Apparatus and method for detecting leaks in packages
First Claim
1. A method of inspecting a package for gross leaks, the method comprising the steps of:
- a) placing the package in a chamber,b) varying the pressure in the chamber by an amount sufficient to deform a surface of the package by a small integral number of wavelengths of light,c) recording an interferometric image of the surface of the package,d) waiting for an interval of several seconds,e) varying the pressure in the chamber at a known rate, while simultaneously recording a series of second interferometric images of the surface observed in step (c),f) comparing the second images with the image of step (c) to determine whether the surface has moved during the interval of step (d), andg) determining whether the package is leaking by analyzing movement of said surface.
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Accused Products
Abstract
This invention detects leaks in small, hermetically sealed packages, especially microchips or other packages of electronic circuits. The invention includes a procedure for detecting fine leaks, and a somewhat different procedure for finding gross leaks. To detect gross leaks, one places the package in a chamber, and varies the pressure in the chamber slightly. If the leak is not too big, one wall of the package, such as its lid, initially becomes deformed, but quickly returns to its original position, due to the leak. If the leak is very large, the wall of the package may not move at all. The position of the wall is monitored with an interferometer, such as an electronic shearography apparatus. The movements of the wall show whether there is a gross leak. In the fine leak test, the package is placed in the chamber and the pressure is changed substantially, thus causing the walls of the package to deform. If there is a fine leak, a deformed wall gradually returns to its initial position. Preferably, the chamber is pressurized with helium to increase the sensitivity of the test. The gradual return of the deformed wall can be measured by the interferometer, and the rate at which the wall returns to its starting position can be used to calculate the leak rate. In another embodiment, a single pixel of a series of interferometric images is analyzed to determine the number of times the pixel changes from a maximum to a minimum and back to a maximum. The latter number is related to the number of wavelengths of deformation, and can be used to compute the leak rate of the package.
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Citations
29 Claims
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1. A method of inspecting a package for gross leaks, the method comprising the steps of:
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a) placing the package in a chamber, b) varying the pressure in the chamber by an amount sufficient to deform a surface of the package by a small integral number of wavelengths of light, c) recording an interferometric image of the surface of the package, d) waiting for an interval of several seconds, e) varying the pressure in the chamber at a known rate, while simultaneously recording a series of second interferometric images of the surface observed in step (c), f) comparing the second images with the image of step (c) to determine whether the surface has moved during the interval of step (d), and g) determining whether the package is leaking by analyzing movement of said surface. - View Dependent Claims (2, 3, 4, 5)
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6. A method of inspecting a package for gross leaks, the method comprising the steps of placing the package in a chamber, and varying the pressure in the chamber at a known rate, while simultaneously recording a series of interferometric images of a surface of the package, comparing said images with each other to determine how much the surface has moved, and determining whether the package is leaking by analyzing movement of said surface.
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7. A method of inspecting a package for fine leaks, the method comprising the steps of:
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a) placing the package in a chamber, b) varying the pressure in the chamber by an amount sufficient to deform a surface of the package by a large number of wavelengths of light, c) recording a first interferometric image of the surface of the package, after completion of step (b), d) recording a series of second interferometric images of the surface observed in step (c), e) comparing the second images with the first image to detect changes in displacement of the surface while said second interferometric images are being recorded, and f) determining whether the package is leaking by analyzing the changes in displacement of said surface, wherein the chamber is pressurized with helium before the second interferometric images are recorded. - View Dependent Claims (8, 9, 10)
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11. A method of inspecting a package for leaks, the method comprising the steps of:
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a) placing the package in a chamber, b) varying the pressure in the chamber by an amount sufficient to deform a surface of the package by a small integral number of wavelengths of light, c) generating a series of interferometric images of at least a portion of the surface, during an interval of time, each image including at least one pixel, d) determining the number of times that a given pixel changes from a maximum to a minimum to a maximum intensity, during said interval of time, and using said number to determine the deformation of the surface during said interval, and e) determining whether the package is leaking by analyzing the deformation of said surface. - View Dependent Claims (12, 13, 14, 15, 16, 17)
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- 18. A method of inspecting a package for leaks, the method comprising the steps of placing the package in a chamber, varying the pressure in the chamber, generating a series of interferometric images of at least a portion of the surface, during an interval of time, each image including at least one pixel, determining the number of times that a given pixel changes from a maximum to a minimum to a maximum intensity, during said interval of time, using said number to determine the deformation of the surface during said interval, and determining whether the package is leaking by analyzing the deformation of said surface.
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22. A method of determining the stiffness of a surface of a package, the method comprising the steps of:
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a) placing the package in a chamber, b) generating a series of interferometric images of at least a portion of the surface, during an interval of time, each image including at least one pixel, c) varying the pressure in the chamber at a known rate, so as to deform the surface of the package by a small integral number of wavelengths of light, and d) determining the number of times that a given pixel changes from maximum to minimum to maximum intensity, during said interval of time, and using said number to determine the deformation of the surface of the package, and e) determining whether the package is leaking by analyzing the deformation of said surface. - View Dependent Claims (23, 24, 25)
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26. A method of inspecting a pressurized package for leaks, the method comprising the steps of:
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a) generating a series of interferometric images of at least a portion of the surface, during an interval of time, each image including at least one pixel, and b) determining the number of times that a given pixel changes from maximum to minimum to maximum intensity, during said interval of time, and using said number to determine the deformation of the surface during said interval, and c) determining whether the package is leaking by analyzing the deformation of said surface. - View Dependent Claims (27, 28)
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29. A method of measuring fine movements or deformations of a surface, the method comprising the steps of:
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a) generating a series of interferometric images of at least a portion of the surface, during an interval of time, each image including at least one pixel, and b) determining the number of times that a given pixel changes from maximum to minimum to maximum intensity, during said interval of time, and using said number to determine the travel or deformation of the surface during said interval.
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Specification