Index matched fluidic packaging of high power UV LED clusters on aluminum substrates for improved optical output power
We present an improved cooling for a high power density UV LED module for a wavelength of 395 nm. The module consists of 98 LED chips soldered on a thick film printed alumina substrate on an area of 2.11 cm2. We investigated cooling by a commercial water cooler as well as by a surface micro cooler developed by our own. Further we describe a technology to replace alumina by aluminum as substrate material. A module consisting of 25 UV LEDs was optically characterized without and with liquid encapsulation. Finally we conducted numerical studies to develop an easily producible, sufficiently powerful, and robust water cooler. Based on the results we present a water cooler design with cooling channels embedded in the aluminum substrate of an LED module, removing the interface between LED substrate and heat sink.
Study on die-bonding key technology of UV LED packaging
Due to its potential market value, the packaging and application technology of UV LED are paid more and more attention. In this paper, the die-bonding interface and thermal resistance of UV LED were investigated by using different TIMs, and the influence of junction temperature on photochromic properties was studied. The results show that the traditional silver glue as a thermal interface material has the highest junction temperature, and its advantage is that it is cheap. Compared with SnAgCu solder, Nano Ag paste has better thermal conductivity and better thermal stability, but the price is higher. Moreover, the reflow process of Sn based solder is more mature. Compared with AuSn and SnAgCu solder, the research results show that the problem of solid-state interface of Sn based solder is poor thermal stability. Under the action of electric stress and thermal stress, the interface will have atomic migration. After high temperature aging, the interface of AuSn solder-boning interface even has serious atom migration and relatively large voids. The study indicated that with the increase of junction temperature, the radiation power and photochromic characteristics of all tested samples decrease.
Pedagogy of the “Not”: Negation, Exodus, and Postdigital Temporal Regimes
Postdigital capitalist time is an incessant acceleration that acts to homogenize time and wed us to the present, to which we have to constantly catch up. While the impulse of this is no doubt economic (the realization of value), it is crucially undergirded by a pedagogical logic wherein we have to perpetually learn and re-learn the latest apps, social media configurations, operating systems, and so on. Political strategies of resistance thus need to be bolstered by an alternative mode of educational life, and I propose a pedagogy of the “not” as one possibility. Such a pedagogy is an act of suspension that sustains a detachment from the present, clearing out oppositions and thereby exposing us to a radical indeterminacy and potentiality that is always untimely. Suspension is the praxis of negation, which means that negation operates by keeping sense indeterminate to meaning and signification. Rather than suppressing, disavowing, or annihilating the stated content, negation retains even that which is negated. While this would appear as a form of exopedagogy, which withdraws from the dialectic of the private/public, I instead argue that it redefines the terms of any dialectic, redefining the very categories exopedagogy withdraws from. Before concluding, I spend some time with Sandy Grande’s important critiques of Eurocentrism and progress in Western critical education, demonstrating how negation as suspension circumvents these errors through its accommodation of—or, better, insistence on—variegated temporalities and forms of life.