Metal fusion bonding – Process – With subsequent treating other than heating of bonded parts...
Patent
1991-06-12
1993-01-26
Ramsey, Kenneth J.
Metal fusion bonding
Process
With subsequent treating other than heating of bonded parts...
228240, 432 66, 432197, H05K 334
Patent
active
051816482
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method and an apparatus for removing solder residues from products, in particular from printed-board assemblies or circuit modules after the vapor phase soldering.
Although the invention is described in the following mainly as aftertreatment in connection with the vapor phase soldering of electronic components on printed circuit boards, the invention is not restricted thereto. The vapor phase soldering is the preferred field of application, but it is also possible to apply the cleaning measures according to the invention generally to differently pretreated soldered products.
The U.S. Pat. No. 3,724,418 discloses a soldering apparatus in which the water soluble solder residues can be removed from the soldered circuit boards by means of a hot water spray.
The German Offenlegungsschrift 30 06 045 discloses a method for cleaning flat products, such as printed circuit boards and flat circuit modules. According to this publication, the products are preferably upright and continuously transported through a chamber in horizontal direction, the cleansing fluid being simultaneously sprayed from both sides onto the surface of the products to be cleaned by spray nozzles which are disposed on both sides. In this connection, it is the task of the fluid jets to guide the flat products on the transport path as well as to clean them by dissolving and rinsing the impurities. The used cleansing fluid dissolves the impurities.
The German Offenlegungsschrift 30 28 325 discloses a method for cleaning printed circuit boards wherein the substances to be removed, such as soldering fluxes, are also eliminated by a cleansing fluid spray. The German Offenlegungsschrift describes various measures, such as direction, pressure and speed of the cleansing fluid jets, in order to remove impurities also from relatively inaccessible areas.
The German Offenlegungsschrift 34 22 562 discloses a further method for cleaning printed circuit boards after the soldering. The impurities are first removed by washing and brushing using a liquid solvent. Thereafter the thus cleaned printed circuit boards are dried. The used solvent is cleaned in a distilling apparatus and then used again as solvent in a closed cycle.
The various previously known methods have in common that the cleansing fluid dissolves the impurities to be removed, such as soldering fluxes. As a result, the cleansing fluid which leaves the cleaning step is charged with the impurities. Therefore, if the reuse of the cleansing fluid is desired, it must be cleaned before it can be employed again for the actual cleaning of the printed circuit boards. In addition, the cleaning of circuit boards with such cleansing fluids causes substantial problems particularly in the case of printed circuit boards with a high component density. This can also be taken from the above mentioned publications. This problem has recently been further aggravated by the fact that the increasingly used surface mounted devices (SMD) are in very close contact to the printed circuit board and the connections are in many cases soldered to the printed circuit board directly below the actual component. This narrow space makes it extremely difficult, if not impossible, to transport the conventionally used cleansing fluid to the soldering joints in sufficient quantity to dissolve the impurities and to carry the fluid off as fast as possible. This problem has so far been solved by using very strong and thus aggressive cleansing fluids which in turn attack the components and the printed circuit boards in an unacceptable manner. The fluorocarbons used in known cleaning devices escape during operation and are harmful to the environment.
A further problem would arise if the known cleaning apparatuses were operated immediately after the vapor phase soldering apparatuses. If these two devices are successively operated in a continuous operation, a certain amount of the heat transfer medium is carried over from the vapor phase soldering apparatus to the cleaning apparatus when the assemblies are fed into the
REFERENCES:
patent: 3724418 (1973-04-01), McLain
patent: 4022371 (1977-05-01), Skarvinko et al.
patent: 4032033 (1977-06-01), Chu et al.
patent: 4321031 (1982-03-01), Woodgate
patent: 4389797 (1983-06-01), Spigarelli et al.
patent: 4589926 (1986-05-01), Holmstrand
patent: 4612712 (1986-09-01), Pescotore et al.
Research Disclosure, No. 304, Aug. 1989, "Solder Cooling Technique" p. 304-37 by Kenneth Mason Publications Ltd., England.
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