What Is Solder Ball - How to Fix Solder Balls Defect On PCB?

Jun 21,2024

During the Soldering process on printed circuit board (PCB) small spherical blobs of solder appear are called Solder balls. Solder balls issue in PCB manufacturing are very common, but can directly affect the performance and reliability of electronic devices. Solder balls are mostly found on the side of chip components and around the pins of connectors and integrated circuits (ICs).

What is Solder Ball in PCB?

This Solder balls formation and this soldering process and particularly in reflow soldering, where solder paste is applied to the PCB and then heated to melt the solder and create joints which involves heating a metal alloy like tin, copper, brass or silver beyond its melting point. Once the alloy is melted, it’s applied to a circuit board where it solidifies to form soldered joints. The main purpose of solder balls on PCB in the electronics manufacturing is to facilitate the reliable electrical connections between components and the printed circuit board.
Understanding what solder balls on PCB are, their causes, and how to fix and prevent them is crucial for anyone involved in PCB design and PCB assembly.
Solder balls are integral components in the soldering process, Its paly important role in functions like:

  • Electrical Connections.
  • Provide Mechanical Stability.
  • Aid in Heat Dissipation.
  • Long-term Reliability of Electronic Assemblies.

Their proper formation and functioning are essential for the efficient performance and longevity of electronic devices.

What is Solder Balls Defects?

A PCB that has more than five solder balls (<=0.13mm) within 600mm² is considered defective, according to IPC-A-610, since any diameter greater than 0.13mm goes over the minimum electrical clearance principle. Solder balls are considered defects because they can negatively impact the functionality, reliability, and aesthetics of electronic assemblies.

What Causes Solder Balls Defects?

Solder ball defects can arise on printed circuit board from various factors related to the materials used, the soldering process, and the manufacturing environment. Here are some factors that can contribute to the formation of solder balls defects on PCB during the soldering process.

Excessive Solder Paste: Applying too much solder paste to the PCB which can overflow during reflow and causing solder balls to form on the PCB surface or between solder joints.

High Reflow Temperature: Excessive Heat during the reflow soldering process can cause solder to splatter and form balls.

Improper Stencil Design:  Misalignment between the stencil and the PCB can result in uneven solder paste application, and dirty stencil with paste sticking on its underside.

Contaminated PCB Surface: Dust, oil, or other contaminants on the surface of the PCB prevent the solder paste from properly wetting the PCB pads, leading to poor solder joints and the formation of solder balls on PCB. 

Moisture in Solder Paste: Moisture contamination in solder paste can cause the solder to spatter during reflow. 

Incorrect Reflow Profile: Using an incorrect reflow profile, such as a rapid heating or cooling rate, can lead to the formation of Circuit Board Solder balls.

Inadequate Solder Mask Coverage: Insufficient solder mask coverage or misalignment of the solder mask openings can result in solder paste spreading beyond the intended areas during reflow.

Component Misalignment: Misalignment of components during placement on the PCB can result in excess solder paste being deposited such as a misalignment when components are placed on the board or the pads are spaced too close to one another.

Impact of Defective Solder Balls on PCB Performance:

Defective solder balls on printed circuit boards (PCBs) can significantly impact the overall performance and reliability of electronic devices. These small unexpected spheres of solder can create an array of challenges, from minor inconveniences to major failures. Here's an in-depth look at how defective solder balls could impact PCB performance:

Electrical Shorts: Solder balls can create unintended electrical connections between adjacent conductive paths, such as traces and pads, on a Circuit Board. These shorts can lead to.
  • Device Malfunction.
  • Component Damage.
Reduced Mechanical Integrity: The presence of solder balls on Circuit Board Solder can compromise the mechanical strength of solder joints.
  • Weak Joints.
  • Component Detachment.
Testing and Inspection Challenges: Solder balls can interfere with various testing and inspection processes.
  • In-Circuit Testing (ICT) Failure.
  • Functional Testing Issues.
  • Visual Inspection Concerns.
Thermal Management Problems: Solder balls can affect the thermal performance of a PCB
  • Impaired Heat Dissipation.
  • Hot Spots.
Aesthetic and Perception Issues: While primarily functional, the appearance of a solder PCB can influence customer perceptions.
  • Quality Perception.
  • Aesthetic Concerns.
Reliability and Longevity: Long-term reliability is a critical concern in electronics, and solder balls on Printed Circuit Board can significantly impact this.
  • Accelerated Wear and Tear.
  • Increased Failure Rates.

How to Fix Solder Ball Defects on Printed Circuit Boards?

Solder ball defects on Printed Circuit Board can compromise the functionality, reliability, and aesthetic quality of PCBs. Correcting these defects is crucial for ensuring the overall performance and longevity of electronic assemblies.

Steps to fix solder ball defects on PCBs:

Step 1: Identify and Inspect the Defects:
  • Visual Inspection: Use magnification tools like microscopes to visually inspect the Solder PCB and locate solder balls.
  • Automated Inspection: Employ Automated Optical Inspection (AOI) or X-ray inspection to detect solder balls on PCB, especially those not visible to the naked eye.
Step 2: Prepare the PCB for Repair:
  • Clean the Work Area: Ensure the workbench is clean and free of contaminants that could interfere with the repair process.
  • Gather Tools: Obtain Printed Circuit Board soldering irons, de-soldering tools, flux, solder wick, solder paste, tweezers, and cleaning solvents.
Step 3: Remove Excess Solder:
  • De-soldering Braid (Solder Wick): Place the solder wick over the solder ball and apply the heated soldering iron to the wick. The wick will absorb the excess solder.
  • Vacuum De-soldering Tool: Use a vacuum de-soldering tool to suck up the molten solder from the PCB surface. 
Step 4: Clean the Affected Area:
  • Flux Application: Apply flux to the cleaned area to help remove any residual solder and to prepare the surface for re-soldering.
  • Solvent Cleaning: Use isopropyl alcohol or a specialized PCB cleaning solvent to clean the flux residue and any remaining contaminants.
Step 5: Reapply Solder:
  • Solder Paste: Apply a small amount of solder paste to the pads or areas where solder balls were removed.
  • Reflow Soldering: Heat the area with a reflow soldering tool to melt the solder paste and form solid solder joints.
Step 6: Inspect the Repaired Joints:
  • Visual Inspection: Use magnification tools to inspect the solder joints for proper formation and to ensure no new solder balls have formed on circuit board.
  • Electrical Testing: Perform in-circuit testing (ICT) or functional testing to verify that the repaired PCB operates correctly.

Measures to Prevent Solder Balls in PCB Soldering:

Optimize Solder Paste Application: Ensuring that stencil designs are precise and aligned with the PCB layout facilitates accurate paste deposition. Additionally, it's crucial to carefully control the volume of solder paste applied to the PCB. Striking the right balance between too much and too little paste ensures consistent and reliable solder joints, minimizing the risk of defects such as solder balls.

Control Reflow Soldering Process: Optimizing the reflow profile and implementing gradual heating techniques. Involves fine-tuning parameters such as temperature, ramp-up rate, soak time, and cooling rate to match the specific requirements of the solder paste and components being soldered. Gradual heating allows the solder paste to reach its melting point more evenly, reducing the likelihood of spattering and ensuring proper wetting of the solder joints.

Maintain Clean Work Environment: Maintaining a clean work environment is critical for ensuring high-quality soldering processes. It's essential to ensure that all surfaces involved in the soldering process, including PCBs, soldering equipment, and workbenches, are free from contaminants such as dust, oil, and debris. Maintaining a controlled environment is vital to minimize external factors that could affect the soldering process. This includes controlling temperature, humidity, and airflow in the soldering area to ensure stable conditions conducive to optimal soldering performance.

Use High-Quality Materials: Using quality solder paste and ensuring the use of fresh materials. Selecting quality solder paste is crucial for achieving consistent and reliable solder joints. High-quality solder paste is formulated with precise particle sizes and flux compositions, ensuring optimal wetting and adhesion properties during the soldering process. Use of fresh materials in the soldering process to maintain their effectiveness and reliability. Using fresh materials ensures that the solder paste remains within its optimal working condition, maximizing its effectiveness in creating reliable solder joints.

Proper Handling and Storage: Proper handling and storage procedures are critical for avoiding problems such as solder balls in PCB assemblies. This entails regulating moisture levels in order to protect the integrity of materials such as solder paste, which is sensitive to moisture absorption. To avoid contamination and damage, use careful handling procedures. Surfaces and equipment should be kept clean, and materials should be handled carefully to prevent oil and debris transfer.

Optimize PCB Design: Ensure proper solder mask coverage and optimize pad design. Adequate solder mask coverage helps to avoid solder bridging and excess solder accumulation, which reduces the possibility of solder ball formation. Optimizing pad design includes properly spacing and sizing pads to allow for effective soldering and prevent solder ball defects.

Regular Equipment Maintenance: Reflow oven and stencil printer maintenance. Reflow oven maintenance ensures that the oven operates within stated temperature ranges and that heating profiles remain constant, preventing temperature changes that might cause solder ball formation. Similarly, stencil printer maintenance confirms accurate and uniform deposition of solder paste, reducing the possibility of defects.

Training and Process Control: Effective operator training ensures employees have the skills and knowledge required to perform soldering tasks accurately and consistently, reducing the possibility of errors that could result in defects. Process monitoring is regularly examining and analyzing soldering processes to identify potential problems and variations from specified standards.

Quality Control and Inspection: AOI systems use advanced imaging technology to inspect solder joints and identify any abnormalities or defects, including solder balls, with high precision and efficiency. Regular audits involve systematic evaluations of soldering processes, equipment, and personnel to ensure adherence to quality standards and identify areas for improvement.

Using high-quality materials, managing the reflow Printed Circuit Board soldering process, applying PCB solder paste optimally, keeping a clean work area, and making sure handling and storage are all important in preventing solder balls in PCB soldering. These steps can help manufacturers drastically lower the frequency of solder ball errors, which will lead to electronic assemblies that are more dependable and of higher quality. Maintaining these best practices and getting consistent outcomes in PCB assembly requires constant observation, routine maintenance, and in-depth training.