Process for cooling soldered objects

Details Process for cooling soldered objects Process for cooling soldered objects

1999-03-11

2001-05-15

Ryan, Patrick (Department: 1725)

Metal fusion bonding

Process

With protecting of work or filler or applying flux

C228S046000, C228S200000, C228S234200

Reexamination Certificate

active

06230962

ABSTRACT:

This invention relates to a process for cooling soldered objects, in particular in vapour phase soldering.
When modules or module units are to be soldered it is decisive that the object to be soldered be heated so well that no cold soldered joints will occur. This requires thorough heating of the soldering partners. In many cases it is extremely important that the soldered object is cooled rapidly subsequent to soldering. While it is relatively unproblematical in many soldering processes to conduct e. g. cooling air to the soldered object, this is not the case in the vapour phase soldering process. In vapour soldering it is of great importance that the climate conditions of the processing chamber are kept stable. It is therefore impossible to start cooling of the soldered object immediately after soldering. Moreover, entrainment of the soldering medium in the form of vapour molecules is to be avoided, because the vapour phase soldering liquids are very expensive. After the soldered object has been removed from the vapour layer it dries and cools relatively slowly by way of natural convection. According to the prior art, cooling of the soldered object normally takes place far away from the vapour zone. As a rule, the cooling zone is furthermore locked by lockages which prevent that too many molecules from the vapour phase are entrained.
Cooling of the soldered objects can also be effected by spraying a cold liquid onto them. Such cooling is disclosed in DE-39 15 040.
EP-A-0 138 707 (which corresponds to U.S. Pat. No. 4,612,712) discloses a vapour phase heating apparatus. DE-C-38 40 098 discloses an apparatus for removing soldering residues by means of a drying step using a blower.
It is known that rapid cooling of the soldered joint after soldering is advantageous with respect of the metal structure of the soldered joints. As long as the solder is in the liquid stage, alloying of the participating metals takes place. In general, this leads to drawbacks with respect to the metallurgy of the soldered joints and should be avoided, if possible. Rapid cooling of the soldered objects after soldering is thus decisive. One can proceed from the assumption that the shorter the liquid phase of the solder the better the quality of the soldered joint. It is known from various studies that very rapid cooling of the soldered joint can yield higher strength. In this process the soldered joints were cooled almost in a shock-like manner. This type of cooling, though it would be desirable with respect to the quality criteria to be achieved, is accomplished in none of the soldering processes used in modern mass production.
It is the object of this invention to provide a process for cooling soldered objects, according to which rapid cooling of the soldered objects is achieved directly after soldering.
It is a further object of this invention to cool parts of the soldered objects outside the soldered joints.
These objects are achieved by means of the features of the claims.
To achieve these objects the invention proceeds from the basic idea to apply a liquid onto the soldered objects and to subject them to accelerated evaporation. Evaporation heat is thus withdrawn from the soldered objects and they are thus cooled rapidly.
According to an advantageous embodiment, the process is used in vapour phase soldering. The invention utilizes the special climatic conditions prevailing above the vapour phase. Directly above the vapour phase the temperature decreases from e.g. 200° C. (boiling point of the vapour phase liquid) to about 50° C. within a few centimeters of height. Moreover, vapour phase molecules and e.g. ambient air are in the region above the vapour phase. The invention proceeds from the basic idea that the humidity of the atmosphere above the vapour phase which is substantially determined by the vapour molecules, is forced e.g. by means of a blower to condensation onto the soldered object. By means of the condensation of the liquid in connection with forced convection caused by the blower and the resulting cold due to evaporation it is possible to achieve rapid cooling of the soldered objects directly after removal from the vapour phase, i. e. within a few seconds.


REFERENCES:
patent: 4348174 (1982-09-01), Spigarelli
patent: 4389797 (1983-06-01), Spigarelli et al.
patent: 4771929 (1988-09-01), Bahr et al.
patent: 4840305 (1989-06-01), Ankrom et al.
patent: 5333774 (1994-08-01), Mishina et al.
patent: 5514414 (1996-05-01), Gao et al.
patent: 3840098 C1 (1989-12-01), None
patent: 92 18 177 U (1993-11-01), None
patent: 0 138 707-A1 (1983-10-01), None
Patent Abstracts of Japan, vol. 13, No. 365 (M-859) [3713], Aug. 15, 1989.
Japanese Abstract No. JP 01 122663 A (Mitsubishi Denki K.K.).

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