Title of Invention	"A PROCESS FOR THE PREPARATION OF SILVER EPOXY PASTE"
Abstract	This invention relates to a process for the preparation of silver epoxy paste comprising in the step of mixing 3-8% epoxy resin and 2-9% phenolic resin, crushing the mixture to powder, adding 16-26% of solvent mixture herein described to dissolve the powdered mixture, mixing 56-67% of silver powder homogenously to get the silver epoxy composition.

Full Text

This invention relates to a process for the preparation of a silver epoxy paste for hybrid microelectronics and chip bonding applications. Silver epoxy composition are based on thermosetting property of the resin system used. During curing, the cross linking of the polymer resin takes place which imparts good adhesion strength of the cured place which imparts good adhesion strength of the cured paste/print to the surface. The paste is either brushed or screen printed on a variety of substrates. The main object of this invention is to propose a process for the preparation of a silver epoxy composition. Another object of this invention is to propose a silver epoxy composition for hybrid microelectronics and chip bonding applications. According to this invention there is provided a process for the preparation of silver epoxy paste comprising in the step of mixing 3-8% epoxy resin and 2-9% phenolic resin, crushing the mixture to powder, adding 16-26% of solvent mixture herein described to dissolve the powdered mixture, mixing 56-67% of silver powder homogenously to get the silver epoxy paste. Further according to this invention there is provided the silver epoxy composition comprises 56-67% silver powder, 3-8% epoxy resin, 2-9% phenolic resin and 16 to 26% solvent mixture mixed with each other homogeneously. In accordance with this invention 3-8% of epoxy resin is first mixed with 2-9% of phenolic resin and the mixture is crushed to powder. 16-26% of solvent mixture is added to the above mixture to dissolve the epoxy resin therein. 56-67% of silver powder is then added to the above solution and a homogenous mix is prepared to get the silver epoxy composition. The silver powder used for the preparation of silver epoxy composition is prepared by preparing a silver nitrate solution and a hydroquinone solution. The silver powder is precipitated by adding the hydroquinone solution to the silver nitrate solution in the ratio of 0.8-1.2: 4.5-5.5 slowly at a temperature of 60-70°C. The precipitate of silver powder so obtained is washed with warm water till it is free of nitrate and the precipitate is subsequently dried in vacuum oven at 30-70°C for 1 to 3 hours which is then subjected to the step of milling (ball milling) to get the silver powder. The solvent mixture used comprises 30 to 40X by weight methylethyl ketorte, 30 to 407. by weight butyl acetate and 30 to 40% by weight butyl cellosolove mixed with each other preferably in equal proportion. The epoxy resin used has epoxide equivalent 1650—2050 available in lumps/granules of light yellow colour. The epoxy resin preferably comprises: Epichlorohydrin and Bisphenol A Derived Resin Epichlorohydrin and diphenylolpropane Resin Epoxy Creso1—Novolak Resin or Epoxy phenol—Novolak Resin The phenolic resin used is preferably metacresol formaldehyde phenolic resin, ortho cresol formaldehyde resin or phenol formaldehyde resin. In accordance with the process of this invention epoxy resin is weighed and transferred to stainless steel mortar. The phenolic resin is weighed and added to the epoxy resin in the mortar. The Mixture is then crushed to powders. The solvent mixture is then added to the resin mixture and the mixture is allowed to settle for 5-110 minutes and the contents are then stirred so as to dissolve them. Now the silver powder is added to the mixture and a homogenous paste is prepared to get the silver epoxy composition. A silver epoxy composition and the process for the preparation thereof according to a preferred embodiment is herein described and illustrated in the following examples. According to this invention silver powder is first prepared by preparing a silver nitric solution and hydroquinone solution. Silver powder is precipitated by adding the hydroquinone solution to the silver nitric solution in the ratio of 0.08-1.2:4.5-5.9, slowly at the temperature of 60-70%. The precipitate of silver powder so obtained is washed with warm water and is subsequently dried in a vacuum oven at 30-70° C for 1 to 3 hours. The dried powder is then subjected to the step of ball milling to get the silver powder. 3-8% epoxy resin as mentioned herein above is mixed with 2-9% phenolic resin and is subjected to the step of crushing to obtain the powder thereon. 16-26X solvent mixture consisting of methylethyl ketone, butyl acetate and butyl cellosolove are mixed together preferably in the equal ratio, is added to the above mixture of epoxy resin, phenolic resin so as to resolve the epoxy resin therein. 56-70% of silver powder is then added to the above solution and a homogenous mix is prepared to get the silver epoxy composition. The process for the preparation of silver powder composition is further explained in the following examples:— EXAMPLE:-1 0.66 grains Epikote resin is taken into a stainless steel mortar. 0.38 grams phenolic resin was added to said resin into the steel mortar. The mixture was slowly crushed to powder. 2 grams solvent mixture was added to the resin mixture into the steel mortar and the solution so obtained was allowed to settle for 9 minutes. The contents were slowly stirred to dissolve the resins when the resins were completely dissolved the solution appeared like brown in colour. 6 grams silver powder was then added to the resinous mass and the mixing was done very carefully with the steel pestle. The small lumps were crushed under the pestle. The silver powder was dispersed in the resins media and the silver shiny paste was formed. The mixing yielded and uniform and homogenous paste even the smallest cruster of powder was dispersed and mixed, the paste adhered to the sides of a water around the pestle was removing using plastic spatula and scooped to a place in the water several times and is mixed again to get the product finally homogenous. A three roller mill was used and then the mixture was transferred to the g1asses/bott1es. EXAMPLE: -2 1.35 grains Epikote resin is taken into a stainless steel mortar. 0.65 grams phenolic resin was added to said resin into the steel mortar. The mixture was slowly crushed to powder. 1 gram solvent mixture was added to the resin mixture into the steel mortar and the solution so obtained was allowed to settle for 17 minutes. The contents were slowly stirred to dissolve the resins when the resins were completely dissolved the solution appeared like brown in colour. 4 grams silver powder was then added to the resinous mass and the mixing was done very carefully with the steel pestle. The small lumps were crushed under the pestle. The silver powder was dispersed in the resins media and the silver shiny paste was formed. The mixing yielded and uniform and homogenous paste even the smallest cruster of powder was dispersed and mixed, the paste adhered to the sides of a water around the pestle was removing using plastic spatula and scooped to a place in the water several times and is mixed again to get the product finally homogenous. A three roller mill was used and then the mixture was transferred to the glasses/bottles. I CLAIM; 1. A process for the preparation of silver epoxy paste comprising in the step of mixing 3-8% epoxy resin and 2-9% phenolic resin, crushing the mixture to powder, adding 16-26% of solvent mixture herein described to dissolve the powdered mixture, mixing 56-67% of silver powder homogenously to get the silver epoxy paste. 2. A process as claimed in claim 1, wherein the solvent Mixture consist of methylethyl ketone butyl acetate and Butyl cellosolove preferably in the equal ratio. 3. A process for the preparation of paste silver epoxy thereof substantially as herein described and illustrated in the examples.

Documents:

3865-del-1998-abstract.pdf

3865-del-1998-claims.pdf

3865-del-1998-correspondence-others.pdf

3865-del-1998-correspondence-po.pdf

3865-del-1998-description (complete).pdf

3865-del-1998-form-1.pdf

3865-del-1998-form-19.pdf

3865-del-1998-form-2.pdf

3865-del-1998-form-5.pdf

3865-del-1998-gpa.pdf

3865-del-1998-petition-137.pdf

3865-del-1998-petition-138.pdf