Tips & Tricks: Avoiding Solder Escape/Wick during Reflow

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Understanding Solder Escape and Its Impact on PCB Assembly

Solder escape, also known as Solder Wicking, is a common issue faced by PCB Manufacturers during the reflow soldering process. It occurs when molten solder flows away from the intended area, causing defects and potential reliability issues in the final product. In this article, we will delve into the causes of solder escape, its impact on PCB assembly, and provide practical tips and tricks to minimize its occurrence.

What is Solder Escape?

Solder escape is an unwanted phenomenon where molten solder flows along the surface of a PCB or component lead, away from the intended solder joint. This can happen due to various factors, such as improper pad design, incorrect solder paste application, or inadequate reflow profile settings.

The consequences of solder escape can be significant:

  1. Insufficient solder in the intended joint, leading to weak or open connections
  2. Solder bridges between adjacent pads or traces, causing short circuits
  3. Contamination of nearby components or connectors
  4. Decreased reliability and performance of the assembled PCB

Causes of Solder Escape

To effectively prevent solder escape, it is essential to understand its root causes. Some of the primary factors contributing to solder escape include:

Pad Design and Solder Mask Clearance

Improper pad design and inadequate solder mask clearance can lead to solder escape. If the pads are too small or the solder mask opening is too large, the molten solder may flow away from the intended area during reflow. Additionally, if the solder mask dam between adjacent pads is too narrow, solder bridging can occur.

Solder Paste Application

Incorrect solder paste application can also contribute to solder escape. Applying too much solder paste or using a stencil with oversized apertures can result in excess solder on the pads. During reflow, this excess solder may flow along the surface, causing escape or bridging.

Reflow Profile Settings

Inadequate reflow profile settings, such as incorrect peak temperature, insufficient soak time, or rapid cooling, can exacerbate solder escape. If the peak temperature is too high or the soak time is too short, the solder may become excessively fluid and prone to wicking. On the other hand, rapid cooling can cause the solder to solidify before it has a chance to flow back to the intended joint.

Component Placement and Alignment

Misaligned or poorly seated components can also lead to solder escape. If a component is not properly aligned with the pads or if there is insufficient pressure during placement, the solder may flow away from the intended area during reflow.

Tips and Tricks for Avoiding Solder Escape

Now that we understand the causes of solder escape, let’s explore some practical tips and tricks to minimize its occurrence during the reflow soldering process.

Optimize Pad Design and Solder Mask Clearance

  1. Ensure that pad sizes are appropriate for the component leads and the amount of solder required for a reliable joint.
  2. Maintain adequate solder mask clearance around the pads to prevent solder from flowing onto adjacent areas. A minimum clearance of 50-75 microns is recommended.
  3. Increase the width of solder mask dams between adjacent pads to prevent solder bridging. A minimum dam width of 100-150 microns is typically used.
Pad Size Solder Mask Clearance Solder Mask Dam Width
0402 50-75 microns 100-150 microns
0603 75-100 microns 150-200 microns
0805 100-125 microns 200-250 microns
1206 125-150 microns 250-300 microns

Control Solder Paste Application

  1. Use a stencil with appropriately sized apertures to deposit the correct amount of solder paste on the pads. Avoid oversized apertures that can lead to excess solder.
  2. Ensure proper stencil alignment and pressure during solder paste printing to achieve consistent solder paste deposits.
  3. Implement regular stencil cleaning and maintenance to prevent solder paste buildup and ensure consistent print quality.

Optimize Reflow Profile Settings

  1. Determine the appropriate reflow profile for the specific solder paste and PCB assembly. Consider factors such as the solder paste composition, component thermal requirements, and PCB substrate material.
  2. Set the peak temperature and soak time according to the solder paste manufacturer’s recommendations. Avoid excessively high peak temperatures or insufficient soak times that can lead to solder escape.
  3. Control the cooling rate to allow the solder to solidify gradually and flow back to the intended joint. Rapid cooling can cause premature solidification and solder escape.
Reflow Profile Parameter Typical Value Range
Peak Temperature 230-250°C
Soak Time 60-90 seconds
Cooling Rate 2-4°C/second

Ensure Proper Component Placement and Alignment

  1. Use pick-and-place machines with high placement accuracy to ensure precise component alignment with the pads.
  2. Implement vision systems to verify component placement and detect any misalignment before reflow.
  3. Apply sufficient pressure during component placement to ensure proper seating and contact with the solder paste.

Implement Quality Control Measures

  1. Conduct regular visual inspections of the assembled PCBs to identify any instances of solder escape or bridging.
  2. Use automated optical inspection (AOI) systems to detect solder defects and ensure consistent quality control.
  3. Perform cross-sectional analysis on a sample of assembled PCBs to verify the integrity of solder joints and identify any internal solder escape issues.

Frequently Asked Questions (FAQ)

  1. Q: What is the difference between solder escape and solder bridging?
    A: Solder escape refers to the flow of molten solder away from the intended solder joint, while solder bridging occurs when solder flows between adjacent pads or traces, creating an unintended connection.

  2. Q: Can solder escape be completely eliminated?
    A: While it may not be possible to completely eliminate solder escape, implementing the tips and tricks discussed in this article can significantly reduce its occurrence and minimize its impact on PCB assembly quality.

  3. Q: How does the choice of solder paste affect solder escape?
    A: The solder paste composition, particle size, and flux chemistry can influence solder escape. Using a solder paste with the appropriate characteristics for the specific application and reflow profile can help minimize solder escape.

  4. Q: What role does PCB Surface Finish play in solder escape?
    A: The PCB surface finish can affect the wetting and flow characteristics of the solder. Choosing a suitable surface finish, such as immersion silver or electroless nickel immersion gold (ENIG), can promote better solder wetting and reduce the likelihood of solder escape.

  5. Q: Can solder escape be repaired after reflow?
    A: In some cases, solder escape can be repaired using manual soldering techniques, such as adding additional solder or using a soldering iron to reflow the affected area. However, prevention is always preferable to repair, as manual rework can be time-consuming and may not always yield consistent results.


Solder escape is a common challenge faced by PCB manufacturers during the reflow soldering process. By understanding its causes and implementing the tips and tricks discussed in this article, you can significantly reduce the occurrence of solder escape and improve the quality and reliability of your PCB assemblies.

Remember to optimize pad design and solder mask clearance, control solder paste application, fine-tune reflow profile settings, ensure proper component placement, and implement robust quality control measures. By taking a proactive approach to preventing solder escape, you can achieve consistent and reliable solder joints, leading to higher-quality PCB assemblies and improved product performance.