Photo-switchable Adhesives (Brandeis Ref. 2019-041)

Organic photo-switching systems absorb solar radiation, store energy in chemical bonds, and release it in the form of thermal energy upon triggering. The capability of the system to store energy for a variable time frame (hours, days, weeks) and the triggerable release of the stored energy present exciting opportunities in solar energy harvesting and potential applications in de-icing of windshields and windows, wearable heating devices, and general heating systems. A novel class of light-responsive molecules was discovered to show adhesive properties which can be modulated by the irradiation with UV light (Figure 1(a) The process of UV-activated structural change of a spiropyran photo-switch that leads to the change of adhesive strength; (b) A schematic of two substrates melt-bonded by a photo-switchable adhesive layer). The pre-adhesive powders are first melted to bond substrates, and the debonding process is triggered by the irradiation with UV. This debonding process is gentle and leaves negligible residue of adhesives on the substrate. Micron-thick silicon wafers break throughout multiple patterning steps involving bonding to carriers and subsequent debonding. Current acrylic temporary adhesives have fixed adhesive strengths and require peel-off process during which residue remains and additional chemical treatments/flipping processes increase the failure rate. For example, a well-known temporary adhesive used for silicon wafer backgrinding process is 3M Liquid UV-Curable Adhesive, which is limited in that three additional chemical treatment steps are required for the debonding process: LTHC release layer, dicing tape, and peel-off tape are applied for its removal.The temporary adhesive will be tested for silicon wafer processing steps as the initial application. Our temporary adhesive technology could potentially be implemented in packaging tapes and hanging strips, which could be removed easily and cause little damage to the substrate such as packages and walls. The specific light-activated debonding and the lack of residue from removal will be favorable for recycling and home decoration.The designed light-responsive adhesives are advantageous in that the glue can be selectively removed from the desired substrate (i.e. silicon wafer), through one-step specific triggering procedure. A more gentle process leads to lower rates of substrate damage, which produces a higher yield of finer quality industrial products. Because the debonding process is triggered by light, it could be operated locally and controlled more precisely with a narrow beam of light enabling meticulous work such as the detachment of micron-scale components on electronics for the optimization of multi-step assembly and the customization of intricate devices. Rong Zhou 7817368753

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