Interfacial reaction between SAC305 lead–free solders and ENImAg surface finish and bare copper

Different surface finishes on printed circuit board strongly influence the formation of intermetallic compounds (IMCs), and solder joint reliability. In this paper the effect of two different substrates namely electroless nickel/immersion silver (ENImAg) and bare copper on interfacial reaction when exposed to a reflow soldering process are presented. The result revealed that the black line nickel disappeared on the electroless nickel/immersion silver surface finish after the plating process. Subsequently, the intermetallic compound formed on electroless nickel/immersion silver surface finish are (Cu,Ni)6Sn5, and (Ni,Cu)3Sn4 with a chuck-shape, rode-type, and needle-shape after reflow soldering. Meanwhile, only Cu6Sn5 layer is found on bare copper with a spherical-shape. The results also indicated that different surface finishes are affected by the growth of intermetallic formation and shear strength, where tin-3.0silver-copper0.5/copper (SAC305/Cu) produced a thicker intermetallic layer, larger grain size, and less shear strength compared with tin-3.0silver-copper0.5/electroless nickel immersion silver (SAC305/ENImAg) surface finish

Impact of multiple reflow on intermetallic compound of nickel-doped tin-silver-copper on ENImAg substrate

The growth of intermetallic compounds (IMCs) of the tin-silver-copper-nickel/electroless nickel immersion silver (SACN/ENImAg) at the 230 °C during multiple reflows was investigated. The characterization analysis of the samples was conducted using scanning electron microscopy and assisted by a dispersive x-ray analysis. A layer of continuous (Cu, Ni)6Sn5 and discontinuous (Ni, Cu)3Sn4 intermetallic were formed at the interface after up to the third reflow, while Ag3Sn nanosized was formed on the intermetallic surface. The total thickness of the intermetallic layer increased as the reflow increased. The findings also revealed that the intermetallic thickness became thicker with the mass percentage of nickel increased. Hence, the intermetallic growth was controlled mainly by reflow times and nickel content in solders

Effect of cutting speed on bio-corrosion of AISI 316L stainless steel

Stainless steel of AISI 316L type (SS316L) has been widely used as metallic biomedical implants material because of it offers good characteristics, including high mechanical properties and biocompatibility, and relatively low cost. However, its machinability an issue, with relation between cutting parameters and surface roughness is of interest to be considered. Related to this, its corrosion behavior related to cutting parameters also needs to be taken into consideration due to its application in implants. This study investigates the biocorrosion behavior of AISI 316L stainless steel which was machined by face milling at different cutting speeds. The cutting speeds were 100, 300 and 500 m/min while feed rate and depth of cut was kept constant. Initial assessment was done on the surface roughness of the face milled samples, with initial hypothesis that the surface roughness should be constant for all cutting speeds, with Ra to be within 0.8 - 1.2 μm. Biocorrosion test was then performed on the samples by Potentiodynamic Polarization Test under a simulated body fluid (SBF) electrolyte. It was found that although similar surface roughness is expected, the cutting speed affected the surface roughness in which the surface roughness tended to be inversely proportional to the cutting speed. Samples machined at the highest cutting speed was observed to have smooth surface with less defects, such as pits and grooves, compared to samples machined at lower cutting speeds. Related to this, the corrosion behavior of the AISI 316L stainless steel was also affected by the cutting speed during its face milling where the corrosion rate is inversely proportional to the cutting speed

Microstructural and shear strength properties of RHA-reinforced Sn–0.7Cu composite solder joints on bare Cu and ENIAg surface finish

In this study, the joint effect of rice husk ash (RHA) reinforcement as an alternative silica source and electroless nickel immersion silver (ENIAg) surface finish on the intermetallic compound (IMC) formation and shear strength of the Sn– 0.7Cu solder system was investigated. A series of plain and composite lead-free solder systems (Sn–0.7Cu−xRHA; x = 0, 0.01, 0.05 and 0.1 wt%) was successfully developed and subjected to reflow soldering on bare Cu and ENIAg surface finish. After conducting a comprehensive microstructural study using the scanning electron microscopy and energy dispersive spectroscopy techniques, the Cu6Sn5 and Cu3Sn intermetallic compound (IMC) phases were observed at the interface of the Sn–0.7Cu−xRHA/Cu composite solder joints. On the other hand, the (Cu,Ni)6Sn5 and Ni3Sn4 IMC phases dominated the interface of the Sn–0.7Cu−xRHA/ENIAg counterparts. Given the promising potential of the ENIAg surface finish, the Sn–0.7Cu−xRHA/ENIAg exhibited IMC thickness values within a range of 3.81–4.74 μm as compared to the 6.13–9.3 μm range exhibited by the Sn–0.7Cu−xRHA/Cu counterpart. More so, the ENIAg surface finish was effective in improving the shear strength of the plain solder joint, with the Sn–0.7Cu/ENIAg exhibiting 13.44 MPa relative to the 11.5 MPa exhibited by the Sn–0.7Cu/Cu counterpart. Overall, the strengthening effect of the RHA reinforcement was well marked in the Sn–0.7Cu−xRHA/Cu composite solder joints with the composite having 0.1 wt% RHA exhibiting the highest shear strength (14.6 MPa) across the board

Influence of Difference Solders Volume on Intermetallic Growth of Sn-4.0Ag-0.5Cu/ENEPIG

In recent years, portable electronic packaging products such as smart phones, tablets, notebooks and other gadgets have been developed with reduced size of component packaging, light weight, high speed and with enhanced performance. Thus, flip chip technology with smaller solder sphere sizes that would produce fine solder joint interconnections have become essential in order to fulfill these miniaturization requirements. This study investigates the interfacial reactions and intermetallics formation during reflow soldering and isothermal aging between Sn-4.0Ag-0.5Cu (SAC405) and electroless nickel/immersion palladium/immersion gold (EN(P)EPIG). Solder diameters of 300 μm and 700 μm were used to compare the effect of solder volume on the solder joint microstructure. The solid state isothermal aging was performed at 125°C starting from 250 hours until 2000 hours. The results revealed that only (Cu,Ni)6Sn5 IMC was found at the interface during reflow soldering while both (Cu,Ni)6Sn5 and (Ni,Cu)3Sn4 IMC have been observed after aging process. Smaller solder sizes produced thinner IMC than larger solder joints investigated after reflow soldering, whereas the larger solders produced thinner IMC than the smaller solders after isothermal aging. Aging duration of solder joints has been found to be increase the IMC’s thickness and changed the IMC morphologies to spherical-shaped, compacted and larger grain size

Comparative study on the isothermal aging of bare Cu and ENImAg surface finish for Sn-Ag-Cu solder joints

The surface finish of electroless nickel/immersion silver (ENImAg) has been developed as an alternative to lead-free surface finish in electronic industry for the reduction of metal cost without affecting the reliability and solderability performance. In this study, different types of lead-free solders, Sn-3.0Ag-0.5Cu (SAC305) and Sn-4.0Ag-0.5Cu (SAC405) were involved along with ENImAg and bare copper substrate in order to investigate the formation of intermetallic compounds (IMCs) under reflow and aging time. The characterization and analysis of the samples conducted through scanning electron microscopy and energy dispersive x-ray. As a result, the IMCs of SAC/Cu which were formed on the interface were Cu6Sn5 and Cu3Sn. Unlike the reaction displayed by SAC/Cu, the IMCs of SAC/ENImAg which were formed on the interfaces, were identified as (Cu,Ni)6Sn5) and (Ni,Cu)3Sn4. The kinetic growth of each IMC was analyzed. It was found that IMC of SAC/Cu was thicker than IMC of SAC/ENImAg. Upon the revelation of these observations, ENImAg surface finish reduced the growth of IMC and smaller grains size compared to bare Cu

Microstructural and shear strength properties of GNSs-reinforced Sn-1.0Ag-0.5Cu (SAC105) composite solder interconnects on plain Cu and ENIAg surface finish

In this study, the combined effect of GNSs (graphene nanosheets) and ENIAg (Electroless Nickel Immersion Silver) surface finish on the formation of intermetallic compounds (IMCs) and shear strength of the Sn-1.0Ag-0.5Cu (SAC105) solder system was studied. Both plain and composite solder systems (SAC105-xGNS; x = 0, 0.01, 0.05 and 0.1 wt%) were successfully prepared using the powder metallurgy technique and thereafter soldered on the plain Cu and ENIAg surface finish substrates. From the microstructural analysis, the Cu6Sn5 IMC was observed at the solder/substrate interface of the SAC105-xGNS/Cu solder joints. Moreover, the Ni3Sn4 and (Cu,Ni)6Sn5 IMC phases were observed at the solder/substrate interface of the SAC105-xGNS/ENIAg counterparts. The GNSs and ENIAg surface finish provided huge barrier for Sn and Cu atoms diffusion required for IMC formation. The interfacial IMC layer thickness decreased with increasing addition of GNSs for both sample grades. The SAC105-xGNS/ENIAg demonstrated lower IMC thicknesses that ranged between 2.98 and 2.53 μm relative to the 5.23–3.35 μm exhibited by the SAC105-xGNS/Cu. In general, the strengthening potential of the GNSs was well marked in both sample grades, with the SAC105-0.01GNS/Cu and SAC105-0.01GNS/ENIAg demonstrating the highest shear strengths of 11.2 MPa and 12.1 MPa, respectively

Interfacial microstructure evolution and shear strength of MWCNTs-reinforced Sn-1.0Ag-0.5Cu (SAC105) composite solder interconnects on plain Cu and ENIAg surface finish

The combined effect of MWCNTs (multi-walled carbon nanotubes) and ENIAg (Electroless Nickel Immersion Silver) surface finish on the formation of interfacial microstructure and shear strength of the Sn-1.0Ag-0.5Cu (SAC105) solder was investigated in this study. Plain and composite solders (SAC-xCNT; x = 0, 0.01, 0.05 and 0.1 wt%) were successfully synthesized through the powder metallurgy route and afterwards soldered on the ENIAg surface finish and plain Cu substrates. Detailed analysis of the microstructure revealed the formation of the Cu6Sn5 IMC at the SAC solder/Cu substrate interface of the SAC-xCNT/Cu solder interconnects. Whereas, the Ni3Sn4 IMC and (Cu,Ni)6Sn5 IMC appeared at the SAC solder/ENIAg substrate interface of the SAC-xCNT/ENIAg. The MWCNTs-reinforced SAC composite solder interconnects exhibited thinner interfacial IMC layer thicknesses relative to the plain counterparts for both substrates used. Given the prospects of the ENIAg as a reliable surface finish material, the SAC-xCNT/ENIAg exhibited IMC thickness values within the range of 2.98–2.65 µm as compared to the 5.23–3.61 µm demonstrated by the SAC-xCNT/Cu. Overall, the strengthening capacity of the MWCNTs was well-defined in both sample grades, with the SAC-0.05CNT/Cu and SAC-0.05CNT/ENIAg exhibiting the highest shear strength values of 10.23 MPa and 11.14 MPa, respectively