1. SMT Technology Overview and Definition
Technologie de montage en surface (SMT) is the most mainstream technology and process in the electronics assembly industry. It refers to the direct mounting of surface mount components (SMC/SMD, chip components) without leads or with short leads onto the surface of printed circuit boards (PCBs) or other substrates, achieving circuit connection through reflow soldering or dip soldering processes.
2. Basic SMT Process Flow
2.1 Complete Process Chain
Solder Paste Printing → Component Placement → Reflow Soldering → AOI Optical Inspection → Rework → Panel Separation
2.2 Core Process Details
Processus d'impression de la pâte à braser
- Function: Transfer solder paste or adhesive to PCB pads in preparation for component soldering
- Equipment: Fully automatic high-precision stencil printer
- Position: Front end of SMT production line
- Technical requirements: Printing accuracy ±0.05mm, thickness consistency >90%
Component Placement Process
- Function: Accurate installation of surface-mount components to fixed positions on PCB
- Equipment: High-precision multi-function pick-and-place machine
- Position: Process after stencil printing
- Technical indicators: Placement accuracy ±0.025mm, speed >30,000 CPH
Reflow Soldering Process
- Function: Precise temperature control melts solder paste to achieve a reliable connection between components and PCB
- Equipment: Multi-zone reflow oven
- Process parameters:
- Preheat zone: Room temperature→150℃, heating rate 1-3℃/second
- Soak zone: 150→180℃, duration 60-120 seconds
- Reflow zone: Above 183℃, peak temperature 210-230℃
- Cooling zone: Cooling rate 2-4℃/second
AOI Inspection optique
- Function: Automated inspection of soldering quality and assembly quality
- Detection capabilities: Missing parts, incorrect parts, misalignment, reversed polarity, solder joint defects, etc.
- Equipment types: 2D/3D AOI, X-Ray inspection systems
3. SMT Process Types and Applications
3.1 Single-Side Assembly Process
Incoming Inspection → Solder Paste Printing → Component Placement → Drying → Reflow Soldering → Cleaning → Inspection → Rework
Application scenarios: Consumer electronics products, simple circuit modules
3.2 Double-Side Assembly Process
Solution A (Full reflow soldering):
Side A: Solder paste printing→Component placement→Reflow soldering
↓
Flip PCB
↓
Side B: Solder paste printing→Component placement→Reflow soldering
↓
Cleaning→Inspection→Rework
Solution B (Mixed soldering):
Side A: Solder paste printing→Component placement→Reflow soldering
↓
Flip PCB
↓
Side B: Adhesive dispensing→Component placement→Curing→Wave soldering
↓
Cleaning→Inspection→Rework
3.3 Mixed Assembly Process Solutions
SMD First, DIP Second Process (SMD > DIP):
Incoming Inspection → Side B Adhesive Dispensing → Component Placement → Curing
↓
Flip → Side A Component Insertion → Wave Soldering
↓
Cleaning → Inspection → Rework
DIP First, SMD Second Process (DIP > SMD):
Incoming Inspection → Side A Component Insertion → Flip
↓
Side B Adhesive Dispensing → Component Placement → Curing
↓
Flip → Wave Soldering → Cleaning → Inspection → Rework
4. SMT Technical Advantages Analysis
4.1 Miniaturization Advantages
- Component size reduced to 1/10 of traditional DIP components
- Weight reduced by 60-80%
- Assembly density increased by 3-5 times
- Lead pitch minimized to 0.3mm
4.2 Electrical Performance Improvement
- Parasitic inductance and capacitance were reduced by more than 50%
- Signal transmission delay reduced by 30%
- High-frequency characteristics improved, operating speed increased
- Electromagnetic compatibility (EMC) has significantly improved
4.3 Production Efficiency and Cost
- Automation degree >95%
- Production efficiency increased by 2-3 times
- Comprehensive cost reduced by 30-50%
- Material utilization rate increased by 40%
4.4 Quality and Reliability
- Solder joint defect rate <50ppm
- Vibration resistance improved by 5-10 times
- Product failure rate reduced by 60%
- Mean Time Between Failures (MTBF) extended
5. Quality Control System
5.1 Combination of Detection Methods
- Online inspection: AOI, SPI (Solder Paste Inspector)
- Offline inspection: X-Ray, ICT flying probe test
- Functional test: FCT functional tester
- Microscopic analysis: Microscope, electron microscope
5.2 Key Process Control Points
- Solder paste printing thickness control: 0.1-0.15mm
- Placement accuracy control: ±0.05mm
- Real-time monitoring of the reflow soldering temperature profile
- Moisture-sensitive device (MSD) management
6. Technology Development Trends
6.1 Miniaturization Progress
- Mass production application of 01005-size components
- 0.3mm pitch micro-spacing technology
- 3D stacked packaging (SiP) integration
6.2 Intelligent Manufacturing
- Manufacturing Execution System (MES)
- Machine vision AI quality inspection
- Optimisation du processus de jumelage numérique
- Systèmes de maintenance prédictive
6.3 Green Manufacturing
- Lead-free soldering process
- Low VOC cleaning agents
- Energy consumption reduced by 30%
- Waste recycling rate >95%
7. Application Field Expansion
- Electronique grand public: Smartphones, tablets, wearable devices
- Communication equipment: 5G base stations, optical communication modules
- Électronique automobile: ADAS systems, in-vehicle entertainment
- Industrial control: PLC, industrial computers
- Électronique médicale: Monitoring equipment, diagnostic instruments
- Aérospatiale: Satellite communication, flight control
As the fundamental core process of modern electronics manufacturing, SMT technology continues to drive electronic products toward smaller size, higher performance, and greater reliability through continuous technological innovation and process optimization, providing important support for the technological progress of the electronic information industry.