1. As we all know, designers are pushing for greater performance from printed circuit boards. Power density is increasing, and the resulting high temperatures can severely damage conductors and dielectrics.
2. Elevated temperatures—whether due to I2R losses or environmental factors—affect thermal resistance and electrical impedance, leading to unstable system performance, even if it doesn’t result in complete failure.
3. The difference in thermal expansion rates between conductors and dielectrics (the tendency of a material to expand when heated and contract when cooled) can create mechanical stress, potentially causing cracks and connection failures, especially with periodic heating and cooling of the circuit board.
4. If temperatures reach high enough levels, the dielectric may completely lose its structural integrity, setting off a chain reaction of problems.
5. Heat has consistently impacted PCB performance. Designers are familiar with incorporating heat sinks into PCBs; however, today’s high power density design demands often exceed the capabilities of traditional PCB thermal management techniques.
6. Addressing the effects of high temperatures not only significantly impacts the performance and reliability of high-temperature PCBs but also affects the following factors:
7. Component (or system) weight
8. Application size
9. Cost
10. Power requirements
1. A high-temperature PCB is generally defined as having a Tg (glass transition temperature) higher than 170°C.
2. For continuous thermal loads, with operating temperatures below Tg by 25°C, high-temperature PCBs should adhere to a basic guideline.
3. Thus, if your product operates within the temperature range of 130°C or higher, it is advisable to use high Tg materials.
4. This article will delve into design methods and techniques used in high-temperature PCB manufacturing and PCBA to help designers manage high-temperature applications.
5. PCB heat dissipation technology and design considerations
6. Heat is dissipated through one or more mechanisms (radiation, convection, conduction), and the design team must consider these factors when managing system and component temperatures.
7. Heavy copper PCB
8. Radiation
9. Radiation involves the emission of energy in the form of electromagnetic waves. While often associated with light, any object above absolute zero radiates heat. Although radiation typically has minimal impact on circuit board performance, it can occasionally be a critical factor. To effectively remove heat, electromagnetic waves should have a clear path away from the source. Reflective surfaces hinder photon outflow and regroup many photons at the source. If reflective surfaces form a parabolic mirror effect, they may concentrate radiant energy on a specific part of the system, causing significant issues.
10. Convection
11. Convection transfers heat to fluids (air, water, etc.). Natural convection occurs as fluid absorbs heat from the source, decreases in density, rises, cools, increases in density, and returns to the source, repeating the process (similar to the “rain cycle”). Forced convection involves fans or pumps. Key factors affecting convection include the temperature difference between source and coolant, heat transfer difficulty, coolant absorption capacity, flow rate, and surface area for heat transfer. Liquids generally absorb heat more effectively than gases.
12. Conductivity
13. Conduction involves heat transfer through direct contact between the heat source and sink. It is analogous to electric current: the temperature difference is similar to voltage, heat transfer rate to amperage, and ease of heat flow to electrical conductivity. Good electrical conductors often also make good thermal conductors, as both involve molecular or atomic motion. For example, copper and aluminum are excellent heat and electricity conductors. Larger conductor cross-sections can enhance heat and electron conductivity. As with electrical circuits, long and convoluted paths can significantly reduce conductor efficiency.
14. Typically, heat removal from a circuit board involves conducting heat to a suitable heat sink, while convection transfers heat to the environment. Radiation removes some heat directly from the source, but most heat is usually dissipated through specially designed channels (called “hot aisles”). The PCB heat sink is relatively large, with a high emissivity surface (often corrugated or finned to increase surface area), bonded with a conductive backing (such as copper or aluminum), a labor-intensive process. The PCB heat sink can also be attached to the device chassis to utilize its surface area. Fans are commonly used to provide cooling airflow, and in extreme cases, the cooling air can be chilled in a gas-liquid heat exchanger.
2. Elevated temperatures—whether due to I2R losses or environmental factors—affect thermal resistance and electrical impedance, leading to unstable system performance, even if it doesn’t result in complete failure.
3. The difference in thermal expansion rates between conductors and dielectrics (the tendency of a material to expand when heated and contract when cooled) can create mechanical stress, potentially causing cracks and connection failures, especially with periodic heating and cooling of the circuit board.
4. If temperatures reach high enough levels, the dielectric may completely lose its structural integrity, setting off a chain reaction of problems.
5. Heat has consistently impacted PCB performance. Designers are familiar with incorporating heat sinks into PCBs; however, today’s high power density design demands often exceed the capabilities of traditional PCB thermal management techniques.
6. Addressing the effects of high temperatures not only significantly impacts the performance and reliability of high-temperature PCBs but also affects the following factors:
7. Component (or system) weight
8. Application size
9. Cost
10. Power requirements
1. A high-temperature PCB is generally defined as having a Tg (glass transition temperature) higher than 170°C.
2. For continuous thermal loads, with operating temperatures below Tg by 25°C, high-temperature PCBs should adhere to a basic guideline.
3. Thus, if your product operates within the temperature range of 130°C or higher, it is advisable to use high Tg materials.
4. This article will delve into design methods and techniques used in high-temperature PCB manufacturing and PCBA to help designers manage high-temperature applications.
5. PCB heat dissipation technology and design considerations
6. Heat is dissipated through one or more mechanisms (radiation, convection, conduction), and the design team must consider these factors when managing system and component temperatures.
7. Heavy copper PCB
8. Radiation
9. Radiation involves the emission of energy in the form of electromagnetic waves. While often associated with light, any object above absolute zero radiates heat. Although radiation typically has minimal impact on circuit board performance, it can occasionally be a critical factor. To effectively remove heat, electromagnetic waves should have a clear path away from the source. Reflective surfaces hinder photon outflow and regroup many photons at the source. If reflective surfaces form a parabolic mirror effect, they may concentrate radiant energy on a specific part of the system, causing significant issues.
10. Convection
11. Convection transfers heat to fluids (air, water, etc.). Natural convection occurs as fluid absorbs heat from the source, decreases in density, rises, cools, increases in density, and returns to the source, repeating the process (similar to the “rain cycle”). Forced convection involves fans or pumps. Key factors affecting convection include the temperature difference between source and coolant, heat transfer difficulty, coolant absorption capacity, flow rate, and surface area for heat transfer. Liquids generally absorb heat more effectively than gases.
12. Conductivity
13. Conduction involves heat transfer through direct contact between the heat source and sink. It is analogous to electric current: the temperature difference is similar to voltage, heat transfer rate to amperage, and ease of heat flow to electrical conductivity. Good electrical conductors often also make good thermal conductors, as both involve molecular or atomic motion. For example, copper and aluminum are excellent heat and electricity conductors. Larger conductor cross-sections can enhance heat and electron conductivity. As with electrical circuits, long and convoluted paths can significantly reduce conductor efficiency.
14. Typically, heat removal from a circuit board involves conducting heat to a suitable heat sink, while convection transfers heat to the environment. Radiation removes some heat directly from the source, but most heat is usually dissipated through specially designed channels (called “hot aisles”). The PCB heat sink is relatively large, with a high emissivity surface (often corrugated or finned to increase surface area), bonded with a conductive backing (such as copper or aluminum), a labor-intensive process. The PCB heat sink can also be attached to the device chassis to utilize its surface area. Fans are commonly used to provide cooling airflow, and in extreme cases, the cooling air can be chilled in a gas-liquid heat exchanger.
