Analysis of Defects in PCBA Soldering

During the production process of PCBA soldering, operational errors can easily lead to defects such as: cold solder joints, short circuits, component lifting, missing components, solder balls, component misalignment, excessive solder, incorrect components, cold soldering, reverse soldering, white/reverse side issues, misalignment, component damage, insufficient solder, excessive solder, solder sticking to gold fingers, and glue overflow. It is necessary to analyze these defects and implement improvements to enhance product quality.

1. Cold Solder Joints

1. Weak activity of solder paste;

2. Poor stencil opening;

3. Excessive spacing between copper pads or using large copper pads for small components;

4. Excessive pressure from the squeegee;

5. Poor flatness of component leads (lifting, deformation);

6. Rapid temperature rise in the preheating zone of the reflow oven;

7. Dirty or oxidized PCB copper pads;

8. Moisture in the PCB;

9. Machine placement misalignment;

10. Solder paste printing misalignment;

11. Loose machine fixture tracks causing placement misalignment;

12. Incorrect marking point illumination causing component misalignment, leading to cold solder joints;

2. Short Circuits

1. Excessive distance between the stencil and PCB leading to thick solder paste printing causing short circuits;

2. Low placement height setting causing solder paste to be squeezed leading to short circuits;

3. Rapid temperature rise in the reflow oven causing short circuits;

4. Component placement misalignment causing short circuits;

5. Poor stencil opening (excessive thickness, long lead openings, oversized openings);

6. Solder paste unable to support component weight;

7. Deformation of the stencil or squeegee causing excessive solder paste printing;

8. Strong activity of solder paste;

9. Excessive solder paste printing around empty placement points due to adhesive tape rolling up;

10. Excessive vibration or unevenness in the reflow soldering;

3. Component Lifting

1. Uneven tension due to different sizes of copper pads;

2. Too rapid preheating rate;

3. Machine placement misalignment;

4. Uneven thickness of solder paste printing;

5. Uneven temperature distribution in the reflow oven;

6. Solder paste printing misalignment;

7. Loose machine fixture tracks causing placement misalignment;

8. Machine head shaking;

9. Excessive activity of solder paste;

10. Improper furnace temperature settings;

11. Excessive spacing between copper pads;

12. Incorrect marking point illumination causing component misalignment;

4. Missing Components

1. Poor vacuum pump carbon sheet causing insufficient vacuum leading to missing components;

2. Blocked or faulty suction nozzle;

3. Improper component thickness detection or faulty detector;

4. Improper placement height setting;

5. Excessive or insufficient suction from the nozzle;

6. Improper vacuum setting for the nozzle (applicable to MPA);

7. Excessive speed for placing irregular components;

8. Broken air tube at the head;

9. Worn sealing ring of the air valve;

10. Foreign objects on the edge of the reflow oven track scraping off components from the board;

5. Solder Balls

1. Insufficient preheating in reflow soldering, rapid temperature rise;

2. Solder paste refrigerated, not fully warmed up;

3. Solder paste absorbing moisture causing splattering (excessive indoor humidity);

4. Excessive moisture in the PCB;

5. Excessive diluent added;

6. Poor stencil opening design;

7. Uneven solder powder particles.

6. Misalignment

1. Unclear reference points on the circuit board;

2. Reference points on the circuit board not aligned with the stencil reference points;

3. Loose clamping of the circuit board in the printer, positioning pins not in place;

4. Fault in the optical positioning system of the printer;

5. Solder paste leaking from the stencil openings not matching the design files of the circuit board.

To improve defects in PCBA soldering, strict quality control must be implemented at each stage to minimize the transfer of issues from one process to the next.

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