Process Optimization of Injection Overmolding Structural Electronics with Regard to Film Distortion

Area of Science:

• Materials Science
• Manufacturing Engineering
• Polymer Science

Background:

• Integrating structural electronics into injection-molded parts presents significant manufacturing challenges due to harsh processing conditions.
• Molten thermoplastics exert shear stresses and high temperatures on embedded electronic films, risking damage.

Purpose of the Study:

• To investigate the influence of injection molding parameters on the distortion of thermoplastic polyurethane (TPU) films with integrated flexible printed circuit boards (flexPCBs).
• To establish a correlation between processing conditions, material properties, and film integrity.

Main Methods:

• Manufacture of test films using polycarbonate (PC) outer layers and two distinct TPU middle layers with flexPCBs.
• Overmolding with PC and conducting parameter studies on melt temperature, mold temperature, injection speed, and TPU type.
• Visual inspection of molded parts and comparison with numerical simulations to derive a shear distortion factor.

Main Results:

• Film distortion decreased with higher melt temperatures, lower mold temperatures, and faster injection speeds.
• TPU with a higher melting temperature exhibited significantly better resistance to distortion.
• Reduced distortion was observed with increased distance from the gate and greater cavity thickness, correlating with the shear distortion factor.

Conclusions:

• Injection molding parameters critically influence the successful integration of flexPCBs within thermoplastic parts.
• The derived shear distortion factor effectively links processing conditions to film integrity, aiding in damage-free manufacturing.
• Material selection (TPU type) and process optimization are key to minimizing distortion and ensuring the reliability of structural electronics.