Ball Shear Research Articles

High-Frequency and Low-Temperature Thermosonic Bonding of Lead-Free Microsolder Ball on Silver Pad Without Flux

Lead-free solder balls are environment friendly; however, they require a high bonding temperature, which causes problems in the microelectronics package industry. To reduce the bonding temperature, a 60 kHz high-frequency thermosonic bonding method is proposed and realized using a lab bonder. Experimental results showed that this method could be used to bond a 300 μm-diameter Sn–Ag–0.5Cu microsolder ball onto a silver pad without flux at a low temperature of 160 °C in 3 s. A ball shear test showed that the high frequency led to a high bonding strength of 58.8 MPa, and a dimpled structure was observed at the bonding interface by SEM. Compare with the reflow method or laser soldering method, the proposed method requires a low bonding temperature and leads to a high bonding strength.

Pronounced effects of Ni(P) thickness on the interfacial reaction and high impact resistance of the solder/Au/Pd(P)/Ni(P)/Cu reactive system

The effects of Ni(P) thickness, δNi(P), on the interfacial reaction and high impact resistance of Sn-3Ag-0.5Cu/Au/Pd(P)/Ni(P)/Cu microelectronic solder joints were investigated. During soldering, the surface layers of Au (0.1μm) and Pd(P) (0.2μm) were readily eliminated from the interface, and the Ni(P)/Cu structure underneath subsequently came into contact with the solder. When δNi(P) was 0μm, a solder/Cu reaction occurred, and the intermetallic compounds (IMCs) Cu3Sn and Cu6Sn5 (dissolved with 1–3at.% Pd) formed at the interface. When δNi(P) was sufficiently thick (i.e., 7μm), the reaction between the components transformed the system into a solder/Ni(P) system with multilayer IMCs, which included (Cu,Ni)6Sn5, (Ni,Cu)3Sn4, Ni2SnP, and Ni3P. On the submicron scale (e.g., δNi(P)=0.9μm), the solder/Ni(P) and solder/Cu reactions can occur sequentially, indicating that a submicron-thick Ni(P) layer did not function as an efficient diffusion barrier between solder and Cu. With the aid of Cu–Ni–Sn phase diagram, diffusion path predictions can be made about the IMC translation in response of different δNi(P). High-speed ball shear testing showed that the impact resistance of the solder joints was significantly reduced with increasing δNi(P). These findings suggested that δNi(P) is an important factor in the interfacial microstructure and the resulting mechanical properties of solder joints and that the direct deposition of an Au/Pd(P) dual layer (i.e., δNi(P)=0μm) on top of the Cu pads can offer an appropriate solderability for the lead-free Sn–Ag–Cu alloy.

Effects of PCB ENIG and OSP Surface Finishes on the Electromigration Reliability and Shear Strength of Sn-3.5Ag PB-Free Solder Bump

The effects of printed circuit board electroless nickel immersion gold (ENIG) and organic solderability preservative (OSP) surface finishes on the electromigration reliability and shear strength of Sn-3.5Ag Pb-free solder bump were systematically investigated. In-situ annealing tests were performed in a scanning electron microscope chamber at 130, 150, and <TEX>$170^{\circ}C$</TEX> in order to investigate the growth kinetics of intermetallic compound (IMC). Electromigration lifetime and failure modes were investigated at <TEX>$150^{\circ}C$</TEX> and <TEX>$1.5{\times}10^5A/cm^2$</TEX>, while ball shear tests and failure mode analysis were conducted under the high-speed conditions from 10 mm/s to 3000 mm/s. The activation energy of ENIG and OSP surface finishes during annealing were evaluated as 0.84 eV and 0.94 eV, respectively. The solder bumps with ENIG surface finish showed longer electromigration lifetime than OSP surface finish. Shear strengths between ENIG and OSP were similar, and the shear energies decreased with increasing shear speed. Failure analysis showed that electrical and mechanical reliabilities were very closely related to the interfacial IMC stabilities.

Effects of Pd layer thickness on mechanical properties and microstructures of Sn-3.0 Ag-0.5 Cu solder joints

In order to investigate effects of Pd layer thickness on the mechanical properties and microstructures of Sn-3.0 Ag-0.5 Cu solder joints, three different Pd layers, i.e., 0.05, 0.1, 0.15 µm, were employed on the electroless nickel immersion gold [ENIG, Ni-P(5 µm )/Au(0.08 µm)] surface finished flame retardant type 4 (FR4) printed circuit board (PCB) substrates. Our studies showed that the addition of Pd layer in ENIG treatment, i.e., ENEPIG, enhanced the bonding strength of solder joints by reducing the formation of intermetallic compounds (IMCs), (Cu, Ni)6Sn5 and (Ni, Cu)3Sn4. The different failure modes were also observed – the crack propagation occurred along the interface between P-rich Ni layer and Cu layer in 0.05 µm Pd specimens while specimens with 0.1 µm and 0.15 µm Pd layers showed the crack propagation proceeded mostly inside solders. In this study the effects of Pd layer thickness in ENEPIG surface finish on the bonding strength of solder joints were investigated by means of drop test and ball shear test, followed by observation of microstructures and interfaces using a scanning electron microscope (SEM) and an energy dispersive spectrometer (EDS).

Effect of reflow temperature on the mechanical drop performance of Sn-Bi solder joint

The effect of reflow peak temperatures from 160°C to 180°C on the mechanical drop performance of Sn-58Bi solder joint was studied. The mechanical drop performance was evaluated through the three point dynamic bending test in which the strain of PCB was step increased until the failure of daisy chain circuit was detected with 50 kHz sampling rate. The wetting behaviour of Sn-58Bi on Cu was investigated by wetting balance tests at various pot temperatures from 150°C to 190°C. The dynamic bending behaviour of solder joint decreased significantly with the decrease of temperatures from 170°C to 160°C. Microstructural observation and ball shear test results revealed that the decrease of joint area on Cu pad affected the deterioration of mechanical drop performance. From wetting balance tests at various pot temperatures, it was considered that the abrupt change in wetting activation energy at temperatures between 165°C and 170°C was responsible for the wetting behaviour on Cu pad and resultantly the mechanical drop performance of Sn-58Bi solder. It was also considered that the change of wetting activation energy was caused from the change of interface reaction mechanism which was due to the change in IMC formation behaviour with reflow peak temperature.

Shear strengths of CBGA/PBGA solder ball joints with lead-free solder pastes

The present study is carried out to characterise the ball shear strengths of ceramic ball grid array (CBGA) and plastic ball grid array (PBGA) packages with lead-free solder pastes. Three commercially available Sn/Ag/Cu (SAC) solder pastes such as Sn 96.5/Ag3.0/Cu0.5 and 95.5/Ag3.8/Cu0.7 with a no-clean flux are employed. The effects of temperature profiles during reflow on the strength of solder joints are studied. Their printing abilities are also observed. Of particular concern for ceramic ball grid array packages is the interaction between 90/10 Pb/Sn compound solder balls and SAC solder pastes. The composition of the solder paste region between the I/O pad and the solder ball is analysed using the energy dispersive X-ray (EDX) machine.

Evaluation of mechanical properties of low-Ag ball grid array solder joints using a high-speed ball shear test

Solder joints of Sn–1.0Ag and Sn–1.0Ag–0.1Ce on electroless nickel/electroless palladium/immersion gold (ENEPIG) were studied and mechanically evaluated using a high-speed shear test. The effect of Pd thickness in ENEPIG on the reliability of solder joints was evaluated after multiple reflows. Microstructural observations of the solder joint interfaces and fractures after shear tests are shown. For comparison, conventional SAC305 Pb-free solder was also mechanically evaluated under the same conditions. By adding a thin Pd layer in ENEPIG surface finish, the intermetallic compound (IMC) layer’s morphology of SAC305 change from needle type (as Pd thickness=0μm) to scallop type (as Pd thickness=0.1μm). While the intermetallic compounds (IMCs) layer’s morphology of 1.0Ag solders change from facet type (as Pd thickness=0μm) to needle type (as Pd thickness=0.1μm). ENEPIG with thicker Pd layers was suitable for 1.0Ag solders during high speed shear test whereas conventional SAC305 showed the highest shear strength with an ENIG surface finish.

Microstructural evaluation of interfacial intermetallic compounds in Cu wire bonding with Al and Au pads

A comparative study on the difference in interfacial behavior of thermally aged Cu wire bonding with Al and Au pads was conducted using transmission electron microscopy. During high-temperature lifetime testing of Cu wire bonding with Al and Au pads at 175°C for up to 2000h, different growth rates and growth characteristics were investigated in the Cu–Al intermetallic compounds (IMCs), including CuAl2, CuAl and Cu9Al4, and in the Cu–Au IMCs, including (Au,Cu), Cu3Au and (Cu,Au). Because of the lower growth rates and greater ductility of Cu–Au IMCs compared to those of Cu–Al IMCs, the Cu wire bonding with the Au pad showed relatively better thermal aging properties of bond pull strength and ball shear strength than those with the Al pad counterpart. In this study, the coherent interfaces were found to retard the growth of IMCs, and a variety of orientation relationships between wire, pad and interfacial IMCs were identified.

Reliability and Bondability Study on Interfacial Behavior between SnAgCu Solder and Cu-Ni-Au OSP Pads

In this paper, micro interfacial behavior for Sn3.5Ag0.5Cu (SAC305) lead-free solder on Cu-Ni-Au substrate has been carefully investigated. It is observed that the intermetallic compound (IMC) ingredients along the SAC305 solder on the Cu-Ni-Ag substrate are (Ni, Cu)3Sn4 and (Cu, Ni)6Sn5 after reflow process. Reliability analysis for IMC ((Ni, Cu)3Sn4 and (Cu, Ni)6Sn5) was conducted based on the measurement of IMCs thickness and ball shear force. Temperature effects were also included in the analysis. The ingredients of IMC remain un-change if the working temperature is below 400 OC. Diffusion rate of interfacial controlled reaction was found to be depended on the annealing temperature. The IMC layer thickness decreased as the ramp-up rate of reflow temperature was increased for all cases studies. Preliminary results demonstrated that the measured ball shear force slightly changed for all different IMC thicknesses.

Optimization of the Ni(P) Thickness for an Ultrathin Ni(P)-Based Surface Finish in Soldering Applications

The effects of the Ni(P) thickness δNi(P) on the interfacial reaction between an Sn-3Ag-0.5Cu solder and an Au/Pd(P)/Ni(P)/Cu pad (thickness: 0.05/0.05/0.1–0.3/20 μm) and the resulting mechanical properties were investigated using scanning electron microscopy equipped with an electron backscatter diffraction system, a focused ion beam system, electron probe microanalysis, and high-speed ball shear (HSBS) testing. Regardless of δNi(P), all of the Au/Pd(P)/Ni(P) surface finishes examined were completely exhausted in one reflow, exposing the Cu pad underneath the solder. Cu6Sn5 dissolved with various Ni contents, termed (Cu,Ni)6Sn5, was the dominant intermetallic compound (IMC) species at the solder/Cu interface. Additionally, Ni2SnP and Ni3P IMCs might form with the (Cu,Ni)6Sn5 in the thick Ni(P) case, i.e., δNi(P) = 0.3 μm, and the two IMCs (Ni2SnP and Ni3P) were gradually eliminated from the interface after multiple reflows. A mass balance analysis indicated that the growth of the Ni-containing IMCs, rather than the dissolution of the metallization pad, played a key role in the Ni(P) exhaustion. The HSBS test results indicated that the mechanical strength of the solder joints was also δNi(P) dependent. The combined results of the interfacial reaction and the mechanical evaluation provided the optimal δNi(P) value for soldering applications.

Effects of la addition on microstructure and mechanical properties of SN–58BI solders joints with osp pads

Rapid whisker growth was significantly alleviated in a Sn–58Bi alloy doped with 0·5 wt-%La. Experimental results showed that many thin, plate form intermetallic phases appeared in the solder matrix. The absence of tin whiskers was correlated to the shape effect of RE containing intermetallic plates. After reflowing, Cu6Sn5 intermetallic compounds appeared at the solder/pad interfaces of Sn–58Bi and Sn–58Bi–0·5La packages with OSP pads, which grow linearly during the aging at 75 and 100°C for various times ranging from 100 to 1000 h. In addition, the interfacial intermetallics layers in Sn–58Bi–0·5La solder joints were also observed thinner than those in undoped Sn–58Bi joints. However, RE containing interfacial intermetallic compounds in Sn–58Bi–0·5La solder joints led to lower bonding strengths in both ball shear tests (0·4 mm s−1) and high speed ball shear tests (2000 mm s−1). All the reflowed and aged solder joints of both packages were ruptured through the solder balls indicating brittle characteristic.On a réduit significativement la croissance rapide de barbe dans un alliage de Sn–58Bi dopé avec 0·5% en poids de La. Les résultats expérimentaux ont montré que plusieurs phases intermétalliques fines en forme de plaque apparaissaient dans la matrice du métal d’apport. On a corrélé l’absence de barbes d’étain aux effets de la forme des plaques intermétalliques contenant de la terre rare. Après la refusion, les composés intermétalliques de Cu6Sn5 apparaissaient à l’interface du métal d’apport et des pastilles des paquets de Sn–58Bi et de Sn–58Bi–0·5La avec pastilles d’OSP, lesquels s’accroissent linéairement lors du vieillissement à 75 et à 100°C pour des durées variées allant de 100 à 1000 heures. De plus, on a observé que les couches intermétalliques de l’interface dans les joints à brasure tendre de Sn–58Bi–0·5La étaient plus minces que celles des joints non dopés de Sn–58Bi. Cependant, les composés intermétalliques de l’interface contenant de la terre rare dans les joints à brasure tendre de Sn–58Bi–0·5La menaient à des résistances de cohésion plus faibles tant dans les épreuves de cisaillement de bille (0·4 mm s−1) que dans les épreuves de cisaillement de bille à haute vitesse (2000 mm s−1). Tous les joints à brasure tendre avec refusion et vieillissement des deux paquets se fracturaient à travers les billes de soudure, indiquant une caractéristique fragile.

Microstructural and mechanical analysis of Cu and Au interconnect on various bond pads

Effects of High Temperature Storage (HTS) and bonding toward microstructure change of intermetallic compound (IMC) at the wire bonding interface of 3 types of bond pad (Al, AlSiCu and NiPdAu) were presented in this paper. Optical and electron microscope analyses revealed that the IMC growth rate of samples under 175 and 200 °C HTS increased in the order of Al > AlSiCu > NiPdAu. Besides, higher HTS and bonding temperatures also promoted higher IMC thickness. The compositional study showed that higher HTS and bonding temperature developed rapid interdiffusion in bonding interface. In the mechanical ball shear test, a decrease of the shear force of Al and AlSiCu bond pads after 500 h HTS was believed due to poorly developed IMC at bonding interface. On the other hand, shear force degradation at 1000 h was due to excessive growth of IMC that in turn causes the formation of defects. For NiPdAu bond pad, increasing trend of shear force with HTS duration at 175 °C implied a good reliability of the Cu wire bonding. The rapid microscopic inspection on Cu wired Al bond pad under HTS 175 °C showed the IMC development from the periphery to the center of the ball bond. However, after 500 h voids started to develop until the crack was observed at 1000 h.

Effect of graphene doping on microstructural and mechanical properties of Sn–8Zn–3Bi solder joints together with electromigration analysis

Abstract In this study, various weight percentages (0, 0.05 and 0.1 wt.%) of graphene nanosheet doped lead-free Sn–8Zn–3Bi solder alloys were investigated in order to analyze the electromigration induced microstructural development and mechanical properties, such as the shear strength and microhardness, as well as the melting characteristics of the novel composite solders. The effect of electromigration on the solder joint was systematically studied by using a newly developed wire-type testing configuration. The samples were stressed under a current density of 5 × 10 3 A/cm 2 at 100 °C for different aging periods in order to study the electromigration induced reliability issues. For solders with and without the graphene, γ-Cu 5 Zn 8 intermetallic compounds (IMCs) were found at the solder and Cu pad interface. The majority of the added graphene nanosheets were proved to be uniformly distributed in the β-Sn matrix. After the graphene addition, needle-like Zn-rich phases with a finer microstructure were discovered in the solder matrix. The growth rate of the IMC layers of the graphene doped solder was slower in comparison to IMC layers in plain solder at the interfaces. With 0.1 wt.% graphene addition, the measured IMC growth rate was decreased from 30.9 × 10 −14 to 24.9 × 10 −14 cm 2 /s. The melting temperature of the doped solder measured by differential scanning calorimeter (DSC) showed little difference from that of the plain solder. The Vickers hardness, up to 29.9 Hv with 0.1 wt.% graphene addition, is 9.1% higher than that of plain solder. The graphene doped solder consistently demonstrated higher ball shear strength as a function of aging time. The ball shear strength value was increased by 10.2 ± 0.8% than that of plain solders during the whole aging period. The improvement was due to the dispersion-strengthening mechanism, refined microstructure and excellent intrinsic mechanical properties of graphene. Moreover, fracture occurred at the IMC interface of the doped samples showed a ductile fracture pattern with a large distribution of dimples on the rough surface.

Effect of surface treatment on the high-speed drop reliability of Pb-free solder interconnect

This study utilized a solder ball shear test to evaluate the mechanical behavior of Sn–3.0Ag–0.5Cu/Cu and Sn–3.0Ag–0.5Cu/electroless Ni-immersion Au solder joints under high speed loading and hence the drop reliability. The combination of the force–displacement graphs captured from the shear tests and the fracture morphology analysis discloses three fracture modes active in our samples, which include a ductile fracture occurring through the solder (Mode I), a brittle fracture along the interface with intermetallic compound (IMC) layer after some plastic deformation in the solder (Mode II), and a brittle fracture through the IMC layer with almost no plastic deformation (Mode III). Identifying a fracture mode dominant in the samples for different solder joints and shear speeds leads us to conclude that the drop reliability of solder joints is highly related to the morphology of the IMC formed at the interface and the strain rate applied to the joints. These results underscore the utility of the experimental methodology adopted in this study to evaluate the drop reliability of solder joints.

Shear Toughness Evaluation of Solder Joints for the Reliability Tests

The effects of isothermal aging and the thermal cycling loading on the shear toughness of different solder materials and ball sizes have been explored. The difference between shear toughness values of traditional Sn/37Pb eutectic solder ball joints and the lead free Sn/3.0Ag/0.5Cu solders are chosen for discussion. The experiment measurements under the ball shear test (BST) have been compared and studied for both solder joints. The fracture behaviors of the solder joints under the high temperature aging and thermal cycling testing are examined by scanning electron microscope (SEM). The variation of shear toughness of different ball joints reveals that the high temperature aging and thermal cyclic loading reduce the shear toughness significantly. The measured shear toughness values indicate that the Sn/3.0Ag/0.5Cu solder joints have better ductility for the joints undergoing the high temperature aging and the thermal cycle loadings. Based on the measured results, the better reliability for the Sn/3.0Ag/0.5Cu ball joints is expected, due to the aging and cycling load testing.

Reliability of wire-bonded electronic devices in combined high temperature and vibrational environments

High temperature electronic systems need to operate in extreme conditions that exceed the current levels specified by the military and aerospace standards. In high temperature and wide operating temperature applications, electronics can suffer from failure modes caused by a combination of environmental and operational loadings such as temperature, vibration, humidity, pressure, external stresses, etc. This work reports the findings and observations of the investigation of the combined effects of thermal and vibrational environments on wire-bonded interconnections used in high temperature electronic components. The work is focused on combined testing at temperatures up to 250°C and vibration loading with the sine frequency swept cycles ranging from 5Hz to 2000Hz and acceleration up to 20g rms. Analysis is focusing on the wire bond connections which has shown an increasing occurrence of wire deformation at a test temperature of 250°C whilst being subjected to vibration, particularly for wires with large loop shapes. Wire bonded samples have been evaluated through visual inspection, electrical characterization and ball shear tests to identify failure mechanisms.

Effect of Fe content on the interfacial reliability of SnAgCu/Fe-Ni solder joint

Fe-Ni films with compositions of Fe-75Ni, Fe-50Ni, and Fe-30Ni were used as under bump metallization (UBM) to evaluate the interfacial reliability of SnAgCu/Fe-Ni solder joints through ball shear test, high temperature storage, as well as temperature cycling. The shear strength for Fe-75Ni, Fe-50Ni, and Fe-30Ni solder joints after reflow were 42.57, 53.94, 53.98 MPa respectively, which are all satisfied with the requirement of industrialization (&amp;gt;34.3 MPa ). High temperature storage was conducted at 150°C and 200°C respectively. It was found that higher Fe content in Fe-Ni layer had the ability to inhibit the mutual diffusion at interface region at 150°C, and the growth speed of intermetallic compound (IMC) decreased with the increase of Fe concentration. When stored at 200°C, the thickness of IMC would reach a limitation for all these three films after 4 days, and cracks occurred at the interface between IMC and Fe-Ni layer. Temperature cycling tests revealed that SnAgCu/Fe-50Ni solder joint had the lowest failure rate (less than 10%), which has the best interfacial reliability among three compositions.

Sn–Ag–Cu solder reaction with Au/Pd/Ni(P) and Au/Pd(P)/Ni(P) platings

A comparative study between pure Pd and Pd(P) films on the solderability was performed. In the Sn–3Ag–0.5Cu/Au/Pd/Ni(P) system (pure Pd case), (Cu,Ni)6Sn5 and Ni3P were the predominant intermetallic species at the interface after the removal of the Au/Pd dual layer in soldering. We found that a significant growth of (Ni,Cu)3Sn4 occurred between (Cu,Ni)6Sn5 and Ni3P after aging at 180°C for 500h. This phenomenon was not observed in the reference case, in which a Pd(P) film had replaced the pure Pd layer before the reaction. The (Cu,Ni)6Sn5/(Ni,Cu)3Sn4 interface provided a crack initiation site, seriously deteriorating the high-speed ball shear resistance of the solder joints. The retarded growth of (Ni,Cu)3Sn4 in the Pd(P) case was attributed to the presence of an additional Ni2SnP nanolayer between (Cu,Ni)6Sn5 and Ni3P that prevented the outward diffusion of Ni, thereby inhibiting the formation of the undesired (Cu,Ni)6Sn5/(Ni,Cu)3Sn4 structure. The results of this study indicate Pd(P) film is more beneficial to the solderability than pure Pd.

PCB 표면처리에 따른 Sn-1.2Ag-0.7Cu-0.4In 무연솔더 접합부의 기계적 신뢰성에 관한 연구

Ball shear test was performed by test variables such as loading speed and annealing time in order to investigate the effect of surface finishes on the bonding strength of Sn-1.2Ag-0.7Cu-0.4In Pb-free solder. The shear strength increased and the ductility decreased with increasing shear speed. With increasing shear speed, the electroless nickel immersion gold (ENIG) finish showed dominant brittle fracture mode, while organic solderability preservative (OSP) finish showed pad open fracture mode. The shear strength and toughness for both surface finishes decreased with increasing annealing time under the high-speed shear test of 500 mm/s. Typically, the thickness of intermetallic compound increased with increasing annealing time, which means that exposure of brittle fracture became much easier. With increasing annealing time, the both ENIG and OSP finishes exhibited the pad open fracture mode. Overall, ENIG finish showed higher shear strength rather than OSP finish due to its superior barrier stability.

Sn-58Bi 솔더 페이스트와 ENIG 표면 처리된 기판 접합부의 계면 반응 및 접합강도

Sn-Bi eutectic alloy has been widely used as one of the key solder materials for step soldering at low temperature. The Sn-58Bi solder paste containing chloride flux was adopted to compare with that using the chloride-free flux. The paste was applied on the electroless nickel-immersion gold (ENIG) surface finish by stencil printing, and the reflow process was then performed at <TEX>$170^{\circ}C$</TEX> for 10 min. After reflow, the solder joints were aged at <TEX>$125^{\circ}C$</TEX> for 100, 200, 300, 500 and 1000 h in an oven. The interfacial microstructures were obtained by using scanning electron microscopy (SEM), and the composition of intermetallic compounds (IMCs) was analyzed using energy dispersive spectrometer (EDS). Two different IMC layers, consisting of <TEX>$Ni_3Sn_4$</TEX> and relatively very thin Sn-Bi-Ni-Au were formed at the solder/surface finish interface, and their thickness increased with increasing aging time. The wettability of solder joints was investigated by wetting balance test. The mechanical property of each aging solder joint was evaluated by the ball shear test in accordance with JEDEC standard (JESD22-B117A). The results show that the highest shear force was measured when the aging time was 100 h, and the fracture mode changed from ductile fracture to brittle fracture with increasing aging time. On the other hand, the chloride flux in the solder paste did not affect the shear force and fracture mode of the solder joints.