Metal treatment – Stock
Reexamination Certificate
1997-10-14
2001-02-13
Ip, Sikyin (Department: 1742)
Metal treatment
Stock
C420S557000, C420S560000, C420S561000, C420S562000, C228S056300, C148S022000
Reexamination Certificate
active
06187114
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a lead-free high-temperature solder material that has excellent thermal fatigue properties and is environmentally-friendly. The solder material is specifically useful for die bonding electronic elements and for soldering of heat-generating parts for a hybrid IC as well as other uses. This invention also relates to electronic parts using the same.
BACKGROUND OF THE INVENTION
Lead-free solder has been much more required recently due to problems such as waste disposal of electronic devices and for protecting the environment.
On the other hand, Pb—Sn based solder is generally used for soldering electronic parts. Pb—Sn based solder has good connectability, and thus the melting point can be selected in a wide range by controlling the ratio. In such solders, 63 wt % Sn—Pb eutectic solder generally has been used since it enables soldering of electronic parts at a lower temperature with less thermal influence on the electronic parts since its melting point is only 183° C.
During a process for installing electronic parts, the soldered portion may be heated once again in an installed electronic part. For example, in a process for manufacturing a semiconductor device, the die is heated after the semiconductor element chip is soldered to a lead frame (e.g. a die) for wire-bonding. In a hybrid IC where electronic parts are installed on both surfaces of a printed circuit board, one side is provided with electronic parts and soldered after the other side is treated likewise. The electronic elements will be heated also by their own heat even after the installation.
In order to avoid the above-mentioned problems, the first soldering materials are required to have a higher liquidus temperature, so that the first-bonded parts will not fall out during a second heating. Such a high temperature soldering material should have a liquidus temperature ranging from 200 to 350° C.
Unexamined Published Japanese Patent Application No. 61-156823 discloses a lead-free high-temperature solder material whose liquidus temperature ranges from 200 to 350° C. The Sn—Cu based material mainly comprises Sn to which small amount of Cu is added. Unexamined Published Japanese Patent Application No. 61-55774 discloses Sn—In based lead-free solder material and No. 62-163335 discloses Sn—Cu—Zn based material.
Unexamined Published Japanese Patent Application No. 6-685 discloses that metallic or insulator particles are added to a material to be die-bonded by pressure-adhering in order to control the thickness of the die bond material.
However, if the conventional lead-free high temperature solder materials such as Sn—Cu are used for die-bonding or soldering of heating parts such as a hybrid IC, the high temperature solder is cracked and the conduction is worsened after the electronic device is used for a long time. This is caused by thermal fatigue due to the heat cycle. Heat cycle means repeated temperature change, for example the inside of an electronic device being heated by its electronic parts when used, and the temperature returning to room temperature after that. As previously known, the conventional lead-free high temperature solder material is inferior in the thermal fatigue properties. Therefore, lead-containing high temperature solder has been widely used in order to improve thermal fatigue property. Some other conventional lead-free high temperature soldering materials are not good in soldering properties.
SUMMARY OF THE INVENTION
In order to solve these and other problems of the prior art, this invention aims to provide a lead-free high temperature solder material and an electronic part using the same. The composition of the solder material is substantially lead-free, and its liquidus temperature is from 200 to 350° C. The thermal fatigue property of the solder material is improved and the reliability of the electronic parts is raised. The solder material is environmentally-friendly.
Another object of this invention is to solve the problem of partial distribution of composition and reduce the graded junction caused by the difference in specific gravity of the elements in the solder material composition, so that problems such as increased heat resistance and deteriorated reliability can be avoided when electric parts and substrates are die-bonded via solder materials.
In order to achieve such aims, a first solder material of this invention comprises 0.005-3.0 wt % of palladium (Pd) and 97.0-99.995 wt % of tin (Sn), and its liquidus temperature ranges from 200 to 350° C.
A second solder material of this invention comprises 0.005-3.0 wt % of at least one of palladium and germanium (Ge), the total amount of which is at most 5.0 wt %, and the solder material comprises 95.0-99.995 wt % of tin.
The first solder material preferably contains 0.005-2.0 wt % of at least one element selected from the group consisting of Ag, Ge, P, Zn, Cu, B, Sb, Bi, and In in place of a portion of Pd and/or Sn.
The second solder material preferably contains 0.005-2.0 wt % of at least one element selected from the group consisting of Ag, P, Zn, Cu, B, Sb, Bi, and In in place of a portion of at least one element selected from the group consisting of Pd, Sn and Ge.
It is also preferable that the first solder material contains 0.001-5.0 wt % of metallic or alloy particles in place of a portion of Pd and/or Sn.
It is also preferable that the second solder material contains 0.001-5.0 wt % of metallic or alloy particles in place of a portion of at least one element selected from the group consisting of Pd, Sn and Ge.
It is further preferable that the specific gravity of the metallic or alloy particles is within plus or minus 2 of the specific gravity of Sn (7.28).
It is preferable that the metallic or alloy particles are selected from the group consisting of oxides, carbides, nitrides, alloys and metals that are selected from the group consisting of Cu, Ni and Fe.
It is preferable that the average particle diameter of the metallic or alloy particles ranges from 5 to 100 &mgr;m.
It is preferable that the average particle diameter ranges from 20 to 60 &mgr;m.
It is preferable that the melting point of the metallic or alloy particles is at least 400° C.
It is preferable that the purity of Sn in the material is at least 99.9 wt %.
It is preferable that the material is substantially lead-free, namely, the amount of lead is reduced to a trace as an inevitable impurity.
A first electronic part of this invention is formed by bonding a substrate and an electronic element, by using a solder material that comprises 0.005-3.0 wt % of palladium and 97.0-99.995 wt % of tin. The liquidus temperature of the solder material is from 200 to 350° C.
A second electronic part of this invention is formed by bonding a substrate and an electronic element by using a solder material that comprises 0.005-3.0 wt % of palladium and/or germanium, the total amount of which is at most 5.0 wt %, and the material comprises 95.0-99.995 wt % of tin.
It is preferable that the first electronic part contains 0.005-2.0 wt % of at least one element selected from the group consisting of Ag, Ge, P, Zn, Cu, B, Sb, Bi, and In in place of a portion of Pd and/or Sn.
It is preferable that the second electronic part contains 0.005-2.0 wt % of at least one element selected from the group consisting of Ag, P, Zn, Cu, B, Sb, Bi, and In in place of a portion of at least one element selected from the group consisting of Pd, Sn and Ge.
It is also preferable in the first electronic part that the first and second electronic parts materials contain 0.001-5.0 wt % of metallic or alloy particles in place of a portion of Pd and/or Sn.
It is also preferable in the second electronic part that the first and second electronic parts materials contain 0.001-5.0 wt % of metallic or alloy particles in place of a portion of at least one element selected from the group consisting of Pd, Sn and Ge.
It is further preferable in the first and second electronic parts that the specific gravity of the metallic or alloy particles is within plus or minus 2 of the specific gravit
Aoi Kazuhiro
Arikawa Takatoshi
Ogashiwa Toshinori
Sawada Yoshiharu
Yokozawa Masami
Ip Sikyin
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
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