Welding Metallurgy of

http://doras.dcu.ie/17607/1/Review_of_residual_stresses-Final.pdf

Methods of measuring residual stresses in components

Electrical discharge machining of titanium alloy (Ti–6Al–4V)

Micro and Nano Machining by Electro-Physical and Chemical Processes

https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1275&context=mechengfacpub

Review of Electrochemical and Electrodischarge Machining

Relationship between EDM parameters and surface crack formation

This paper studies the solder joints of an Sn–Ag lead-free solder system with pure copper wires. The study focuses upon the interrelationships, which exist between the adhesive strength of the joint, its shear strength, the formation of interfacial intermetallic compounds (IMC) and the fractographic morphology. Additionally, the paper determines how these characteristics, and the relationships between them, are influenced by the storage duration and the storage temperature. Experimental results show that both the adhesive strength and the shear strength of the solder joints decrease significantly following short-term thermal storage. As the storage time is increased, it is noted that both the thickness and the roughness of the interfacial IMC layers increase. Regarding the fracture of the solder joints, fractographic observation reveals that fracture morphology under adhesive loading are similar to those observed under shear loading conditions. In the as-soldered condition, the fracture surface appears to be flat, and some broken Cu6Sn5 and residual solder pieces are evident. When the total thickness of the IMC layer lies within the range 1–10 μm, it is observed that the fracture morphology gradually becomes a dimple-like structure. This phenomenon may be attributed to the residual stresses caused by phase transformation, and by the increasing roughness of the IMC layers which causes an increase in the stress concentration within the Cu6Sn5 layer, and which ultimately results in fracturing of this layer. When the total thickness of the interfacial IMC layers exceeds 10 μm, the roughness of the IMC layers and the residual stress between them and the solder both continue to increase. Eventually this results in a fracture being initiated and propagated within the Cu6Sn5 layer. Fractographic observation shows the fracture to have a cleavage-like morphology.

Influence of interfacial intermetallic compound on fracture behavior of solder joints

The present study performs the small area electro-discharge machining (EDM) process with a low wear-rate copper–tungsten electrode of diameter 1.5 mm to establish the influence of the EDM parameters on various aspects of the surface integrity of AISI 1045 carbon steel. The residual stress induced by the EDM process is measured using the Hole-Drilling Strain-Gage Method. The experimental results reveal that the values of material removal rate (MRR), surface roughness (SR), hole enlargement (HE), average white layer thickness (WLT), and induced residual stress tend to increase at higher values of pulse current and pulse-on duration. However, for an extended pulse-on duration, it is noted that the MRR, SR, and surface crack density all decrease. Furthermore, the results indicate that obvious cracks are always evident in thicker white layers. A smaller pulse current (i.e. 1 A) tends to increase the surface crack density, while a prolonged pulse-on duration (i.e. 23 μs) widens the opening degree of the surface crack, thereby reducing the surface crack density. The EDM hole drilling process induces a compressive residual stress within the workpiece. A linear relationship is identified between the maximum residual stress and the average white layer thickness. It is determined that the residual stress can be controlled effectively by specifying an appropriate pulse-on duration.

Study of surface integrity using the small area EDM process with a copper–tungsten electrode

This study investigates the influence of intermetallic compound (IMC) growth on the adhesive strength of solder joints. 100Sn and 60Sn40Pb solders were used to solder electrolytic copper wires end to end. Soldered samples were then subjected to high temperature storage testing. The resulting interfacial IMCs in both solders were composed of Cu6Sn5 and Cu3Sn. IMC in the 100Sn solder joint grew faster than in the 60Sn40Pb. The growth behavior of Cu6Sn5 and Cu3Sn were subject to lead concentration. Results of tensile testing revealed an adhesive strength for 60Sn40Pb of 77.3 MPa, higher than the 50.0 MPa for 100Sn. 60Sn40Pb was found more sensitive to high temperature storage than 100Sn.

Influence of intermetallic compounds on the adhesive strength of solder joints

The effect of Sb contents (0–10 wt%) on the reliability of Sn–Ag–Sb solder has been investigated with isothermal low cycle mechanical fatigue tests. The solders tested were Sn–3.5Ag with Sb contents of 1.73, 3.85, 5.12 and 10.05 wt%, respectively, in the form of solder balls. Single-lap specimens were used to simulate real solder joints with the solder balls reflowed between two pure Cu substrates. Experimental results showed that under a fixed controlled displacement of 0.025 mm, fatigue life of the as-soldered joint increased with the amount of Sb additions due to less plastic strain the hardened solders produced. Load drop rate in the final stage increased as Sb addition increased. Fatigue cracks initiated at locations between the neck of the hourglass-shaped solder joint and the intermetallic compound (IMC) layer formed between the solder and copper. With the increase of Sb contents, the fracture mode evolved from within the bulk solder to a mixed fracture mode of solder and IMC layer, and finally, along the IMC layer.

Hwa-Teng Lee

Papers

Relationship between EDM parameters and surface crack formation

Influence of interfacial intermetallic compound on fracture behavior of solder joints

Study of surface integrity using the small area EDM process with a copper–tungsten electrode

Influence of intermetallic compounds on the adhesive strength of solder joints

Reliability of Sn-Ag-Sb lead-free solder joints