Kim Kyung-Yeol, Myung Woo-Ram, Jeong Haksan, Sung Yong-Gue, Jung Seung-Boo
School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon-Si, 440-746, Korea.
SKKU Advanced Institute of Nanotechnology (SAINT), Sungkyunkwan University, Suwon-Si, 440-746, Korea.
J Nanosci Nanotechnol. 2018 Sep 1;18(9):6162-6166. doi: 10.1166/jnn.2018.15623.
The ball-grid array (BGA) is widely used to reduce component size and it had advantages such as high I/O pins and fine pitch. Typical Sn-Ag-Cu (SAC) solder alloys are used for formation of BGA because SAC solder has excellent characteristics among lead-free solders. However, the electronic components assembled by SAC solder were easily damaged by heat during manufacture process because SAC solder had high melting point of 220 °C. To prevent these thermal damages, SAC305 BGA component assembled by Sn-58Bi solder paste has been studied because Sn-58Bi solder had low melting point of 139 °C. In generally, Sn-58Bi solder was improved by additional elements or polymer such as epoxy because Sn-58Bi had a brittle property. However, the epoxy Sn-58Bi solder did not guaranteed high environmental reliability such as high-temperature high-humidity (HTHH) test. Thus, we evaluated the shear strength of solder joints assembled by SAC305 BGA components with Sn-58Bi solder paste and epoxy Sn-58Bi solder paste. The shear strength of solder joints was evaluated by die shear test after HTHH test at the 85 °C/85% RH conditions. The Cu6Sn5 intermetallic-compound (IMC) at the interface of solder joints was observed by scanning electron microscope (SEM). The IMC thickness of Sn-58Bi solder joints was smaller than that of epoxy Sn-58Bi solder. The shear strength was improved up to 20% by epoxy addition. The shear strength of epoxy Sn-58Bi solder joints dramatically decreased after HTHH test for 100 h.
球栅阵列（BGA）被广泛用于减小元件尺寸，它具有诸如高输入输出引脚数和细间距等优点。典型的锡银铜（SAC）焊料合金用于形成BGA，因为SAC焊料在无铅焊料中具有优异的特性。然而，在制造过程中，由SAC焊料组装的电子元件容易因热而损坏，因为SAC焊料的熔点高达220℃。为了防止这些热损伤，已经对由Sn-58Bi焊膏组装的SAC305 BGA元件进行了研究，因为Sn-58Bi焊料的熔点低至139℃。一般来说，Sn-58Bi焊料通过添加诸如环氧树脂等附加元素或聚合物来改进，因为Sn-58Bi具有脆性。然而，环氧Sn-58Bi焊料不能保证高环境可靠性，如高温高湿（HTHH）环境下的可靠性。因此，我们评估了用Sn-58Bi焊膏和环氧Sn-58Bi焊膏组装的SAC305 BGA元件焊点的剪切强度。在85℃/85%相对湿度条件下进行高温高湿试验后，通过芯片剪切试验评估焊点的剪切强度。通过扫描电子显微镜（SEM）观察焊点界面处的Cu6Sn5金属间化合物（IMC）。Sn-58Bi焊点的IMC厚度小于环氧Sn-58Bi焊点的IMC厚度。添加环氧树脂后，剪切强度提高了20%。环氧Sn-58Bi焊点在高温高湿试验100小时后，剪切强度显著下降。
