| With environmental regulations and the relevant international law are being implemented, the development and reliability on lead-free solder are flourished in all countries in which the SnAgCu lead-free solder with its excellent mechanical properties and the use of performance is considered one of the best alternative solder SnPb.To meet the growing reliability requirements of electronic products, and to ensure that it can operate reliably in the service process, the new lead-free solder process should not only have good performance, but also have higher mechanical properties, particularly creep performance, and has drawn wide attention. But the performances of SnAgCu solder joints under multi-field coupling conditions are rarely reported in the literature, has become a key issue to be solved in practice. Therefore, the research relevant aspects have important scientific significance and industrial applications.In this paper, use the wide application of Sn-3.0Ag-0.5Cu lead-free solder as the research object, independently developed multi-field coupling creep test device and test methods. By tensile creep tests to confirm the effects of temperature on the conditions under coupling SAC305/Cu lead-free solder creep characteristics, obtained stress exponent and creep activation energy in the current range of stress and temperature, and identified creep constitutive equation. In order to study the relationship between the intermetallic compounds and lead-free solder creep properties, using the new in-situ observation method through nano-nick, have studied creep organizational characteristics under different temperature conditions of SAC305 / Cu lead-free solder, also have studied the creep performance and organizational changes under current and the magnetic field on the SAC305 / Cu lead-free solder joints were at high and low stress in the same experimental conditions.Coupling creep experiments shows that: Coupled creep device designed is effective and reliable which can be used in creep tests under different environmental conditions. The creep performance parameters through this experiment conditions measured: the n of stress exponent is 8.24, the activation energy is 43.76KJ/mol, and constructed the creep constitutive equation. We can thought initially that the creep mechanism of SAC305 / Cu lead-free solder is mainly the result of dislocation climb, and the climb rate is mainly controlled through the sliding process of ?-Sn grain boundary. The higher of the temperature, the greater of the Ag3 Sn second phase particles’ speed and volume precipitated.The applied current SAC305/Cu lead-free solder joints under multiple field coupling, under 15 MPa stress, creep life was significantly reduced with current density increasing, the less unconspicuous of steady-state the greater of current; The steady-state creep rate when the current density of 70A/cm2、 600A/cm2 and 1?103A/cm2 is not applied current joints 2.5 times, 3.3 times and 10 times; The thickness of the interface compound increases 0.16?m compared with no current applied. Under 7 MPa stress, creep curve can be observed three typical creep stage, the steady-state creep range of solder joints become narrower with current increasing; The steady-state creep rate when the current density of 70A/cm2、 600A/cm2 and 1?103A/cm2 is not applied current joints 1.5 times, 2.1 times and 3 times, the steadystate creep rate did not increase sharply compared with high stress; Compared with zero current conditions within the same loading time, the thickness of interface increases gradually with current increasing, and the morphology of IMC changes from the scallop shape into the layered shape; Matrix organization begin to precipitate dot Ag3 Sn, and the quantity and volume is increased and enlarged gradually.The applied magnetic SAC305/Cu lead-free solder joints under multiple field coupling, under 15 MPa stress, Solder joint failure occurs quickly, and go straight to accelerating creep stage almost undistinct steady-creep stage; The steady-creep rate of sample decreases with the intensity of magnetic field increasing, but little impact; The morphology of interface layer and compound particles are not observed significant differences, fluctuant scalloped and cellular respectively. Under 15 MPa stress, the main characteristics of creep curve is steady-state creep; The creep life decreases gradually with the intensity of magnetic field increasing; The steady-state creep rate is not applied magnetic joints 1.1 times, 1.2 times; The morphology of IMC layer growing up from tiny cellular to a long strip with the magnetic field increasing, and the greater magnetic the more strip polygon particle. Current on SAC305/Cu lead-free solder joints are stronger in the creep rate and changes of interface morphology compared with the magnetic field. |
PDF Full Text Request