X-ray or gamma ray systems or devices – Specific application – Absorption
Reexamination Certificate
1998-10-26
2001-02-06
Porta, David P. (Department: 2876)
X-ray or gamma ray systems or devices
Specific application
Absorption
C378S062000
Reexamination Certificate
active
06185273
ABSTRACT:
The invention relates to a process and a circuit arrangement for testing solder joints.
The quality of solder joints on printed circuit boards can be checked for defects by means of X-rays. In the process, solder-joint-specific quality information is formed, either the information “solder joint defect-free” or the information “solder joint defective” being formed for each solder joint. This information is printed out with reference to printed circuit boards, this print-out, together with the associated printed circuit board, being supplied to a repair workstation. There, the printed circuit boards which have at least one solder joint for which the information “solder joint defective” was formed is subjected to subsequent treatment, the allegedly defective solder joint being checked visually. If the result is that the solder joint is actually defective, the contact point having the original defective solder joint is re-soldered. A test is then carried out again to see whether this solder joint is now defect-free. These operations are noted in a report which, if necessary, is available for statistical evaluation.
EP 0 236 001 B1 has already disclosed a process and a device for measuring structural properties of selected regions of a manufactured printed circuit board having solder joints provided thereon. The device has an X-ray device for generating an X-ray beam, an imaging device for registering the X-rays transmitted through the printed circuit board in order to generate a corresponding electronic image, a processing device for converting the electronic image into an image encoded in accordance with a grey scale, and a computing device which carries out measurements on the image that has been encoded in accordance with a grey scale on the basis of measuring algorithms which are selected from a data library and which relate to predefinable electronic standard components and arrangements and to specific types of solder-joint defect that are associated with these (including “solder ball”, “excess solder”, “cold solder joint”). The computing device also generates an output signal which corresponds to a change in the measurements of the image encoded in accordance with a grey scale from predetermined measuring standards which, for their part, correspond to desired structural properties which are contained in the library. The output signal may also contain measurement data for the process control of printed circuits produced in the future. However, these measurement data are not used in the continuous production process in which the properties of the printed circuit boards are measured.
Processes for testing solder joints are also known from U.S. Pat. No. 5,291,535, from Soron, E.: “X-Ray Systems keep Pace with SMT”, in Test & Measurement World incorp. Electronic Test 11 (1991) February 15, No. 3, San Francisco, Calif., US, pages 21/22 and from Driels, M. R. and Nolan, D. J.: “Automatic Defect Classification of Printed Wiring Board Solder Joints”, in: IEEE Transactions on Components, Hybrids, and Manufacturing Technology 13 (1990), No. 2, New York, US, pages 331-340.
Furthermore a process for testing solder joints is known from Feldmann, K. and Sturm, J.: Closed Loop Quality Control in Printed Circuit Assembly, in IEEE Transactions on Components, Packaging and Manufacturing Technology—Part A 17 (1994) June, No. 2, New York, US, pages 270-278. The quality of the solder joints is tested by means of a X-ray inspection system. This system generates x-ray images of the solder joints as well as a list of actual defects as well as of pseudo defects and transmits said list to a repair station.
At the repair station a light beam is directed to solder joints having an actual defect or having a pseudo defect. Thereby a local indication of the solder joints having an actual defect or having a pseudo defect is generated on the circuit board. The operator at the repair station performs a defect verification on basis of said local indication of solder joints having an actual defect or having a pseudo defect.
On the basis of this prior art, the invention is based on the object of specifying a process and a circuit arrangement of the type mentioned at the beginning which improve the quality of the test of solder joints.
According to the invention, this object is achieved by a process and a circuit arrangement which are defined in the claims.
The invention is associated with a plurality of advantages. The operator at the repair work station receives comprehensive information on the position of a solder joint having a defect as well as an information on characteristics of this solder joint.
This comprehensive information is provided on a visual display device but not on the circuit boards having defective solder joints. Therefor, it is not required to transport the circuit boards having the actual defects or having pseudo defects to the repair work station; on the contrary said circuit boards can remain in another location. Thereby time and transport costs are saved.
The quality of the defect verification is considerably improved by means of the display of defective solder joints together with associated defect data. Thereby the number of repair operations based on pseudo defects is reduced on the one hand. On the other hand the information provided at the visual display device of the repair work station allows that operators having a relatively low qualification are able to perform the defect verification operations.
In summary, the invention allows that the tests of the quality of the solder joints can be performed in relatively short time and with high efficiency.
REFERENCES:
patent: 4809308 (1989-02-01), Adams et al.
patent: 4852131 (1989-07-01), Armistead
patent: 5291535 (1994-03-01), Baker et al.
patent: 5687209 (1997-11-01), Adams
patent: 5754621 (1998-05-01), Suzuki et al.
patent: 0 236 001 B1 (1991-08-01), None
Fish & Richardson P.C.
Macrotron Process Technologies GmbH
Porta David P.
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