During the SMT patch production process, soldering defects often occur, including solder balls, short circuits, misalignment, tombstoning, and voids. These defects are caused by various factors, and in order to avoid them, it is necessary to analyze the problems step by step in a clear manner to solve the root cause. DiskMFR will now analyze the common defects in SMT patch production to provide some assistance.
1. Main Causes of Solder Ball Defects
- Rapid temperature rise during reflow soldering;
- Insufficient thawing of frozen solder paste before printing;
- Failure to perform timely surface mount after solder paste printing, leading to solvent evaporation;
- Excessive pressure during component placement, causing solder paste overflow;
- Improper storage of PCBs, resulting in high humidity;
- Inappropriate solder paste particle size;
- Poor steel mesh opening design.
2. Main Causes of Short Circuit Defects
- Excessive reflow peak temperature or duration;
- Poor stencil design, resulting in poor demolding after solder paste printing;
- Low metal content or too thin solder paste, causing it to collapse and short circuit;
- Improper printing pressure, resulting in solder paste collapse;
- Solder paste particles are too large, and the surface tension of the flux is too small.
3. Main Causes of Misalignment Defects
- Inconsistent PCB pad design with component pin layout;
- Insufficient solder paste activity;
- Inadequate component placement accuracy.
4. Main Causes of Tombstoning Defects
- Component misalignment, resulting in uneven stress on both sides;
- Poor solderability due to oxide formation on the pads, causing uneven stress at both ends;
- The long period of time between solder paste printing and placement results in reduced flux activity;
- Non-uniform temperature distribution on the PCB surface, resulting in uneven stress after melting.
5. Main Causes of Void Defects
- Through-hole around the PCB pad, causing liquid solder to flow into the hole during reflow;
- Uneven heating causes excessive heat on the component pins, preventing the solder paste from entering the pad;
- Deformed or oxidized component pins causing poor soldering during reflow;
- Poor component coplanarity, resulting in incomplete contact with the PCB pad.