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When the electronics are tested with thermal shock for Pb-free solder joint reliability, there are temperature conditions with use environment but number of cycles for test don't clearly exist. To obtain the long term reliability data, electronic companies have spent the cost and times. Therefore this studies show the test method and number of ther...
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Mounting several chips on one semiconductor package can achieve a high integration density. Therefore, this decreases the solder size, owing to which, several bonding processes are performed when implementing such a package. In this study, Sn-3.0Ag-0.5Cu solder balls with 200, 300, 450, and 600 μm in diameter were mounted on ball grid array substra...
Citations
... The big cavity between the lead and the pad may be caused by the fracture of IMCs. Hong et al. [34] studied the reliability of QFP solder joint soldered with Sn-3.0Ag-0.5 Cu solder under the thermal shock test between 243 K and 398 K. Their research results indicated that the cracks were formed at the interface between the solder and IMC layer after 2000 cycles. In this study, cracks were formed at solder/IMC layer interface only after 250 cycles. ...
The microstructure evolution and growth mechanism of interfacial intermetallic compounds (IMCs) as well as the mechanism for early formation of cracks in Sn-3Ag-0.5Cu solder joints of quad flat packages (QFPs) during extreme temperature thermal shock between 77 K and 423 K were investigated. The Cu-Sn IMC layer at the Cu lead/solder interface and the Ni-Cu-Sn IMC layer at the solder/ENIG pad interface gradually thickened as well as the IMCs morphologies changed during extreme temperature thermal shock. Scallop-like Cu-Sn IMC layer and needle-like Ni-Cu-Sn IMC layer both transformed to plane-like IMCs. New Cu3Sn phase was formed at the interface between Cu lead and Cu6Sn5 IMC layer after 250 cycles. The (Ni, Cu)3Sn4 IMC layer was completely converted into (Cu, Ni)6Sn5 IMC layer after 150 cycles resulting from the diffusion of Cu atoms from Cu lead and Sn-3Ag-0.5Cu solder to the solder/pad interface. The time exponent (n) values of Cu-Sn and Ni-Cu-Sn IMC layers were 0.66 and 0.34, respectively, indicating that the controlling mechanisms for Cu-Sn and Ni-Cu-Sn IMC growth were bulk diffusion and grain-boundary diffusion, respectively. Cracks were formed both at the solder/Cu-Sn layer interface and at the solder/Ni-Cu-Sn layer interface after 250 cycles, due to the CTE difference between the solder and IMC, and to the thickened and flattened IMC layer. The great stress concentration resulting from the large temperature variation (∆T=346 K) led to the early formation of cracks. With the increase of thermal shock cycles, the pull strength of Sn-3Ag-0.5Cu solder joints decreased and the fracture location changed from within the solder to partly in Cu-Sn IMC layer and partly along the solder/Ni-Cu-Sn layer interface, which indicated that the fracture mechanism transformed from ductile fracture mode to brittle fracture mode.
In this study, the laser soldering process of probe-multilayer ceramic (MLC) substrates was optimized using Type 4 (T4) and Type 7 (T7) Sn-3.0Ag-0.5Cu (SAC305), T7 Sn-0.7Cu solders to improve the high-temperature durability of probe solder joints and satisfy the fine pitch requirements of the soldering process. Thermal cycle tests (TCTs) were performed to compare the heat resistance characteristics of the probe solder joint. The results showed that the bonding strength degradation rates of the SAC305 and Sn-0.7Cu solders after the TCT were within 40% compared to that of the as-soldered state. Because the probe surface and MLC were plated with Ni/Au, various intermetallic compounds (IMCs) were observed at the solder joint. The total IMC thickness of the T7 solder joint was thinner than that of the T4 solder because of the difference in redox reactions according to the particle size of the solder paste. The fracture surface of the probe-MLC solder joint after the shear strength test exhibited a mixed ductile and brittle fracture, and that of the Sn-0.7Cu solder joint exhibited a ductile fracture with numerous dimples.
To confirm the possibility of simultaneous bonding between Si chip and multilayer ceramic capacitors (MLCCs), vacuum reflow soldering is performed between a Si chip and each of 2012, 1608, 1005, 0603, and 0402 MLCCs using Type-7 Sn-3.0Ag-0.5Cu (SAC305) and Sn-0.7Cu solder pastes. To enable an unbiased comparison with the vacuum reflow process, the Si chip and MLCCs are bonded via thermo-compression (TC) bonding and hot air reflow soldering, respectively. The maximum void content of Si chip solder joints bonded via vacuum reflow is 8%. At the MLCC solder joints, the void content yielded by vacuum reflow is lower than that yielded by hot air reflow. The bonding strength of the MLCC solder joint afforded by vacuum reflow is higher than that afforded by hot air reflow. Vacuum reflow is superior to hot air reflow in terms of the void content and bonding strength of the MLCC solder joint. After performing a thermal cycle test (TCT), a crack appeared at the Si chip solder joint bonded by TC bonding. The Cu pillar/Sn-2.5Ag bump is susceptible to cracks after the TCT owing to the insufficient bonding layer thickness yielded; however, the SAC305 sample from vacuum reflow is stable. Meanwhile, (Cu,Ni)6Sn5, Ni3P, and Ag3Sn intermetallic compounds are formed at the MLCC solder joints and then further developed after the TCT. The results of this study indicate the possibility of co-bonding Si chip with MLCCs for semiconductor packaging.
This research investigated the effects of rapid thermal shock cycle on the internal cracks, microstructure and internal cracks of SAC305 ball by applying non-destructive high energy-X-ray diffraction measurements. The experimental results firstly indicated that the surface cracks of the solder ball widen and deepen as the increase of the rapid thermal shock cycles. Secondly, the microstructure of SAC305 ball was observed that the grain orientation of the solder ball tends to be consistent, and the grains are gradually refined due to the recrystallization of the solder ball after rapid thermal shock. From the perspective of internal cracks, the total volume and surface area of internal cracks in the solder ball increase at first and then decrease as the growth of thermal shock cycles, as well as the volume and surface area of the largest internal crack. But the internal cracks are repaired by the atomic diffusion and recrystallization after 4500 cycles. Another important factor observed is that the occurrence of internal cracks is related to the grain orientation inside the solder ball. The spreading of internal cracks of the solder ball is confirmed along the grain boundary.
In this study, the laser soldering process of microelectromechanical system (MEMS) probes and multilayer ceramic (MLC) substrates was optimized with Type 4 (T4) and Type 7 (T7) Sn-3.0Ag-0.5Cu (SAC305), Type 4 Sn-0.3Ag-0.7Cu (SAC0307), and Type 4 Sn-5.0Sb (SnSb) soldering, and the probe solder joint properties were compared. SAC0307 and SnSb were used to confirm the bonding property of the low-Ag solder and the high-temperature durability. We conducted a thermal cycling test (TCT) with 500 cycles at temperatures of -25 ℃ to 105 ℃ with a 10-min dwell time at each temperature. Before and after the TCT, the microstructure of solder joint as well as the shear strength between the probe and the MLC were examined. The results revealed that, after the TCT, the degradation rate of T7 SAC305 solder was lower than that of T4 SAC305, and the SnSb solder did not exhibit bonding strength degradation. The fracture mode of the SAC solder joint was ductile-brittle. In the case of the SnSb joint, brittle fracture was the major fracture mode because of the Sn-Sb intermetallic compounds. The SnSb solder had an excellent bonding strength and degradation property after the TCT, but the lack of toughness caused brittle fracture. These results confirm the applicability of T4 SnSb and T7 SAC305 solders for high-temperature response and fine pitch bonding.
After the joining of small 1005 and 0603 multilayer ceramic capacitor (MLCC) components for a semiconductor package using Type 4 (T4) and Type 7 (T7) Sn-3.0Ag-0.5Cu (SAC305), T4 Sn-1.0Ag-0.5Cu (SAC105), and T4 Sn-0.3Ag-0.7Cu (SAC0307) solder pastes, the differences between hot air reflow and vacuum soldering processes were compared in terms of void content, shear strength, and microstructure. Results showed that the hot air reflow soldering process exhibited a stable joint with a void content of 5% or less, and the vacuum soldering condition significantly reduced the void content of the solder joint as the soldering proceeded in a vacuum state. The shear strength of the SAC305 solder joint with the same powder particle size was measured to be greater for the shear strength of the vacuum soldered joint as compared to the reflow process. The vacuum soldering process was effective in removing voids during the void joining process and contributed to an improved joint strength of the solder joint by reducing the void content. When the same soldering process was applied using the 1005 MLCC chip component, the bonding strength of the T4 SAC305 solder was slightly higher than those of the SAC105 and SAC0307 solders. However, the overall initial bonding strengths were similar. The e ffects of Ag content within 0.3-3.0 wt% on the initial bonding strengths of the solders were judged to be the same. Diverse Cu6Sn5, Ag3Sn, (Ni,Cu,Pd)3Sn4, (Cu,Ni)6Sn5, NiP, and Ni3P intermetalli ccompounds (IMCs) were formed at the interfaces between the electroless nickel/electroless palladium/immersion gold finish substrate and SAC solder joint. The IMC types were constant regardless of Ag content and solder type, and the IMCs contributed to the initial solder joint strength.
To suppress the bonding strength degradation of solder joints in automotive electronics, we proposed a mid-temperature quaternary Pb-free Sn-0.5Cu solder alloy with minor Pd, Al, Si and Ge alloying elements. We manufactured powders and solder pastes of Sn-0.5Cu-(0.01,0.03)Al-0.005Si-(0.006–0.007)Ge alloys (Tm = 230°C), and vehicle electronic control units used for a flame-retardant-4 printed circuit board with an organic solderability preservative finish were assembled by a reflow soldering process. To investigate the degradation properties of solder joints used in engine compartments, thermal cycling tests were conducted from −40°C to 125°C (10 min dwell) for 1500 cycles. We also measured the shear strength of the solder joints in various components and observed the microstructural evolution of the solder joints. Based on these results, intermetallic compound (IMC) growth at the solder joints was suppressed by minor Pd, Al and Si additions to the Sn-0.5Cu alloy. After 1500 thermal cycles, IMC layers thicknesses for 100 parts per million (ppm) and 300 ppm Al alloy additions were 6.7 μm and 10 μm, compared to the as-reflowed bonding thicknesses of 6 μm and 7 μm, respectively. Furthermore, shear strength degradation rates for 100 ppm and 300 ppm Al(Si) alloy additions were at least 19.5%–26.2%. The cause of the improvement in thermal cycling reliability was analyzed using the (Al,Cu)-Sn, Si-Sn and Al-Sn phases dispersed around the Cu6Sn5 intermetallic at the solder matrix and bonding interfaces. From these results, we propose the possibility of a mid-temperature Sn-0.5Cu(Pd)-Al(Si)-Ge Pb-free solder for automotive engine compartment electronics.
Many researches related to the reliability of Pb-free solder joints with PCB (printed circuit board) surface finish under thermal or vibration stresses are in progress, because the electronics is operating in hash environment. Therefore, it is necessary to assess Pb-free solder joints life with PCB surface finish under thermal and mechanical stresses. We have investigated 4-points bending fatigue lifetime of Pb-free solder joints with OSP (organic solderability preservative) and ENIG (electroless nickel and immersion gold) surface finish. To predict the bending fatigue life of Sn-3.0Ag-0.5Cu solder joints, we use the test coupons mounted 192 BGA (ball grid array) package to be added the thermal stress by conducting thermal shock test, 500, 1,000, 1,500 and 2,000 cycles, respectively. An 4-point bending test is performed in force controlling mode. It is considered that as a failure when the resistance of daisy-chain circuit of test coupons reaches more than 1,000 Q Finally, we obtained the solder joints fatigue life with OSP and ENIG surface finish using by Weibull probability distribution.
The long-term reliability of Sn-0.3wt%Ag-0.7wt%Cu solder joints was evaluated and compared with Sn-3.0wt%Ag-0.5wt%Cu under thermal shock conditions. Test vehicles were prepared to use Sn-0.3Ag0.7Cu and Sn-3.0Ag-0.5Cu solder alloys. To compare the shear strength of the solder joints, 0603, 1005, 1608, 2012, 3216 and 4232 multi-layer ceramic chip capacitors were used. A reflow soldering process was utilized in the preparation of the test vehicles involving a FR-4 material-based printed circuit board (PCB). To compare the shear strength degradation following the thermal shock cycles, a thermal shock test was conducted up to 2,000 cycles at temperatures ranging from -40°C to 85°C, with a dwell time of 30 min at each temperature. The shear strength of the solder joints of the chip capacitors was measured at every 500 cycles in each case. The intermetallic compounds (IMCs) of the solder joint interfaces werealso analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The results showed that the reliability of Sn-0.3Ag-0.7Cu solder joints was very close to that of Sn-3.0Ag-0.5Cu Consequently, it was confirmed that Sn-0.3Ag-0.7Cu solder alloy with a low silver content can be replaced with Sn-3.0Ag-0.5Cu.
Due to ELV banning, automotive electronics cannot use four kinds of heavy metal element (Pb, Hg, Cd, Cr^{6 }) from 2016. Therefore, this study was focused on degradation characteristics of Sn-3.0Ag-0.5Cu Lead-free solder joint with OSP and ENIG finsh under various reliability assessment method, as like to thermal shock test and high temeprature/high humidity test with test duration for cabin electronics. Also, we compared bonding strength degradation to other advanced research results of electronic control unit for engine room because of difference service temperature with mount location in automotive. Whisker growth phenomenon and mitigation method which were essentially consideration items for Pb-free car electronics were examined. Conformal coating is a strong candidate for mitigating whisker growth in automotive electronics. Necessary condition to adapt Pb-free in car electronics was shown.
