Metal fusion bonding – Process – With protecting of work or filler or applying flux
Patent
1997-05-08
2000-06-06
Ryan, Patrick
Metal fusion bonding
Process
With protecting of work or filler or applying flux
164 47, 2282481, 2282341, 228258, B23K 120, H05K 334
Patent
active
060707887
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of soldering terminal faces of a substrate using molten solder, as well as to a method of manufacturing a solder alloy of at least two solder components.
2. Description of the Related Art
The demands being imposed on the quality and reliability of soldered connections are constantly growing, not the least because of the increasing miniaturization of electronic components and the ever higher integration levels of ICs. Meeting said demands using the known, industrially applicable techniques requires a considerable outlay which is correspondingly reflected in manufacturing costs. Meanwhile, use of the solder paste technique in conjunction with the reflow method has become widespread. Here, in a first process, paste-like solder material is applied onto the terminal faces and, in a second process, the heat needed for the soldering reaction is introduced. In practice, a serious problem which is frequently encountered here is the introduction of the heat quantity needed for the reflow method in such a targeted and metered manner that, on the one hand, a solder application with as homogeneous a structure as possible is formed and, on the other hand, the occurrence of irreparable damage inside the electronic components as a result of overheating is avoided.
Furthermore, with the known reflow method, depending on the level of quality demanded of a soldered connection it is necessary to effect the method in an inert atmosphere, with the result that the costs merely of providing suitable operating equipment are extremely high.
The object of the present invention is to provide a method which enables the production of high-quality and reliable soldered connections with a substantially reduced outlay for equipment and a lower number of process steps and so allows such electronic components to be manufactured at a far lower cost.
SUMMARY OF THE INVENTION
The present invention is directed to a method of soldering terminal faces 13 of a substrate 12 using molten solder. Substrate 12, which is provided with a solder-wettable surface 13 or with an at least one wettable sub-surface of an otherwise non-wettable surface, is introduced into a liquid organic medium, which has a boiling temperature equal to or above the melting temperature of the solder. The solder is then applied onto the terminal face 13 in the form of a surface or sub-surface so as to form a solder bump 14. The solder quantity associated with the terminal face is situated, at least at the moment of wetting, inside the medium, and the temperature of the medium is equal to or above the melting temperature of the solder.
The method according to the invention enables the selective soldering of terminal faces of a substrate in an environment formed by a liquid, organic medium. The substrate may be any carrier material provided with one or more terminal faces, such as for example wafers, printed circuit boards, ceramic substrates etc. Both the solder application and the structural improvement of the applied solder, which is otherwise achieved with the known reflow method in a subsequent process, are effected in a single process. Firstly, such a method makes use of the advantageous effects of the liquid organic medium which, as tests have revealed, both acts reductively upon the surface to be wet and increases the wettability of the solder material. Secondly, tempering of the solder material by the liquid, organic medium enables a uniform, highly controllable heat input into the solder material. The result is a substantially homogeneous structural constitution in the solder application and a precisely adjustable diffusion depth between the solder application and the terminal face in order to achieve a soldered connection having the desired properties.
Compared to the conventional invention methods, which besides splitting the process into an application of solder paste and a subsequent reflow method require a heating device of a--particularly in terms of hardware--comple
REFERENCES:
patent: 3110100 (1963-11-01), Hill
patent: 3214827 (1965-11-01), Phohofsky
patent: 3589590 (1971-06-01), Fitzsimmons
patent: 4563974 (1986-01-01), Price
patent: 5125560 (1992-06-01), Degani et al.
Welding Journal, vol. 53, No. 7, Jul. 1974, Solder Fusing with Heated Liqs, pp. 498-509.
Edmondson Lynne
Fraunhofer-Gesellschaft zur Forderung der ange-wandten Forschung
Ryan Patrick
LandOfFree
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