Improved polymer–glass adhesion through micro-mechanical interlocking

Abstract

Mechanical interlocking provides a simple and effective means of improving adhesion between dissimilar materials in micro-electro-mechanical systems (MEMS). Following successful implementation in hybrid Si-polymer systems (Larsson, Syms and Wojcik 2005 J. Micromech. Microeng. 15 2074–82), it was established that maximum interface strengthening does not necessarily rely on the presence of overhang between interlocking lobes. Instead, careful design of the lobe profile is advised in order to balance the opposing actions of physical restraint and lobe pull-out and to obtain optimal interface strength. When an interlocked interface is immersed in aggressive liquid media, however, the situation is clearer: chemical bonds are degraded or completely destroyed and lobe overhang provides the only source of physical restraint. Generating overhanging features in Si substrates is possible through reactive ion etching (RIE), but in the case of glass, the situation is more problematic. A straightforward, robust process is now described that extends mechanical interlocking to generic MEMS substrates, avoiding the need for RIE. By using inexpensive and established processes such as electroplating and wet etching, interlocking features with an overhanging profile are generated in glass substrates. Peel tests on cured strips of SU-8 confirm an increase in average peel strength by a factor of 3.5, compared with strips peeled from smooth substrates. The method can readily be applied to a number of substrates, including Si, providing a low-cost route towards attaining mechanical interlocking.

Photolithographic Fabrication of Microapertures with Well-Defined, Three-Dimensional Geometries for Suspended Lipid Membrane Studies

“…In tandem to forming sloped wall apertures, we addressed the need to remove the thin films from their supportive substrates by developing an SU-8 lift-off process. Since SU-8 exhibits poor adhesion to glass, 45 we utilized the glass photomask directly as the handle material during photolithographic patterning of SU-8 (Figure 1A), which facilitated lift-off and ensured hard-contact between the SU-8 film and the photomask during UV irradiation, thereby eliminating the possibility of misalignment during rotation and UV exposure. While characteristically poor SU-8/glass adhesion was observed when SU-8 films were coated directly on the photomasks, the adhesion was sufficient to cause fracturing when polymerized SU-8 films were lifted from the photomask.…”

Accelerated growth of oxide film on aluminium alloys under steam: Part II: Effects of alloy chemistry and steam vapour pressure on corrosion and adhesion performance

“…The adhesion provided by the mechanical interlocking is one aspect which depends on the surface morphology of the conversion coating [21,22]. The adhesion mechanism also depends on the acid/base properties of the surface due to the possibility of forming chemical bonds with the top layer [23].…”

Correlation of surface roughness and surface energy of silicon-based materials with their priming reactivity

“…1) [13][14][15]. In this process HMDS first reacts with adsorbed water (yielding hexamethyldisiloxane and ammonia) and subsequently with hydroxyl groups on the surface (yielding surface-bound trimethylsilyl groups and ammonia) [16].…”