Optics: measuring and testing – Inspection of flaws or impurities
Reexamination Certificate
2001-05-25
2003-06-17
Pham, Hao Q. (Department: 2877)
Optics: measuring and testing
Inspection of flaws or impurities
C356S237500, C356S241400, C359S798000
Reexamination Certificate
active
06580501
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an apparatus for the visual inspection in particular of concealed soldered joints, in particular between an electric or electronic component disposed on the surface of a printed circuit board and the printed circuit board.
BACKGROUND OF THE INVENTION
In the field of soldering technology, in particular with the use of SMDs (Surface Mounted Devices), and here in turn in particular with so-called BGAs (Ball Grid Arrays), chip scale packages (CSPS) and Flip Chips (FCs), the problem arises that because of the small gap height between the underside of the components and the printed circuit board the quality of the soldered joint both of the outer and of the inner pin arrays with the corresponding contact points of the printed circuit board can no longer be checked merely by visual inspection. The corresponding electric or electronic components or assemblies are therefore in general subjected to an electric function test after the soldering. This is first of all, however, time-consuming and therefore expensive and can secondly only supply information as to whether the soldered joints conduct current or whether open or short-circuits occur. Information on the quality and hence solidity of the individual soldered joints and expected life-time cannot be supplied by this test method.
It is further known to check soldered joints non-destructively by means of x-rays. With this known method also it is possible in the end to check only undesirable soldering jumpers between adjacent pins, which cause a short-circuit, or the correct position of the pins of the components on the contact points of the printed circuit board; a statement on the quality of the individual soldered joints or the visual quality of the surface of the individual soldered joints or for example on undesirable flux residues in the area of the solderings is not possible. In addition such units are very expensive to procure and maintain and the application of this known method is not completely risk-free in terms of exposure to radiation. Furthermore, such units can only be operated by highly trained and specialized persons.
A further known method for determining the quality of a soldered joint is the production of a micrograph in cross-section through the respective soldered joint. Although it is certainly possible in this way to obtain reliable information on the quality of the soldered joint, for example on sufficient melting of the solder point of the component and hence satisfactory wetting of the contact point on the printed circuit board, a destructive test method is nevertheless involved here, which can be used only on a random sample basis for the drawing of conclusions on the operating parameters of the soldering process. Moreover, a visual inspection of the surface of the individual soldered joints is also not possible in this case.
Finally, there are known from the field of medicine and engineering endoscopes with illuminating devices, with which inaccessible areas can be inspected visually. The known endoscopes have a substantially tubular layout, at the axially outer end of which a deflection unit with illumination is disposed, which deflects the light exiting out of the tubular arrangement in the gap direction or deflects the gap image in the direction of the ocular. Because of its type of construction, however, viewing into gaps of small height, in particular in the range below 1 mm gap height, as is regularly the case in particular with BGAs and other SMDS, is not possible.
SUMMARY AND OBJECTS OF THE INVENTION
Starting from this prior art it is the object of the present invention to create a generic apparatus which permits the visual inspection of in particular concealed soldered joints nondestructively in a comparatively simple and cost-effective manner.
According to the invention, an apparatus for the visual inspection of concealed soldered joints, between an electric or electronic component disposed on the surface of a printed circuit board and the printed circuit board, is provided with an ocular unit, a lens head, an image transmission unit for transmitting the image received by the lens head to the ocular unit and an illuminating device for illuminating the soldered joints to be tested. The lens head comprises a device for image deviation which extends up to the axially outer end of the lens head. The illuminating device is disposed in the lens head in such a way that the exit angle of the light of the illuminating device out of the lens head is substantially equal to the deviation angle of the image deviation. The exit point of the light is disposed next to the device for image deviation in the area of the axially outer end of the lens head.
It is also a further object of the invention to provide a method with which the quality of a soldered joint between an electric or electronic component disposed on the surface of a printed circuit board or similar, in particular an SMD or BGA component, and the printed circuit board is checkable in a simple manner.
According to the invention the apparatus for the visual inspection of concealed soldered joints comprises, in particular between an electric or electronic component soldered to a printed circuit board, for example a BGA, and the printed circuit board, for the checking of the quality of the soldered joint, first and foremost an ocular unit, a lens head, an image transmission unit for transmitting the image received by the lens head to the ocular unit and an illuminating device for illuminating the soldered joints to be tested. In other words, the apparatus according to the invention comprises first and foremost the basic constructional form of an industrial or medical endoscope. Further there is provided in the area of the lens head in a manner first and foremost also known per se a device for image deflection.
In contrast to the known endoscopes, however, in which the lens or the deflection device is by virtue of the type of construction located at least a short distance from the axially outer “distal” end of the lens head, with the apparatus according to the invention the device for image deflection extends up to the axially outer end of the lens head. For this reason alone the image exit or image entry point of the lens can be placed considerably closer to the printed circuit board in comparison with the prior art, so that gaps of smaller height or soldered joints disposed therein are visually inspectable.
Likewise in contrast to the known endoscopes, in which the illuminating device or the light exit is disposed above or below the lens or the deflection unit, whereby the gap height to be reached visually is increased and/or an undesirable light shadow is generated in the gap area, according to the invention the illuminating device is disposed in the lens head in such a way that the exit angle of the light of the illuminating device from the lens head is substantially equal to the deviation angle of the image deviation and the exit point of the light is disposed next to the device for image deviation in the vicinity of the axially outer end of the lens head. This means in other words that on the one hand the illuminating device is disposed at substantially the same height, referred to the printed circuit board surface or gap plane, as the image exit or image entry point of the lens and on the other the image illumination takes place without any vertical shading.
Overall, soldered joints in gaps with a height of less than 1 mm and well below this can be inspected visually in a simple manner with the apparatus according to the invention. This means in particular that the individual soldered joints for example in BGAS, CSPs or FCs which as a rule have a gap height of approx. 0.02 to 0.8 mm between component underside and printed circuit board, are visually checkable nondestructively for soldering defects, undesirable jumper formation, contaminations and similar.
In basically any manner the exit of the light of the illuminating device can take place monolaterally at the lens head. According to a preferred e
ERSA GmbH
McGlew and Tuttle , P.C.
Pham Hao Q.
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