Microelectronic unit forming methods and materials

Abstract

Electrically conductive elements such as terminals and leads are held on a support structure by a degradable connecting layer such as a adhesive degradable by heat or radiant energy. After connecting these elements to a microelectronic element such as a chip or wafer, the conductive elements are released from the support structure by degrading the connecting layer. The support structure desirably has a predictable, isotropic coefficient of thermal expansion and such coefficient of thermal expansion may be close to that of silicon to minimize the effect of the temperature changes. The conductive elements may be mounted on a plurality of individual tiles rather than on an unitary sheet covering an entire wafer to minimize dimensional changes when the dielectric is released from the support structure.

What is claimed is:  
     
         1 . A method of making a microelectronic assembly comprising: 
 (a) providing leads physically connected to a bottom surface of a support, each said lead having a tip end and a terminal end;    (b) engaging said support with a microelectronic element having contacts thereon so that the tip ends of the leads are aligned with the contacts of the microelectronic element, and bonding the tip ends of the leads to the contacts;    (c) during or after said bonding, selectively degrading the connection between the support and the leads at and adjacent the tip ends thereof so as to free the tip ends from the support and leave the terminal ends secured to the support.