Optics: measuring and testing – By polarized light examination – With light attenuation
Patent
1991-11-22
1995-08-08
Pham, Hoa Q.
Optics: measuring and testing
By polarized light examination
With light attenuation
356237, G01N 2188
Patent
active
054403910
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method for determining a position of at least one lead of an electronic component, especially a semi-conductor element, with respect to a reference plane, wherein said lead is illuminated from a first position situated sideways and out of a plane defined by the electronic component, and wherein a first image of at least a part of said lead is formed on an image plane. The invention also relates to a device for performing the method.
BACKGROUND OF THE INVENTION
Such a method is used for determining the mutual position differences between leads of an electronic component, in particular a semi-conductor element. There are several reasons for which the leads of an electronic component are not always aligned accurately. However, for the assembling of a chip on a card it is important that the leads are positioned well with respect to the soldering areas. A deviation between a lead and a soldering area can end in that there is no mechanical contact between soldering area and lead and therefore that no electronic contact will be realised so that the whole card can become useless. However, since the leads are frequently bent with respect to the desired distance, it is necessary to verify to which extend this bending can lead to an inoperational card. The known method allows to check, by a position determination whether the leads are arranged correctly. To this end, a two-dimensional image is generated from the underside of the electronic component for example by means of a television camera. The image is realized by the fact that the electronic component is illuminated by a coherent light beam which is arranged at a certain angle with respect to the camera. The position in the image of the light source reflected on the lead comprises the necessary information to deduce herefrom the position of the lead.
A drawback of the known method and of the device used therein is the necessity to use a coherent light beam for giving the beam reflected on the lead a sufficient intensity in order to form a clear image. The latter requires the use of a laser as a light source, which involves on the other hand that the device has to be covered adequately, which renders in its turn the used device and method expensive.
SUMMARY OF THE INVENTION
An object of the present invention is to realise a method and a device for determining a position of at least one lead of an electronic component, wherein use is made of simplier and therefore cheaper means without influencing the reliability of the measurement negatively.
To this end, a method according to the invention is characterized in that a shadow image is formed when forming said first image and said lead is illuminated from a second position different from said first position for forming a second shadow image on said image plane, and said first and respectively second shadow image is located and a third respectively fourth position is determined to this end and in that said position is determined from said third and fourth position. Due to the use of shadow images, it is not necessary to use a coherent light source, such as a lazer, and it is therefore also not necessary to cover the device against light of a too high intensity. By determining further two shadow images it is possible to establish unambiguously the position of the lead. Indeed, each deviation from a standard position automatically results in that both shadow images will be located in a position different from the position of the standard images, so that the position of the lead can always be determined unambiguously and reliably from the position of the set of shadow images.
A first preferred embodiment of a method according to the invention is characterized in that said third and respectively fourth position is located substantially in the middle of said first and respectively second shadow image. Due to this, the third and fourth position is simply to locate.
Advantageously, illuminating from said first and second position is done from substantially opp
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Smeyers Gust
Vanderheydt Luc
ICOS Vision Systems n.v.
Pham Hoa Q.
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