Reliability Design of Conductive Adhesive Connection in Electronic Packages

利用各向异性导电胶膜（ACF）和导电树脂的电子封装用导电胶连接，因其易于小型化、低温下的制造工艺和不含铅等优点，有望逐年增加，但目前的可靠性低于可靠性技术已发展起来的焊接。发展电子封装胶接可靠性的评估和设计技术，对促进电子封装胶接技术的发展具有重要意义。倒装芯片通常与其它表面贴装器件一起使用，通过焊点与电路板连接。在回流焊过程中，电路板被加热到150℃至200℃的范围内进行预热，并在240℃至245℃的范围内达到峰值温度。在回流焊制程中，部分黏着式覆晶会发生断裂或不连接的现象，本研究提出一种新的覆晶设计技术，利用活性碳纤维（ACF）来对抗回流焊的敏感度测试。首先，扩散系数，和亨利的低系数进行了测量，然后进行吸湿的有限元分析，以估计在回流焊过程中在大气中吸湿后，在倒装芯片中引起的蒸汽压力。将由估计的蒸气压引起的倒装芯片中的假定裂纹周围的应力强度因子与ACF和组成部件的材料（铝端子、铜端子或Si芯片）之间的界面的分层韧性进行比较。估计的临界吸收时间，导致分层在回流焊过程中与实验结果吻合良好。

Conductive adhesive connection for electronic packaging using anisotropic conductive adhesive film (ACF) and conductive resin are expected to increase year after year due to its easiness for downsizing, manufacturing process under low temperature and including no lead and so on. However, the reliability of adhesive connection is currently lower than that of soldering which has the developed reliability technologies. Developing the evaluation and the design technique for the reliability of adhesively connected electronic packages is very important for the promotion of the adhesive connection technique for electronic packages.Flip chips are often used with other surface mount devices, and are connected with a circuit board using solder joints. During a solder reflow process, a circuit board is heated to the range from 150℃ to 200℃ for the pre-heating, and reached to the peak temperature around, the range from 240℃ to 245℃. During the solder reflow process, some flip chip using adhesive connection are broken or unconnected.In this study, we developed a new design technique for a flip chip using the ACF against the solder reflow sensitivity test. At first, the coefficient of diffusion, and Henry's low coefficient were measured, then the finite element analysis of the moisture absorption was performed to estimate the vapor pressure induced in a flip chip during solder reflow process after moisture absorption in an atmosphere. The stress intensity factors around assumed cracks in a flip chip caused by the estimated vapor pressure were compared with the delamination toughness of an interface between the ACF and the material of a component part (Aluminum terminal, Cu terminal or Si chip). Estimated critical absorption time that causes the delamination during the solder reflow process corresponds well with experimental result.