| Aluminum and its alloys have been widely used in making LED lighting system components,communication equipment,electronic devices and so forth,because of their lightweight,high specific strength,good thermal conductivity and low cost.However,there is a dense oxide film on the surface of aluminum and its alloys,resulting in very poor solderability,in particular for the soldering at low-temperature.To meet the industrial requirements in the field of electronic manufacturing including LED,the aluminum soldering paste should possess excellent printing performance and good storability besides the sufficient soldering activity.Compared to the copper solder paste,the active agent of the aluminum soldering paste is much stronger,which reacts strongly with alloy powders,leading to some serious problems such as roughening of the solder paste and weakening of the activity.Therefore,the difficulty in preparing the aluminum soldering paste is to find the appropriate active agents and develop the preparation method,which should make the solder paste possess weak activity yet good storage stability at room temperature,while ensuring high activity of removing oxide film on the surface of aluminum and its alloys completely in the processing process and facilitating the wetting of the solder and formation of the joint,as well as finally realizing the reliable joining of aluminum or its alloys.With the rapid development of high-power LED lighting system components,the cooling problem of LED is becoming more and more severe.Thus,there is an increasing need to develop the aluminum soldering paste to be used to achieve low-temperature soldering aluminum and its alloys.The main aim of the present study is to develop the appropriate solder paste for low-temperature soldering aluminum alloy in packages of LED lighting components.At first,single component or multicomponent orthogonal experiment were designed and optimized for different components such as active agent,solvents,film-forming agent,thixotropic agent and other additives were added in the flux.In order to analyze comprehensively the mechanism of the active agent in the flux during the low-temperature soldering process of aluminum alloy,the the heating rate,peak soldering temperature and solder volume were used as the variables on the basis of the optimal design of formula and proportion of the flux,the soldering active and processing performance of aluminum soldering pastes were evaluated based on experimental results of solderability and mechanical properties of solder joints,The qualitative or quantitative relationship among the factors such as active agent,soldering process and reliability of solder joint has been obtained.For improving the formation of solder joints and reducing the residue after reflow process,the desige and preparation of the aluminum soldering paste and soldering process were optimized by adding active salt to improve the storage life of the solder paste with new system under the pre-experimental data and analysis.Finally,the low-temperature aluminum soldering paste has been developed,which has the advantage of good solderability yet high storage stability.Results show that the compound of organic amine and inorganic acid has a good soldering activity to aluminum alloy during the soldering process.The addition of the active salt can further improve the soldering activity of the aluminum soldering paste but is highly corrosive to the solder powders.There are no intermetallic compounds or solid solutions formed at the interface between 6061 Al and Sn-0.3Ag-0.7Cu solder as confirmed by SEM-EDS analysis results.The main factors influencing the strength of solder joints are the depth of corrosion pits,the number of voids and the size of voids.In the new system aluminum soldering paste,the solubility of specific alcohol ether to the active salt increases greatly with increasing temperature.Therefore,by means of this feature a high storage stability aluminum soldering paste can be developed by adding additional active salt. |
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