Journal of Manufacturing Processes 16 (2014) 183–189 Contents lists available at ScienceDirect Journal of Manufacturing Processes j ourna l h o me page: www.elsevier.com/locate/manpro Electrical performance of laser braze-welded aluminum–copper interconnects Tobias Solchenbach a,∗ , Peter Plapper a , Wayne Cai b a University of Luxembourg, FSTC, 6, rue Coudenhove-Kalergi, 1359 Luxembourg, Luxembourg b GM Global R&D, 30500 Mound Road, Warren, MI 48090-9055, USA a r t i c l e i n f o Article history: Received 16 October 2013 Received in revised form 9 December 2013 Accepted 18 December 2013 Available online 11 January 2014 Keywords: Laser braze-welding Aluminum–copper Contact resistance Weld seam layout a b s t r a c t The reported investigation is related to laser beam braze-welding technology for dissimilar aluminum–copper interconnects for Li-ion battery assembly. The correlation between the brittle and high-resistivity intermetallic compounds and the electrical contact resistance showed that a thin inter- metallic layer is highly desirable. It was proved that highest shear strength and lowest contact resistance can be achieved within the same parameter set which is of particular interest to battery electrical vehicle applications requiring both high mechanical reliability and electrical performance. A study on the weld seam layout further showed that two parallel weld seams with optimized spacing and overlap design provide lowest contact resistance. © 2013 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved. 1. Introduction Lithium-ion batteries are key components in the pursuit of high performance energy storage for electric vehicles. Their good volu- metric power and energy density and the high open-circuit voltage are the main advantages compared to other battery types, e.g. NiMH cells [1]. Prismatic cells are increasingly replaced by pouch cells, even in space applications [2], which are characterized by a thin housing and two flat connection terminals typically made of aluminum and copper. Several cells are combined into battery modules which usually include monitoring electronics to track the state of health and state of charge of each cell. A number of battery modules are assem- bled to the traction battery pack designed specifically to meet the geometry requirements of the vehicle [3]. For the battery module assembly, cell-to-cell as well as cell-to-busbar joining operations are required. Hence, Al–Al and Cu–Cu joining for parallel connec- tions, and dissimilar materials Al–Cu joining for serial joining have to be made, see Fig. 1. The gauge of the battery terminals is typically 0.2 mm, the gauge of the bus bars ranges from 0.5 to 1.0 mm. A battery pack for electric (EV) or hybrid electric vehicles (HEV) consists of hundreds of individual battery cells. Thus, a reliable and robust joining process is mandatory for the large number ∗ Corresponding author. Tel.: +352 466644 5849. E-mail addresses: tobias.solchenbach@uni.lu (T. Solchenbach), peter.plapper@uni.lu (P. Plapper), wayne.cai@gm.com (W. Cai). of joining operations per vehicle. In addition to good static and fatigue strength, excellent electrical contact resistance is crucial for battery connections since the power loss at each joint is directly proportional to the contact resistance which can be calculated by P loss = R contact × I 2 . The commonly used mechanical fastening with bolts and nuts provides for easy disassembly but adds extra parts with added cost and mass. Mechanical fastening, however, has a distinctive disad- vantage: the form locking mechanism between the mating parts leads to a small effective conducting area, so called a-spots, caused by the roughness of the surface [4]. It is estimated that the contact resistance for this case can be expressed as: R contact =  2a +  a 2 (1) where  is the contact resistivity, a the radius of the surface-to- surface contact area and  the resistance per area of oxide, sulfide or other inorganic films which are generally present on metal surfaces. Thus, fusion welding processes are desirable, providing full bonding between both parts. Only minor bonding defects would cause imperfections and increase the resistance. Besides ultrasonic welding [5,6], friction stir welding [7] and roll-plating [8], many research efforts have been made in the area of laser beam welding. Laser light has the advantage of high power density and excellent controllability which enables welding of dis- similar material combinations [9–12]. During the fusion welding process, materials are mixed and consequently alloyed. In the Al–Cu binary system, several inter- metallic compounds (IMC) are formed which are characterized by 1526-6125/$ – see front matter © 2013 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jmapro.2013.12.002