Development of an apparatus for measuring normal adhesion force during TPU injection molding process

In integrated circuit (IC) packaging encapsulation, epoxy molding compound (EMC) adheres to mold surface after curing process. This phenomenon is called mold adhesion effect and it happens not only to thermosetting material but also to thermoplastic material. In injection molding process, mold adhesion phenomenon affects demolding process seriously. In order to decrease adhesive force between mold surface and product, release agent was usually applied to improve the adhesion problem, but the mold release agent will make the de-mold efficiency poor and possible flow marks on product surface if the release agent was not applied uniformly. In addition, the design of ejection mechanism will be tougher for separating product from mold surface if the mold adhesion phenomenon is serious. The productivity of a process will decrease and defect rate will increase. In this study, a mechanism designed with a mold that could measure normal adhesion force in injection molding process was successfully developed. The apparatus quantified the normal adhesion force. So engineers can use the measured adhesion force to understand the effectiveness of mold release agent and adhesion release coating. In this study, three different surface roughness (Ra) conditions were compared. It was found that when Ra=0.08μm without coating, the smallest normal adhesion force would obtained. It was found that single-layer CrN coating and modifying CrN coating were effective in reducing the normal adhesion force and multi-layer CrN was not effective. In addition, normal adhesion force was directly proportional to ejecting speed, melt temperature and cooling time.