Cutters – for shaping – Comprising tool of specific chemical composition
Reexamination Certificate
2000-02-04
2002-08-13
Tsai, Henry (Department: 3722)
Cutters, for shaping
Comprising tool of specific chemical composition
C407S118000, C264S642000, C501S102000
Reexamination Certificate
active
06431800
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns an edged ceramic member, and a manufacturing method thereof, a punch used for lead frames and a method of manufacturing lead frames.
2 Discussion of the Prior Art
Since zirconia series ceramics can develop toughness not found in usual ceramics, as a result of a stress relaxation mechanism based on stress-induced transformation of a partially stabilized zirconia phase, their application has made progress, for example, in molds or tools used for shearing such as punching or cutting or deep drawing, as well as in cutlery such as scissors or cooking knives.
Further, since such zirconia series ceramics can be improved in various characteristics inherent to zirconia and can be provided with new characteristics by compositing an appropriate second phase to the partially stabilized zirconia phase, more extended application uses are possible. For example, Japanese Patent Laid-Open No. 275977/1992 discloses a technique capable of increasing the flexural strength by a factor of two or more by incorporation of 20% by weight of alumina to zirconia. Further, Japanese Patent Laid-Open 221358/1997 discloses a technique for enabling electric spark discharge machining by incorporating electroconductive particles.
However, although improvement for various characteristics and provision of new characteristics are possible for the zirconia ceramic type ceramic members as described above at the laboratory level, troubles are often caused in the stage of developing them into actual products. Particularly, in those parts concerning molds requiring sharp edges (punches or dies), even ceramics of excellent flexural strength or hardness can not be used as parts for molds if edge portions are chipped, because they cause errors in the dimensional accuracy of products or form burrs, warps or flaws (marks) to works.
For example, lead frames used for the mounting of substrates of integrated circuit chips such as IC or LSI generally have shapes in which a plurality of leads corresponding to chip terminals of integrated circuits are arranged in complicated manners. While such lead frames were manufactured by chemical etching of metal plate blanks, an efficient manufacturing method by using punching has been adopted mainly in recent years along with a remarkable progress in mechanical working techniques. However, as can be seen from the fact that the etching was used, punching patterns for lead frames are extremely fine and even slight dimensional error or occurrence of burrs or warps results in a problem that directly leads to defects fatal to electric circuit parts such as contact failure with integrated circuit chips to be mounted and short-circuits. Accordingly, upon punching lead frames, higher dimensional accuracy is required for punched openings or finishing accuracy than that for other punched parts. Then, particularly accurate and sharp edge finishing are demanded for mold parts used for punching of such lead frames, particularly, for the edge of a top end surface of a punch that shears a metal blank plate between the edge and the inner edge of a die hole in a punching die, since even slight chipping or disturbance gives a direct effect on the accuracy of forming the punched openings.
In the case of a ceramic member requiring a sharp edge such as the punch or the die for use in the mold as described above, it is necessary to finally apply edge finishing by accurate grinding. However, in a case of existing zirconia series ceramics, there is a problem that such edge grinding tends to cause chipping at the edge portion. Therefore, a method of sacrificing the sharpness at the edge portion to some extent has been adopted for avoiding the occurrence of large chipping but this can not attain favorable working accuracy. However, if sharp edge finishing is performed excessively, chipping becomes significant making it sometimes impossible for the manufacture of products.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an edged ceramic member and a manufacturing method thereof capable of effectively suppressing. the occurrence of chipping and, as a result, finishing the edge portion to such a sharpness as can not be attained so far and, thus, capable of remarkably improving the accuracy of working such as punching by using the same, as well as a punch for manufacturing lead frames capable of punching the lead frames at an extremely high accuracy and a method of manufacturing lead frames by using the ceramic member described above.
For achieving the foregoing object, the edged ceramic member according to the present invention is characterized by comprising a zirconia-containing ceramic material containing 20% by volume or more of a zirconia series ceramic phase mainly composed of a zirconium oxide, in which
the zirconia-containing ceramic material satisfies:
KC
/(
d
A
)≧5 (1)
by using an exponential value A set within a range from −0.41 to −0.37, d being an average grain size (unit: &mgr;m) and KC being a fracture toughness value (unit: MPa·m
½
) thereof, and
one or more of edged portions each present in the form of a ridge at an intersection between two edge forming surface are formed to the outer surface of the member, and at least one of the edge portions is formed as a sharp edge portion having a width for the edge top end of 0.15 mm or less present on a cross section taken along an arbitrary plane in perpendicular to the direction of the ridge.
In the present invention, the average grain size d of the zirconia-containing ceramic material means a value obtained by mirror-finishing the surface of a material by surface grinding and lapping, thermally etching the same in a nitrogen atmosphere under a normal pressure at 1300° C. conducing SEM observation (magnification: 5000×), and determining on an observed image as explained below. That is, crystal grains appearing on an observed image are approximated as a circles and the diameter distribution of them is determined and, further, a crystal grain size distribution is determined while approximating them as spheres by applying the Schwarts-Saltykov method (assuming the range for the grain size group as 0.1 &mgr;m), and the central value for the grain size group at which the cumulative frequency from the side of the smaller grain size reaches 50% is defined as the average grain size d. Further, the fracture toughness value means a value measured by the SEPB method in accordance with JIS:R1607.
Since chipping tends to be formed in the zirconia-containing ceramics as described above, it has been considered impossible to form a sharp edge portion with a top end width for the edge of 0.15 mm or less by usual grinding. However, as a result of an earnest study by the present inventor, it has been unexpectedly found that occurrence of chipping can be prevented extremely effectively even when the sharp edge as described above is formed and the present invention has been accomplished. That is, in the edged ceramic member of the invention, an edged ceramic member with excellent chipping resistance can be obtained when the zirconia series ceramic phase of the composition described above is contained and when the value B defined by:
KC
/(
d
A
)= B (2)
is 5 or more with the exponential value A being defined within a range from −0.41 to −0.37.
As a result, the accuracy for punching or the like by using the member can be improved remarkably.
When the exponential value A is out of the range from −0.41 to −0.37, the value B according to the formula (2) no more indicates the difficulty or easiness for the occurrence of chipping of the zirconia-containing ceramic material and it loses a meaning as an index representing the chipping resistance. Further, it is essential that the value B is 5 or more, and a greater value is more advantageous in view of ensuring the chipping resistance. However, since it is difficult to set the crystal grain size in the zirconia series ceramic phase to 0.1 &mgr;m or
NGK Spark Plug Co. Ltd.
Sughrue & Mion, PLLC
Tsai Henry
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