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Applications of Reactive Multilayer Foils
Applications of Reactive Multilayer Foils Timothy P. Weihs
Over the past two decades, many scientific studies have shown that one can control the ignition thresholds, the heat of reactions, and the velocities of self-propagating formation reactions in multilayer foils through the careful selection of chemistry, bilayer thickness, and total thickness [1–3]. Given this control, the nanolayered foils are ideal local heat sources for joining or sealing components, for heating devices or chemicals, for initiating other chemical reactions, and for producing optical signals. Here we consider their commercial use as heat sources for soldering, and then we briefly consider some of these other applications that are under development. Reactive foils were developed as local heat sources for soldering and brazing components starting in 1995 and became commercially available as the NanoFoil product in 2003 [4,5]. Today they are actively used for soldering together small and large components. The process consists of placing a foil between two components that have been coated with solder or wetting layers; applying pressure to the sandwich structure; and then igniting a reaction within the foil, which produces a rapid burst of heat, melts the solder, and forms a bond, as shown schematically in Fig. 1A. By controlling the chemistry and thickness of the foils, the total heat released by the formation reaction can be tuned to ensure that the solder layers melt but the bulk of the components remain cool. Typically, only 30–40 μm of solder are melted on either side of reactive foil, as shown in Fig. 1B, and millimeter thick components rise only a few degrees in temperature [5]. With such small changes in temperature, the components do not undergo any significant expansion or contraction during bonding, even if their coefficients of thermal expansion (CTE) differ significantly [2,5]. Thus bonding with reactive multilayer foils enables the formation of relatively stress-free, metallic bonds between materials with dissimilar CTEs. This ability is particularly beneficial in bonding together large components such as sputtering targets and backing plates [6], and it is commercially available as the NanoBond process. More recent developments show an ability to bond Si wafers together using thinner but hotter Pd/Al patterning multilayer foils utilizing standard IC processing techniques [7]. The very localized heating offered by reactive multilayer foils helps in the joining of temperature-sensitive microelectronic components [2,5]. An exciting example, shown schematically in Fig. 2, is the bonding of chips and LED packages to heat sinks. To enhance heat dissipation from the chips or LEDs, one seeks very conductive interfaces Concise Encyclopedia of Self-Propagating High-Temperature Synthesis http://dx.doi.org/10.1016/B978-0-12-804173-4.00008-9
Copyright © 2017 Elsevier Inc. All rights reserved.
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Concise Encyclopedia of Self-Propagating High-Temperature Synthesis
Fig. 1 (A) Schematic of bonding with reactive multilayer foils, (B) cross-sectional image of a bond of two components.
Fig. 2 Schematic of bonding a chip module to a heat sink using reactive multilayer foils and solder.
between the chip and the heat sink. Often this is a thermal paste, but well-bonded, metallic interfaces can dissipate heat more effectively. However, not all microelectronic components can be furnace soldered to achieve a conductive metallic interface, particularly at the later stages of assembly. Bonding with NanoFoil limits the thermal exposure of the front side of silicon dies to 100°C for less than a second [8]. The resulting interfaces are very conductive and could prove advantageous for CPUs, GPUs, solar cells, and LED devices [8]. Another example is the sealing of packages containing microelectronic components. The localized heating also allows one to form a metallic or polymeric seal along the perimeter of a package without heating the contents of the package [7,9]. This has been demonstrated at the micron and centimeter scale.
Applications of Reactive Multilayer Foils
Beyond joining and sealing applications, the heat and light released by reactive multilayer foils can be used for a range of commercial and defense applications. In the area of pyrotechnics and explosives, one can ignite flares [10] or initiate reaction trains that lead to air bag deployment or explosive detonation [11]. As a stable and rapid source of energy, electrolytes in thermal batteries can be heated [12] or can act as a heater for other devices. The controllable burning rates can be utilized in chemical time delays [13], and the controllable ignition threshold can be beneficial in novel munitions [14]. All of these applications rely on the ability to store chemical energy for long periods of time and then release it in a tunable and precise manner. Additional investigations into the basic properties and reaction mechanisms within these novel reactive materials will help expand their utilization as controlled sources of heat and light.
REFERENCES [1] Rogachev AS, Mukasyan AS. Comp Expl Shock Waves 2010;46:243–66. [2] Weihs TP. In: Barmak K, Coffey KR, editors. Metallic films for electronic, magnetic, optical and thermal applications. Structure, processing and properties. Swaston: Woodhead Publishing; 2014. p. 160–243 [chapter 6]. [3] Adams DP. Thin Solid Films 2015;576:98–128. [4] Makowiecki D, Bionta R. US Patent 5381944; 1995. [5] Duckham A, Levin J, Weihs T. Adv Sci Technol 2006;45:1578–87. [6] Duckham A. Vacuum technology & coating 2007;65–9. [7] Braeuer J, Gessner T. J Micromech Microeng 2014;24:115002. [8] Van Heerden D, Rude T, Newson J, Knio O, Weihs T, Gallus D. In: Proceedings of the twentieth annual IEEE semiconductor thermal measurement and management symposium; 2004. p. 46–9. [9] Van Heerden D, Deger D,Weihs T, Knio O. US Patent 7,143,568; 2006. [10] Nielson D, Tanner R, Dilg C. US Patent 7,690,308; 2010. [11] Baginski T, Parker T, Fahey W. US Patent 6,925,938; 2005. [12] Ding M, Krieger F, Swank J, Poret J, McMullan C, Chen G. In: 43rd power sources conference, Philadelphia, July 7–10; 2008. [13] Kelly P, Tinston S, Arnell R. Surf Coat Technol 1993;60:597–602. [14] Hugus G, Sheridan E. US Patent 7,955,451, June 7; 2011.
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Over the past two decades, many scientific studies have shown that one can control the ignition thresholds, the heat of reactions, and the velocities of self-propagating formation reactions in multilayer foils through the careful selection of chemistry, bilayer thickness, and total thickness [1–3]. Given this control, the nanolayered foils are ideal local heat sources for joining or sealing components, for heating devices or chemicals, for initiating other chemical reactions, and for producing optical signals. Here we consider their commercial use as heat sources for soldering, and then we briefly consider some of these other applications that are under development. Reactive foils were developed as local heat sources for soldering and brazing components starting in 1995 and became commercially available as the NanoFoil product in 2003 [4,5]. Today they are actively used for soldering together small and large components. The process consists of placing a foil between two components that have been coated with solder or wetting layers; applying pressure to the sandwich structure; and then igniting a reaction within the foil, which produces a rapid burst of heat, melts the solder, and forms a bond, as shown schematically in Fig. 1A. By controlling the chemistry and thickness of the foils, the total heat released by the formation reaction can be tuned to ensure that the solder layers melt but the bulk of the components remain cool. Typically, only 30–40 μm of solder are melted on either side of reactive foil, as shown in Fig. 1B, and millimeter thick components rise only a few degrees in temperature [5]. With such small changes in temperature, the components do not undergo any significant expansion or contraction during bonding, even if their coefficients of thermal expansion (CTE) differ significantly [2,5]. Thus bonding with reactive multilayer foils enables the formation of relatively stress-free, metallic bonds between materials with dissimilar CTEs. This ability is particularly beneficial in bonding together large components such as sputtering targets and backing plates [6], and it is commercially available as the NanoBond process. More recent developments show an ability to bond Si wafers together using thinner but hotter Pd/Al patterning multilayer foils utilizing standard IC processing techniques [7]. The very localized heating offered by reactive multilayer foils helps in the joining of temperature-sensitive microelectronic components [2,5]. An exciting example, shown schematically in Fig. 2, is the bonding of chips and LED packages to heat sinks. To enhance heat dissipation from the chips or LEDs, one seeks very conductive interfaces Concise Encyclopedia of Self-Propagating High-Temperature Synthesis http://dx.doi.org/10.1016/B978-0-12-804173-4.00008-9
Copyright © 2017 Elsevier Inc. All rights reserved.
19
20
Concise Encyclopedia of Self-Propagating High-Temperature Synthesis
Fig. 1 (A) Schematic of bonding with reactive multilayer foils, (B) cross-sectional image of a bond of two components.
Fig. 2 Schematic of bonding a chip module to a heat sink using reactive multilayer foils and solder.
between the chip and the heat sink. Often this is a thermal paste, but well-bonded, metallic interfaces can dissipate heat more effectively. However, not all microelectronic components can be furnace soldered to achieve a conductive metallic interface, particularly at the later stages of assembly. Bonding with NanoFoil limits the thermal exposure of the front side of silicon dies to 100°C for less than a second [8]. The resulting interfaces are very conductive and could prove advantageous for CPUs, GPUs, solar cells, and LED devices [8]. Another example is the sealing of packages containing microelectronic components. The localized heating also allows one to form a metallic or polymeric seal along the perimeter of a package without heating the contents of the package [7,9]. This has been demonstrated at the micron and centimeter scale.
Applications of Reactive Multilayer Foils
Beyond joining and sealing applications, the heat and light released by reactive multilayer foils can be used for a range of commercial and defense applications. In the area of pyrotechnics and explosives, one can ignite flares [10] or initiate reaction trains that lead to air bag deployment or explosive detonation [11]. As a stable and rapid source of energy, electrolytes in thermal batteries can be heated [12] or can act as a heater for other devices. The controllable burning rates can be utilized in chemical time delays [13], and the controllable ignition threshold can be beneficial in novel munitions [14]. All of these applications rely on the ability to store chemical energy for long periods of time and then release it in a tunable and precise manner. Additional investigations into the basic properties and reaction mechanisms within these novel reactive materials will help expand their utilization as controlled sources of heat and light.
REFERENCES [1] Rogachev AS, Mukasyan AS. Comp Expl Shock Waves 2010;46:243–66. [2] Weihs TP. In: Barmak K, Coffey KR, editors. Metallic films for electronic, magnetic, optical and thermal applications. Structure, processing and properties. Swaston: Woodhead Publishing; 2014. p. 160–243 [chapter 6]. [3] Adams DP. Thin Solid Films 2015;576:98–128. [4] Makowiecki D, Bionta R. US Patent 5381944; 1995. [5] Duckham A, Levin J, Weihs T. Adv Sci Technol 2006;45:1578–87. [6] Duckham A. Vacuum technology & coating 2007;65–9. [7] Braeuer J, Gessner T. J Micromech Microeng 2014;24:115002. [8] Van Heerden D, Rude T, Newson J, Knio O, Weihs T, Gallus D. In: Proceedings of the twentieth annual IEEE semiconductor thermal measurement and management symposium; 2004. p. 46–9. [9] Van Heerden D, Deger D,Weihs T, Knio O. US Patent 7,143,568; 2006. [10] Nielson D, Tanner R, Dilg C. US Patent 7,690,308; 2010. [11] Baginski T, Parker T, Fahey W. US Patent 6,925,938; 2005. [12] Ding M, Krieger F, Swank J, Poret J, McMullan C, Chen G. In: 43rd power sources conference, Philadelphia, July 7–10; 2008. [13] Kelly P, Tinston S, Arnell R. Surf Coat Technol 1993;60:597–602. [14] Hugus G, Sheridan E. US Patent 7,955,451, June 7; 2011.
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