Soldering is one of the main steps in the PCB manufacturing and assembly process. In the soldering process, the SMD (Surface Mount Device) and PTH (Plated Through Hole) components are joined with a circuit board using solder material. Solder material acts as a conductive path between components and the circuit board, providing electrical connections and conductivity in PCB. Solder material comes in a solid state and has a melting point in the range of 90° C to 450° C depending upon the type and chemical composition. Melted solder is applied on the PCB and then cooled down. Thus, the electrical connections are made on PCB.
Common Types of Defects in PCB Soldering
Soldering is done manually or by soldering machines. In large-scale production, soldering machines like reflow soldering and wave soldering are used instead of manual soldering. As soldering is a process and needs to be done with proper skills and precision, it leaves some defects during manufacturing if not done carefully. Below are some major types of soldering defects: –
- Unsolder: In this defect, solder is not applied at the required places. In this condition, an electrical connection is not established between components and circuits.
- Dry Solder: In this defect, the solder is not properly soldered to the required places. This happens due to improper heating of the solder material.
- Solder Bridge: Solder bridges occur when an excess amount of solder shorts or connects the components and tracks on the PCB. The main reason for a solder bridge is the improper soldering process and excess amount of solder in usage.
- Solder Balls: Solder balls are small spherical-like shapes deposited on the PCB. This also occurs due to excess soldering, improper soldering, and improper cleaning.
Effects of Solder Defects on Printed Circuit Boards
Improper soldering affects the products in many ways. Below are some of the major effects due to a defective soldering process: –
- Unsolder Issues: Unsolder points lead to improper or no electrical connection between components. This leads to degradation in circuit output parameters.
- Dry Solder Defects: Dry solder points also affect the electrical conductivity of the components. During vibrations and mechanical stress conditions, joints may lose contact with pads and tracks, leading the electrical disconnection.
- Solder Bridge Problems: Solder brides provide direct connections to components unintentionally. This may lead to product failure during working conditions.
- Solder Balls Issues: Solder balls do not directly affect the circuit. When a circuit goes under heating conditions or during operation, solder balls may melt and cause shorting between tracks and components. In this way, a product can fail.
In short, soldering defects are harmful to the products and can compromise the life, reliability, and safety of the products. To avoid these failures, soldering must be done with precise methods and checked with proper techniques.
Inspection Techniques Used to Check Soldering Defects
To verify the quality of the soldering process, various inspection methods and advanced tools are used by manufacturers. Below are some of the regular methods: –
Visual Checks
This is the most common and regular method used in PCB manufacturing. Skilled & experienced operators are allowed to check defects like unsolder, dry solder, solder balls, and solder bridges in PCBs. It requires no heavy machinery and tools as inspection is done by the operator itself. Only a few equipment like magnifying glasses, microscopes, and visual cameras are used. However, visual inspection can be done only for PCBs with fewer components. For PCBs with hundreds and thousands of components assembled, advanced inspection techniques and tools are required to avoid any defects.
Electrical Connection Test
Continuity tests or electrical connection tests are important in PCB manufacturing. To verify the functionality of the circuit, various electrical tests are done to ensure that all the components are soldered properly. Various jigs, fixtures and multimeters are used by PCB manufacturers for electrical tests.
Vibration Test
Vibration tests are performed to check the solder joint stability on the circuit. As solder is melted and applied on pads for contact. Loose contact may not be seen at first but can be observed during mechanical stress conditions. To avoid this defect, vibration and stress testing is done on PCBs.
X-ray Inspection
The X-ray inspection method is applicable in large-scale PCB manufacturing and for multi-layer compact PCB assemblies. Since visual inspection has some limitations in compact areas, the X-ray inspection method provides a detailed analysis of solder joints, component misalignment, and many other factors.
Automated Optical Inspection (AOI)
Automated Optical Inspection (AOI) is also an advanced technique to identify various manufacturing defects in PCBs including soldering defects. In this method, machines are equipped with high-resolution and faster cameras to verify the visual defects in detail. A perfect image of PCB without defects is programmed in the software. The machine compares the PCBs with reference data and generates detailed reports.
Solderability Testing
In this method, the solder output is checked on parameters like soldering index, solder joint shape, contact angle, etc. These parameters are studied and are further used in thermal profiling, solder material selection, and defining the soldering process parameters.
Key Measures to Avoid Defects in PCB Soldering
Soldering is a key step in PCB manufacturing and must be done with proper skills and methods. Soldering defects can occur due to process gaps or materials. Below are key measures that should be taken to avoid soldering defects in PCB manufacturing: –
- Follow IPC-J-STD-001 standard in PCB manufacturing for soldering.
- The Soldering process should be taken care of by skilled and experienced manpower.
- Use an adequate amount of flux before soldering.
- Before the soldering step, ensure that the PCB and components are not oxidized and properly cleaned.
- Soldering machines are properly calibrated and maintained.
- Proper thermal profiling of the wave soldering machines should be done.
- High-quality solder should be used in the soldering process.
- Proper inspection methods should be adopted to verify the quality of soldering.
- Document and analyze all the results and data to maintain the in-process quality of the PCB manufacturing.
Conclusion
At last, it can be concluded that soldering defects are harmful to electronic circuits & assemblies and badly affect the quality of products. By following best manufacturing practices and improving testing & inspection of soldering output, the defects can be reduced and controlled.
