Study of immersion silver and tin printed-circuit-board surface finishes in lead-free solder applications
Study of immersion silver and tin printed-circuit-board surface finishes in lead-free solder applications
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DOI：
10.1007/s11664-004-0025-x
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发表时间：
2004-09-01
影响因子：
2.1
通讯作者：
Ristolainen, E
中科院分区：
文献类型：
--
作者：
Arra, M;Shangguan, D;Ristolainen, E
以Ni/Au（化学镀镍/浸金）和有机可焊性保护剂（OSP）为基准，研究了Sn/Ag/Cu和Sn/Pb共晶钎料对I-Ag（浸银）和I-Sn（浸锡）印刷电路板（PCB）镀层的润湿性。对新鲜电路板和经过不同预处理的电路板进行润湿测试，这些预处理模拟了老化、储存和多次回流循环的影响。当板是新鲜的时，I-Sn和Ni/Au饰面的润湿性优于I-Ag和OSP饰面。然而，在预处理后，I-Sn涂层的润湿性降低最快，而I-Ag和OSP涂层的润湿性通过不同的预处理降低较少。Ni/Au涂层的润湿性在所有预处理过程中都保持优异。老化处理过程中完成的化学和微观结构的变化进行了评估，使用电子能谱化学分析（ESCA），X射线衍射（XRD），和横截面，然后扫描电子显微镜（SEM）。结果表明，由于Sn/Cu金属间化合物（IMC）的形成，单个无铅回流循环比Sn/Pb回流循环更快地消耗I-Sn层。因此，具有类似于1 μ m的原始Sn厚度的I-Sn成品板将不能承受多次无铅回流循环而不会显著降低润湿性，但是高达两次Sn/Pb回流循环仍然是可行的。通过比较不同老化处理后的润湿性，评估了充分润湿所需的I-Sn的最小厚度。I-Sn样品暴露于85 ℃/85%相对湿度（RH）条件下会增加Sn氧化物层的厚度，超过一定厚度时，会降低润湿性。在暴露于85 degreesC/85%RH处理之后，在I-Ag表面的顶部上形成氧化的铜区域，并且这被认为是影响润湿的主要因素。检测到I-Ag上硫化物的形成，但它们的总量仍然太小，无法对润湿产生可检测的影响。
The wetting of I-Ag (immersion silver) and I-Sn (immersion tin) printed-circuit-board (PCB) finishes by Sn/Ag/Cu and eutectic Sn/Pb solders was studied in this work with Ni/Au (electroless nickel/immersion gold) and organic solderability preservative (OSP) finishes as baselines. Wetting tests were performed on fresh boards and boards subjected to different preconditioning treatments that simulated the effects of aging, storage, and multiple reflow cycles. When the boards are fresh, the wetting of the I-Sn and Ni/Au finishes is better than that on the I-Ag and OSP finishes. However, after the preconditioning treatments, the wetting of the I-Sn finish degrades the fastest, whereas the wetting of the I-Ag and OSP finishes degrade less through the different preconditioning treatments. The wetting of the Ni/Au finish remains excellent through all the preconditioning treatments. The chemical and microstructural changes in the finishes during aging treatments were evaluated using electron spectroscopy chemical analysis (ESCA), x-ray diffractometry (XRD), and cross-sectioning followed by scanning electron microscopy (SEM). The results indicate that a single lead-free reflow cycle consumes the I-Sn layer faster than a Sn/Pb reflow cycle because of the formation of the Sn/Cu intermetallic compound (IMC). Consequently, I-Sn finished boards having an original Sn thickness of similar to1 mum will not withstand multiple lead-free reflow cycles without significant degradation in wetting but up to two Sn/Pb reflow cycles are still feasible. The minimum thickness of I-Sn required for adequate wetting was evaluated by comparing the wetting after different aging treatments. The exposure of I-Sn samples to 85degreesC/85% relative humidity (RH) conditions increases the thickness of the Sn-oxide layer, which, above a certain thickness, can degrade wetting. Oxidized copper areas formed on top of the I-Ag surface after exposure to 85degreesC/85% RH treatment, and this was considered a major factor influencing wetting. The formation of sulfides on I-Ag was detected, but their overall quantity remained too small to have a detectable impact on the wetting.