Metal fusion bonding – Process – Specific mode of heating or applying pressure
Patent
1997-12-12
2000-09-12
Ryan, Patrick
Metal fusion bonding
Process
Specific mode of heating or applying pressure
228 37, B23K 108
Patent
active
061164976
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method and an apparatus for wave and/or vapor phase soldering of electronic components.
The invention may be used in the fabrication of electronic components in which soldering has nowadays to be performed in through-hole mounting on conventional components as well as on surface mount devices (SMD). Another field of application of the invention is soft-soldering of metallic semi-fabricated components.
2. State of the Art
It is well known that for soldering surface mount devices, reflow soldering processes are used. In such processes, the desired solder connections are fabricated by solder being reflowed and remelted as a solder paste by the application of energy. In known reflow soldering processes infrared radiation (infrared soldering) or hot gas (convection soldering), more particularly nitrogen, or laser radiation (laser soldering) or saturated vapor as in vapor phase soldering, are used. The most common processes utilized nowadays are infrared soldering, convection soldering and vapor phase soldering. Whereas infrared soldering is primarily used in connection with components of average complexity, low product variety and high volume, vapor phase soldering is particularly well suited for a high throughput or high volume at small spacings and high package densities, and it is for this reason used in SMD technology. With the development of new vapor phase soldering processes without fluorohydrocarbons as a secondary medium, these soldering processes have gained the greatest significance among the reflow soldering processes, particularly in view of the still more complex SMD components.
Conventional vapor phase soldering processes have been described, for instance, in German patent No. 3,518,444, European patent No. 0.349,094 and in the paper Produktronik, 1/2, 1993, pages 28-32, "Dampfphasenlo tanlagen in neuer Technik, Zum Leben erweckt" (Vapor Phase Soldering Equipment in New Technology, Resurrected) by H. Beine, in which the products or components to be heated are moved completely into the vapor range and are heated completely to the melting temperature of the medium used. In this connection, see in particular the operations diagram of FIG. 2 of the last mentioned paper in which the vapor line rises above the product to be soldered as soon as the solder material is heated to the boiling temperature of the used medium. In vapor phase soldering energy is released as heat on the surfaces of the solder material when a saturated vapor phase condenses. The solder reflows because of the released condensation heat, wets the components to be joined and leads to a material connection between the component connector and the associated contact structure on the component support. The thickness of the condensation film at or on the component to be connected determines the soldering time on the basis of the surface resistance. The vapor condensate also acts as a cleaning agent as it rinses dirt and other sediments off the component (contacts). The saturated vapor phase is generated by a boiling primary fluid. Thus, the boiling point of the primary fluid determines the operating temperature of the soldering process, which remains constant relative to the process. In principle, a thermal overload of the component is avoidable by the components being heat resistant at least up to the soldering temperature. The selection of a primary fluid scaled to the boiling temperature serves to process different solder material.
The characteristics of a vapor phase soldering process are precisely defined soldering or operating temperature, inert atmosphere, uniform heating of the soldering goods, and it is suited particularly for processing components of very different heat capacities.
Its disadvantage is that aside from SMD components (more particularly tantalum capacitors) it does not also possible with reasonable effort to solder through-hole mounting components. Moreover, selective heating is not possible, i.e. the individual components must all b
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Hafner Willi
Leicht Helmut
Ring Karl
Scheel Wolfgang
Fraunhofer-Gesellschaft zur Foerderung der angewandten Forschung
Hormann Karl
Ryan Patrick
Stoner Kiley
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