Poor Soldering on Lithium Battery Control Boards? A Real Improvement Case Using Singway Solder Wire

Lead-Free Solder Wire for Lithium Batteries
With the explosive growth of the new energy vehicle and energy storage industries, the lithium battery control board (BMS/PCM) is a critical component of the battery system, and its soldering quality directly affects battery safety and service life. However, a lithium battery intelligent manufacturing company encountered the following difficulties in lithium battery soldering: a defective rate of up to 20% on control boards, mainly manifested as cold joints, cracked solder joints, weak soldering, as well as “solder balls” and “tombstoning.”
The company tested various brands of soldering iron solder wire and lead-free solder wire but still could not solve the core issue of joint strength and reliability. In response, the Singway solder wire technical team went to the site to investigate. They found that the lithium battery control boards extensively used materials such as nickel sheets, aluminum substrates, and stainless steel coatings. These materials easily form dense oxide films on their surfaces, preventing ordinary solder wire from wetting them effectively, leading directly to “solder repellence” and “false soldering.” Second, the control boards had both high-current thick copper pads (3oz–10oz) and precision packaged ICs and NTC thermistors, resulting in large thermal mass differences. During soldering, either large joints absorbed heat too quickly, causing cold joints, or small components overheated and were damaged. Finally, the working environment of lithium batteries demands high vibration resistance and high-temperature shock resistance. If there are microcracks or brittle IMC layers inside the solder joints, long-term use may lead to signal interruption, increased internal resistance, or even thermal runaway risks.

To address this, Singway Solder Wire tailored a comprehensive solution for the customer:

1. Special Alloy Adjustment for Lithium Battery Solder Wire: Based on the soldering characteristics of different areas on the lithium battery control board, Singway selected Sn99.3Cu0.7 environmentally friendly lead-free no-clean solder wire as the base formula, supplemented with trace element optimization. This alloy offers excellent electrical conductivity, ductility, and fatigue resistance, making it particularly suitable for withstanding thermal expansion and contraction stress during battery charge-discharge cycles. For high-current thick copper pads (3oz–10oz), Singway recommended a special 2.0mm diameter solder wire, ensuring “fast wetting” and one-shot forming even on rough, fast-heat-absorbing surfaces.

2. Flux Activity and Flux Content Optimization: The dense oxide films on materials like nickel sheets and aluminum substrates on lithium battery control boards cannot be penetrated by the rosin activity of ordinary solder wire. The Singway technical team adjusted the flux formulation inside the solder wire, moderately increasing the activator ratio while maintaining halogen-free environmental compliance, enhancing wetting capability on stubborn coatings. The improved lithium battery-specific solder wire can quickly spread upon contact with the solder joint, forming smooth, full joints with significantly improved solder wicking.

After testing sample formulations of the adjusted lithium battery solder wire, Singway’s dedicated lithium battery solder wire resolved issues such as residual solder balls and unreliable solder joints. All production successfully switched to Singway lead-free solder wire. Singway Solder Wire, as a national high-tech enterprise with over ten years of experience in solder material R&D and manufacturing, focuses on high-quality lithium battery solder wire, lead-free solder wire, silver-containing solder wire, and customized soldering materials. The solder wire factory is certified under ISO9001 and ISO14001, and its products comply with RoHS, REACH, halogen-free, and other environmental standards. If you have any questions about lithium battery soldering, Singway can provide “one-to-one material matching” customized lithium battery soldering services. Please feel free to contact us!