细间距倒装芯片互连过程中焊点界面金属间化合物的形成与演化

Evolution of interfacial intermetallic compound in small solder joint of fine pitch flip chip during reflow

利用凸点间距为100μm,高度约为45μm,焊料成分为Sn-3.0Ag-0.5Cu(质量分数,%)(SAC305)的倒装芯片与树脂基板互连封装,研究芯片单侧凸点及芯片与BT基板焊点互连回流过程中界面金属间化合物(intermetalic compound,IMC)的形成和演化.结果表明,封装互连前,在芯片单侧镍焊盘界面上形成了长针状(Ni,Cu)3Sn4和薄层状Ni3P,由于反应过程中焊料基体中Cu原子的大量消耗,没有形成典型的(Cu,Ni)6Sn5.封装互连过程中,由于大量Cu原子从铜界面扩散到镍界面,促使镍焊盘界面(Ni,Cu)3Sn4逐渐转化成(Cu,Ni)6Sn5,形貌由针状转变成短棒状,反应后(Cu,Ni)6Sn5成为主要IMC层;在铜焊盘界面上,形成了一层短棒状的(Cu,Ni)6Sn5,由于从镍焊盘界面扩散过来的Ni原子对Cu3Sn生长的限制作用,反应后没有形成典型的Cu3Sn.

The flip chips with 100 μm solder pitch and 45μm stand-off height were assembled onto substrates. The solder composition is Sn-3. 0Ag-0. 5Cu( SAC305). This work studies intermetallic compound microstructure in single-pad side of solder bumps and both pad sides of solder joints during reflow of flip chip assemblies. The study shows that before assembly reflow,the long needle-shaped( Ni,Cu)3Sn4and the thin layer-shaped Ni3P appear on the Ni pad interface of chip. Due to the Cu overconsumed in the small size solder bump, the typical( Cu,Ni)6Sn5is not formed. During assembly reflow on the chip Ni pad interface,a great number of Cu atoms diffuse from Cu pad interface which can promote( Ni,Cu)3Sn4to transfer to rodshaped( Cu,Ni)6Sn5. After reflow only one thin layer of( Ni,Cu)3Sn4is remained on the interface,while the( Cu,Ni)6Sn5becomes the predominant IMC layer. On the substrate Cu pad interface,a layer of short rod-shaped( Cu,Ni)6Sn5appears on the Cu interface. Due to the limitation effect of Ni atoms on the Cu3Sn formation and growth,the typical Cu3Sn does not appear on the interface between the Cu pad and( Cu,Ni)6Sn5.