间歇式电沉积-低温固相烧结法制备W-Cu梯度热沉材料及其结构调控研究

Tungsten-copper functionally graded materials (W-Cu FGM) has been regarded as an ideal heat sink materials for microelectronics packaging, owing to the low coefficient of thermal expansion which matches well with ceramic substrate and good thermal conductivity. Since the differences of density and melting point between W and Cu are huge, and they are almost immiscible at liquid and solid states, the composition and structure of W-Cu composite could not be properly regulated by using the current fabrication processes, such as liquid filtration and powder sintering.As a result, it is difficult to achieve W-Cu composite with the full Cu-network structure and excellent thermal performance.In this research, a new fabrication route for W-Cu FGM was proposed, which combines the self-developed intermittent electroplating (IE method) and low-temperature solid-state sintering (LSS method)..Firstly, copper coated tungsten powders were fabricated by IE method. The influence of parameters such as stirring frequency and current density were studied. The deposition mechanism of copper coating under IE method were clarified. With the coated W powders, the sintering mode between powders transferred from W-Cu to Cu-Cu, which improves the sinterability of powders. Secondly, LSS method was used to prepare W-Cu FGM. The effect of parameters including sintering temperature and time, as well as holding time was investigated.Sintering densification mechanism of W-Cu composite was illustrated. Synergistic regulation of IE and LSS methods on the structure of W-Cu FGM was studied based on research results. This research could provide theoretical foundation and technical guidance for the fabrication of W-Cu FGM used as heat sink materials.

W-Cu梯度材料具有与陶瓷基片相匹配的低热膨胀系数和良好的导热性能，是理想的微电子封装用热沉材料 。由于W和Cu的密度、熔点相差极大，几乎不互溶，传统制备方法如熔渗法和粉末烧结法等难以对W-Cu复合材料的组分和结构进行准确调控，不易获得理想的Cu贯穿网络结构和优异的导热能力。本项目提出新的制备方法，即先采用自行研发的间歇式电沉积法制备具有核壳结构的铜包覆钨复合粉体，使粉体之间的烧结转变为Cu-Cu烧结，提高粉体的可烧结性；然后采用低温固相烧结获得具有Cu贯穿网络结构的烧结组织。拟通过研究间歇式电沉积工艺参数对包覆粉体铜镀层结构的影响，实现包覆粉体含铜量的可控，揭示间歇式电沉积机理；设计复合材料的成分梯度，探索常压和热压条件下低温固相烧结工艺，阐明固相烧结致密化机理，研究间歇式电沉积工艺参数和烧结制度与梯度材料结构和性能的关联，为制备高品质W-Cu梯度热沉材料提供理论基础和技术指导。

W-Cu梯度材料具有与陶瓷基片相匹配的低热膨胀系数和良好的导热性能，是理想的微电子封装用热沉材料 。由于W和Cu的密度、熔点相差极大，几乎不互溶，传统制备方法如熔渗法和粉末烧结法等难以对W-Cu复合材料的组分和结构进行准确调控，不易获得理想的Cu贯穿网络结构和优异的导热能力。本项目提出新的制备方法，即先采用自行研发的间歇式电沉积法制备具有核壳结构的铜包覆钨复合粉体，使粉体之间的烧结转变为Cu-Cu烧结，提高粉体的可烧结性；然后采用低温固相烧结获得具有Cu贯穿网络结构的烧结组织。拟通过研究间歇式电沉积工艺参数对包覆粉体铜镀层结构的影响，实现包覆粉体含铜量的可控，揭示间歇式电沉积机理；设计复合材料的成分梯度，探索常压和热压条件下低温固相烧结工艺，阐明固相烧结致密化机理，研究间歇式电沉积工艺参数和烧结制度与梯度材料结构和性能的关联，为制备高品质W-Cu梯度热沉材料提供理论基础和技术指导。具体结论如下：.1. 分别以焦磷酸盐体系电镀液和酸性硫酸盐体系电镀液，成功制得Cu含量可控、分散性好、镀层均匀致密、镀层厚度均匀、纯度高的包覆粉体。结果表明，除电沉积时间外，其他因素对Cu镀层表面形貌有较大影响。Cu镀层的形核和长大过程均遵循Volmer-Weber模式。.2.采用热压烧结的方法制备出Cu含量分别为20~40 wt.%的W-Cu复合材料。在1050 ℃-35 MPa-2 h的烧结条件下，W-20~40 wt.% Cu复合材料均实现致密化。随着铜含量的增加，硬度与抗弯强度降低，热导率增加。W-20 wt.% Cu的热导率达到213.82 W/(m·K)，W-30 wt.% Cu的热导率达到256.86 W/(m·K)，W-40 wt.% Cu的热导率达到274.23 W/(m·K)。.3. 在制备功能梯度材料时，选择与基板材料热膨胀系数相匹配的W-10 wt.% Cu复合材料作为封接层，选择高散热性能的W-30 wt.% Cu复合材料作为散热层，中间过渡层的成分配比分别是W-15 wt.% Cu和W-21 wt.% Cu。所制备W-Cu功能梯度材料的梯度层之间的界面结合良好；抗弯强度沿着Cu含量增加的方向呈现梯度性的减小；热导率达到227 W/(m·K)，获得了较高的导热性能。