Method for inspecting a region of interest

Abstract

An inspection method utilizing vertical slice imaging. A number of horizontal slice images, extending through an object of interest, are acquired. A vertical region of interest is defined from the data representing the horizontal slice images. A vertical slice image is constructed based upon the horizontal slice image data falling within the vertical region of interest. The vertical slice image data may be analyzed to detect defects. In addition, a method is provided to detect defects in a BGA joint. The method includes locating a center of the joint. The method may further include measuring a number of diameters through the center of the joint and applying a rule to compare the measured diameters to an expected diameter.

1 - 8 . (canceled) 
     
     
         9 . A method for inspecting a region of interest, comprising:
 acquiring data corresponding to a number of horizontal slice images extending through an object of interest;   locating a horizontal slice image from the number of horizontal slice images, the locating step comprising:
 computing, for at least two of the horizontal slice images, an amount of solder within each of the at least two horizontal slice images; 
 reviewing a distribution of the computed amounts of solder; and 
   based on the review, locating a horizontal slice having a better quality for a characteristic to be analyzed than another horizontal slice; and   analyzing the located horizontal slice image for the characteristic.   
     
     
         10 . The method of  claim 9 , wherein the characteristic is a defect. 
     
     
         11 . The method of  claim 9 , wherein the characteristic is a pad/lead interface. 
     
     
         12 . The method of  claim 9 , further comprising synthesizing a vertical slice based on the located horizontal slice. 
     
     
         13 . The method of  claim 9 , wherein the step of computing an amount of solder comprises computing a weighted summation of gray scale data points over a gray scale histogram. 
     
     
         14 . The method of  claim 9 , wherein the following equation is used to calculate the amount of solder: 
       
         
           
             
               
                 ∑ 
                 
                   gray 
                   = 
                   0 
                 
                 bgd_gray 
               
                
               
                   
               
                
               
                 
                   ( 
                   
                     background_gray 
                     - 
                     gray 
                   
                   ) 
                 
                 * 
                 
                   histogram 
                   [ 
                   gray 
                   ] 
                 
               
             
           
         
       
     
     
         15 . The method of  claim 9 , further comprising selecting the at least two horizontal slice images in accordance with the sampling theorem. 
     
     
         16 . The method of  claim 9 , wherein the object of interest comprises a ball grid array joint comprising a solder ball, and the located horizontal slice represents a horizontal slice passing through the approximate center of the solder ball. 
     
     
         17 . The method of  claim 9 , wherein the step of locating comprises identifying a first peak in the distribution. 
     
     
         18 . The method of  claim 9 , wherein the step of locating comprises determining a most significant peak in the distribution, applying an algorithm to the most significant peak and at least one other point in the distribution, and locating a slice other than a slice associated with the most significant peak. 
     
     
         19 . The method of  claim 9 , wherein the step of locating comprises identifying a noise level and locating a slice having a solder amount which falls below the noise level. 
     
     
         20 . The method of  claim 9 , wherein the step of locating comprises identifying unobstructed anchor devices. 
     
     
         21 . The method of  claim 9 , wherein the data is acquired using tomosynthesis. 
     
     
         22 . A method of identifying a cross-sectional image of an object for analysis, comprising:
 acquiring data corresponding to a plurality of cross-sectional images extending through the object;   computing a value for each cross-sectional image based on the data;   identifying a cross-sectional image having a better quality for analysis than other cross-sectional images based on the values of each cross-sectional image.   
     
     
         23 . The method of  claim 22 , further comprising analyzing the identified cross-sectional image for defects or to identify a pad/lead interface. 
     
     
         24 . The method of  claim 23 , wherein the step of computing a value is based on a summation operation and a histogram of the data. 
     
     
         25 . The method of  claim 24 , wherein the data is acquired using tomosynthesis and the object comprises an electrical interconnection. 
     
     
         26 . The method of  claim 22 , further comprising selecting the plurality of cross-sectional images in accordance with the sampling theorem. 
     
     
         27 . An inspection system for identifying a cross-sectional image of an object for analysis, comprising:
 a system configured to acquire data corresponding to a plurality of cross-sectional images extending through the object, to compute a value for each cross-sectional image based on the data, and to identify a cross-sectional image having a better quality for analysis than other cross-sectional images based on the values of each cross-sectional image.   
     
     
         28 . The system of  claim 27 , wherein the system is configured to analyze the identified cross-sectional image for defects or to identify a pad/lead interface.