Welding and Dewelding Surface Mount Components in Electronics

The following instructions are designed to help you overcome the challenges you face in the early stages of welding surface mount components. After completing this tutorial, you will have mastered welding components with pins that have a pitch of 0.5 mm.

Shenzhen Pcbandassembly, as a professional SMT patch processing company, will introduce you to the relevant knowledge of welding and de-welding surface mount components in electronics.

Tools and Materials List

1. A welding iron, model x1, digital or analog.

2. A PCB (printed circuit board) equipped with appropriate pads.

3. SMD (surface mount device) matching the pad size.

4. Welding, water-soluble type is recommended, rosin core welding is also acceptable.

5. Dewelding braid for removing welding joints.

6. Flux and matching applicator.

7. A pair of tweezers.

8. If using rosin core welding, you must prepare rubbing alcohol.

9. If using water-soluble welding, you need to prepare clean water.

10. An anti-static cloth.

Step 1: Prepare the Printed Circuit Board (PCB)

1. Make sure to check whether the PCB pad size corresponds exactly to the SMD pin.

2. Thoroughly remove dust and residue from the PCB surface.

3. Turn on the welding iron and adjust the temperature to 600 to 700 degrees.

Warning: When the welding iron is heated to this temperature range if you accidentally touch the welding iron head, it may cause burns.

Step 2: Use Tweezers to Position the Component Accurately

Precisely align the component’s pins with the pads on the board. Since most surface mount components have the same number of pins on both sides, it is important to accurately identify “Pin 1” each time you install a new component.

Step 3: Solve a Corner Problem

1. Use tweezers to keep one hand steady and ensure the component is in place.

2. By now, the welding iron should be heated. Create a good-sized welding joint at the tip.

3. Select a pin in any corner of the component.

4. Gently touch and hold the welding iron to the pad corresponding to the pin.

5. If done correctly, the welding should transfer naturally from the board pad to the component pin, even if there are unconnected pins.

Step 4: Flux

The main function of welding flux is to prevent welding from beading and to facilitate the smooth flow of welding from the welding iron to the board. Applying flux to the board is intended to reduce bridging and generally make welding easier.

1. Due to the messy nature of this substance, it must be applied with the aid of an applicator (toothpick, brush, etc.). In this case, I used an applicator with a metal tip.

2. Make sure to get the right flux on the applicator.

3. Apply the flux evenly to the pins on the other side of the component fixing step.

Step 5: Welding

1. Hold the welding iron in one hand and the other hand as shown.

2.The welding iron should heat the pad, not the component pin.

3. If the pin is overheated, place the pad between the pad and the pin. The heat will melt the

4. Repeat the above steps as needed.

Step 6: Heat the Wick to Ensure Stable Adhesion

It is quite common to see welding bridges during the previous steps. The exact appearance of a welding bridge can be seen in the figure below.

This process will also remove electronic components from a circuit board.

1. Remove the core of the welding machine and place it over the welding to be removed.

2. Gently apply pressure to the core of the welding machine with the welding iron to ensure that the heat is effectively transferred to the welding.

WARNING: It is important to remember that the heat transfer during welding depends primarily on the welding, not the pressure applied. Excessive pressure may cause the pads or pins of the component to be removed, resulting in damage to the components or circuit board.

Step 7: Welding

Now that the welding has been removed, repeat step 5 to treat this side of the circuit board.

Step 8: Repair any Remaining Welding Joint Connections

Use the method described above to remove unnecessary bridges further.

Step 9: Wipe with Alcohol

If using water-soluble welding, use water instead of rubbing alcohol.

1.Take an anti-static cloth and pour an appropriate amount of alcohol.

2. Gently wipe the area around the newly welded components and any areas where excess flux remains. This will give a more professional look.