Method of Enhancing Fatigue Life of Grid Arrays

Abstract

A method is presented that improves reliability for the mechanical electrical connection formed between a grid array device, such as a pin grid array device (PGA) or a column grid array device (CGA), and a substrate such as a printed circuit board (PCB). Between adjacent PCB pads, the method increases a spacing pattern toward the periphery of the CGA, creating a misalignment between pads and columns. As part of the method, columns align with the pads, resulting in column tilt that increases from the center to the periphery of the CGA. An advantage of the method is that the column tilt reduces the amount of contractions and expansions of columns during thermal cycling, thereby increasing the projected life of CGA. Another advantage of the method is that it reduces shear stress, further increasing the projected life of the CGA.

1 . (canceled) 
     
     
         2 . An electronic assembly comprising:
 a printed circuit board having an array of connecting pads and a board coefficient of thermal expansion; and   an electronic component having an array of connecting lands, the electronic component having a different coefficient of thermal expansion than the board coefficient of thermal expansion, an array of high melting temperature conducting posts connecting the electronic component from the array of connecting lands to respective pads of the array of connecting pads on the printed circuit board through connective material having a lower melting temperature than melting temperature of the conducting posts, angled conducting posts of the array of conducting posts having an angular tilt outwardly away from a center of the electronic component to the circuit board at 20 degrees Celsius and over a temperature range of 0 degrees Celsius to 100 degrees Celsius.   
     
     
         3 . The assembly of  claim 2 , wherein the angled conducting posts include peripheral conducting posts that are peripheral with respect to the center of the electronic component. 
     
     
         4 . The assembly of  claim 2 , wherein the board coefficient of expansion is greater than the electronic component coefficient of thermal expansion. 
     
     
         5 . The assembly of  claim 2 , wherein the array of conducting posts is an array of conducting columns connected at lands of the electronic component with solder and connected to pads of the printed circuit board with solder. 
     
     
         6 . The assembly of  claim 2 , wherein the angled conducting posts have the angular tilt outwardly away from the center of the electronic component to the circuit board over a temperature range of negative 55 degrees Celsius to 125 degrees Celsius. 
     
     
         7 . The assembly of  claim 2 , wherein a first connective material connects each of the conducting posts of the array of conducting posts to the electronic component, and a second connective material connects each of the conducting posts of the array of conducting posts to a pad, the first connective material and the second connective material having a lower melting point than a melting point of each of the conducting posts of the array of conducting posts. 
     
     
         8 . The assembly of  claim 7 , wherein the first connective material is solder and the second connective material is solder, and a length-to-width ratio of each of the conducting posts of the array of conducting posts is greater than or equal to a ratio of 4:1. 
     
     
         9 . The assembly of  claim 2  wherein the connective material is solder. 
     
     
         10 . The assembly of  claim 2 , wherein each of the conducting posts of the array of conducting posts is comprised of solder, and each of the conducting posts of the array of conducting posts is connected to a land of the electronic component with solder. 
     
     
         11 . The assembly of  claim 2 , wherein each post of a center sub-array of the array of conducting posts is vertical, and each post not within the center sub-array is angled. 
     
     
         12 . The assembly of  claim 2 , wherein the angled conducting posts of the array of conducting posts have the angular tilt at an increasing angle toward a periphery of the electronic component. 
     
     
         13 . The assembly of  claim 2 , wherein the angled conducting posts include outermost conducting posts of the electronic component, proximate to a periphery of the electronic component and at least conducting posts inward of the outermost conducting posts of the electronic component. 
     
     
         14 . The assembly of  claim 2 , wherein the angled conducting posts of the array of conducting posts include peripheral conducting posts. 
     
     
         15 . A device comprising:
 an electronic component with a group of high melting temperature conducting posts connected to an array of connecting lands of the electronic component through solder, the electronic component having a first coefficient of thermal expansion;   a printed wiring board with a group of connecting pads, the printed wiring board having a second coefficient of thermal expansion greater than the first coefficient of thermal expansion;   the group of connecting pads placed on the printed wiring board, the group of connecting pads associated with the group of conducting posts on the electronic component, such that:   at least one pad of the group of connecting pads is aligned with an associated at least one conducting post of the group of conducting posts, and the at least one conducting post of the group of conducting posts is located centermost to the electronic component, where there is an initial gap distance which is a constant value, between any adjacent pads of the at least one pad of the group of connecting pads;   a remaining set of pads of the group of connecting pads is misaligned at 20 degrees Celsius with a corresponding set of the array of connecting lands of the electronic component, by an increased gap distance between adjacent pads of the remaining set of pads of the group of connecting pads, the increased gap distance being greater than the initial gap distance; and   the electronic component connects to the printed wiring board through a connection process such that:   each of the conducting posts of the group of conducting posts connects to an associated proximate pad of the group of connecting pads;   each of the conducting posts of the remaining set of conducting posts has an angular tilt outwardly away from the center of the electronic component toward a periphery of the electronic component at 20 degrees Celsius and over a temperature range of 0 degrees Celsius to 100 degrees Celsius.   
     
     
         16 . The device of  claim 15 , wherein the increased gap distance is a constant value. 
     
     
         17 . An electronic assembly comprising:
 a printed circuit board having an array of connecting pads and a board coefficient of thermal expansion;   an electronic component having coefficient of thermal expansion less than the board coefficient of thermal expansion, an array of conducting posts connected through solder to the electronic component at respective lands of an array of connecting lands of the electronic component and connecting the electronic component to the printed circuit board, peripheral conducting posts of the array of conducting posts having an angular tilt outwardly away from the electronic component to the circuit board when the temperature is at 20 degrees Celsius and when the temperature is in a range of 0 degrees Celsius to 100 degrees Celsius;   connective solder connecting each of the conducting posts of the array of conducting posts to a respective land of the array of connecting lands of the electronic component and to a pad of the printed circuit board; and   each of the conducting posts of the array of conducting posts being comprised of high melting temperature solder having a higher melting point than the melting point of the connective solder.