Using cone shaped search models to locate ball bonds on wire bonded devices

• US 5,550,763 A
• Filed: 05/02/1994
• Issued: 08/27/1996
• Est. Priority Date: 05/02/1994
• Status: Expired due to Term

• Current Assignee: Cognex Corporation
• Original Assignee: Cognex Corporation
• Inventors: Michael, David J., Koljonen, Juha, Garakani, Arman
• Primary Examiner(s): Voeltz, Emanuel T.
• Assistant Examiner(s): Shah, Kamini S.
• Application Number:
  US08/236,211
• Time in Patent Office: 848 Days
• Field of Search: 228/102, 356/394, 356/237, 356/376, 348/131, 348/126, 348/87, 364/491, 364/492, 364/582, 364/560, 382/8, 382/25, 382/48, 382/126, 382/145, 382/169, 382/199
• US Class Current: 702/155
• CPC Class Codes: G01N 21/88 Investigating the presence of flaws or contamination
• CPC Class Codes: H01L 2224/05599 Material
• CPC Class Codes: H01L 2224/45099 Material
• CPC Class Codes: H01L 2224/48465 the other connecting portion not on the bonding area being a wedge bond, i.e. ball-to-wedge, regular stitch
• CPC Class Codes: H01L 2224/859 involving monitoring, e.g. feedback loop
• CPC Class Codes: H01L 24/48 of an individual wire connector
• CPC Class Codes: H01L 24/85 using a wire connector wire bonding in general B23K20/004
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H01L 2924/14 Integrated circuits

Abstract

Method and apparatus for automatically locating the center of a ball bond of a wire to a lead frame and semiconductor chip or similar device; analyzing the optically sensed images; a bonding mechanism; and a host controller connected to the bonding mechanism, the movable platform. The present invention constructs a synthetic flattened cone model using a center radius, and monotonically increasing slope values to generate a model having a variation in grey levels, and inner and outer radii that will encompass expected size variations in a ball bond; sets a threshold for acceptable normalized correlation search results; acquires a digitized image of the bond, including a nominal location for the bond; conducts a normalized correlation search of the digitized image at the bond location, using the flattened synthetic cone model; and indicates the presence and location of the expected circular object as the location having the largest coefficient which exceeds a threshold.

Claims

1. An apparatus for automatically locating the center of a ball bond formed on a bonded semiconductor pad in a digitized image of said ball bond comprising:

a. means for constructing a flattened synthetic cone shaped model having a monotonically increasing slope value for concentric circles having varying grey levels, where each circle has inner and outer radii encompassing at least one expected size variation in said ball bond;

b. means for conducting a normalized correlation search in a vision processing system using said flattened synthetic cone shaped model as a search model to generate correlation coefficient signals;

c. means for evaluating said correlation coefficient signals to generate signals indicating the presence and center of said ball bond to an inspection means so that the quality of said ball bond can be inspected.

2. The apparatus of claim 1, wherein said flattened synthetic cone shaped model is created by setting pixel values in said flattened synthetic cone shaped model to a first value for pixels to be ignored by said normalized correlation search, to a second value for pixels within an outer radius (r outer) of said flattened synthetic cone shaped model corresponding to the largest expected size of said ball bond, to a third value for at least one intermediate center radius of said flattened synthetic cone shaped model and to a plateau value for the innermost radius (r inner) of said flattened synthetic cone shaped model, where the formula ##EQU2## is used to provide a monotonically increasing slope value.

3. The apparatus of claim 1, wherein said flattened synthetic cone shaped model is created by setting pixel values in said flattened synthetic cone shaped model to a first value for pixels to be ignored by said normalized, correlation search, to a second value for pixels within an outer radius (r outer) of said flattened synthetic cone shaped model corresponding to the largest expected size of said ball bond, to a third value for at least one intermediate center radius of said flattened synthetic cone shaped model and to a plateau value for the innermost radius (r inner) of said flattened synthetic cone shaped model, where the said first value, second value, and said plateau values are predetermined constants that differ from each other.

4. The apparatus of claim 1, further comprising:

means for not defining said flattened synthetic cone shaped search model at angles plus and minus a specified number of degrees around the incident wire angle, (w) in said digitized image of said ball bond.

5. A method for automatically locating the center of a ball bond formed on a bonded semiconductor pad in a digitized image of said ball bond comprising:

a. constructing a flattened synthetic cone shaped model having a monotonically increasing slope value for concentric circles having varying grey levels, where each circle has inner and outer radii encompassing at least one expected size variation in said ball bond;

b. conducting a normalized correlation search in a vision processing system using said flattened synthetic cone shaped model as a search model to generate correlation coefficient signals;

c. evaluating said correlation coefficient signals to generate signals indicating the presence and center of said ball bond to an inspection means so that the quality of said ball bond can be inspected.

6. The method of claim 5, wherein said flattened synthetic cone shaped model is created by setting pixel values in said flattened synthetic cone shaped model to a first value for pixels to be ignored by said normalized correlation search, to a second value for pixels within an outer radius (r outer) of said flattened synthetic cone shaped model corresponding to the largest expected size of said ball bond, to a third value for at least one intermediate center radius of said flattened synthetic cone shaped model and to a plateau value for the innermost radius (r inner) of said flattened synthetic cone shaped model, where the formula ##EQU3## is used to provide a monotonically increasing slope value.

7. The method of claim 5, wherein said flattened synthetic cone shaped model is created by setting pixel values in said flattened synthetic cone shaped model to a first value for pixels to be ignored by said normalized correlation search, to a second value for pixels within an outer radius (r outer) of said flattened synthetic cone shaped model corresponding to the largest expected size of said ball bond, to a third value for at least one intermediate center radius of said flattened synthetic cone shaped model and to a plateau value for the innermost radius (r inner) of said flattened synthetic cone shaped model, where the said first value, second value, and said plateau values are predetermined constants that differ from each other.

8. The method of claim 5, further comprising the step of:

not defining said flattened synthetic cone shaped search model at angles plus and minus a specified number of degrees around the incident wire angle, (w) in said digitized image of said ball bond.