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Procedure for assembling a single BGA structure solder joint by planting solder ball and reflow soldering
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The shear performance and fracture behavior of micro-scale ball grid array (BGA) structure Cu/Sn–3.0Ag–0.5Cu/Cu joints under coupled electromechanical loads with the increasing current density (from 6 × 10³ to 1.1 × 10⁴ A/cm²) were investigated systematically. Severe Joule heating and current crowding effects on actual temperature, shear strength,...
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In this study, the shear performance and fracture behavior of microscale ball grid array (BGA) structure Cu/Sn–3.0Ag–0.5Cu/Cu joints with same solder volume and different heights at increasing current density were systematically investigated by experimental characterization, theoretical analysis, and finite element simulation. The results showed th...
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... As the current density increased, the fracture position shifted from the solder matrix to the solder/IMC interface with a ductile-to-brittle fracture mode transition. The interfacial fracture occurred near either the cathode side or the anode side, which was J Mater Sci different from the fracture preference at the cathode side of the solder joint after longtime electric current stressing [102]. However, an abnormal shear mechanical behavior appears in the Cu/Sn-3.0Ag-0.5Cu/Cu ...
... solder joints under current stressing coupled loads. Reproduced with permission from[102]. Copyright 2019, Springer Nature. ...
Mechanical performance is one of the most important factors influencing the reliability of solder joints. Heretofore, plenty of works have been conducted on reliability of solder joints under various mechanical loads. However, with the miniaturization of electronic products, the current density flowing through the solder joints is increasing. Electric current stressing can induce microstructure evolution, and mechanical performance of solder joints may be altered consequently, which leads to electric current stressing becoming an important factor affecting the mechanical reliability of solder joints. Therefore, this review focuses on summarizing the influence of electric current stressing on the mechanical performance, which involves tensile, shear, creep, fatigue and thermal cycling, shock, vibration and nano-indentation performances, of solder and solder joints. Moreover, the mechanical performance of solders and solder joints can be tested after and concurrent with electric current stressing. Although the mechanical test of solders and solder joints with electric current stressing is more valuable for assessing the serving reliability of solder joints, the mechanical test of solders and solder joints after electric current stressing can be inspiring and enlightening for clarifying the failure mechanism of solder joints in the former condition. Therefore, they will be elaborated separately and sequentially in this review. Furthermore, the remained key issues and possible research directions on the current topic are also pointed out.
Graphical abstract
... Therefore, numerous investigations have been conducted on the creep [17][18][19], thermal fatigue [20][21][22], and tensile [23][24][25] behaviors of solder joints under current stressing, while the shear behavior of solder joints under current stressing has received less attention. A recent study reported that the shear strength of dual-interface ball grid array (BGA) Cu/SAC305/Cu solder joints decreases as the current density increases from 6.0 × 10 3 to 1.1 × 10 4 A/cm 2 , and the fracture location changes from the solder matrix to the interface between the solder matrix and IMC layer (the solder/IMC layer interface) [26]. Owing to the excessively high current density, severe Joule heat is generated in the solder joints, which causes the athermal effect of current stressing being easily concealed and ignored in the analysis. ...
... As the simulation and measurement results of temperature in solder joints under current stressing are quite close (see Figure 5), the influence of Joule heating on the shear strength of solder joints can be estimated through the influence of the TJoule on shear strength. The TJoule in the BGA structure solder [26] joints can be expressed as: ...
... As the simulation and measurement results of temperature in solder joints under current stressing are quite close (see Figure 5), the influence of Joule heating on the shear strength of solder joints can be estimated through the influence of the T Joule on shear strength. The T Joule in the BGA structure solder [26] joints can be expressed as: ...
The shear performance and fracture behavior of microscale ball grid array structure Cu/Sn–3.0Ag–0.5Cu/Cu solder joints with increasing electric current density (from 1.0 × 103 to 6.0 × 103 A/cm2) at various test temperatures (25 °C, 55 °C, 85 °C, 115 °C, 145 °C, and 175 °C) were investigated systematically. Shear strength increases initially, then decreases with increasing current density at a test temperature of no more than 85 °C; the enhancement effect of current stressing on shear strength decreases and finally diminishes with increasing test temperatures. These changes are mainly due to the counteraction of the athermal effect of current stressing and Joule heating. After decoupling and quantifying the contribution of the athermal effect to the shear strength of solder joints, the results show that the influence of the athermal effect presents a transition from an enhancement state to a deterioration state with increasing current density, and the critical current density for the transition decreases with increasing test temperatures. Joule heating is always in a deterioration state on the shear strength of solder joints, which gradually becomes the dominant factor with increasing test temperatures and current density. In addition, the fracture location changes from the solder matrix to the interface between the solder matrix and the intermetallic compound (IMC) layer (the solder/IMC layer interface) with increasing current density, showing a ductile-to-brittle transition. The interfacial fracture is triggered by current crowding at the groove of the IMC layer and driven by mismatch strain at the solder/IMC layer interface, and the critical current density for the occurrence of interfacial fracture decreases with increasing test temperatures.
... Dimensi ketinggian bahan pateri menyusut selepas proses pematerian kerana proses metalurgi pematerian yang melibatkan peleburan bahan pateri bagi pembentukan sambungan pateri pada substrat (Le et al. 2019;Qin et al. 2015;Xu, Liu & Sun 2019). Rajah 1 menunjukkan illustrasi perubahan dimensi ketinggian bahan pateri sebelum dan proses pematerian. ...
Aloi pateri bebas plumbum telah digunakan secara meluas sebagai bahan antarasambungan bagi peranti elektronik yang memberikan sambungan elektrik bagi kebolehfungsian dan sokongan mekanik bagi integriti struktur. Rawatan termomekanik merupakan proses metalurgi yang melibatkan gabungan rawatan terma dan pembebanan mekanik. Kajian ini bertujuan untuk mengkaji kesan rawatan termomekanik dengan mampatan tunggal ke atas perubahan mikrostruktur dan sifat mikromekanik aloi pateri Sn-0.7Cu. Aloi pateri Sn-0.7Cu berbentuk bar dipotong kepada lapan sampel berbentuk kiub dengan ukuran 6 mm (p) × 6 mm (l) × 10 mm (t). Empat sampel yang pertama menjalani rawatan haba pada suhu 30 ℃, 60 ℃, 90 ℃ dan 120 ℃ selama 20 minit, diikuti dengan proses mampatan tunggal sebanyak 20% dan pelindapan di dalam medium air. Empat sampel yang berikutnya hanya didedahkan pada rawatan haba sahaja, diikuti pelindapan di dalam medium air digunakan sebagai sampel kawalan. Cerapan mikrostruktur menunjukkan butiran yang kecil dan seragam aloi pateri Sn-0.7Cu terbentuk dengan rawatan termomekanik mampatan tunggal pada suhu 120 °C akibat daripada penghabluran semula butiran. Keputusan kekerasan bagi aloi pateri Sn-0.7Cu selepas rawatan termomekanik mampatan tunggal pada suhu 120 °C telah menunjukkan perubahan yang sedikit iaitu sebanyak 19% berbanding sampel rawatan haba sebanyak 64%. Keputusan modulus terkurang juga menunjukkan tren yang sama iaitu perubahan yang lebih rendah bagi sampel dengan rawatan termomekanik mampatan tunggal pada suhu 120 °C sebanyak 52% manakala sampel rawatan haba sebanyak 69%. Penemuan kajian ini menunjukkan bahawa kesan suhu dalam rawatan termomekanik mampatan tunggal berupaya untuk mengubah suai mikrostruktur dan memberikan kestabilan sifat mikromekanik aloi pateri Sn-0.7Cu berbanding dengan rawatan haba.
... Several major Sn-based binary solders alloys were reported in the relevant investigations, such as Sn-Zn [12,13], Sn-Cu [14][15][16], Sn-Ag [17] and Sn-Bi [3,[18][19][20] etc. To enhance the combination properties of lead-free solder alloys further, the ternary or multi-elements solder alloys are designed by alloy element additions and the Sn-Ag-Cu ternary leadfree solder alloys have been considered as the best choice of substituting the conventional Sn-Pb solder alloys [21][22][23]. The main difficulty in the development of lead-free solder alloys is to obtain the optimal combination of wettability, mechanical performance, electrical characteristic, corrosion resistance, cost etc [9]. ...
Sn-based lead-free solder alloys have been investigated widely to replace the traditional Sn–Pb solder alloys. Since the miniaturization of electronic products and the expansion of application field, the corrosion resistance of solder alloys play a key factor in the reliability of electronic products in long-term service. In this article, we review the recent progress on the corrosion behavior of Sn-based lead-free solder alloys by summarizing the results in representative ones of Sn–Bi, Sn–Cu, Sn–Zn, Sn–Ag, Sn–Ag–Cu and other multi-elements lead-free solder alloys. Specifically, the relationship between microstructure morphology and corrosion behavior, the corrosion mechanism of Sn-based lead-free solder alloys after incorporation of alloy elements or particles are summarized. It is hoped that this overview will provide some useful information in clarifying the corrosion mechanism and development of lead-free solder alloys. Furthermore, remaining difficulties and future trends in this research field are proposed.
In this study, the shear performance and fracture behavior of microscale ball grid array (BGA) structure Cu/Sn–3.0Ag–0.5Cu/Cu joints with same solder volume and different heights at increasing current density were systematically investigated by experimental characterization, theoretical analysis, and finite element simulation. The results showed that the shear strength of the solder joint decreased with increasing current density, while it increased with decreasing joint height. These changes were mainly due to Joule heating, the non-thermal effect of current stressing, and mechanical constraint in the solder joint. As current density increased, both Joule heating and the non-thermal effect of current stressing aggravated solder joint shear strength more and more severely. At the same current density, Joule heating’s deterioration on the shear strength was less serious in the smaller height joint, and the non-thermal effect was insensitive to the change in joint height. The higher shear strength of the smaller height joint was due to the larger mechanical constraint in the solder matrix induced by the substrate. Moreover, as current density increased, the fracture position changed from the solder matrix to the solder/IMC layer interface. The fracture mode shifted from ductile one to ductile–brittle-mixed one, and the critical current density corresponding to the fracture mode transition increased with decreasing joint height. The above findings indicate that the BGA structure solder joint with a smaller joint height is more reliable.
Sn-Ag-Cu system lead-free solders are considered to be promising solder series. The growth of Sn whiskers on the solder surface is an important factor that threatens the reliability of electronic products. In this study, the IMC evolution and whiskers growth of Sn-0.3Ag-0.7Cu (SAC0307) microsolder joints under thermal-mechanical-electrical coupling were investigated by the combination of molecular dynamics simulation and experimental methods. The simulation and experimental results revealed that the electric field intensity had the greatest influence on the atomic diffusion. When the electric field intensity was 0.004 V/Å, the diffusion speed of copper atom to solder reached the maximum, and the intermetallic compounds Cu6Sn5 and Cu3Sn were formed at the interface, which provided the long-term driving force for the growth of tin whiskers at the weak oxide film on the surface. Tin whiskers were inclined to grow at the anode, while holes and cracks were tend to produce at the cathode. When the external pressure stress was 0.03 nN, most of tin atoms were precipitated. When the temperature was 393 K, the whiskers slowly grew to 3.3 μm in length at the growth rate of 0.0182 Å/s. The results can provide the basis for the growth mechanism of tin whisker in real service situations.
With the development of electronic products toward high density and high reliability, the size of interconnect solder joints and interconnect pitch continues to decrease. Under normal service conditions, solder joints are subjected to thermal–electric–mechanical loads simultaneously, resulting in reliability problems for many package structures. This article investigated the effects of interconnect shape and thermal-electro-migration on solder creep of copper-pillar flip chip joints and analyzed the corresponding failure modes and mechanisms. In this article, solder joints with different shapes were obtained by adjusting the thermal compression bonding process parameters, and creep experiments were performed on the solder joints under different temperature and stress conditions. In addition, we have performed thermoelectric coupling experiments and finite element simulations for different shapes of solder joints. Moreover, creep experiments were conducted on three types of solder joints after 10 and 40 h of thermoelectric coupling pretreatment. The results show that the three solder joints exhibit typical creep characteristics under different experimental conditions and the creep strain rate increases with the increase of shear stress and temperature. Under the same conditions, the creep strain rate of the hourglass-shaped solder joint is always higher than that of the other two solder joints. The electromigration reliability of the hourglass-shaped solder joint is the worst, and the electromigration reliability of the cylinder-shaped solder joint is the best. With the increase of thermoelectric coupling pretreatment time, the creep strain rate of solder joints increased significantly, and the fracture mode of solder joints gradually changed from ductile fracture to brittle fracture. Among the three types of solder joints, the creep resistance of the hourglass-shaped solder joints is greatly affected by the thermoelectric coupling pretreatment.
Joint size effects on interfacial intermetallic compound (IMC) morphology, shear performance, and fracture behavior of micro-scale ball grid array (BGA) structure Cu/Sn–3.0Ag–0.5Cu/Cu (Cu/SAC305/Cu) joints under coupled electromechanical loads are investigated systemically by combined experimental characterization, theoretical analysis, and finite element simulation. Results show that the decreasing joint size (standoff height) brings about increase in grain size of interfacial Cu6Sn5 grains and change in morphology of the grains from rod-like to scallop-like. Decreasing standoff height also leads to an initial increase and then a decrease in shear strength of joints subjected to coupled electromechanical loads, and imposing electric current stressing on shear stress causes a significant decrease in shear strength of the joints. Current crowding appears at the interfaces near the electron entry and exit corners of the joints, and the localized maximum current density in large joints with rough solder/IMC interface is higher than that of small joints. There is a distinct size effect on fracture mode and facture path of BGA joints under coupled electromechanical loads. For large joints, the crack initiates and propagates simultaneously at the interfaces on both cathode and anode sides, and fracture is more likely to take place by a brittle mode mainly along the solder/IMC interface on both sides; while for small joints, the crack preferentially initiates and propagates at the interface on the cathode side, leading to final fracture occurring mainly on the cathode side and partially on the anode side. This study provides a better understanding on the shear performance and fracture behavior as well as the underlying mechanism of BGA solder joints with different sizes, thereby being highly significant for reliability assessment and lifetime prediction of BGA packages.
