Fabrication, assembly and heat transfer testing of low-profile copper-based microchannel heat exchangers

This paper presents the feasibility of highly reliable and repeatable copper–tin transient liquid phase (Cu–Sn TLP) bonding as applied to die attachment in high temperature operational power modules. Electrified vehicles are attracting particular interest as eco-friendly vehicles, but their power modules are challenged because of increasing power densities which lead to high temperatures. Such high temperature operation addresses the importance of advanced bonding technology that is highly reliable (for high temperature operation) and repeatable (for fabrication of advanced structures). Cu–Sn TLP bonding is employed herein because of its high remelting temperature and desirable thermal and electrical conductivities. The bonding starts with a stack of Cu–Sn–Cu metal layers that eventually transforms to Cu–Sn alloys. As the alloys have melting temperatures (Cu3Sn: > 600 °C, Cu6Sn5: > 400 °C) significantly higher than the process temperature, the process can be repeated without damaging previously bonded layers. A Cu–Sn TLP bonding process was developed using thin Sn metal sheets inserted between copper layers on silicon die and direct bonded copper substrates, emulating the process used to construct automotive power modules. Bond quality is characterized using (1) proof-of-concept fabrication, (2) material identification using scanning electron microscopy and energy-dispersive x-ray spectroscopy analysis, and (3) optical analysis using optical microscopy and scanning acoustic microscope. The feasibility of multiple-sided Cu–Sn TLP bonding is demonstrated by the absence of bondline damage in multiple test samples fabricated with double- or four-sided bonding using the TLP bonding process.

Section: Die-attachment Bonding Technologies For High Temperature Pow...mentioning

confidence: 99%

Reliable and repeatable bonding technology for high temperature automotive power modules for electrified vehicles

Yoon¹,

Glover

Mantooth

et al. 2012

“…Subsequent bonding of Al and Cu caps to open 1D microchannel arrays led to the formation of Al-and Cubased, enclosed, microchannel heat exchangers (MHEs) [5]. Such Al and Cu MHEs can be made with low profile and high cooling capacity in the single-phase, forced flow, convective heat transfer regime [6].…”

Section: Introductionmentioning

confidence: 99%

Aluminum-based one- and two-dimensional micro fin array structures: high-throughput fabrication and heat transfer testing

Primeaux

Zhang

et al. 2017

Microscale fin array structures were replicated onto surfaces of aluminum 1100 and aluminum 6061 alloy (Al1100/Al6061) sheet metals through room-temperature instrumented roll molding. Aluminum-based micro fin arrays were replicated at room temperature, and the fabrication process is one with high throughput and low cost. One-dimensional (1D) micro fin arrays were made through one-pass rolling, while two-dimensional (2D) micro fin arrays were made by sequential 90° cross rolling with the same roller sleeve. For roll molding of 1D micro fins, fin heights greater than 600 µm were achieved and were shown to be proportional to the normal load force per feature width. At a given normal load force, the fin height was further shown to scale inversely with the hardness of the sheet metal. For sequential 90° cross rolling, morphologies of roll molded 2D micro fin arrays were examined, which provided clues to understand how plastic deformation occurred under cross rolling conditions. A series of pool boiling experiments on low profile Al micro fin array structures were performed within Novec 7100, a widely used commercial dielectric coolant. Results for both horizontal and vertical surface orientations show that roll molded Al micro fin arrays can increase heat flux at fixed surface temperature as compared to un-patterned Al sheet. The present results further suggest that many factors beyond just increased surface area can influence heat transfer performance, including surface finish and the important multiphase transport mechanisms in and around the fin geometry. These factors must also be considered when designing and optimizing micro fin array structures for heat transfer applications.

“…While many investigations into microchannel heat exchangers (MHEs) focused on Si-based devices [8,9], Cu and Al have higher bulk thermal conductivities than Si [10]. Lu et al fabricated Cu-based, single-layered MHEs, which yielded a heat flux removal capacity of ~240 W cm −2 at a Reynolds number (Re) of ~1200 [11]. Double-layered Cu MHEs were also fabricated, which decreased the pressure drop for liquid flow by over 50% as compared to single-layered MHEs [12].…”

Section: Introductionmentioning

confidence: 99%

“…Double-layered Cu MHEs were also fabricated, which decreased the pressure drop for liquid flow by over 50% as compared to single-layered MHEs [12]. Metal-based MHEs combine high heat transfer performance and low area/volume footprint, as well as high mechanical robustness [11,12].…”

Section: Introductionmentioning

confidence: 99%

Internal passivation of Al-based microchannel devices by electrochemical anodization

Hymel

Guan

et al. 2015

Metal-based microchannel devices have wide-ranging applications. We report here a method to electrochemically anodize the internal surfaces of Al microchannels, with the purpose of forming a uniform and dense anodic aluminum oxide (AAO) layer on microchannel internal surfaces for chemical passivation and corrosion resistance. A pulsed electrolyte flow was utilized to emulate conventional anodization processes while replenishing depleted ionic species within Al microtubes and microchannels. After anodization, the AAO film was sealed in hot water to close the nanopores. Focused ion beam (FIB) sectioning, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) were utilized to characterize the AAO morphology and composition. Potentiodynamic polarization corrosion testing of anodized Al microtube half-sections in a NaCl solution showed an order of magnitude decrease in anodic corrosion current when compared to an unanodized tube. The surface passivation process was repeated for Al-based microchannel heat exchangers. A corrosion testing method based on the anodization process showed higher resistance to ion transport through the anodized specimens than unanodized specimens, thus verifying the internal anodization and sealing process as a viable method for surface passivation of Al microchannel devices.