不同金属的电偶腐蚀

{0>Not all metals play well together.<}0{>并非所有的金属都能够相互兼容得很好。<0}{0>And this spills over in to the world of electronics and the materials used therein.<}0{>这些涉及到电子品的世界及在那里使用的材料。<0}{0>A relatively new and relevant example came about with the advent of RoHS and the desire to identify a "drop-in" replacement for SnPb(Ag) solders.<}0{>一个相当新的及相关的例子是RoHS的出现以及“直接”替代元件SnPb(Ag)焊锡膏的愿望。<0}{0>A eutectic blend of Sn (tin) and Zn (zinc) was very attractive as a possible replacement.<}0{>共熔混合Sn(锡)和Zn(锌)作为一种可能替代品很有吸引力。<0}{0>91Sn 9Zn is eutectic, does not contain any RoHS materials, and melts at 199C, only 16 degrees higher than eutectic SnPb solder and ~20 degrees lower than common SAC blends, and does not contain any expensive precious metals.<}0{>91Sn9Zn是共熔的，不含任何的RoHS材料，在199℃下熔融，只比共熔的SnPb焊锡膏高出16℃，比SAC混合物低~20℃，不含任何贵重的金属。<0}

{0>But the alloy contains Zn.<}0{>但合金含有Zn。<0}{0>And that is a show-stopper for two reasons.<}0{>那样会停止工作，原因有两个。<0}{0>Zn is quite reactive, making it very difficult to create a flux-vehicle that would allow for a stable solder paste (possess an appreciable shelf life).<}0{>锌的反应性活跃，使它很难产生一种适用于稳定焊锡膏(有明显的使用寿命)的助焊剂载体。<0}{0>The second, the one which we will go into detail in this post, is the electrode potential of Zn.<}0{>其次，我们在本帖子里详细研究的是锌的电极电势。<0}

{0>The greater the difference in electrode potential between metals, the higher the likelihood that galvanic corrosion will occur.<}0{>金属之间的电极电势差异越大，发生电偶腐蚀的可能性越大。<0}{0>The electrode potential of Cu (copper) is +0.334V.<}0{>Cu(铜)的电极电势是+0.334V。<0}{0>The electrode potential of Sn (tin) and Pb (lead) is -0.140V and -0.126V respectively.<}0{>Sn(锡)和Pb(铅)的电极电势分别是-0.140V和-0.126V。<0}{0>Whereas, the electrode potential of Zn is -0.761V.<}0{>其中，锌的电极电势是-0.761V。<0}{0>So, incidental contact of Zn to Cu can create a potential difference of 1.095V.<}0{>所以，Zn偶然接触Cu可产生1.095V的位差。<0}{0>Throw in a little humidity (moisture), and one has a prime scenario for galvanic corrosion to occur.<}0{>增加一点湿度(水分)，假设可能产生电偶腐蚀。<0}{0>It can be further aggravated by the presence of halide ions (salt spray).<}0{>卤离子（盐喷雾）的存在又会进一步加重。<0}

{0>So, given all this, would a solder alloy of 91%Sn and 9%Zn be a problem?<}0{>所以，既然如此，由91%Sn和9%Zn组成的焊锡膏不成问题吗?<0}

{0>I did a simple experiment to find out.<}0{>我做了一个简单的实验才找出来。<0}

{0>I took some SnZn solder ribbon and copper coupons, simply laid them on one another and exposed them to 85C/85%RH over the long Labor Day weekend (>72 hours).<}0{>我取一些SnZn焊带和铜片，只需要将彼此叠放并暴露在85C/85%RH下超过劳动节的周末(大于72小时)。<0}

{0>Below is an image of the SnZn solder ribbon before it was submitted to the conditions mentioned above.<}0{>下面是SnZn焊锡带在达到上述条件后的图像。

{0>The next image shows the SnZn solder ribbon after having been exposed to the 85C/85%RH for >72 hours.<}0{>下面是SnZn焊锡带暴露在85C/85%RH下超过72小时的图像。<0}{0>This sample of ribbon was not in contact with any other metals.<}0{>焊锡带的样品没有接触任何其他金属。<0}{0>I was trying to determine what "normal" oxidation of this alloy, under these conditions, would be.<}0{>我正在测定该合金在这些条件下会是怎样“正常的”氧化。<0}{0>I likewise did this with the copper coupons.<}0{>同样，我还利用铜片做了实验。<0}{0>(Next Image)<}0{>(下图)<0}

{0>This last image shows the effect of incidental contact of copper with the SnZn solder ribbon.<}0{>下图显示铜偶然接触SnZn焊锡带的效果。<0}{0>Take note of how much worse the oxidation/corrosion of the copper coupons is.<}0{>请注意铜片的氧化/腐蚀多么糟糕。<0}

{0>In this simple experiment we can see the effects of galvanic corrosion that happens through incidental contact of SnZn solder alloy to copper.<}0{>在这个简单的实验里，我们SnZn焊锡膏偶然接触铜发生电偶腐蚀的效果。<0}{0>I say "incidental contact" because the materials are merely touching each other, they have not been soldered together.<}0{>我说"偶然接触"是因为材料只是相互接触，它们还没有被焊接在一起。<0}{0>It would be interesting to see if the effect would be as great if the materials were bonded together with no gap for water to penetrate.<}0{>材料被粘合在一起，使水没有缝隙渗透，如果看到效果理想则是有趣的。<0}

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