Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Of specified material other than unalloyed aluminum
Reexamination Certificate
2000-12-06
2003-08-05
Potter, Roy (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Of specified material other than unalloyed aluminum
C257S741000
Reexamination Certificate
active
06603205
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to materials for electronic components and, more specifically, to materials for electronic components providing connecting portions to be electrically connected to a substrate, a signal line or the like, by soldering. The present invention further relates to the method of connecting such materials for electronic components. The present invention further relates to ball grid array type electronic components and the method of connecting the ball grid array type electronic components.
2. Description of the Background Art
A contact pin, as one of the materials for the electronic components of this type is sometimes electrically connected to a signal line by soldering, in order to improve wettability (solderability) of the contact pin. When electrical connection with the signal line is to be established by soldering of the contact pin, gold plating or palladium plating is used where very severe contact resistance is required. As the gold plating or platinum plating is expensive, however, silver plating, tin plating or the like is sometimes used for the surface of the contact pin.
The tin plating mentioned above has a problem that because of aging of the plated surface, tin crystals grow, resulting in generation of needle-like or dendrite texture (hereinafter referred to as whiskers) on the surface.
When the whiskers are generated, the tin plated surface becomes very coarse, increasing contact resistance of a contact or a terminal, or electrode terminals come to be in contact with each other, degrading durability and reliability. Therefore, generation of the whiskers must be prevented.
As one of the methods to prevent generation of the whiskers, a method is known in which solder plating is used in place of the tin plating. In addition, in order to improve wettability (solderability) of the contact pin, a technique has been known, as one of the techniques of solder plating, in which a solder of tin-lead is plated on the surface of the contact pin. Lead, however, is toxic, and therefor, a contact pin that is surface-finished without using lead is desirable, because of environmental concerns.
For solder plating not using lead, various solders such as tin-silver solder and tin-zinc solder have been developed. As one of such solder platings, a technique of plating tin-copper solder on a surface of the contact pin has been known.
The tin-copper solder, however, plate finish, especially gloss finish, tends to be inferior as compared with the conventional tin-lead solder.
Further, the plating is prone to oxidation and aging while the electric or electronic components with tin-copper solder plate coatings are in storage, resulting in unsatisfactory solderability at the time of subsequent flow or reflow soldering.
Recently, electronic equipments such as portable telephones, personal computers and the like have been much reduced in size and weight while they come to have higher functions and higher performances, and such improvements are largely dependent on the reduction in size and improvement of performances of ICs. Reduction in size and improvement of functions of the ICs necessarily required increase in number and narrower pitches between input/output terminals of the IC chip. As to the manner of mounting the ICs, conventionally, dual-in line-package and quad-flat-package using lead frames have been dominant. In these methods of mounting, however, electrode arrangement is provided at a periphery of the structure, and hence electrodes can be drawn out only from the periphery of the IC. Accordingly, increase in number and narrowing of pitches of the input/output pins have been limited. In view of the foregoing, a ball grid array type electronic component has been attracting attention. According to this method of mounting, solder balls are arranged in a matrix, and therefor it is possible to draw out electrodes using a surface of the IC, which is advantageous to increase the number of input/output terminals and to reduce the size.
A solder ball as an electrode portion is sometimes formed of a tin-lead alloy. The solder ball formed of the tin-lead alloy sometimes exhibit poor wettability with the counterpart of soldering, and in that case, a relatively strong flux is used. When a relatively strong flux is used, however, electric conductivity between the solder ball and the counterpart may possibly be hindered. Accordingly, washing by a washing agent containing fron (chlorofluorocarbon), for example, becomes necessary to remove the flux. As is well known, fron is environmentally problematic.
Further, in the solder ball as electrode portion formed of a tin-lead alloy, lead is toxic, and therefor, use of lead is undesirable in view of environment. When a tin-copper alloy or a tin-silver alloy is used for the solder ball as the electrode portion, in order to avoid lead, solder wettability may be inferior to the solder ball formed of tin-lead.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the above described problems, and to provide material for electronic components that maintains good solder wettability, prevents degradation in solderability and appearance, and prevents generation of whiskers. Further, the present invention provides a method of connecting a material for electronic components that enables connection of such a material for an electronic component with other components with good wettability. Further, the present invention provides a ball grid array type electronic component that enables connection of solder balls with good wettability and a method of connecting the ball grid array type electronic component.
The above described objects can be attained by the present invention in the following manner.
According to an aspect, the present invention provides a material for an electronic component, having a plating layer A formed of a metal X and a metal Y mixed with each other, on a metal material as a base material, and a coating layer B formed of the metal X, on the plating layer A.
According to another aspect of the present invention, the metal X is tin, and the metal Y is selected from a group consisting of silver, copper, zinc, bismuth and indium.
According to a still further aspect, the present invention provides a material for an electronic component having a plating layer A containing tin and at least one of silver, copper, zinc, bismuth and indium, formed on a metal material as a base material, and a coating layer B formed of tin, on the plating layer A.
According to a still further aspect, the present invention provides the material for an electronic component wherein the coating layer B has a thickness of 0.05 to 1.0 &mgr;m.
According to a still further aspect, the present invention provides a method of electrically connecting a material of an electronic component, having a plating layer A formed of a metal X and a metal Y mixed with each other, on a metal material as a base material, and a coating layer B formed of the metal X on the plating layer A, with another component, including the steps of: soldering the material for the electronic component with the solder mainly consisting of the metal X, and moving an oxide of the metal X existing at a surface of the coating layer B by the heat of soldering, to expose unoxidized metal X.
According to a still further aspect, the present invention provides a method of electrically connecting a material of an electronic component with another component, the electronic component having a plating layer A formed of a metal X and a metal Y mixed with each other, on a metal material as a base material, and a coating layer B formed of the metal X on the plating layer A, wherein the metal X is tin and the metal Y is silver, copper, zinc, bismuth or indium, the method including the steps of: soldering the material for the electronic component with the solder mainly consisting of the metal X, and moving an oxide of the metal X existing at a surface of the coating layer B by the heat of soldering, to expose unoxidized metal X.
Accordin
Birch Stewart Kolasch & Birch, LLP.
FCM Co., Ltd.
Potter Roy
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