Metal deforming – With cutting – By composite tool
Reexamination Certificate
1999-03-31
2001-03-06
Crane, Daniel C. (Department: 3725)
Metal deforming
With cutting
By composite tool
C112S412000, C029S827000, C076S107100
Reexamination Certificate
active
06196042
ABSTRACT:
The present invention relates in general to the field of microelectronic connection components, and more particularly, to coining tools and to methods of making coining tools for use in manufacturing microelectronic connection components.
Connection components for microelectronic devices, such as semiconductor chips, form electrical connections between the microelectronic device and external circuitry or other microelectronic devices. These connection components commonly incorporate conductive elements such as fine metallic leads and terminal structures disposed on a dielectric layer such as a polymeric layer. In conventional tape automated bonding (“TAB”), a prefabricated array of leads is provided on a flexible dielectric tape. The leads are bonded to contacts on the microelectronic device. The connection components illustrated in U.S. Pat. Nos. 5,489,749; 5,518,964; 5,148,265; 5,148,266; 5,491,302; and International Publication WO 94/03036, the disclosures of which are hereby incorporated by reference herein, also incorporate leads and other electrically conductive elements. Leads for use with modern semiconductor chips having large numbers of closely-spaced contacts must be very fine. They may be, for example, about 15 to about 40 microns wide. These leads must be provided in precise locations on the connection component.
The metallic elements in these and other components have been fabricated by various processes, most commonly by photochemical processes. In one photochemical process, patternwise etching of a metallic layer is utilized to form the leads. A photographically patterned etch resist is used to selectively etch unwanted portions of the metal layer so that the resist-protected portions form the leads of the connection component. In another method, a metal is plated in areas defined by a photographically patterned resist.
Photochemical processes suffer significant drawbacks in that they require several steps. The resist must be exposed to illumination in the desired pattern, typically by use of a mask. The resist is thereby developed so as to cure only the resist in exposed areas or only the resist in the unexposed areas. The uncured resist is then removed, leaving a mask which has openings in areas where metal is to be removed or added. After etching or plating, the cured resist forming the mask is then removed. These steps entail significant cost and limit the speed of fabrication. In addition, photochemical processes typically cannot form features smaller than a certain size. This size depends on the type of resist used and the developing process.
Conventional stamping processes have been used to fabricate relatively large metallic elements such as large leads for lead frame packaging, such as lead-in surface mount packages, e.g., TSOP or QFP. In a simple stamping process, a sheet of metal is passed between a pair of matched tools referred to as a punch and a die. The punch has a protrusion corresponding to the shape of the part to be formed, whereas the die has a hole precisely matched to the shape of the punch, and just slightly larger than the punch. As the tools are forced together, the punch enters the hole in the die and shears a portion of the metal sheet corresponding in shape to the punch from the remainder of the sheet. Stamping processes can be performed rapidly. Although stamping processes can be used to form relatively large, coarse parts, it is typically not practical to stamp very fine leads for use with microelectronic connection components having closely spaced contacts.
Despite the substantial time and effort expended to solve the problems associated with fabrication of leads and features thereof for connection components and other metallic parts, further improvement in such processes would be desirable. Improved processes for fabricating metallic parts such as the leads of connection components using a die are disclosed in copending prior U.S. patent application filed Dec. 12, 1997, application Ser. No. 08/989,587, 6,053,837 entitled Fabrication of Components by Coining naming Marcus Millet as the inventor, which patent is incorporated herein by reference. The '837 patent discloses a method of fabricating leads of a connection component for connecting a microelectronic element such as taught in U.S. Pat. No. 5,629,239, the disclosure of which is incorporated herein by reference.
The leads are formed to include frangible portions using a die and backing element in an embossing process commonly referred to as “coining”. The die includes recessed portions including lead-forming portions of a constant depth, interrupted by frangible element forming portions. The frangible element forming portions are recessed to a lesser depth relative to the die surface than the lead-forming portions. The die also includes bus-forming portions, and terminal-forming portions of the same depth as the lead-forming portion. The die is used with a planar backing element. The forming process yields a lead structure including lead portions having a thickness substantially greater than the frangible portions which interrupt each lead portion. After forming, the leads are provided with a supporting dielectric layer overlying one surface thereof. The dielectric layer is then etched to form an opening, as by laser ablation, leaving the leads projecting across the opening, each having a frangible portion. The metallic lead structures thus formed can be plated with a bondable material such as gold over a barrier layer. These leads can be connected to a microelectronic component in the manner discussed in WO 94/03036. As each lead is bent downwardly, each lead is broken at the frangible portion.
Accordingly, it can be appreciated that there is a need for further improvements in the manufacturing of microelectronic connection components, and particularly, in the formation of leads having frangible portions by use of a coining tool.
SUMMARY OF THE INVENTION
In accordance with the present invention, an embossing or coining tool and process of manufacturing same is disclosed for use in making connection components having frangible leads for connection to microelectronic components. One of the limiting factors in manufacturing microelectronic components is the stringent requirements for fabrication of the frangible portion of the leads. The very small features required of the frangible portion, e.g., about 12 microns, is typically beyond the manufacturing capabilities for most otherwise capable manufacturers. One way to ameliorate this problem is to remove the requirement for fabricating the frangible portion in the lead using photolithographic techniques. To accomplish this, an embossing or coining tool is proposed in accordance with the present invention. The tool would mechanically notch the metal lead in forming the frangible portion by means of a coining projection. The depth of the notch is controlled by an etching process used during the manufacturing process for the tool profile, where the etch depth for the tool is approximately ½ the thickness of the lead being notched. The tool is produced from the same data used to create the tape artwork and contains all necessary tool features required for good registration. A second element of the tool is the formation of a pedestal supporting the coining projection which may be required for “circuits up” constructions. In this regard, it is envisaged that the notch will preferably be on the side opposite the bonding tool to assure a clean break of the lead at the frangible portion formed by the notch. However, the notch forming the frangible portion can also be formed in the top surface of the lead which is engaged by the bonding tool by using a backing plate provided with the coining projection.
The present invention can be employed to form frangible portions in various lead configurations, including conventional tape automated bonding leads and those depicted in U.S. Pat. Nos. 5,489,749; 5,491,302; 5,629,239; and 5,518,964, the disclosures of which are hereby incorporated by reference herein. As discussed in these p
DiStefano Thomas H.
Fjelstad Joseph
Haba Belgacem
Crane Daniel C.
Lerner David Littenberg Krumholz & Mentlik LLP
Tessera Inc.
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