CN1969064A - 锡-基镀膜及其形成方法 - Google Patents

锡-基镀膜及其形成方法 Download PDF

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CN1969064A
CN1969064A CNA2005800196393A CN200580019639A CN1969064A CN 1969064 A CN1969064 A CN 1969064A CN A2005800196393 A CNA2005800196393 A CN A2005800196393A CN 200580019639 A CN200580019639 A CN 200580019639A CN 1969064 A CN1969064 A CN 1969064A
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tin
alloy
plated film
film
weight
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郭振华
郭艳华
中岸丰
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Forever Chemical (hongkong) Co Ltd
Okuno Chemical Industries Co Ltd
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Okuno Chemical Industries Co Ltd
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Abstract

本发明提供一种晶须生长得到抑制的锡-基镀膜。所述的锡-基镀膜具有两层结构,包含:由锡镀膜或锡合金镀膜形成的下层,所述锡合金镀膜包含小于等于5重量%的选自钴、铜、铋、银和铟的至少一种金属和大于等于95重量%的锡,和由锡镀膜或锡合金镀膜形成的上层,所述锡合金镀膜包含小于等于5重量%的选自钴、铜、铋、银和铟的至少一种金属和大于等于95重量%的锡。本发明的锡-基镀膜是无铅的锡镀膜或锡合金镀膜,表现出对晶须生长的长期抑制,并且还可以在不经过复杂步骤的情况下相对容易地形成。

Description

锡-基镀膜及其形成方法
技术领域
本发明涉及一种晶须生长得到抑制的锡-基镀膜及其形成方法。
背景技术
Sn-Pb电镀提供具有良好外观、突出的焊接性的镀膜,并且使电镀浴管理相对容易,因此,被称作焊料电镀并且广泛用于电镀电气和电子元件。然而,近年来,有迹象表明焊料被酸雨等从电子元件废物中浸出,从而成为地下水的污染源。由于对人体特别有害的铅造成工作环境和废水处理上的问题,因此迫切需要开发出无铅的锡合金。
已知的具有良好焊接性和低熔点的无铅Sn合金电镀层的实例为含有Ag、Cu、In、Tl、Zn等的那些(参见下面的专利文件1)。
然而,当使用这种无铅锡合金电镀液形成镀膜时,得到的镀膜易于形成称作“晶须”的发状单晶。在形成于电气和电子元件上的镀膜上生长的晶须造成电路和接线柱的短路,从而使电气和电子元件的性能和可靠性显著下降。为此,对于用于电气和电子元件的镀膜,防止这种晶须形成已经成为一个重要目标。
考虑到成本和麻烦的电镀浴管理,单独使用锡的电镀是有利的;然而,由于这种电镀不能防止由晶须形成造成的电镀表面上的短路,因此通常不按照原样用于电镀电气和电子元件。
防止锡和锡合金晶须生长的一种已知方法是在电镀后进行熔融处理。然而,这种熔融处理造成以下缺点:昂贵并且不适用于复杂形状,从而限制了可适用对象的形状。
另一种已知方法是在电镀后使用磷酸溶液进行化学后处理。然而,当大量生产其上形成有锡或锡合金镀膜的电子元件时,产生这样的问题:后处理溶液容易被污染,并且一旦污染,则镀膜的性能下降。
专利文件1:未审查的日本专利公开No.1996-13185
发明内容
本发明要解决的问题
本发明是考虑到现有技术的上述现状而完成的,并且其主要目的是提供一种锡-基镀膜如无铅的锡镀膜或锡合金镀膜,该锡-基镀膜能够长期抑制晶须生长,并且能够相对容易形成而无需复杂步骤。
解决问题的手段
本发明的发明人进行了深入细致的研究以达到上述目的。结果,本发明的发明人发现,双层锡-基镀膜能够长期防止晶须的形成,所述双层锡-基镀膜包含锡镀膜或锡合金镀膜的下层和形成在所述下层上的较薄的锡镀膜或锡合金的上层。本发明的发明人还发现,当适当选择构成上镀膜层的合金组成时,可以任意确定软熔温度,而对镀膜整体的性能没有影响。基于这些发现完成了本发明。
更具体而言,本发明提供表现出抑制晶须生长的以下锡-基镀膜和形成它们的方法。
项1.一种表现出抑制晶须生长的锡-基的双层镀膜,其包含,
锡镀膜或锡合金镀膜的下层,所述锡合金镀膜包含小于等于5重量%的选自钴、铜、铋、银和铟的至少一种金属和大于等于95重量%的锡,和
锡镀膜或锡合金镀膜的上层,所述锡合金镀膜包含小于等于5重量%的选自钴、铜、铋、银和铟的至少一种金属和大于等于95重量%的锡。
项2.根据项1的锡-基镀膜,其中所述下层的膜厚度为0.1~20μm,并且所述上层的膜厚度为0.025~5μm。
项3.根据项1或2的锡-基镀膜,其中所述下层是无光的或半光亮的锡镀膜或锡合金镀膜,并且所述上层是光亮的或半光亮的锡镀膜或锡合金镀膜。
项4.根据项1~3中任一项的锡-基镀膜,其中所述下层是无光的锡镀膜,并且所述上层是光亮的锡合金镀膜。
项5.根据项1~4中任一项的锡-基镀膜,其还包含在锡-基的双层镀膜下层之下的底镀层,所述底镀层是:
(1)Ni或Cu的镀膜,
(2)Sn、Sn-Co合金、Sn-Cu合金、Sn-Bi合金、Sn-Ag合金或Sn-In合金的镀膜,或者
(3)由Ni或Cu的第一层和形成在第一层上的Sn、Sn-Co合金、Sn-Cu合金、Sn-Bi合金、Sn-Ag合金或Sn-In合金的第二层构成的双层镀膜。
项6.一种包含形成在衬底上的项1~5中任一项的锡-基镀膜的产品。
项7.一种用于形成表现出抑制晶须生长的锡-基镀膜的方法,所述方法包括以下步骤:通过电镀或化学镀膜,在衬底上形成锡镀膜或锡合金镀膜的下层,所述锡合金镀膜包含小于等于5重量%的选自钴、铜、铋、银和铟的至少一种金属和大于等于95重量%的锡,随后通过电镀或化学镀膜形成锡镀膜或锡合金镀膜的上层,所述锡合金镀膜包含小于等于5重量%的选自钴、铜、铋、银和铟的至少一种金属和大于等于95重量%的锡。
项8.一种用于形成表现出抑制晶须生长的锡-基镀膜的方法,所述方法包括以下步骤:通过电镀或化学镀膜在衬底上形成底镀层作为屏蔽层,所述底镀层是:
(1)Ni或Cu的镀膜,
(2)Sn、Sn-Co合金、Sn-Cu合金、Sn-Bi合金、Sn-Ag合金或Sn-In合金的镀膜,或者
(3)由Ni或Cu的第一层和形成在第一层上的Sn、Sn-Co合金、Sn-Cu合金、Sn-Bi合金、Sn-Ag合金或Sn-In合金的第二层构成的双层镀膜,随后采用项7的方法形成锡镀膜或锡合金镀膜作为下层,并且形成锡镀膜或锡合金镀膜作为上层。
本发明的锡-基镀膜具有由下层和上层构成的两层结构,所述下层为:锡镀膜或锡合金镀膜,所述的锡合金镀膜包含小于等于5重量%的选自钴、铜、铋、银和铟的至少一种金属和大于等于95重量%的锡;所述上层为:锡镀膜或锡合金镀膜,所述的锡合金镀膜包含小于等于5重量%的选自钴、铜、铋、银和铟的至少一种金属和大于等于95重量%的锡。
采用这种具有两层结构的锡-基膜,作为上层形成的非常薄的锡镀膜或锡合金镀膜能够长期防止晶须生长,而与下层是否是锡镀膜或锡合金镀膜无关。
上镀层和下镀层可以是光亮、半光亮或无光(无光的)表面光洁度的,并且可以根据用途适当选择。
特别优选下层是锡镀膜。此外,优选下层是半光亮的或无光的,其中更优选是无光的。由于它们大的晶粒大小和大的应力消除效果,半光亮的和无光的锡镀膜能够有效地延迟晶须生长。即使当下层是锡合金镀膜时,由上述两层结构,也较不容易生长晶须,并且几乎不发生如软熔温度变化、焊接性下降、出现裂纹等的问题。因此,与单层锡合金镀膜相比,这种两层结构能够省却合金组成的严格控制并且使电镀处理更容易。
优选上层是光亮或半光亮的表面光洁度的锡镀膜或锡合金镀膜,其中特别优选光亮的镀膜。由于它们的晶粒尺寸小,光亮和半光亮的镀膜能够堵塞孔。而且,由于这种膜较硬,膜表面几乎不被划伤。拥有了这些特性,它们能够非常有效地防止晶须的形成。
当下层是半光亮或无光的锡或锡合金镀膜并且上层是光亮或半-光亮的锡或锡合金镀膜时,可以在不增加总硬度的情况下抑制内应力和裂纹出现。特别优选下层是无光的锡镀膜并且上层是光亮的锡合金镀膜。
当形成锡合金镀膜作为上层时,通过选择锡合金的组成可以任意设置软熔温度,从而容易提供具有满足使用目的的软熔温度的膜。将这种结构与仅由锡合金镀层形成的膜相比,由于形成上层的锡合金镀层是薄膜,合金组成相对稳定并且可以容易地控制软熔温度。此外,由于这种结构要求锡合金层的上层含有非常薄的膜,因此只有软熔温度能够在对锡镀膜或锡合金电镀膜的下层的性能不产生不利影响的情况下被随意控制。
可以使用含有例如晶粒细化剂和/或类似添加剂的已知的锡电镀浴或锡合金电镀浴,形成光亮或半-光亮的锡镀膜或锡合金镀膜的上层。
对锡镀膜或锡合金镀膜下层的厚度没有限制,但是典型地优选其为约0.1~约20μm。特别是对于电镀连接器,下层的厚度优选为约1.5~约5μm,更优选约2.5~约5μm。当电镀IC元件、引线框等时,下层的厚度优选为约8~约20μm,更优选约10~约15μm。
对锡镀膜或锡合金镀膜上层的厚度没有限制,但是优选比下层的厚度薄,其中典型地优选约0.025~5μm。上层的膜厚度应优选在上述范围内,并且同时为下层膜厚度的约50%或更薄,更优选约25%或更薄。
对形成上述双层锡-基镀膜的锡镀膜和锡合金镀膜的方法没有限制,并且可以使用公知的锡和/或锡合金电镀浴,采用典型方式形成所需的锡和/或锡合金镀膜。电镀浴和化学镀膜浴都可以使用。
电镀浴的实例为各种已知的锡和锡合金电镀浴,如有机磺酸浴、硫酸浴、焦磷酸浴、酒石酸浴等。对这些电镀浴的具体组成没有限制,可以采用任何组成,只要它们能够形成所需的锡和锡合金镀膜即可。
有机磺酸浴的实例包括含有甲磺酸、乙磺酸、羟基甲磺酸(methanolsulfonic acid)、羟基乙磺酸(ethanolsulfonic acid)、羟基苯磺酸、羟基萘磺酸等的那些浴。下面给出了甲磺酸浴的组成作为锡电镀液的浴组成的一个实例。
甲磺酸                                100~250ml/l
甲磺酸锡(作为300g/l水溶液)            100~350ml/l
光亮剂                                0.1~2g/l
湿润剂                                30~1000g/l
添加剂(晶粒细化剂)                    0.1~5g/l
当形成锡合金镀膜时,还可以将含与锡形成合金的金属组分的甲磺酸金属盐等加入到锡电镀液中。例如,当形成锡-钴合金时,可以将甲磺酸钴和/或类似物以基于金属浓度为约20mg/l~约1500mg/l的范围加入。可以根据所需的合金组成在这种范围内选择加入的金属盐的量。
对电镀条件没有限制;浴温可以为约5~约65℃,并且阴极电流密度可以为约1~约50A/dm2
备选地,可以采用高速电镀如环镀(hoop plating)和喷镀或者脉冲电镀。
对形成锡或锡合金镀膜的预处理没有限制,可以根据典型的方式进行。
例如,可以采取典型方式进行脱脂,并且随后根据需要进行化学抛光、蚀刻等处理。之后形成锡或锡合金镀膜的下层,随后可以形成锡或锡合金镀膜的上层。
在上述双层锡-基镀膜和衬底之间,可以根据需要形成起屏蔽层作用的Ni或Cu的底镀层,或者Sn、Sn-Co合金、Sn-Cu合金、Sn-Bi合金、Sn-Ag合金或Sn-In合金的底镀层。备选地,在形成Ni或Cu的底镀层后,可以形成Sn、Sn-Co合金、Sn-Cu合金、Sn-Bi合金、Sn-Ag合金或Sn-In合金的另一底镀层。
这些当中,优选Ni或Cu底镀层具有半光亮或无光的表面光洁度,其具有较大的晶粒大小。这种底镀层的形成提高了应力消除效果。此外,这种底镀层和衬底一起形成可以抑制晶须生长的金属夹层,所述晶须生长由来自衬底的内应力和来自衬底的迁移应力等造成。这种Ni或Cu底镀层的膜厚度优选为约0.1~约10μm,更优选约0.1~约2μm。
优选Sn、Sn-Co合金、Sn-Cu合金、Sn-Bi合金、Sn-Ag合金或Sn-In合金的底镀层是具有较小晶粒大小的光亮或半光亮的镀膜。这种底镀层的形成能够堵塞微孔,从而抑制晶须生长。如果由于制造设备、组装步骤等的环境因素而不能形成作为屏蔽层的Ni镀层,则由这种底镀层和衬底形成金属夹层,并且可以延迟由来自衬底的内应力和来自衬底的迁移应力等造成的晶须生长。Sn、Sn-Co合金、Sn-Cu合金、Sn-Bi合金、Sn-Ag合金或Sn-In合金的底镀层的膜厚度优选为约0.01~约3μm,更优选约0.01~约1μm。此外,优选在Sn-Co合金、Sn-Cu合金、Sn-Bi合金、Sn-Ag合金或Sn-In合金中含有大于等于约60重量%的锡。
对形成作为屏蔽层的底镀层的方法没有限制,可以使用公知的电镀浴通过典型的方式形成所需的镀膜。可以使用电镀浴和化学镀膜浴以达到此目的。
对所镀物品的材料没有限制,只要其上能够形成上述镀膜即可。其实例可以包括铜、铜合金、铁、铁合金等。对于不能进行电镀的材料,在进行电镀之前通过化学镀膜等用金属涂覆所述材料的表面以使其具有导电性。
对所镀物品的种类和形状没有限制,其典型实例为需要焊接的电子元件如引线框、半导体包装、芯片元件等。
在采用上述方法形成双层锡-基镀膜后,还可以根据需要进行化学后处理。
可以按照常规方法进行这种化学后处理,其实例包括这样一种方法,其中将镀膜在处于30~约50℃温度的含有约30~70g/l磷酸三钠的溶液中浸渍约5~约60秒。
发明效果
与包含锡或锡合金单层的常规镀膜相比,本发明的双层锡-基镀膜能够极大地抑制晶须形成,从而提供高度稳定的电气和电子元件。
特别是采用这种结构,当上层是锡合金镀膜时,其薄的膜厚度使合金组成稳定,从而有助于更容易地控制软熔温度。此外,由于锡合金镀膜的膜厚度薄,因此可以在基本上不影响下层镀膜特性的情况下控制软熔温度。
当下层是半光亮或无光(不亮的)锡或锡合金镀膜,并且在其上形成半光亮或光亮的锡或锡合金镀膜时,厚的半光亮或无光的下层的存在有助于总的应力消除,此外,非常硬的表面层的存在可以抑制划痕形成,从而对防止晶须生长有突出的效果。
附图简述
[图1]从SEM图像的电子数据打印的图,所述SEM图像是在使形成在黄铜板上的锡-钴镀层和纯锡镀层构成的样品在室温放置后拍摄的。
[图2]从SEM图像的电子数据打印的图,所述SEM图像是在使形成在黄铜板上的纯锡镀层构成的样品在室温放置后拍摄的。
[图3]从镀膜表面的SEM图像的电子数据打印的图,所述SEM图像是在使形成在磷青铜板上的锡-钴合金镀层和无光的锡镀层构成的样品在高湿和高温下放置后拍摄的。
实施本发明的最佳方式
下面将参考实施例详细描述本发明。
实施例1
使用6.5×10cm黄铜板作为衬底,进行电镀脱脂处理,并且将板在环境温度下在酸性水溶液中浸渍1分钟作为活化处理,接着浸渍在含有10重量%的70%甲磺酸溶液的水溶液中。
随后,使用具有以下组成的锡电镀浴,形成厚度约3μm的光亮的锡镀膜。
(锡电镀浴组成)
甲磺酸                            175ml/l
甲磺酸锡                          45g/l(作为锡金属量)
湿润剂                            100g/l
光亮剂                            0.3g/l
添加剂                            0.5g/l
(晶粒细化剂)
(电镀条件)
浴温:室温
阴极电流密度:10A/dm2
电镀时间:1分钟
接着,使用具有以下组成的锡-钴电镀浴,形成厚度约1.25μm的锡-钴镀膜。合金镀膜的组成为99.5重量%的锡和0.5重量%的钴。
(锡-钴电镀浴组成)
甲磺酸钴                          400mg/l(作为钴金属量)
硫酸锡                            45g/l(作为锡金属量)
98%H2SO4                      100ml/l
湿润剂                            80g/l
光亮剂                            0.3g/l
添加剂                            0.5g/l
(晶粒细化剂)
(电镀条件)
浴温:15℃
阴极电流密度:15A/dm2
电镀时间:0.3分钟
根据上述方法,在黄铜板上形成由厚度约3μm的纯锡镀层和厚度约1.25μm的锡-钴镀层构成的双层锡-基镀膜。
图1显示了由此获得的样品的镀膜表面的SEM图像(500×),该样品在室温放置5个月。
为了比较,图2示出了包含采用与上述相同的方式在黄铜板上形成的厚度约3μm的纯锡镀膜的样品的镀膜表面的SEM图像(500×),所述样品在室温放置5个月。
从图1和2清楚的是,只具有纯锡镀膜的样品(图2)在5个月后生长出许多晶须,而具有形成在锡镀层上的非常薄的锡-钴镀层的样品(图1)在5个月后基本上没有晶须生长。
实施例2
使用6.5×10cm磷青铜板作为衬底,以与实施例1相同的方式进行预处理。随后,使用具有以下组成的锡电镀浴,形成约11μm厚度的无光(不光亮的)锡镀膜。
(无光锡电镀浴组成)
甲磺酸                            175mg/l
甲磺酸锡                          45g/l(作为锡金属量)
添加剂                            0.5g/l
(晶粒细化剂)
(电镀条件)
浴温:室温
阴极电流密度:10A/dm2
电镀时间:2.4分钟
然后采用与实施例1相同的方式,形成厚度为1.25μm的锡-钴合金镀层作为上层。
由此获得的样品具有无光的表面光洁度,然而由于存在具有小的晶粒大小和高硬度的锡-钴合金上镀层,膜表面具有高硬度因而不容易划伤。图3显示了该样品镀膜表面的SEM图像(300×),所述SEM图像是在将样品在湿度为85%、温度为85℃的高湿和高温条件下放置500小时后拍摄的。从该图清楚的是,证实了包含形成在无光的锡镀层上的锡-钴合金上层的样品具有优异的晶须生长抑制效果。

Claims (8)

1.一种表现出抑制晶须生长的锡-基的双层镀膜,其包含,
锡镀膜或锡合金镀膜的下层,所述锡合金镀膜包含小于等于5重量%的选自钴、铜、铋、银和铟的至少一种金属和大于等于95重量%的锡,和
锡镀膜或锡合金镀膜的上层,所述锡合金镀膜包含小于等于5重量%的选自钴、铜、铋、银和铟的至少一种金属和大于等于95重量%的锡。
2.根据权利要求1所述的锡-基镀膜,其中所述下层的膜厚度为0.1~20μm,并且所述上层的膜厚度为0.025~5μm。
3.根据权利要求1所述的锡-基镀膜,其中所述下层是无光的或半光亮的锡镀膜或锡合金镀膜,并且所述上层是光亮的或半光亮的锡镀膜或锡合金镀膜。
4.根据权利要求1所述的锡-基镀膜,其中所述下层是无光的锡镀膜,并且所述上层是光亮的锡合金镀膜。
5.根据权利要求1所述的锡-基镀膜,其还包含在锡-基的双层镀膜下层之下的底镀层,所述底镀层是:
(1)Ni或Cu的镀膜,
(2)Sn、Sn-Co合金、Sn-Cu合金、Sn-Bi合金、Sn-Ag合金或Sn-In合金的镀膜,或者
(3)由Ni或Cu的第一层和形成在第一层上的Sn、Sn-Co合金、Sn-Cu合金、Sn-Bi合金、Sn-Ag合金或Sn-In合金的第二层构成的双层镀膜。
6.一种包含形成在衬底上的权利要求1~5中任一项所述的锡-基镀膜的产品。
7.一种用于形成表现出抑制晶须生长的锡-基镀膜的方法,所述方法包括以下步骤:通过电镀或化学镀膜,在衬底上形成锡镀膜或锡合金镀膜的下层,所述锡合金镀膜包含小于等于5重量%的选自钴、铜、铋、银和铟的至少一种金属和大于等于95重量%的锡,随后通过电镀或化学镀膜形成锡镀膜或锡合金镀膜的上层,所述锡合金镀膜包含小于等于5重量%的选自钴、铜、铋、银和铟的至少一种金属和大于等于95重量%的锡。
8.一种用于形成表现出抑制晶须生长的锡-基镀膜的方法,所述方法包括以下步骤:通过电镀或化学镀膜在衬底上形成底镀层作为屏蔽层,所述底镀层是:
(1)Ni或Cu的镀膜,
(2)Sn、Sn-Co合金、Sn-Cu合金、Sn-Bi合金、Sn-Ag合金或Sn-In合金的镀膜,或者
(3)由Ni或Cu的第一层和形成在第一层上的Sn、Sn-Co合金、Sn-Cu合金、Sn-Bi合金、Sn-Ag合金或Sn-In合金的第二层构成的双层镀膜,随后采用权利要求7的方法形成锡镀膜或锡合金镀膜作为下层,并且形成锡镀膜或锡合金镀膜作为上层。
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