Radiant energy – Photocells; circuits and apparatus – With circuit for evaluating a web – strand – strip – or sheet
Reexamination Certificate
1998-10-21
2001-01-23
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
With circuit for evaluating a web, strand, strip, or sheet
C250S559120, C356S237400, C382S150000
Reexamination Certificate
active
06177682
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the inspection of solder balls in a ball grid array (BGA) on an integrated circuit chip package or similar structure. More particularly it relates to a method and apparatus for the inspection of the BGA to determine if the components of the BGA or similar structure meet certain predefined parameters.
BACKGROUND OF THE INVENTION
The inspection of packaging of electronic devices such as integrated chip (IC) packaging is well known in the art and is widely used in the electronic industry. ICs, electronic chip or chip packages, in this case of BGA types, are passed in a tray through the inspecting device. The purpose of the inspection is to measure the coplanarity (relative heights), colinearity (alignment) and the height of each individual ball of the solder balls on the BGA of an IC chip. As is known in the prior art these height measurements can be accomplished with laser triangulation methods, interferometry, and other non-contact measurements. However all tend to be complex and difficult to implement in a manufacturing setting.
A number of methods also exist wherein some part of the measuring device touches a portion of the BGA as exemplified by U.S. Pat. No. 5,621,530: “Apparatus and Method for Verifying the Coplanarity of a Ball Grid Array”, issued Apr. 15, 1997. That patent describes an apparatus and method that places the IC with a BGA in the so-called live bug mode (i.e. the BGA is facing down) on a transparent surface and directs light through a series of mirrors onto the BGA. The reflected image is then analyzed to determine if the tips of all of the solder balls rest on the transparent surface. The focus information is then used to determine the distance to each solder ball which provides an indication of the coplanarity of the solder balls of the BGA. U.S. Pat. No. 5,465,152: “Method for Coplanarity Inspection of Package or Substrate Warpage for Ball Grid Arrays, Column Arrays and Similar Structures”, issued Nov. 7, 1995, provides another apparatus and method for determining coplanarity and warpage. This invention uses index pads which are positioned on the substrate of the BGA. The pads reflect specific incident radiation from which the alignment and heights of the solder ball tops with respect to the surrounding array can be determined. The invention, from the information so obtained, allows one to determine the degree of coplanarity or substrate warpage.
However, the current methods tend to be limited in the parameters each can verify and check. The current methods like the ones described in the two patents mentioned above, for the most part use triangulation methods and specialize in the inspection of one or two parameters (e.g. coplanarity in the examples noted above). Thus, what is needed is a non-invasive easily implemented system which can measure and verify a wide variety of parameters in an expeditious manner. A system which would be able to measure such parameters as height, position, shape, colinearity, and coplanarity all in one simple and straight forward process during the manufacturing process. A method which allows a full three dimensional (3-D) inspection of the chip quality during the manufacturing process.
SUMMARY OF THE INVENTION
Among the goals of the present invention are the providing of a non-invasive easily implemented system which can measure and verify a wide variety of parameters of a solder ball grid array on an integrated circuit chip in an expeditious manner. A method which has a much wider scope than current methods which allows the full 3-D inspection of the chips quality during the manufacturing process.
In brief, the invention achieves these goals by using one or more X-ray or light sources to create shadows of the solder balls of a ball grid array on the substrate on which the BGA is located, then to image the BGA with the shadows cast by the balls of the array and then analyze the images so obtained to determine if they meet predefined parameters.
According to the invention there is provided a system for verifying that a ball grid array on an integrated circuit conforms to specific position parameters. This system includes a source of electromagnetic radiation which projects that radiation at a predetermined angle onto a substrate of the integrated circuit on which substrate surface is said array, an imaging device to obtain an image or images of shadows cast by the minute objects and means to analyze said image to obtain contour data of the shadows cast. In an additional aspect of the invention, it provides the ability to analyze the contour data to determine if the balls meet certain predefined parameters.
In yet another aspect of this invention, the radiation used to illuminate the solder balls of the BGA can either be x-rays or light. Generally, if x-rays, the x-ray source and the imaging device are positioned on opposite sides of the chip being imaged. If light, the light source and imaging device are positioned on the same side of the chip being imaged.
In yet another aspect of this invention, in the preferred embodiment, the predetermined angle at which the axis of illumination of the radiation projected at the BGA strikes the substrate can vary from 10 to 40 degrees. Additionally, in the preferred embodiment, a projection onto the substrate of the path of the axis of illumination of the radiation used to illuminate the BGA can be any angle of from 5 to 40 degrees with the primary orthogonal axis of the BGA.
In one variation of the invention, multiple sources of illumination are provided to illuminate the BGA at the same predetermined angle but from different directions. Generally, the number of sources are two or four in the preferred embodiment of this variation and the sources are positioned at equidistant angles from each other. Thus, by using multiple sources of illumination a more precise image is obtained for analysis and the option exists to create a three dimensional image of the BGA for analysis.
In yet another variation of the invention multiple imaging devices are used, generally two or three imaging devices in the preferred embodiment of this variation. Using the multiple images obtained, the system can preform sophisticated analysis on the BGA and produce a three dimensional image of the BGA for analysis.
The invention also provides a method for verifying that an array of minute objects on a workpiece conform to specific parameters. The method includes: projecting electromagnetic radiation at a predetermined angle onto a substrate surface of the workpiece on which substrate surface are positioned an array of minute objects, imaging the shadows cast by the minute objects as a result of being illuminated by the electromagnetic radiation, and analyzing the images so obtained to determine if the array of minute objects on the substrate meet certain predefined parameters.
REFERENCES:
patent: 5465152 (1995-11-01), Bilodeau et al.
patent: 5574801 (1996-11-01), Beillon
patent: 5621530 (1997-04-01), Marrable, Jr.
Bartulovic Vuk
Lucic Miljenko
Zacek Gabriele
Anglehart James
Le Que T.
Novacam Tyechnologies Inc.
Swabey Ogilvy Renault
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