Microelectronic assembly formation with releasable leads

Abstract

A first microelectronic element is provided with leads having anchor ends connected to contacts and tip ends moveable with respect to the first microelectronic element. The leads can be provided on a carrier sheet that is assembled to the first microelectronic element, or may be formed in situ on the surface of the first element. The leads may be unitary strips of a conductive material, and the anchor ends of the leads may be bonded to the contacts of the first microelectronic element by processes such as thermosonic or ultrasonic bonding. Alternatively, stub leads may be provided on a separate carrier sheet or formed in situ on the front surface of the first microelectronic element, and these stub leads may be connected by wire bonds to the contacts of the first microelectronic element so as to form composite leads. The tip ends of the leads are joined to a second microelectronic element that is moved away from the first microelectronic element so as to deform the leads.

1 . A microelectronic assembly comprising: 
 (a) a first microelectronic element having a front surface and contacts exposed at said front surface;    (b) a second microelectronic element overlying said front surface of said first microelectronic element;    (c) a plurality of leads having anchor ends connected to said contacts on said first microelectronic element and having tip ends electrically connected to said second microelectronic element, at least some of said leads being multiple-section leads, each said multiple-section lead including a unitary elongated strip sloping upwardly between the anchor end and the tip end, each such strip having a bend point, the slope per unit length along such strip changing at the bend point, each said strip being substantially unconstrained in bending between the contact connected to such lead and the tip end of such lead.    
     
     
         2 . An assembly as claimed in  claim 1  further comprising a sheet overlying said front surface of said first microelectronic element, said sheet having a top surface facing away from said first element, a bottom surface facing towards said first element, and one or more apertures extending between said top and bottom surfaces in alignment with said contacts, said strip-like elements of said multiple-section leads extending into the apertures of said sheet.  
     
     
         3 . An assembly as claimed in  claim 2  wherein the bend point in each said strip-like element is disposed above the top surface of the sheet and out of contact with the sheet.  
     
     
         4 . A microelectronic assembly comprising: 
 (a) a first microelectronic element having a front surface and contacts exposed at said front surface;    (b) a second microelectronic element overlying said front surface of said first microelectronic element;    (c) a plurality of leads, at least some of said leads being composite leads, each said composite lead including a stub lead having a bonding terminal and a tip end electrically connected to the second microelectronic element, each said composite lead further including an additional lead portion formed separately from said stub lead and bonded to the bonding terminal of the stub lead, the additional lead portion of each said composite lead extending to a contact of the first microelectronic element, said stub leads being elevated above the first microelectronic element and movable with respect thereto.    
     
     
         5 . An assembly as claimed in  claim 4  wherein each said additional conductive element is a round wire.