Liquidus Temperature Of Solder Research Articles

Effect of the reflow process on IMC growth for different devices and complex components

Intermetallic compound (IMC), as an inevitable part between pad and solder, has a severe effect on the strength and reliability of microelectronic interconnection. Here, an investigation was carried out on IMC growth for different devices and complex components. The device-level experiments were conducted with five factors: peak temperature, time duration above solder liquidus temperature, the thickness of solder paste, surface finish types, and package types including ball grid array (BGA) and quad flat package (QFP). Meanwhile, four complex components with the same reflow profile were conducted and compared for component-level experiments. A scanning electron microscopy (SEM) was used to measure the thickness and determine the spatial distribution of the elements through the IMC. The multivariate analysis of the formation and growth of IMC during reflow soldering was studied based on Nernst–Shchukarev’s equation and the results of the experiments. The difference in IMC thickness between BGA and QFP with different factors was discussed and compared separately. The results showed that the peak temperature and time above liquidus played a vital role in the IMC growth and the solder paste thickness and different pad metallization could not be ignored. SEM pictures of the solder and statistical results were revealed that the surface finish type has a marked impact on the formation of the IMC. For printed circuit board (PCB) with numbers of components, the IMC thickness and uniformity of solder joints at corner and center positions showed some regularity differences. Meanwhile, the bump shape (Cu1−x Ni x )6Sn5 IMC was observed for small size BGA with electroless nickel and immersion gold during the reflow process. The results have a significant meaning to optimize its reflow process parameters for complex components, to improve the interconnection reliability in engineering.

Selection of soldering temperature for ultrasonic-assisted soldering of 5056 aluminum alloy using Zn–Al system solders

The conditions for sound butt-joints of 5056 aluminum alloy containing 4.6 mass% Mg using Zn– xAl ( x = 5, 13, and 38 mass%) solder at the relevant temperatures were investigated. Each solder foil was inserted between faying surfaces of 5056 aluminum rods. Ultrasonic vibration at a frequency of 19 kHz was applied to the faying surfaces through an aluminum substrate at soldering temperatures for 4 s in air. The strength of obtained solder joints was measured by tensile tests. The microstructure in the solder layer after the soldering process was evaluated with an SEM-EDX. The results of tensile tests revealed that joints soldered under the liquidus temperature of Zn–Al solders showed higher strength than joints soldered over the liquidus temperature. In the joints soldered over the solder liquidus temperature, the joint strength decreased with an increase in soldering temperature. It was caused by the formation of MgZn 2 in the solder layer due to dissolution of 5056-Al into the solder liquid during the soldering process. On the other hand, ultrasonic-assisted soldering under the solder liquidus temperature suppressed dissolution of 5056-Al and improved the joint strength by reducing the formation of MgZn 2.

Effects of reflow profile and thermal conditioning on intermetallic compound thickness for SnAgCu soldered joints

PurposeThe purpose of this paper is to investigate the effects of reflow time, reflow peak temperature, thermal shock and thermal aging on the intermetallic compound (IMC) thickness for Sn3.0Ag0.5Cu (SAC305) soldered joints.Design/methodology/approachA four‐factor factorial design with three replications is selected in the experiment. The input variables are the peak temperature, the duration of time above solder liquidus temperature (TAL), solder alloy and thermal shock. The peak temperature has three levels, 12, 22 and 32°C above solder liquidus temperatures (or 230, 240 and 250°C for SAC305 and 195, 205, and 215°C for SnPb). The TAL has two levels, 30 and 90 s. The thermally shocked test vehicles are subjected to air‐to‐air thermal shock conditioning from −40 to 125°C with 30 min dwell times (or 1 h/cycle) for 500 cycles. Samples both from the initial time zero and after thermal shock are cross‐sectioned. The IMC thickness is measured using scanning electron microscopy. Statistical analyses are conducted to compare the difference in IMC thickness growth between SAC305 solder joints and SnPb solder joints, and the difference in IMC thickness growth between after thermal shock and after thermal aging.FindingsThe IMC thickness increases with higher reflow peak temperature and longer time above liquidus. The IMC layer of SAC305 soldered joints is statistically significantly thicker than that of SnPb soldered joints when reflowed at comparable peak temperatures above liquidus and the same time above liquidus. Thermal conditioning leads to a smoother and thicker IMC layer. Thermal shock contributes to IMC growth merely through high‐temperature conditioning. The IMC thickness increases in SAC305 soldered joints after thermal shock or thermal aging are generally in agreement with prediction models such as that proposed by Hwang.Research limitations/implicationsIt is still unknown which thickness of IMC layer could result in damage to the solder.Practical implicationsThe IMC thickness of all samples is below 3 μm for both SnPb and SAC305 solder joints reflowed at the peak temperature ranging from 12 to 32°C above liquidus temperature and at times above liquidus ranging from 30 to 90 s. The IMC thickness is below 4 μm after subjecting to air‐to‐air thermal shock from −40 to 125°C with 30 min dwell time for 500 cycles or thermal aging at 125°C for 250 h.Originality/valueThe paper reports experimental results of IMC thickness at different thermal conditions. The application is useful for understanding the thickness growth of the IMC layer at various thermal conditions.

Investigation of the Lead-free Solder Joint Shear Performance

Reflow profile has significant impact on solder joint performance because it influences wetting and microstructure of the solder joint. The purpose of this study is to investigate the effects of reflow profile and thermal shock on the shear performance of eutectic SnPb (SnPb) and Sn3.0Ag0.5Cu (SAC305) solder joints. Test boards were assembled with four different sized surface mount chip resistors (1206, 0805, 0603 and 0402). Nine reflow profiles for SAC 305 and nine reflow profiles for SnPb were developed with three levels of peak temperature (12°C, 22°C, and 32°C above solder liquidus temperature, or 230°C, 240°C, and 250°C for SAC 305; and 195°C, 205°C, and 215°C for SnPb) and three levels of time above solder liquidus temperature (30 sec., 60 sec., and 90 sec.). Half of the test vehicles were then subjected to air-to-air thermal shock conditioning from −40 to 125°C. The shear force data were analyzed using the Analysis of Variance (ANOVA). The fracture surfaces were studied using a Scanning Electron Microscopy (SEM) with Energy Dispersive Spectroscopy (EDS). It was found that thermal shock degraded both SnPb and SnAgCu joints shear strength, and that the effect of thermal shock on solder joint shear strength is much more significant than that of reflow profile. The SnAgCu solder joints have weaker shear strength than the SnPb solders. The SnAgCu solder joint after thermal shock retains more of its shear strength than that of SnPb for small components and vice versa for larger components.

The effect of reflow profile on SnPb and SnAgCu solder joint shear strength

Purpose – The purpose of this work is to study the effect of the reflow peak temperature and time above liquidus on both SnPb and SnAgCu solder joint shear strength.Design/methodology/approach – Nine reflow profiles for Sn3.0Ag0.5Cu and nine reflow profiles for Sn37Pb have been developed with three levels of peak temperature (230°C, 240°C, and 250°C for Sn3.0Ag0.5Cu; and 195°C, 205°C, and 215°C for Sn37Pb) and three levels of time above solder liquidus temperature (30, 60, and 90 s). The shear force data of four different sizes of chip resistors (1206, 0805, 0603, and 0402) are compared across the different profiles. The shear forces for the resistors were measured after assembly. The fracture interfaces were inspected using scanning electron microscopy with energy dispersive spectroscopy in order to determine the failure mode and failure surface morphology.Findings – The results show that the effects of the peak temperature and the time above solder liquidus temperature are not consistent between differe...

Ｓｎ‐Ａｇ‐Ｂｉ‐Ｃｕ系無鉛はんだの引け巣と合金組成

Correlation between composition and shrinkage cavity of Sn-Ag-Bi-Cu lead-free solder alloys was investigated. Incidence of surface cracks on solder fillets, caused by shrinkage cavity, was significantly influenced by Ag content of solder alloys (1.0-2.5wt%) ; for solder fillets with less than 2.0wt% of Ag content, surface cracks decreased in accordance with a reduction in Ag content. On the other hand, incidence of surface cracks was independent of Bi content of solder alloys (0-4.0wt%) . Compositional mapping analysis with EDX revealed that less Ag3Sn phases were formed for solder fillets with less Ag content, suggesting that the formation of the Ag3Sn/Sn eutectic network band triggers the formation of surface cracks, i.e., shrinkage cavity. Wettability of solder alloys with various Ag contents was also investigated. It was clarified that a decrease in Ag content leaded to degradation of solder wettability, indicating an increase in liquidus temperature of solder.