Metal fusion bonding – Process – Preplacing solid filler
Patent
1997-11-21
1998-12-08
Heinrich, Samuel M.
Metal fusion bonding
Process
Preplacing solid filler
228220, 427 96, H05K 334, H01L 2160
Patent
active
058458387
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a process for remelting a contact surface metallization applied to a substrate in an inert or reducing medium.
BACKGROUND OF THE INVENTION
Processes of the above-mentioned kind are known, for example, as so-called reflow solder processes from micro-connection technology. In these processes a contact surface metallization previously applied to the substrate is melted open again in order to achieve a connection with a structural component or, particularly in cases where the contact surface metallization has several components, a homogenization of the contact surface metallization. Particularly in the formation of so-called solder bumps on the terminal surfaces of chips, the remelting process also serves to form a more uniform bump geometry.
In order, when remelting, to prevent oxidation of the contact surface metallization or moreover to achieve a reduction of the contact surface metallization the remelting process is carried out in an inert or reducing atmosphere. An example of this is the so-called vapour phase soldering, in which, for remelting purposes, the contact surface metallization is heated in a saturated fluorine inert gas. This and other known processes require complex control of the heating because on the one hand it must be ensured that the melting point of the contact surface metallization is reached in order to make remelting possible and on the other hand the temperature must be limited in the upwards direction so as to prevent overheating of the contact surface metallization and of the substrate, such as a chip, to avoid damage.
From the complex demands described above, which arise in the known remelting processes, it is easy to conclude that the costs alone, which are associated with the provision of corresponding operating equipment, are extremely high.
BACKGROUND OF THE PRIOR ART
From JP 1-205 551 A a process for remelting a contact surface metallization is known in which the alloy desired for the contact surface metallization is already applied in wire from to the terminal surfaces by means of an ultrasonic bonder before the alcoholic medium is applied. This creates the requirement to provide the particular alloy desired for the contact surface metallization in wire form. Furthermore, because of the already formed alloy, the quality of the alloy formation can no longer be influenced.
From JP 3-218-645 A a temporary pre-contacting of a chip provided with bumps on a carrier substrate in known which makes use of holding forces which form as a result of a diffusion between a metallization of the substrate contacts and the bumps which occurs at elevated temperature. A wetting of the contact points with glycerol then takes place, followed by a connection process by means of remelting.
OBJECT OF THE INVENTION
The object of the invention is therefore to provide a process which simplifies the production of high-quality and reliable alloyed contact metallizations.
According to the invention the contact surface metallization is formed from at least two metallization components, initially present in a separate manner, which are remelted only in the alcoholic medium for the alloyed contact surface metallization.
Particularly when the boiling point of the medium is set in such a way that it is the same as the melting point of the allow which forms, the medium serves to form a system which is self-limiting with respect to temperature, since a corresponding evaporation of the medium prevents overheating of the contact surface metallization.
SUMMARY OF THE INVENTION
In the process according to the invention, during the remelting process the contact surface metallization is screened with respect to the environment in a liquid, alcoholic medium which is heated. The contact surface metallization may be heated via the medium and/or the substrate. In any event the alcoholic medium is selected or set in such a way that its boiling point is the same as or above the melting point of the contact surface metallization. Particularly when the boil
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Gwiasda Jorg
Kloeser Achim
Oppermann Hans Hermann
Weiss Stefan
Zakel Elke
Fraunhofer-Gesellschaft zur Forderung der Angewandten Forschung
Heinrich Samuel M.
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