Solder Ball Joints Research Articles

Thermal Cycling Performance of Heterogeneous Solder Ball Joints with Sn-3.0Ag-0.5Cu and Sn-0.75Cu(-Ni,Bi) Solder Ball Composition for BGA Package

Sn-3.0Ag-0.5Cu (SAC305) is one of the most commonly used Pb-free solder composition nowadays. A minor alloying element addition can improve mechanical properties and thermal reliability of the solder joint. Minor amount of Bithmuth (Bi) or Nickel (Ni) addition can improve mechanical properties of solder by solid solution strengthening, or ensure the structural stability of the intermetalllic compounds. Also, low melting temperature solder with Bithmuth can reduce the cost of soldering process and keep components from deterioration. In this study, reliability of heterogeneous and homogeneous solder joint in the ball-grid-array (BGA) package solder joint were investigated. Using Sn-3.0Ag-0.5Cu (SAC305) solder paste and two kinds of solder balls, we have investigated which combination of solder joint improves the thermo-mechanical reliability. SAC305 and SCN (Sn-0.75Cu-Ni,Bi) balls were used for homogeneous and hetrogeneous joints. Solder balls were attached in BGA package. To examine the solder joint reliability, thermal cycling test was conducted after reflow soldering. Shear strength measurement and cross-sectional analysis of the BGA package solder joints were carried out before and after 2000 cycles of the test. The shear strength of homogeneous solder joint decreased to 68.2% and heterogeneous decreased to 43.5%. The cross-sectional analysis using scanning electorn microscopy (SEM) and electorn back-scattered diffraction (EBSD) showed the (Ni,Cu)<sub>6</sub>Sn<sub>5</sub> and Cu<sub>6</sub>Sn<sub>5</sub> IMCs which were generated in the solder joint, and the crack propagated longer in the homogeneous solder joint of SAC305 after the thermal cycling test. IPFM showed the grain refinement effect of the SCN solder joint after thermal cycling. The minor addition of Bi had played a role as dislocation pinning site and became to equiaxied grain, so that the lifetime of heterogeneous SCN solder joint was superior than that of the SAC305.

Mechanical Properties of Doped Solder SAC-Q for High Strain Rate Testing at Extreme Surrounding Temperatures for 6 Months of Isothermal Aging

Abstract In various industries, including automobile industry, oil and gas, aerospace, and medical technology, electronic components are subjected to significant strain during shocks, vibrations, and drop conditions. Electronic components of this type are frequently subjected to extreme temperatures ranging from –65 °C to 200 °C. These electronic equipment are frequently subjected to strain rates of 1 to 100 sec−1 in sensitive conditions. SAC-Q, SAC-R, Innolot, and other doped SAC solder alloys have recently been introduced to electronic components and packages. SAC-Q refers to the addition of Bi to the Sn-Ag-Cu composition. The mechanical characteristic results and statistics for lead-free solder alloys are particularly important for increasing electronic package stability and high-temperature storage and strain rates. Furthermore, the mechanical characteristics of solder alloys can be dramatically altered owing to thermal aging, which causes microstructure alteration. For high-temperature aging for longer durations and testing at extremely low to very high working temperatures, SAC-Q solder alloy data is not available. The SAC-Q solder material was tested and studied at working temperatures ranging from −65 °C to 200 °C, with strain rates of up to 75 sec−1, for this study. A comparison was also done with the SAC305 solder, which had been thermally aged and tested under identical conditions. Isothermal aging specimens were kept at 100 °C for up to 180 days following manufacturing and reflowing when tensile studies were conducted at various operating temperatures. This study develops and describes stress–strain curves for a wide variety of strain rates and test temperatures. In addition, the test results and data collected were matched to the Anand viscoplasticity model, and Anand constants were calculated by estimating high strain rate behavior throughout a wide range of operating temperatures and stress levels. In addition, for BGA package assembly with PCB, FE analysis was performed for drop/shock events. For varied aging circumstances of SAC-Q solder ball joints, hysteresis stress–strain curves and plastic work density curves are generated.

Effect of Sb Addition on Microstructure and Shear Strength of Sn-3.0Ag-0.5Cu Solder Ball Joints

The effect of a small amount of Sb addition to Sn-3.0Ag-0.5Cu (mass%) solder on microstructures and impact properties of the solder ball joint was investigated. Cross-sectional microstructural observation revealed that scalloped Cu6Sn5 is formed at the solder/Cu interface, and Cu3Sn is formed at the interface between Cu6Sn5 and Cu with aging. It was confirmed that the growth of the reaction layer is suppressed by the addition of Sb. Moreover, the result of the impact ball shear test showed that the decrease in impact properties with aging can be suppressed in Sn-3.0Ag-0.5Cu-1.5Sb (mass%). It was also suggested that the suppression of linear crack propagation at the Cu3Sn/Cu6Sn5 interface is effective to prevent the reduction of absorbed energy.

Numerical Investigation of the Evolving Inelastic Deformation Path of a Solder Ball Joint under Various Loading Conditions

Solder joints of ball grid arrays (BGA) have been widely used to connect electronic components to printed circuit boards (PCBs) and are often subjected to mechanical stress. Several studies have been conducted on the mechanical reliability of solder joints. While these studies have been useful in the industry, detailed studies on how the inelastic deformation path of the solder ball joints evolves under specific loading conditions have not been sufficiently reported. This study aims to understand how the inelastic deformation path evolves when a solder joint is subjected to a constant external force by utilizing the theory of mechanics. It has also been found that the mechanical failure is strongly influenced by the evolution history of the deformation modes in materials. For this study, an elastoplastic constitutive model and a ductile fracture criterion were implemented into the vectorized user-defined material (VUMAT) subroutine of the ABAQUS program for finite element (FE) analysis. With the model, the evolution of the inelastic deformation path of a single solder ball under different loading conditions was numerically analyzed. Three loadings (shear, compression, and bending) were chosen as the basic loading conditions. In addition, combinations of the basic loadings resulted in three dual loadings and one complex loading. The simulation results showed that the shear and bending caused the fracture for both single and dual loadings, but when combined with compression, the fracture was suppressed. The results indicate that fracture is not solely determined by the magnitude of equivalent plastic strain but also by the evolution of inelastic deformation mode. This research offers an improved understanding of the significance of the inelastic deformation path and fracture.

Bonding Property of Middle Temperature Sn-Ag-Cu Solder Ball Joint of Ball Grid Array Package

Alloying effects of Nickel and Bismuth in SAC solder to achieve mechanical and microstructural evolution were investigated by comparing three different chemical composition of solders. Sn-3.0Ag-0.5Cu (SAC305) is the most commonly used for Pb-free solder and solder balls are based on Sn-Ag-Cu alloy composition. Compositions of solder balls were Sn-3.0Ag-0.5Cu (SAC305), Sn-1.2Ag-0.5Cu-0.05Ni (SAC1205N) and Sn-Ag-Cu-Ni-Bi based solder (SACNB). Organic solderability preservative (OSP) surface finished substrate, ball grid array (BGA) package arranged by 300 ㎛ diameter solder ball and Type 4 solder paste were used. Solder ball shear test of the BGA package was conducted before the reflow soldering. Board level package bonding process was carried out by hot air reflow soldering. Void content of the BGA solder joint was investigated after soldering. The microstructure evolution before and after thermal cycle test (TCT) was observed using scanning eletron microscopy (SEM) and energy dispersive spectroscopy (EDS). After TCT, intermetallic compound (IMC) refinement and solid solution strengthening effects of Bi element addition were observed in the solder matrix, and also any segregation of Bi element was not founded. Based on these result, it was found that the solder joint reliability of the middle and low temperature solder joints was improved.

Board-Level Drop Impact Reliability Analysis of Dual-Side Molding System-in- Package (SiP) Modules

System-in-package (SiP) modules are widely used in portable electronics such as Internet of Things (IoT) devices and mobile consumer equipment since they integrate multiple components in a single package and thus facilitate device miniaturization. An advanced packaging technology referred to as dual-side molding (DSM) has recently been proposed as a means of achieving even smaller form factors and lower cost solutions. However, shrinking the package size reduces the solder joint connection area between the SiP module and the printed circuit board (PCB). Consequently, the board-level drop reliability may be severely impaired. Accordingly, the present study utilizes a numerical model to investigate the board-level solder joint reliability of a DSM SiP package in drop impact tests performed in accordance with the Joint Electron Device Engineering Council (JEDEC) standard. The validity of the numerical model combined with a full-factorial design method is then employed to examine the effects of the main design parameters of the DSM SiP package on the reliability of the solder joints in the drop impact test. Overall, the present results show that a higher EMC coverage of the solder ball joints yields a significant improvement in the solder joint reliability. In addition, a larger solder joint volume is beneficial in reducing the solder joint stress by absorbing a greater proportion of the impact load and energy produced in the drop impact event.

A Study on Transmission properties of AuNi coated polymer ball joint and Sn58Bi solder joint for flex-on-board interconnection

Flex-on-board (FOB) interconnection plays an important role in display applications. Due to the thinness of the interconnect, the contact resistance of anisotropic conductive film (ACF) joints is very small; however, the transmission property of ACF joints are still unknown. In this study, we designed a novel coplanar waveguide structure to characterize the transmission properties of ACF joints in FOB interconnections. Specifically, we compared the differences between the Au/Ni coated polymer ball joint and low melting point Sn58Bi solder ball joint in terms of their high frequency performance. Both were bonded under the same conditions of 200 °C for 10 s at 2 MPa. A high frequency test was then carried out in the range of 300 MHz to 20 GHz. The results showed that 14 GHz was the resonant frequency of FOB package that contained the Au/Ni coated polymer ball joints, while 1 GHz increased by using Sn58Bi solder joints in FOB package. To our knowledge, there is the first study to determine the high frequency performance of flex-on-board interconnections using ACFs joints and the coplanar waveguide method.

Drop test analysis of ball grid array package using finite element methods

Hand held devices like laptop, smart phone, tab etc. are likely to be mishandled or dropped during their usage. High performance and multitasking of the electronic devices have driven towards thinner and sleeker products. Reliability of the devices is a real challenge when they are dropped. Damage caused due to the Drop- impact, is the most predominant modes of failure experienced by the electronic products. The solder joints tend to fail when they are mishandled or dropped. This paper is intended to study the stresses developed in the solder ball joints which are used to connect the Electronic Package with that of the Printed Circuit Board. Drop test under Dynamic implicit analysis is carried out to investigate the stresses developed in solder joints at different locations of the package and the most stressed balls are identified using Abaqus Software.

Backplate-reinforced structures for enhancing solder joint reliability of server CPU assembly under thermal cycling

ABSTRACT To meet the requirement of the high I/O and fine-pitch interconnects, the conventional insertion-mount socket for central processing unit (CPU) has been changed to surface-mount one with ball grid array. The solder ball joint reliability of the socket used in the CPU assembly becomes very important. In this study, the socket's solder joint reliability of the backplate-reinforced CPU assembly and its related mechanics under mechanical and thermal loadings are investigated experimentally using strain gauge and shadow moiré, and numerically by a finite element method (FEM). The validated FEM results have suggested that maximum stress of solder balls increases almost linearly with decreasing the backplate thickness under mechanical loading during the CPU assembly, but is insensitive to the backplate thickness under thermal loading during the thermal cycling. It is also found that the residual (bending) strain on the PCB proportional to the maximum von Mises stresses of solder joints (or balls) can be used as a key parameter to correlate with the solder joint failures or cracks during the thermal cycling. Overall, experimental and FEM results in this study reveal that solder joint reliability in the CPU assembly during thermal cycling can be improved by adopting the thicker reinforced backplate.

Effects of bismuth and nickel on the microstructure evolution of Sn-Ag-Cu (SAC)-based solders

The addition of alloying elements to the SAC alloy composition changes the growth behavior of thick Cu6Sn5 and Cu3Sn intermetallic compounds (IMCs) and their influences on mechanical responses. The purpose of this study is to investigate the effects of Bi and Ni on the growth kinetics of interfacial IMCs (Cu6Sn5 and Cu3Sn) and the mechanical strength of the bulk solders during high temperature aging. Reflowed samples of the SAC405 solder balls and the SAC + Bi,Ni solder balls were stored in high-temperature storage (HTS) chamber at 150 °C and 175 °C each for 0 h, 500 hs, 1000 hs, and 2000 hs. The microstructure evolutions of bulk solder and its interfacial areas were evaluated and the associated microhardness values were measured on the solder balls. During aging, the presence of Bi was seen only in the bulk solder region, resulting in increased hardness by a factor of ∼ 2 and resistance to the age softening due to solid solution strengthening. On the other hand, Ni was observed in both the solder ball and IMC regions. After aging at 150 °C, SAC + Bi,Ni solder balls had a thinner Cu3Sn IMC layer at its interface when compared to that in SAC solders with no Ni. At 175 °C, however, Ni addition did not decrease the growth of Cu3Sn. Long aging (2000 h) of the SAC405 sample at 175 °C resulted in the complete consumption of the Cu layer, which was slowed in SAC + Bi,Ni. The presence of Bi and Ni, therefore, show the potential to improve the reliability of the SAC solder ball joint during aging by restricting the solder deformation and the growth of the Cu3Sn layer.

Device architecture optimization of solder ball joints fatigue lifetime under random vibration frequencies

Purpose This study aims to investigate the vibration effects on ball grid array lifetime. Design/methodology/approach Several finite element method simulations and experiments were performed. Findings An optimized circuit configuration was found. Originality/value The originality of paper is confirmed by authors.

Reliability assessment of ball grid array joints under combined application of thermal and power cycling: solder geometry effect

Purpose This study aims to investigate simultaneous power and thermal loading. Design/methodology/approach Finite element method simulations coupled with experiments. Findings The effects of power cycling have been determined. Originality/value This paper aims to testify the combined effects of thermal and power cycling loads on the reliability of solder ball joints with barrel- and hourglass-type geometries in an electronic system. The finite element simulation outcomes showed that the maximum strain energy was accumulated at the edges of barrel-type solder, whereas the hourglass-type was vulnerable at the necking side. It was also found that the hourglass-type solder showed a reliable behavior when the sole thermal cycling was exerted to the electronic system, whereas the barrel-type solder was a better choice under simultaneous application of thermal and power loadings. The experimental results also confirmed the finite element simulation and indicated that the solder joint reliability strongly depends on the geometry of interconnection in different operating conditions. An extensive discussion was presented to shed light on the paramount importance of combined thermal/power cycling on the reliability of solder joints.

Electroless Ni/Pd/Au Plating for Semiconductor Package Substrates (III) —Influence of the Electroless Pd Plating Thickness on the Solder Ball Joint Reliability and the IMC Growth—

Electroless Ni/Pd/Au Plating for Semiconductor Package Substrates (III) —Influence of the Electroless Pd Plating Thickness on the Solder Ball Joint Reliability and the IMC Growth—

無電解Ni/Pd/Auめっきにおけるはんだボール接続信頼性-金属間化合物の成長に及ぼす電解Pdめっき膜厚の影響

無電解Ni/Pd/Auめっきにおけるはんだボール接続信頼性-金属間化合物の成長に及ぼす電解Pdめっき膜厚の影響

Interaction of thermal cycling and electric current on reliability of solder joints in different solder balls

This paper deals with the effects of electric current on the thermomechanical lifetime of solder joint as the most vulnerable part in electronic packages. The main focus of this paper is located on the Sn3.8Ag-0.5Cu based solder. Different current densities from 1 A mm−2 to 10 A mm−2 are under considered in two well-known solder ball joints, namely barrel- and hourglass-type, in the temperature cycling conditions. Electrical properties of the interested solder joints are experimentally extracted and applied to the finite element analysis in order to reveal the thermomechanical coupling effects of thermal cycling and electric current. Two most important phenomena including joule heating effects and induced triaxility play major roles in determination of solder joint types in the electronic packages. The results reveal that at the lower current density in which the joule heating effects are insignificant, the sharp triaxiality in the barrel-type solder joint is evident due to sharp tilting angle of solder joint. However, in the higher current densities in which the joule heating effects come into play, the number of cycle to failure of hourglass-type solder joint is lower in comparison with barrel-type solder joint. This event may be due to the lower diameter of hourglass-type solder joint in its neck so that more losses in the neck of hourglass-type solder joint, the more effective joule heating is occurred.

High-Speed Camera Investigation into Fracture Behavior of Solder Ball Joints Under Dynamic Loading

Themechanical integrity of solder ball joints under dynamic loading is generally evaluated bymeans of a JEDEC standard impact test at high speed (0.01–1m/s). Such tests result in a higher incidence of interfacial fracture than low-speed shear tests, and provide valuable insights into the load–displacement response and failure mode of the solder ball joint. This study proposes an experimental technique for observing the interfacial fracture phenomenon by means of a high-speed framing camera that captures approximately 500,000 frames per second (fps). It is shown that by selecting an appropriate frame rate (78,212 fps), the resulting sequence of images provides a useful understanding of themanner in which the fracture originates, propagates, and leads to various types of failure mode, such as interfacial and bulk solder cracks.

열시효 처리된 무연 솔더 볼 연결부의 충격 전단강도 평가

The present study investigates the impact shear strength of thermal aged Sn-3Ag-0.5Cu lead-free solder joints at impact speeds ranging from 0.5 m/s to 2.5 m/s. The specimens were thermal aged for 24, 100, 250 and 1000 hours at . The experimental results demonstrate that the shear strength of the solder joint decreases with an increase in the load speed and aging time. The shear strength of the solder joint aged averagely decreased by 43% with an increase in the strain rate. For the as-reflowed specimens, the mode II stress intensity factor () of interfacial IMC between Sn-3.0Ag-0.5Cu and a copper substrate also was found to decrease from to in the speed range tested here. The degradations in the shear strength and fracture toughness of the aged solder joints are mainly caused by the growth of IMC layers at the solder/substrate interface.

Comparison of the fracture toughness of Cu6Sn5 intermetallic compound as measured by nanoindentation and other methods

In this work, nanoindentation tests using a three-sided Berkovich indenter were performed for a Cu6Sn5 intermetallic compound (IMC) in interfacial specimens of lead-free Sn–3Ag–0.5Cu solder ball joints at room temperature to investigate effect of the strain rate on the mechanical properties of this IMC. The fracture toughness was found to have an approximately linear relationship with the logarithmic nanoindentation strain rate, implying that the fracture toughness decreased in a range of (1.64–0.63) MPam0.5 with an increase in the strain rate ranging from 0.01s−1 to 0.33s−1. This characteristic was similar to the KC values of Cu6Sn5 under shear or tensile tests. It was, however, when measured by nanoindentation tests, found to be less sensitive to the strain rate compared to measurements gained through shear or tensile tests. The results here were discussed and compared to those from other studies.

The tensile impact properties of aged Sn–3Ag–0.5Cu/Cu solder joints

The present study aims to evaluate the effects of isothermal aging on the mechanical properties of solder joints. To achieve this objective, the tensile impact behavior of lead-free Sn–3Ag–0.5Cu solder ball joints aged at 373K for times ranging from 24h to 1000h was investigated using an altered miniature Charpy impact-testing system. The experimental results showed that the tensile strength, the work-of-fracture and the fracture toughness of solder joints were found to decrease as the effective strain rate (or the loading speed) as well as the aging time increased due to a thicker IMC layer with a coarser nodule under thermal aging. In addition, the joint strength after isothermal aging under a tensile load was more sensitive to the strain rate than those in the shear loading mode. Specifically, equations representing the relationships among the effective stress, the strain rate and the aging time were established for the solder joints aged at 373K in this study. Furthermore, the mode II fracture toughness values were less than the mode I fracture toughness for each aging time condition of the solder joints.

Solder Ball Robustness Comparison between SAC 387 and Polymer Solder Balls under AC and TC Reliability Test

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.