By a News Reporter-Staff News Editor at Journal of Transportation -- A patent application by the inventors Ogawa, Takayuki (Yokohama-shi, JP); Nishi, Mizuki (Matsusaka-shi, JP); Furuhashi, Kazunori (Matsusaka, JP), filed on March 2, 2012, was made available online on December 26, 2013, according to news reporting originating from Washington, D.C., by VerticalNews correspondents.
This patent application is assigned to Central Glass Company, Limited.
The following quote was obtained by the news editors from the background information supplied by the inventors: "Some of automotive or architectural glass plate articles may be formed with conductive wires for electrical heating as a defogger for securing visibility. Furthermore, a glass antenna may be used on an automotive rear window or side window. In conductive wires for electrical heating and a glass antenna, a pattern of conductive wires is formed by baking a conductive paste in the form of a thin film onto the surface of a glass plate. Thus, a glass plate with a conductive portion formed of a pattern of conductive wires prepared by baking a conductive thin film onto the surface of a glass plate is referred to in the following as a glass plate with a conductive portion.
"These conductive wires are provided with a metal terminal for feeding (a feeding terminal). Conventionally, the feeding terminal and a glass plate have been connected with each other with a lead-containing solder by using a single terminal seat or, as shown in, for example, Patent Publication 2, two terminal seats (seats) (cited in FIG. 9) (Patent Publications 1-3). However, in general, lead is an environmental pollution substance with a high toxicity. Therefore, there is a concern about effects on health and environment, and particularly adverse effects on ecosystem and its pollution are seen as being problematic. In particular, in case that a glass plate article utilizing a lead-containing solder has been dumped, there is a risk that lead leaches into the environment when acid rain or the like is attached to the solder.
"From this point, in the household appliance industry, the production of lead-free solders for electronic substrates is rapidly expanding. However, as compared with solders for electronic substrates, a solder for connecting a glass plate with a metal terminal has a higher requirement of adhesion strength. Furthermore, due to the difference of thermal expansion coefficient between a metal terminal and a glass plate, etc., in case that an abrupt environmental temperature change occurs or in case that a repeated temperature change is large, it tends to cause a problem that stress concentrates on a soldered portion, where the glass plate and the metal terminal are connected with each other, to cause a lowering of the connection strength or cracks on the surface of the glass plates, etc.
"Nowadays, a Sn--Ag--Cu-series, lead-free solder, such as Sn-3Ag-0.5Cu (a Sn alloy containing 3 mass % of Ag and 0.5 mass % of Cu), which has become the mainstream of solders for electronic substrates, is high in terms of connection strength too in electronic substrates and is one of highly reliable solder alloys. This alloy is, however, high in Young's modulus and a metal high in stiffness. For example, an alloy having a composition of 3.5 mass % Ag, 1.0 mass % Cu and the balance being Sn is reported to have a Young's modulus of 41.6 GPa at ordinary temperature (Comparative Example No. 3 described in Patent Publication 4). Thus, Sn--Ag--Cu-series, lead-free solders do not have a softness as that of Sn--Pb alloy-series solders, and it is difficult to relax a stress generated in a soldered article. Therefore, it cannot be used in the original condition for the use of a connection between a glass plate with a high stiffness and a metal terminal.
"As to a technique for connecting a terminal structure, which has a structure by connecting two terminal seats with a stem portion, by using a lead-free solder, Patent Publication 5 discloses a structure in which a thermal stress accompanying soldering is relaxed to prevent the occurrence of cracks on the surface of the glass plate after a thermal shock test, by connecting a conductive film formed by baking a silver paste, with a lead-free solder alloy containing Ag by 1.5 mass % to 5 mass % and by defining the total area of a connecting surface of the terminal and the volume of the solder.
"Furthermore, Patent Publication 6 discloses a vehicular glass panel prepared by using a lead-free solder containing a stress relaxing component selected from Bi, In and Sb and Sn by an amount of less than 90%. This lead-free solder takes into account the lowering of stress generated at the initial stage accompanying the soldering. However, due to being high in Young's modulus, if it is used in the cold such as a cold district, there is a risk that the solver shrinks to cause cracks in the glass, thereby lowering strength of the glass during using the vehicle."
In addition to the background information obtained for this patent application, VerticalNews journalists also obtained the inventors' summary information for this patent application: "Ag--Sn alloy-series, lead-free solder as an alternative to Pb--Sn solder, which has a low melting point and is superior in adhesion, has a high melting point of 217 to 219.degree. C. Therefore, in the case of soldering to a glass plate, it is necessary to prevent the occurrence of a stress by a partial thermal expansion of the glass plate. Thus, as shown in Patent Publication 5, there have been proposed in the past some means for preventing the occurrence of cracks in the soldering step.
"In a terminal structure prepared by connecting a metal terminal with a conductive portion of a glass plate with the conductive portion, formed with the conductive portion, by a solder, there has been a tendency to use a lead-free solder as the solder. In lead-free solders with high contents of Sn, however, the connection with the conductive portion formed by a Ag-containing paste is made insufficient by a Ag-free solder or a solder with a low content of Ag. As a result, there is a risk that the terminal comes off to lose electrical conduction performance.
"On the other hand, the use of a Sn alloy-series, lead-free solder with a high content of Ag improves the strength of a connection with the conductive portion, but Young's modulus of the solder layer becomes high. Thus, even if the occurrence of stress upon soldering can be prevented, it is difficult to relax stress generated in the glass plate of the soldered portion by the environmental temperature change during the use, particularly due to the difference of thermal expansion coefficient between the terminal structure and the glass plate. As shown in FIG. 8, there is a risk to generate cracks 7 in the direction of thickness of the glass plate in the vicinity of a corner of the terminal seat when soldering the conductive portion 5 of the glass plate 6 and the terminal seat 1 by the solder layer 4. Thermal expansion coefficient of copper or brass used for the terminal structure is around 16.times.10.sup.-6 to 19.times.10.sup.-6/.degree. C., and thermal expansion coefficient of glass is around 8.5.times.10.sup.-6 to 9.times.10.sup.6/.degree. C.
"Thus, in the case of using a Sn--Ag--Cu-series, lead-free solder with a high Young's modulus, the metal terminal to be connected with the conductive portion of the glass plate with the conductive portion, formed with the conductive portion, has a problem that the occurrence of cracks of the glass plate by the environmental temperature change during the use cannot be prevented unless both conditions of the solder component and the terminal structure are satisfied. Such characteristic can be judged by measuring the connection strength after a cooling/heating cycle resistance test.
"According to the present invention, there is provided a glass plate article having a feed terminal structure (in the following, it may be expressed as simply 'the terminal structure') to be connected with a feeding portion of a glass plate with a conductive portion, the glass plate article (a first article) being characterized by that the feed terminal structure has at least one terminal seat subjected to a surface connection with the feeding portion through a lead-free solder alloy,
"that the terminal seat has a laminar form prepared by removing corner portions (soldering avoidance regions), each defined by a line connecting two points that are away from each of two vertices of one side of a square or rectangle by 1.6 mm or greater and are on two sides extending from each vertex, from the square or rectangle,"that a connection area per each surface connection is from 8 mm.sup.2 to 98 mm.sup.2, and
"that the terminal seat is soldered to the feeding portion by using the lead-free solder alloy, the lead-free solder alloy is a Sn--Ag--Cu-series, lead-free solder alloy that has a dispersion/precipitation strengthened structure containing 1.5 to 4 mass % of Ag and 0.5 to 2 mass % of Cu and has a Young's modulus of 40 GPa or higher at room temperature.
"The first article may be a glass plate article (a second article) characterized by that thermal expansion coefficient of a material of the feed terminal structure is 16.times.10.sup.-6 to 19.times.10.sup.6/.degree. C.
"The first or second article may be a glass plate article (a third article) characterized by that the conductive portion is a conductive wire of a vehicular glass antenna or defogger.
"Any one of the first to third articles may be a glass plate article (a fourth article) characterized by that the terminal seat is formed of a pair of terminal seats, and the feed terminal structure comprises a stem portion formed to bridge the pair of the terminal seats.
"Any one of the first to fourth articles may be a glass plate article (a fifth article) characterized by that Cu content of the lead-free alloy is 0.55 to 2 mass %.
"Any one of the first to fifth articles may be a glass plate article (a sixth article) characterized by that material of the terminal seat is copper or brass.
"Any one of the first to sixth articles may be a glass plate article (a seventh article) characterized by that thickness of the terminal seat is 0.2 to 1.0 mm.
"Any one of the first to seventh articles may be a glass plate article (an eighth article) characterized by that thickness of the solder layer between the terminal seat and the conductive portion is 0.1 to 2.0 mm.
"Furthermore, according to the present invention, there is provided a process for connecting a terminal structure with a feeding portion of a glass plate with a conductive portion, which is characterized by that the feed terminal structure according to any one of the first to eighth articles is soldered to a feeding portion of a glass plate with a conductive portion by using the Sn--Ag--Cu-series, lead-free solder alloy according to any one of the first to eighth articles."
