Propagation of adhesives in joints during capillary adhesive bonding of microcomponents

Abstract

Capillary adhesive bonding is used successfully to integrate microsystems. To ensure high reliability and quality of the interconnection technique, it is imperative that the propagation of adhesives in the joints be controlled. Two adhesives frequently used in capillary adhesive bonding were examined: a one-component, UV-curing methacrylate adhesive (Dymax 191-M), and a two-component epoxy resin bonding adhesive curing at room temperature (Epo-tek 302-3M). The propagation of these adhesives in joints with different gap heights of 2-20 m between two PMMA surfaces and between one PMMA and one PI surface was measured and compared with the theoretical adhesive propagation in accordance with the Hagen-Poiseuille equation for a gap flow, with the capillary pressure taken into account.Once the dynamic viscosity, the wetting angle and the surface tension of the adhesive have been determined as a function of the measuring time, the measured propagation of the Epo-tek 302-3M and Dymax 191-M adhesives can be described in good agreement with the theory for all the gap heights under study.

Gas permeability of adhesives and their application for hermetic packaging of microcomponents

“…These techniques, as a rule, are associated with high process temperatures and high process costs. Adhesives can be employed in packaging technology at low process temperatures and with a large variety of materials [6,7]. Process costs can be reduced also because of the ease of handling.…”

Capillary-driven automatic packaging

“…As liquid in the capillary bridge continues evaporating, its height gradually reduces and the negative pressure rises inside as predicted by Laplace equation. 19 As previously reported, the pressure inside capillary bridges can be as high as À17 bar, 21 which provides significant and uniform lifting (hydrostatic nature) force for the bottom substrate to establish close physical contact with the top for the subsequent covalent bonding between two functionalized surfaces. Eqn (3) shows the relationship among the three related forces:…”

“…17 Specifically, the capillary interactions include two force components, capillary force (F C ) along the wetting boundaries and suction force (F S ) from the negative Laplace pressure (DP) inside induced by liquid menisci. 19 As illustrated in Fig. 1, the lateral component of the capillary force (F C t ) attempts to spontaneously align the identical comb-shaped wetting patterns between two surfaces in order to minimize liquid surface energy.…”

“…16 The structurally defined wetting boundaries have been both theoretically and experimentally investigated to achieve the optimal self-alignment performance as the capillary force increases linearly with the capillary length. Moreover, the capillary bridge formed between two surfaces results in elevated Laplace pressure (negative) for the surface self-engagement, 19 as the sandwiched liquid film gradually evaporates (and the film thickness reduces too). As a consequence, two surfaces are brought into intimate contact and form seamless joints through covalent bonding of pre-activated functional groups on surfaces.…”

<title>Large-area polymer replication for microfluidic devices</title>

“…For this, however, additional microstructures are required. Capillary bonding [13] is associated with the risk of the adhesive not only filling the joints, but also the fluidic structures, if no additional stopping grooves are provided. In contrast to this, solvent bonding [14] is associated with the risk of surface modification.…”