Study On The Preparation And Stability Of Low Silver Lead-free Solder Paste

The development tendency of electronic products is getting miniaturization and portability,which makes the integration of electronic packaging getting higher and higher.The dimension of components and welding points become smaller and smaller,meanwhile,loads from heat,electricity and force which acts on the welding point are getting bigger.As an important connection material in electronic assembly,the performance of solder paste affects the reliability of solder joints and directly determines the quality of electronic products.Solder paste is always wasted due to the strict storage conditions of solder paste,which makes the cost of electronic products getting more expensive.Laboratory has studied on the lead-free solder paste for many years,and aimed at developing a lead-free solder paste which can be preserved at room temperature.Through a systematic study,when the self-made solder paste Y1 was sealed at room temperature,the surface of Y1 would become dried,the wettability got bad and there was a severe contraction around the wet spots as well.The capability of molten solder to form tin-bead got weak and the tin-bead was not luster and not round.The content of organic acids in flux(D acid 3.0g,E acid 2.6g)was more than their maximum solubility in the original solvent system.The solder powder surface has been seriously corroded during the storage process.The composition of the flux was adjusted after studied the performance of the solder paste Y1.The amounts of moisturizing agent,thixotropic agent and organic acid were adjusted.Considering the durability and stability of the surfactant,glutaric acid was chosen as the alternative acid in 10 organic acids according to the spreading tests,the thermal reanalysis and solubility test in solvent system.Glutaric acid was used to prepare solder paste with D acid and E acid respectively.Unfortunately,it was found that the corrosivity of glutaric acid was too high to be used as active agent.Finally,the composition of the flux was optimized and determined,the addition amount of moisturizer,thixotropic agent,adipic acid and succinic acid were 6g,1.6g,1.4g and 1.56 g,respectively.The amount of the triethanolamine was 1wt% which was added as the anti-corrosion agent.New solder paste Z was obtained,in which the quality ratio of the solder powder Sn0.3Ag0.7Cu and the flux was 88.5:11.5.The optimized solder paste Z was placed at room temperature for 5 months.Corresponding performance was evaluated according to the standard of solder paste general specification(SJ/T 11186-2009).It was found that the wettability and weldability of the optimized solder paste Z were good,and the performance stability of the paste was improved compared with solder paste Y1.