弯曲应力状况下微型BGA封装可靠性比较

Comparative Research of Micro-BGA Reliability Under Bending Stress

文中采用传统的表面贴装技术进行焊接,研讨μBGA的PCB装配及可靠性。弯曲循环试验(1000με～-1000με),用不同的热因数(Q_η)回流,研究μBGA、PBGA和CBGA封装的焊点疲劳失效问题。确定液相线上时间,测定温度,μBGA封装的疲劳寿命首先增大,接着随加热因数的增加而下降。当Q_η接近500s·℃时,出现寿命最大值。最佳Q_η范围在300 s·℃～750s·℃之间,此范围如果装配是在氮气氛中回流,μBGA封装的寿命大于4 500个循环。采用扫描电子显微镜(SEM),来检查μBGA和PBGA封装在所有加热因数状况下焊点的失效。每个断裂接近并平行于PCB焊盘,在μBGA封装中裂纹总是出现在焊接点与PCB焊盘连接的尖角点,接着在Ni_3Sn_4金属间化合物(IMC)层和焊料之间延伸。CBGA封装可靠性试验中,失效为剥离现象,发生于陶瓷基体和金属化焊盘之间的界面处。

Assembly and reliability of the μ BGA＇s PCB, which is soldered by conventional surface mount technology, has been studied used to investigate the fatigue failure of solder joints of μ BGA, PBGA, and CBGA packages reflowed with different heating factors （Q η ）, defined as the integral of the mea- sured temperature over the dwell time above liquidus （ 183 ℃ ）. The fatigue ligetime of the μ BGA assemblies firstly increases and then decreases with increasing heating factor. The greatest lifetime happens while Qη is near 500s·℃. The optimal Qη range is between 300s·℃ and 750s·℃. In this range, the lifetime of the μBGA assembly is greater than 4 500 cycles if the assemblies are reflowed in nitrogen ambient. SEM micrographs reveal that both la BGA and PBGA assemblies fail in the solder joint at all heating factors. All fractures are near and parallel to the PCB pad. In the μ BGA assemblies cracks always initiate at the point of the acute angle where the solder joint joins the PCB pad, and then propagate in the section between the Ni3Sn4 intermetallic compound （IMC） layer and the bulk solder. In the CBGA assembly reliability test, the failures are in the form of delamination, at the interface between the ceramic base and metallization pad.