芯片烧毁失效分析

[{"attributes":{"color":"var(--weui-LINK)"},"insert":"半导体工程师"},{"insert":" "},{"attributes":{"color":"var(--weui-FG-2)"},"insert":"2023-04-21 09:15"},{"insert":" "},{"attributes":{"color":"var(--weui-FG-2)"},"insert":"发表于北京"},{"insert":"\n"},{"attributes":{"bold":true},"insert":"引言"},{"attributes":{"align":"justify"},"insert":"\n"},{"insert":"   大多数电子元器件失效的主要原因为元器件内部电路与参考地之间存在不同电位形成短路状况，产生过电流而造成元器件损坏，即EOS损伤。元器件的结构设计、生产工艺、储存运输等都有可能致其产生EOS失效，且难以从表面观察出来。"},{"attributes":{"align":"justify"},"insert":"\n\n"},{"insert":"   本文以芯片烧毁失效为例，通过无损检测、缺陷定位、开封检查、切片分析等方法，分析芯片失效原因与机理，并提出改善建议。"},{"attributes":{"align":"justify"},"insert":"\n\n"},{"attributes":{"bold":true},"insert":"一、案例背景"},{"attributes":{"align":"justify"},"insert":"\n"},{"insert":"   终端用户反馈机器有SIM卡无信号，无法连接网络。该机器生产后测试功能正常，在仓库放置一段时间后失效，初步分析是PA物料本体不良，异常是PA的供电pin损坏。现进行测试分析，查找其失效原因。"},{"attributes":{"align":"justify"},"insert":"\n\n"},{"attributes":{"bold":true},"insert":"二、分析过程"},{"attributes":{"align":"justify"},"insert":"\n\n"},{"attributes":{"bold":true},"insert":"1.失效现象确认"},{"attributes":{"align":"justify"},"insert":"\n"},{"insert":"   测试电容的阻值，可以确认其PCBA上PA芯片的失效现象，因此对失效样品电容两端的阻值进行测试，确认失效现象。"},{"attributes":{"align":"justify"},"insert":"\n\n"},{"insert":"   测试结果显示：失效样品电容两端的阻值接近短路，与功能正常PCBA电容两端阻值存在明显差异，说明失效PCBA芯片短路失效。"},{"attributes":{"align":"justify"},"insert":"\n\n\n"},{"attributes":{"bold":true},"insert":"2.外观检查"},{"attributes":{"align":"justify"},"insert":"\n"},{"insert":"   为确认失效PCBA上PA芯片外观是否存在明显异常，去除失效PCBA上PA芯片外围的屏蔽盒后对其进行外观检查。"},{"attributes":{"align":"justify"},"insert":"\n\n"},{"insert":"   检查结果显示：未发现失效PCBA上PA芯片外观存在裂纹、破损、金属迁移等异常现象。"},{"attributes":{"align":"justify"},"insert":"\n\n\n"},{"attributes":{"bold":true},"insert":"3.X-ray检查"},{"attributes":{"align":"justify"},"insert":"\n"},{"insert":"   为确认失效芯片内部是否存在明显异常，对失效芯片进行X-ray检查。"},{"attributes":{"align":"justify"},"insert":"\n\n"},{"insert":"   检查结果显示：失效芯片底部焊盘都存在焊接不饱满的现象，芯片底部焊盘是起散热作用的，底部焊盘不饱满可能会引起芯片散热不良；失效芯片内部结构与功能正常芯片内部结构一致，未发现明显异常。"},{"attributes":{"align":"justify"},"insert":"\n"},{"attributes":{"align":"center"},"insert":"\n"},{"attributes":{"color":"#4e4d4d"},"insert":"图1.失效芯片X-ray检查形貌"},{"attributes":{"align":"center"},"insert":"\n"},{"attributes":{"align":"justify"},"insert":"\n\n"},{"attributes":{"bold":true},"insert":"4.超声扫描"},{"attributes":{"align":"justify"},"insert":"\n"},{"insert":"   为确认失效芯片内部是否存在明显的分层现象，对失效芯片进行超声扫描。"},{"attributes":{"align":"justify"},"insert":"\n\n"},{"insert":"   扫描结果显示：对比未使用芯片，失效芯片内部都发现有分层现象（右侧为未使用芯片声扫图）。"},{"attributes":{"align":"justify"},"insert":"\n"},{"attributes":{"align":"center"},"insert":"\n"},{"insert":"图2.失效芯片超声扫描形貌"},{"attributes":{"align":"center"},"insert":"\n"},{"attributes":{"align":"justify"},"insert":"\n\n"},{"attributes":{"bold":true},"insert":"5.缺陷定位"},{"attributes":{"align":"justify"},"insert":"\n"},{"insert":"   前面分析可知：失效芯片存在短路现象，为确认芯片内部的短路位置，利用Thermal EMMI热点定位技术对多个失效芯片进行定位分析。"},{"attributes":{"align":"justify"},"insert":"\n\n"},{"attributes":{"bold":true},"insert":"定位结果显示："},{"attributes":{"align":"justify"},"insert":"\n"},{"insert":"   （1）失效芯片上均发现异常热点，热点位置都位于同一个位置，说明失效芯片短路位置为同一个位置；"},{"attributes":{"align":"justify"},"insert":"\n\n"},{"insert":"   （2）通过对比X-ray图，推测失效芯片都为内部同一个芯片有短路现象。"},{"attributes":{"align":"justify"},"insert":"\n"},{"attributes":{"align":"center"},"insert":"\n"},{"insert":"图3.失效芯片热点定位形貌"},{"attributes":{"align":"center"},"insert":"\n"},{"insert":"  "},{"attributes":{"align":"center"},"insert":"\n\n"},{"insert":"图4.X-ray与热点定位对比图"},{"attributes":{"align":"center"},"insert":"\n"},{"attributes":{"align":"justify"},"insert":"\n\n"},{"attributes":{"bold":true},"insert":"6.CT扫描"},{"attributes":{"align":"justify"},"insert":"\n"},{"insert":"   为确认失效芯片内部短路位置是否存在明显异常，切割下失效芯片进行CT扫描。"},{"attributes":{"align":"justify"},"insert":"\n\n"},{"insert":"   扫描结果显示：失效芯片热点位置的芯片内部都发现疑似烧毁现象，芯片内部走线、载板都未发现明显异常，但部分失效芯片在疑似烧毁位置都存在银浆缺失的现象。"},{"attributes":{"align":"justify"},"insert":"\n"},{"attributes":{"align":"center"},"insert":"\n"},{"attributes":{"color":"#4e4d4d"},"insert":"图5.失效芯片CT扫描形貌"},{"attributes":{"align":"center"},"insert":"\n"},{"attributes":{"color":"#4e4d4d"},"insert":" "},{"attributes":{"align":"center"},"insert":"\n\n"},{"attributes":{"color":"#4e4d4d"},"insert":"图6.未使用芯片CT扫描形貌"},{"attributes":{"align":"center"},"insert":"\n"},{"attributes":{"align":"justify"},"insert":"\n\n"},{"attributes":{"bold":true},"insert":"7.开封观察"},{"attributes":{"align":"justify"},"insert":"\n"},{"insert":"   为确认芯片内部是否存在明显烧毁的现象，对多个失效芯片进行开封观察。"},{"attributes":{"align":"justify"},"insert":"\n\n"},{"attributes":{"bold":true},"insert":"观察结果显示："},{"attributes":{"align":"justify"},"insert":"\n"},{"insert":"   （1）失效芯片内部都发现有烧毁现象，烧毁位置也一致，说明为同一种失效模式，为EOS烧毁；"},{"attributes":{"align":"justify"},"insert":"\n\n"},{"insert":"   （2）失效芯片内部其他功能芯片未发现烧毁现象，内部载板也未发现明显的金属残留。"},{"attributes":{"align":"justify"},"insert":"\n"},{"attributes":{"align":"center"},"insert":"\n"},{"attributes":{"color":"#4e4d4d"},"insert":"图7.失效芯片开封后形貌"},{"attributes":{"align":"center"},"insert":"\n"},{"attributes":{"color":"#4e4d4d"},"insert":"  "},{"attributes":{"align":"center"},"insert":"\n\n"},{"attributes":{"color":"#4e4d4d"},"insert":"图8.未使用芯片开封后形貌"},{"attributes":{"align":"center"},"insert":"\n"},{"attributes":{"align":"justify"},"insert":"\n\n"},{"attributes":{"bold":true},"insert":"8.切片分析"},{"attributes":{"align":"justify"},"insert":"\n"},{"insert":"   为确认失效芯片内部是否存在金属迁移或其他异常，对部分失效芯片、功能正常芯片、未使用芯片进行切片分析，切片到失效芯片烧毁位置。"},{"attributes":{"align":"justify"},"insert":"\n\n"},{"attributes":{"bold":true},"insert":"切片结果显示："},{"attributes":{"align":"justify"},"insert":"\n"},{"insert":"   （1）失效芯片内部有芯片烧毁，烧毁位置伴随着裂纹及树脂层碳化，应是烧毁导致的，烧毁位置一致，因此都属于同一种失效模式，属于EOS烧毁；"},{"attributes":{"align":"justify"},"insert":"\n\n"},{"insert":"   （2）失效芯片烧毁区域底部都存在银浆填充存在缺失；功能正常芯片该区域同样存在银浆少量缺失的现象，缺失主要集中在GND引脚下方，失效芯片烧毁区域下方填充良好；银浆缺失可能会导致该区域热量集中，无法散热，最终导致芯片EOS烧毁。"},{"attributes":{"align":"justify"},"insert":"\n\n"},{"attributes":{"bold":true},"insert":"   以上分析说明："},{"insert":"芯片失效是由于芯片同一位置出现了EOS烧毁导致的，且烧毁区域底部银浆都有缺失的现象，因此芯片内部出现EOS烧毁的可能原因有①外部存在过电应力；②底部银浆缺失导致芯片散热不良，该区域热量累积，最终导致芯片EOS烧毁失效。"},{"attributes":{"align":"justify"},"insert":"\n"},{"attributes":{"align":"center"},"insert":"\n"},{"attributes":{"color":"#4e4d4d"},"insert":"图9.失效芯片切片形貌"},{"attributes":{"align":"center"},"insert":"\n"},{"attributes":{"align":"justify"},"insert":"\n"},{"attributes":{"align":"center"},"insert":"\n"},{"attributes":{"color":"#4e4d4d"},"insert":"图10.功能正常失效芯片、未使用芯片切片形貌"},{"attributes":{"align":"center"},"insert":"\n"},{"attributes":{"align":"justify"},"insert":"\n\n"},{"attributes":{"bold":true},"insert":"9.电应力排查"},{"attributes":{"align":"justify"},"insert":"\n"},{"insert":"   前面分析可知：芯片内部因出现了EOS烧毁导致的失效，且烧毁的位置为同一位置，因此对PCBA上电应力进行排查分析。"},{"attributes":{"align":"justify"},"insert":"\n\n"},{"insert":"   （1）芯片烧毁位置边沿的两个键合丝之间，通过CT扫描图可知最右侧键合连接到了载板，因此应属于芯片的GND，另外跟键合芯片内部通孔、走线最终连接到外围的VCC2-2，而VCC2-2的供电端为VAP-VCC2；"},{"attributes":{"align":"justify"},"insert":"\n\n"},{"insert":"   （2）对失效PCBA更换未使用芯片后测试VAP-VCC2电压，打开4G移动数据及打开WIFI未发现明显异常波形，且PCBA工作正常，因此芯片是由于底部银浆缺失，引起的局部散热不良，最终导致EOS烧毁的可能性较大。"},{"attributes":{"align":"justify"},"insert":"\n"},{"attributes":{"align":"center"},"insert":"\n\n"},{"attributes":{"color":"#4e4d4d"},"insert":"图11.电应力来源示意图"},{"attributes":{"align":"center"},"insert":"\n\n\n"},{"attributes":{"color":"#4e4d4d"},"insert":"图12.失效PCBA更换未使用芯片后VAP-VCC2引脚电压"},{"attributes":{"align":"center"},"insert":"\n"},{"attributes":{"align":"justify"},"insert":"\n"},{"attributes":{"bold":true},"insert":"三、总结分析"},{"attributes":{"align":"justify"},"insert":"\n"},{"insert":"   通过测试发现失效芯片内部存在短路现象；外观检查未发现失效芯片表面存在明显的破损、裂纹、金属迁移等异常现象；"},{"attributes":{"align":"justify"},"insert":"\n\n"},{"insert":"   X-ray检查未发现失效芯片内部结构存在明显异常，但底部焊接焊盘存在焊接不饱满、不完整的现象，底部焊盘是起散热作用的，焊接不饱满，会导致芯片不能有效散热；"},{"attributes":{"align":"justify"},"insert":"\n\n"},{"insert":"   超声扫描确认失效芯片都存在分层的现象，而后续的分析可知失效芯片表面都存在烧毁现象，因此分层可能是由于芯片烧毁、树脂层碳化引起的；"},{"attributes":{"align":"justify"},"insert":"\n\n"},{"insert":"   通过缺陷定位，确认失效芯片内部同一个功能芯片失效导致；通过CT扫描确认该功能芯片存在疑似烧毁的现象，且在烧毁区域都发现芯片银浆粘接存在缺失；"},{"attributes":{"align":"justify"},"insert":"\n\n"},{"insert":"   通过开封观察确认失效芯片内部存在烧毁现象，烧毁位置位于功能芯片同一个位置，因此应属于同一种失效模式，通过烧毁形貌判断应属于EOS烧毁失效；"},{"attributes":{"align":"justify"},"insert":"\n\n"},{"insert":"   通过切片分析发现失效芯片都为同一个区域存在烧毁导致的失效，通过切片确认多个失效芯片烧毁区域都存在银浆填充缺失的现象，未使用芯片银浆填充良好。"},{"attributes":{"align":"justify"},"insert":"\n\n"},{"insert":"   通过电应力排查可知，失效PCBA更换正常芯片后，PCBA正常工作，打开4G移动数据时VAP-VCC2供电电压未发现异常，可排除因过电应力导致的芯片失效。"},{"attributes":{"align":"justify"},"insert":"\n\n"},{"insert":"   此次失效芯片为大功率发热芯片，本身功耗大，内部烧毁晶元位置专门做了基板通孔散热处理，银浆缺失将导致热量分布不均匀，局部热量累积，因此芯片内部同一区域出现EOS烧毁的可能原因有："},{"attributes":{"align":"justify"},"insert":"\n"},{"insert":"   ①外存在过电应力，通过电应力排查，未发现过压现象，可排除因过电应力导致的芯片失效；"},{"attributes":{"align":"justify"},"insert":"\n"},{"insert":"   ②热击穿导致芯片失效，通过切片发现失效芯片都存在银浆缺失现象，这将导致芯片工作时热量累积、散热不良，最终出现烧毁。"},{"attributes":{"align":"justify"},"insert":"\n\n"},{"attributes":{"bold":true},"insert":"四、结论与建议"},{"attributes":{"align":"justify"},"insert":"\n"},{"insert":"   综上所述，芯片失效直接原因为内部晶圆出现EOS烧毁，而晶圆出现EOS烧毁的原因为内部银浆缺失，引起芯片内部局部散热不良，热量累积最终导致的烧毁。"},{"attributes":{"align":"justify"},"insert":"\n"},{"attributes":{"italic":true,"bold":true},"insert":"   建议："},{"insert":"（1）加强芯片的来料检验；"},{"attributes":{"align":"justify"},"insert":"\n"},{"insert":"   （2）改进芯片焊接工艺，使芯片底部有效散热。"},{"attributes":{"align":"justify"},"insert":"\n"},{"insert":"来源于电子制造资讯站 ，作者美信检测\n\n"}]