Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Patent
1997-11-07
1999-11-02
Ball, Michael W.
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
29832, 29840, 228175, 22818022, B32B 3100, H05K 330
Patent
active
059763027
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for the temporary fixing of an electronic component having elevated contact metallizations on a substrate provided with terminal surfaces for a subsequent thermal connection of the contact metallizations to the terminal surfaces, wherein a bonding agent is applied to the component and/or the substrate.
Methods of the type referred to in the introduction are used for example in order to obtain a detachable mechanical preliminary fixing in so-called flip-chip contacting. In this contacting method the chip is applied to the terminal surfaces of a substrate with its elevated contact metallizations, also referred to as bumps, facing downwards. The actual connection between the chip and the substrate is then produced by subjecting the bumps to thermal energy whereby a remelting of the bumps occurs. To fix the relative positioning between the chip and the substrate prior to the remelting, it is known to provide an application of fluxing agent between the bumps and the terminal surfaces, which fluxing agent establishes a bond between the chip and the substrate for such time as the bumps have not yet melted. When the bumps are in the molten state, the fixing action of the fluxing agent ceases and therefore the chip is mounted on the substrate in quasi-floating fashion. Here a self-aligning method can occur which is brought about by the surface tension of the contact metallization material and which provides for an exact positioning of the chip on the substrate.
In the above described method for temporary fixing, this advantageous exploitation of the self-aligning effect is acquired together with the disadvantage that anionic or cationic fluxing agent residues remain on the remelted bumps even after the formation of the connection between the chip and the substrate. This frequently has a disadvantageous effect on the reliability of the provided connection.
Another known method for temporary fixing consists in that, before the production of the final connection between chip and substrate, a pressure welding connection is effected between the chip bumps and the substrate terminal surfaces, said pressure welding connection being released again when the subsequent thermal connection is established, whereby here again the advantageous self-aligning effect is facilitated. However, the high mechanical stress upon the chip associated with the pressure welding proves disadvantageous as in this method relatively high reject quotas due to mechanical damage to the chips are noted.
Therefore the object of the present invention is to propose a method which facilitates a temporary fixing of electronic components, such as for example chips, on a substrate without entailing the disadvantageous accompanying phenomena described in the foregoing.
This object is fulfilled by a method comprising the features of claim 1.
In the method according to the invention, the bonding agent selected is an alcoholic liquid medium containing an alcohol whose surface tension is used to form bonding forces between the contact metallizations and the terminal surfaces and whose boiling point is below the remelting temperature of the contact metallization.
When an alcoholic medium of this kind is employed, which can be applied to part of or all of the surface of the substrate or component, use is made of the property of many alcohols of forming--by virtue of their high interfacial or surface tensions--correspondingly high surface forces in the contact region between contact metallization and terminal surface, these resulting in high bonding forces. Use is also made of the advantageous property of alcohol of evaporating with no residue so that, in contrast to the methods employing conventional fluxing agents, no anionic or cationic residues, which disadvantageously influence the reliability of the connection, remain on the remelted contact metallizations. The setting of the boiling point below the remelting temperature of the contact metallization ensures that on the one hand the bonding forces are effective until t
REFERENCES:
patent: 3765938 (1973-10-01), Cranston
patent: 3869787 (1975-03-01), Umbaugh
patent: 4340167 (1982-07-01), Packer et al.
patent: 5075253 (1991-12-01), Sliwa, Jr.
IBM Technical Disclosure Bulletin, "Flip Chip Substrate Joining Process", r. 1970, US, vol. 12, No. 11, pp. 1-2.
Kallmayer Christine
Kloeser Achim
Oppermann Hans Hermann
Zakel Elke
Ball Michael W.
Fraunhofer-Gesellschaft zur Forderung der ange-wandten Forschung
Mitchell Shawn A.
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