Papers by Keyword: Lead-Free Solder

Abstract: Thermal cycling tests were conducted on solder joints of wafer-level chip scale packages with Sn-3.0Ag-0.5Cu (mass%) to investigate the effect of difference in the thermal cycle profile on the thermal fatigue properties. The tests were conducted using three different types of chambers and the temperature range was-40°C to 125°C. The result showed that the thermal fatigue life tends to be shorter when the temperature change rate in the thermal cycle profile is slow. This means that the effect of creep on thermal fatigue life is large. The analogous analysis result was obtained by finite element analysis. The microstructural analysis of damaged joints revealed that recrystallized grains form in the solder and crack progresses at their grain boundaries. Thus the thermal fatigue life was suggested to be dominated by the ease of formation of recrystallized grains in solder.

Abstract: Due to tighter restrictions on the use of hazardous lead-bearing solder alloys, lead-free solder research has seen significant growth in recent years. The most common SAC alloys have emerged as viable candidates for the substitution of conventional Sn-Pb alloys among the representative lead-free solders (Sn-Cu, Sn-Bi, Sn-Zn, Sn-In, Sn-Ag, and Sn-Ag-Cu (SAC)). These alloys have limited use in contemporary microelectronic packaging devices due to various worries about the existence of brittle intermetallic compounds (IMCs) like Ag₃Sn and Cu₆Sn₅ in these materials. Over the years, numerous lead-free solder alloy alternatives with nanoparticle reinforcement have been proposed as an alternative to limit the growth of IMCs and enhance solder joint durability. This paper details the development of lead-free solders with selected fillers and reinforcements to date. The thermal cyclic test method was also discussed as one of the alternatives for reliability test techniques to be explored in future studies on this topic. In conclusion, fillers and reinforcements are also essential for enhancing interconnection’s heat cycle efficiency. Exploring various fillers and reinforcements that can be used to advance lead-free solder technology with thermal cyclic methods will open more investigation opportunities for lead-free solders.

Abstract: This research aimed to study the effects of Ni content on melting behaviors and wettability of SnBiAgNi lead-free solder. Sn-58Bi-0.05Ag was used as the base solder, and Ni was then put in by 0.05, 0.10, 0.50 or 1.00 wt%. Solidus and liquidus temperatures of the solder alloys were examined to study melting behaviors. The Ni content changed the solidus and liquidus temperatures, and Sn-58Bi-0.05Ag-0.10Ni possessed the lowest solidus and liquidus temperatures. Sn-58Bi-0.05Ag-0.10Ni also provided the narrowest pasty range. Wettability of the solders on the copper substrate was expressed in terms of spread factor. The addition of Ni improved the wettability of the base solder, and Sn-58Bi-0.05Ag-0.10Ni provided the highest spread factor.

Abstract: The different composition material of copper substrate significantly affects the intermetallic compound (IMC) formation and the solder joints durability. This study was conducted on the interfacial reaction between lead-free solder and the different copper substrates via reflow soldering. The selected substrate is copper (Cu) and copper-beryllium (Cu-Be). The lead-free solder involved is Sn-3.8Ag-0.7Cu (SAC3807) solder ball with a diameter of 700 μm. All the samples were subjected to the isothermal aging process. The material characterization and analysis on the IMC formation were examined by scanning electron microscopy (SEM), optical microscope (OM), and energy dispersive X-ray analysis (EDX). After the reflow process, the result revealed that Cu₃Sn, Cu₆Sn₅ IMC layer formed at SAC3870/Cu and SAC3870/Cu-Be interface. The changes to a rod-like shape Cu₆Sn₅ and irregular needle-shaped Cu₃Sn₄ occur after the aging treatment on SAC3870/ Cu. Meanwhile, the IMC layer for SAC3870/Cu-Be shows a rod-like shape transformed into a blocky-like shape Cu₆Sn₅ and Cu₃Sn₄ diamond-shape. This result indicates that Ag₃Sn nanosized was formed on the intermetallic surface during the aging process for both SAC3807/Cu and SAC3807/Cu-Be. The Ag₃Sn nanosized element at SAC3807/Cu-Be is many compared to SAC3807/Cu. In addition, IMC thickness for SAC3807/Cu-Be shows a thicker layer than SAC3807/Cu. Lastly, in this research, the element of Be in SAC3807/Cu-Be cannot be defined because the beryllium element is not easily detected as the percentage was very low.

Abstract: Microstructures and tensile properties at 233 K, 300 K and 398 K of Sn-3.0 mass%Ag-0.5 mass%Cu (SAC305) and Sn-Ag-Cu-In-Sb solder were investigated by using miniature size specimens with 0.5 mm diameter, which can reproduce the microstructure of the real solder joint. In this study, three kinds of Sn-Ag-Cu-In-Sb solder (SAC305-6.0 mass%In-1.0, 2.0 and 3.0 mass%Sb) were used. The microstructure of SAC305 consisted of a single crystal grain. On the other hand, the microstructures of Sn-Ag-Cu-In-Sb solder consisted of polycrystalline. The number of crystal grains per the cross section of SAC305-6.0In-1.0Sb was stably several tens or more. The tensile strength of Sn-Ag-Cu-In-Sb was improved approximately 2 times that of SAC305. Also, the variation in tensile strength of SAC305 at 233 K was large due to anisotropy of the crystal grain. In contrast, the variation in tensile strength of Sn-Ag-Cu-In-Sb at 233 K was lower than that of SAC305. In particular, that of SAC305-6.0In-1.0Sb was reduced to approximately a sixth of that of SAC305. It seems that the effect of anisotropy of the crystal grain is decreased by polycrystallization in SAC305-6.0In-1.0Sb.

Abstract: Surface finish is coating layer plated on a bare copper board of printed circuit board (PCB). Among PCB surface finishes, Electroless Nickel/Immersion Gold (ENIG) finish is a top choice among electronic packaging manufacturer due to its excellent properties for PCB. However, the use of gold element in ENIG is very high cost and the black pad issue have not been resolved. Thus, by introducing an Electroless Nickel/Immersion Silver (ENImAg) as alternative surface finish hopefully can reduce the cost and offer better properties. The aim of this study is to investigate the effect of bismuth on interfacial reaction during reflow soldering between Sn-2.5Ag (SA25), Sn-3.4Ag-4.8Bi (SAB3448) and ENIMAG surface finish. Solder balls with sizes of 500μm diameters were used. The characteristics of intermetallic compound (IMC) were analyzed by using scanning electron microscopy (SEM), optical microscope and energy dispersive x-ray (EDX). After reflow soldering, the result revealed that only the irregular circle-shape of (Cu,Ni)₆Sn₅ IMC layer was formed at the interface and change to an irregular rod-like shape meanwhile the irregular needle-shape (Ni,Cu)₃Sn₄ was appeared after aging treatment. The result also indicated that, the grain size and thickness of IMC for SAB3448 is smaller and thinner compared to the SA25. The IMC thickness is proportional to the aging duration and IMC morphology for both solder are became thicker, larger and coarser after isothermal aging. No bismuth particle has been detected on SAB3448 solder during top surface examination. In addition, the Bi has been observed can reduce the grain size and the growth rate of IMC. Keywords: ENIMAG, reflow soldering, lead-free solder, intermetallic compound, bismuth

Abstract: Tensile and low cycle fatigue properties of Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge (mass%) lead-free solder were investigated using miniature size specimens and obtained data were compared to those of Sn-3.0Ag-0.5Cu (mass%). The microstructure of Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge consists of dendritic β-Sn phases and ternary eutectic phases surrounding them which are composed of β-Sn, (Cu,Ni)₆Sn₅ and Ag₃Sn. Tensile strength and 0.1% proof stress of Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge are superior to those of Sn-3.0Ag-0.5Cu at 25°C and 150°C. However, elongation of it is inferior to that of Sn-3.0Ag-0.5Cu at both temperatures. Fatigue lives of both alloys obey the Manson-Coffin equation and are analogous at 25°C. Although fatigue lives of both alloys decrease at 150°C, the fatigue life of Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge is inferior to that of Sn-3.0Ag-0.5Cu. At 150°C, the crack mainly progresses at grain boundaries of recrystallized grains. Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge has several grain boundaies which can be the origin of the crack so that fatigue lives degrade at 150°C.

Abstract: Sn whisker growth on Cu substrate Pb-free solder is a serious problem in electric and electronic devices and as well as in aerospace applications. Due to the concern on the toxicity of lead by Restriction of Hazardous Substances Directive (RoHS), new lead free materials have been developed, and this resulted in the resurfacing of Sn whisker. The compressive stress, corrosionand surface oxide have been identified as the driving force for Sn whisker formation induced by mechanical alloying and oxidation. In this paper, we report the study to understand the mechanism of Sn whisker growth that control whisker formation on Sn finished.Based on the review, a preliminary conclusion has been made, where the analysis of the topography and microstructural characterization can be determined by evaluating under various environmental influences.Furthermore, the whisker growth happening on lead-free soldered can be considerably reduced by controlling the compressive stress in the solder which initiates the growth of intermetallic compounds (IMCs).

Abstract: A non metallic reinforcement has attracted most of the worldwide researchers to enhance solder performance. Silicon carbide (SiC) particle is a semiconductor which had been used as a non metallic reinforcement in this research study.The fabrication of Sn-0.7Cu lead free solder paste was done by mixing the solder powder with flux. Then, Sn-0.7Cu/SiC composite solder paste was prepared by mixing solder powder, flux and various weight percentage (wt%) of SiC. The amount of SiC particles added was 0, 0.25, 0.50, 0.75 and 1.0 wt%. The influence of SiC addition was analyzed based on its wettability, IMC layer formation and microhardness properties. The addition of SiC particles had decreased the contact angle as well as thinner the IMC layer. The morphology of IMC layer changed from scallop like shape to combination of scallop and planar like shape with the addition of SiC particle. Apart from that, the microhardness was enhanced with addition of SiC particle into Sn-0.7Cu lead free solder paste.

Abstract: While various mechanical properties of SnAgCu (SAC) solder has been reported in the literature the corrosion resistance of solder materials has not been widely reported. This study shows regions adjacent to the Cu₆Sn₅ intermetallic compounds (IMCs) as the corroded region. To investigate the possible formation of a galvanic cell at the interface of SAC solder and the Cu substrate the surface potential distribution at this interface has been evaluated. Results exhibited a comparatively large surface potential difference between SAC solder and the Cu₆Sn₅ IMC indicating SAC solder and Cu₆Sn₅ IMC as the anode and cathode in this system, respectively.