重构晶圆封装过程翘曲的数值模拟

Huaibin Zhen, Zhao Wei, Gu Xiao, Chen Dong, Che Haijie, Xu Hong, K. Tan
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引用次数: 0

摘要

目前,一般的扇出封装一般采用成型工艺,使用环氧成型化合物(EMC)材料完成晶圆的重构,但对小尺寸芯片和高扇出比封装类型不友好。为了解决小尺寸和高扇出比等扇出封装的问题,捷胜先进封装有限公司推出了一种新型封装材料,扇出封装中的晶圆重构工艺是通过层压工艺、流平工艺和硅支撑工艺三个基本工艺来完成的。但固化后也面临翘曲问题。过度翘曲对随后的RDL制造,中期测试和过程自动化提出了重大挑战。本文在合理假设实际工艺的基础上,采用有限元方法研究了芯片厚度、扇出面积、封装材料性能和支撑硅片对固化后翘曲的影响。层压过程是气囊将封装材料缓慢挤压到扇出区,气囊的压力可以通过气体的进出来调节。晶圆片经过层压工艺后表面不平整,需要通过找平工艺进行找平。整平工艺是用厚重、适量的钢板使凹凸不平的表面平整。由于封装材料较软,因此为了增强结构的强度,需要对硅片进行支撑。本文将固化过程分为两个过程:预固化过程和后固化过程。预固化的主要作用是使封装材料成型,然后后固化可以使封装材料、芯片和支撑硅有更好的结合。层压、流平和硅支撑过程不涉及更高的温度,因此可以假设重构晶片没有残余应力和翘曲。为了节省计算机资源,缩短验证周期,在保证精度的前提下,对仿真的几何模型进行了简化。通过有限元法探索结构特性和材料特性对晶圆翘曲的影响,根据实际情况确定参数的选择,以满足结构的可制造性。结果表明,随着封装材料厚度的增加,晶圆翘曲量逐渐增大,而低模量和小CTE的封装材料可以改善翘曲性能。高模量、较厚的支撑硅对减小翘曲有显著效果,较大的CTE支撑硅也能有效减小晶圆翘曲,因为较大的CTE支撑硅减少了与封装CTE的不匹配程度。较薄的晶片和较高的扇出面积往往会增加再造晶圆的翘曲。对包装结构翘曲和材料性能翘曲的研究可以为产品设计和评价阶段的翘曲预测和改进提供理论依据。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Numerical simulation on the warpage of reconstructed wafer during encapsulation process
At present, the general fan-out package generally uses the molding process and uses epoxy molding compound (EMC) material to complete the reconstruction of wafer, but it is not friendly to small-size chips and high fan-out ratio packaging types. In order to solve the problem of small size and high fan-out ratio and other fan-out packaging, JCET ADVANCED PACKAGING CO., LTD. introduced a new kind of encapsulation material, and the wafer reconstruction process in the fan out package is accomplished through three basic processes, such as the lamination process, the leveling process and the silicon support process. However, it also faces warpage problems after curing. Excessive warpage poses a significant challenge to subsequent RDL fabrication, mid-testing and process automation. In this paper, the actual process is reasonably assumed and finite element methods are used to study the effects of chip thickness, fan-out area, the encapsulation material properties and support silicon wafer on the warpage after curing. The lamination process is that an airbag slowly squeezes the encapsulation material into the fan-out area, and the pressure of the airbag can be adjusted by the gas in and out. The wafer surface is uneven after the lamination process, so it needs to be leveled by the leveling process. Leveling process is to make the uneven surface smooth by a heavy and proper amount of steel plate. The encapsulation material is soft, so it is necessary to support the silicon wafer in order to enhance the strength of the structure. In this paper, the curing process is divided into two processes: pre curing process and post curing process. The main function of pre curing is to shape the encapsulation material, and then post curing can make the encapsulation material, chip and supporting silicon have a better combination. The lamination, leveling, and silicon support processes do not involve higher temperatures, so it can be assumed that the reconstructed wafer has no residual stress and warpage. In order to save computer resources and shorten the verification period, the geometric model of simulation is simplified under the condition of ensuring accuracy. Through the finite element method to explore the influence of structural characteristics and material characteristics on the wafer warpage, the selection of parameters is determined according to the actual situation, so as to meet the manufacturability of the structure. The results indicate that with the increase of the thickness of the encapsulated material the encapsulation, wafer warpage is gradually increasing, while the encapsulation material with low modulus and small CTE can improve warpage performance. High modulus, thicker support silicon has a significant effect on reducing warpage, and larger CTE support silicon can also effectively reduce wafer warpage because the larger CTE support silicon reduces the degree of mismatch with the encapsulation CTE. Thinner chips and high fan-out areas tend to increase the warpage of the reconstituted wafer. The study of warpage of package structure and material properties can provide theoretical basis for predicting and improving warpage during the design and evaluation phase of the product.
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