Adaptive threshold determination for ball grid array component modeling

• US 20030156748A1
• Filed: 02/21/2002
• Published: 08/21/2003
• Est. Priority Date: 02/21/2002
• Status: Active Grant

• Current Assignee: Siemens AG
• Original Assignee: Siemens Corporate Research Incorporated (Siemens AG)
• Inventors: Fang, Ming, Fang, Tong
• Granted Patent: US 7,027,637 B2
• Time in Patent Office: Days
• US Class Current: 382/145
• CPC Class Codes: G01R 1/0483 Sockets for un-leaded IC's having matrix type contact fields, e.g. BGA or PGA devices; Sockets for unpackaged, naked chips for IC's with connecting points around the edges only G01R1/0433
• CPC Class Codes: G01R 31/2889 Interfaces, e.g. between probe and tester G01R31/31905 and G01R1/07364 take precedence
• CPC Class Codes: G06T 2207/30141 Printed circuit board [PCB]
• CPC Class Codes: G06T 2207/30148 Semiconductor; IC; Wafer
• CPC Class Codes: G06T 7/0004 Industrial image inspection
• CPC Class Codes: G06T 7/73 using feature-based methods
• CPC Class Codes: G06T 7/77 using statistical methods

Abstract

A method for determining a number of balls in a projection space comprises determining a projection of a portion of a ball grid array, determining at least one local maximum of the projection space for a given threshold, and determining at least a distance between adjacent maximum. The method further comprises determining an inter-peak histogram of the distances, determining an inter-ball distance for each pair of adjacent balls that has the maximum value of the inter-peak distance histogram corresponding to the pair of adjacent balls, and determining a position of a first ball and a position of a last ball. The method comprises verifying the position of the first ball and the position of the last ball based on a general inter-ball distance, and determining the number of balls.

Claims

1. A method for determining a number of objects comprising the steps of:

determining a projection space including the objects, wherein a distance between two adjacent objects is substantially the same for each pair of adjacent objects;

determining an adaptive threshold according to a number of objects determined to be in the projection space;

determining an inter-object distance according to an average inter-peak distance at the adaptive threshold; and

determining a number of objects in the projection space according to the inter-object distance.

2. A method for determining a number of balls in a projection space comprising the steps of:

determining a projection of a portion of a ball grid array;

determining at least one local maximum of the projection space for a given threshold;

determining a distance between adjacent maximum;

determining an inter-peak histogram of the distances;

determining an inter-ball distance for each pair of adjacent balls that has the maximum value of the inter-peak distance histogram corresponding to the pair of adjacent balls;

determining a position of a first ball and a position of a last ball;

verifying the position of the first ball and the position of the last ball based on a general inter-ball distance; and

determining the number of balls.

3. The method of claim 2, wherein the step of determining a projection further comprises the step of projecting a row/column of ball image a direction, wherein the direction is one of horizontally and vertically.

4. The method of claim 2, wherein an inter-peak distance bin width is a tolerance of the general inter-ball distance.

5. The method of claim 2, wherein the number of balls is determined according to:

6. The method of claim 2, wherein the given threshold is determined.

7. The method of claim 6, wherein determining the threshold comprises the steps of:

determining the number of balls in the projection space for one or more given threshold values in a threshold searching range based on the general inter-ball distance of ball grid array components;

determining a histogram for the number of balls;

determining a threshold range comprising a plurality of threshold values, wherein each threshold value corresponds to a maximum number of balls at the threshold value; and

setting the threshold to one of a mean threshold value and a median threshold value of the threshold range.

8. The method of claim 7, wherein the histogram shows a maximum frequency of the number of balls.

9. The method of claim 2, wherein the general inter-ball distance is an average of the distances between each pair of adjacent balls.

10. A program storage device readable by machine, tangibly embodying a program of instructions executable by the machine to perform method steps for determining a number of balls in a projection space, the method steps comprising:

determining a projection of a portion of a ball grid array;

determining at least one local maximum of the projection space for a given threshold;

determining a distance between adjacent maximum;

determining an inter-peak histogram of the distances;

determining an inter-ball distance for each pair of adjacent balls that has the maximum value of the inter-peak distance histogram corresponding to the pair of adjacent balls;

determining a position of a first ball and a position of a last ball;

verifying the position of the first ball and the position of the last ball based on a general inter-ball distance; and

determining the number of balls.

11. The method of claim 10, wherein the step of determining a projection further comprises the step of projecting a row/column of ball image one a direction, wherein the direction is one of horizontally and vertically.

12. The method of claim 10, wherein an inter-peak distance bin width is a tolerance of the general inter-ball distance.

13. The method of claim 10, wherein the number of balls is determined according to:

14. The method of claim 10, wherein the given threshold is determined.

15. The method of claim 14, wherein determining the threshold comprises the steps of:

determining the number of balls in the projection space for one or more given threshold values in a threshold searching range based on the general inter-ball distance of ball grid array components;

determining a histogram for the number of balls;

determining a threshold range comprising a plurality of threshold values, wherein each threshold value corresponds to a maximum number of balls at the threshold value; and

setting the threshold to one of a mean threshold value and a median threshold value of the threshold range.

16. The method of claim 15, wherein the histogram shows a maximum frequency of the number of balls.

17. The method of claim 10, wherein the general inter-ball distance is an average of the distances between each pair of adjacent balls.