Alloys or metallic compositions – Tin base
Reexamination Certificate
2001-01-30
2001-11-20
Ip, Sikyin (Department: 1742)
Alloys or metallic compositions
Tin base
C148S400000, C420S560000, C420S561000, C420S562000
Reexamination Certificate
active
06319461
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to lead-free solder alloys for soldering oxide materials, such as ceramics and glass, at a low temperature.
BACKGROUND OF THE INVENTION
As a preparation for soldering oxide materials such as ceramics and glass, a process of applying an electroplating or electroless plating, such as gold plating, copper plating, and nickel plating, on the oxide materials is widely known. However, it is expensive and complicated to solder plated surfaces. Therefore, it is desired to develop an economic solder alloy.
To comply with the aforementioned demand, Japanese patent publication 49-22299B and Japanese patent publication 52-21980B disclose Pb—Sn solder alloys which can be directly soldered to glass and ceramics.
However, lead is toxic and has been recognized as hazards to injure human health and to hurt the environment, affecting the ecosystem, so the use of lead poses a problem. The trend to use no lead in solder alloy has been rapidly increased.
The solder alloy disclosed in the above Japanese patent publication 49-22299B is a Pb—Sn—Cd—Sb solder alloy which can be directly soldered to an oxide film material such as glass and ceramics, but includes toxic lead. The lead elutes from the abandoned products using the solder alloy to cause serious problem to the environment when the products are exposed to acid rain.
The solder alloy disclosed in the above Japanese patent publication 52-21980B is a solder alloy containing rare earth metals which is useful for bonding oxide materials such as glass and ceramics. However, the solder alloy has the same problems as above because it contains lead as a main component.
Development has been actively carried out to provide improved lead-free solder alloys especially for mounting electronic components to a printed wiring board. For example, an Sn—Ag—In solder alloy is disclosed in Japanese patent publication 9-326554A, and an Sn—Zn—Bi solder alloy is disclosed in Japanese patent publication 8-164495A. However, their bonding strengths are not enough for oxide materials such as glass and ceramics.
As an example of lead-free solder alloys for soldering metal oxide materials, an Sn—Ag—Al—Zn solder alloy is disclosed in Japanese patent publication 55-36032B. The resultant solder layer easily separates from oxide material such as glass and ceramics because this solder alloy is for soldering metal and therefore the coefficient of thermal expansion of the solder alloy is greatly different from that of the oxide material.
OBJECT AND SUMMARY OF THE INVENTION
The present invention has been made taking the aforementioned prior art into consideration and the object of the present invention is to provide lead-free solder alloys which contain no toxic lead and have sufficient bonding strength to oxide materials such as glass and ceramics.
The present invention is made to provide a solder alloy for bonding oxide materials such as glass and ceramics, wherein the solder alloy contains Ag, Cu, Zn, Al in addition to essential constituents, Sn and Ti, and further contains O wherein O content is defined. It should be noted that each composition for all of the constituents is an average composition in the solder alloy because the lead-free solder alloy of the present invention contains elements such as Zn, Ti, Al which are extremely easy to be oxidized and are easily segregate on the surface of the solder alloy.
A lead-free solder alloy of this invention is characterized by containing Sn and Ti and having a liquidus temperature equal to or less than 400° C.
In lead-free solder alloy of the present invention, the temperature of the liquidus line is preferably not lower than 200° C. in view of long-term stability under the condition that a portion to be soldered is subjected to high temperature.
The temperature of the liquidus line means the temperature at which a lead-free solder alloy of the present invention is completely melted and can be measured by, for example, a differential scanning calorimetry (DSC).
The lead-free solder alloy of the present invention preferably contains at least 0.0001% by weight O as a constituent. More preferably, the content of O is greater than 0.01% by weight.
The lead-free solder alloy of the present invention preferably further contains from 0.1% to 6.0% by weight Ag as a constituent.
The lead-free solder alloy of the present invention preferably further contains from 0.001% to 6.0% by weight Cu as a constituent.
The lead-free solder alloy of the present invention preferably further contains from 0.001% to 1.0% by weight Ti as a constituent.
The lead-free solder alloy of the present invention preferably further contains from 0.001% to 3.0% by weight Zn as a constituent.
The lead-free solder alloy of the present invention preferably further contains from 0.001% to 3.0% by weight Al as a constituent.
The lead-free solder alloy of the present invention preferably further contains at least one element selected from a group consisting of Bi, Si, and Sb in a range not greater than 10% by weight altogether.
The lead-free solder alloy of the present invention preferably further contains from 0.001% to 1.0% by weight Si.
The lead-free solder alloy of the present invention preferably further contains at least one trace constituent selected from a group consisting of Fe, Ni, Co, Ga, Ge, and P in a range not greater than 1.0% by weight altogether.
Preferred Embodiments
The followings are reasons of employing constituents of lead-free solder alloys according to the present invention. The contents of constituents will be represented by weight percent.
Sn (tin) is not toxic and can give good wetting property on materials to be bonded so that Sn is an indispensable constituent for solder alloy. The content of Sn is preferably equal to or more than 90.0%.
Ti (titanium) is extremely easy to be oxidized, but has an advantage in facilitating bonding between oxide materials and the solder alloy. However, addition of Ti increases the liquidus temperature of the solder alloy. If the liquidus temperature exceeds 400° C., the solder alloy has poor workability. It is preferable to add Ti within a range in which the liquidus temperature of the resultant solder alloy does not exceed 400° C. When Sn is used singly as solder, there is a possibility of phase transition due to temperature change and the phase transition may be detrimental to long-term stability. By adding Ti in a suitable amount, the phase transition of the solder alloy can be prevented. The content of Ti is preferably in a range from 0.001 to 1.0%.
O (oxygen) is an indispensable constituent for lead-free solder alloy for soldering oxide materials such as ceramics and glass. By adding a suitable amount of O in the solder alloy, bonding is made on interfaces between the oxide material and the solder alloy via O, thereby increasing the bonding strength of the resultant solder layer. In this case, the content of O is preferably in a range not less than 0.0001%. More preferably, the content of O is in a range not less than 0.01%. However, when an excess amount of O is contained in the solder alloy, oxides may be undesirably produced in the resultant solder layer by the soldering process. Accordingly, the content of O is preferably in a range not greater than 1.5%. The adjustment of the content of O in the solder alloy can be achieved by suitably selecting the concentration of oxygen in the ambient atmosphere where predetermined raw materials are melted to prepare the solder alloy and suitably selecting the melting period of time.
Ag (silver) has a good effect on improving the mechanical strength of the resultant solder alloy. When the content of Ag is less than 0.1%, such effect of improving the mechanical strength is not enough. Addition of Ag in an amount exceeding 6.0% increases the melting point of the resultant solder alloy and produces a lot of Ag—Sn intermetallic compounds, and thus, on the contrary, reduces the mechanical strength. Accordingly, the content of Ag is preferably in a range from 0.1 to 3.5%.
Cu (copper) has a good effect on improving the me
Domi Shinjiro
Nakagaki Shigeki
Sakaguchi Koichi
Suganuma Katsuaki
Ip Sikyin
Kanesaka & Takeuchi
Nippon Sheet Glass Co. Ltd.
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