Alloys or metallic compositions – Copper base – Zinc containing
Reexamination Certificate
2001-05-21
2003-05-06
Ip, Sikyin (Department: 1742)
Alloys or metallic compositions
Copper base
Zinc containing
C148S434000
Reexamination Certificate
active
06558617
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention concerns a copper alloy for use in electric and electronic parts used, for example, in semiconductor lead frames, terminals, connectors and bus bars and, more in particular, it relates to a copper alloy available at a reduced cost and having a conductivity of 50% IACS or more while having high strength substantially comparable with that of 42 alloy, as well as having softening resistance, favorable shearing formability, bending formability, Ag plating property and soldering wettability.
2. Description of Related Art
As lead frames for use in semiconductors, ferreous materials represented by 42 alloys and cupreous materials such as Cu—Ni—Si series alloys, Cu—Sn series alloys, Cu—Cr series alloys, Cu—Fe—P series alloys have been used so far. The cupreous materials have higher conductivity compared with ferreous materials and, accordingly, have an advantageous feature of excellent heat dissipation. Further, since the recent trend of using Pd (palladium) for exterior plating of IC or LSI results in a problem of peeling due to aging deterioration of the plating in the ferreous materials, the cupreous materials has been used more and more. On the contrary, since the cupreous materials has low strength, various improvements have been made for enhancing the composition or in the manufacturing method for increasing strength. This was considered extremely important, particularly, in the past stage where LSI packages using lead frames represented by QFP (Quad Flat Package) in which the number of leads exceeds 200 pin were developed vigorously.
In recent years, area mounted type packages represented by BGA (Ball Grid Array) have been developed and most of LSIs exceeding 200 pin have now been replaced progressively with such packages. However, such area mounted type packages are not suitable in a situation where the heat generation amount of semiconductor chips is increasing along with increase in the degree of integration and operation speed of LSIs. Therefore, it is necessary to attach heat dissipating plates or heat spreaders for enhancing the heat dissipation which makes the packaging complicated.
As described above, a reasonable heat dissipation method is one of subjects in packages mounting chips of large heat generation amount and packages using the former lead frames have now been re-estimated. In the packages using the lead frames, most of heat is dissipated by way of paths the leads to the substrate.
In this case, high heat conductivity due to the material of the lead per se has an effect on the heat dissipation of the entire packaging. Since the heat conductivity is in a linear relationship with the electroconductivity, a material of high electroconductivity is demanded in other words. In this regard, the ferreous 42 alloy has an electroconductivity as low as 3% IACS but the cupreous materials have higher electroconductivity and are advantageous.
Accordingly, a cupreous material having not only general characteristic as the lead material but also strength comparable with that of 42 alloy is demanded. Thus, copper alloys such as Cu—Ni—Si series or Cu—Sn series alloys capable of providing high strength, or Cu—Cr series or Cu—Fe—P series alloys capable of providing high electroconductivity have been used.
As the method of overcoming such problems, copper alloys of high strength and high electroconductivity by improving Cu—Fe—P series alloys have been proposed, for example, in JP-A-Nos. 298679/1998, 298680/1998 and 199952/1999.
Since any of the alloys described above contains 0.5% or 0.3% or more of Fe and 0.1% or more of P, so-called internal oxidation tends to occur frequently upon heat treatment. The oxide layers extremely deteriorate the soldering wettability even when they are formed by such a slight thickness as can not be measured by instrumental analysis. In addition, since Mg is incorporated by 0.05% or more in JP-A-No. 199952/1999, it may be a worry of abnormal precipitation in Ag plating (hereinafter referred to as Ag plating protrusion).
A copper alloy as disclosed in JP-A-No. 54043/2000 has been proposed intending for high strength and high electroconductivity by incorporation of Ni, Fe and P. However, no consideration is made there on the softening resistance.
SUMMARY OF THE INVENTION
In view of the above, this invention intends to provide a copper alloy of high strength and high electroconductivity which is excellent in characteristics such as strength, electroconductivity and bending formability required as copper alloys for use in electric and electronic parts such as lead frames, terminals and connectors, as well as excellent in the characteristics such as softening resistance, shearing formability, plating property and soldering wettability by overcoming the foregoing problems.
A copper alloy for use in electric and electronic parts according to this invention comprises:
Ni: 0.1 to 1.0 mass %
Fe: 0.01 to 0.3 mass %
P: 0.03 to 0.2 mass %
Zn: 0.01 to 1.5 mass %
Si: 0.01 mass % or less and
Mg: 0.001 mass % or less, wherein
the relation for the Ni content, Fe content, P content and Si content satisfies the following relations simultaneously:
P content/Si content≧10
5≦(Ni content+Fe content)/P content≦7
4≦Ni content/Fe content≦9.
In the copper alloy described above, it is preferred to precipitate precipitates of Ni/Fe/P of (0.5 to 5)/(0.1 to 2)/1 at the mass ratio.
The copper alloy may comprises one or both of {circumflex over (1)} one or more of Co, Cr and Mn by 0.005 to 0.05% in total and {circumflex over (2)} one or more of Al, Sn, Zr, In, Ti, B, Ag and Be by 0.005 to 0.05% in total. Copper alloys containing the elements described above by less than the lower limit as inevitable impurity can of course be included in this invention.
It is preferred to restrict O: 100 ppm or less and H: 5 ppm or less among in the inevitable impurities.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The reasons for restricting the ingredients and conditions as described above are to be explained.
[Ni Content]
Ni precipitates an intermetallic compound together with P to be described later to enhance the strength of a copper alloy. Since the NiP compound is an not intermetallic compound stable at high temperature, it is poor in the softening resistance. However, the softening resistance is outstandingly improved while keeping the strength as it is by the incorporation of Fe to the Ni—P precipitates to form a ternary intermetallic compound. In addition, the shearing formability is also improved.
When the Ni content is less than 0.1%, since the precipitation amount of the intermetallic compound is small, desired high strength and shearing formability can not be obtained. On the other hand, when the Ni content exceeds 1.0%, a great amount of coarse precipitates of the Ni—P compound is formed during casting to extremely deteriorate the hot formability. The Ni—P compound deteriorates the hot formability particularly in a temperature region of 700 to 900° C. This temperature range is most required practically since hot working at high working rate is possible with a low energy because of the low transformation resistance. Further, even when the hot fabrication or working is possible below this temperature region, the remaining NiP compound scarcely contributes to the improvement of the strength and deteriorates the bending formability of products.
Accordingly, the Ni content is defined as 0.1 to 1.0%. A more preferred range is from 0.3 to 0.7%.
[Fe Content]
Fe causes both high strength and high softening resistance for the copper alloy by forming an intermetallic compound with Ni and P as described above. When the Fe content is less than 0.01%, the Ni—P compound can not be transformed into an Ni—Fe—P ternary compound and the copper alloy can not effectively satisfy the demand for high softening resistance required for lead frames, terminals and connectors. For coping with the recent requirement for reduction of thickness and size and improvement for the mounting density in various k
Ip Sikyin
Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel Ltd).
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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