A Novel Process of Fabrication of Ultrafine Microvias for Advanced Electronic Packaging

我们建议研究和开发一种新的飞秒准分子激光工艺，用于制造用于下一代电子封装应用的超细（20-50 pm）高纵横比(5)微通孔。这些微孔将采用无损伤激光播种和低电流电镀技术进行铜金属化。通孔将采用聚酰亚胺柔性、硅（Si）和氧化铝（A1203）基片制造，这些基片通常用于包装应用。在制造完成后，将对通孔进行机械测试和电学表征。该研究将在位于费耶特维尔的阿肯色大学的高密度电子中心（HiDEC）和材料与制造研究实验室（MRL）进行。在这项合作研究中，先进封装领域的领先公司Irvine Sensors， CA将在实际应用中实现制造的微通孔（附承诺书）。包装行业对超细微孔的需求日益增长。正如《国家电子互连技术路线图》[由IPC互连与封装电子电路研究所发布]所讨论的那样，封装的通孔技术的技术进步趋势明显落后于集成电路产业的进步。因此，迫切需要一种能够在技术上重要的基板上制造这种微孔的技术。在这个项目中，我们确定聚酰亚胺、硅和A1203衬底是广泛接受和使用的材料，分别用于各种高密度多芯片模块（MCM）封装组件，MCM- l、MCM- d和MCM- c。在该项目中，将使用380飞秒（fs）， UV （Z=248 nm）准分子泵浦染料激光器来研究透孔和盲孔的制造。目前，各种技术，如湿蚀刻，反应离子蚀刻，光敏聚合物光刻和激光，用于制造封装应用的过孔。尺寸均匀性、机械完整性和化学清洁度对过孔的成功和封装的可靠性至关重要。脉冲纳秒级紫外准分子激光是一种主要的候选激光。这种激光器是已知的[1,2]，通常用于蚀刻直径约100微米的通孔。通孔直径直接影响单位面积和体积内可能的最终通孔密度，但密度也间接取决于通孔周围基板的化学降解。这反过来又完全依赖于制造过孔的工艺。近年来，利用纳秒准分子激光钻取高纵横比通孔，观察到[3]脆性断裂。失效机理确定为纳秒激光诱导热影响区[1]导致聚合物过度“燃烧”。这种热影响区导致热失控，这进一步限制了使用纳秒紫外激光制造的通孔的最终尺寸。飞秒激光加工被认为是优越的。因此，使用超快激光脉冲是不可避免的。鉴于我们实验室最近取得的令人兴奋的fs激光微孔钻孔结果和fs激光器的重大技术进步，我们提出fs准分子激光器是先进封装应用中微孔制造科学和技术进步的重要候选者。此外，随着嵌入式被动元件成为高密度封装的一个组成部分，衬底的厚度也在增加。使用fs激光器是实现高纵横比通孔的最佳选择(5)，并且这些通孔也可以钻穿集成的无源元件，而不像ns激光器那样对周围的几何结构或化学结构产生热干扰。这种技术的发展将证明有利于公司，如欧文传感器，摩托罗拉，谢尔达尔，克雷等，并将提供我们在激烈的全球市场的前沿。该项目进一步促进了校园内外的教育基础设施，因为学生将接触到最先进的研究经验和实践教育。HiDEC和MRL是阿肯色大学包装和表面工程的卓越中心（http://www.engr.uark.edu/~apm2）。我们与工业伙伴的合作是独一无二的，将在电子、生物医学、汽车、电信以及许多其他民用和战略应用等各个领域广泛应用

9900238RailkarWe propose to study and develop a novel, femtosecond (fs) excimer laser based process for fabricating ultra-fine (20-50 pm) high aspect ratio ( 5) microvias for next generation electronic packaging applications. These microvias will be metallized using copper by damage-free fs-laser seeding followed by low current electroplating techniques. The vias will be fabricated in polyimide flex, silicon (Si) and alumina (A1203) substrates which are commonly used in packaging applications. Subsequent to the ir fabrication, the vias will be undergo mechanical testing and electrical characterization. The research will be performed at High Density Electronics Center (HiDEC), and Materials and Manufacturing Research Laboratory (MRL) at the University of Arkansas at Fayetteville. In this collaborative research, Irvine Sensors, CA, a leading company in advanced packaging, will implement the fabricated microvias in real application (letter of commitment attached).There is an ever growing need for ultra-fine microvias in packaging industry. As discussed in the National Technology Roadmap for Electronic Interconnections [issued by Institute for Interconnecting and Packaging Electronics Circuits (IPC)], the technological progress trend of via formation technology for packaging is significantly falling behind the progress in IC industry. Consequently, there is a extraordinary need for a technology that could fabricate such microvias on technologically important substrates. In this project, we identify polyimide, silicon, as well as A1203 substrates as those are widely accepted and used material for various high density multi-chip module (MCM) packaging assemblies, MCM-L, MCM-D and MCM-C, respectively.In the proposed project, a 380 femtosecond (fs), UV (Z=248 nm) excimer pumped dye laser will be used to investigate the through- and blind- microvia fabrication. Currently, various technologies such as wet etch, reactive ion etching, photosensitive polymer lithography and lasers - are used for fabricating vias for packaging applications. Dimensional uniformity, mechanical integrity and chemical cleanliness are critical for success of vias and thus the reliability the package. One of the leading candidates is pulsed nanosecond UV excimer laser. This laser is known [1,2] and typically used to etch vias of about 100 um diameter. The via diameter directly affects the ultimate density of vias possible within a unit area and volume, but the density indirectly depends also on the chemical degradation of the substrate surrounding the via. This, in turn completely relies on the process employed to fabricate vias. Recently, brittle fracture of high aspect ratio vias, drilled using nanosecond excimer laser has been observed [3]. The failure mechanism was identified as excessive polymer "burning" due to nanosecond laser induced heat affected zone [1]. This HAZ causes thermal run-away which further puts a natural limit on the ultimate size of the via fabricated using nano second UV laser. Femtosecond laser processing is known to be superior [3]. Consequently, use of ultrafast fs pulse lasers is inevitable. In view of the recent exciting results of fs laser microvia drilling in our laboratory and significant technological advances in fs lasers, we propose that fs excimer laser is a serious candidate for the advancement of science and technology of microvias fabrication for advanced packaging applications. Further, with embedded passives becoming an integral part of high density packaging, the thickness of substrates is on the increase. Use of fs lasers is the best choice for realization of high aspect ratio vias (5), and those could be drilled through integrated passive elements too, without thermally disturbing the surrounding geometry or chemistry, unlike ns lasers. Development of such technology will prove beneficial to companies such as Irvine Sensors, Motorola, Sheldahl, Cray, etc. and will provide us a cutting edge in the fierce global market. This program further benefits educational infrastructure, on and off campus, as students will be exposed to the state-of-the-art research experience and hands-on education. HiDEC and MRL are centers of excellence for packaging and surface engineering at the University of Arkansas (http://www.engr.uark.edu/~apm2). Our collaborations with industrial partners is unique and will benefit a wide range of applications in various fields such as electronics, bio-medical, automobile, telecommunication, and numerous other civilian and strategic applications.***