通过锡球延展性、常规可焊性、黑盘和焊盘拉脱强度测试验证了金层厚度对沉金(ENIG)印刷电路板(PCB)焊锡延展性的影响，并用扫描电镜评估了金属间化合物(IMC)。结果表明，金层越厚，焊锡延展性越好。但金层只起保护镍层的作用，沉金 PCB焊点的可靠性建立在IMC基础上，只要能在镍层与焊料之间能形成良好的金属间化合物，即可保证焊点的可靠性。另外，金层越厚，黑盘的风险越高，且有可能引起金脆问题，因此不能一味地追求沉金层的厚度以提高焊锡延展性。
The effect of gold thickness on solder spread of electroless nickel/immersion gold (ENIG) printed circuit board (PCB) was verified through solder ball spread test, normal weldability test, black pad test, and pad pull strength test. The intermetallic compounds (IMCs) were assessed by scanning electron microscope. The results showed that the solder spread gets better with increasing thickness of gold layer. However, gold layer is only used to protect the nickel layer. The reliability of solder joint is built on the basis of IMCs, and can be guaranteed as long as good IMC can be formed between nickel layer and solder. The thicker the gold layer, the higher risk of black pad will be, and gold embrittlement problem may be caused. The thickness of immersion gold should not be blindly pursued for improving the solder ductility.
参考文献
| [1] | 白蓉生.看图说故事(15)[J].电路板会刊,2009(45):4-17. |
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