SMT chip defective repair skills and process requirements

In our common SMT patch processing process, there will be more or less poor welding after reflow soldering. Therefore, it is necessary for us to manually use tools to perform rework to obtain qualified PCBA solder joints.

1. Repair techniques

1. When manual rework and welding, the SMT chip components should be welded in accordance with the principle of first small and then large, first low and then high. First, weld chip resistors, chip capacitor transistors, and then small IC devices and large IC devices.

2. When welding chip components, the width of the soldering iron tip should be consistent with the width of the component. If it is too small, it will be difficult to position during assembly and soldering.

3. When welding devices with pins on two or four sides such as SOP, QFP, PLCC, etc., you should first weld a few positioning points on both sides or four sides. Carefully check to confirm that each pin matches the corresponding pad before proceeding. Drag soldering to complete the soldering of the remaining pins.

4. Don’t drag the soldering speed too fast. The IC can be dragged through 1-2 solder joints in about 1 second.

5. After welding, use a 4 to 6 times magnifying glass to check whether there are bridges between the solder joints. The same part should be welded no more than twice in a row. If the solder is not soldered well at one time, wait until it cools down before soldering again to prevent the pad from falling off.

6. When welding IC devices, apply a layer of solder paste evenly on the pads, which not only can wet and flux the solder joints, but also improve maintenance efficiency.

2. Rework process requirements

1. Operators should wear an anti-static wristband. It is generally required to use an anti-static constant-temperature soldering iron. When using an ordinary soldering iron, it must be well-grounded.

2. When repairing chip components, a low-power soldering iron of 15 ~ 20W should be used. The temperature of the soldering iron tip is controlled below 250°C.

3. The welding time should not be too long, otherwise the components will be easily burned. The welding time of chip components should not exceed 5 seconds, and the same solder joint should not be welded more than twice.

4. The solder joint should be in the shape of a sinusoidal wave peak, the surface should be bright and smooth, without tin thorns, and the amount of tin should be moderate.

5. After the soldering is completed, use alcohol to clean the remaining flux on the circuit board to prevent the carbonized flux from affecting the normal operation of the circuit.

6. When removing components for SMT chip rework, you should wait until the solder is completely melted before removing the components to prevent damage to the coplanarity of the device pins.

Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top