Wettability Of Lead-free Solders Research Articles

<i>In Situ</i> Evaluation of the Joining Defects in a Pb-Free Soldered Joint

Conventionally, brass has toughness more than other metals, so there is a concern about its poor machinability. Therefore, improvement of machinability was attempted by adding lead to brass. This brass called free cutting brass, typified by JIS C3771. This free-cutting brass is used for piping components and machine parts. There is a concern about elution of the lead into drinking water. Hence, Drinking Water Quality Standards Law has been amended and it restricts lead content in the free cutting brass. Therefore, lead-free free-cutting brass with no lead or minimized content of lead is required.Consequently, a lead-free free-cutting brass had been developed to improve in machinability such as JIS C6931 and JIS C6803 that are added Si and Bi instead of lead respectively. Lead was also used for the solder for joining among pure copper pipes and brass valves. That causes elution of lead from the solder into drinking water. For this reason, Lead-free solder such as Sn-Sb and Sn-Ag-Cu have been used.A fire torch technology often was used for soldering of brass. The purpose of this study is investigating soldering-ability and wettability of lead-free solder on lead-free free-cutting brass. Hence, we investigated the soldering ability of lead-free solders, Sn-5%Sb and Sn-3%Ag-0.5%Cu, for pure Cu and brass joints with nonuniform heating by hot plate.

Investigation of microstructure and wettability of selected lead-free solders for higher application temperatures

The work deals with the investigation of thermal properties and wettability of lead-free solders for higher application temperatures. For the research, the experimental solders SnSb5, ZnAl4, ZnAl6Ag6 and BiAg11 were used. For investigation of wettability, Ag, Cu and Ni substrates was used. To measure the solders melting intervals and their thermal properties, the DSC analysis was realized. The measurement of wettability was carried out in a controlled atmosphere by trigonometric method. Zn based solders wets none of the examined substrates. SnSb5 solder wets only Cu substrate with wetting angle of 54°. Soldering alloy BiAg11 wets all substrates, wherein the best result (23°) was achieved on Ag substrate. Shear strength of BiAg11 and SnSb5 joints reached higher value then classic PbSn5 solder.

Wettability of Selected Lead-Free Solders for Higher Application Temperatures

The work deals with the research of wettability of lead-free solders for higher application temperatures. For the research of wettability, SnSb5, ZnAl4, ZnAl6Ag6 and BiAg11 solders were used on Ag, Cu and Ni substrates. The measurement was carried out in a controlled atmosphere by trigonometric method. Zn based solders wets none of the examined substrates. SnSb5 solder wets only Cu substrate with wetting angle of 54o. Soldering alloy BiAg11 wets all substrates, wherein the best results (23 o) was achieved on Ag substrate.

Wettability optimization analysis of lead-free solders with Taguchi method

In this paper, the wettability of lead-free solders on substrates with fluxes was studied based on reflow process and Taguchi method. Effects of different control factors, including solder materials, fluxes, substrate materials and atmosphere on the wettability of the lead-free solder joints were examined and calculated. Moreover, the effect of rare earth Eu on the wetting of SnAgCu solder was investigated, the effect mechanism was analyzed too. The wettability optimal design in the lead-free solders system has the combination of the SnAgCu-0.04Eu solder, RMA flux, Au/Ni/Cu substrate, and vacuum atmosphere. Moreover, the flux is the most important factor among the control factors in the wettability system.

Investigation of Wettability of Lead Free-Solder on Bare Copper and Organic Solder Preservatives Surface Finishes

Wettability plays an important role in the integrity of solder joints especially in critical safety operations. It helps in attaining successful soldering and reliable solder joints. The angle of wettability determines the degree of solder contact and strength of the solder joint. Moreover, the contact angle between the solid substrate and the molten solder determines the interconnection reliability. This paper focuses on the wettability of lead free solder on OSP and bare copper substrate surface finishes. The wetting behaviour of lead free solder pastes on bare copper board and Organic Solderability Preservatives (OSPs) substrates were investigated. The test vehicles consist of FR4 PCB single sided 100% copper clad with a thick film metallization and FR4 PCB single sided OSP. The substrate dimension was 100 mm×160 mm×1.6 mm. A total of 480 bumps of Lead-free solder pastes (96Sn-3.8Ag-0.5Cu and 96.5Sn-3.0Ag-0.7Cu alloy composition) were deposited for the investigation. The printing parameters and their values for the experiments include print gap of 0 mm, squeegee speed of 20 mm/s, pressure of 8kg and separation speed of 3 mm/sec. The pastes are screen printed on the substrates using 0.125mm thick stencil mounted on DEK 260 series printing machine. After the stencil printing process, the solder bumps deposited on the substrates were reflowed using a Novostar 2000HT horizontal convention reflow oven with 4-stage (preheat-soak-reflow-cooling). The FTA188 Analyser was employed for measuring the angle of contact between the substrates and the bumps. The results showed that the wetting contact angle of copper surface finish is lower as compared to the organic solderability preservatives surface finish and the wetting angle decreases as the contact surface area increases.

A Study on the Thermal Oxidation and Wettability of Lead-free Solders of Sn-Ag-Cu and Sn-Ag-Cu-In

The surface oxidation mechanism of lead-free solder alloys has been investigated with multiple reflow using X-ray photoelectron spectroscopy. It was found that the solder surface of Sn-Ag-Cu-In solder alloy is surrounded by a thin InOx layer after reflow process; this coating protects the metallic surface from thermal oxidation. Based on this result, we have performed a wetting balance test at various temperatures. The Sn-Ag-Cu-In solder alloy shows characteristics of both thermal oxidation and wetting balance better than those of Sn-Ag-Cu solder alloy. Therefore, Sn-Ag-Cu-In solder alloy is a good candidate to solve the two problems of easy oxidation and low wettability, which are the most critical problems of Pb-free solders.

Wettability of Lead-Free Solders on Gold-Plated Copper Substrates

Wettability of lead-free solders (Sn-3Ag-0.5Cu, Sn-8Zn-3Bi, and Sn-9Zn) on Au-plated copper substrate was investigated with three different thicknesses of Au layer (0.1 μm, 0.3 μm, and 0.5 μm). The contact angles of solder alloys did not show a dependence on Au thickness. The contact angles of Sn-3Ag-0.5Cu and Sn-9Zn decreased, whereas the contact angle of Sn-8Zn-3Bi remained constant with an increase in temperature. Wetting balance test results indicated that thickness of Au plating affects wetting force, with thinner plating showing stronger wetting force and therefore, lower wetting time. Effects of different fluxes on wettability were also studied.

Influence of an Immersion Gold Plating Layer on Reliability of a Lead-Free Solder Joint

Electroless Ni/Au plating is often performed on a surface of a Cu pad to improve the wettability of lead-free solders on such a pad. Generally, electroless Au plating is performed by an immersion plating method. Since a substitution reaction of Ni and Au occurs selectively on the surface of a Ni layer in immersion plating, the Au layer does not uniformly form on the Ni layer and microvoids or microcracks easily form at the Ni/Au interface. Such defects induce void formation at the joint interface in soldering, and consequently degrade the reliability of the lead-free solder joint. In this study, the influences of immersion plating time on microvoid formation at the joint interface and the reliability of a solder ball joint with a Sn-3 mass%Ag-0.5 mass%Cu lead-free solder were investigated.

The effect of reflow process variables on the wettability of lead-free solders

A quantitative dynamic solder wettability measurement was utilized to evaluate the effects of reflow processing on the wettability parameters associated with the lead-free solders 96.5Sn-3.5Ag and 58Bi-42Sn. Solder wettability was determined with respect to the final degree of spread and the extent of solder wetting onto the terminal areas of surface-mount components. The solder alloy composition of 96.5Sn-3.5Ag exhibited better wetting characteristics than the 58Bi-42Sn alloy. This wetting behavior was enhanced under the reflow conditions of a nitrogen atmosphere and the use of a gold metallization. The wetting of the conventional 63Sn-37Pb solder alloy was improved over the comparatively processed 58Bi-42Sn alloy. However, the 63Sn-37Pb solder alloy displayed a greater sensitivity to reflow atmosphere than the 96.5Sn-3.5Ag alloy, which generally exhibited better wetting characteristics than the Sn-Pb alloy.