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53results about How to "Minimize dissolution" patented technology

Controlled plating on reactive metals

A direct displacement plating process provides a uniform, adherent coating of a relatively stable metal (e.g., nickel) on a highly reactive metal (e.g., aluminum) that is normally covered with a recalcitrant oxide layer. The displacement reaction proceeds, preferably in a nonaqueous solvent, as the oxide layer is dissolved by a fluoride activator. Halide anions are used to provide high solubility, to serve as an anhydrous source of stable metal ions, and to control the rate of the displacement reaction. A low concentration of activator species and little or no solution agitation are used to cause depletion of the activator species within pores in the surface oxide so that attack of the reactive metal substrate is minimized. Used in conjunction with electroless nickel deposition to thicken the displacement coating, this process can be used to render aluminum pads on IC chips solderable without the need for expensive masks and vacuum deposition operations. Such coatings can also be used to preserve or restore wire bondability, or for corrosion protection of aluminum and other reactive structural metals and alloys. A thin layer of immersion gold can be used to protect the thickened coating from oxidation. The solderable aluminum IC chip pads provide the basis for a maskless bumping process for flip chip attachment.
Owner:CALLAHAN CELLULAR L L C

Process for producing a solder preform having high-melting metal particles dispersed therein

[Problems] A conventional process for producing a solder preform in which a predetermined amount of high-melting metal particles are directly put into molten solder and stirred, requires a long time for dispersing the high-melting metal particles by stirring. Therefore, in the conventional method for producing a solder preform, dissolution of the high-melting metal particles into the molten solder occurred during stirring, and their particle diameters became small. If a semiconductor chip and a substrate are soldered with a solder preform containing metal particles having such decreased diameters, the space between portions being soldered becomes narrow, and a sufficient bonding strength is not obtained.
[Means for Solving the Problems] In the present invention, a premixed master alloy having a higher proportion of the high-melting metal particles in solder is first prepared, then the premixed master alloy is put into molten solder to disperse the high-melting metal particles. Aa a result, the high-melting metal particles can be uniformly dispersed in solder in a short length of time. Accordingly, a solder preform which is obtained by the process for producing a solder preform according to the present invention can maintain a predetermined clearance between portions being soldered, and a sufficient bonding strength is obtained.
Owner:SENJU METAL IND CO LTD
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