Impact response of gradient CNT-reinforced epoxy encapsulating materials with a printed circuit board

The encapsulation process is an effective method to protect electronic components from the threat of the external environment. However, traditional encapsulating materials are brittle and easily crack due to their low impact strength. Therefore, it is necessary to toughen encapsulating materials. The gradient structure can effectively improve the performance of materials but is not yet used in the field of encapsulation. This study prepared several homogeneous and gradient materials for experimentation, including epoxy plates with different carbon nanotube (CNT) distributions, such as "EP" (no CNT), "X" (a high CNT content in the top and bottom and a low CNT content in the middle), "V" (a CNT content that gradually decreases from top to bottom), and "?" (contrary to "V"), and epoxy plates encapsulating a printed circuit board (PCB), such as "V-P" (an "V" epoxy gradient with a PCB). The quasistatic tensile tests and dynamic impact tests show that the tensile and impact strengths of the homogeneous composites with 0.7 wt% CNT are the highest. The drop-weight tests show that regardless of the inclusion of a PCB, gradient materials have better impact strength and energy absorption than pure epoxy materials. In particular, among the gradient plates without a PCB, the impact strength and critical failure energy of the "?-5" plate ("?" with five layers) are the highest, 125% and 8 times higher than those of the pure epoxy ("EP") plate. Among the plates encapsulating PCBs, the impact strength and critical failure energy of the "V-5-P" plate are the highest, with values 40% and 15.8% higher than those of the "EP-P" plate. The more continuous the CNT distribution is, the higher the impact strength of the material. These results provide feasibility for the application of gradient materials in the field of encapsulation and provide a reference for encapsulation design.