铝合金微波组件镀镍钯钴金的可焊性与可靠性研究

Solderability and reliability of nickel/palladium–cobalt/gold plated aluminum alloy microwave components

摘要

[目的] 针对微波组件壳体传统化学镀 Ni–P 合金+电镀金工艺中 Au 层厚度难以兼顾可焊性与可靠性、且黄金成本高昂的问题，提出化学镀 Ni–P 合金+电镀 Pd–Co 合金+电镀 Au 的 3 层复合镀覆工艺。[方法] 以 6061-T651 铝合金盒体为基材，分别镀覆 Ni–P/Au(NiAu)和 Ni–P/Pd–Co/Au(NiPdCoAu)。采用 SnPb(183 ℃)和 SnAgCu(217 ℃)两种焊料，对 NiPdCoAu 盒体焊接超小型推入式射频同轴连接器(SMP)，评价其气密性与漏率；对比研究两种镀层盒体焊接 6002 高速射频板及环氧树脂板后的可焊性、界面金属间化合物(IMC)生长行为及温度冲击(−65 ~ 125 ℃，100 次)前后的剪切强度与漏率。通过扫描电镜和能谱仪(SEM/EDS)分析镀层界面结构与焊点失效机理。[结果] NiPdCoAu 镀层对 SnPb 和 SnAgCu 焊料均表现出优异的润湿性，焊料铺展均匀连续。SMP 焊接后氦质谱漏率稳定在 10 −9 Pa·m 3/s 量级，100 次温度冲击后漏率无明显变化；PCB 焊接后钎透率高于 90%，剪切力测试表明破坏均发生于母材 Cu 层与基板之间，而非焊料界面。微观结构分析显示，NiPdCoAu 镀层有效抑制了脆性 AuSn ₄ 及过量 Ni ₆Sn ₅、(Cu,Ni) ₆Sn ₅ 等 IMC 的生长，IMC 厚度显著低于 NiAu 镀层，避免了“金脆”和“黑盘”问题。NiPdCoAu 工艺的金属成本约为 NiAu 工艺的 32.6%，综合镀覆成本降低 63.4%。[结论] 化学镀 Ni–P 合金+电镀 Pd–Co 合金+电镀 Au 的工艺能够在保证优异可焊性与高可靠性的前提下，大幅降低黄金用量和制造成本，满足微波组件批量化、低成本、高可靠封装要求，适用于铝合金微波组件壳体表面处理。

Abstract

[Objective] In the conventional process of electroless Ni–P alloy plating followed by gold electroplating for microwave component housings, the Au layer thickness cannot simultaneously satisfy both solderability and reliability requirements, and the process also incurs a high cost of gold. To address these issues, a three-layer composite plating process consisting of successive electroless Ni–P alloy plating, Pd–Co alloy electroplating, and Au electroplating was proposed. [Method] Ni–P/Au (NiAu) and Ni–P/Pd–Co/Au (NiPdCoAu) coatings were respectively plated on 6061-T651 aluminum alloy housings. Two solders including SnPb (183 °C) and SnAgCu (217 °C) were used. The NiPdCoAu-coated housings were soldered with ultra-miniature push-on RF coaxial connectors (SMP) to evaluate their hermeticity and leak rate. A comparative study was conducted on the solderability, interfacial intermetallic compound (IMC) growth behavior, as well as shear strength and leak rate before and after thermal shock (−65 °C to 125 °C, 100 cycles) for the two types of coated housings after soldering with 6002 high-speed RF boards and epoxy resin boards. The coating interfacial structure and solder joint failure mechanisms were analyzed by scanning electron microscopy and energy-dispersive spectroscopy (SEM/EDS). [Result] The NiPdCoAu coating exhibited excellent wettability with both SnPb and SnAgCu solders, with uniform and continuous solder spreading. After SMP soldering, the helium mass spectrometry leak rate remained stable at the order of 10 ⁻⁹ Pa·m ³/s, without significant change after 100 cycles of thermal shock. The solder fillet filling rate of PCB soldering was higher than 90%. The shear force test showed that failure always occurred between the Cu layer of the base material and the substrate, rather than at the solder interface. Microstructural analysis revealed that the NiPdCoAu coating effectively inhibited the growth of brittle AuSn ₄ and excessive IMCs such as Ni ₆Sn ₅ and (Cu,Ni) ₆Sn ₅, and the IMC thickness was significantly lower than that of the NiAu coating, thus avoiding “gold embrittlement” and “black pad” issues. The metal material cost of NiPdCoAu process was about 32.6% of that of the NiAu process, and the overall plating cost was reduced by 63.4%. [Conclusion] The process of successively conducting electroless Ni–P alloy plating, Pd–Co alloy electroplating and Au electroplating can greatly reduce gold consumption and manufacturing cost while ensuring excellent solderability and high reliability. It meets the requirements of batch production, low cost, and high reliability for microwave component packaging, and is suitable for surface treatment of aluminum alloy microwave component housings.

关键词

铝合金 / 微波组件 / 镀镍钯钴金 / 可焊性 / 可靠性

Key words

aluminum alloy / microwave component / nickel/palladium–cobalt/gold plating / solderability / reliability

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