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Surface-mount technology
Published in Andrea Chen, Randy Hsiao-Yu Lo, Semiconductor Packaging, 2016
Andrea Chen, Randy Hsiao-Yu Lo
In addition, changes extend beyond the package, to the circuit board. As printed circuit boards must also meet the new criteria, they have undergone changes of their own, from new, nonoxidizing finishes on the land pads instead of eutectic lead-tin solder plating to changes in the composition and appearance of the solder mask to the type and composition of the laminate material. As one example, green has been a popular color for solder masks, but it turns out that to achieve that color, the use of materials with unacceptable levels of halogens, especially chlorine, is often required. Another is the various options of finishes and coatings to prevent oxidation of lands, whether an organic solderability preservative (OSP) or using the combination of electroless nickel plating followed by immersion abbreviated as ENIG.
Effect of isothermal ageing on the microstructure, shear behaviour and hardness of the Sn58Bi/SnAgCuBiNi/Cu solder joints
Published in Welding International, 2021
Jian Chang, Yang Liu, Hao Zhang, Min Zhou, Xue Yuxiong, Xianghua Zeng, Rongxing Cao, Penghui Chen
Improving the surface finish of the substrate is another effective method to improve the performance of SnBi solder joints. Common substrate surface finish treatment methods include organic solderability preservative (OSP) [11], electroless nickel immersion gold (ENIG) [12] and electroless nickel immersion palladium gold (ENEPIG) [13]. Zhang et al. [14] found that adding Ni element to the surface of the Cu substrate can refined the IMC grain and improved the shear strength of the solder joints. Hu et al. [15] and Zou et al. [16] added trace amounts of Ag, Al, Sn or Zn elements into Cu substrate and found that the interfacial Bi embrittlement in the SnBi/Cu solder joint was restrained. Meanwhile, the void at the interface was eliminated. The SAC solder coated with a thickness of about 5 μm was obtained on the Cu pad using hot air solder levelling (HASL) by Wang et al. [17]. The study found that the SAC coating helped to inhibit the growth of the IMC layer at the interface of the SnBi/Cu solder joint during soldering and isothermal ageing and improved the shear strength and ductility of the SnBi/Cu solder joint.