TY - BOOK

T1 - Development of pressure sensitive adhesive tapes for temporary applications at high temperatures

AU - Bandl, Christine

N1 - embargoed until 30-09-2022

PY - 2019

Y1 - 2019

N2 - Besides their application as decorative films, tapes and sticky notes in household and office, pressure sensitive adhesive (PSAs) tapes are widely used in various industries. Typical applications include surface protection, labeling, packaging, the assembly of automotive parts, the construction of printed circuit boards (PCBs) and the manufacture of electronic devices. In general, PSAs are based on elastomers and visco-elastic polymers such as natural and synthetic rubbers, polyacrylates, polysiloxanes, etc., which may be formulated with additives such as tackifiers, plasticizers, stabilizers, fillers and pigments. In the present work, a PSA tape for temporary applications in the microelectronic industry is designed. The adhesive has to provide high initial tack and adhesive strength during use, while easy and clean removability after exposure to high temperatures (200 °C) and pressures (20 bar) are required in the end of the application. These requirements are met by adjustment of the adhesive properties of the PSA and the incorporation of a release function, enabling debonding on demand. The latter is realized by UV-triggered crosslinking, which decreases adhesion but increases cohesion and the glass transition temperature (Tg) of the adhesive. Firstly, adhesive polymers based on polyacrylics and epoxides are synthesized. The composition of the polymers is varied in order to adjust the adhesive properties. Moreover, aromatic monomers are incorporated to increase the thermal stability of the adhesives, while vinyl and acryl groups are introduced to the side chains to provide photo-reactive moieties for UV-crosslinking. The synthesized polymers are characterized by IR- and NMR-spectroscopy as well as by GPC, TGA and DSC. In the second part of this thesis, PSA tapes are prepared by coating the adhesive polymers onto PET carriers. Based on first adhesion experiments, it was decided to use acrylic polymers, which are blended with multifunctional acrylic monomers and a photoinitiator in order to generate semi-interpenetrating networks (semi-IPN) upon UV-irradiation. The photocuring kinetics of the adhesive layers in dependence of the PSA formulation is characterized by IR-spectroscopy. Moreover, DSC and TGA measurements provide information about the Tg and the thermal stability of the respective adhesive layers. The performance of the prepared PSA tapes and their removability after exposure to temperature ≤ 240 °C is evaluated by the use of optical light microscopy. In the course of these experiments, the impact of the substrate surface quality, the PSA composition, different processing parameters and the preparation method was examined. To summarize the most important findings, the removability of the PSA tape is improved by the use of high Tg adhesive polymers and highly functional acrylic monomers, which yield highly crosslinked semi-IPN with high cohesion. This is advantageous with regard to interactions with the adherent, which is influenced by both, the chemistry and the topography of the substrate. Moreover, corona treatment of the carrier and the application of adhesion promoters significantly improved the anchorage of the PSA to the carrier and in turn the removability of the PSA tape. Two methods for tape preparation were elaborated, providing different crosslinking gradients, which influence the performance in dependence of the surface quality of the substrate. The developed photo-sensitive PSA tape meets all requirements stated above providing sufficient adhesive strength during application and clean peel from roughened and adhesion promoted surfaces (BondFilm® treated copper) without leaving residues after application at 180 °C for one hour.

AB - Besides their application as decorative films, tapes and sticky notes in household and office, pressure sensitive adhesive (PSAs) tapes are widely used in various industries. Typical applications include surface protection, labeling, packaging, the assembly of automotive parts, the construction of printed circuit boards (PCBs) and the manufacture of electronic devices. In general, PSAs are based on elastomers and visco-elastic polymers such as natural and synthetic rubbers, polyacrylates, polysiloxanes, etc., which may be formulated with additives such as tackifiers, plasticizers, stabilizers, fillers and pigments. In the present work, a PSA tape for temporary applications in the microelectronic industry is designed. The adhesive has to provide high initial tack and adhesive strength during use, while easy and clean removability after exposure to high temperatures (200 °C) and pressures (20 bar) are required in the end of the application. These requirements are met by adjustment of the adhesive properties of the PSA and the incorporation of a release function, enabling debonding on demand. The latter is realized by UV-triggered crosslinking, which decreases adhesion but increases cohesion and the glass transition temperature (Tg) of the adhesive. Firstly, adhesive polymers based on polyacrylics and epoxides are synthesized. The composition of the polymers is varied in order to adjust the adhesive properties. Moreover, aromatic monomers are incorporated to increase the thermal stability of the adhesives, while vinyl and acryl groups are introduced to the side chains to provide photo-reactive moieties for UV-crosslinking. The synthesized polymers are characterized by IR- and NMR-spectroscopy as well as by GPC, TGA and DSC. In the second part of this thesis, PSA tapes are prepared by coating the adhesive polymers onto PET carriers. Based on first adhesion experiments, it was decided to use acrylic polymers, which are blended with multifunctional acrylic monomers and a photoinitiator in order to generate semi-interpenetrating networks (semi-IPN) upon UV-irradiation. The photocuring kinetics of the adhesive layers in dependence of the PSA formulation is characterized by IR-spectroscopy. Moreover, DSC and TGA measurements provide information about the Tg and the thermal stability of the respective adhesive layers. The performance of the prepared PSA tapes and their removability after exposure to temperature ≤ 240 °C is evaluated by the use of optical light microscopy. In the course of these experiments, the impact of the substrate surface quality, the PSA composition, different processing parameters and the preparation method was examined. To summarize the most important findings, the removability of the PSA tape is improved by the use of high Tg adhesive polymers and highly functional acrylic monomers, which yield highly crosslinked semi-IPN with high cohesion. This is advantageous with regard to interactions with the adherent, which is influenced by both, the chemistry and the topography of the substrate. Moreover, corona treatment of the carrier and the application of adhesion promoters significantly improved the anchorage of the PSA to the carrier and in turn the removability of the PSA tape. Two methods for tape preparation were elaborated, providing different crosslinking gradients, which influence the performance in dependence of the surface quality of the substrate. The developed photo-sensitive PSA tape meets all requirements stated above providing sufficient adhesive strength during application and clean peel from roughened and adhesion promoted surfaces (BondFilm® treated copper) without leaving residues after application at 180 °C for one hour.

KW - pressure sensitive adhesive

KW - photo-triggered release

KW - acrylic copolymer

KW - radical polymerization

KW - removability

KW - surface modification

KW - organosilane

KW - Haftklebstoff

KW - UV-induzierte Vernetzung

KW - Acrylcopolymer

KW - radikalische Polymerisation

KW - Ablösbarkeit

KW - Oberflächenmodifizierung

KW - Organosilan

M3 - Doctoral Thesis

ER -