JP3786405B2 - Tin-zinc-based lead-free solder powder and method for producing the same - Google Patents
Tin-zinc-based lead-free solder powder and method for producing the same Download PDFInfo
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Description
【０００１】
【発明の属する技術分野】
本発明は、たとえば電子回路素子の実装工程などに使用されるはんだ粉末であって、特に、その中でも環境調和型の錫―亜鉛系鉛フリーはんだ粉末およびその製造方法に関する。
【０００２】
【従来の技術】
従来、各種機器のはんだ付けには、融点が低く、酸化性雰囲気の中でも濡れ性が良好であること等の利点を有することから、錫―鉛系はんだが多く用いられていた。ところが、最近、鉛は毒性を有していることから、電子機器の廃棄処理に伴う環境汚染を防止する観点から、はんだの鉛フリー化が急速に進んでいる。この環境重視の流れの中でも、たとえば電子回路素子の実装工程の一つであるリフローはんだ付けにおいて、鉛フリー化が緊急の課題になっている。
【０００３】
そこで、従来、リフローはんだ付け用に実用化された鉛フリーはんだの１つに、亜鉛を９重量％（共晶点組成）前後含有した錫―亜鉛系はんだが提案されている。錫―亜鉛合金の共晶温度は１９９℃であり、錫を主成分とした鉛フリーはんだの中では、最も錫―鉛合金の共晶点に近く、また、原料コストの面でも、他の鉛フリーはんだより安価であるというメリットがある。
【０００４】
【発明が解決しようとする課題】
ところで、一般に、上記リフローはんだ付けに用いられるクリームはんだは、はんだ粉末とフラックスを混合したものであり、フラックスには、はんだ溶融時に、はんだ付け対象物の表面を清浄にし、はんだの濡れ性を良くするための活性剤が添加されている。この活性剤は、通常、酸を主成分にしている。しかも、従来の錫―亜鉛系はんだの場合、製造されたはんだ粉末の表面および内部に亜鉛を主成分とする相が存在し、表面においては、この亜鉛が酸化物を形成している。
【０００５】
したがって、従来、錫―亜鉛系はんだ粉末をフラックスと混合してクリームはんだに加工すると、亜鉛が活性な金属元素であるため、保存中に、フラックス中の活性剤と容易に反応し、クリームはんだの粘度上昇が錫―鉛はんだよりも急速且つ大幅に発生し、プリント基板への印刷が不可能になってしまうという課題があった。
【０００６】
一方、この粘度上昇を防止するために活性剤の強さや添加量を抑えると、はんだ加熱時に生成する亜鉛酸化物を還元することができず、その結果、はんだの濡れ広がり性が低下してしまうという問題があった。このように従来では、これら濡れ性と長期保存性を両立させることが極めて困難であり、それが環境保全に有効な鉛フリーのクリームはんだを普及させるに当たって、大きな障害となっていた。
【０００７】
そこで、本発明の目的は、クリームはんだの良好な濡れ性を保持しつつ、長期の保存性にも優れた錫―亜鉛系鉛フリーはんだ粉末を提供することにある。
【０００８】
【課題を解決するための手段】
本発明者らは、上述した従来の課題を解決すべく、鋭意研究を重ねた結果、特に亜鉛が一部の酸と難溶性の金属塩を生成することに着目し、錫を主成分とし、少なくとも７〜１０重量％の亜鉛を必須含有元素とする錫―亜鉛系はんだ粉末を、適宜の種類・濃度の酸溶液に浸漬することにより粉末表面の亜鉛部分に難溶性の金属塩を生成せしめ、もってフラックス中での活性剤と亜鉛の反応を抑え得ることを見い出し、本発明を完成するに至った。
【０００９】
すなわち、請求項１に記載の発明による錫−亜鉛系鉛フリーはんだ粉末は、７〜１０重量％の亜鉛および０〜４重量％のビスマスを含有し、残部が錫及び不可避的不純物からなるはんだ粉末であって、該はんだ粉末を硫酸とエタノールからなる溶液に浸漬して粉末表面に硫酸亜鉛を生成し、その硫酸亜鉛で前記粉末表面を被覆してなることを特徴とする。
【００１０】
請求項２に記載の発明による錫−亜鉛系鉛フリーはんだ粉末は、７〜１０重量％の亜鉛および０〜４重量％のビスマスを含有し、残部が錫及び不可避的不純物からなるはんだ粉末であって、該はんだ粉末を炭酸と水からなる溶液に浸漬して粉末表面に炭酸亜鉛を生成し、その炭酸亜鉛で前記粉末表面を被覆してなることを特徴とする。
【００１１】
請求項３に記載の発明による錫−亜鉛系鉛フリーはんだ粉末の製造方法は、７〜１０重量％の亜鉛および０〜４重量％のビスマスを含有し、残部が錫及び不可避的不純物からなるはんだ粉末を、硫酸とエタノールからなる溶液に浸漬して粉末表面に硫酸亜鉛を生成する処理を施し、次いで洗浄して後に、乾燥させてなることを特徴とする。
【００１２】
また、請求項４に記載の発明による錫−亜鉛系鉛フリーはんだ粉末の製造方法は、７〜１０重量％の亜鉛および０〜４重量％のビスマスを含有し、残部が錫及び不可避的不純物からなるはんだ粉末を、炭酸と水からなる溶液に浸漬して粉末表面に炭酸亜鉛を生成する処理を施し、次いで洗浄して後に、乾燥させてなることを特徴とする。
【００１５】
【発明の実施の形態】
以下、本発明の実施の形態について詳細に説明する。
【００１６】
本発明によるはんだ粉末は、その化学組成が、錫を主成分とし、少なくとも７〜１０重量％の亜鉛を必須含有元素とするはんだ粉末であって、このはんだ粉末を酸溶液に浸漬して粉末表面の亜鉛部分を難溶性の金属塩とした錫―亜鉛系鉛フリーはんだ粉末である。
【００１７】
また、本発明の錫―亜鉛系鉛フリーはんだ粉末は、錫を主成分とし、少なくとも７〜１０重量％の亜鉛を必須元素とするとともに、０〜４重量％のビスマスを同時に含有し、このはんだ粉末を酸溶液に浸漬して粉末表面の亜鉛部分を難溶性の金属塩にする構成とすることもできる。
【００１８】
本発明において、前記酸溶液に使用する酸としては、たとえばシュウ酸、或いは硫酸が好適でる。また、炭酸などを用いることもできる。酸の溶媒としては、たとえば水、エタノールなどが考えられるが、上述した酸を溶解することができ、さらに生成した金属塩の溶解度が小さいものであれば、何れの溶媒を用いてもよい。
【００１９】
ここで、本発明における難溶性の金属塩とは、上述した酸溶液に対して難溶性を有する亜鉛の金属塩を意味する。はんだ粉末の表面の亜鉛と酸との反応により、この難溶性の亜鉛金属塩が生成されるのである。
【００２０】
したがって、以上の如く構成した本発明の錫―亜鉛系鉛フリーはんだ粉末では、粉末表面に存在する反応性に富んだ亜鉛が、難溶性の金属塩で覆われることになる。そこで、このはんだ粉末を原料としてクリームはんだに加工した場合、室温以下では、亜鉛―活性剤間の反応が抑えられるために長期の保存性に優れ、且つ加熱時には、はんだが溶融するまで粉末内部の亜鉛が著しく酸化することがなく、濡れ性が阻害されることもない。加えて、はんだ粉末の平均組成は初期の値を維持しているため、低融点という錫―亜鉛系鉛フリーはんだ本来の特徴は生かされるのである。
【００２１】
さて、本発明において、上述した錫―亜鉛系鉛フリーはんだ粉末を製造する場合は、たとえば以下に示す工程を経て作製する。
【００２２】
まずは、錫を主成分とし、少なくとも７〜１０重量％の亜鉛を必須元素とするはんだ粉末を用い、これを酸溶液に浸漬して粉末表面に難溶性の金属塩を生成する処理を施し、粉末表面に存在する反応性に富んだ亜鉛を難溶性の金属塩で覆う。ここで使用する酸としては、前述したようにシュウ酸、硫酸などが好適である。
【００２３】
次いで、この難溶性の金属塩で覆ったはんだ粉末を洗浄する。さらに洗浄工程の後、はんだ粉末を乾燥させる。以上のような所定の製造工程を経ることにより、初めて保存性および濡れ性に優れた錫―亜鉛系鉛フリーはんだ粉末が作製される。
【００２４】
なお、本発明は、化学組成として、以上に例示した錫・亜鉛・ビスマス以外に、他の各種少量元素を含有する錫―亜鉛系鉛フリーはんだ粉末を排除するものではないことは、勿論である。
【００２５】
【実施例】
次に、以下に示す実施例を基づいて、本発明をさらに具体的に説明するが、本発明は、この実施例に限定されるものでないことは、勿論である。
【００２６】
本発明者らは、本発明の効果を確認するための実験を行った。実験に用いたはんだ粉末は、錫―亜鉛系の粒径３２〜４５μｍの真球粉である。実験を行ったはんだ粉末（試料A〜H）の組成（重量％）、詳細な処理方法および特性評価結果は、下記の表１に示した。はんだ粉末は、表１に示した処理条件で処理を行い、水洗と乾燥を施した後、フラックスと混合してペーストにして各種評価試験に供している。表中のはんだ付け性については、JIS-Z-3284に準拠した方法で行ない、濡れ広がり性を評価した。試験は、より厳しい条件を模擬するため、大気雰囲気中で、プリヒートも１５０℃で２分間行った。試験の結果、濡れ広がり性が不良のものを「×」、良好なものを「○」、非常に良好なものを「◎」で示した。
【００２７】
保存性に関しては、はんだ粉末とフラックスを混合した後に、約４℃に保った冷蔵庫中で１週間保存した後の、ペーストの粘度上昇具合および印刷性により判定した。濡れ広がり性と同様に、不良のものを「×」、良好なものを「○」、非常に良好なものを「◎」で示した。表１に示すように、本発明によるはんだ粉末を用いたペーストは、濡れ性と共に保存性にも優れることが確認された。
【００２８】
【表１】
なお、酸は、上記表１中で使用した酸以外でも、生成する亜鉛の金属塩の溶媒への溶解度が小さいものであれば、何れの酸でも必要な効果を得ることができる。
【００３０】
【発明の効果】
上述のように構成した本発明によれば、次のような顕著な効果が得られる。
【００３１】
本発明によれば、錫―亜鉛系鉛フリーはんだ粉末として、錫を主成分とし、少なくとも７〜１０重量％の亜鉛を必須含有元素とするはんだ粉末を用い、該はんだ粉末を酸溶液に浸漬して粉末表面に難溶性の金属塩を生成し、その難溶性金属塩で粉末表面を被覆した構成とするため、このはんだ粉末を原料としてクリームはんだに加工するとき、室温以下では活性剤と亜鉛の反応を抑えて保存性を高めることができ、且つ加熱時においては、はんだが溶融するまで粉末内部の亜鉛を酸化させないで、良好な濡れ性を保持することができ、しかも、はんだ粉末の平均組成は初期の値が維持されるため、低融点という錫―亜鉛系はんだの長所を生かしつつ、上記濡れ性および保存性に優れた錫―亜鉛系はんだペーストを得ることができる。
【００３２】
さらに、本発明によれば、前記酸溶液の酸としてシュウ酸や硫酸を用いることから、はんだ粉末を酸溶液に浸漬したとき、これら酸と粉末表面の亜鉛の反応によって粉末表面に難溶性の金属塩をより効果的に生成し、その結果、濡れ性および保存性の点において一層優れた錫―亜鉛系はんだペーストを得ることができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a solder powder used in, for example, a mounting process of an electronic circuit element, and more particularly to an environmentally friendly tin-zinc-based lead-free solder powder and a manufacturing method thereof.
[0002]
[Prior art]
Conventionally, tin-lead solders are often used for soldering various devices because of their advantages such as a low melting point and good wettability in an oxidizing atmosphere. However, since lead has toxicity recently, lead-free solder has been rapidly promoted from the viewpoint of preventing environmental pollution associated with disposal of electronic equipment. In this environment-oriented flow, for example, reflow soldering, which is one of the mounting processes of electronic circuit elements, has become an urgent issue.
[0003]
Therefore, conventionally, a tin-zinc based solder containing about 9% by weight of zinc (eutectic point composition) has been proposed as one of lead-free solders practically used for reflow soldering. The eutectic temperature of tin-zinc alloy is 199 ° C, and it is the closest to the eutectic point of tin-lead alloy among lead-free solders mainly composed of tin, and other lead in terms of raw material cost. There is an advantage that it is cheaper than free solder.
[0004]
[Problems to be solved by the invention]
By the way, generally, the cream solder used for the reflow soldering is a mixture of solder powder and flux, and the flux cleans the surface of the soldering object when the solder is melted and improves the wettability of the solder. An activator has been added. This activator is usually based on an acid. In addition, in the case of conventional tin-zinc based solder, a phase mainly composed of zinc exists on the surface and inside of the manufactured solder powder, and this zinc forms an oxide on the surface.
[0005]
Therefore, conventionally, when tin-zinc solder powder is mixed with flux and processed into cream solder, since zinc is an active metal element, it easily reacts with the activator in the flux during storage. There was a problem that the viscosity increase occurred more rapidly and significantly than tin-lead solder, making it impossible to print on a printed circuit board.
[0006]
On the other hand, if the strength and addition amount of the activator are suppressed in order to prevent this increase in viscosity, the zinc oxide produced during solder heating cannot be reduced, and as a result, the wettability of the solder is reduced. There was a problem. Thus, conventionally, it has been extremely difficult to achieve both wettability and long-term storage, which has been a major obstacle to the spread of lead-free cream solder effective for environmental conservation.
[0007]
Accordingly, an object of the present invention is to provide a tin-zinc-based lead-free solder powder that retains good wettability of cream solder and is excellent in long-term storage.
[0008]
[Means for Solving the Problems]
As a result of intensive research to solve the above-described conventional problems, the inventors of the present invention pay particular attention to the fact that zinc forms a part of acid and a sparingly soluble metal salt. By immersing tin-zinc-based solder powder containing at least 7 to 10% by weight of zinc as an essential element in an acid solution of an appropriate type and concentration, a slightly soluble metal salt is formed on the zinc portion of the powder surface, Thus, it has been found that the reaction between the activator and zinc in the flux can be suppressed, and the present invention has been completed.
[0009]
That is, the tin-zinc-based lead-free solder powder according to the invention of claim 1 contains 7 to 10% by weight of zinc and 0 to 4% by weight of bismuth, with the balance being tin and inevitable impurities. The solder powder is immersed in a solution of sulfuric acid and ethanol to produce zinc sulfate on the powder surface, and the powder surface is coated with the zinc sulfate.
[0010]
The tin-zinc-based lead-free solder powder according to the invention of claim 2 is a solder powder containing 7 to 10% by weight of zinc and 0 to 4% by weight of bismuth, with the balance being tin and inevitable impurities. The solder powder is immersed in a solution comprising carbonic acid and water to produce zinc carbonate on the powder surface, and the powder surface is coated with the zinc carbonate.
[0011]
A method for producing a tin-zinc-based lead-free solder powder according to the invention as claimed in claim 3 contains 7 to 10% by weight of zinc and 0 to 4% by weight of bismuth, with the balance being tin and inevitable impurities. It is characterized in that the powder is immersed in a solution composed of sulfuric acid and ethanol to perform a treatment for generating zinc sulfate on the surface of the powder, then washed and then dried.
[0012]
The method for producing a tin-zinc-based lead-free solder powder according to the invention of claim 4 contains 7 to 10% by weight of zinc and 0 to 4% by weight of bismuth, with the balance being tin and inevitable impurities. The resulting solder powder is immersed in a solution of carbonic acid and water to perform a treatment for generating zinc carbonate on the powder surface, then washed and then dried.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
[0016]
The solder powder according to the present invention is a solder powder having a chemical composition mainly composed of tin and containing at least 7 to 10% by weight of zinc as an essential element. The solder powder is immersed in an acid solution to obtain a powder surface. This is a tin-zinc-based lead-free solder powder in which the zinc part is made of a sparingly soluble metal salt.
[0017]
The tin-zinc-based lead-free solder powder of the present invention contains tin as a main component, contains at least 7 to 10% by weight of zinc as an essential element, and simultaneously contains 0 to 4% by weight of bismuth. The powder may be immersed in an acid solution to make the zinc portion on the surface of the powder into a hardly soluble metal salt.
[0018]
In the present invention, for example, oxalic acid or sulfuric acid is suitable as the acid used in the acid solution. Carbonic acid or the like can also be used. Examples of the acid solvent include water and ethanol. Any solvent may be used as long as it can dissolve the above-described acid and the solubility of the generated metal salt is small.
[0019]
Here, the hardly soluble metal salt in the present invention means a zinc metal salt which is hardly soluble in the acid solution described above. This hardly soluble zinc metal salt is produced by the reaction of zinc and acid on the surface of the solder powder.
[0020]
Therefore, in the tin-zinc-based lead-free solder powder of the present invention configured as described above, the highly reactive zinc present on the powder surface is covered with a hardly soluble metal salt. Therefore, when this solder powder is processed into cream solder as a raw material, the reaction between the zinc and the activator is suppressed at room temperature or lower, so that it is excellent in long-term storage, and during heating, the inside of the powder is melted until the solder melts. Zinc does not oxidize significantly and wettability is not hindered. In addition, since the average composition of the solder powder maintains the initial value, the inherent characteristic of tin-zinc-based lead-free solder, which has a low melting point, is utilized.
[0021]
In the present invention, when producing the above-described tin-zinc-based lead-free solder powder, for example, it is produced through the following steps.
[0022]
First, a solder powder containing tin as a main component and containing at least 7 to 10% by weight of zinc as an essential element is immersed in an acid solution to form a hardly soluble metal salt on the powder surface. The highly reactive zinc present on the surface is covered with a sparingly soluble metal salt. As the acid used here, oxalic acid, sulfuric acid and the like are suitable as described above.
[0023]
Next, the solder powder covered with the hardly soluble metal salt is washed. Further, after the cleaning process, the solder powder is dried. Through the predetermined manufacturing process as described above, a tin-zinc-based lead-free solder powder having excellent storage stability and wettability is produced for the first time.
[0024]
Of course, the present invention does not exclude tin-zinc-based lead-free solder powders containing various other minor elements in addition to the above exemplified tin, zinc, and bismuth as the chemical composition. .
[0025]
【Example】
Next, the present invention will be described more specifically based on the following examples, but the present invention is of course not limited to these examples.
[0026]
The present inventors conducted an experiment for confirming the effect of the present invention. The solder powder used in the experiment is a tin-zinc-based true sphere powder having a particle size of 32 to 45 μm. Table 1 below shows the composition (% by weight) of the solder powder (samples A to H), the detailed treatment method, and the property evaluation results. Solder powder is processed under the processing conditions shown in Table 1, washed with water and dried, and then mixed with flux to form a paste for various evaluation tests. The solderability shown in the table was performed by a method based on JIS-Z-3284, and the wettability was evaluated. In order to simulate more severe conditions, the test was performed in air at a preheat of 150 ° C. for 2 minutes. As a result of the test, “x” indicates that the wettability is poor, “◯” indicates that it is good, and “◎” indicates that it is very good.
[0027]
Preservability was determined by mixing the solder powder and the flux and then storing the paste for 1 week in a refrigerator maintained at about 4 ° C., and the degree of increase in paste viscosity and printability. Similar to the wetting and spreading property, poor samples were indicated with “×”, good samples with “◯”, and very good samples with “で”. As shown in Table 1, it was confirmed that the paste using the solder powder according to the present invention was excellent in wettability and storage stability.
[0028]
[Table 1]
In addition, as long as the acid is a thing other than the acid used in the said Table 1, if the solubility to the solvent of the metal salt of zinc to produce | generate is small, a required effect can be acquired.
[0030]
【The invention's effect】
According to the present invention configured as described above, the following remarkable effects can be obtained.
[0031]
According to the present invention, as a tin-zinc-based lead-free solder powder, a solder powder containing tin as a main component and containing at least 7 to 10% by weight of zinc as an essential element is used, and the solder powder is immersed in an acid solution. In order to produce a hardly soluble metal salt on the powder surface and coat the powder surface with the hardly soluble metal salt, when this solder powder is processed into cream solder as a raw material, below the room temperature, the activator and zinc The reaction can be suppressed to improve the storage stability, and during heating, the zinc inside the powder is not oxidized until the solder melts, and good wettability can be maintained, and the average composition of the solder powder Since the initial value is maintained, the tin-zinc solder paste having excellent wettability and storage stability can be obtained while taking advantage of the low melting point of the tin-zinc solder.
[0032]
Furthermore, according to the present invention, since oxalic acid or sulfuric acid is used as the acid of the acid solution, when the solder powder is immersed in the acid solution, a metal that is hardly soluble on the powder surface by the reaction of these acids and zinc on the powder surface. A salt can be generated more effectively, and as a result, a tin-zinc solder paste that is more excellent in terms of wettability and storage stability can be obtained.
Claims (4)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2001318364A JP3786405B2 (en) | 2001-10-16 | 2001-10-16 | Tin-zinc-based lead-free solder powder and method for producing the same |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2001318364A JP3786405B2 (en) | 2001-10-16 | 2001-10-16 | Tin-zinc-based lead-free solder powder and method for producing the same |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JP2003126991A JP2003126991A (en) | 2003-05-08 |
| JP3786405B2 true JP3786405B2 (en) | 2006-06-14 |
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| Application Number | Title | Priority Date | Filing Date |
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| JP2001318364A Expired - Fee Related JP3786405B2 (en) | 2001-10-16 | 2001-10-16 | Tin-zinc-based lead-free solder powder and method for producing the same |
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| JP (1) | JP3786405B2 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| JP6102280B2 (en) * | 2013-01-28 | 2017-03-29 | 三菱マテリアル株式会社 | Manufacturing method of SnAgCu solder powder and solder paste using this powder |
| CN114434039B (en) * | 2021-01-15 | 2024-07-30 | 重庆理工大学 | Solder for copper-aluminum dissimilar material low-temperature interconnection and welding method |
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| JP2003126991A (en) | 2003-05-08 |
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