Semiconductor device manufacturing: process – Chemical etching – Combined with the removal of material by nonchemical means
Reexamination Certificate
2000-01-28
2001-02-06
Powell, William (Department: 1765)
Semiconductor device manufacturing: process
Chemical etching
Combined with the removal of material by nonchemical means
C216S014000, C216S020000, C216S052000, C438S754000
Reexamination Certificate
active
06184140
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods of making microelectronic packages and metallic parts and components for the same.
BACKGROUND OF THE INVENTION
Microelectronic packages include components for forming electrical connections between microelectronic devices such as microelectronic chips or wafers and external circuitry. microelectronic packages 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 or “TAB” a prefabricated array of leads is provided on a flexible dielectric tape. The leads are bonded to contacts on the microelectronic device. Certain embodiments illustrated in U.S. Pat. Nos. 5,489,749; 5,518,964; 5,148,265; 5,148,266, and 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 about 20 to about 40 microns wide. These leads must be provided in precise locations on the connection component. Other components such as circuit panels also include fine metallic features such as conductors.
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. Electroplating produces unacceptable irregularities in the metal elements formed when performed too rapidly, also limiting the speed with which the leads may be fabricated. 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. 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. In variants of these processes, the tools may perform additional operations such as bending the parts. 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.
Thus, despite the substantial time and effort expended to solve the problems associated with fabrication of leads used in packaging microelectronic elements and other metallic parts, further improvement in such processes would be desirable.
SUMMARY OF THE INVENTION
The present invention improves upon processes for fabricating metallic parts such as the leads of microelectronic packages.
A method of packaging a microelectronic element in accordance with one aspect of the present invention includes making one or more microelectronic components by embossing a layer of metal having a first and a second face by engagement between a pair of forming elements, thereby deforming the metal layer into thick and thin regions. Embossing processes of this type are commonly referred to as “coining”, perhaps because these processes are similar to those used to form the raised features on coins. After the embossing or coining step, the thin regions are then removed by a nonselective removal process acting on at least one of the two faces of the metal layer. The nonselective removal process is halted before the thick regions of metal are removed, leaving the thick regions of the metal layer as elements which constitute the metallic part. The component or components are assembled with one or more microelectronic elements.
The embossing step may be performed on either or both faces of the metal layer. One or both of the forming elements have raised and recessed portions arranged so that the recessed portions are in the pattern of the desired conductive elements. The forming elements may be moved linearly towards one another. Alternatively, one or both of the forming elements may be rollers, so that the metal layer is squeezed in a nip between the forming elements as the roller or rollers rotate.
The nonselective removal process may be performed on either or both faces of the metal layer, regardless of which face or faces are embossed. The nonselective removal process may be performed, for example, by etching, reverse electroplating, sputtering or abrading the metal layer.
The embossing step may be performed at an extremely rapid rate, forming impressions in the metal layer at production rates on the order of tens or hundreds of impressions per minute. The nonselective removal process can also be performed rapidly, without the need for time-consuming steps such as selective exposure and development of a photoresist. For example, where the nonselective removal process involves etching or reverse electroplating, the entire layer is simply immersed in the etching or reverse electroplating solution and processed. An unlimited number of components can be subjected to the nonselective removal process simultaneously. Thus, even where the removal process requires substantial time, a high throughput rate can be maintained.
A process according to this aspect of the invention can be used to form extremely small conductive elements which are impractical to form using mechanical processes such as conventional stamping. One limit on the size of the conductive elements formed in processes according to this aspect of the invention is the size of the raised and recessed portions which can be provided in the forming elements. However, the raised and recessed portions in the forming elements may be formed by relatively expensive, precise processes without adding substantially to the cost of the finished product since the die is utilized repeatedly once shaped.
A method according to this aspect of the present invention may include the step of forming a first layer of metal on the metallic elements. For example, certain preferred embodiments include the step of forming a first layer of metal by electroplating onto the metallic elements a layer of metallic material different than the metallic material of the metallic elements. Certain preferred embodiments include forming a second layer of metal on the metallic elements so that the first layer of metal comprises a layer of barrier material to prevent interdiffusion of metallic material between the metallic elements and the second layer of metal.
In certain embodiments, the one or more microelectronic components are made in the form of a plurality of microelectronic components in a continuous strip. The microelectronic components of the strip may be assembled with the one or more microelectron
Lerner David Littenberg Krumholz & Mentlik LLP
Powell William
Tessera Inc.
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