Effect of Temperature on the Chip Soldering Process with AuGa0.03 Alloy Solder

In this study, soldering is conducted between a chip and a CLCC-3 shell base with a sheet-like AuGa0.03 alloy solder as the encapsulating material. X-ray images of chip soldering samples, XRD diffraction analysis of the joints, SEM images reflecting the microstructures of the joints, and EDS of the cross sections of the chip soldering samples show that with gradually increasing soldering temperature, the phase composition is not affected, and all the joint structures are an Au + Si eutectic structure; the Au–Si eutectic reaction occurs during the soldering process. No deposition of meta-stable phases, such as Au7Si, Au5Si, or Au3S, is found. A soldering temperature of 420 °C can reduce the negative impacts of secondary cap welding soldering on the joint and improve the structure and mechanical properties of the joint.

Flip Chip Joining with Quaternary Low Melting Temperature Solder Bump Fabricated with Injection Molded Solder

IBM has developed and has been enhancing the injection molded solder (IMS) technology as an advanced solder bumping technology with flexible solder alloy composition applicable even to fine pitch and small diameter systems. IMS is a simple bumping technology that can form solder bumps by injection of molten solder into via holes patterned in a photoresist layer. IMS is applicable to formation of solder caps for Cu pillar bumping which is a technology widely used for fine pitch applications. One of the advantages of IMS is the capability of using ternary, quaternary, or more compositions solder alloys for bumping, which is not achievable by current plating technology. In this study, the feasibility of IMS bumping and flip chip joining with quaternary solder alloys is demonstrated through assembling of 2.5D package test vehicles using low melting temperature (135°C) SnBi based quaternary alloy solder and associated reliability test. The test vehicles passed the 2250 cycles criteria of thermal cycling test and the observation of microstructures showed that there is no significant crack at the solder joints after flip chip joining or after the 2250 cycles of thermal cycling test. In addition, the tensile test on SnBi based quaternary alloy solder, Sn-58wt%Bi-2.0wt%In with small amount of Pd (less than 1wt%) was conducted using fine diameter specimens. From the SS curve obtained from the test, Young's modulus of the solder was determined as 7.3 GPa and 0.2% proof stress was obtained as 73 MPa both at 25°C. The creep property of the solder was evaluated and the constants for Norton's creep law for the solder were determined at 25, 80 and 110°C. The microstructure observation and Energy Dispersive X-ray (EDX) analysis of the flip chip joints revealed the formation of a thick bismuth (Bi) layer between CuSn intermetallic compound (IMC) layers within a joint. The mechanical simulation of the 2.5D test vehicles showed that the thermomechanical stress of a flip chip joint with Bi/CuSn IMCs at thermal cycling condition is comparable to those of CuSn IMC or Sn-3.0Ag-0.5Cu (SAC305) solder joints consistent with the thermal cycling test result. The advantage of using low temperature quaternary solder materials in flip chip packages is confirmed by mechanical simulation of 2D packages at reflow condition which showed lower stress on low-k dielectric layers for the packages with quaternary solder joints than for the packages with SAC305 solder joints.

Effect of Aging Treatment on Microstructural Evolution of Rapidly Solidified Eutectic Sn-Pb Alloy Powders

The microstructural stability of rapidly solidified eutectic Sn–Pb alloy solder powders was investigated through aging at room temperature (25 °C) and temperatures of 40 °C–120 °C. The coarsening behavior of the Pb-rich phase both at room and elevated temperatures was observed. The evident coarsening of the Pb-rich phase was detected upon storage after 40 days. At elevated temperatures, a similar sequence of Pb-rich phase coarsening was observed; however, it occurred substantially more quickly. Pb-rich coarsening rate kinetics at different temperatures were estimated using the Arrhenius equation. The apparent activation energy was 45.53 ± 4.23 KJ/mol, which indicates that grain boundary diffusion is a crucial mass transport mechanism controlling Pb-rich phase coarsening under annealing.

Die-Attach Voiding Reduction in Gold Alloy Solder Preforms

The need for high-temperature solders is growing as RF and power semiconductor devices continue to get smaller, with power density increasing both as a consequence of the shrink and as a result of increased power ratings. AuSn20 eutectic solder (Indalloy®182) has been the workhorse for high-temperature, high-reliability, small die-attach applications for many years; however, as junction temperatures (Tj) increase, the gold-tin eutectic is beginning to reach its limit of utility. Higher temperatures cause increased thermal fatigue, and even delamination is seen at the solder joints. The next option for RF and power semiconductor manufacturers needing these higher temperatures is either AuGe12 (Indalloy®183) or AuSi3.2 (Indalloy®184) eutectic alloy (see Table I).Table 1.Key properties of Au-based eutectic alloys. Over the years, many customers have tried AuGe12 and the feedback has been that the alloy has poor solderability, which manifests as large voids in the bond. Voids are poor conductors of heat, which create hot spots, and are the primary cause of premature failures.

Effects of the degradation of methane sulfonic acid electrolyte on the collapse failure of Sn–Ag alloy solders for flip-chip interconnections

The degradation mechanism of the methanesulfonic acid based electroplating bath used for the electrodeposition of Sn–Ag alloy solder bumps and its effects on the collapse failure of flip-chip solder bumps.

A New Lead-Free Solder Joint Utilizing Superplastic Al-Zn Eutectoid Alloy for Next Generation SiC Power Semiconductor Devices

A new high-temperature lead-free solder joint which withstands up to 300°C utilizing superplasticity in the Al-Zn eutectoid alloy has been developed to realize SiC power semiconductor devices. The new solid state joining process consists of interfacial cleaning of joints utilizing superplasticity of the Al-Zn-eutectoid alloy at 250°C followed by diffusion bonding between 350 and 390°C. The bonding strength of the new joints exhibits almost the same value at the temperature range from RT to 300°C, above which it decreases slightly with increasing temperature. It is also found that the bonding strength of the new joints is 8 times as high as those of a high-temperature Pb-5wt%Sn-1.5wt%Ag solder and the Al-Zn eutectoid alloy solder without utilizing superplasticity at 250°C. The Al-Zn eutectoid alloy solder joint has shown high reliability in the temperature cycle testing between 50°C and 300°C up to 300 cycles.

Fabrication of Carbon Fiber Reinforced Magnesium-Based Composite Laminates by Vibration Assisting Hot Pressing

Carbon fibers reinforced AZ31 composite laminates were fabricated by vibration aided mechanical hot pressing. Optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to analyze their phase components and microstructure. The interfacial bonding strength was measured by uniaxial tension testing. The results showed that Mg-Zn-Al eutectic alloy solder had a strong bonding with carbon fibers and a noticeable diffusion with AZ31 alloy. No debonding was observed on the interface of carbon fibers, and no carbide was detected in this system. The bonding strength of composite laminate reached up to ~17.48MPa which was close to the bonding strength of AZ31/Al composite laminate. It was indicated that vibration assisting hot pressing was a feasible technique for the fabrication of Mg-based composite laminates reinforced with uncoated carbon fibers.