1. As the carrier for various components and the central hub for circuit signal transmission, the PCB board has become a crucial element in electronic information products.
2. Its quality and reliability directly affect the overall performance and dependability of the entire equipment.
3. With the trend towards miniaturization of electronic information products and the push for lead-free and halogen-free materials, PCBs are evolving towards higher density, increased Tg, and improved environmental sustainability.
4. However, due to cost and technical constraints, many failure issues have arisen during the production and application of PCBs, leading to numerous quality disputes.
5. To address these failures, identify their causes, and determine responsibility, it is essential to perform a thorough failure analysis.
### Basic Procedure of Failure Analysis
1. To determine the exact cause or mechanism of PCB failure, basic principles and analysis processes must be followed. Otherwise, valuable failure information may be missed, hindering further analysis or leading to incorrect conclusions.
2. The general process begins with identifying the failure location and mode through information collection, functional testing, electrical performance testing, and visual inspection. For simple PCBs, failure location is easily determined, but for complex BGA or MCM packages, defects may not be visible under a microscope, requiring alternative methods.
3. Next, analyze the failure mechanism using physical and chemical methods to investigate the causes of PCB defects, such as soldering issues, contamination, mechanical damage, moisture stress, medium corrosion, fatigue, CAF, ion migration, or stress overload.
4. Then, conduct failure cause analysis, which involves finding the root cause based on the failure mechanism and process analysis, and performing test verifications if necessary. Test verifications are crucial for pinpointing the exact cause of failure and guiding improvements.
5. Compile the failure analysis based on experimental data, facts, and conclusions from the analysis process. Ensure clarity, logical reasoning, and strong rationality. Avoid speculative assumptions.
6. During analysis, adhere to the principle of progressing from simple to complex methods and from external to internal examination, without damaging the sample. This approach helps avoid losing key information and introducing new, artificial failure mechanisms.
7. Failure analysis of PCBs is akin to investigating a traffic accident. If the scene is tampered with or destroyed, accurate responsibility determination becomes difficult. Similarly, if PCB samples are damaged or altered, the analysis becomes compromised, especially when few samples are available.
### Failure Analysis Technology
8. **Optical Microscope**: Primarily used for visual inspection to identify failure parts and related physical evidence, and to preliminarily judge the failure mode. This includes checking for contamination, corrosion, broken board locations, circuit wiring, and whether the issue is batch-related or localized.
9. **X-ray (X-ray)**: Utilized for inspecting parts not visible to the naked eye, as well as internal defects in through-holes. X-ray fluoroscopy uses different material densities and thicknesses for imaging, aiding in the detection of internal defects in solder joints, through-holes, and high-density packaging like BGA or CSP devices.
10. **Slicing Analysis**: Involves obtaining a cross-sectional view of the PCB through sampling, inlaying, slicing, polishing, corrosion, and observation. This destructive method provides detailed microstructural information that is valuable for quality improvement but results in the destruction of the sample.
1. **Scanning Acoustic Microscope:** Currently, the C-mode ultrasonic scanning acoustic microscope is primarily used for analyzing electronic packaging or assembly. It images by utilizing changes in amplitude, phase, and polarity caused by high-frequency ultrasonic reflections on discontinuous interfaces within the material. The scanning method involves gathering information in the XY plane along the Z axis. Consequently, the scanning acoustic microscope can detect components, materials, and various defects within PCBs and PCBAs, including cracks, delamination, inclusions, and voids. If the frequency bandwidth of the scanning acoustics is sufficient, internal defects in solder joints can also be directly detected. Typical scanning acoustic images use red warning colors to indicate defects. The widespread use of plastic-packaged components in SMT processes has led to significant moisture reflow sensitivity issues during the transition from leaded to lead-free processes. Moisture-absorbing plastic-packaged devices may experience internal or substrate delamination and cracking during reflow at higher lead-free process temperatures, while ordinary PCBs may burst at these high temperatures. The scanning acoustic microscope demonstrates its unique advantages in non-destructive flaw detection of multi-layer, high-density PCBs. Generally, obvious bursts can be detected visually on the surface.
2. **Micro-Infrared Analysis:** Micro-infrared analysis combines infrared spectroscopy with microscopy. It leverages the principle of varying infrared absorption by different materials (primarily organic matter) to analyze the compound composition of materials. When combined with a microscope, it allows visible light and infrared light to share the same optical path, making it possible to identify trace organic pollutants visible within the field of view. Without a microscope, infrared spectroscopy typically requires a larger sample size. However, in electronic technology, micro-pollution can significantly impact the solderability of PCB pads or lead pins. Thus, addressing process issues without a microscope-assisted infrared spectroscopy can be challenging. The primary aim of micro-infrared analysis is to assess organic contaminants on welded surfaces or solder joints and analyze causes of corrosion or poor solderability.
3. **Scanning Electron Microscope (SEM) Analysis:** The scanning electron microscope is a valuable tool for failure analysis, particularly for topographical observation. Modern SEMs are highly advanced, capable of magnifying fine structures and surface features up to hundreds of thousands of times. In PCB and solder joint failure analysis, SEM is primarily used to study failure mechanisms. Specifically, it helps observe the topographic structure of pad surfaces, the metallographic structure of solder joints, and measure intermetallic compounds and solderability, coating analysis, and tin whisker analysis and measurement. Unlike optical microscopes, SEM produces electronic images in black and white. SEM samples must be conductive; non-conductors and some semiconductors require a coating of gold or carbon to prevent charge accumulation that could interfere with observation. SEMs also have a significantly greater depth of field compared to optical microscopes, making them crucial for analyzing uneven samples such as metallographic structures, microscopic fractures, and tin whiskers.
4. **Thermal Analysis:**
– **Differential Scanning Calorimetry (DSC):** DSC measures the difference in power between a sample and a reference material as a function of temperature (or time) under programmed temperature control. This analytical method examines the relationship between heat and temperature to study materials’ physical, chemical, and thermodynamic properties. In PCB board analysis, DSC is primarily used to assess the curing degree and glass transition temperature of polymer materials used on PCBs, which are critical for the board’s reliability in subsequent processes.
– **Thermal Mechanical Analysis (TMA):** TMA measures the deformation properties of solids, liquids, and gels under thermal or mechanical forces under programmed temperature control. It studies the relationship between deformation and temperature (or time) to analyze the physical, chemical, and thermodynamic properties of materials. In PCB board analysis, TMA is used to measure key parameters such as the linear expansion coefficient and glass transition temperature. A base material with a high expansion coefficient can lead to fractures and failures of metallized holes after welding and assembly.
– **Thermogravimetry Analysis (TGA):** TGA measures the relationship between a substance’s mass and temperature (or time) under programmed temperature control. Using a sophisticated electronic balance, TGA monitors subtle changes in material mass during temperature changes. It helps analyze the physical, chemical, and thermodynamic properties of materials based on mass changes. In PCB board analysis, TGA is used to measure the thermal stability or decomposition temperature of PCB materials. A low thermal decomposition temperature can cause printed circuit boards to burst or delaminate during high-temperature soldering processes.
2. Its quality and reliability directly affect the overall performance and dependability of the entire equipment.
3. With the trend towards miniaturization of electronic information products and the push for lead-free and halogen-free materials, PCBs are evolving towards higher density, increased Tg, and improved environmental sustainability.
4. However, due to cost and technical constraints, many failure issues have arisen during the production and application of PCBs, leading to numerous quality disputes.
5. To address these failures, identify their causes, and determine responsibility, it is essential to perform a thorough failure analysis.
### Basic Procedure of Failure Analysis
1. To determine the exact cause or mechanism of PCB failure, basic principles and analysis processes must be followed. Otherwise, valuable failure information may be missed, hindering further analysis or leading to incorrect conclusions.
2. The general process begins with identifying the failure location and mode through information collection, functional testing, electrical performance testing, and visual inspection. For simple PCBs, failure location is easily determined, but for complex BGA or MCM packages, defects may not be visible under a microscope, requiring alternative methods.
3. Next, analyze the failure mechanism using physical and chemical methods to investigate the causes of PCB defects, such as soldering issues, contamination, mechanical damage, moisture stress, medium corrosion, fatigue, CAF, ion migration, or stress overload.
4. Then, conduct failure cause analysis, which involves finding the root cause based on the failure mechanism and process analysis, and performing test verifications if necessary. Test verifications are crucial for pinpointing the exact cause of failure and guiding improvements.
5. Compile the failure analysis based on experimental data, facts, and conclusions from the analysis process. Ensure clarity, logical reasoning, and strong rationality. Avoid speculative assumptions.
6. During analysis, adhere to the principle of progressing from simple to complex methods and from external to internal examination, without damaging the sample. This approach helps avoid losing key information and introducing new, artificial failure mechanisms.
7. Failure analysis of PCBs is akin to investigating a traffic accident. If the scene is tampered with or destroyed, accurate responsibility determination becomes difficult. Similarly, if PCB samples are damaged or altered, the analysis becomes compromised, especially when few samples are available.
### Failure Analysis Technology
8. **Optical Microscope**: Primarily used for visual inspection to identify failure parts and related physical evidence, and to preliminarily judge the failure mode. This includes checking for contamination, corrosion, broken board locations, circuit wiring, and whether the issue is batch-related or localized.
9. **X-ray (X-ray)**: Utilized for inspecting parts not visible to the naked eye, as well as internal defects in through-holes. X-ray fluoroscopy uses different material densities and thicknesses for imaging, aiding in the detection of internal defects in solder joints, through-holes, and high-density packaging like BGA or CSP devices.
10. **Slicing Analysis**: Involves obtaining a cross-sectional view of the PCB through sampling, inlaying, slicing, polishing, corrosion, and observation. This destructive method provides detailed microstructural information that is valuable for quality improvement but results in the destruction of the sample.
1. **Scanning Acoustic Microscope:** Currently, the C-mode ultrasonic scanning acoustic microscope is primarily used for analyzing electronic packaging or assembly. It images by utilizing changes in amplitude, phase, and polarity caused by high-frequency ultrasonic reflections on discontinuous interfaces within the material. The scanning method involves gathering information in the XY plane along the Z axis. Consequently, the scanning acoustic microscope can detect components, materials, and various defects within PCBs and PCBAs, including cracks, delamination, inclusions, and voids. If the frequency bandwidth of the scanning acoustics is sufficient, internal defects in solder joints can also be directly detected. Typical scanning acoustic images use red warning colors to indicate defects. The widespread use of plastic-packaged components in SMT processes has led to significant moisture reflow sensitivity issues during the transition from leaded to lead-free processes. Moisture-absorbing plastic-packaged devices may experience internal or substrate delamination and cracking during reflow at higher lead-free process temperatures, while ordinary PCBs may burst at these high temperatures. The scanning acoustic microscope demonstrates its unique advantages in non-destructive flaw detection of multi-layer, high-density PCBs. Generally, obvious bursts can be detected visually on the surface.
2. **Micro-Infrared Analysis:** Micro-infrared analysis combines infrared spectroscopy with microscopy. It leverages the principle of varying infrared absorption by different materials (primarily organic matter) to analyze the compound composition of materials. When combined with a microscope, it allows visible light and infrared light to share the same optical path, making it possible to identify trace organic pollutants visible within the field of view. Without a microscope, infrared spectroscopy typically requires a larger sample size. However, in electronic technology, micro-pollution can significantly impact the solderability of PCB pads or lead pins. Thus, addressing process issues without a microscope-assisted infrared spectroscopy can be challenging. The primary aim of micro-infrared analysis is to assess organic contaminants on welded surfaces or solder joints and analyze causes of corrosion or poor solderability.
3. **Scanning Electron Microscope (SEM) Analysis:** The scanning electron microscope is a valuable tool for failure analysis, particularly for topographical observation. Modern SEMs are highly advanced, capable of magnifying fine structures and surface features up to hundreds of thousands of times. In PCB and solder joint failure analysis, SEM is primarily used to study failure mechanisms. Specifically, it helps observe the topographic structure of pad surfaces, the metallographic structure of solder joints, and measure intermetallic compounds and solderability, coating analysis, and tin whisker analysis and measurement. Unlike optical microscopes, SEM produces electronic images in black and white. SEM samples must be conductive; non-conductors and some semiconductors require a coating of gold or carbon to prevent charge accumulation that could interfere with observation. SEMs also have a significantly greater depth of field compared to optical microscopes, making them crucial for analyzing uneven samples such as metallographic structures, microscopic fractures, and tin whiskers.
4. **Thermal Analysis:**
– **Differential Scanning Calorimetry (DSC):** DSC measures the difference in power between a sample and a reference material as a function of temperature (or time) under programmed temperature control. This analytical method examines the relationship between heat and temperature to study materials’ physical, chemical, and thermodynamic properties. In PCB board analysis, DSC is primarily used to assess the curing degree and glass transition temperature of polymer materials used on PCBs, which are critical for the board’s reliability in subsequent processes.
– **Thermal Mechanical Analysis (TMA):** TMA measures the deformation properties of solids, liquids, and gels under thermal or mechanical forces under programmed temperature control. It studies the relationship between deformation and temperature (or time) to analyze the physical, chemical, and thermodynamic properties of materials. In PCB board analysis, TMA is used to measure key parameters such as the linear expansion coefficient and glass transition temperature. A base material with a high expansion coefficient can lead to fractures and failures of metallized holes after welding and assembly.
– **Thermogravimetry Analysis (TGA):** TGA measures the relationship between a substance’s mass and temperature (or time) under programmed temperature control. Using a sophisticated electronic balance, TGA monitors subtle changes in material mass during temperature changes. It helps analyze the physical, chemical, and thermodynamic properties of materials based on mass changes. In PCB board analysis, TGA is used to measure the thermal stability or decomposition temperature of PCB materials. A low thermal decomposition temperature can cause printed circuit boards to burst or delaminate during high-temperature soldering processes.