Electric heating – Metal heating – By arc
Patent
1997-07-31
1999-11-02
Mills, Gregory
Electric heating
Metal heating
By arc
21912168, 21912176, 21912184, B23K 2600
Patent
active
059775122
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention refers to a method and an apparatus for the flux-free application of a solder to a substrate or a chip.
2. Description of Prior Art
In the prior art various methods are known by means of which solders can be applied to a substrate. The solder to be applied can be present in the form of so-called solder balls.
In one known method, solder balls are arranged on a substrate making use of a template. Subsequently, these solder balls are remelted making use of fluxes. When this method is used, the flux is applied to the substrate before the solder balls are applied so as to fix the solder balls on the substrate.
A further known method makes use of the screen printing technology. A soldering paste is here applied to the substrate by means of the screen printing technique. The soldering paste consists of fine solder balls and of a flux. When the soldering paste has been printed onto the substrate, remelting is carried out in a furnace.
The above-described screen printing method according to the prior art is disadvantageous insofar as the possibility of using the method for soldering in the so-called fine-pitch range is limited.
The use of a flux leads to increased environmental pollution when the methods described hereinbefore are used.
When aluminium is to be soldered, the oxidized surface must be cleaned prior to the soldering process, since soldering on aluminium oxide is not possible. This cleaning by means of etching is a very expensive process step.
This problem arises especially in connection with chip contacting, when the contacting is to be carried out not by means of the known bonded connections, but when a soldered connection is desired. Conventional chips are provided with so-called pads or contact pads which consist of aluminium. Although a bonded connection with these aluminium pads can be established by means of bonding wires, the production of a soldered connection requires a metallization of the initial pad with solderable metals, such as gold. Direct, soldered contacting of the chip on the aluminium pads is not possible due to the oxidation occurring, i.e. the formation of an aluminium oxide layer on the pad. The use of a flux cannot solve this problem either.
SUMMARY OF THE INVENTION
It is the object of the present invention to provide a method and an apparatus by means of which solders can be applied to the surface of a substrate without making use of fluxes or by means of which a solder can be applied directly to the pads of a chip without making use of fluxes.
The present invention provides a method for the flux-free application of a solder to a substrate or a chip.
In the first step, an area on a surface of the substrate or a pad of the chip to which the solder is applied is cleaned. Subsequently, the cleaned area is isolated from the surroundings by means of a protective gas prior to applying the solder to the cleaned, isolated area.
The steps of cleaning and isolating the cleaned area may be carried out at the same time so that it is guaranteed that a renewed contamination of the cleaned area, which may occur already in the course of the cleaning process, is excluded.
The solder may be present in solid form, e.g. in the form of so-called solder balls. In this case, the application of the solder to the cleaned, isolated area comprises the step of arranging the solid solder on the area and the step of melting or rather remelting the solid solder.
The present invention provides an apparatus for the flux-free application of a solder to a substrate or a chip. The apparatus includes a laser light source, a deflection means for directing the laser beam, which has been produced by the laser light source, onto a frequency multiplication device, a reservoir unit containing the solder in solid form, a protective gas source, means with the aid of which the reservoir unit and the protective gas source are effectively connected to an area on a surface of the substrate or to a pad of the chip, to which the solder can be appli
REFERENCES:
patent: 5193738 (1993-03-01), Hayes
patent: 5272309 (1993-12-01), Goruganthu et al.
patent: 5484979 (1996-01-01), Gao
Azdasht Ghassem
Lange Martin
Fraunhofer-Gesellschaft Zur Forderung der Angewandten Forschung
Mills Gregory
LandOfFree
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