at least one of Ge and Mg in a range of mass% or less, Mg in a range of 0.01 mass% or more and 3.0 mass% or less, and consists of the balance Zn and inevitable impurities. This is a method for producing a Pb-free solder alloy as a component.

  The present invention is excellent in wettability, bondability, workability, reliability, etc., and can sufficiently withstand a reflow temperature of about 300 ° C. 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 can be provided.

It is explanatory drawing which defines the thickness of the oxide layer from the solder surface.

The Pb-free solder alloy containing Zn as a main component according to the present invention does not contain Pb, contains Zn as a main component, has an oxide layer of 120 nm or less, and a surface roughness Ra of 0.60 μm or less.
Zn is easily oxidized, and wettability and bondability are greatly reduced by the oxide (oxide layer) formed on the solder surface when bonding electronic components and the like. For this reason, the solder alloy of the present invention reduces the solder surface area by thinning the oxide layer on the solder surface and reducing the surface roughness, thereby reducing the amount of oxide per unit amount of solder (for example, unit weight, unit volume). It is improved so that the wettability and bondability are remarkably excellent by reducing the amount.

Further, the solder composition preferably contains Al, may contain at least one of Ge, Mg, Ag, and P, and is composed of the balance Zn and inevitable impurities. In particular, by using a Zn-Al eutectic composition, good workability and stress relaxation properties can be obtained, and by containing at least one of Ge, Mg, Ag, and P, the solder material such as wettability can be obtained. Various required characteristics can be adjusted.
Hereinafter, the oxide layer, surface roughness, roll surface roughness, solder composition and the like of the solder alloy in the present invention will be described in detail.

<Oxide layer on solder alloy surface>
In the present invention, it is an essential condition that the oxide layer on the surface of the solder alloy is 120 nm or less. Zn has many advantages such as having a melting point suitable as a main component of high-temperature solder at 419 ° C., having a thermal conductivity of about 3 times that of Pb, and being an inexpensive raw material. On the other hand, Zn is easily oxidized and has a defect that wettability is very poor. An important condition for overcoming this drawback is to thin the oxide layer.

In other words, the greatest cause of reducing wettability and bondability is an oxide on the surface of the solder alloy existing between the bonding surface of the substrate or electronic component and the solder matrix. Usually, metals are alloyed if they are selected appropriately.
For example, Cu or Ni, which may be provided on the uppermost layer of the substrate, and Zn are easily dissolved in a molten state. On the other hand, an oxide such as Zn is naturally solid at a junction temperature (for example, 350 ° C. to 450 ° C.) and does not react with a metal surface such as a substrate, and solder metal (Zn etc.) and a substrate surface metal (Cu etc.) Will not be able to contact and as a result will not be able to join. Conversely, when joining a Zn-based solder alloy to a substrate or the like, if there is no oxide on the surface of the solder alloy, the metals can be in contact with each other and joining is possible. From the above, it is one of the most important conditions for a Zn-based solder alloy that the oxide layer does not exist on the solder surface as much as possible.

  Although the oxide layer on the surface of the Zn-based solder alloy greatly reduces wettability and the like, it is difficult not to make it exist at all, and since it can be covered with bonding conditions and the like if it has a certain thickness, the thickness of the oxide layer is 120 nm or less. In the case of Zn-based solder, although it depends on the contained elements, if the oxide layer has a thickness of approximately 120 nm or less, the oxide layer is broken at the time of joining, and the molten solder metal comes out of the oxide layer and It can be in direct contact with the metal surface and can be joined.

  For example, when supplying a Zn-based solder wire to a Cu substrate, using a forming gas (mixed gas of hydrogen and nitrogen) and reducing the Cu substrate with hydrogen while supplying the wire at high speed, an oxide at the tip of the wire The layer is broken and reduced, and the molten solder can be directly supplied to the Cu surface substantially free of the oxide layer, so that bonding is possible. In this way, if the solder and the substrate are bonded without using the oxide layer, the bonding strength is high, and excellent reliability that can sufficiently withstand even in a harsh environment can be obtained.

<Surface roughness of solder alloy>
In the present invention, the essential condition as with the oxide layer of the solder alloy is the surface roughness of the solder alloy.
When the oxide layer of the solder alloy is set to 120 nm or less and the surface roughness Ra is set to 0.60 μm or less, the effects of the present invention are obtained.

  As already described, the major cause of the decrease in solder wettability and bondability is the oxide layer. More specifically, the amount of oxide present in the vicinity of the solder alloy surface. In other words, no matter how thin the oxide layer is, if the surface is rough and there are many irregularities, the surface area increases, so the amount of oxide present on the solder alloy surface (near the surface) increases, and the oxide layer is substantially thick. The same phenomenon occurs, and the wettability and bondability are greatly reduced.

When the surface roughness is large, that is, when the surface is rough, the amount of oxide is not only large, but worse, the contact area is small. For example, when an electronic component and a substrate are to be joined with a sheet-like solder, the substantial contact area greatly affects the wettability and the like.
Conversely, when the surface roughness of the solder sheet is very small, the bonding area of the electronic component becomes a substantial bonding area. On the other hand, if the surface roughness is extremely large, the solder and the electronic component will be in contact with each other at a point, resulting in a very small bonding area. In such a case, it is difficult to bond even if the oxide layer is thin. turn into.

  The fact that the surface roughness Ra of the solder alloy is preferably 0.60 μm or less is a result obtained experimentally and is qualitatively as already described. As a result of the experiment, when the surface roughness Ra exceeded 0.60 μm, it was difficult to join even if the oxide layer and the solder composition were adjusted. Furthermore, even if solder was supplied while reducing the substrate using a forming gas during bonding, bonding could not be performed. For this reason, the surface roughness Ra of the solder alloy is set to 0.60 μm or less.

<Manufacturing method>
The raw material may be dissolved by a resistance heating method, a reduction diffusion method, a high-frequency dissolution method, or the like. In particular, the high-frequency dissolution method is preferable because even a metal having a high melting point can be efficiently dissolved in a short time.
When processing the solder into a sheet, the rolling method may be cold rolling, warm rolling, hot rolling, press rolling, or the like. In particular, since Zn-based solder is harder than Pb-based solder or Sn-based solder, it is preferable to first perform thin rolling to a certain thickness by hot rolling, and then perform cold rolling.
By combining the two types of rolling in this manner, cracks and burrs are less likely to occur during rolling, improving the quality and increasing the production efficiency such as increasing the rolling speed.

The roll used for rolling preferably has a surface roughness Ra of 0.60 μm or less.
When performing two or more types of rolling such as hot rolling and cold rolling, the surface roughness Ra is preferably 0.60 μm or less only for the rolling roll used in the final rolling.
The reason why such a roll having a small surface roughness is used is, of course, to reduce the surface roughness of the product. If a roll having a surface roughness Ra exceeding 0.60 μm is used, even if the thickness of the oxide layer is controlled to 120 nm or less, the wettability and the bonding property will be very poor. is there.

In order to reduce the thickness of the oxide layer on the surface of the solder alloy and reduce the surface roughness, polishing or acid cleaning may be performed before, during or after the processing of the sheet or wire.
The acid cleaning is not limited to the type of acid, but it is preferable to use a weak acid. Cleaning may be performed using a strong acid, but depending on the conditions, the dissolution rate of the metal constituting the solder alloy into the acid solution is fast, the dissolution proceeds partially, and the surface roughness is likely to increase. . Therefore, it is preferable to use a weak acid and perform cleaning while adjusting the time longer depending on the situation.

There is no particular limitation on the polishing of the solder. For example, it may be polished by sandwiching a solder sheet or wire with abrasive paper with an appropriate force and winding it while pulling. Furthermore, polishing may be performed by reciprocating the polishing paper in a direction perpendicular to the solder polishing direction (winding direction).
By polishing the solder as described above, acid cleaning, rolling with a roll having a surface roughness Ra of 0.60 μm or less, and further combining these methods, the oxide layer is thin and the surface roughness is reduced. Manufacturing a small solder alloy.

<Solder composition>
The Pb-free solder alloy containing Zn as a main component provided by the present invention contains 0.01 mass% or more and 9.0 mass% or less of Al, 0.01 mass% or more and 8.0 mass% or less of Ge, Mg, 0.01 mass% or more, 5.0 mass% or less, Ag in the range of 0.1 mass% or more and 4.0 mass% or less, P in the range of 0.5 mass% or less, Ge, Mg, Ag, It contains any one or more of P and is composed of the remaining Zn and inevitable impurities.
Next, effects of these elements will be described.

<Zn>
Zn is a main component in the solder alloy of the present invention.
Zn has a melting point of 419 ° C. and is very suitable as a main component of high-temperature solder that is desired to be joined at 300 to 400 ° C. In addition, since the thermal conductivity is three times that of Pb, it has excellent heat dissipation and has a very favorable property as a bonding material. Although it has many advantages such as being inexpensive and available everywhere, Zn has a drawback that wettability is very bad due to easy oxidation.

  Therefore, in the present invention, wettability and the like are mainly improved by making the oxide layer thin and reducing the surface roughness, but some improvement can be achieved by adjusting the composition, and in addition, workability and the like are improved. In order to achieve this, it is necessary to contain other elements. The Zn content in the present invention depends on the elements to be contained in order to improve various properties required for solder, such as workability and stress relaxation properties.

<Al>
Al forms a eutectic alloy with Zn, and dramatically improves the workability and stress relaxation of Zn.
For this reason, it is preferable to make it contain in a solder and it is good to make content of Al into 0.01 mass% or more and 9.0 mass% or less.
If it is 0.01% by mass or less, the content is too small and the effect does not appear. If it exceeds 9.0% by mass, the liquidus temperature becomes about 420 ° C., which is slightly higher as the bonding temperature, and the proportion of brittle intermetallic compounds generated with other elements increases. In addition, since Al is more likely to be oxidized than Zn, a strong oxide layer may be formed thickly.
For the above reasons, the Al content is preferably 0.01% by mass or more and 9.0% by mass or less, and more preferably 3.0% by mass or more and 7.0% by mass or less. This is because Zn-5% by mass Al has a eutectic composition, and thus exhibits excellent workability and stress relaxation properties in the vicinity of the composition range.

<Ge>
When Ge is contained in the Pb-free solder alloy of the present invention, it exerts an effect of improving workability and contributes to improvement of wettability.
In other words, Ge is only slightly dissolved in Zn and Al, and when cooled and solidified after melting the solder, Ge in the molten solder first precipitates, which serves as a nucleus for the microcrystallization of the solder. Contributes and improves its workability. Further, Ge forms an eutectic alloy with Zn, and has the effect of improving the workability by refining the crystal particularly in the vicinity of the Zn—Ge eutectic composition (Zn-6 mass% Ge).

Such an effect of Ge not only improves workability but also improves wettability. Although the wettability is remarkably improved by containing Ge, the reason is considered as follows.
That is, since Ge has a specific gravity smaller than that of Zn (specific gravity: Ge = 5.4, Zn = 7.1), it is easy to be exposed on the solder surface during melting, and a reduction effect can be exhibited with a small amount.

The content of Ge having the effect of improving the wettability and workability is specifically 0.01% by mass or more and 8.0% by mass or less, more preferably 0.1% by mass or more, It is 3.0 mass% or less.
As already described, the role of Ge is to improve the wettability due to the property of being easily exposed on the surface of the molten solder and the reduction effect, or as the nucleus of solder microcrystallization. For this reason, there is often no need to add a large amount, and if the Ge content is less than 0.01% by mass, the content is too small to obtain these effects. On the other hand, if the content exceeds 8.0% by mass, the nucleus of Ge itself becomes large and does not crystallize, or the Ge oxide film becomes too thick. More preferably, they are 0.1 mass% or more and 3.0 mass% or less, and if it exists in this range, it will be easy to exhibit the outstanding effect of Ge.

<Mg>
Mg is an element that is appropriately contained when adjusting various characteristics of the Pb-free solder alloy mainly composed of Zn 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 Zn-Al alloy, it is contained when it is desired to further lower the melting point of the solder alloy.

Furthermore, since Mg is easier to oxidize than Zn and Al, it has the 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 solder surface, so care must be taken in the amount of addition.
Although there are various bonding conditions, the content is preferably 0.01% by mass or more and 5.0% by mass or less, more preferably 3.0% by mass or less in consideration of the melting point lowering effect and the wettability improving effect. is there. If the content is less than 0.01% by mass, the content of Mg is too small to fully exhibit the effect of Mg. On the other hand, if it exceeds 5.0% by mass, the wettability is lowered or the liquidus temperature becomes too high.

<Ag>
By adding Ag as necessary, the wettability and the bondability of the solder alloy can be further improved.
As can be seen from the fact that Ag is formed in the uppermost layer of an electronic component or a Cu substrate, the effect of improving wettability is great. In the present invention, addition of Ag is aimed at improving wettability. That is, Ag is difficult to oxidize and improves wettability by preventing oxidation of the solder surface. Therefore, when the wettability is insufficient, the wettability can be improved by adding Ag.

The Ag content is preferably 0.1% by mass or more and 4.0% by mass or less.
If the Ag content exceeds 4.0% by mass, brittle intermetallic compounds such as Zn and Al are produced, and the amount may exceed the allowable range. On the other hand, when the Ag content is less than 0.1% by mass, the expected effect may not be obtained.

<P>
By including P in the Pb-free solder of the present invention, the wettability can be remarkably improved. The reason is that P is highly reducible and reduces the bonding surface of the solder surface, electronic parts, etc., removes the oxide film, and facilitates the reaction between the metals in direct contact.

Furthermore, P has an effect of reducing the generation of voids during bonding.
That is, since P has strong reducibility and tends to oxidize itself, the oxidation proceeds preferentially over Bi, which is the main component of the solder, and the solder is reduced to remove the oxide film on the solder surface. And the reduction effect is similarly exhibited also in joint surfaces, such as an electronic component. As a result, since the metals are in direct contact with each other without interposing an oxide film, voids are hardly generated.

P exhibits the effect of improving the wettability even when added in a very small amount, because the reducibility is very strong. Therefore, the amount in the case of containing P is 0.001% by mass or more and 0.500% by mass or less. On the other hand, even if it is contained in a certain amount or more, the effect of improving wettability is saturated and does not change, and if it is contained excessively, P compound may be generated on the solder surface, or P may form a brittle phase and become brittle. . When P exceeds this upper limit value, the oxide covers the solder surface, and there is a risk that wettability is reduced.
Further, P generates an intermetallic compound with Zn. In general, intermetallic compounds are fragile because transition is difficult to progress, and the same can be said for P-Zn alloys. Therefore, when the content of P increases, the proportion of intermetallic compounds increases, and further segregation causes a decrease in reliability. The inventor has experimentally confirmed that it is likely to cause disconnection particularly when processing into a wire or the like.
Hereinafter, further description will be made using examples.

  As raw materials, Zn, Al, Ge, Mg, Ag and P 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 is weighed from these raw materials, put into a graphite crucible for a high-frequency melting furnace, the crucible containing each raw material is charged into the high-frequency melting furnace, and nitrogen gas is added to 1 kg of raw material to suppress oxidation. The flow rate was 0.7 liter / min or more. 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 solder mother alloy containing Zn of Samples 1 to 30 was produced by changing the mixing ratio of each raw material.
About each solder mother alloy of the obtained samples 1-30, the component composition is analyzed using an ICP emission spectroscopic analyzer ("SHIMAZU S-8100" manufactured by Shimadzu Corporation), and the obtained analysis results are used as the solder composition. As shown in Table 1.

Next, each solder mother alloy of Samples 1 to 30 shown in Table 1 was processed into a sheet shape with a rolling mill under the conditions shown in Table 2, and the workability of each sample was evaluated. Moreover, about each sample processed into the sheet form, evaluation of sheet workability, evaluation of wettability (bondability), and reliability evaluation by a heat cycle test were performed by the following method. The obtained results are shown in Table 3.
Note that the evaluation of solder wettability, bondability, and the like does not depend on the solder shape, and may be evaluated by the shape of a wire, a ball, a paste, or the like.

<Processability evaluation>
Each solder mother alloy (plate-shaped ingot having a thickness of 5 mm) of Samples 1 to 30 shown in Table 1 was roughened to a thickness of 400 μm while being heated to 230 ° C. using a hot rolling mill having a 4-inch work roll. Rolled.
Next, the removal of the surface oxide film and the surface roughness of each of the samples 1 to 30 were adjusted under the conditions shown in Table 2.

  The polishing of the sample is performed by using abrasive paper, and by performing fine abrasive paper in order from coarse number # 150 to # 240, # 360, # 700, # 1000, # 2500, # 6000. Table 2 shows the number of the last used abrasive paper. After final polishing, the sample was washed thoroughly with pure water, further washed with alcohol, and then vacuum dried at room temperature for 1 hour using a vacuum oven.

  The acid washing of the sample was performed using acetic acid, and Table 2 shows the acetic acid washing time. After acid cleaning, water was washed three times with pure water, alcohol was further washed, and the liquid was thoroughly wiped off with a waste cloth, followed by vacuum drying at room temperature for 1 hour using a vacuum oven.

The sample was polished and / or acid-washed, and then finish-rolled to a thickness of 50 μm using a cold rolling mill having a 3-inch work roll.
Three types of rolls having different surface roughness were used as the rolls used for finish rolling. Table 2 shows the surface roughness (Ra) of the rolls used for finish rolling of each sample. Thereafter, it was cut into a width of 25 mm by slitting.

After processing into a sheet shape in this way, each of the obtained sheet-shaped samples was observed and the processability was evaluated as follows. The results are shown in Table 3.
The case where there were no scratches or cracks was indicated as “◯”, the case where there were 1 to 3 cracks or cracks per 10 m of the sheet length was indicated as “Δ”, and the case where there were 4 or more points was indicated as “X”.

Next, the thickness and surface roughness of the oxide layers of Samples 1 to 30 were measured.
The thickness of the oxide layer was measured using a field emission Auger electron spectrometer (manufactured by ULVAC-PHI, model: SAM-4300).
The surface roughness was measured using a surface roughness measuring apparatus (manufactured by Tokyo Seimitsu Co., Ltd., model: Surfcom 470A).
The thickness of the oxide layer was defined as follows.
That is, as shown in FIG. 1, the amount of oxygen in the portion 1000 nm in the depth direction (perpendicular to the solder surface) from the solder surface is set to 0%, and the maximum oxygen concentration between the solder surface and the depth of 1000 nm is set to 100%. %, The penetration depth from the solder surface where the oxygen concentration was reduced to 10% was defined as the thickness of the oxide layer.
Table 2 shows the thickness of the oxide layer and the surface roughness (Ra) in addition to the production conditions (polishing conditions, pickling conditions, roll surface roughness) of Samples 1-30.

<Evaluation of wettability (bondability)>
Each sample processed into a sheet was evaluated using a wettability tester (device name: atmosphere control type wettability tester).
That is, the heater part of the wettability tester was covered with a double cover, and heated at a heater set temperature of 410 ° C. while flowing nitrogen at a flow rate of 12 liters / minute from four locations around the heater part. 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 the bonded portion was observed.
The joint between the solder alloy and the Cu substrate of each sample is visually observed, “x” when not joined, “△” when joined but poorly wet (the solder is raised), and joined. In addition, the case where the wet spread was good (the state where the solder was thin and spread) was evaluated as “◯”.

<Heat cycle test>
The reliability of solder joints was evaluated by a heat cycle test.
In this test, a sample in which the solder alloy was able to be bonded to the Cu substrate in the above wettability evaluation (samples having a wettability evaluation of “◯” and “Δ”) was used. Tested. The test conditions were two Cu substrates to which a solder alloy was bonded, and a heat cycle test was performed with “cooling at −40 ° C.” and “heating at + 150 ° C.” as one cycle. The heat cycle test was repeated up to 300 cycles for confirmation in the middle and the other one up to 500 cycles.

Then, about each sample which performed the heat cycle test of 300 cycles and 500 cycles, Cu substrate with which the solder alloy was joined was embedded in resin, cross-section grinding | polishing was performed, and the digital scanning electron microscope (Hitachi Kyowa Engineering Co., Ltd. SEM, The bonding surface was observed by apparatus name: HITACHI S-4800.
The case where peeling occurred on the joint surface 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 maintained as “◯”.
The results of the above workability, wettability, and heat cycle (bonding reliability) are summarized in Table 3.

As is apparent from Tables 2 and 3, it can be seen that the solder alloys of Samples 1 to 22 which are the products of the present invention in the present invention exhibit good characteristics in all evaluation items.
That is, even when processed into a sheet, there was no generation of scratches or cracks, and wettability and reliability were good. The reason why this sheet workability was good is that the solder composition range is appropriate and is based on the vicinity of Zn-Al eutectic composition or Zn-Ge eutectic composition, and the effect of improving workability by microcrystallization appears. it is conceivable that.
The reason why the wettability was good was that the solder composition range was appropriate, the oxide film on the solder surface was thin, and the surface roughness was small. It is thought that it is because it is suppressed.
Furthermore, in the heat cycle test, no cracks or the like occurred up to 500 times, and good bondability and reliability were shown.
This high reliability is due to the connection under the condition that the presence of oxygen is suppressed as much as possible, and is the result of polishing the solder alloy, pickling the acid, and rolling with a roll having a small surface roughness.

On the other hand, each of the solder alloys of Samples 23 to 30, which are comparative products that are out of the scope of the present invention, has the thickness and surface roughness of the oxide layer of the solder due to inappropriate manufacturing conditions and contained element amounts. This is outside the scope of claims of the invention, and satisfactory characteristics are not obtained.
That is, scratches and cracks are generated in the samples 26 to 30 as to the workability, and good wettability is not obtained in all samples. In particular, in the heat cycle test, defects occurred in all samples (excluding samples 23 to 28 that could not be joined) up to 300 times.

Claims (8)

  The oxide layer on the surface of the solder alloy is 120 nm or less, and the average surface roughness Ra (hereinafter abbreviated as “surface roughness Ra”) is 0.60 μm or less. Solder alloy.   The solder alloy contains 0.01 mass% or more and 9.0 mass% or less of Al, 0.01 mass% or more and 8.0 mass% or less of Ge, 0.01 mass% or more of Mg, In the range of mass% or less, Ag of 0.1 mass% or more and 4.0 mass% or less, and P of 0.5 mass% or less, containing one or more of Ge, Mg, Ag, and P, and the balance 2. The Pb-free solder alloy containing Zn as a main component according to claim 1, comprising Zn and inevitable impurities. 3.   The solder alloy contains Al of 3.0% by mass or more and 7.0% by mass or less, Ge of 0.1% by mass or more and 3.0% by mass or less, Mg of 0.01% by mass or more, 3.0% 2. The Pb-free solder alloy containing Zn as a main component according to claim 1, wherein the Pb-free solder alloy contains Zn or an inevitable impurity as a main component and contains at least one of Ge and Mg within a mass% range.   A method for producing a Pb-free solder alloy containing Zn as a main component, wherein the surface of the solder alloy is polished so that the thickness of the oxide layer on the surface is 120 nm or less and the surface roughness Ra is 0.60 μm or less.   A method for producing a Pb-free solder alloy containing Zn as a main component, characterized in that the surface of the solder alloy is subjected to acid cleaning so that the thickness of the oxide layer on the surface is 120 nm or less.   Pb-free solder mainly composed of Zn, using a rolling roll having a surface roughness Ra of 0.3 μm or less, rolling a solder alloy, and making the surface roughness Ra of the solder alloy 0.60 μm or less Alloy manufacturing method.   The solder alloy contains 0.01 mass% or more and 9.0 mass% or less of Al, 0.01 mass% or more and 8.0 mass% or less of Ge, 0.01 mass% or more of Mg, In the range of mass% or less, Ag of 0.1 mass% or more and 4.0 mass% or less, and P of 0.5 mass% or less, containing one or more of Ge, Mg, Ag, and P, and the balance The method for producing a Pb-free solder alloy containing Zn as a main component according to any one of claims 4 to 6, comprising Zn and inevitable impurities. The solder alloy contains Al of 3.0% by mass or more and 7.0% by mass or less, Ge of 0.1% by mass or more and 3.0% by mass or less, Mg of 0.01% by mass or more, 3.0% 7. The Pb-free material containing Zn as a main component according to claim 4, wherein the Pb-free material contains at least one of Ge and Mg in a range of mass% or less, and consists of the balance Zn and inevitable impurities. Solder alloy manufacturing method.

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