Title of Invention

"AN IMPROVED SOLDER PASTE COMPOSITION"

Abstract "An improved solder paste composition" This invention relates to an improved solder paste composition comprising 6-15% a flux preparation mixed with 85-94% powder preparation blended together homogeneously wherein said flux comprises 35-40% base material/rosin, 0.5-1% activator, 50-60% organic solvent, 3-7% binder and 5-10% surfctant mixed together to form a blended mixture; and said powder is of an alloy comprising 60-65% Sn, 30-40% Pb and 1-5% Ag.
Full Text FIELD OF. INVENTION
This invention relates to an improved solder paste composition and to a process for the preparation thereof.
BACKGROUND OF INVENTION
It is generally known that solder paste can advantageously be employed for hybrid microcircuits (HMCs), printed circuits boards (PCBs) and component manufacturing- In both HMCs and PCBs, solder paste is used to interconnect active and passive components/devices, connectors and other components onto the board. In component assembly, solder serves as a joining material for attaching leads, lead frames and the structural units to make end-use components. The solder pastes are usually transferred on to the Intended solder pads by techniques such as Screen/Stencil Printing, Pneumatic Dispensing & Pin Transfer and reflowed by usinq various techniques.
The residue left on or around the solder Joints after reflow is generally the mixture of ingredients in the flux or the interreaction products among the ingredients. It can also be the reaction products between the ingredients and the substrate or solder sample. If it is a RMA (Rosin mildly activated) system, the residue may contain either the rosin or its derivatives, the lead, tin or copper salt of rosin acid, carboxylic acid, hydrocarbon etc. The cleaning solvent should be able to blend, dissolve and carry the residue away from the component through flushing and with adequate mobility. With the increasing complexities and intricate designs of the hybrid electronics circuitry, the cleaning of residues becomes a problem, since access to solvent becomes difficult if the residue reaches underneath the components and between densely packed components and devices. Hence it is very important that the residue left after refiow is minimum and easily cleanable.
OBJECT OF THE INVENTION
An object of this invention is to propose an improved soldo- paste composition yielding less and easily cleanable residue.
Another object of this invention is to propose an improved solder paste composition which remains homogeanous even after storage for a long time
Still another object of this invention is to propose an improved solder paste composition which can be dispensed on to the solder pads either by pin transfer or by screen/stencil printing, and also by other methods also
Further objects and advantages of this invention will be more apparent from the ensuing description.
According to this invention there is provided an improved solder paste composition comprising 6-15% a flux prepration mixed with 85-94% powder preparation blended together homogesieously wherein said flux comprises 35-40% base material/rosin, 0.5-1% activator, 50-60% organic solvent 3-7% binder and 5-10% surfactant mixed together to form a blended mixture; and said powder- is of an alloy comprising 60-65% Sn, 30-40% Pb and 1 -5% Ag.
In accrordance with this invention the flux preparation comprises 35—40% by weight of a'base, 0-5—1% by weight of an activator, 50-60% by weight of a vehicle, 2—7% by weight of a binder and 5—1.0% by weight of surfactant. Similarly the powder composition comprises Sn,Pb,Ag powder. The organic solvent comprises butyl cellusolve, butyl carbitol acetate and butyl terpeneol.
The paste composition and a process for the preparation thereof according to a preferred embodiment is herein described and illustrated in the following example.
The solder paste composition according to this invention comprises 85-94% by weight of solder powder being mixed with 6-15% by weight of flux preparation.
The flux preparation according to this invention comprises 35—40% by weight of a base for example wood rosin, gum rosin, modified rosin or tall oil rosin, 0-5%—1% by weight of ammonium activator, 50—60% by
weight of a vehicle/organic solvent for example aromatic alcohols, glycol ethers such as ethyl cellusolve and glycol ether esters. 3-7% by weight of polymer binder for example cellusolve or cornstarch or its derivatives like ethyl cellusolve. 5-10X surfactant for example glycerin, triacetate or phosphate ester.
The powder preparation comprises 60-65%- Sn, 30-40% Pb, 15% Ag- The powder preparation is cleaned by using dilute mineral acid followed by distilled water and dried by using organic solvents under controlled conditions. The powder is then coated with special additives (0.3%) such as glycerin esters and then activated under controlled conditions. 85-94% by weight of solder powder is mixed with 6-15% by weight of a flux preparation and is blended to make a homogenous solder paste.
According to the process of this invention 50-60% solvent/organic solvent is taken in a silica crucible.
3—7% binder/thixotropic agent for example cellusolve, cornstarch or ethyl cellusolve together with 35-40% rosin for example wood rosin, gum rosin, modified rosin or tall oil rosin is added to the said solvent and a blend is prepared. 0.5-1% hy weight of an activator for example halogenated amines, zinc; chloride, aliphatic primary amines, tetramethyl ammonium bromide or dimethyl ammonium chloride is added to said blend. Finally 5-10% surfactant/nonionic surfactant like glycerine, triacetate, phosphate ester is added to the mixture and a homogenous blend is prepared by the thorough mixing. This flux is used for the preparation of the solder paste.
The solder powder is made of an alloy comprising 60—65X Sn, 30-40% Pb and 1-5% Ag- The powder is first cleaned using dilute mineral acid and subsequently distilled water. The cleaned powder is then dried using organic solvent under controlled conditions. The powder is then coated with 0-3% special additives for example glycol ether ester under controlled conditions.
The solar paste is pnepared by the dispensing method using 85-94% solder powder and 6-15% weight of the flux mixed together to form a homogenous blended mix. the synergistic propery of the solder paste composition is its soldering property which is not possessed by any of its ingredients The solder paste composition and a process for the preparation thereof is herein described and illusated in the following examples:-
EXAMPLE 1
Flux was prepared using 49 gms of organic solvent typically containing 40% ß-terpineol, 30% butyl cellusolve and 30% butyl carbitol acetate, 5 gms of ethyl cellusolve and 40 gms of rosin.1 gm of hydroxylamine hydrogen chloride is used as activator and 5 gms of glycarine triacetate is used as the surfactant. Solder paste made with the procedure mentioned above using 89 gms of solder powder, 1 gin of glycerol mono sterate additive and 10 gms of the above mentioned flux Solder paste made this way showed good reflow characteristics and residue, which could be easily cleanable with conunon organic solvents. The solder paste showed good dispensing with pin transfer. By changing the flux percentage in the paste, the paste could be dispensed by other method such as stencil printing too.
EXAMPLE II
Flux was made as per the procedure mentioned in the patent using 52 gms of organic -solvent with a possible mixture of 35% ß-perpineal, 30% butyl cellusolve and 35X butyl carbitol acetate, 2 gms of ethyl cellulose and 35 gms of rosin. I gm of zinc chloride is used as activator and 10 gms of glycerine monost.earate as the surfactant. Solder paste was made using 90 gms of solder powder, I gm of glycerol mono sterate additive and 9 gms of the above mentioned flux. Solder paste made this way showed good reflow characteristics and residue, which could be easily cleanable with common organic solvents. The solder pasted showed good dispensing with pin transfer. By changing the flux percentage in the paste, the paste could be dispensed by other method such as stencil printing too-






WECLAIM;
1. An improved solder paste composition comprising 6-15% a flux preparation mixed with 85-94% powder preparation blended together homogeneously wherein said flux comprises 35-40% base material/rosin, 0.5-1% activator, 50-60% organic solvent, 3-7% binder and 5-10% surfactant mixed together to form a blended mixture; and said powder is of an alloy comprising 60-65% Sn, 30-40% Pb and 1 -5% Ag.
2. An improved solder paste composition as claimed in claim 1 wherein said rosin comprises wood rosin, gum rosin, modified rosin or tall oil rosin
3. An improved solder paste composition as claimed in claim 1 wherein said activator comprises halogenated amines, zinc chloride, aliphatic primary amines, tetramethyl ammonium feromide or dimethyl ammonium chloride.
4. An improved solder paste composition as claimed in claim 1 wherein said aromatic alcohols, glycol ethers such as ethyl cellusolve, methyl cellusolve and glycol ethen esters.
5. An improved solder paste composition as claimed in claim 1 wherein said binders comprises cellusolve, cornstarch or the derivatives of cellusolve like ethyl cellusolve.
6. An improved solder paste composition as claimed in claim 1 wherein said nonionic surfactant for example glycerine, triacetate, phosphate ester
7. An improved solder paste composition substantially as herein described and illustratad.

Documents:

856-del-1999-abstract.pdf

856-del-1999-claims.pdf

856-del-1999-complete specification(granted).pdf

856-del-1999-correspondence-others.pdf

856-del-1999-correspondence-po.pdf

856-del-1999-description (complete).pdf

856-del-1999-description (provisional).pdf

856-del-1999-form-1.pdf

856-del-1999-form-19.pdf

856-del-1999-form-2.pdf

856-del-1999-form-3.pdf

856-del-1999-form-4.pdf

856-del-1999-form-5.pdf

856-del-1999-gpa.pdf


Patent Number 243604
Indian Patent Application Number 856/DEL/1999
PG Journal Number 44/2010
Publication Date 29-Oct-2010
Grant Date 27-Oct-2010
Date of Filing 10-Jun-1999
Name of Patentee THE SECRETARY,DEPARTMENT OF ELECTRONICS
Applicant Address ELECTRONICS NIKETAN 6, CGO COMPLEX, NEW DELHI-110 003, INDIA.
Inventors:
# Inventor's Name Inventor's Address
1 DINESH PUNDALIK AMALNERKAR CENTRE FOR MATERIAL FOR ELECTRONICS TECHNOLOGY, SCIENTIFIC SOCIETY DEPARTMENT OF ELECTRONICS, PANCHWATI,OFF PASHAN ROAD, PUNE-411 008, MAHARASHTRA, INDIA.
2 SUNIT BARASEN RANE CENTRE FOR METERIALS FOR ELECTRONICS TECHNOLOGY, DEPARTMENT OF ELECTRONICS, PANCHWATI OFF PASHAN ROAD, PUNE-411 008, MAHARASHTRA ,INDIA.
3 MANTRALA VENKATA HUMUMANTHA RAO CENTRE FOR METERIALS FOR ELECTRONICS TECHNOLOGY, DEPARTMENT OF ELECTRONICS, PANCHWATI OFF PASHAN ROAD, PUNE-411 008, MAHARASHTRA ,INDIA.
4 VIJAYA KADAM CENTRE FOR METERIALS FOR ELECTRONICS TECHNOLOGY, DEPARTMENT OF ELECTRONICS, PANCHWATI OFF PASHAN ROAD, PUNE-411 008, MAHARASHTRA ,INDIA.
5 SHANY JOSEPH CENTRE FOR METERIALS FOR ELECTRONICS TECHNOLOGY, DEPARTMENT OF ELECTRONICS, PANCHWATI OFF PASHAN ROAD, PUNE-411 008, MAHARASHTRA ,INDIA.
PCT International Classification Number B23K 35/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA