金层厚度对沉金PCB焊锡延展性及焊点可靠性的影响-李伏.pdfVIP

金层厚度对沉金PCB 焊锡延展性及焊点可靠性的影响 李伏*，李斌 （汕头超声印制板公司，广东汕头 515065 ） 摘要：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。 关键词：电路板；沉金；厚度；焊锡延展性；金属间化合物；可靠性 中图分类号：TN405; TG40 文献标志码：A 文章编号：1004 – 227X (2015) 04 – 0196 – 05 Effect of gold thickness on ENIG PCB solder spread and joint reliability // LI Fu*, LI Bin Abstract: 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. Keywords: printed circuit board; electroless nickel/immersion gold; thickness; solder spread; intermetallic compound; reliability First-author’s address: China Circuit Technology (Shantou) Corporation, Shantou 515065, China 沉金也叫无电镍金或沉镍浸金，是一种在印制线路板(PCB)裸铜表面涂覆可焊性涂层的工艺，其集焊接、 接触导通、打线、散热等功能于一身，满足了日益复杂的 PCB 装配焊接要求，受到 PCBA (printed circuit board assembly，即PCB 装配)客户的广泛亲睐。但在实际装配过程中，偶尔也有客户反映沉金焊锡延展性差，进而怀 疑沉金板件存在可焊性不良的问题。图 1 是某客户反馈的沉金焊锡延展性差的图片，从中可见锡膏在屏蔽框位 置表现出较明显的延展性差异[其余 BGA (球栅阵列)结构及较大焊盘的锡膏均润