TY - BOOK

T1 - Press Cycle Time Reduction of A Reinforced Epoxy Resin and the Influence On Its Mechanical/Thermal Properties

AU - Tao, Qi

N1 - embargoed until 09-05-2023

PY - 2018

Y1 - 2018

N2 - Lamination or pressing is one of the most important processes in the printed circuit board (PCB) manufacturing, because the reinforced epoxy resin (prepreg) will be cured and consequently relevant mechanical and thermomechanical properties, such as stiffness, glass transition temperature (Tg) and coefficient of thermal expansion (CTE) etc., of the PCBs are formed during this procedure. However, this process is also time-consuming. Although material suppliers will normally offer the manufacturer’s recommended cure cycles (MRC) for every specific material to the PCB manufacturers, these MRCs often need to be adapted in terms of cycle time and/or temperature in order to reduce the production time and/or enhance the utilization of the press machine. In this thesis the mechanism of the epoxy curing kinetics was first studied in order to understand its polymerization procedure during lamination. Afterwards, the way to reduce the press cycle time of a reinforced epoxy resin, CE688, at the lamination process based on the study and the influence on its mechanical, thermal, fracture mechanical properties, as well as on the reliability performance, are presented. Since the main function of the lamination process is to cure the epoxy resin at elevated temperatures with high pressure, the evolution of the curing degree during this heating process is one of the key indicators for press cycle time reduction. Therefore, the well-known model free kinetics (MFK) approach was applied first to a model resin for the feasibility study of the method and then to the CE688 epoxy resin. Although small deviations to the experimental curves were found in the predicted ones due to the absence of diffusion correction in the MFK approach, the results can be well accepted. However, this commonly applied MFK approach can only predict the curing under either isothermal or non-isothermal (i.e., with fixed heating rate) heating conditions, which cannot be directly used for predicting a real case. Meanwhile, due to the lag of the heat transfer within a press book, the curing degree of the epoxy will vary depending on the location. For instance, the closer to the heating plate, the faster the curing advances. Hence, a mathematical algorithm was proposed by the author to couple the MFK with the powerful finite element approach (FEA) in order to predict the curing behavior more accurately. The proposed algorithm was eventually implemented in Abaqus® by integrating the discretized analytical solution of the MFK into its user subroutines. This method was verified by non-isothermal and isothermal differential scanning calorimetry (DSC) experiments. By means of this method, the real manufacturing press cycle can be simulated regarding the temperature distribution within the whole press book and the curing degree of the epoxy resin at every location. Besides, in contrast to other FEA curing simulations, the present method can easily simulate arbitrary geometries with advanced curing degree-dependent material properties, such as density, CTE, thermal conductivity, specific heat and even the chemical shrinkage during polymerization. Moreover, the developed MFK can also be used for the decomposition study which is very important for characterizing the thermal stability of the material. DSC is one of the most commonly used methods for obtaining the necessary parameters required by the MFK approach. But sometimes the reaction peaks of polymerization in the DSC thermographs are not discernable due to higher filler content or whatever other reasons. In these cases, the Fourier transform infrared (FTIR) spectroscopy can be utilized as a complementary method. Therefore, the FTIR curing kinetics for CE688 was studied and compared to the DSC one in this PhD work in order to develop an alternative method for the future application.

AB - Lamination or pressing is one of the most important processes in the printed circuit board (PCB) manufacturing, because the reinforced epoxy resin (prepreg) will be cured and consequently relevant mechanical and thermomechanical properties, such as stiffness, glass transition temperature (Tg) and coefficient of thermal expansion (CTE) etc., of the PCBs are formed during this procedure. However, this process is also time-consuming. Although material suppliers will normally offer the manufacturer’s recommended cure cycles (MRC) for every specific material to the PCB manufacturers, these MRCs often need to be adapted in terms of cycle time and/or temperature in order to reduce the production time and/or enhance the utilization of the press machine. In this thesis the mechanism of the epoxy curing kinetics was first studied in order to understand its polymerization procedure during lamination. Afterwards, the way to reduce the press cycle time of a reinforced epoxy resin, CE688, at the lamination process based on the study and the influence on its mechanical, thermal, fracture mechanical properties, as well as on the reliability performance, are presented. Since the main function of the lamination process is to cure the epoxy resin at elevated temperatures with high pressure, the evolution of the curing degree during this heating process is one of the key indicators for press cycle time reduction. Therefore, the well-known model free kinetics (MFK) approach was applied first to a model resin for the feasibility study of the method and then to the CE688 epoxy resin. Although small deviations to the experimental curves were found in the predicted ones due to the absence of diffusion correction in the MFK approach, the results can be well accepted. However, this commonly applied MFK approach can only predict the curing under either isothermal or non-isothermal (i.e., with fixed heating rate) heating conditions, which cannot be directly used for predicting a real case. Meanwhile, due to the lag of the heat transfer within a press book, the curing degree of the epoxy will vary depending on the location. For instance, the closer to the heating plate, the faster the curing advances. Hence, a mathematical algorithm was proposed by the author to couple the MFK with the powerful finite element approach (FEA) in order to predict the curing behavior more accurately. The proposed algorithm was eventually implemented in Abaqus® by integrating the discretized analytical solution of the MFK into its user subroutines. This method was verified by non-isothermal and isothermal differential scanning calorimetry (DSC) experiments. By means of this method, the real manufacturing press cycle can be simulated regarding the temperature distribution within the whole press book and the curing degree of the epoxy resin at every location. Besides, in contrast to other FEA curing simulations, the present method can easily simulate arbitrary geometries with advanced curing degree-dependent material properties, such as density, CTE, thermal conductivity, specific heat and even the chemical shrinkage during polymerization. Moreover, the developed MFK can also be used for the decomposition study which is very important for characterizing the thermal stability of the material. DSC is one of the most commonly used methods for obtaining the necessary parameters required by the MFK approach. But sometimes the reaction peaks of polymerization in the DSC thermographs are not discernable due to higher filler content or whatever other reasons. In these cases, the Fourier transform infrared (FTIR) spectroscopy can be utilized as a complementary method. Therefore, the FTIR curing kinetics for CE688 was studied and compared to the DSC one in this PhD work in order to develop an alternative method for the future application.

KW - Epoxidharz

KW - Leiterplatten

KW - Pressenzykluszeitreduktion

KW - Modellfreie Kinetik-Ansatz

KW - Aushärtungskinetik

KW - Finite Elemente Analyse

KW - Epoxy Resin

KW - Printed Circuit Board

KW - Press Cycle Time Reduction

KW - Model Free Kinetics

KW - Curing Kinetics

KW - Finite Element Approach

U2 - 10.34901/mul.pub.2023.65

DO - 10.34901/mul.pub.2023.65

M3 - Doctoral Thesis

ER -