Cleaning compositions for solid surfaces – auxiliary compositions – Cleaning compositions or processes of preparing – For cleaning a specific substrate or removing a specific...
Reexamination Certificate
2000-12-07
2003-02-25
Webb, Gregory E. (Department: 1751)
Cleaning compositions for solid surfaces, auxiliary compositions
Cleaning compositions or processes of preparing
For cleaning a specific substrate or removing a specific...
C510S174000, C510S177000, C134S002000, C134S003000, C134S038000, C134S042000
Reexamination Certificate
active
06525009
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to low foam aqueous cleaning compositions for cleaning metal-polymer composite paste residue from the surface of screening masks, associated screening equipment and the like in the manufacture of ceramic substrates for semiconductor packaging applications. More particularly, the present invention is concerned with aqueous alkaline cleaning solutions comprising carboxylate or aminocarboxylate polymer salts and low foam surface active agents as a solvent replacement in high speed cleaning of paste screening masks, associated screening equipment and the like in the fabrication of multi-layer ceramic substrates.
BACKGROUND OF THE INVENTION
Standard processing for ceramic substrate production, particularly for multilayer ceramic substrates, involves a series of operations starting with preparation of ceramic slurry comprising ceramic filler, organic binder, solvent vehicle and plasticizer; green sheet casting; blanking; via punching; circuit personalization or screening of conductive paste through a screen mask, followed by singulation/sizing; inspect/collate/register operations; stack and lamination; and finally binder burn-off and sintering.
In the circuit personalization process step in the formation of ceramic substrates, conductive metal features for wiring and via metallurgy on the substrate are defined by screening metal-polymer composite paste through a contact mask, such as a metal mask having a closely spaced fine dimension pattern etched in molybdenum (Mo) foil or electroform mask such as copper-nickel or copper-nickel-copper masks. Paste screening through such masks leaves paste residue on the mask surface as well as on the side walls of the mask features. This residue must be removed after each screening pass or multiple screening passes depending on the paste composition and mask type in order to assure consistent quality defect-free screened patterns. Associated screening equipment can also be contaminated with this paste residue and must be cleaned periodically.
Conductive pastes used in screening processes for the wiring and via metallurgy basically comprise metal particles dispersed in an organic binder and solvent vehicle along with wetting agents, dispersants/surfactants, plasticizers, and other additives such as rheology modifiers, thickening agents, antioxidants, and coloring agents.
The conductive pastes commonly used in multi-layer ceramic substrate production are dispersions of a metal powder as the predominant component, typically molybdenum (Mo), copper (Cu), tungsten (W), copper in combination with nickel (Ni), in a polymer binder such as ethyl cellulose, polyalkyl methacrylate (for example, polymethyl methacrylate or polyethyl methacrylate), and a high boiling solvent such as 2,4,4-trimethyl-1,3-pentane diol monoisobutyrate (Texanol), butylcarbitol acetate (BCA), a suitable surfactant or dispersant and a thickening agent or rheology modifier. Selection of a conductive paste for a particular layer pattern in multi-layer ceramic substrate is dictated by the requirement for the desired circuit pattern and compatibility of the paste with green sheet material.
The above fabrication processes and equipment used to produce ceramic substrates with paste-screened metallization are well known in the art.
Because of the variety and complex chemical make-up of the polymer/metal dispersions which form the pastes, it is required that the mask cleaning medium and process selected be such that it provides complete and efficient cleaning of paste residue on screening masks, associated screening equipment and the like regardless of the paste characteristics in terms of wettability, solubility, polarity, etc.
An automated in-line paste-screening and mask cleaning process using perchloroethylene as a cleaning agent for metal masks used in multilayer ceramic technology is described in Davis et al. U.S. Pat. No. 4,362,486 and Magee et al. U.S. Pat. No. 4,483,040, the disclosures of which are incorporated by reference herein. This process is designed for real time operation to provide compatibility with high throughput screening in a production environment.
Chlorinated solvents such as 1,1,1-trichloroethane, perchloroethylene, fluorochlorocarbons, and related halogenated hydrocarbons are non-flammable and highly effective solvents which have been used in the past for a multitude of industrial applications. It would be desirable to replace these chlorinated solvents.
The challenge is to replace an effective solvent-based mask cleaning composition with an aqueous cleaning process that is equally as effective as the chlorinated solvent-based cleaning process for paste residue from screening masks and associated screening parts.
Therefore, this invention is concerned with the aqueous cleaning of screening masks, associated screening equipment and the like that are used in the process of screening metal-polymer conductive paste onto green sheets in the manufacture of ceramic substrates.
Winston et al. U.S. Pat. Nos. 5,431,847 and 5,433,885, the disclosure of which are incorporated by reference herein, disclose an aqueous cleaning composition comprising an alkaline salt and concentrates of anionic polymers comprising polyacrylic acid in conjunction with a hydrotrope to stabilize alkali metal silicates to prevent silicate precipitation when used in the removal of Rosin fluxes from electronic circuit assemblies.
Ilardi et al. U.S. Pat. No. 5,498,293, the disclosure of which is incorporated by reference herein, discloses aqueous cleaning compositions for cleaning silicon wafers to remove metal contamination from the wafer surface without increasing surface micro-roughness of silicon wafers. The cleaning compositions are comprised of a metal ion-free base, an amphoteric surfactant, a metal complexing agent, and propylene glycol ether as an organic solvent.
Kleinstuck et al. U.S. Pat. No. 5,523,023, the disclosure of which is incorporated by reference herein, discloses alkaline cleaning compositions and process for industrial water treatment according to which polyaspartic acid-based compositions carrying phosphonic acid are used for inhibition of incrustation or scale formation due to Ca
++
and CO
3
-2 ions which lead to limescale deposits.
Kroner et al. U.S. Pat. No. 5,574,113, the disclosure of which is incorporated by reference herein, discloses the use of co-polymers derived from aspartic acid polymers used in the form of free acids or neutralized with ammonia, amines, or alkali metal hydroxide, as additives to detergents or cleaners as scale inhibitors or as dispersants.
Cala et al. U.S. Pat. No. 5,593,504, the disclosure of which is incorporated by reference herein, discloses a method of cleaning solder paste from metal stencils and screens with an aqueous cleaner based on alkali metal carbonate, a surfactant, alkali metal silicate, and a stabilizer for silicate to prevent gel formation, as a safer replacement of alcohol solvents.
Perner et al. U.S. Pat. No. 5,656,646, the disclosure of which is incorporated by reference herein, discloses the synthesis and use of polyamino carboxylic acids and/or polymers of mono- or dicarboxylic acids as additives for phosphate-free or low phosphate textile detergents or dispersants or coating inhibitors in cleaners.
Notwithstanding the efforts of those skilled in the art, there still remains a need for an effective, aqueous cleaning composition for removing screening paste residue from screening masks, associated screening equipment and the like while maintaining the cycle time requirement in automated mask cleaning operations without adverse impact on product throughput and product reliability.
Therefore, it is a purpose of the present invention to provide an alternate method for cleaning screening masks, is associated screening equipment and the like used in the production of ceramic substrates without an adverse impact on the mask integrity, cleaning quality, process reproducibility and cycle time in a manufacturing environment.
It is another purpose of this invention to provide an aq
Mackin Daniel S.
Pomerantz Glenn A.
Sachdev Krishna G.
Blecker Ira D.
Webb Gregory E.
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