Wave soldering is a process in which the soldering surface of a printed circuit board (PCB) comes into direct contact with high-temperature liquid tin to create a strong and reliable electrical connection. The liquid tin is maintained at an angle, forming a wave-like motion through special mechanisms, hence the term "wave soldering." The primary material used is a solder bar, and modern wave soldering machines typically use heat radiation for preheating. Common preheating methods include forced hot air convection, electric heating plates, infrared heating, and electric heating rods.
**Wave Soldering Procedure Flow**
1. **Preparation Before Wave Soldering**
Ensure that the PCB has already undergone SMD adhesive application, component placement, adhesive curing, and THC insertion. Check that the soldering areas of the component sockets and gold fingers are coated with solder resist or covered with high-temperature adhesive tape to prevent solder from clogging the connectors. For larger slots or holes, apply high-temperature tape to avoid solder flow onto the top side of the PCB. Connect the flux hose to the sprayer.
2. **Turn On the Wave Soldering Furnace**
- Power on the wave soldering machine and the exhaust fan.
- Adjust the conveyor belt or fixture width according to the PCB size.
3. **Set Wave Soldering Parameters**
- **Flux Flow Rate:** Adjust based on how well the flux covers the bottom of the PCB. A small amount should seep up through the via holes but not penetrate the entire assembly.
- **Preheating Temperature:** Typically 90–130°C on the top surface of the PCB. Thicker boards or those with more components may require higher temperatures.
- **Conveyor Speed:** Usually set between 0.8–1.92 m/min, depending on the machine and PCB design.
- **Solder Pot Temperature:** Should be about 5–10°C higher than the peak temperature.
- **Probe Height:** Adjust so that the probe is positioned 2/3 of the PCB thickness from the bottom.
4. **Wave Soldering and Inspection**
- Place the PCB on the conveyor belt. The machine will automatically spray flux, dry, preheat, solder, and cool.
- Hold the PCB at the exit point.
- Follow factory inspection standards to evaluate quality.
5. **Adjust Parameters Based on Results**
If defects are found, adjust the parameters accordingly.
6. **Continue Production**
- Weld PCBs one by one.
- At the exit, inspect and place the PCB in an anti-static box for repair.
- Continuously check each board during production. If severe defects occur, re-solder immediately and adjust parameters if needed.
7. **Inspection Standards**
All inspections must follow the factory’s defined standards.
8. **Notes**
- Preheating rate should not exceed 3°C per second to avoid overheating.
- Keep at least 3 cm between PCBs when the furnace is full.
- If the wave soldering temperature is out of range, stop the machine immediately and have engineers check it before resuming.
- Technicians must check and measure the wave soldering temperature daily to ensure it remains within the specified range.
**Wave Soldering Technical Requirements**
Meeting the above conditions provides a foundation for good soldering. To achieve high-quality results, technical parameters must be carefully set and optimized. Key aspects include avoiding issues like insufficient soldering, bridging, pinholes, bubbles, cracks, and poor tinning. These parameters should be tested, analyzed, and recorded for future reference. Flux flow control and tilt angle adjustment are critical. For general through-hole components, a flow rate of 1.8 L/H is typical, and the tilt angle should be between 6–10 degrees.
**Wave Soldering Furnace Temperature and Time Control**
The dwell time in wave soldering refers to the time the PCB spends in contact with the solder wave. It can be calculated as: dwell time = wave width / conveyor speed. Different machines may have varying wave widths, so adjusting the conveyor speed ensures a minimum of 2.5 seconds of contact. In practice, visual inspection is often used, but this doesn’t guarantee solder joint strength or conductivity, leading to potential "cold solder" issues. According to research, the metallographic structure of the solder joint changes in three stages: initial bonding, full alloy formation, and brittle phase development. Controlling these stages is crucial for high-quality joints. Proper temperature, time, and tilt angle settings help reduce defects and improve reliability.
**Wave Soldering Temperature Curve**
The temperature profile of the wave soldering process is determined by the equipment's zone settings, molten solder temperature, and conveyor speed. Testing is essential to establish the correct curve. During testing, the conveyor speed is first set, then the temperature is measured at key points. Adjustments are made until the desired curve is achieved. Process documentation should include all relevant parameters such as flux settings, solder wave characteristics, and solder quality checks.
**Wave Soldering Structure**
Understanding the structure of the wave soldering machine helps in controlling the temperature curve effectively. This diagram illustrates the internal layout and key components involved in the wave soldering process.
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