Metal fusion bonding – Process – With protecting of work or filler or applying flux
Reexamination Certificate
2001-06-28
2003-08-05
Dunn, Tom (Department: 1725)
Metal fusion bonding
Process
With protecting of work or filler or applying flux
C228S056300
Reexamination Certificate
active
06601754
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of bonding metal, and more particularly, a method of connecting the wiring on two circuit boards.
BACKGROUND OF THE INVENTION
In Japanese unexamined patent application publication Heisei 8-330726, a method of connecting the metal wiring on two circuit boards is disclosed, in which board electrodes are bonded together by solder due to the fact that the oxide film formed on the surface of the solder is broken down by the dilation energy of a boiling hydrocarbon compound.
However, when using the dilation energy of a hydrocarbon compound, even if the oxide film on the metal surfaces of the solder fused can be broken down at the time of bonding, the oxide film on the surfaces of the base metal composing the board electrodes cannot be removed because this base metal will not be fused. Thus, when solder is applied to only one side of a board electrode, sufficient bonding strength cannot be obtained.
Presently, methods exist for using a press-bond connector which press-bonds and fixes two circuit boards and a method of using ACF (anisotropic conductive film). However, the method of using a press-bond connector does not prevent increased cost of the connector and an increased space for connection. The method of using the ACF, which is based on the point contact of conductive particles, does not prevent increased connection resistance and is also uncertain of the conductive reliability of the connecting section.
For dealing with this matter, there is disclosed a method of using insulating adhesive in JP-A No. S60-140896 referred to here as prior art 1, and a method of using conductive adhesive in JP-A No. H9-320662 referred to here as prior art 2.
However, both of the above-mentioned prior art references use adhesive and therefore take time for fixing regardless whether it is hot melt type or thermosetting adhesive. Therefore, these methods are not capable of bonding boards in a short time and necessitate much work for connection. Specifically, prior art 1 takes 20 seconds for heat-press-bonding of the connecting section.
Moreover, none of the prior art performs extremely low-cost bonding. Particularly, prior art 1 is designed to bond metallic lugs having a special shape which protrude from the printed circuit board, and therefore it is difficult to connect for low cost.
Moreover, insulating adhesive or thermoplastic resin used for bonding may flow into the terminal connecting section, resulting possibly in faulty conduction. The use of conductive adhesive can cause short-circuiting between adjacent terminals. Accordingly, none of the prior art references is sufficiently reliable for connection between terminals.
Also, flux that is an active compound is used to remove oxide on the surface in order to render the surface wettable to solder when metal is to be connected by soldering. The used flux is cleaned off after connecting heretofore, but cleaning has become unacceptable to the public because of environmental reasons. As such, the residual flux dissolves metal to yield ions, and results in poor insulation. However, no flux soldering results in insufficient reliability because of the adverse effect of oxide. To solve such problems, JP-A No. Hei 8-330726 discloses a method in which oxide film on the soldering surface is broken without using flux by utilizing volume expansion energy generated from boiling of hydrocarbon and substrate electrodes connected with solder. However, in this method, though oxide film on the metal surface of solder (that is fused for connection) is broken, mother metal of the substrate electrode is not fused. As such, the oxide film on the mother metal surface is not broken. Therefore, application of the method is limited.
SUMMARY OF THE INVENTION
Accordingly, the object of the present invention is to provide a method of bonding metal in which sufficient bonding strength can be obtained.
Another object of the present invention is to provide a method of connecting a printed circuit board and a flexible circuit board, the method being capable of connecting these members at low cost and in a short time, while having sufficient reliability.
It is another object of the present invention to provide a metal connecting composition for removing oxide film on the mother material surface without using flux for connection, to provide a highly reliable connection between mounted parts and substrates.
Accordingly, in a one aspect of the invention, a metal connecting composition is provided containing metal particles and hydrocarbon compound having C—H bonding dissociation energy of a value equal to or lower than 950 KJ/mol. When such metal connecting composition interposed between metals is heated, hydrocarbon compounds are thermally decomposed and hydrogen is separated from the hydrocarbon compound to form radicals. The hydrocarbon compound radical reduces oxide film formed on metal surface to be connected. As such, metals are connected together with interposition of the metal particles.
In another aspect of the invention, a hydrocarbon compound in which the energy of disassociation of the C—H bond is less than 950 kJ/mol is interposed between the connecting portion of the wiring on a first and a second circuit board. By heating the hydrocarbon compound, the hydrocarbon compound is decomposed and a radical is formed in which hydrogen has been separated from the hydrocarbon compound. Bonding occurs as the oxide film formed on the surface of the metal is reduced by this radical.
Here, the C—H bond disassociation energy Delta H, as shown in
FIG. 6
, is the energy necessary for the alkyl group and the hydrogen to disassociate while the hydrocarbon compound retains each of their electrons, and is calculated after the electron orbit of each compound is determined. In other words, the C—H bond disassociation energy Delta H of each compound is the ease in which alkyl groups and hydrogen on the hydrocarbon compound can be disassociated. The smaller this compound's energy is, the easier it is for alkyl groups and hydrogen to disassociate.
Then, as shown in
FIG. 6
, when the alkyl group and hydrogen disassociate while retaining each of their electrons, that alkyl group becomes a radical, takes away oxygen from copper oxide or the like, or in other words, reduces the copper oxide, and turns into a stable alkane oxide compound. In this way, sufficient bonding strength can by obtained by using a hydrocarbon compound which demonstrates a reducing action by means of its heat decomposition.
In another aspect of the invention, a circuit board connecting method comprises using an alkane application step of applying an alkane group to at least the surface of a printed circuit board where printed wire terminals exist or a portion of the surface of a flexible circuit board where conductive thick-film terminals exist, and a heat-press-bonding step of bonding the flexible circuit board to the printed circuit board by heat-pressing, while positioning the printed wire terminals and the conductive thick-film terminals to face one another.
The base plate of the printed circuit board has an epoxy glass board not confined. For example, resin boards based on other resin excluding multiple boards and multiple materials can be used, or other ceramic circuit boards, etc. can also be used. The printed wire terminals are typified by a printed pattern of copper foil, etc. that is not confined. For example, a gold or silver foil, a gold-plated conductor, or a conductive paste, etc. called a conductive thick film can be used.
The flexible circuit board is also called flexible printed circuit board, and is a flexible and plastic printed circuit board. The thermoplastic resin for forming the film which is the base of the flexible circuit board is typified by PEN (polyethylene naphtalate having a fusing point of around 270-280° C.), but it is not confined. For example, PET (polyethylene terephthalate having a fusing point of around 340° C.), PEEK (polyether ketone having a fusing point of around 340° C.), or PPS (polyphenylensulfide having a fu
Miyake Toshihiro
Yazaki Yoshitaro
Denso Corporation
Dunn Tom
Johnson Jonathan
Posz & Bethards, PLC
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