This final part of the four-part series will explain the mechanical assembly and soldering process used to make joints during electric vehicle (EV) battery production. Although these two mechanisms are somewhat primitive in nature, they still find applications for making low-cost EVs where the makers do not have access to automation and advanced technologies. (If you haven’t followed along, start with Part 1 here.)
Mechanical assembly
Several joining methods are used to mechanically build battery systems for EVs, each designed to meet specific structural and functional needs. Nut-and-bolt assembly (Figure 1) is a basic method that works especially well for prismatic cell battery modules, providing strong mechanical links for integrating the battery pack. This method precisely controls torque and keeps contact pressure constant across electrical connections.
Figure 1. A nut and bolt assembly connects the prismatic battery cells of EVs. (Image: MDPI)
Figure 2. A spring clasp technology uses a spring mechanism and interconnections to build a battery pack. (Image: Amazon)
Spring clasp technology (Figure 2) changes how batteries are put together by introducing a new type of dynamic link. Spring parts in this method keep the contact pressure constant while allowing for heat expansion and vibration.
Since the system is naturally flexible, adding and removing parts quickly is easy. This makes modular battery architectures possible, which improves serviceability and industrial efficiency.
Snap-fit (Figure 3) mechanisms are another way to integrate mechanical parts because they keep the structure’s integrity without needing extra fixing tools.
The geometric shapes in these engineered interfaces are well thought out and allow positive mechanical interaction through elastic deformation. The connections made are now mechanically stable and easier to assemble, which is especially helpful in settings with a lot of production.
Figure 3. An example of a casing using a snap-fit mechanism to lock two structures. (Image: First Mold)
Self-pierce riveting (Figure 4) is a type of riveting technology used to join parts to assemble battery compartments. This cold-forming method makes strong mechanical links between different types of materials while keeping the electrical conductivity constant. The method can join several layers together without digging first, which speeds up production and makes the structure more reliable.
Figure 4. A rivet mechanism to join two metal sheets during EV battery production by punching through the rivet. (Image: ScienceDirect)
Advantages of mechanical assembly
The mechanical building method has several important advantages for integrating battery systems. It is easy to disassemble things, making them more recyclable and efficient for end-of-life processing. The system’s modular design also facilitates repair procedures and prevents thermal stress during construction, protecting the integrity of the parts.
Disadvantages of mechanical assembly
Mechanical fasteners add extra weight to the system, affecting how efficiently the EV works. Higher electrical resistance at connection places could affect how well the system works, and the cost of making it is higher because of the unique parts and precise assembly needs.
Additionally, mechanical links can come loose during use because they are always moving. Therefore, they need to be carefully designed and maintained regularly.
Soldering
Soldering in EV battery manufacturing involves melting a filler material (solder) to create electrical and mechanical connections between battery components. The process of soldering battery parts is a planned series of steps that start with carefully cleaning the surfaces to eliminate contaminants that might weaken the joint. Next, flux compounds are strategically applied to help the solder flow and adhere to the surfaces.
Once the parts are perfectly lined up, a temperature-controlled soldering iron applies localized thermal energy to the connection interface. This lets the solder alloy change to its liquid phase and flow through capillary action between the prepared metal surfaces. Eventually, a metallurgical bond is formed as the molten solder goes through controlled solidification, establishing mechanical and electrical connectivity between the joined parts. The complete soldering process and identification of the correct solder quality are illustrated in Figure 5.
Figure 5. Different stages of soldering and identifying the correct solder quality. (Image: AutoEdu)
Advantages of soldering
The capacity to join dissimilar materials proves useful in battery pack assembly, where copper bus bars interface with aluminum terminals and various sensing components. This capability facilitates the creation of complex electrical pathways while maintaining optimal conductivity across material boundaries.
The widespread implementation of electronics enables standardized processes for integrating battery management systems and thermal monitoring circuits. Figure 6 shows the EV battery system of the Honda Civic.
Figure 6. A soldered EV battery pack of the Honda Civic using a lead-free Sn-Cu-Ni-Ge alloy. (Image: Japanese Science and Technology Agency)
Disadvantages of soldaering
The process temperatures (180 – 350° C) can compromise the integrity of battery cell seals and introduce thermal stress near critical safety components. The necessity for flux compounds introduces additional complexity in battery environments, where any residual chemical contamination could impact cell chemistry or long-term reliability.
Debris generation and flux neutralization requirements demand stringent quality control protocols, as any conductive particles or corrosive residues could compromise battery safety systems. The labor-intensive nature of precision soldering operations impacts production scalability, particularly in high-volume EV manufacturing environments where thousands of connections require consistent quality.
Summary
The mechanical assembly and soldering type connections mentioned in this article are the least preferred types of all the discussed joining methods during EV battery production. Mechanical assembly leads to connection loosening during shocks and vibrations, and soldering continues to be labor-intensive.
However, these connections are preferred for low cost when very economical EVs are produced and there is an increased supply of labor work. It is expected that as EV battery production evolves, these two mechanisms will be left behind more and more.
References
- Joining Technologies for Automotive Battery Systems Manufacturing, World Electric Vehicle Journal, MDPI
- Automotive battery pack manufacturing – a review of battery to tab joining, Elsevier
- Design Guide for Snap-Fits | Product Design Series, First Mold
- Fasteners for the Battery in Electric Vehicles, Bossard India
- Scaling Up EV Battery Manufacturing, Assembly Magazine
- What is the Temperature for Soldering PCB, NEXTPCB
- EV Battery Module Assembly Solutions, Cognex
- Soldering iron, AutoEdu
Related EE World content
- Ensuring EV battery safety with advanced temperature monitoring
- How advanced conveyors can support EV battery manufacturing
- How is “cell-to-pack” revolutionizing EV battery pack designs?
- Have you considered resistance soldering? Part 2
- Have you considered resistance soldering? Part 1
Filed Under: Battery Power - EV Engineering, FAQs