Adaptive threshold determination for ball grid array component modeling

• US 7,027,637 B2
• Filed: 02/21/2002
• Issued: 04/11/2006
• 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
• Primary Examiner(s): Mehta, Bhavesh M.
• Assistant Examiner(s): STREGE, JOHN B
• Application Number:
  US10/080,805
• Publication Number:
  US 20030156748A1
• Time in Patent Office: 1,510 Days
• Field of Search: 382/145, 382/146, 382/141, 382/168, 382/170, 382/171, 382/172, 382/192, 382/195, 382/270, 382/271, 382/272, 382/273, 382/204, 382/150, 250/559.47, 348/96, 348/86, 348/92, 348/125
• 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 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.

2. The method of claim 1, wherein the step of determining the projection further comprises the step of projecting a row or column of an image of the balls in a direction, wherein the direction is one of horizontal and vertical.

3. The method of claim 1, wherein an inter-peak distance bin width is a tolerance of the general inter-ball distance.

4. The method of claim 1, wherein the number of balls is determined according to:

$N=\frac{\mathrm{distance}<br><br><br><br>\mathrm{between}<br><br><br><br>\mathrm{the}<br><br><br><br>\mathrm{first}<br><br><br><br>\mathrm{and}<br><br><br><br>\mathrm{the}<br><br><br><br>\mathrm{last}<br><br><br><br>\mathrm{ball}}{\mathrm{inter}<br><br>\text{-}<br><br>\mathrm{ball}<br><br><br><br>\mathrm{distance}}+1$

where N is the number of balls and the inter-ball distance is determined according to a maximum value of the inter-peak distance histogram.

5. The method of claim 1, wherein the given threshold is an adaptive threshold.

6. The method of claim 5, further comprising determining the adaptive threshold, comprising the steps of:

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

determining a histogram for the preliminary 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 adaptive threshold to one of a mean threshold value and a median threshold value of the threshold range.

7. The method of claim 6, wherein the histogram shows a maximum frequency of the number of balls.

8. The method of claim 1, wherein the general inter-ball distance is an average of the distances between each pair of adjacent balls.

9. 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.

10. The method of claim 9, wherein the step of determining the projection further comprises the step of projecting a row or column of an image of the balls in a direction, wherein the direction is one of horizontal and vertical.

11. The method of claim 9, wherein an inter-peak distance bin width is a tolerance of the general inter-ball distance.

12. The method of claim 9, wherein the number of balls is determined according to:

$N=\frac{\mathrm{distance}<br><br><br><br>\mathrm{between}<br><br><br><br>\mathrm{the}<br><br><br><br>\mathrm{first}<br><br><br><br>\mathrm{and}<br><br><br><br>\mathrm{the}<br><br><br><br>\mathrm{last}<br><br><br><br>\mathrm{ball}}{\mathrm{inter}<br><br>\text{-}<br><br>\mathrm{ball}<br><br><br><br>\mathrm{distance}}+1$

where N is the number of balls and the inter-ball distance is determined according to a maximum value of the inter-peak distance histogram.

13. The method of claim 9, wherein the given threshold is an adaptive threshold.

14. The method of claim 13, further comprising determining the adaptive threshold, comprising the steps of:

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

determining a histogram for the preliminary 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 adaptive threshold to one of a mean threshold value and a median threshold value of the threshold range.

15. The method of claim 14, wherein the histogram shows a maximum frequency of the number of balls.

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