Key Points of SMD Spring Finger Contacts Welding Process and Performance Optimization

With the rapid development of electronic technology, SMD (Surface Mounted Device) components are increasingly used in various electronic devices. As critical connection components, the performance of SMD spring finger contacts directly affects the stability and reliability of the entire circuit. The welding process plays a crucial role in the performance of SMD spring finger contacts. This article will delve into how the welding process impacts the performance of SMD spring finger contacts and provide corresponding optimization strategies to help improve product quality and reliability.

소개

SMD Spring Finger Contacts are widely used in the following industries due to their compact design, high reliability, and excellent electrical performance:

1. Electronics and Communication Equipment
   • Mobile Devices: PCB interconnects and battery contacts in smartphones, wearables (e.g., smartwatches).
   • RF Modules: High-frequency signal transmission in 5G communication base stations and microwave modules, leveraging their low contact resistance and anti-interference properties.
2. 자동차 전자 제품
   • New Energy and Smart Vehicles: Reliable connections in battery management systems (BMS), onboard sensors, and electronic control units (ECUs), designed to withstand vibrations and temperature fluctuations.
   • Automotive ECUs: Signal transmission for engine control and ADAS systems.
3. Industrial Automation and Power Equipment
   • High-Voltage Switchgear: Used in compact control circuits for gas-insulated switchgear (GIS), while traditional spring finger contacts (e.g., beryllium copper types) are more common in medium/high-voltage conductor connections.
   • Industrial Sensors and Controllers: Signal interfaces for harsh-environment applications (e.g., temperature/pressure sensors).
4. 의료 기기
   • Portable Medical Instruments: Low-power connections in ECG monitors, glucose meters, and other precision devices requiring long-term stability and biocompatibility.
5. 항공우주 및 방위
   • 항공 전자 공학: High-density interconnects for onboard communication and navigation systems, resistant to extreme temperatures and vibrations.
   • Satellites and Radar Systems: Lightweight designs and high-frequency performance requirements.
6. Renewable Energy and Energy Storage Systems
   • Photovoltaic Inverters and Energy Storage: Compact battery pack interconnects and power modules compatible with automated SMT manufacturing.

1. Impact of Welding Process on Performance

1.1 Electrical Performance

• 접촉 저항: Poor welding quality, such as cold solder joints, insufficient or excessive solder, can lead to unstable electrical connections between SMD spring finger contacts and the circuit board, thereby increasing contact resistance. An increase in contact resistance may cause energy loss during signal transmission, resulting in signal attenuation and affecting the performance of the entire circuit, especially in high-frequency and high-speed signal transmission applications.
• 전도성: Improper temperature control during welding may cause oxidation or other chemical reactions in the metal material of the contact points, altering their conductive properties. For example, excessively high welding temperatures may damage the gold-plated layer of the spring finger, reducing its good conductivity and thus affecting the conduction performance and signal transmission quality of the entire circuit.

1.2 Mechanical Performance

• Connection Strength: The welding process directly determines the connection strength between SMD spring finger contacts and the PCB. If the welding temperature is too low or the time is too short, the solder cannot fully melt and wet the surface of the solder joints, leading to weak connections. In subsequent use, the spring finger is prone to loosening or detachment due to external forces. Conversely, if the welding temperature is too high or the time is too long, it may cause overheating of the solder pads or the metal materials of the spring finger, resulting in a decline in material performance or even brittleness of the solder joints, which will also reduce the connection strength and affect product reliability.
• Elasticity Performance: Improper welding processes may affect the elasticity of the spring finger. Excessive welding temperatures may cause annealing of the metal material of the spring finger, reducing its elastic modulus and making the spring finger less elastic. This means it cannot provide sufficient contact pressure, affecting the contact effect with other components and potentially leading to poor contact over time.

1.3 Thermal Performance

• 열 전도성: Welding quality affects the thermal conductivity between SMD spring finger contacts and the PCB. Good welding can form an effective thermal conduction path, helping to dissipate heat generated by the spring finger during operation onto the PCB promptly and lower its own temperature. Poor welding increases thermal resistance, causing heat to accumulate at the spring finger, raising local temperatures. This not only affects the performance of the spring finger itself but may also adversely impact surrounding electronic components. For example, in high-temperature environments, poorly welded solder joints may fail due to mismatched coefficients of thermal expansion, resulting in disconnection between the spring finger and the PCB.
• 열 안정성: The welding process affects the thermal stability of the solder joints. In different working temperature environments, the solder joints need to maintain stable performance. If the welding process is inappropriate, the solder joints may crack or deform when temperatures change, affecting the performance of SMD spring finger contacts and the stability of the entire circuit.

1.4 Solderability and Appearance

• Solderability: If there are issues with the welding process, such as improper selection of flux or incomplete cleaning of the welding surface, it may result in poor wetting of the solder on the surface of the spring finger, affecting the quality and reliability of the welding. This not only increases the probability of welding defects but also makes subsequent maintenance and replacement work more difficult.
• Appearance: The welding process also affects the appearance of SMD spring finger contacts. During welding, if there is solder splashing, rough solder joints, or bridging issues, it will affect the overall appearance of the product and give a sense of poor quality. Moreover, poorly appearing solder joints may hide internal quality problems that require further inspection and evaluation.

2. Welding Process Optimization Strategies

To improve the performance of SMD spring finger contacts, optimization measures can be taken from the following aspects: welding preparation, welding process control, post-welding treatment, and inspection.

2.1 Welding Preparation

• Component Selection and Evaluation: Choose SMD spring finger contacts and appropriate solder and flux according to specific application requirements. Ensure good solderability of the spring finger, and that the solder’s melting point, wettability, and other properties meet the requirements. The flux should have suitable activity and residue characteristics.
• PCB Design Optimization: Rationally design the layout and shape of the PCB’s solder pads to ensure they match the size of SMD spring finger contacts and provide a good basis for welding. At the same time, consider factors such as spacing between solder pads and solder mask design to avoid short circuits and bridging issues during welding.
• Surface Treatment: Clean the surfaces of SMD spring finger contacts and PCB solder pads to remove impurities such as oxide layers, oil stains, and dust, improving the wettability and bonding strength of the welding. Chemical cleaning and mechanical polishing can be used for surface treatment, but care must be taken to avoid damaging the components and solder pads.

2.2 Welding Process Control

• Welding Equipment Selection and Parameter Setting: Accurately set the welding temperature based on the characteristics of SMD spring finger contacts and solder. Generally, the peak temperature of reflow soldering should be 30 – 50℃ higher than the solder’s melting point, and the temperature of wave soldering is usually between 240 – 260℃. Ensure stability and uniformity of the temperature curve to avoid local overheating or insufficient temperature. Reasonably control the welding time. The dwell time of reflow soldering is generally 60 – 120 seconds, and the peak temperature holding time is 5 – 10 seconds; the dipping time of wave soldering is usually 2 – 4 seconds. Adjust appropriate welding speed for wave soldering based on PCB size, thickness, and component density, generally between 0.8 – 1.5 meters/minute.
• Welding Atmosphere Control: Use nitrogen protection and other measures during welding to reduce oxygen content, prevent oxidation of metal surfaces, and improve welding quality. The purity of nitrogen should generally reach above 99.9%.
• Welding Techniques: Operators should have skilled welding techniques to ensure stability and consistency during the welding process. When manually welding, pay attention to the angle and pressure of the soldering iron to avoid mechanical damage or displacement to SMD spring finger contacts.

2.3 Post-Welding Treatment and Inspection

• 청소: Clean the PCB immediately after welding to remove residual flux and other impurities on the surface, preventing them from adversely affecting the performance of SMD spring finger contacts. Methods such as water cleaning and solvent cleaning can be used, ensuring the PCB surface is dry after cleaning.
• Appearance Inspection: Visually inspect the appearance of welded SMD spring finger contacts to check if the solder joints are full and smooth, without defects such as cold solder joints, missing solder, bridging, or solder splashing. Repair or rework any poorly appearing solder joints promptly.
• Performance Testing: Use professional testing equipment and methods to test the electrical and mechanical properties of SMD spring finger contacts, such as measuring contact resistance with a multimeter, testing connection strength with a tensile testing machine, and detecting thermal performance with a thermal imager to ensure their performance meets design requirements.

In summary, the welding process has a significant impact on the performance of SMD spring finger contacts. By optimizing various links in the welding process, including preparation before welding, process control during welding, and treatment and inspection after welding, we can effectively improve the performance of SMD spring finger contacts and enhance the overall quality and reliability of electronic products.