Low Profile Stacking System and Method

Abstract

The present invention provides a system and method that mounts integrated circuit devices onto substrates and a system and method for employing the method is stacked modules. The contact pads of a packaged integrated circuit device are substantially exposed. A solder past that includes higher temperature solder paste alloy is applied to a substrate or to the integrated circuit device to be mounted. The integrated circuit device is positioned to contact the contacts of the substrate. Heat is applied to create high temperature joints between the contacts of the substrate and the integrated circuit device resulting in a device-substrate assembly with high temperature joints. The formed joints are less subject to re-melting in subsequent processing steps. The method may be employed in devising stacked module constructions such as those disclosed herein as preferred embodiments in accordance with the invention. Typically, the created joints are low in profile.

1 . A high temperature joint in a stacked circuit module in which a first integrated circuit element is disposed above a second integrated circuit element, the high temperature joint comprising: 
 an alloy comprised of lead and antimony having the proportion of no more that 95% tin and at least 5% antimony, the alloy having a melting point between 235° C. to 260° C.    
   
   
       2 . A high temperature joint in a stacked circuit module in which a first integrated circuit element is disposed above a second integrated circuit element, the high temperature joint comprising: 
 an alloy comprised of lead and tin, the alloy having a melting point between 275° C. 312° C.    
   
   
       3 . A high temperature joint in a stacked circuit module in which a first integrated circuit element is disposed above a second integrated circuit element, the high temperature joint comprising: 
 an alloy comprised of lead, the alloy having a melting point of between 235° C. and 312° C.