Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1999-03-23
2001-04-24
Gerrity, Stephen F. (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S740000, C029S840000, C029S846000, C029S877000, C029S878000
Reexamination Certificate
active
06219911
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to flip chip mounting methods, and in particular relates to flip chip mounting techniques that employ an insulating, adhesive film.
Various methods of conventional flip chip mounting are known. One representative example is the flip chip mounting technique using an insulating adhesive film. As opposed to other flip chip mounting methods, this technique has features which enable simplification of the mounting process, like bonding of an integrated circuit (IC) chip to a substrate such as a circuit board, and underfilling around the bonding point with a resin sealant.
This mounting technique has attracted attention recently, and in 1997 Japanese Public Patent Report No. 97815, Paragraphs [0018] and [0020] disclose a mounting technique where gold (Au) bumps on the IC chip are directly bonded to substrate electrodes; this method is referred to hereinafter as direct mounting. Also, Paragraph [0014] describes a mounting technique where Au bumps on the IC chip are indirectly bonded to substrate electrodes; this method is referred to hereinafter as indirect mounting.
However, with indirect mounting, electrical bonding of an IC chip and a substrate is achieved via a conductive adhesive layer which fills through-holes in an insulating adhesive film placed on both the chip and the board. In the direct mounting method, on the other hand, a mediating electrically conductive adhesive layer is not used, and bonding is achieved by bringing the Au bumps of the IC chip into contact with electrodes of the circuit board by inserting the bumps into through-holes pierced in the insulating adhesive film. Thus the indirect method has the problem of lower reliability than the direct method, as well as susceptibility to conductivity defects.
Therefore, although priority is being placed on direct mounting even in this case, the insulating adhesive film must have in it many minute through-holes that were, e.g., pierced, to enable insertion of the Au bumps of the chip through the holes; the processing requiring this technique can be troublesome and the method lacks general applicability.
SUMMARY OF THE INVENTION
The present invention overcomes the problems and limitations of prior flip chip mounting methods by providing polymer bumps, formed of electrically conductive adhesive, instead of conventional bumps like solder bumps formed by, e.g., a ball bonding method, or Au bumps formed by, e.g., a plating method, as the bumps of an IC chip to be bonded to a substrate on which is provided an insulating adhesive film. With the use of polymer bumps, it has been discovered that satisfactory bonding can be achieved by piercing the polymer bumps through the insulating adhesive film to make electrical contact between the IC chip and the substrate.
More specifically, in a flip chip mounting method incorporating the invention, polymer bumps formed on bond pads of an IC are bonded directly to electrodes, i.e., bond pads, of a substrate, such as a circuit board, on which is provided an insulating adhesive film, by piercing the film with the bumps to directly contact the substrate bond pads, whereby the bumps make connection between the bond pads of the IC and the bond pads of the substrate. The insulating adhesive film thereby mediates between the upper IC chip and lower circuit board, as an underfill. The IC polymer bumps are preferably composed of electrically-conducting paste.
Preferably, the polymer bumps are formed by stenciling. Also preferably, prior to bonding of the IC to the substrate such as a circuit board, the insulating adhesive film is pressed against the substrate, with the application of heat employed to bring the film into close contact with the substrate electrodes; then the bump bonding is carried out. Preferably, the substrate is held with a suction stage; i.e., held by vacuum. It is preferred to employ a resin, i.e., polymeric, substrate in a technique wherein the board is employed with a suction stage. A thermally-curable insulating adhesive film is preferred.
Other features and advantages of the flip chip mounting method of the invention will be apparent from the following description and accompanying drawing, and from the claims.
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Akita Masanori
Estes Richard H.
Ito Koji
Mori Toshihiro
Gerrity Stephen F.
Kim Paul D.
Lober Theresa A.
Polymer Flip Chip Corp.
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