**The Impact of Humidity and Temperature on PCBA Manufacturing**
Humidity plays a crucial role in the PCBA (Printed Circuit Board Assembly) manufacturing process, affecting material properties, assembly quality, and production efficiency. This article explores the influence of temperature and humidity, focusing on how both extremes can negatively impact PCBA processing.
### Low Humidity Effects
When humidity is too low, several issues arise in the manufacturing process. First, low humidity increases the likelihood of electrostatic discharge (ESD) due to the drying of materials and components, which can lead to damage or failure of sensitive electronic parts. Additionally, low humidity can cause higher levels of dust accumulation, which contaminates components and reduces cleanliness in the assembly environment. Template openings are also more likely to become blocked, which can lead to issues with solder paste application and ultimately, reduced yield.
Furthermore, low humidity accelerates template wear due to the increased friction between surfaces. This friction is particularly significant on metal surfaces where the relative humidity is below 20% RH. At these low humidity levels, the friction between metal parts increases by 1.5 times compared to higher humidity conditions (80% RH). This can cause premature wear of equipment and lower the overall efficiency of the production process.
### High Humidity Effects
On the other hand, high humidity introduces its own set of challenges. Excess moisture in the environment causes materials to absorb water, leading to potential issues such as delamination, the popcorn effect, and the formation of solder balls during reflow soldering. These defects are caused by the expansion of absorbed moisture when it turns into vapor during the reflow process, leading to internal stress in the material.
Additionally, moisture reduces the glass transition temperature (Tg) of the PCB material, which makes the material more susceptible to deformation and warpage during reflow soldering. This can lead to increased dynamic warpage, causing misalignment of components, poor solder joints, and reduced reliability of the final product.
### The Role of Surface Wetness in Humidity-Related Issues
Almost all solid surfaces, including metals, glass, ceramics, and silicon, have a moisture-absorbing layer. This layer can be a monomolecular or multi-molecular film that forms when the surface temperature is equal to the dew point of the surrounding air, depending on temperature, humidity, and air pressure. When the humidity level is low, this moisture-absorbing layer becomes less visible, but it still affects the properties of the material.
At very low relative humidity (below 20% RH), the friction between metal surfaces increases significantly, which can hinder the movement of parts in automated assembly processes. This increased friction can also contribute to mechanical wear on equipment, particularly in high-precision environments like PCB assembly.
For organic materials such as epoxy resins, plastics, and fluxes, the moisture-absorbing layer can penetrate the material. Even if the surface temperature is lower than the dew point, no visible moisture is detected, yet the absorbed moisture still affects the material. This moisture, stored within the monomolecular layers, can migrate into plastic-encapsulated devices (MSDs) and lead to failure during the reflow soldering process.
As the moisture absorbed by the material builds up over time, it can eventually result in catastrophic failure during reflow soldering. This is because the moisture expands as it turns into steam, creating internal pressure that can cause delamination or cracks in the solder joints, leading to functional failures of the finished PCB.
### Conclusion
Both excessively low and high humidity levels have significant, detrimental effects on PCBA manufacturing. Low humidity increases ESD risk, enhances friction, and promotes dust accumulation, while high humidity leads to moisture absorption, delamination, and warping. It is crucial to maintain controlled humidity levels to avoid these problems and ensure a smooth and efficient assembly process. Humidity control, therefore, is essential to improving both the quality and reliability of PCBA production.
### The Popcorn Effect: Impact of Humidity on PCB Manufacturing
The “Popcorn Effect,” as outlined by IPC-STD-020, refers to the impact of humidity on plastic packaged devices during the manufacturing process. The effects of humidity are often invisible, except for the weight gain on the components, yet they can have significant consequences such as pores, voids, solder spatter, solder balls, and underfill voids. Humidity, especially when it leads to moisture condensation, can severely degrade material performance, affect process reliability, and reduce the overall quality of PCB assemblies.
### Humidity’s Role in Manufacturing
Humidity plays a crucial role during the PCB manufacturing process. The worst-case scenario is moisture condensation, which occurs when the moisture levels exceed the material’s tolerance, leading to defects. For most coating processes, such as spin coating and metal coatings in silicon semiconductor manufacturing, the dew point of the environment must be carefully controlled in relation to the substrate temperature. This principle ensures that the moisture level on the substrate does not cause issues during production.
While the PCB assembly industry has not traditionally focused on environmental conditions, the importance of controlling humidity is becoming clearer. As device features become finer, components shrink, and substrate densities increase, the requirements for precise environmental control mirror those found in the microelectronics and semiconductor industries. Issues such as dust control have been recognized, but now the effects of humidity on materials and processes are gaining attention. High humidity can lead to solder paste degradation, stencil issues, and problems with underfill materials, compromising both performance and reliability.
### Impact on Solder Paste and Coatings
Solder paste is typically made by suspending solids in a liquid medium such as water or solvent. The purpose of this liquid is to promote adhesion between the metal substrate and the paste. However, when the metal surface is near the dew point, moisture may condense. This trapped moisture can affect the adhesion of the solder paste, causing issues like bubbles under the coating or poor bonding. To avoid this, equipment manufacturers can use dew point meters to ensure proper adhesion.
The dew point meter works by accurately measuring the humidity level around the metal substrate. It then calculates the temperature difference (∆T) between the substrate and the dew point. If the temperature difference is too small (typically below 3-5°C), poor adhesion occurs, leading to voids and other defects. For instance, if the substrate temperature is 19°C and the dew point is 15°C, the ∆T is 4°C, which is at the lower limit of acceptable adhesion conditions. A substrate temperature must be 5°C higher than the dew point for optimal coating adhesion.
### Moisture Absorption and its Effects
The relationship between moisture absorption, relative humidity (RH), and dew point is important for understanding how humidity affects materials. At around 20% RH, a monolayer of water molecules bonds to the substrate surface and remains relatively stable. This monolayer does not significantly affect electrical properties and is generally harmless. However, the situation changes when the relative humidity increases, causing more water molecules to bond and potentially leading to moisture absorption in materials such as epoxy, flux, and OSP (organic solderability preservative). Metal surfaces, however, do not absorb water in the same way.
### Real-World Example: DEK Press Settings
In a typical workshop environment, DEK ECU might set the temperature at 26°C with a relative humidity of 45%. Under these conditions, the dew point temperature of the substrate is 15°C. When the substrate enters the screen printer, it is recorded at 19°C. The temperature difference (∆T) between the substrate and the dew point is 4°C, which falls within the ASTM and ISO coating specifications (minimum of 4±1°C). However, under real-world conditions, this might not be enough to avoid issues such as porous surface coatings, which require a temperature difference of at least 5°C.
If the substrate temperature is 19°C and the relative humidity in the workshop exceeds 60%, the dew point will be higher, resulting in a ∆T of just 2°C. This does not meet ASTM/ISO specifications and increases the risk of poor adhesion due to excessive moisture. Therefore, it is important to maintain a substrate temperature at least 5°C above the dew point to ensure optimal coating quality.
### Workshop Measurement and Humidity Control
The amount of moisture absorbed by the substrate depends on the surface temperature, ambient air temperature, and relative humidity. When the substrate temperature is close to the dew point, water forms a thick multi-molecular layer on the surface. This layer can reduce the adhesion of solder paste, affecting its viscosity and causing poor paste release during printing.
For example, when the relative humidity exceeds 50% RH, and the surface temperature is within 4-5°C of the dew point, poor wetting and adhesion problems arise. We conducted a test where a clean substrate was placed in a refrigerator for half an hour, cooling it to the dew point temperature. When tested with a dyne pen, the dyne value dropped from over 40 dyne to 37 dyne, indicating a significant reduction in surface wettability. This result highlights how humidity, particularly at higher levels, impacts process quality. In real production environments with RH levels of 60-65%, the effect on dyne values would be even more pronounced.
### Conclusion
The Popcorn Effect is a critical issue in PCB manufacturing, particularly as component sizes shrink and process requirements become more stringent. Proper humidity control is essential to prevent material degradation, process defects, and reliability issues. By monitoring and controlling environmental factors such as substrate temperature and relative humidity, manufacturers can significantly reduce the risk of defects like poor solder paste adhesion and void formation. As the industry moves towards more advanced manufacturing techniques, a deeper understanding of moisture’s impact will be crucial for maintaining high-quality production standards.
Humidity plays a crucial role in the PCBA (Printed Circuit Board Assembly) manufacturing process, affecting material properties, assembly quality, and production efficiency. This article explores the influence of temperature and humidity, focusing on how both extremes can negatively impact PCBA processing.
### Low Humidity Effects
When humidity is too low, several issues arise in the manufacturing process. First, low humidity increases the likelihood of electrostatic discharge (ESD) due to the drying of materials and components, which can lead to damage or failure of sensitive electronic parts. Additionally, low humidity can cause higher levels of dust accumulation, which contaminates components and reduces cleanliness in the assembly environment. Template openings are also more likely to become blocked, which can lead to issues with solder paste application and ultimately, reduced yield.
Furthermore, low humidity accelerates template wear due to the increased friction between surfaces. This friction is particularly significant on metal surfaces where the relative humidity is below 20% RH. At these low humidity levels, the friction between metal parts increases by 1.5 times compared to higher humidity conditions (80% RH). This can cause premature wear of equipment and lower the overall efficiency of the production process.
### High Humidity Effects
On the other hand, high humidity introduces its own set of challenges. Excess moisture in the environment causes materials to absorb water, leading to potential issues such as delamination, the popcorn effect, and the formation of solder balls during reflow soldering. These defects are caused by the expansion of absorbed moisture when it turns into vapor during the reflow process, leading to internal stress in the material.
Additionally, moisture reduces the glass transition temperature (Tg) of the PCB material, which makes the material more susceptible to deformation and warpage during reflow soldering. This can lead to increased dynamic warpage, causing misalignment of components, poor solder joints, and reduced reliability of the final product.
### The Role of Surface Wetness in Humidity-Related Issues
Almost all solid surfaces, including metals, glass, ceramics, and silicon, have a moisture-absorbing layer. This layer can be a monomolecular or multi-molecular film that forms when the surface temperature is equal to the dew point of the surrounding air, depending on temperature, humidity, and air pressure. When the humidity level is low, this moisture-absorbing layer becomes less visible, but it still affects the properties of the material.
At very low relative humidity (below 20% RH), the friction between metal surfaces increases significantly, which can hinder the movement of parts in automated assembly processes. This increased friction can also contribute to mechanical wear on equipment, particularly in high-precision environments like PCB assembly.
For organic materials such as epoxy resins, plastics, and fluxes, the moisture-absorbing layer can penetrate the material. Even if the surface temperature is lower than the dew point, no visible moisture is detected, yet the absorbed moisture still affects the material. This moisture, stored within the monomolecular layers, can migrate into plastic-encapsulated devices (MSDs) and lead to failure during the reflow soldering process.
As the moisture absorbed by the material builds up over time, it can eventually result in catastrophic failure during reflow soldering. This is because the moisture expands as it turns into steam, creating internal pressure that can cause delamination or cracks in the solder joints, leading to functional failures of the finished PCB.
### Conclusion
Both excessively low and high humidity levels have significant, detrimental effects on PCBA manufacturing. Low humidity increases ESD risk, enhances friction, and promotes dust accumulation, while high humidity leads to moisture absorption, delamination, and warping. It is crucial to maintain controlled humidity levels to avoid these problems and ensure a smooth and efficient assembly process. Humidity control, therefore, is essential to improving both the quality and reliability of PCBA production.
### The Popcorn Effect: Impact of Humidity on PCB Manufacturing
The “Popcorn Effect,” as outlined by IPC-STD-020, refers to the impact of humidity on plastic packaged devices during the manufacturing process. The effects of humidity are often invisible, except for the weight gain on the components, yet they can have significant consequences such as pores, voids, solder spatter, solder balls, and underfill voids. Humidity, especially when it leads to moisture condensation, can severely degrade material performance, affect process reliability, and reduce the overall quality of PCB assemblies.
### Humidity’s Role in Manufacturing
Humidity plays a crucial role during the PCB manufacturing process. The worst-case scenario is moisture condensation, which occurs when the moisture levels exceed the material’s tolerance, leading to defects. For most coating processes, such as spin coating and metal coatings in silicon semiconductor manufacturing, the dew point of the environment must be carefully controlled in relation to the substrate temperature. This principle ensures that the moisture level on the substrate does not cause issues during production.
While the PCB assembly industry has not traditionally focused on environmental conditions, the importance of controlling humidity is becoming clearer. As device features become finer, components shrink, and substrate densities increase, the requirements for precise environmental control mirror those found in the microelectronics and semiconductor industries. Issues such as dust control have been recognized, but now the effects of humidity on materials and processes are gaining attention. High humidity can lead to solder paste degradation, stencil issues, and problems with underfill materials, compromising both performance and reliability.
### Impact on Solder Paste and Coatings
Solder paste is typically made by suspending solids in a liquid medium such as water or solvent. The purpose of this liquid is to promote adhesion between the metal substrate and the paste. However, when the metal surface is near the dew point, moisture may condense. This trapped moisture can affect the adhesion of the solder paste, causing issues like bubbles under the coating or poor bonding. To avoid this, equipment manufacturers can use dew point meters to ensure proper adhesion.
The dew point meter works by accurately measuring the humidity level around the metal substrate. It then calculates the temperature difference (∆T) between the substrate and the dew point. If the temperature difference is too small (typically below 3-5°C), poor adhesion occurs, leading to voids and other defects. For instance, if the substrate temperature is 19°C and the dew point is 15°C, the ∆T is 4°C, which is at the lower limit of acceptable adhesion conditions. A substrate temperature must be 5°C higher than the dew point for optimal coating adhesion.
### Moisture Absorption and its Effects
The relationship between moisture absorption, relative humidity (RH), and dew point is important for understanding how humidity affects materials. At around 20% RH, a monolayer of water molecules bonds to the substrate surface and remains relatively stable. This monolayer does not significantly affect electrical properties and is generally harmless. However, the situation changes when the relative humidity increases, causing more water molecules to bond and potentially leading to moisture absorption in materials such as epoxy, flux, and OSP (organic solderability preservative). Metal surfaces, however, do not absorb water in the same way.
### Real-World Example: DEK Press Settings
In a typical workshop environment, DEK ECU might set the temperature at 26°C with a relative humidity of 45%. Under these conditions, the dew point temperature of the substrate is 15°C. When the substrate enters the screen printer, it is recorded at 19°C. The temperature difference (∆T) between the substrate and the dew point is 4°C, which falls within the ASTM and ISO coating specifications (minimum of 4±1°C). However, under real-world conditions, this might not be enough to avoid issues such as porous surface coatings, which require a temperature difference of at least 5°C.
If the substrate temperature is 19°C and the relative humidity in the workshop exceeds 60%, the dew point will be higher, resulting in a ∆T of just 2°C. This does not meet ASTM/ISO specifications and increases the risk of poor adhesion due to excessive moisture. Therefore, it is important to maintain a substrate temperature at least 5°C above the dew point to ensure optimal coating quality.
### Workshop Measurement and Humidity Control
The amount of moisture absorbed by the substrate depends on the surface temperature, ambient air temperature, and relative humidity. When the substrate temperature is close to the dew point, water forms a thick multi-molecular layer on the surface. This layer can reduce the adhesion of solder paste, affecting its viscosity and causing poor paste release during printing.
For example, when the relative humidity exceeds 50% RH, and the surface temperature is within 4-5°C of the dew point, poor wetting and adhesion problems arise. We conducted a test where a clean substrate was placed in a refrigerator for half an hour, cooling it to the dew point temperature. When tested with a dyne pen, the dyne value dropped from over 40 dyne to 37 dyne, indicating a significant reduction in surface wettability. This result highlights how humidity, particularly at higher levels, impacts process quality. In real production environments with RH levels of 60-65%, the effect on dyne values would be even more pronounced.
### Conclusion
The Popcorn Effect is a critical issue in PCB manufacturing, particularly as component sizes shrink and process requirements become more stringent. Proper humidity control is essential to prevent material degradation, process defects, and reliability issues. By monitoring and controlling environmental factors such as substrate temperature and relative humidity, manufacturers can significantly reduce the risk of defects like poor solder paste adhesion and void formation. As the industry moves towards more advanced manufacturing techniques, a deeper understanding of moisture’s impact will be crucial for maintaining high-quality production standards.
If you have any questions about PCB or PCBA, feel free to reach out to me at info@wellcircuits.com.
