A Drop-in Die-Attach Solution for the High Temperature Lead-Free BiAgX Solder Paste System (original) (raw)
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High temperature lead-free solder joints via mixed powder system
2011 12th International Conference on Electronic Packaging Technology and High Density Packaging, 2011
Although lead-free soldering has been the main stream of industry since 2006, with the replacement of eutectic SnPb system by SnAgCu system, the development of drop-in lead-free alternatives for high melting high lead solder alloys is still far from mature. BiAg alloy exhibits acceptable bulk strength but very poor ductility and wetting, therefore it is not acceptable as an option. In current work, a mixed powder BiAgX solder paste system has been developed as a viable alternative, high temperature lead free solder. The metal powder in the paste is composed of a high melting first alloy powder as majority and the additive powder as minority. The additive contains a reactive element to react with various metallization surface finishes. The additive will melt and react on the parts before or together with the melting of the majority solder. The reactive element in the additive is designed to be converted completely into IMCs during the reflow process, hence resulting in a high melting solder joint. In the mixed powder paste system, a melting temperature above 260°C was verified by both DSC and TMA data. The mixed powder solders show a significantly improved wetting comparing to Bi11Ag. The voiding and TCT performance are comparable with high lead solders. The IMC layer thickness of the mixed powder system is insensitive toward thermal aging at 175°C, while the high lead ones do show a considerable increase.
High-reliability, high-melting, lead-free, mixed solder paste System—BiAgXⓇ
Review of Scientific Instruments
BiAgX ® , a mixed solder powder paste composed of a primary high-melting solder powder and an additive low-melting solder powder, exhibited a melting temperature above 260 ○ C and was comparable to, or even better than, the reliability of high-lead solders. The additive solder is designed to react preferentially with various surface metallizations and form a controllable intermetallic layer. Inside the joints, sub-micron AgSn particles are dispersed surrounding Bi colonies, which constrain the dislocation movement, thus enhancing strength, ductility, and associated joint reliability.
International Symposium on Microelectronics
Development of high-temperature lead-free (HTLF) solders to replace high-lead solders for die-attachment in power device applications is driven by (1) the harmful effects of lead to human health and the environment, and (2) the demand of the improved bonding materials serving under high-power density and high-junction temperatures, especially for wide-band-gap power devices. A novel design, based on a mixed solder powder paste technology—Durafuse™—has been developed to deliver a Sn-rich HTLF paste, presenting the merits of both constituent powders. The combination of the rigid, high-melting SnSbCuAgX and the ductile, low-temperature Sn-rich solder in one paste enables reflow at a relatively low temperature (barely above the liquidus temperature of the final joint composition) and maintains the joint strength above 15MPa in the temperature range between 270°C and 295°C. The sufficient high-temperature strength has demonstrated the capability of maintaining the joint integrity during ...
IMAPSource Proceedings
Sn-based high-temperature lead-free (HTLF) solder pastes have been developed as a drop-in solution to replace the high-Pb solder pastes in power discrete applications. The pastes were designed to combine the merits of two constituent powders. A SnSb-based Ag/Cu-containing high temperature powder, with the melting temperature above 320° C, was designed to maintain a high-temperature performance. A Sn-rich SnAgCu-Sb powder, with a melting temperature around 228° C, was added to the paste to enhance wetting and improve joint ductility. In the design, the final joint will have the low-melting phase (the melting temperature >228o C) in a controllable quantity embedded into the high-melting SnSb matrix. HTLF-1, one of the designs, maintained the bond shear strength up to 15MPa, even around 290° C. Another design, HTLF-2, has a similar bond shear strength as Pb92.5/Sn5/Ag2.5 around 290° C, but exceeds substantially below 250° C. The power discrete components had been built with both HTL...
A Novel Lead-Free Low-Temperature Solder Paste for Wafer-Level Package Application
IMAPSource Proceedings
An In-containing low-temperature solder paste (DFLT) has been developed and successfully used in mobile phone board-stacking application. It is now being tried for main-board application, targeting at using lower-temperature reflow profiles but delivering at least the comparable reliability to the mainstream SAC305. The customized drop-shock packages and the daisy-chained WLP256 assemblies were reflowed under a variety of reflow profiles, in which peak temperatures ranged from 200o C up to 240o C. SAC305 has been used as the control leg reflowed under a traditional 240o C peak temperature lead-free reflow profile. The joint morphology changed with the reflow profiles. Under the 200o C peak reflow, hybrid joints were formed in which the mixing zone, dominated by DFLT, was present at the PCB side while the SAC305 ball at the chip side maintained the original morphology. Increasing the reflow peak temperature led to the fully-merged SAC305 ball with DFLT and, finally the formation of t...
Die attach properties of Zn-Al-Mg-Ga based high-temperature lead-free solder on Cu lead-frame
Journal of Materials Science-Materials in Electronics, 2012
Several candidate alloys have been suggested as high-temperature lead-free solder for Si die attachment by different researchers. Among them, Zn-Al based alloys have proper melting range and excellent thermal/electrical properties. In this study, Zn-Al-Mg-Ga solder wire was used to attach Ti/Ni/Ag metallized Si die on Cu lead-frame in an automatic die attach machine. Die attachment was performed in a forming gas environment at temperature ranging from 370 to 400 °C. At the interface with Cu lead-frame, CuZn 4, Cu 5Zn 8 and CuZn intermetallic compound (IMC) layers were formed. At the interface with Si, Al 3Ni 2 IMC formed when 200 nm Ag layer was used at the die back and AgZn and AgZn 3 IMC layers when the Ag layer was 2,000 nm thick. Microstructure of the bulk solder consists of mainly two phases: one with a brighter contrast (about 80.9 wt% Zn) and the other one is a mixture of light (about 73.7 wt% Zn) and dark phases (about 45 wt% Al). Zn-Al-Mg-Ga solder wetted well on Cu lead-frame, covered entire die area and flowed in all directions under the Si die. Less than 10% voids were found in the die attach samples at die attach temperatures of 380 and 390 °C. Die shear strength was found within the acceptable limit (21.8-29.4 MPa) for all the die attach temperatures. Die shear strength of standard Pb-Sn solder was also measured for comparison and was found to be 29.3 MPa. In electrical test, maximum deviation of output voltage after 1,000 thermal cycles was found 12.1%. http://link.springer.com/content/pdf/10.1007%2Fs10854-011-0511-x.pdf
Room temperature lead-free soldering of microelectronic components using a local heat source
2004
This paper describes a new joining process that enables fluxless, lead-free soldering of similar and dissimilar materials at room temperature with no thermal damage to surrounding components. The joining process is based on the use of a reactive multilayer foil as a local heat source. The foils are a new class of nano-engineered materials, which consist of thousands of alternating nanoscale layers comprised of elements with large negative heats of mixing. With a small thermal or electrical stimulus, a controlled, self-propagating reaction can be initiated in these foils at room temperature. By inserting a multilayer foil between two solder layers and two components, heat generated by the reaction melts the solder and consequently bonds the components. Since the heat generated is localized to the bonding interface, components are not exposed to high temperature and hence thermal damage is avoided. Materials with dissimilar coefficients of thermal expansion can also be joined, due to the localized heating of the components. This paper focuses on an application where surface mount connectors are joined to printed circuit boards using a eutectic Au-Sn solder alloy. Details on thermal exposure of the components during joining, performance verification testing, and the process advantages are presented.
2009 59th Electronic Components and Technology Conference, 2009
The transition from tin-lead to lead free soldering in the electronics manufacturing industry has been in progress for the past 10 years. In the interim period before lead free assemblies are uniformly accepted, mixed formulation solder joints are becoming commonplace in electronic assemblies. For example, area array components (BGA/CSP) are frequently available only with lead free Sn-Ag-Cu (SAC) solder balls. Such parts are often assembled to printed circuit boards using traditional 63Sn-37Pb solder paste. The resulting solder joints contain unusual quaternary alloys of Sn, Ag, Cu, and Pb. In addition, the alloy composition can vary across the solder joint based on the paste to ball solder volumes and the reflow profile utilized. The mechanical and physical properties of such Sn-Ag-Cu-Pb alloys have not been explored extensively in the literature. In addition, the reliability of mixed formulation solder joints is poorly understood.
Ultra-fine package assembly using TiO2 nanoparticle reinforced lead-free solder paste was carried out in the reflow soldering process. TiO2 nanoparticles were mixed with the SAC solder paste at 0.01, 0.05 and 0.15 wt.%. The ultra-fine package (passive capacitor) was mounted on PCB with a thickness of 2.0 mm using the nanocomposite solders. Voids, microstructure and TiO2 nanoparticle distributions were inspected through the X-ray, SEM and HRTEM. The ultra-fine solder joints were formed perfectly without any void formation. The TiO2 nanoparticles are distributed homogenously in the solder joint. The mechanism of IMC reaction during the reflow soldering process is also discussed. Homogeneous mixing of
34th International Electronics Manufacturing Technology Conference, IEMT 2010, 2010
Interfacial reactions during Si die attachment with Zn-Al-Mg-Ga high-temperature lead (Pb)-free solder on bare Cu lead-frame (Tamac 4) and Ni metallized Cu lead-frame were investigated using an optical microscope, scanning electron microscope (SEM) and energy dispersive x-ray (EDX). Die attachment was performed in an automatic die attach machine in a forming gas environment at temperature 380C. The back side of the die was metallized with Ti/Ni/Ag layers. Comparative studies of die attach properties such as wetting, void and die shear strength on bare and Ni metallized Cu lead-frame was made. Cross sectional microstructural investigation revealed that as many as three intermetallic compound (IMCs) layers form at the solder/lead-frame interface for bare Cu lead-frame. A CuZn intermetallic layer forms close to copper, a scallop shaped CuZn 4 forms at the solder side, while Cu 5Zn 8 forms at the middle. At the interface with Si die, IMC layer could not be detected by SEM. With Ni metallized Cu lead-frame, no IMC layer was observed at the solder/lead-frame as well as Si die/solder interface by SEM. Wetting on Ni metallized Cu lead-frame was found to be lower as compared to that at bare Cu lead-frame. Die shear strength was found to be higher on bare Cu lead-frame (24.2 MPa) as compared to Ni metallized Cu lead-frame (20.5 MPa). Die shear strength of standard Pb-5Sn solder was also measured for comparison and found to be 28.2 MPa. http://ieeexplore.ieee.org/xpls/abs\_all.jsp?arnumber=5746721