Electricity: electrical systems and devices – Electrostatic capacitors – Fixed capacitor
Reexamination Certificate
2003-04-02
2004-03-09
Lam, Cathy (Department: 1775)
Electricity: electrical systems and devices
Electrostatic capacitors
Fixed capacitor
C361S306100, C361S309000
Reexamination Certificate
active
06704189
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electronic device with external terminals using a high temperature lead-free solder and a method of production of the same.
2. Description of the Related Art
In general, an electronic device such as a composite multilayer capacitor is provided with external terminals bonded to terminal electrodes for electrical connection with a circuit board etc. As the method for bonding the external terminals of such an electronic device to a circuit board etc., methods using soldering are frequently used. Further, since the external terminals of the electronic device will be mounted on the circuit board by solder, they have solder heat resistance and solder wettability.
The terminal electrodes of an electronic device have underlayer electrodes comprised of copper etc. formed by coating and baking a paste on the material of the body of the electronic device, nickel plating for giving solder heat resistance, and tin plating for giving solder wettability. These plating layers and external terminals are bonded by a high temperature solder.
The external terminals and circuit board are also connected using a high temperature solder. This high temperature solder is required not to melt or be difficult to melt at a high temperature (that is, have reflow resistance) and to be able to retain mechanical strength at a high temperature. Here, a “high temperature solder” means a solder having a solidus temperature of at least 183° C.
In general, among solders comprised of various types of metal compositions, in the Pb—Sn system, a high temperature solder having 95 wt % of Pb and 5 wt % of Sn (solidus temperature 307° C. and liquid temperature 327° C.) or a high temperature solder having 90 wt % of Pb and 10 wt % of Sn (solidus temperature 270° C. and liquid temperature 301° C.) is being used. Further, in the Pb—Ag system, a high temperature solder having 97.5 wt % of Pb and 2.5 wt % of Ag (solidus temperature 304° C. and liquid temperature 304° C.) is being used. Further, in the Pb—Ag—Sn system, a high temperature solder having 97.5 wt % of Pb, 1.5 wt % of Ag, and 1 wt % of Sn (solidus temperature 309° C. and liquid temperature 309° C.) is being used.
The above high temperature solders include at least 90 wt % of Pb to reduce the cost or to obtain reflow resistance.
Further, for example, inside a coil, transformer, etc. of an electronic device, an insulated conductor is wound around a magnetic material or other support. When bonding the end of such a winding with the device etc., soldering is generally used. At the time of this soldering, unless the coating portion comprised of polyurethane etc. of the insulated conductor is destroyed by the heat of the solder etc., soldering is not possible. Therefore, as the temperature of soldering, one inside a temperature range of 380° C. to 420° C. is generally employed. For this reason as well, the above high temperature solders contain at least 90 wt % of Pb.
Note that at the present time, to bond a circuit board etc. and an electronic device etc., in the Pb—Sn system, a solder having 37 wt % of Pb and 63 wt % of Sn (solidus temperature 183° C. and liquid temperature 183° C.) and in the Pb—Ag—Sn system, a solder having 36 wt % of Pb, 2 wt % of Ag, and 62 wt % of Sn (solidus temperature 179° C. and liquid temperature 190° C.) are being used. With these solders, generally soldering is performed at a reflow temperature of a temperature range of 220° C. to 240° C.
Note that if the solder used for internal bonding of an electronic device etc. mounted on a circuit board melts at the time of soldering, the molten solder flows out and the flowing solder becomes spherical and for example bridges circuits on a circuit board with circuits arranged at a high density and fine pitch. To avoid this, it is necessary to use a solder which does not melt or is difficult to melt (that is, has reflow resistance) even at the above reflow temperature. Therefore, in general, it is desirable to use a high temperature solder having a solidus temperature of at least 240° C. or more even for the solder used for internal bonding of an electronic device etc.
As explained above, Pb is a metal essential for solder. Solder containing Pb is being used as the most effective solder after a long time in the process of bonding in electronic apparatuses. Its reliability has also been established. However, due to dumping etc. of electronic products using such solder in the natural world, the Pb contained in the solder gradually leaches out and is liable to lead to Pb pollution of the ground water.
Therefore, instead of the above Pb-containing Pb—Sn eutectic solder or close to eutectic solder, demand is rising for the development of Pb-free solder (lead-free solder). As such lead-free solder, Sn—Ag, Sn—Zn, and Sn—Bi solders are promising, but the liquid temperatures of these solders are 10° C. to 20° C. higher than the liquid temperatures of the solders currently being used in connection of circuit boards etc. and electronic devices.
The general reflow temperature at the time of soldering is expected to be in the range from 230° C. to 260° C. Accordingly, it becomes necessary to use high temperature lead-free solder which will not melt or will be difficult to melt (that is, has reflow resistance) even at such a reflow temperature.
Further, solders having performances equal to those of a Pb-system solder in the point of the tensile strength, load resistance, and other mechanical strength properties of the soldered parts between the terminal electrodes and external electrodes of the electronic device after soldering are also being demanded.
When generally soldering composite multilayer capacitors, circuit modules, and other electronic devices, high temperature solder is often used, but for example a medium-high temperature lead-free solder having a solidus temperature of at least 200° C. sufficient in bond strength etc. has not been obtained.
That is, soldering of a conventional electronic device and external terminals is bonding by a melting reaction at the outside (electronic device side) of the nickel plating formed for the solder heat resistance of the external terminals. Therefore, the bond strength between the electronic device and external terminals was not sufficient and there were problems in mounting.
SUMMARY OF THE INVENTION
A first object of the present invention is to provide an electronic device with external terminals superior in the tensile strength, load resistance, and other mechanical strength properties of the soldered parts, superior in reflow resistance as well, and free from concern over environmental pollution, and a method of production of the same.
A second object of the present invention is to provide an electronic device with external terminals having a large tensile strength, that is, bond strength, between the terminal electrodes and external terminals, superior in reflow, and not containing lead and therefore completely environmentally friendly.
To achieve the above objects, according to a first aspect of the present invention, there is provided an electronic device with external terminals having terminal electrodes and external terminals of the electronic device body electrically bonded through solder layers, wherein said solder layers are comprised of an Sn—Sb high temperature lead-free solder, the ratio of Sn and Sb in the solder layers being, by weight percent, within a range of Sn/Sb=70/30 to 90/10, and said solder layers and terminal electrodes are formed between them with diffusion layers formed by diffusion of the conductive ingredients of said terminal electrodes to the solder layers.
According to the first aspect of the present invention, since the metal composition of the solder layers is an Sn—Sb system, no lead is contained and there is no concern over environmental pollution. Further, since the metal composition of the solder layers is, by ratio of weight percent, Sn/Sb=70/30 to 90/10 and the conductive ingredients of the terminal electrodes of the electron
Kamiya Takashi
Kikuchi Hiromi
Kikuchi Kazuhiko
Yoshii Akitoshi
Lam Cathy
TDK Corporation
LandOfFree
Electronic device with external terminals and method of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electronic device with external terminals and method of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electronic device with external terminals and method of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3214104