Cu@Sn核壳粉体制备及其高熔点焊缝的性能与组织演变

发布时间：2018-05-23 12:40

本文选题：Cu@Sn核壳结构 + 芯片贴装　；参考：《哈尔滨工业大学》2017年博士论文

【摘要】：电子产品高集成度和高功率化的发展趋势,推动了基于Si C、Ga N等宽禁带半导体材料的新型功率器件迅猛发展。以Si C为代表的宽禁带半导体功率器件最高可以在600℃下工作,然而能与之匹配的芯片高温连接材料却十分缺乏。过高的回流温度将造成较大的热应力,并可能破坏同一系统中其他温度敏感型器件,因此要求焊接材料最好可以在低温短时的回流条件下即可实现焊接,所得焊点能够耐受更高的服役温度。并且出于焊点热-机械可靠性的考虑,焊缝最好具有一定厚度以缓解应力集中问题。为此,本文成功制备出Cu@Sn核壳结构双金属粉,将其作为新型焊接材料引入到功率器件封装领域,能够满足第三代半导体器件对封装材料的一系列要求,提供了一种有效的芯片贴装解决方案。本文成功制备出微米级Cu@Sn核壳结构双金属粉,该粉体具有以下特征:低温回流时外表Sn镀层即可熔化并连接相邻Cu核,充足的Cu原子来源和颗粒较高的表面活性使得Sn层短时间回流即可生成具有更高熔点的Cu-Sn金属间化合物。通过Cu-Sn相变的方式实现了低温短时回流后所得焊点具有更高熔点的目的,并且焊缝厚度可以通过调整Cu@Sn金属粉的添加量而精确控制。选取1μm、5μm以及30μm三个尺寸的颗粒详细阐述了Cu粉的粒径对Sn镀层厚度以及后期焊接质量的影响,发现粒径越小,焊缝微观组织均匀一致性越好,但导电导热能力越差。总结了Cu球表面化学镀Sn过程中随着镀覆环境不同而出现的一系列镀Sn结果及其对应的形成机制。研究了不同粒径、不同镀Sn层厚度的Cu@Sn核壳金属粉以钎料膏和预置片两种形式制成的焊点微观组织和机械强度。Cu@Sn钎料膏制备简单且应用灵活,但膏体流动性差且焊缝中存在孔洞缺陷;预置片焊点组织均匀致密且机械强度高。最终确定粒径30μm的Cu球表面镀Sn层厚度为2μm时,Cu@Sn核壳颗粒以预置片的方式进行焊接得到的焊缝性能最优。确定了250℃下回流8min、16min和40min后相组成分别为Cu+Cu6Sn5、Cu+Cu6Sn5+Cu3Sn和Cu+Cu3Sn。室温下钎料膏焊点最大剪切强度仅有2.3MPa,而预置片焊点分别回流处理8min和40min后在400℃和500℃下高温剪切强度分别高达29.35MPa和18.78MPa。预置片中由于Cu核均匀存在使其具有优良的导电导热能力,平均粒径为30μm的颗粒制备的预置片其平均电阻率为6.5μΩ·cm;在30℃、150℃和250℃下平均热导率分别为154.26W·m-1·K-1、130.64W·m-1·K-1和127.99W·m-1·K-1。冷热冲击实验中发现,Cu@Sn预置片焊点会出现纵向裂纹,对焊点整体性能影响不大。进一步地将预置片应用于实际功率器件IGBT(PCG40N65SMW)与DBC的焊接并进行冷热冲击,测试冷热冲击后焊缝的Ic-Vce曲线与反向击穿电压,确定其可以满足实际功率器件对焊缝的电气要求。研究了不同Sn镀层厚度的Cu@Sn颗粒在经受差异化的高温服役条件时微观组织的演变行为。确定了Sn镀层厚度为2μm的Cu@Sn颗粒制备的焊点当Sn完全相变生成Cu6Sn5金属间化合物时,体积增大2.60%,而当Cu-Sn继续相变生成Cu3Sn金属间化合物时,体积减小5.60%。发现高温短时(450℃,1h)的服役条件下焊缝中出现了新的δ-Cu41Sn11相。确定了不同镀层厚度的Cu@Sn核壳颗粒制备的焊点经受高温服役时两种相变路径:薄镀Sn层(2μm)的,微观组织的相变发生过程依次为Cu@Sn→Cu@η-Cu6Sn5→Cu@ε-Cu3Sn→Cu@δ-Cu41Sn11→Cu@γ-phase(520℃)→Cu@β-phase(586℃),这是由于镀Sn层较薄不能完全通过相变消耗全部Cu核,焊缝始终保持核壳结构的典型特征,只在外部金属间化合物包覆层区域的相组成发生上述一系列转变;而对厚镀Sn层(≥4μm)的Cu@Sn核壳颗粒制备的焊点经受高温服役条件时,微观组织发生的相变过程依次为Cu@Sn→Cu@η-Cu6Sn5→Cu@ε-Cu3Sn→ε-Cu3Sn+δ-Cu41Sn11,最终焊缝失去核壳结构的典型特征,转而形成微观组织均匀一致的焊缝结构。
[Abstract]:The development trend of high integration and high power of electronic products has promoted the rapid development of new power devices based on Si C, Ga N wide band gap semiconductor materials. The wide band gap semiconductor power device, represented by Si C, can work at 600 degrees centigrade, but the high temperature connection material matching with it is very short. The temperature will cause large thermal stress and may destroy the other temperature sensitive devices in the same system, so it is required that the welding material can be welded under the low temperature and short reflux condition. The solder joints can withstand the higher service temperature. And the weld is best for the consideration of the welding point thermal mechanical reliability. In order to alleviate the stress concentration problem, this paper successfully prepared Cu@Sn nuclear shell structure double metal powder and introduced it as a new welding material into the field of power device encapsulation, which can satisfy a series of requirements of third generation semiconductor devices to package materials and provide an effective chip mounting solution. Rice Cu@Sn core shell structure Bimetallic Powder has the following characteristics: the surface Sn coating can melt and connect adjacent Cu nuclei at low temperature reflux. Sufficient Cu atomic source and high surface activity make the Sn layer be refluted for a short time to produce the Cu-Sn intermetallic compound with higher melting point. It is realized through the Cu-Sn phase transition. The solder joints obtained at low temperature and short reflux have a higher melting point, and the thickness of the weld can be accurately controlled by adjusting the addition of Cu@Sn metal powder. The effects of the particle size of Cu powder on the thickness of the Sn coating and the quality of the later welding are elaborated in detail. The smaller the particle size is, the microstructure of the weld is found. The weld thickness can be accurately controlled by adjusting the addition of Cu@Sn metal powder. The better the uniform uniformity of the tissue, the worse the conductive and thermal conductivity. A series of Sn results and the corresponding formation mechanism in the process of electroless Sn plating on the Cu sphere with different coating environment were summarized. The solder joints made of two forms, with different particle sizes and different thickness of Sn coating, were made with the solder paste and the preset sheet. Microstructure and mechanical strength.Cu@Sn solder paste preparation is simple and flexible, but the fluidity of the paste is poor and there is hole defect in the weld. The microstructure of the preset solder joint is uniform and dense and the mechanical strength is high. When the thickness of the Sn layer of the Cu ball surface of the Cu ball surface is 2 u m, the welding seam of the Cu@Sn core shell is welded by the preset plate. The performance is optimal. It is determined that the reflux of 8min at 250 C, the post phase composition of 16min and 40min is Cu+Cu6Sn5, and the maximum shear strength of solder paste solder joint at Cu+Cu6Sn5+Cu3Sn and Cu+Cu3Sn. at room temperature is only 2.3MPa, while the high temperature shear strength of the pre-set solder joints at 400 and 500, respectively, reaches to the 29.35MPa and 18.78MPa. preset plates at 400 and 500, respectively. The average resistivity of the prefabricated tablets prepared by the particles with an average particle size of 30 u m is 6.5 Omega cm. The average thermal conductivity at 30, 150 and 250 is found in the cold and heat shock test of 154.26W. M-1, K-1130.64W. M-1. K-1 and 127.99W M-1. K-1. at 30. There will be a longitudinal crack which has little effect on the overall performance of the solder joints. Further, the preset plate is applied to the welding of the actual power device IGBT (PCG40N65SMW) and the DBC, and the cold and heat shock is carried out. The Ic-Vce curve and reverse breakdown voltage of the weld after the cold and hot impact are tested, and the electrical requirements of the actual power devices for the weld are determined. The microstructure evolution behavior of Cu@Sn particles with different Sn coating thickness under different high temperature service conditions is determined. The solder joints prepared by Cu@Sn particles with the thickness of Sn coating are 2 mu m, when the Sn complete phase transition produces Cu6Sn5 intermetallic compounds, the volume increases by 2.60%, and the volume of the Cu-Sn in the continuous phase transition to the Cu3Sn intermetallic compound. 5.60%. found a new delta -Cu41Sn11 phase in the weld seam under the service condition of high temperature and short time (450, 1H). The two phase transition paths of the solder joints prepared by the Cu@Sn core particles with different coating thickness were determined by the thin plating Sn layer (2 mu m). The phase change process of the microstructure was Cu@Sn, Cu@, -Cu6Sn5, Cu@ epsilon -Cu3Sn. Cu@ Delta -Cu41Sn11 to Cu@ gamma -phase (520 C) - Cu@ beta -phase (586 C), this is because the plating Sn layer is thin and can not completely consume all Cu core through phase transition, and the weld always keeps the typical characteristics of the core and shell structure, only the phase composition of the coating area of the outer intermetallic compound occurs, and the Cu@Sn nucleus of the thick plating Sn layer (> 4 mu m). When the solder joints prepared by shell particles are subjected to high temperature service conditions, the phase transformation process of microstructure is Cu@Sn, Cu@, -Cu6Sn5, Cu@ e -Cu3Sn and epsilon -Cu3Sn+ Delta -Cu41Sn11, which eventually loses the typical characteristics of the core shell structure and turns to a uniform and uniform microstructure of the microstructure.
【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TG42

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