Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Bump leads
Reexamination Certificate
2002-06-24
2004-07-27
Nelms, David (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Bump leads
C257S772000, C438S689000
Reexamination Certificate
active
06768197
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a curable flux, a resist for soldering, a semiconductor package reinforced with the curable flux, a semiconductor device reinforced with the curable flux and processes for producing the semiconductor package and the semiconductor device. More particularly, the present invention relates to a curable flux which works as a flux during bonding of solder balls to a semiconductor package and bonding of the semiconductor package to a printed circuit board with solder and reinforces the soldered portion after being cured by heating after the soldering, a semiconductor package and a semiconductor device reinforced with the curable flux and processes for producing the semiconductor package and the semiconductor device.
BACKGROUND ART
As the electronic instruments are recently exhibiting higher functions and having lighter weights and smaller sizes, electronic members are more highly integrated and mounted in the instruments in a higher density. Semiconductor packages are becoming smaller and having a greater number of pins.
Since semiconductor packages of the conventional form using lead frames are approaching the limit of improvement, novel forms of packages of the area mounting type such as the ball grid array (BGA) and the chip scale package (CSP) are proposed as the package having chips mounted on a circuit substrate. In the semiconductor packages, various methods such as the tape automated bonding (TAB) method and the flip chip (FC) method are practically used as the method for electrically connecting electrodes of a semiconductor chip with terminals of a substrate which is constituted with various types of insulating materials such as plastics and ceramics and electrically conductive wiring, i.e., a substrate called a printed circuit board. Recently, many structures of BGA and CSP using the FC method are proposed since these structures are advantageous for decreasing the size of the semiconductor package.
For mounting BGA and CSP to a printed circuit board, soldering using a bump formed by solder balls is used. For the soldering, a flux is used and a solder paste is used occasionally in combination. In particular, the solder ball is used because the amount of supplied solder can be easily controlled and a higher bump can be formed by supplying the solder ball in a greater amount. The soldering is frequently used for electric and mechanical bonding between electrodes of a semiconductor chip and terminals of a printed circuit board in the process for producing BGA and CSP.
In general, a flux for soldering is used in the soldering. By using the flux, foul substances such as oxides on the surface of a metal of an electrode faced to the surface of the solder are removed and the surface of the metal is prevented from being oxidized again during the soldering so that the surface tension of the solder is decreased and the melted solder can wet the surface of the metal easily. As the flux for soldering, heretofore, a flux prepared by adding an activator for removing oxide films to a thermoplastic resin-based flux such as rosin has been used.
However, when the flux is left remaining after the soldering, a problem arises in that electric insulation is adversely affected and corrosion of the printed wiring takes place due to melting of the thermoplastic resin and isolation of active ions in the activator in the condition of a high temperature and a high humidity. To overcome the problem, currently, the residual flux after the soldering is removed by washing. However, the washing has a drawback in that the detergent causes a problem in the environment and the cost increases due to the washing step.
As described above, the function of the flux is to remove oxides on the surfaces of the solder and the metal, to prevent the surface from being oxidized again and to improve the wetting property with the solder. When the flux is present and the surface of the metal is exposed, the entire portions of the surface are wetted with the solder without restriction. Therefore, in general, a solder resist is used on the surface of circuits in a semiconductor package or a printed circuit board so that the introduction of the solder is limited to the soldering portion and the pattern of the electrically conductive wiring pattern is protected. However, when the solder resist is left remaining in the soldering portion, problems arise in that the reliability of the bonding deteriorates and the bonding by the soldering fails. Therefore, the solder resist must be formed with a great care.
As the semiconductor package becomes smaller and has a greater number of pins, bumps become smaller and there is the possibility that the strength and the reliability of the bonded portion decrease. To increase the reliability of the portion bonded with bumps, it is studied that the portion bonded with bumps is sealed and reinforced by filling the gap between a semiconductor chip and a substrate with an insulating resin called an underfill. However, this method has a problem in that a step of filling the gap with the underfill and curing the under fill is necessary and this step requires a sophisticated technology. The production process becomes complicated and the cost increases.
The present invention has an object of providing a curable flux which works as a flux during bonding of solder balls to a semiconductor package and bonding of the semiconductor package to a printed circuit board with solder and reinforces the soldered portion after being cured by heating after the soldering, a semiconductor package reinforced with the curable flux, a semiconductor device reinforced with the curable flux and processes for producing the semiconductor package and the semiconductor device.
DISCLOSURE OF THE INVENTION
As the result of extensive studies by the present inventors to achieve the above object, it was found that, in the mounting of a semiconductor package, a composition comprising a resin having a phenolic hydroxyl group and a curing agent for the resin exhibited an excellent property as the flux for soldering, did not require removing the flux after the soldering and worked as a reinforcing material of a semiconductor device when the flux was cured by heating. The present invention has been completed based on this knowledge.
The present invention provides:
(1) A curable flux which works as a flux during soldering and as a reinforcing material for a soldered portion after being cured by heating;
(2) A curable flux described in (1), which comprises resin (A) having phenolic hydroxyl group and curing agent (B) for the resin;
(3) A curable flux described in (2), wherein resin (A) having phenolic hydroxyl group is a phenol novolak resin, an alkylphenol novolak resin, a polyhydric phenol novolak resin, a phenol aralkyl resin, a resol resin or a polyvinylphenol;
(4) A curable flux described in (3), wherein a polyhydric phenol constituting the polyhydric phenol novolak resin is catechol, resorcinol, hydroquinone, hydroxyhydroquinone or pyrogallol;
(5) A curable flux described in (2), wherein resin (A) having phenolic hydroxyl group has a softening point of 30 to 150° C.;
(6) A curable flux described in (2), wherein curing agent (B) is an epoxy compound or an isocyanate compound;
(7) A curable flux described in (2), which further comprises curable antioxidant (C);
(8) A curable flux described in (7), wherein curable antioxidant (C) is a compound having benzylidene structure;
(9) A curable flux described in (8), wherein the compound having benzylidene structure is a compound represented by general formula [1]:
wherein R
1
, R
3
and R
5
each independently represent hydrogen atom, hydroxyl group or carboxyl group, R
2
and R
4
each independently represent hydrogen atom or an alkyl group, R
6
and R
7
each independently represent hydrogen atom, methyl group, hydroxyphenyl group or carboxyphenyl group;
(10) A curable flux described in (9), wherein the compound represented by general formula [1] is ethylidenediphenol or phenolphthalin;
(11) A curable flux described in (7)
Hosomi Takeshi
Nakamura Kensuke
Okada Ryouichi
Takahashi Toyosei
Nelms David
Nguyen Thinh T
Sumitomo Bakelite Company LTD
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