Image analysis – Applications – Manufacturing or product inspection
Reexamination Certificate
1997-11-12
2001-06-19
Boudreau, Leo (Department: 2621)
Image analysis
Applications
Manufacturing or product inspection
C382S146000, C250S559340
Reexamination Certificate
active
06249598
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for testing soldering states of electronic components mounted on a printed circuit board, and more particularly to a solder testing apparatus for use in a manufacturing process where correct model numbers of electronic components on printed circuit boards cannot be generally identified due to the electronic components having the same electric characteristics being supplied from a plurality of manufactures, or the like.
As for an apparatus for testing soldering states of electronic components mounted on printed circuit boards, there have been failure detecting techniques, for example, as in a high speed solder appearance testing apparatus SV2000 described in Electronic Package Technology, Vol. 9, No. 2, 1993. Specifically, when disturbance occurs, or when a new type of boards are tested for the first time, several boards, appearing to be non-defective, are extracted from a lot and applied to the apparatus to derive a mean value and dispersion from their characterizing amounts, and a failure is determined if the characterizing amounts detected from an object under testing during a test deviate from the mean value of the previously derived characterizing amounts of the non-defective boards by a predetermined amount.
However, the above-mentioned prior art technique has difficulties in supporting disturbance in a process and frequent changes of parts mounted on boards during testing. Generally, even with printed circuit boards under testing of the same type, electronic components labelled with different model numbers, which have the same electric characteristics but possibly slightly different appearances, are often treated as the same components and mounted on the boards. When a plurality of component manufacturers provide electronic components having the same electric characteristics, appearances of the electronic components manufactured by different manufacturers, for example, a lead thickness, a lead width, and so on may slightly differ from each other.
Generally, electronic components used to be mounted on printed circuit boards are supplied from the most beneficial one of manufacturers, which manufacture the components having the same electric characteristics, in terms of the price, delivery time, and so on, at the time the electronic components are to be supplied. For this reason, components from different manufacturers may possibly be mounted on printed circuit boards of the same type depending on manufacturing periods. In the prior art, test data is newly created from non-defective boards only when disturbance occurs in a process during testing. Generally, however, information on used electronic components and changes in processes is not available in a testing step.
For this reason, conventionally, a plurality of components labelled with different model numbers, having electrodes of slightly different design dimensions, have been inevitably subjected to testing using the same image processing parameters and defect determining parameters. Also, while the prior art relies on a mean value for determining a defect, it is difficult for this scheme to conduct a test based on testing specifications used in manufacturing sites. Generally, in manufacturing sites, the testing specifications are generally determined in many cases based on the shapes of leads and pads, for example, a failure is determined when a lead deviates from a pad by three percents or more of the width of the lead. However, since the prior art does not obtain these shapes from images, a highly reliable test cannot be realized.
SUMMARY OF THE INVENTION
It is an object of the present invention to realize a highly reliable test by setting image processing parameters and failure determining parameters based on actual shapes and dimensions of electrode portions (leads) and pads of electronic components mounted on printed circuit boards under testing.
The above object is realized by the following configuration.
A solder testing apparatus comprising image detecting means for detecting an appearance image of a soldered portion of an electronic component under testing mounted by soldering leads of the electronic component to pads on a printed circuit board, image processing means for performing image processing on the appearance image to identify shape characterizing amounts of the soldered portion, test parameter storing means for storing image processing parameters used in the image processing means and defect determining parameters used for determining whether the soldered portion is good or bad, and defect determining means for determining whether the soldered portion is good or bad from data derived from the image processing means and the defect determining parameters stored in the test parameter storing means, wherein the image processing means identifies shape factors of a lead and a pad and/or a shape factor of a solder fillet for each soldered portion as shape characterizing amounts for the soldered portion, and the solder testing apparatus has tested-object shape accumulating means for storing shape characterizing amounts of soldered portions identified by the image processing means, tested-object standard shape estimating means for statistically processing the shape characterizing amounts for soldered portions, accumulated in the tested-object shape accumulating means for each model, to identify, from the stored shape characterizing amounts for soldered portions, shape characterizing amounts corresponding to shape factors of leads and pads and shape factors of defective solder. fillets which exhibit a low detecting frequency or which cannot be normally derived theoretically from a structural viewpoint, as unnecessary shape characterizing amounts, and to identify shape characterizing amounts corresponding to shape factors of leads and pads and/or shape factors of non-defective solder fillets which exhibit a high detecting frequency as standard shape characterizing amounts, and for extracting the standard shape characterizing amounts from the accumulated shape characterizing amount for the soldered portions, and test parameter updating means for updating the image processing parameters and the defect determining parameters stored in the test parameter storing means based on the standard shape characterizing amounts.
A detecting optical system provided in the solder testing apparatus detects an image of a soldered portion under testing, and this image is processed by the image processing means. The image processing means detects shapes and dimensions of leads and pads of electronic components from images, and accumulates the detection results in the tested-object shape accumulating means. At the time the detection has been terminated for a complete board or a plurality of boards, a histogram for detected shapes is derived for each type of lead or pad, and values presenting maximum frequencies are determined to be standard shape characterizing amounts for actual shapes of a lead or a pad and of a solder fillet.
The image processing parameters and the defect determining parameters are updated in test data updating means based on the above-mentioned standard shape characterizing amounts. Since test data are constantly updated, irrespective of before the test or during the test, based on standard shape characterizing amounts for the shapes and dimensions of leads and pads and for solder fillets derived from actually detected images, it is possible to conduct the test using the most appropriate test data for components under test even if model numbers of mounted components have been changed in the middle while a plurality of boards of the same type are being tested in succession.
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Doemens Guenter
Honda Toshifumi
Listl Ludwig
Matsuyama Yukio
Mengel Peter
Antonelli Terry Stout & Kraus LLP
Boudreau Leo
Hitachi , Ltd.
Werner Brian P.
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