Papers by Keyword: IMC

Abstract: The interfacial reaction between pure tin and substrate with the composition of Cu-4.3 at% Ti (C1990HP) was investigated using the reaction couple technique from 240 °C until 270 °C in the range 0.5~4.0h. The SEM images show the Cu₆Sn₅ and small precipitated Ti₂Sn₃ phase formed at the Sn/C1990HP interface. In addition of Ti substantially increased the amount of intermetallic compound (IMC) at the interface which separated parts of Cu₆Sn₅ compounds with the inner region containing more Ti than the outer. The existence of Sn/C1990HP on the liquid/solid state reaction indicates that spalling occurred with changes in reaction time and temperature. With increased reaction temperature and time, the grain produced an abnormal condition resulting in Cu₆Sn₅ not accumulating at the interface and spalling into the solder in addition to grain ripening and an increase in total layer thickness. The hexagonal prism-shaped Cu₆Sn₅ phase is found on the top of the C1990HP substrate when the Cu₆Sn₅ layer detaches. The reaction phase formation, detachment, and split mechanisms are proposed in this study.

Abstract: To create a high reliability solder joint using IMCs dispersed in the joint, the joints with four types of lead-free solder were investigated. The joint with Sn-3.0Ag-0.7Cu-5.0In (mass%) has high die shear force compared to other joints investigated, and the joint with the Ni-electroplated Cu bonded at 300 ^oC for 30 min showed the maximum die shear force due to formation of a large number of fine IMCs. In the joint with Sn-0.7Cu-0.05Ni (mass%), uniform dispersion of a large number of IMCs was achieved, although the die shear force of the joint is lower than that of the joint with Sn-3.0Ag-0.7Cu-5.0In. In the joint with Sn-5.0Sb (mass%), a solder area was remained in the center of the joint although a large number of columnar IMCs form at the joint interface. The die shear force of the joint with Sn-5.0Sb increased with increasing the bonding time due to formation and growth of IMCs. In the joint with Sn-3.0Ag-0.5Cu (mass%), IMCs formed at the joint interface and did not disperse in the entire joint.

Abstract: Lead-free solders are environment friendly and are in great demand for microelectronic applications. In the present study, Sn-9Zn lead free solder alloy was solidified on Cu substrate for different reflow times from 10 to 1000s. The influence of reflow time on wetting, formation of intermetallic compounds (IMCs) and bond shear strength was studied using dynamic contact angle analyzer, bond tester and scanning electron microscopy. The results indicate that, the wettability of the solder alloy increased with increase in reflow time. Microstructure study revealed the presence of Cu₅Zn₈ and CuZn₅ IMCs at the interface. The thickness of an IMC increased with increase in the reflow time. The mean thickness of about 11μm for Cu₅Zn₈ IMC layer was observed for the reflow time of 1000s. The thickness of CuZn₅ layer increased up to a reflow time of 100s and decreases thereafter. The bond shear strength increased up to 100s and decreased with increase in reflow time. The decrement in shear strength at higher reflow time is mainly due to excessive thickness of Cu₅Zn₈ IMC layer and diffusion of Sn from bulk solder towards the substrate. The excessive thick IMC layer exhibited pre micro-cracks led to the brittle failure of bond under the influence of shear stress.

Abstract: Environment and the health concerns due to the hazardous effects of lead resulted in significant activities to find a replacement for lead-contained solders for electronics industrial. Majority of the semiconductor industrial are now replacing lead solders with Tin-Silver-Copper (SAC 387) solder balls. However, dropped balls in SAC 387 for Ball Grid Array (BGA) products due to poor solder joint strength caused by high thermal stress are a major concern in the semiconductor industries. Polymer core inside the solder ball (polymer core/Cu/Sn) is thus integrated to improve the solder ball joint strength. The function of polymer core inside the solder ball is to absorb and released the stress better as compared to the SAC 387 solder ball. Since the diffusion rate of Cu is faster than the diffusion rate of Sn, hence, this could caused the Kirkendall voids tends to form in between the Cu and Sn IMC layer. This would affect the solder ball joint strength and causing drop balls issue. By implement with an extra of Ni layer to the polymer core solder ball (core/Cu/Ni/Sn), could reduce the diffusion from Cu to Sn, thus to overcome the Kirkendall voids and to further improve the solder ball joint strength. This research work studies the performance of the solder ball shear strength of the two types of solder balls applied to MAPBGA device. In this research, both SAC 387 and polymer solder balls were went through under AC (Autoclave) and TC (Temperature Cycle) reliability test up to 144 hours and 1000 cycles, respectively. Solder ball shear strength test was conducted via Dage 4000 series bond tester. From the research work results of the two types of solder balls, the ball shear strength were decreased with an increased of aging and cycles. Overall, it can be concluded that the polymer core solder ball with an additional of Ni layer showed better performance than the polymer core without Ni layer and SAC 387 solder balls, after subjected to the AC and TC reliability test.

Abstract: Industry should gradually replace the tin-lead solder alloys used traditionally in the soft soldering technology by lead-free soldering alloys, which raises a lot of new technological and scientific problems to be solved. The introduction and application of lead-free alloys caused a number of soldering defects not observed earlier; mechanisms of their formation are still unclear. One of such defects is whisker formation, another one is intensified formation of intermetallic phases. The appearance of undesired intermetallic phases in the soldering material spoils its mechanical properties; therefore it is particularly important that these phases do not form in electronic components. Besides, the formation of intermetallic compounds may occur in the soldering bath, thus making the soldering process difficult or even impossible.Tin-copper-nickel and tin-silver-copper alloys are suitable for the replacement of tin-lead alloys. The components of these alloys were studied. After metallographic examination of the specimens the occurrence of intermetallic phases was determined by the XRD method. The identification of intermetallic phases was carried out by using literature data and phase diagrams.

Abstract: With the increasing focus on developing environmentally benign electronic packages, Pb-free alloys have received a great deal of attention. Among the lead-free solder materials, Sn–Ag–Cu alloy has advantages of good wetting property, superior interfacial properties, high creep resistance and low coarsening rate. In this article, the organization and mechanical performance of Sn-Ag-Cu Material are investigated. Series of inspections and analytical research methods are introduced. Experimental results show that Sn-Cu solder organization contains a large number of Cu₆Sn₅ graphic, while Sn-Ag-Cu graphic is IMC Ag₃Sn graphic. The mechanical propersity of Sn-Ag-Cu alloy is better than the Sn-Cu alloy. Fracture surfaces of the Sn-Ag3.0-Cu0.5 alloys specimen have many small size and homogeneously distributed dimples.

Abstract: This paper focuses on the control system design for a process of autothermal reforming (ATR) of ethanol. The targeted application is within an on-board fuel processor of ATR operating at the adiabatic reaction temperature for hydrogen production. An internal model control (IMC) method is designed for controlling the adiabatic reaction temperature of ATR reactor by manipulating the input air flow rate. Two strategies of controller design with and without the feed temperature control of the preheater unit are proposed in order to determine the suitable controller system as the surrounding temperature is a major disturbance for cold weather. Theoretical analysis demonstrates that IMC strategy can achieve desired performance. Two loops of control system of the ATR process combined with the feed temperature control can compensate the surrounding temperature better than without the feed temperature control.

Abstract: The bulk microstructure, melting behavior, mechanical property, and interfacial Intermetallic compound (IMC) morphology were investigated on Sn-Ag-Cu (SAC) lead free solders with different Ag content (0.3,1.0,2.0,3.0,3.8wt%). The result indicates that SAC solders with higher Ag content present finer and denser intermetallic particles in the bulk solder, as a result that the tensile strength of SAC solders increased with the increasing of Ag content, while the ductility decreased. The melting temperature of SAC305 and SAC387 solders are close to eutectic point from the narrow melting range. It was found that the interfacial IMC morphology didnt appear obvious difference regardless of Ag content for as-soldered. Furthermore, the higher Ag contained solders present smaller IMC grain at the interface of aged joints and all aged joints have a tendency of polyhedron morphology.

Abstract: Recently, research of non-square systems mainly focuses on fat system, and control approach to thin systems is less. This paper proposes a new method using improved selection control to square the systems and then design IMC controller for thin systems in which the number of output variables exceeds the number of input variables. This proposed method is applied to the control problem in which there is an output variable that is barely impact on the system. Then we use PSO method to seek the parameters. Then we can come to a conclusion that this method has better performance to reducing loop method through simulation. Moreover, this new method is simple and easy to implement.

Abstract: Since the ban of lead containing solders, eutectic SAC solders has been claimed to posses better properties compared to other series of lead free solders. As the technology trend for portable devices change over time, solder joints are continuously miniaturized. The VLSI in modern devices will subject the solder joints to repeated temperature cycling during both assembling and use due to higher I/O. These lead free solders are prone to excessive intermetallic compound (IMC) growth at the interface between the solder and the substrate due to the reasons cited earlier. The most common substrate used in electronic packaging is Cu while Au or its alloys are often used as metallization layer. In this study PCBs coated with both Cu and Au to study the interfacial morphology of Sn-3.8Ag-0.7Cu (SAC387) alloy with these metals. SEM imaging and EDX analysis were used to observe the interfacial layers and to confirm formation of IMCs. IMCs formed between Au-solder are more blocky-like compared to those formed between Cu-solder. Thus further studies must be conducted to resolve this issue as Au is a commonly used metallization materials.