SMT Process Parameters and Design Requirements

After initially designing the SMT process flow based on the SMT assembly method for electronic assembly, the most critical step is SMT process design (requirements). The design must be carried out in accordance with the component database, circuit design, circuit wiring, process materials in the overall design, as well as the actual conditions of the existing SMT production lines and equipment. 1. Production Volume, Efficiency and Takt Time 1) SMT Production Volume The designed total production volume converted to the single-shift (8h) designed output is calculated as: Single-shift (8h) designed output = Total designed output ÷ 12 months ÷ 20 working days The output and efficiency of an SMT production line mainly depend on the speed of the chip mounter, with an average operating rate of 50%~70%. The mounting speed can be estimated based on the projected output: Mounting speed = Single-shift (8h) designed output × Total number of components ÷ 8 ÷ (50%~70%) The single-shift output can also be calculated based on existing chip mounters: Single-shift output = 8×3600 ÷ [Total number of CHIPs × Placement time (s) per CHIP + Total number of ICs × Placement time (s) per IC] 2) Takt Time Calculation Based on Production Volume Takt time varies significantly across different SMT processes and equipment, with sufficient preparation and waiting time reserved. For fully automatic online screen printers and flippers, the entire line can realize continuous soldering through the process: Screen Printer → Chip Mounter → Reflow Oven → Wave Soldering Machine. Reasonable design of transmission speed ensures matching takt time and production efficiency. For high production volume, parallel production is recommended: two complete production lines (equipped with all process equipment) to avoid bottlenecks, suitable for multi-variety and mass production. In-line sequential chip mounters (multiple units) can be paired with high-capacity reflow ovens or wave soldering machines to form a production line, also applicable for multi-variety and mass production. Using trolleys for material transfer between equipment is a flexible solution, especially for processes requiring board flipping and THT equipment such as wave soldering machines. 2. SMT Equipment Upgrading SMD and SMT technologies are evolving rapidly, and existing equipment may fail to meet new process requirements, necessitating equipment upgrades for the following scenarios: ① For fine-pitch components (pitch < 0.5mm) and double-sided PCBs with micro-packaged devices (CSP, MCM, etc.): High-precision mounting equipment or nitrogen protection equipment must be added if the original screen printers and chip mounters are standard models. ② For lead-free soldering: Dedicated lead-free reflow ovens are required as conventional reflow ovens cannot meet the process standards. ③ For wave soldering of SOP/SOT components: If the original wave soldering machine is incompatible, process optimization, equipment replacement or even circuit design modification is required. 3. Key SMT Process Parameter Design for Equipment ① Screen Printer & Dispenser Determine the use of screen stencil or stencil plate, set stencil thickness, and define the standing time and storage method of solder paste/adhesive after printing. ② Chip Mounter Specify the alignment method (laser alignment or vision alignment) for components with a specific pitch and above; for multi-mounter in-line operation, define the type and quantity of components assigned to each mounter, and confirm the programming method. ③ Reflow Oven Select the reflow soldering type, and determine whether nitrogen protection, no-clean process or lead-free soldering is required, based on component specifications (e.g., maximum withstand soldering temperature) and process material parameters (e.g., solder paste temperature curve), as well as double-sided soldering process requirements. ④ Wave Soldering Machine Confirm the applicability of no-clean process, set soldering temperature and transmission speed; determine whether to adopt through-hole reflow soldering or selective wave soldering. The above content summarizes the SMT process parameters and design requirements for all links, covering production efficiency, production volume, equipment upgrading and equipment process parameter setting. Zhongke Tongzhi www.torchsemi.com A professional one-stop PCBA & SMT manufacturing service provider, offering electronic OEM, PCBA turnkey service and SMT chip mounting processing. Exhibition Invitation Zhongke Tongzhi Invites You to SEMI-e 2025 Shenzhen International Semiconductor Exhibition & Its Dual Carbon Certification Achievement