![]() ![]() Two types of porous Cu, P15 and P25 with the diameter of φ1.7 mm and φ1.0mm respectively were used in this study. The microstructural and mechanical properties of Sn-3.0Ag-0.5Cu lead-free solders added with a porous Cu interlayer were investigated. In contrast, the scallop-liked intermetallic phase together with more uniform but a less defined scallop-liked phase was observed at the interface of porous Cu and solder alloy. ![]() Cu6Sn5 phase with scallop-liked morphology was observed at the interface of the SAC305/Cu substrate. Energy dispersive X-ray spectroscopy (EDX) was used to identify intermetallic phases. The results showed that the propagation of fracture during tensile tests for solder with a porous Cu interlayer occurred in three regions: (i) SAC305/Cu interface (ii) inside SAC305 solder alloy and (iii) inside porous Cu. The fractography of the solder joint was analyzed by optical microscope (OM) and scanning electron microscopy (SEM). The highest strength for solder joints with addition of P25 and P15 porous Cu was 51 MPa (at 180 s and 307 ☌) and 54 MPa (at 300 s and 307 ☌), respectively. The joint strength was evaluated by tensile testing. The soldering process was carried out at soldering time of 60, 180, and 300 s at three temperature levels of 267, 287, and 307 ☌. Two types of porous Cu interlayers, namely 15 ppi-pore per inch (P15) and 25 ppi (P25) were sandwiched in between SAC305/Cu substrate. The joining of lead-free Sn-3.0Ag-0.5Cu (SAC305) solder alloy to metal substrate with the addition of a porous Cu interlayer was investigated. ![]() Temperature cycling test results indicate that the TLP die attach joints have a characteristic life of 5016 cycles when tested at a cycling temperature range from -55☌ to 125☌. An appropriate low pressure is needed to help ensure close contact between the composite preform and the substrates, and thus to reduce voiding in the joint. The composite preform TLP joint has a remelt temperature higher than 450 ☌. The intermetallic compound phases formed in the TLP bonded joints are mainly the Ag-Sn ζ phase, Cu3Sn and Cu6Sn5 phases when a Cu substrate is used. Results show that the TLP bonding with the composite preform is a promising joining technology for die attachment in high temperature power electronics. The microstructures, mechanical properties and reliability of the solder joints made with a SnAg/Ag/SnAg composite preform are investigated. The Ag layer improves the mechanical, thermal and electrical properties of the TLP joint. The resultant TLP joint consists of a remaining Ag layer sandwiched by the IMCs layers at both sides. During TLP bonding, the Ag layer and the liquid solder layer together with the substrate metals react to form high-melting intermetallic compound phases (IMCs) to consume the low-melting phase rapidly. Unlike the conventional TLP bonding process, the solidification reaction in the present process takes place as a result of intermetallics formation. The composite preform is composed of a high-melting, ductile Ag core layer and a low-melting solder coating at both sides of the Ag layer. A transient liquid phase (TLP) bonding process using an innovative composite solder preform has been developed for die attachment bonding applications.
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