This article outlines key considerations for PCB design to ensure efficient and high-quality SMT (Surface Mount Technology) assembly. SYS Tech, a leader in express PCB assembly in Shenzhen, China, provides small and medium-sized SMT PCB assembly production using industry-leading equipment, including multi-functional SMT machines, reflow ovens, wave soldering, BGA rework stations, AOI, and X-RAY testing. The article highlights several design aspects crucial for SMT assembly, such as the proper placement and size of fiducial marks (round or square, 1.0mm diameter), their distance from surrounding copper, and the requirement for marks at the corners of the board. Additionally, it emphasizes the importance of board panel size, component pad pitch, and the positioning of SMT holes. Special considerations for PCB design include ensuring the board is vacuum-packed and pre-baked if it is out of shelf life, and the need for a first article check before mass production.
1. Jian Ding (Wuxi) Electronics Co., Ltd. Main business: Printed Circuit Boards (PCBs) 2. Wuxi Gaode Electronics Co., Ltd. Main business: PCBs 3.Hanyu Bode Technology (Jiangyin) Co., Ltd. Main business: Various types of multilayer printed circuit boards 4.Hushi Electronics Co., Ltd. Main business: S
In PCB design, layout is crucial to ensuring a functional and optimized board. The process begins with creating any missing component package models in the library. Design parameters, such as layer count and size, are then set based on circuit requirements. The netlist is loaded to populate component models in the design window. During layout, components are arranged using a combination of automatic and manual techniques, aiming for neatness and effective routing. Routing follows, with automatic routing first, then manual adjustments if necessary. A design rule check (DRC) ensures no component overlaps or short circuits. Simulation analysis is then conducted to assess and improve the layout's signal integrity. The final PCB design is saved, printed layer-by-layer, and outputted for production.
In SMD (Surface Mount Device) placement, two types of processing methods exist: normal and high-precision. Normal SMD placement requires low precision, often using resistors and capacitors, with small quantities and irregular shapes. Solder paste is typically applied with a semi-automatic or manual printer, and components are mounted manually. Reflow soldering is the common method for welding. High-precision SMD placement, essential for FPCs (Flexible Printed Circuits), requires fiducial marks, flat surfaces, and advanced equipment due to FPC’s difficulty in fixing and maintaining consistency in mass production. The FPC is mounted on a thermally stable pallet using high-temperature-resistant tape. For accurate solder paste application, an elastic scraper and optical positioning system are recommended, with stringent process controls to ensure print and mounting accuracy, as minor discrepancies affect quality more significantly than in rigid PCB assembly.
In the solder paste printing process, various factors can lead to defects. Key issues include delayed addition or poor quality of solder paste, foreign object contamination, and the use of expired paste. PCB pad quality issues, such as solder resist or silkscreen contamination, can also affect solder adhesion. Other common issues are loose clamping of the PCB during printing, uneven stencil thickness, damaged scrapers, and inappropriate equipment settings for pressure, angle, speed, and demoulding speed. Additionally, human error may lead to accidental disturbances post-printing. Addressing these issues is essential to improve print quality and ensure optimal solder paste application.
DIP (Dual In-line Package) processing, also known as through-hole technology, is a method for mounting electronic components on PCBs, either manually or with an automatic plug-in machine, by inserting components into drilled holes and soldering them to the PCB pads. This method offers mechanical strength, making it ideal for robust applications such as aerospace. However, DIP processing requires additional drilling, increasing PCB costs, and limits available wiring areas in multilayer boards, as through-holes extend across all layers. Due to these constraints, DIP is mainly used for larger components, while high-speed or high-frequency designs often prefer SMT to reduce stray inductance and capacitance, essential for circuit performance, particularly in miniaturized prototypes.