Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
2001-10-26
2003-09-02
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of metal
C428S698000, C428S704000, C438S718000, C257S703000, C257S705000
Reexamination Certificate
active
06613443
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to a silicon nitride ceramic substrate, silicon nitride circuit board using the substrate and a method of manufacturing the substrate, and more particularly to a silicon nitride ceramic substrate and a method of manufacturing the same, capable of effectively suppressing a generation of leak current when the above silicon nitride ceramic substrate is assembled into various power modules and circuit boards, and capable of greatly improving insulating property and operative reliability of power modules in which output power and capacity are greatly increased.
2. Description of the Related Art
A ceramic sintered body containing silicon nitride as a main component has an excellent heat resistance in a high temperature environment of 1000° C. or more, and has excellent thermal-shock resistance because of its low thermal expansion coefficient. For this reason, as a structural material for high temperature which can be replaced with a conventional heat resistant super alloy, the ceramic sintered body is tried to be applied to various refractory heat-resistant parts such as gas turbine parts, engine parts, or mechanical parts for making steel. In addition, since the ceramic sintered body has high corrosion resistance to a metal, the ceramic sintered body is tried to be applied as a melt-resisting material for a molten metal. Since the ceramic sintered body has high abrasion resistance, the ceramic sintered body is also tried to be actually applied to a sliding member such as a bearing or a cutting tool.
Various sintering compositions for silicon nitride ceramic sintered bodies are known: such as silicon nitride/yttrium oxide/aluminum oxide system; silicon nitride/yttrium oxide/aluminum oxide/aluminum nitride system; and silicon nitride/yttrium oxide/aluminum oxide/oxide of titanium, magnesium or zirconium system.
The oxides of rare earth elements, such as yttrium oxide (Y
2
O
3
) in the sintering compositions listed above, have been widely used as sintering assistant agents. Such rare earth element oxides enhance the sintering characteristics of sintering materials and, therefore, achieve high density and high strength of the sintered bodies.
According to the conventional art, silicon nitride sintered bodies are generally mass-produced as follows. After a sintering assistant agent as mentioned above is added to the powder of silicon nitride, the material mixture is molded to form a compact by press-molding the mixture under a molding pressure of 80-100 MPa, or by molding the material mixture in accordance with an extrusion method or a Doctor-Blade method. Then, the compact is sintered in a sintering furnace at about 1600-1900° C. for a predetermined period of time followed by naturally cooling (self-cooling) the resultant sintered body in the furnace at a high cooling rate.
However, when various power modules were manufactured in such a manner that the silicon nitride sintered body prepared through the above conventional method was used as a ceramic substrate and a metal circuit plate was bonded to a surface of the ceramic substrate and a semiconductor chip was mounted on the metal circuit plate, since an electrical insulating property of the ceramic substrate was low and a dielectric loss became large, it was difficult to obtain a power module having a high reliability. Further, this tendency has been more remarkable in recent years in accordance with advance of the output power level and a degree of integration of the semiconductor element.
More concretely to say, when various power modules each having a high output power and a large capacity are formed by using the above silicon nitride ceramic substrates, the electrical insulating property between the front and rear surfaces of the ceramic substrate is disadvantageously lowered whereby a leak current is liable to be generated. Further, when the above leak current exceeds a predetermined value, a current flowing in the metal circuit plate leaks to another metal circuit through the ceramic substrate. Therefore, although the metal circuit plates are not electrically connected, the leak current flows to another metal circuit plate, so that there has been posed a problem to cause bad influences such that the semiconductor element takes place malfunction and the leak current damages parts constituting the various power modules.
Further, although the silicon nitride sintered body produced by the conventional method achieves high mechanical strengths such as toughness, the thermal conductivities thereof are significantly lower than those of aluminum nitride (AIN) sintered bodies, beryllium oxide (BeO) sintered bodies or silicon carbide (SiC) sintered bodies. Therefore, conventional silicon nitride sintered bodies are unsuitable for electronic materials, such as ceramic substrate for mounting semiconductor, that needs good heat-radiating characteristics. Accordingly, the use of silicon nitride sintered body is thus limited.
On the other hand, aluminum nitride sintered bodies have high thermal conductivity and low thermal expansion coefficient, compared with other ceramic sintered bodies. Therefore, aluminum nitride sintered bodies have been widely used as packaging materials or materials of circuit boards for semiconductor chips, which have been progressively improved in operational speed, output power, variety of functions and size. However, no conventional aluminum nitride sintered bodies achieve sufficiently high mechanical strengths. Therefore, there is a growing need and technical requirement for a ceramic sintered body having both high thermal conductivity and high strength.
To cope with the growing need described above, the inventor of this invention had developed a silicon nitride sintered body which is excellent in both mechanical strength and thermal conductivity. However, in the conventional silicon nitride sintered body, there was posed a problem such that a size of a pore existing in crystal grain boundary phase was liable to be large so as to provide a diameter of about 1 &mgr;m. Then, when a voltage is applied to the sintered body, there is posed a problem that the leak current is liable to cause via the pore portion. Accordingly, in such sintered body, there is posed a problem that the electrical insulating property is disadvantageously lowered, so that the sintered body cannot be sufficiently available as a substrate for mounting a semiconductor chip.
That is, when various power modules were manufactured in such a manner that the silicon nitride sintered body prepared through the above conventional method was used as a ceramic substrate and a metal circuit plate was bonded to a surface of the ceramic substrate and a semiconductor chip was mounted on the metal circuit plate, since an electrical insulating property of the ceramic substrate was low and a dielectric loss became large, it was difficult to obtain a power module having a high reliability. Further, this tendency has been more remarkable in recent years in accordance with advance of the output power level and a degree of integration of the semiconductor element.
More concretely to say, when various power modules each having a high output power and a large capacity are formed by using the above silicon nitride ceramic substrates, the electrical insulating property between the front and rear surfaces of the ceramic substrate is disadvantageously lowered whereby a leak current is liable to be generated. Further, when the above leak current exceeds a predetermined value, a current flowing in the metal circuit plate leaks to another metal circuit through the ceramic substrate. Therefore, although the metal circuit plates are not electrically connected, the leak current flows to another metal circuit plate, so that there has been posed a problem to cause bad influences such that the semiconductor element takes place malfunction and the leak current damages parts constituting the various power modules.
SUMMARY OF THE INVENTION
The present invention had been achieved for solving t
Komatsu Michiyasu
Naba Takayuki
Yamaguchi Haruhiko
Yamaguchi Hideki
Jones Deborah
Kabushiki Kaisha Toshiba
Koppikar Vivek
LandOfFree
Silicon nitride ceramic substrate, silicon nitride ceramic... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Silicon nitride ceramic substrate, silicon nitride ceramic..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Silicon nitride ceramic substrate, silicon nitride ceramic... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3096325