Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor
Reexamination Certificate
2000-05-24
2001-12-25
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
C438S118000, C438S611000, C438S612000, C438S617000
Reexamination Certificate
active
06333207
ABSTRACT:
BACKGROUND OF THE INVENTION
As described in certain embodiments of U.S. Pat. No. 5,518,964, the disclosure of which is incorporated by reference herein, an element used in a microelectronic assembly may have elongated flexible leads extending along a surface of the element. Each lead has a first or terminal end permanently attached to the element and has a tip end offset from the terminal end. A second element having contacts thereon is engaged with the first element so that the tip ends of the leads are bonded to contacts on the second element. The first and second elements are then moved away from one another so as to deform the leads and provide vertically extensive leads extending between these elements. A compliant material may be introduced between the elements during or after such motion. The resulting structure allows relative movement of the elements without substantial stresses on the leads. This process can be used, for example, to make packaged semiconductor chips. One of the elements may be a connection component desirably having a flexible structure incorporating one or more dielectric layers, and the other one of the elements may be a chip, wafer or assemblage of chips. The leads may be provided either on the connection component or on the chips or wafer.
As described in U.S. Pat. No. 5,763,941, the disclosure of which is also incorporated by reference herein, a releasable lead structure may be made by providing a first region of a lead permanently connected to a component and a second region releasably connected to a surface of the component so that the second region can be peeled away from such surface. Desirably, the second region is attached to the underlying surface by a release interface having a peel strength of less than about 0.35×10
6
dynes/cm; i.e., a peel strength of less then about 2 lbs. per linear inch. For example, certain low-energy vapor deposition processes such as electroless plating or chemical vapor deposition can deposit a thin layer of release metal forming a release interface with the underlying layer. The lead may incorporate a structural metal which may be the same as or different from the release metal. The release metal can be peeled away from the underlying layer. In other embodiments, the interface may include a layer of a first release metal securely bonded to the underlying layer and a second release metal on the lead, the first and second release metals being weakly bonded to one another so that the second region of the lead can be pulled away from the underlying layer, with the first release metal remaining on the underlying layer.
SUMMARY OF THE INVENTION
One aspect of the invention provides a method of making a microelectronic connection component. The method according to this aspect of the present invention preferably includes providing a first element having a surface and a lead extending along the surface having a first end and a second end. The first element may be a microelectronic element such as a wafer, including plural semiconductor chips, a semiconductor chip, or a connection component. When the first element is a wafer, the wafer may be severed to form a plurality of individual units. The second end of the lead preferably adheres to the surface of the first element. Desirably, the adhesion between the second end of the lead and the surface is released by altering the temperature of at least the second portion of the lead. Preferably, the step of altering the temperature includes heating the second end of the lead.
The second end of the lead may be moved away from the surface, typically after the adhesion is released. Preferably, a plurality of leads are provided on the first element. For example, a second element having electrically conductive features may be juxtaposed with the first element, and the second ends of the leads may be bonded to conductive features of the second element. The second element may include a dielectric substrate. Desirably, the step of moving the second ends of the leads includes moving the first and second elements away from one another. In preferred processes according to this aspect of the invention, the second ends of the leads are retained in position during the early stages of the process, but the second ends are released to allow relative movement of the first and second elements. In the most preferred forms of the process, it is not necessary to provide small frangible elements to temporarily secure the second ends of the leads. This simplifies the manufacture of the components used in the process.
Heating may be performed by heating at least one of the elements to thereby heat all of the leads simultaneously. Desirably, the heating which releases the adhesion of the second ends of the leads also serves to activate a bonding material which bonds the second ends of leads to the conductive features of the second element. The elements may be subjected to at least one post-bonding heating step after the second ends of the leads have been bonded to the conductive features of the second element but before moving the elements away from each other. Desirably, the post-bonding heating contributes to the release of the adhesion of the second ends to the first element. In other embodiments, heating to release adhesion is performed cyclically by locally heating less than all of the leads during each cycle so as to release the adhesion between the second ends of some leads while leaving other bonds intact. The local heating may be performed, for example, by directing radiant energy in the vicinity of the leads to be heated during each cycle to thereby release the adhesion between the second ends of these leads and the first element. Each heated lead may be engaged with a bonding tool concomitantly with the release of the adhesion of that lead. Desirably, the first end of each lead is permanently attached to the first element.
A further aspect of the invention provides a method of bonding a lead to a contact. The method of this aspect of the invention preferably comprises providing a lead, preferably an elongated lead, having a portion at least partially overlying a contact and a bonding material on at least one of the lead or the contact. The bonding material is liquefied so that the liquid bonding material forms a droplet in contact with the lead and the contact, desirably wetting the lead and the contact, so that the bonding material moves at least that portion of the lead adjacent the contact relative to the contact so as to increase the degree of overlap between the lead and the contact. Although the present invention is not limited by any theory of operation, it is believed that the surface tension of the bonding material pulls that portion of the lead adjacent the contact into better alignment with the contact.
The lead may bend or flex during movement under the influence of the forces applied by surface tension. For example, the lead may be provided with a fixed end attached to a first element and a tip end movable with respect to the first element, whereas the contact is provided on a second element. In certain embodiments, the tip end of the lead is initially adherent to the first element but is rendered movable by releasing the adhesion in the manner discussed above. Preferably, it is the tip end of the lead that is wetted by the liquefied bonding material. After the bonding material is liquefied, a bond forms between the lead and the contact. The lead may be further deformed by moving the first and second elements away from one another.
The first element may bear plural leads, whereas the second element may have plural contacts. Movement of the leads provides some degree of compensation for misalignment between the various leads and contacts. This reduces the need for precision in placement of the leads and contacts on the first and second elements.
Yet another aspect of the invention provides a method of making a microelectronic assembly. The method of this aspect of the invention preferably comprises providing a dielectric substrate having a first surface and a lead adhered
Light David
Smith John W.
Jones Josetta
Lerner David Littenberg Krumholz & Mentlik LLP
Niebling John F.
Tessera Inc.
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