Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Die bond
Reexamination Certificate
2002-02-27
2003-05-13
Flynn, Nathan J. (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Die bond
C257S783000, C257S771000, C257S772000, C438S118000, C438S612000
Reexamination Certificate
active
06563225
ABSTRACT:
BACKGROUND OF THE INVENTION
Conventionally, Sn—Pb alloy solders have made it possible to perform temperature-hierarchical bonding in which first soldering is performed at a temperature of about 330° C. by use of a high-temperature solder such as Pb-rich Pb-5 mass % Sn (hereinafter the indication of “mass %” is omitted and only numerals are recited) solders (melting point: 314-310° C.) or Pb-10Sn solders (melting point: 302-275° C.) and in which second bonding is then performed by use of a low-melting point solder of Sn-37Pb eutectic (melting point: 183° C.) without melting the first soldered portions. These solders are soft and rich in deformability and, therefore, they can be used for bonding Si chips etc. apt to be broken to a substrate having a different thermal expansion coefficient and also for structural purposes. This temperature-hierarchical bonding is mainly adopted in semiconductor devices in which chips are die-bonded and in semiconductor devices in which chips are flip-chip-bonded such as BGA and CSP etc. In other words, this means that a solder used within a semiconductor device and another solder for bonding the semiconductor device itself to a substrate are used for the temperature-hierarchical bonding. On the other hand, the temperature-hierarchical bonding is used also for bonding power modules etc. used at high temperatures.
SUMMARY OF THE INVENTION
The present invention relates to a Zn—Al alloy solder and a product in which this solder is used. More particularly, the invention relates to a Pb-free solder which makes it possible to perform temperature-hierarchical bonding on the high-temperature side relative to, for example, an Sn—Ag—Cu alloy Pb-free solder and which is a thermal-fatigue-resistant solder excellent in rolling workability, and a product in which the solder is used, such as, for example, a semiconductor device and a semiconductor module.
At present, Pb-free design is prevailing in all fields.
As Pb-free solders, Sn—Ag eutectic solders (melting point: 221° C.), Sn—Ag—Cu eutectic solders (melting point: 221-217° C.) and Sn—Cu eutectic solders (melting point: 227° C.) come to be used. Although it is desirable that soldering temperatures in surface mounting be low in view of the heat resistance of parts, it is necessary to ensure wettability in order to keep the reliability and, for this reason, actual soldering temperatures in the case of the Sn—Ag—Cu eutectic solders capable of bonding at the lowest temperatures among Pb-free solders are about 235 to 250° C. maximum in consideration of temperature variations within a substrate even if a furnace excellent in controlling for even temperature distribution is used. Therefore, solders capable of withstanding this soldering temperature range are required to have a melting point not less than 260° C. At present, there is no soft Pb-free solder for a temperature hierarchical bonding on the high-temperature side which solder can be used in combination with these solders of the low temperature side. As a composition which seems most appropriate for the high temperature side, there is a Sn-5Sb alloy solder (melting point: 240-232° C.). However, because the solder melts at the high temperature range, they cannot be used in the temperature-hierarchical bonding.
Further, although an Au-20Sn solder (melting point: 280° C.) is known as a high-temperature solder, its use is limited to a narrow range because it is a hard material and its cost is high. Especially, in bonding an Si chip to a material having a different coefficient of thermal expansion or in bonding a large-size Si chip, this Au-20Sn solder is not used because there occurs such a fear as the Si chips are broken due to the high hardness of this solder.
In the invention, there are proposed a material, a system and a structure which are suitable for large-area bonding, for example, Si die-bonding and power module bonding. In the large-area bonding are required soft solder joints which have a thermal fatigue-resisting property and which are free from voids. In addition, it is also required that flux-less bonding be possible when forming these joints.
The object of the invention is to provide a new solder by improving and modifying Zn—Al alloy solders which new solder is used as the solder of the high-temperature side. This solder is intended to be used not only in the field of electronic devices, but also in the general structural field.
Representative features of the invention for achieving the object are recited below.
According to the first aspect of the invention, there is provided an electronic device comprising at least one electronic part and a substrate on which the electronic part is mounted, the electronic part and the substrate being bonded to each other by joints comprising Al particles and an Al—Mg—Ge—Zn alloy, and the Al particles being connected to each other by the Al—Mg—Ge—Zn alloy.
According to the second aspect of the invention, there is provided a semiconductor device in which each of pads of the semiconductor chip and each of leads of a substrate on which the semiconductor chip is mounted are electrically connected by a gold wire, the semiconductor chip and the substrate being bonded by solder joints each comprising Al particles and an Al—Mg—Ge—Zn alloy.
According to the third aspect of the invention, there is provided a semiconductor device in which each of pads of the semiconductor chip and each of leads of a substrate on which the semiconductor chip is mounted are electrically connected by a gold wire, the semiconductor chip and the substrate being bonded by solder joints each comprising Cu particles and an Al—Mg—Ge—Zn alloy.
In the semiconductor device, the surfaces of the Al particles may be plated with at least one kind selected from the group consisting of Ni, Cu, Ag, Sn and Au.
Also, in the semiconductor device, the surfaces of the Cu particles may plated with at least one kind selected from the group consisting of Ni, Cu, Ag, Sn and Au.
In the semiconductor device, each of the solder joints may include plastic particles.
In the semiconductor device, the material for the plastic particles may be made of at least one resin selected from the group consisting of polyimide, heat-resistant epoxy, silicone, various types of polymer beads, modified types of these materials and a mixture of these.
Further, in the semiconductor device, each of the solder joints may have Sn and/or In particles in addition to the Al particles. This results in a reduction in the coefficient of thermal expansion of a solder.
Further, in the semiconductor device, each of the solder joints may have Sn and/or In particles in addition to the Cu particles. This results in a reduction in the coefficient of thermal expansion of a solder.
In the semiconductor device, each of the solder joints may include particles of at least one kind selected from the group consisting of invar, silica, alumina, AlN and SiC in addition to the Al particles. AlN is aluminum nitride which is known as a high-thermal conductivity ceramic. SiC is silicon carbide which is known similarly as a high-thermal conductivity ceramic.
Also, in the semiconductor device, each of the solder joints may include particles of at least one kind selected from the group consisting of invar, silica, alumina, AlN and SiC in addition to the Cu particles. This results in a reduction in the coefficient of thermal expansion of the solder.
In the semiconductor device, the Al—Mg—Ge—Zn alloy may consist, by mass, of 3 to 7% Al, 0.5 to 6% Mg, 1 to 5% Ge, and the balance Zn and incidental impurities.
In the semiconductor device, the Al—Mg—Ge—Zn alloy may include a 4Al-3Mg-4Ge—Zn alloy.
According to the fourth aspect of the invention, there is provided an electronic device such as, for example, a semiconductor module or a multi-chip module, in which the semiconductor device is mounted on another circuit board by use of a Pb-free solder (, that is, a solder which does not positively contain any lead) such as an Sn—Ag—Cu alloy solder and etc. In this case, temperature-hierarchical (, that is, high-temperature and low
Hata Hanae
Ishida Toshiharu
Miura Kazuma
Nakatsuka Tetsuya
Okamoto Masahide
Antonelli Terry Stout & Kraus LLP
Flynn Nathan J.
Greene Pershelle
Hitachi , Ltd.
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