Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
1998-06-30
2001-03-27
Chaudhuri, Olik (Department: 2814)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S118000, C438S119000, C438S667000
Reexamination Certificate
active
06207550
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for fabricating a semiconductor device produced by mounting semiconductor elements on a printed circuit board.
2. Description of Prior Art
In recent years, the trends of application for semiconductors with a relatively large number of pins, such as a MPU, have been in the direction of a narrower pitch arrangement of electrodes, two-dimension lattice array of electrodes, or front arrangement of pin electrodes. Semiconductor devices with highly densified multi-pins are therefore coming on so that the electrodes can be formed close to or over the functional portions of elements. For conventional methods for mounting semiconductor elements on a printed circuit board using a flip chip technique, a method is known in which solder bumps are formed on the electrode faces of the semiconductor elements, as described in Japanese Patent Publication JP-A 53-87596. These solder bumps, which are composed of a solder alloy, are connected to the electrode pads on a circuit board by soldering. There are also known methods in which gold-stud bumps are formed on the electrode faces of a semiconductor and these bumps are connected to substrate electrode pads using a conductive adhesive (see Japanese Patent Publication JP-A 62-140264) or using a solder alloy (see Japanese Patent Publication JP-A 6-213615).
In these technologies of forming the bumps on the electrodes of a semiconductor, the substrate on which the semiconductors are mounted, requires the same flatness as a semiconductor chip. Proposal has been made of a method of forming the bump electrodes on a substrate side but the chip (see Japanese Patent Publication JP-A 4-19766). In general, ceramic substrates do not have such a flatness in its surface as semiconductor chips. This imparts the problem that a stable connection to electrode pads of the semiconductor cannot be made since all the tips of the bumps have no coplanarity even if the bumps with the same height are formed on the surface of the substrate.
Furthermore, there are methods in which an anisotropic conductive film is used to bind a semiconductor element to a substrate by hot pressing. In this bonding method, dielectric breakdown in the anisotropic conductive film is caused only at the position between the bump electrode and the electrode pad to electrically connect both of them. In this bonding method, the tips of the bump electrodes on the side of the substrate are also uneven. As there is a difference in intervals between each of the bump electrodes embedded into the adhesive film and the corresponding electrode pad of the semiconductor element, the bump electrodes having a wider gap between their tips and the corresponding electrode pads are not allowed to make electrical contact with the corresponding pads even if the semiconductor element is pressed against the substrate. It is uncertain to secure the electrical contact between all bump electrodes and the corresponding electrode pads.
SUMMARY OF THE INVENTION
In view of this situation, an object of the present invention is to provide a method for fabricating a semiconductor device to enable projection electrodes on a substrate to be formed in a manner that the bump electrodes can establish good and stable electrical contact with electrodes of a semiconductor element. The above object can be attained by the following inventions:
According to a first aspect of the present invention, there is provided a method for fabricating a semiconductor device, generally comprising; disposing electrode faces on the backface of a semiconductor element; forming a plurality of bump electrodes disposed on and projecting from the surface of a multilayer circuit substrate; and securing the semiconductor element to the multilayer circuit substrate using a contractive insulating resin layer, the method being characterized in that conductive resin adhesives applied on the bump electrodes are leveled to form end portions on the same flat plane, causing the end portions of the adhesive on the bumps to contact with all the corresponding electrode faces and to be bonded to the electrode faces by the conductive adhesive.
In the invention, the electrode pad faces of the semiconductor elements have so high flatness that adhesion between each electrode face and the corresponding end portion of each of the bump electrodes is secured thereby establishing good and stable electrical contact by forming each end on the plurality of bump electrodes on the substrate lying in a plane by using a conductive adhesive.
In the method for fabricating a semiconductor device according to the present invention, particularly, a conductive resin adhesive is applied on the top of each bump electrode to form end portions, the end portions on all bump electrodes are leveled to a uniform height and the end portions are brought into contact with the electrode faces and bonded to the electrode faces via the conductive adhesive.
Particularly, in the invention, an anisotropic conductive film may be used instead of the contractive insulating resin layer to bond the above semiconductor element to the multilayer circuit substrate. The anisotropic conductive film is produced by coating a great number of conductive particles with the resin to form insulating coating particles, which are dispersed in the film. As the anisotropic conductive film is locally pressed across the surfaces, in the locally pressed parts the insulating coating over the conductive particles is broken and the conductive particles are brought into contact each other allowing only the local pressed part to electrically conduct. In the invention, a great number of bump electrodes are embedded into the anisotropic conductive film and each end portion on these bump electrodes is adjacent to each of the electrode pad faces in the anisotropic conductive film and is held in electric conduction. Since each end portion is formed to a uniform height, all end portions have an accurate gap with each corresponding electrode pad face. Both corresponding electrodes are thereby held in electric conduction.
According to a further aspect of the present invention, there is provided a method for fabricating a semiconductor device comprising applying a conductive resin adhesive on each bump electrode to form an end portion of the adhesive on the bump electrode; leveling all the end portions of the adhesive on the bump electrodes to a uniform height; then applying an anisotropic conductive film on the surface of the multilayer circuit substrate so as to embed the bump electrodes; and pressing the semiconductor element to the multilayer circuit substrate so that the electrode faces accord with the end portions of the bump electrodes to bond the end portions of the bump electrodes with the corresponding electrode faces, followed by curing the conductive film.
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Bessho Yoshihiro
Hase Nobuhiro
Itagaki Minehiro
Nakamura Yoshifumi
Takezawa Hiroaki
Chambliss Alonzo
Chaudhuri Olik
Matsushita Electric - Industrial Co., Ltd.
Wenderoth , Lind & Ponack, L.L.P.
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