CN101667566B - 一种银基覆金的键合丝线的制造方法 - Google Patents

一种银基覆金的键合丝线的制造方法 Download PDF

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CN101667566B
CN101667566B CN2009101529168A CN200910152916A CN101667566B CN 101667566 B CN101667566 B CN 101667566B CN 2009101529168 A CN2009101529168 A CN 2009101529168A CN 200910152916 A CN200910152916 A CN 200910152916A CN 101667566 B CN101667566 B CN 101667566B
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silk thread
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bonding silk
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郑康定
冯小龙
李彩莲
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NINGBO KANGQIANG ELECTRONICS CO Ltd
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Abstract

本发明公开了一种以银丝线为基材、表面覆有纯金防氧化保护层的键合丝线产品，按照重量百分比金占1.8％-10.0％，其余为银；其制造方法包括：提纯、制备单晶银棒、粗拔、热处理、表面镀金、精拔、热处理、表面清洗和分卷等步骤。本发明专利摒弃了传统思维方式电镀后直接应用的落后工艺，而是先制成直径小于1mm的银丝线后，先电镀一定厚度的纯金防氧化保护层，然后再经多道次工序精密拉拔成不同规格的银基覆金键合丝线成品。本产品镀金层材质致密、均匀，与基材结合强度大幅提高，有效延长了产品保质期限；丝线硬度适中、焊接成球性好；材料成本不到纯金键合丝线的1/3；本发明专利技术可以广泛应用于复合型结构的键合丝线产品制造。

Description

一种银基覆金的键合丝线的制造方法
技术领域
本发明涉及微电子后道封装工序用键合丝线产品的制造技术领域，尤其指键合丝线产品的复合型结构及其制造方法。
背景技术
微电子器件芯片的键合工序，是指在一定温度下采用超声加压的方式将键合丝线两端分别焊接在芯片焊盘和引线框架引脚上，实现芯片内部电路与外部电路的连接。目前，传统的键合丝线多由纯金制成，它具有电导率大、耐腐蚀和韧性好的优点而被广泛应用。但是，随着黄金资源的日益稀缺、价格持续攀升，微电子封装成本大幅上升。为此同行们早已开始寻求工艺性能好、价格低廉的金属材料来替代昂贵的金丝材料；现已相继出现了铝丝、铜丝等连接材料，特别是铜丝产品由于在拉伸、剪切强度和延展性能优于金丝，已经成功应用于如DIP、SOP和功率器件等低端产品的封装生产，比较典型的产品如国家知识产权局于2008年9月24日授权公告的ZL200610154487.4名称为“键合铜丝及其制备方法”和2008年10月22日授权公告的ZL200610154485.5名称为“一种键合铜丝及其制备方法”的发明专利，其键合铜丝价格低廉，且具有较好的机械性能和抗氧化性能，保证了键合封装过程的流畅。但在QFP、QFN、BGA等中高端产品领域，由于铜丝所具备的易氧化发黑、硬度高易损伤芯片等原因，其应用仍然受到限制。当然，人们也在不断地探索由银丝替代金丝的方法，因为银的导电和导热性能为各种金属之冠，分别为金的1.30倍和1.35倍，可是由于无法克服银基键合丝线存在的易氧化问题，直至本发明专利申请日仍未见有此类银基键合丝线专利文献在国家知识产权局网站公开。
发明内容
本发明要解决的技术问题是克服现有中高端微电子产品的键合丝线均由纯金制成而存在的成本高和资源稀缺的缺陷和不足，向社会提供一种以银丝线作为基层、外表覆有纯金防氧化保护层的键合丝线产品的制造方法，以充分利用银导电率优于金的特性，在承载相同额定电流的前提下，进一步缩小键合丝线的直径，缩短焊接间距，更加适用于高密度集成电路封装；又由于基材金属的替换，可以大幅降低中高端微电子器件芯片的封装材料成本。
本发明解决其技术问题所采用的技术方案是：银基覆金的键合丝线以银丝线为基材，银丝线表面覆有纯金防氧化保护层；按照重量百分比，金占1.8％-10.0％，其余为银，两者之和等于100％；所述键合丝线直径为18μm-50μm；银的纯度大于99.9995％，金的纯度大于99.999％，其制造方法包括以下步骤：
①提纯：将国家标准1号银块提纯为纯度大于99.9995％的高纯银，清洗、烘干备用；
②制备单晶银棒：将高纯银置于金属单晶连铸室，连铸得到
Figure GSB00000537696600021
纵向和横向晶粒数均为1个的高纯银棒；
③粗拔：将
Figure GSB00000537696600022
单晶银棒拉拔成直径小于1mm的银丝线；
④热处理：将直径小于1mm的银丝线退火；
⑤表面镀金：对退火后的银丝线电镀纯金防氧化保护层，电镀用金的纯度要求大于99.999％，镀层厚度根据权利要求1所述金的重量百分比，经换算确定；
⑥精拔：将前述电镀有纯金防氧化保护层的银丝线，精密拉拔成
Figure GSB00000537696600023
-50μm的银基覆金键合丝线；
⑦热处理：将银基覆金键合丝线连续退火；
⑧表面清洗：先用酸液酸洗，再由高纯水清洗、烘干；
⑨分卷：单卷定尺。
在所述③粗拔步骤，是将
Figure GSB00000537696600024
单晶银棒拉拔成
Figure GSB00000537696600025
的银丝线。
在所述⑤表面镀金步骤，镀层厚度为0.5μm-3μm。
在所述⑥精拔步骤，将电镀有纯金防氧化保护层的银丝线，精密拉拔成
Figure GSB00000537696600026
的银基覆金键合丝线。
本发明银基覆金的键合丝线的制造方法，摒弃了传统思维方式电镀后直接应用的落后工艺，而是先制成
Figure GSB00000537696600027
的银丝线后，电镀一定厚度的纯金防氧化保护层，其镀层厚度则主要根据成品的键合丝线直径而定，即成品直径越小，拉拔率越大，则所需镀层越厚，耗金多；反之成品直径越大，拉拔率越小，所需镀层越薄，耗金少；一般情况下，在电镀后再经多道次工序精密拉拔成
Figure GSB00000537696600028
-50μm等不同规格的银基覆金键合丝线。在将电镀有纯金防氧化保护层的银丝线精密拉拔成银基覆金键合丝线成品的过程中，其镀金保护层的纯金材质更加致密、均匀，表面光滑、线型一致，且银基表面与镀金层之间金、银分子互相交融、渗透，镀金层与基材的结合强度大幅提高，可以有效提升银丝线的抗氧化性能，延长产品保质期限。本产品线材硬度适中、焊接成球性好；材料成本大幅降低，不到纯金键合丝线的1/3；在承载相同额定电流的前提下，可以进一步缩小键合丝线的直径，缩短焊接间距，更加适用于高密度集成电路封装；本产品具备有良好抗氧化性，可以在常温下长期保存。本发明专利制造方法具有构思新颖、工序简单、受益显著的优点，可以广泛应用于复合型结构的键合丝线产品制造。
附图说明
图1是本发明产品制造方法流程示意图。
具体实施方式
下面结合附图通过对两个实施例的描述，详细叙述本发明银基覆金的键合丝线的制造方法技术方案。
实施例一
①提纯：将硝酸银溶液按1∶4比例加高纯水进行稀释，配制成电解液；以国家标准1号银块作为阳极浸入电解液，并确保有95％体积比的银块浸入电解液中；以高纯银箔作为阴极浸入电解液中，同样确保有95％体积比的高纯银箔浸入电解液中；在阳极、阴极之间输入7-9V、2.5-3.5A的直流电，以补充新鲜电解液方式维持电解液温度不超过60℃；待阴极积聚纯度大于99.9995％的高纯银，及时更换高纯银箔，再以清洗并烘干备用。
②制备单晶银棒：在一个有氮气保护的水平连铸金属单晶的连铸室，加入提纯所得的纯度大于99.9995％高纯银；应用中频感应加热至960-980℃，待完全熔化、精炼和除气后，将熔液注入连铸室中间的储液池保温，在维持2-5L/min净化氮气流量的连铸室中，完成对纯银熔液的水平单晶连铸，得到
Figure GSB00000537696600031
纵向和横向晶粒数均为1个的高纯银棒；单晶银棒可有效降低银丝线的电阻率、提高导电率，增强其抗氧化性能。本工序更为详细的方法及其所应用设备，可参阅国家知识产权局于2008年4月30日授权公告的ZL200510023514.X名称为“金属单晶连铸工艺的控制方法及装备”发明专利技术，属于公知技术范畴。
③粗拔：应用常规拉拔设备和工艺，将
Figure GSB00000537696600032
单晶银棒经多道次工序，拉拔成
Figure GSB00000537696600033
的银丝线。
④热处理：将
Figure GSB00000537696600041
的银丝线置于退火炉中，在300℃温度下保温25min；保温期间通以氮气保护，然后随炉冷却。
⑤表面镀金：应用常规电镀设备和工艺，对退火后的
Figure GSB00000537696600042
银丝线电镀纯金防氧化保护层，电镀用金的纯度要求大于99.999％；电流密度1-1.2A/dm2，银丝线速度为4-5m/min，镀层厚度为0.5μm；镀金后的银丝线产品，按照纯银密度为10.5g/cm3、纯金密度为19.3g/cm3换算，金的重量百分比为1.8％，其余为银。
⑥精拔：应用常规精密拉拔设备和工艺，将前述电镀有纯金防氧化保护层的银丝线，经多道次工序，精密拉拔成
Figure GSB00000537696600044
的银基覆金键合丝线；对于此
Figure GSB00000537696600045
的银基覆金键合丝线，按照金属压延加工中体积不变定律，可能推断任一截面上的金面积与银面积之比维持不变，故可以换算出该成品的纯金防氧化保护层厚度为0.05μm，此厚度镀金层可以有效隔离银丝线表面与空气的接触，大大增强成品抗氧化性能，延长产品保质期。
⑦热处理：将银基覆金键合丝线由退火炉在350℃温度下连续退火，键合丝线速度为65m/min。
⑧表面清洗：先用浓度为1-2％的酸液进行酸洗，再由高纯水清洗两次，最后烘干；
⑨分卷：以500m为单卷定尺，控制绕丝张力为8g，绕丝速度为60-65m/min，线间距4mm。
实施例二
步骤①至步骤④同实施例一。
⑤表面镀金：应用常规电镀设备和工艺，对退火后的
Figure GSB00000537696600047
银丝线电镀纯金防氧化保护层，电镀用金的纯度要求大于99.999％；电流密度4-4.5A/dm2，银丝线速度为3.5-4m/min，镀层厚度为3μm；镀金后的银丝线产品，按照纯银密度为10.5g/cm3、纯金密度为19.3g/cm3换算，金的重量百分比为10.0％，其余为银。
⑥精拔：应用常规精密拉拔设备和工艺，将前述电镀有纯金防氧化保护层的银丝线，经多道次工序，精密拉拔成
Figure GSB00000537696600049
的银基覆金键合丝线；对于此
Figure GSB000005376966000410
的银基覆金键合丝线，按照金属压延加工中体积不变定律，可能推断任一截面上的金面积与银面积之比维持不变，故可以换算出该成品的纯金防氧化保护层厚度为0.33μm，此厚度镀金层足以有效隔离银丝线表面与空气的接触，大大增强成品抗氧化性能，延长产品保质期。
其余步骤⑦至步骤⑨也同实施例一。
本发明银基覆金的键合丝线的制造方法，如实施例一和实施例二所述，摒弃了传统思维方式电镀后直接应用的落后工艺；而是先制成
Figure GSB00000537696600051
的银丝线后，电镀一定厚度的纯金保护层，镀层厚度则主要根据成品的键合丝线直径而定，即成品直径越小，拉拔率越大，则所需镀层越厚；反之成品直径越大，拉拔率越小，所需镀层越薄；一般情况下，金的重量百分比占1.8％-10.0％，其余为银；电镀后再经多道次工序精密拉拔成
Figure GSB00000537696600052
-50μm等不同规格的银基覆金键合丝线。在将电镀有纯金防氧化保护层的
Figure GSB00000537696600053
银丝线精密拉拔成银基覆金键合丝线成品的过程中，其镀金防氧化保护层的材质更加致密、均匀，表面光滑、线型一致，且银基表面与镀金层之间金、银分子互相交融、渗透，镀金层与基材的结合强度大幅提高，可以有效提升银丝线的抗氧化性能，延长产品保质期限。
将按照实施例一和实施例二方法制造的两种银基覆金键合丝线成品应用于封装工序时，其测试结果与纯金丝线的对比结果如下：
从上述对比结果表格可以得知，本发明专利方法制造的银基覆金键合丝线产品，其封装后的拉断力和推球剪切力(铲除焊点力)均明显高于相同规格的纯金键合丝线产品，与芯片焊盘、引线框架引脚的焊接牢固度更高，具备更加稳定的剪切断裂载荷。
将按照实施例一和实施例二方法制造的两种
Figure GSB00000537696600056
银基覆金键合丝线成品理化指标与等径的纯金丝线对比结果如下表：
从上述对比结果表格可以得知，本发明专利方法制造的银基覆金键合丝线产品，机械强度要高于纯金键合丝线产品，线材硬度适中、焊接成球性好；材料成本大幅降低，不到纯金键合丝线的1/3；在承载相同额定电流的前提下，可以进一步缩小键合丝线的直径，缩短焊接间距，更加适用于高密度集成电路封装；本产品具备有良好抗氧化性，可以在常温下长期保存。

Claims (6)

1.一种银基覆金的键合丝线的制造方法，所述键合丝线以银丝线为基材，银丝线表面覆有纯金防氧化保护层；按照重量百分比，金占1.8％-10.0％，其余为银，两者之和等于100％；所述键合丝线直径为18μm-50μm；银的纯度大于99.9995％，金的纯度大于99.999％，其制造方法包括以下步骤：
①提纯：将国家标准1号银块提纯为纯度大于99.9995％的高纯银，清洗、烘干备用；
②制备单晶银棒：将高纯银置于金属单晶连铸室，连铸得到
Figure FSB00000537696500011
纵向和横向晶粒数均为1个的高纯银棒；
③粗拔：将
Figure FSB00000537696500012
单晶银棒拉拔成直径小于1mm的银丝线；
④热处理：将直径小于1mm的银丝线退火；
⑤表面镀金：对退火后的银丝线电镀纯金防氧化保护层，电镀用金的纯度要求大于99.999％，镀层厚度根据金的重量百分比，经换算确定；
⑥精拔：将前述电镀有纯金防氧化保护层的银丝线，精密拉拔成
Figure FSB00000537696500013
-50μm的银基覆金键合丝线；
⑦热处理：将银基覆金键合丝线连续退火；
⑧表面清洗：先用酸液酸洗，再由高纯水清洗、烘干；
⑨分卷：单卷定尺。
2.如权利要求1所述银基覆金的键合丝线的制造方法，其特征在于：在所述③粗拔步骤，是将单晶银棒拉拔成
Figure FSB00000537696500015
的银丝线。
3.如权利要求2所述银基覆金的键合丝线的制造方法，其特征在于：在所述⑤表面镀金步骤，镀层厚度为0.5μm。
4.如权利要求2所述银基覆金的键合丝线的制造方法，其特征在于：在所述⑤表面镀金步骤，镀层厚度为3μm。
5.如权利要求3所述银基覆金的键合丝线的制造方法，其特征在于：在所述⑥精拔步骤，将电镀有纯金防氧化保护层的银丝线，精密拉拔成
Figure FSB00000537696500016
的银基覆金键合丝线。
6.如权利要求4所述银基覆金的键合丝线的制造方法，其特征在于：在所述⑥精拔步骤，将电镀有纯金防氧化保护层的银丝线，精密拉拔成
Figure FSB00000537696500021
的银基覆金键合丝线。
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