Optics: measuring and testing – Inspection of flaws or impurities – Surface condition
Reexamination Certificate
2001-07-26
2004-07-20
Nguyen, Tu T. (Department: 2877)
Optics: measuring and testing
Inspection of flaws or impurities
Surface condition
Reexamination Certificate
active
06765667
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an inspection method for inspecting circuit boards (printed circuit board: PCB) by the image processing, in particular, with respect to circuit boards installed in consumers appliances or electronic apparatus such as computers, and relates to the inspection method for inspecting parts in the circuit board and solders connecting those parts,
There are circuit board visual inspection instruments as the inspection apparatus for inspecting the appearance of circuit boards to be installed in electronic apparatus. The circuit board visual inspection instruments are broadly classified into two classes depending upon the image-picture taking method. One is a 2-dimensional imaging apparatus that is a combination of a CCD camera and a lighting apparatus (special lighting apparatus devising light illumination state using such as a ring-shaped light source), and the other is a 3-dimensional imaging apparatus based on the laser trigonometrical survey or the light-section method.
In the conventional circuit board inspection method, in case of implementing the visual inspection of parts installed on an electronic circuit board in accordance with image data obtained by the measurements using the above-mentioned 2-dimensional imaging apparatus or the 3-dimensional imaging apparatus, a region to be inspected, such as a region of interest, ROI, for each part has been set, and then only the ROI for each part has been inspected.
On the other hand, as for an apparatus for inspecting the whole plane of a circuit board, there is an inspection apparatus disclosed in Japanese Unexamined Patent Application Gazette, Hei 4-208803. In this inspection apparatus, from spatial information at three points at which no part is installed on a circuit board, inclination of this circuit board is detected. In this latter conventional inspection apparatus, calculation is made on a plane that was in parallel with respect to the circuit board as the board-approximated plane, and then having this boardapproximated plane as a threshold value, measured image data were converted into binary data; thereby a binary image data was obtained. In this conventional inspection apparatus, based on obtained binary image data, size, position, and inclination of each parts were calculated, and then the results are compared with predetermined standard values, and thereby the installation state of each part on the board were inspected. In such a manner, in accordance with the inspection apparatus disclosed in the Unexamined Patent Application Gazette, Hei 4-208803, it was possible to inspect the whole plane of a circuit board.
In the aforementioned circuit board visual inspection apparatus using one of conventional circuit board inspection methods, inspection regions are previously set up, and inspection was carried out on only those pre-set regions, whereas no inspection was done on other regions than those set regions; as a result, in those cases that electronic parts and solders were placed mistakenly in those regions other than pre-set regions, these were not detected. There was a problem that any inadequate placement of electronic parts and solders could be the cause that would introduce short-circuiting between wirings or abnormal actions, thereby extremely lowering the quality of the circuit board extremely. That is, in those conventional circuit board visual inspection apparatus in which the inspection regions were limited, there was a problem that any cause of the failure as mentioned above, could not be detected.
As the apparatus which solves such the problem in the conventional circuit board visual inspection, there was an inspection apparatus disclosed in the Unexamined Patent Application Gazette, Hei 4-208803, in which the inspection of the parts installation state in the whole area of a circuit board was carried out. In this inspection apparatus, a method was proposed that an approximated plane of a circuit board was calculated as a threshold value from three points at which no part is installed on a circuit board, then condition of the installed part is extracted from this threshold value and the threedimensional information. In accordance with this method, when the heights of the parts that were the objects of the inspection was higher enough than the amount of the deformation of the circuit board, it was possible to extract the electronic parts and solders by the comparison between the three dimensional information of the circuit board and the approximated plane. However, since an actual circuit board has a three-dimensional deformation, in such cases as for miniature-sized parts wherein heights of the inspection objects are lower with respect to the deformation of the circuit board, such the miniaturesized parts are buried by the deformation of the circuit board, it happened that such the miniaturesized parts could not be extracted by the comparison process with respect to the approximated plane. And at those positions where the amount of the deformation of the circuit board is large, it also happened that the circuit board itself was recognized by mistake as the parts of object to be inspected. Particularly, in case of inspecting the miniature-sized parts, which were the trend of recent years, and the printed solder-pastes for connecting those parts, it was not possible to realize a high accuracy extraction of them.
Then, in the present invention proposed here, which proposes a circuit board inspection method which enables to extract, in high accuracy, all the miniature-sized parts placed on a circuit board excluding the influence due to the amount of deformation of the circuit board, it purposes to improve the accuracy of the inspection.
BRIEF SUMMARY OF THE INVENTION
A circuit board inspection method in accordance with the present invention comprises:
(1) a step of measuring the 3-dimensional shape of a circuit board, which is the object of the inspection, thereby setting the data obtained to be surface-shape measured data,
(2) a step of automatically estimating the amount of distortion of the circuit board from the surface-shape measured data of the whole surface of the measured circuit board,
(3) a step of automatically generating an approximated surface shape from the estimated result at the above-mentioned step (2), and
(4) a step of performing a subtraction process between the approximated surface generated at the above-mentioned step (3) and the surface-shape measured data.
The circuit board inspection apparatus is provided with processing apparatus performing the above-mentioned processing steps, thereby extracting in high accuracy those parts other than the circuit board which are placed on the whole surface of the circuit board. Then the circuit board inspection method and the apparatus using this method can carry out the inspection of circuit board in high accuracy by comparing the extracted data with respect to a preset teaching data showing position information and shape information of objects to be inspected in the qualified condition.
The circuit board inspection method in accordance with the present invention comprises:
a measuring process for measuring the surface-shape data of the circuit board on which parts to be measured are placed,
an approximated surface-shape generating process for generating an approximated surface-shape, which is estimating the surface-shape of a circuit board on which objects of interest are not placed, from measured surface-shape data,
a subtraction process for subtracting the approximated surface-shape generated above from the measured surface-shape data,
an ROI (region of interest) determination process for determining those areas which are different from the approximated surface-shape in accordance with the data obtained by the abovementioned subtraction process to be an ROI (region of interest), and
an inspection process for inspecting if electronic parts placed on the above-mentioned circuit board as well as connecting materials for connecting those electronic parts are in a desired state with respect to th
Higashi Noboru
Kaida Kenichi
Nagai Daisuke
Akin Gump Strauss Hauer & Feld L.L.P.
Nguyen Tu T.
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