激光软钎焊焊点成型控制与质量评价

发布时间：2018-07-20 18:26

【摘要】：激光加工具有非接触加热、加热对象快速升温、不同材质升温效果不同的特性,对单个焊点加工效率高于传统加工方法。而激光由于加热效果明显受到激光器参数(波长、频率等)的影响,这为激光加工引入不稳定因素。激光软钎焊作为新兴的焊接方式,具有高效的优点,也伴随许多实际问题。激光对焊点的加热效果受到材料特性得影响,不同材质对激光的吸收率不同,这也引入了焊接效果难以控制的风险。焊接过程时间短,在过程中产生的缺陷如下:助焊剂裂解和炭化,润湿不良,内部融合不充分,焊接过程不平稳,这些缺陷都会影响到焊点质量。因此,研究制订能消除上述缺陷的工艺方案,对企业提高生产效率具有现实意义。此外,由于激光加工尚未在电子组装领域广泛应用,对焊点的成型质量的评价工作不完善,因此,企业清晰了解到激光软钎焊和传统方式下的焊点质量的差异性,对于开发激光加工设备也具有重大的帮助。针对生产过程中的典型焊接缺陷进行观察,归纳出四种典型的缺陷形式,并对其产生机理进行分析。烧损现象主要出现在焊点表面或焊点附近的PCB基材上,和助焊剂的烧损有较大关系;送锡过程的刚性碰撞现象,和工艺曲线中的峰值温度和时间的配合关系有关;内部气孔的产生,和助焊剂受热后的剧烈运动以及母材情况有关;焊点内部及表面缩孔现象,和冷却过程的速率过快有关。针对现象分析产生机理,结合机理提出了相应的工艺改进方案,成功实现对工艺区间的优化并消除了上述四种缺陷,顺利获得了外观良好、内部充分融合的通孔插装焊点,此种工艺研究方式和方法对企业具有较大的指导意义。此外,多数企业尚未对激光软钎焊点的服役性能提出较为系统的评价,业内对激光焊的质量评价尚未形成标准化体系。本课题中,对焊点形貌和力学性能进行观察发现激光焊和波峰焊的焊点IMC形貌差异较大,激光焊点具有明显针状特性,对于提升力学性能很有帮助。二者断裂方式有较大差异,波峰焊主要沿引脚方向开裂,激光焊点主要在孔壁处开裂。对焊点在环境试验中的性能变化进行观察,发现热冲击后激光焊点IMC形貌针状消失,趋于平滑,高温高湿条件明显促进IMC生长。每种试验条件下,激光焊点的力学性能均优于波峰焊点,呈现出明显优势。通过上述两种试验,让企业对插装焊点的激光加工效果获得清晰的认知,也为提升优化焊点服役能力的工作做好理论铺垫,同时为焊接质量的评价体系构建提供数据参考。
[Abstract]:Laser machining has the characteristics of non-contact heating, rapid heating of heating objects and different heating effects of different materials. The processing efficiency of single solder joint is higher than that of traditional processing methods. The laser heating effect is obviously affected by the laser parameters (wavelength frequency etc.) which introduces unstable factors for laser processing. As a new welding method, laser soldering has the advantages of high efficiency and many practical problems. The effect of laser heating on the solder joint is affected by the properties of the material, and the absorptivity of the laser is different with different materials, which also leads to the risk that the welding effect is difficult to control. The defects in the welding process are as follows: flux cracking and carbonization, poor wetting, inadequate internal fusion and unsteady welding process, all of which will affect the quality of solder joint. Therefore, it is of practical significance for enterprises to improve production efficiency by studying the process scheme which can eliminate the above defects. In addition, because laser processing has not been widely used in the field of electronic assembly and the evaluation of the forming quality of butt joint is not perfect, enterprises clearly understand the difference between laser soft brazing and traditional solder joint quality. It is also of great help to the development of laser processing equipment. Based on the observation of typical welding defects in production process, four typical defects were concluded and the mechanism of their formation was analyzed. The phenomenon of burning loss mainly occurs on the surface of solder joint or on PCB substrate near solder joint, which is related to the burning loss of flux, and the rigid collision phenomenon of tin feeding process is related to the coordination of peak temperature and time in the process curve. The formation of internal pores is related to the violent movement of flux after heating and the phenomenon of shrinkage of solder joints and surface, which is related to the rate of cooling process. According to the mechanism of phenomenon analysis and combining with the mechanism, the corresponding process improvement scheme is put forward. The process interval is optimized and the four defects mentioned above are eliminated successfully. The solder joint with good appearance and full internal fusion is obtained successfully. This process research method and method have great guiding significance to the enterprise. In addition, most enterprises have not yet proposed a systematic evaluation of the service performance of laser soldering joints, and a standardized system has not been formed for the quality evaluation of laser soldering in the industry. In this paper, the morphology and mechanical properties of solder joint were observed. It was found that the IMC morphology of laser welding and wave welding were different, the laser solder joint had obvious needle-like characteristics, which was helpful to improve the mechanical properties. There is a great difference in fracture mode between them. The wave peak welding mainly cracks along the pin direction, and the laser solder joint cracks mainly at the hole wall. The changes of the properties of solder joints in environmental tests were observed. It was found that the morphology of laser welded joint IMC disappeared after thermal shock and tended to smooth. The growth of IMC was promoted by high temperature and high humidity. Under each test condition, the mechanical properties of laser solder joint are better than that of wave peak solder joint, showing obvious advantages. Through the above two kinds of experiments, the enterprises can get a clear understanding of the laser processing effect of the intercalation solder joint, and also make a good theoretical foundation for improving the service ability of the solder joint, and provide the data reference for the construction of the welding quality evaluation system at the same time.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN05

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