International Business Machines Corporation

Lorenza Lombardi

Vittorio Sirtori

Franco Zambon

Michele Monopoli

Luigi Giussani

The method according to a preferred embodiment of the present invention mitigates the problem of gold contamination during the SMT assembly operations in the manufacture of Hybrid Multi Chip Modules (HMCM), achieving a high assembly process yield. This target is accomplished by protecting, at the first process step, the gold with a thin layer (0.02&#x2013;0.03 millimeter) of a paste very soluble in water and washing it off. The protective layer obtained with the above described method is very strong. Furthermore it is very easy to remove, since it is soluble in water.

Ball grid array module

The method according to a preferred embodiment of the present invention mitigates the problem of gold contamination during the SMT assembly operations in the manufacture of Hybrid Multi Chip Modules (HMCM), achieving a high assembly process yield. This target is accomplished by protecting, at the first process step, the gold with a thin layer (0.02-0.03 millimeter) of a paste very soluble in water and washing it off. The protective layer obtained with the above described method is very strong. Furthermore it is very easy to remove, since it is soluble in water.

A method and system for estimating the roughness and the contamination of a surface. A preferred embodiment of the present invention makes use of a mathematical model which gives indications of the metal roughness, expressed as the ratio of metal volume to air volume, and the contamination thickness values of a metal substrate (e.g. gold) for a determined contamination (e.g. organic). This model is based on a series of tables which represent the expected values of &psgr;, i.e. the ratio between the amplitudes of the incident beam on the two polarization planes multiplied by the ratio of the amplitudes of the reflected beam on the polarization planes, and &Dgr;, i.e. the difference between the phases on the two polarization planes of the incident beam and the reflected beam, for a gold substrate having a predetermined roughness and a predetermined type of contamination (organic). Each table is built for a roughness value &phgr; expressed as the ratio of metal volume to air volume and gives the values of &psgr; and &Dgr; for a range of possible contaminations expressed as thickness of the contaminant film. Each table shows, for a predetermined value of &phgr;, the expected values of &psgr; and &Dgr; for an organic contaminant film having a thickness of 0, 10 . . . 100 Angstrom.

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Milan, Italy

Lorenza Lombardi