Session: 14-02-01: General Topics in MEMS and Fabrication

Paper Number: 166385

Demolding of Microstructures and Fabrication of Metallic Molds Using Electroforming 

Demolding is a critical step in the fabrication of microstructures via injection molding, as it separates molded plastic components from the mold and ensures high replication fidelity. Demolding stress arises due to frictional and adhesive forces at the mold/substrate interface, as well as stored elastic stress near the mold/substrate. Reducing demolding stress is essential to prevent damage or deformation in molded microdevices. While factors such as demolding temperature, velocity, and the thermo-mechanical properties of molds significantly influence demolding stresses, experimentally isolating the contribution of each variable is challenging.

 

To address this, we conducted a systematic study on demolding process via a combination of numerical analysis and with experimental validation. Numerical analysis on demolding stress was performed using a commercial finite element software ANSYS. Demolding force was experimentally measured using a mechanical tester equipped with a 5 kN load cell, vacuum chucks, and PID-controlled heaters after microstructures were replicated into PMMA sheets by a thermal press machine. The mold was fabricated in Super Invar 32-5 using a laser etching machine (Shanghai Haizhi Industrial Technology Co., Ltd), which featured 1,936 micropillars with a height and width of 100 microns and a gap of 150 microns. The laser etching process intrinsically introduced draft angles on the pillars and surface roughness on the recessed surface.

 

This study was systematically investigated the influence of key processing parameters on demolding forces during the replication of micropillars into PMMA. Specifically, the effects of molding temperature, demolding temperature, demolding velocity, replicated part thickness (cooling time), and the mold’s mechanical properties, including Young’s modulus and coefficient of thermal expansion (CTE) were examined. The results demonstrated that higher molding temperatures, in combination with surface roughness, facilitated improved material flow and filling within the mold cavity; however, this also led to an increase in demolding forces due to stronger adhesion and thermal effects. We found that demolding forces were minimized when demolding occurred at temperatures slightly below the polymer’s glass transition temperature, as this balance reduced adhesion while maintaining sufficient structural integrity of the replicated features. Additionally, a nonlinear rise in demolding forces was observed with increasing demolding velocity, which eventually stabilized at higher velocities, indicating a saturation effect in force accumulation. Further analysis of polymer thickness emphasized the critical role of cooling time and shrinkage, both of which directly influenced the magnitude of demolding forces. Overall, this study provides a comprehensive evaluation of the interplay between demolding parameters and replication efficiency, offering insights into optimizing the process to minimize demolding forces and structural deformation.

Presenting Author: Mohammad Derikvand Mechanical & Industrial Engineering Department and Center of BioModular Multi-Scale Systems for Precision Medicine (CBM²), Louisiana State University, Baton Rouge, LA 70803, United States

Presenting Author Biography: Mohammad Derikvand is a doctoral candidate in the Department of Mechanical Engineering at Louisiana State University, specializing in micro- and nanofabrication and replication for biomedical applications. He previously earned a Master’s degree in Mechanical Engineering from Iran.

Authors:

Mohammad Derikvand Mechanical & Industrial Engineering Department and Center of BioModular Multi-Scale Systems for Precision Medicine (CBM²), Louisiana State University, Baton Rouge, LA 70803, United States
Michael C. Murphy Mechanical & Industrial Engineering Department and Center of BioModular Multi-Scale Systems for Precision Medicine (CBM²), Louisiana State University, Baton Rouge, LA 70803, United States
Sunggook Park Mechanical & Industrial Engineering Department and Center of BioModular Multi-Scale Systems for Precision Medicine (CBM²), Louisiana State University, Baton Rouge, LA 70803, United States