Hermetic integration of liquids using high-speed stud bump bonding for cavity sealing at the wafer level

Abstract

This paper reports a novel room-temperature hermetic liquid sealing process where the access ports of liquid-filled cavities are sealed with wire-bonded stud bumps. This process enables liquids to be integrated at the fabrication stage. Evaluation cavities were manufactured and used to investigate the mechanical and hermetic properties of the seals. Measurements on the successfully sealed structures show a helium leak rate of better than 10 −10 mbarL s −1 , in addition to a zero liquid loss over two months during storage near boiling temperature. The bond strength of the plugs was similar to standard wire bonds on flat surfaces.

Polymer nanoliter well arrays for liquid storage and rapid on-demand electrochemical release

“…This limits the level of integration and hampers downscaling below volumes of several microliters. Batch scale encapsulation and storage of liquid or dried sample in silicon [17,25], metallic [26], glass [4], and polymer hybrid [1][2][3]16] reservoirs enables long-term storage and often hermetic sealing, but is not compatible with polymer microfluidic integration. Sealing of polymer wells by thermal bonding [5,8] is not suitable for temperature sensitive liquids, and sealing of wells by epoxy gluing [10,16] complicates downscaling of aqueous liquid storage in multiplewell arrays.…”

Unconventional applications of wire bonding create opportunities for microsystem integration

“…Step 4 In subsequent work, wire bonding was used to push free air balls of Au wires into access ports of micro-cavities that contain liquids as shown in figure 17 [139,140]. The free air balls plastically deform and thereby hermetically seal the openings of the cavities.…”

“…Khandros et al [138] propose to utilize wire bonds as flexible contact probes for probe cards that are used as an interface between an electronic test system and a semiconductor wafer that is to be tested. Standard wire bonding using gold wires has also been proposed to seal through substrate holes for the sealing of liquids in cavities [139][140][141]. This approach is described in detail in section 3.3.…”

“…The electrical conductivities and mechanical bond strengths that have been achieved in this work are comparable to those obtained by standard wire-bonds using conventional wire-pad material combinations. In subsequent work, wire bonding was used to push FABs of Au wires into access ports of micro-cavities that contain liquids as shown in figure 17 [139,140]. The FABs plastically deform and thereby hermetically seal the openings of the cavities.…”

Liquid Encapsulation Technology for Microelectromechanical Systems

“…Typical polymers are several orders of magnitude more permeable to gas than metals and ceramics [27]. Therefore, sealing with gold stud bumps has been proposed [32], where reservoirs are filled up with the liquids via microchannels and the inlets and outlets of the channels are then plugged with wire-bonding gold. Firstly, a gold ball is formed at the edge of the gold wire by electrical discharge.…”