Are you dealing with voids in your solder joints and wondering how to avoid this in the future? Millennium Circuits Limited can help. Learn more about why voids are created — and exactly how to prevent this phenomenon from occurring.
WHAT IS VOIDING?
Solder joint voids refer to empty spaces that occur within a joint. Solder voids typically contain air and flux residue trapped within the joint. This phenomenon can lead to mechanical weaknesses, cracks in the joint and general instability. As a result, solder voids can be considered a defect. Joints are generally regarded as defective when the area of all voids in a given joint is more than 25% of the total area.
Voiding can have a range of negative effects on a joint, including threatened reliability, lowered current carrying capacity and reduced thermal conductivity. As a result, it’s crucial to understand exactly what causes it — and how to prevent voids in solder joints.
WHAT CAUSES VOIDS IN SOLDER?
Solder voids occur because of several different factors. We know that trapped gasses generated from the solder paste create voids in the joint — but why does this happen? The common causes include:
- Low preheat temperature. If the temperature is too low, the solvent in the flux will not vaporize out entirely.
- High levels of flux. When too much flux is applied in the solder paste, the flux will not outgas before the solder becomes a solid-state.
- Oxidation. When solder paste oxidizes, voids are likely to occur.
- Solder paste quality. The quality and contents of your solder paste matter. Some pastes, such as those without lead, shrink in volume when cooled to a solid-state. This can cause uneven shaping and spacing.
- Circuit board stencil design. Some circuit boards are more prone to voiding than others. While you may not be able to easily change your circuit board design, you can compensate for recurring issues by changing the printed circuit board (PCB) stencil.
HOW TO PREVENT VOIDS IN SOLDER JOINTS
If you’ve noticed solder joint voids becoming a regular issue, apply these four simple preventive strategies.
1. Extend the Preheat Time
Extending your preheat time will allow solvent in the flux to reach the optimum temperature and vaporize completely. This will reduce your risk of having flux residue left in the joint.
2. Extend the Soak Zone Time
Increase your soak time to help low-boiling volatiles evaporate and escape from the solder paste before it solidifies.
3. Reduce the Solder Paste Volatile Content Quantity
If your solder paste has a lower volatile content, it runs a reduced risk of voiding. It is also less likely to absorb moisture from the air, which could create voids. Opt for pastes with lower volatile content, such as no-clean solder paste, for the best results.
4. Modify Your Circuit Board Stencil
As we mentioned above, some circuit board stencils are more prone to creating solder voids than others. Consider using stencils that provide gas escape routes around holes, so that solder paste has a clearance during reflow.