Process series of power battery pack -Lithium - Ion Battery Equipment
Potting basic process
The potting process can be divided into two types according to the electrical insulation treatment methods: mold forming and moldless forming; mold forming is divided into general pouring and vacuum pouring. Vacuum perfusion is generally used when other conditions are the same. The general potting process flow is shown in the figure below.
Common problems in potting
Mold design, silicone rubber is fluid when used, in order to prevent the rubber material from leaking everywhere, causing waste of rubber material and polluting the environment, the design of the mold is very critical. The mold design generally needs to achieve the following points: easy to assemble, disassemble, and demould; tight fit to prevent rubber leakage; flat support bottom surface to ensure that the thickness of each part of the adhesive layer is basically the same during the drying process, and it is convenient to control the potting height.(Lithium - Ion Battery Equipment)
Bubbles, after the bubbles are mixed in the rubber, not only affect the appearance quality of the product, but more importantly, affect the electrical and mechanical properties of the product. For silicone rubber, due to its good toughness, air bubbles mainly affect the electrical properties of the product. The main reasons for the generation of air bubbles are: low molecular weight or volatile components produced during the reaction process; air bubbles brought in by mechanical agitation; moisture brought in by fillers that are not completely dried; hole. For two-component silicone rubber, the rubber must be fully stirred when mixing. Using a vacuum drying oven to carry out vacuum degassing treatment can significantly improve the quality of the adhesive layer, and simultaneously improve the strength and toughness.
Adhesiveness between the rubber material and the electronic device, and the potting compound makes the electronic device a whole, thereby improving the shock resistance of the electronic device. In order to improve its bonding strength, in addition to choosing a rubber with good bonding performance, attention should also be paid to workpiece cleaning, surface treatment and demoulding during operation.
Polyurethane
Polyurethane potting material has high insulation resistance and bonding strength, so it is an ideal potting material. Polyurethane potting materials are used for the preparation of sealing castings, for electronic products such as circuit boards, electronic components, plug socket potting, and can also be used as adhesives and coatings.
Polyurethane potting process
Surface treatment: If the surface treatment is not good, it will lead to debonding of the potting parts. Some potting parts have low water absorption, and no surface treatment is required. Metal potting parts need surface treatment. After surface treatment, the potting parts generally need to be potted within 24-48 hours.
Water removal: The potted parts will absorb moisture in the air, and need to be dried to remove water. Can be 60~10. ℃ heating 10min to several hours to remove water. It depends on how much water the potting parts absorb and how difficult it is to remove water.
Preheating: material B is preheated to 50-60°C; material A is preheated to 30°C
Blistering: put material A and material B into a vacuum-capable airtight container according to the measured weight ratio, and stir for 1-5 minutes to vacuum, the vacuum degree is lower than 20mm Hg. Stop stirring.
Pouring: Pouring in one direction with minimal shaking.
Curing temperature and time: to choose the appropriate curing temperature and time. Curing at room temperature to 10°C for 3-24 hours, depending on the curing speed. For reactants cured at room temperature, it usually takes 1 to 2 weeks to cure completely.
The above mixing temperature and curing temperature can be adjusted according to requirements. The mixing temperature should ensure that the reactants are transparent or translucent, so that they are in a homogeneous phase. The curing temperature should ensure that the reactants do not separate phases and the reaction is close to complete.
What should be paid attention to in the selection of thermal conductive potting glue?
1) Thermal conductivity, the unit of thermal conductivity is W/m.K, which means the thermal conduction power of a column with a cross-sectional area of 1 square meter and a temperature difference of 1 meter along the axial direction when the temperature difference is 1 Kelvin (K=℃+273.15). The larger the value, the faster the heat passing rate of the material and the better the thermal conductivity.
The thermal conductivity varies greatly, and the basic reason is that there are differences in the thermal conductivity mechanisms of different substances. Normally, metals have the highest thermal conductivity, followed by non-metals and liquids, and gases have the smallest thermal conductivity. Silver has a thermal conductivity of 420, copper is 383, aluminum is 204, and water has a thermal conductivity of 0.58. At present, the thermal conductivity of mainstream thermal silica gel is greater than 1W/m.K, and the high-quality ones can reach more than 6W/m.K.
2) Viscosity. Viscosity is a measure of fluid viscosity. It refers to the resistance of the fluid against movement. It is expressed by the ratio of the shear stress to the shear rate of the fluid. There are many ways to measure viscosity, such as energy viscosity The unit is Poise or Pa. Seconds.
The thermally conductive adhesive has good flatness, and can be easily spread around the surface of the chip under a certain pressure, and guarantees a certain viscosity, so that the excess glue will not overflow after extrusion.
3) Dielectric constant, the dielectric constant is used to measure the performance of the insulator to store electric energy, which refers to the capacitance between two metal plates when the insulating material is used as the medium and the capacitance between the same two plates when the air is used as the medium or vacuum ratio of capacitance.
The dielectric constant represents the polarization level of the dielectric, that is, the ability to restrain the charge. The larger the dielectric constant, the stronger the ability to restrain the charge.
4) Working temperature range, due to the characteristics of thermal conductive adhesive itself, its working temperature range is very wide. The working temperature is an important parameter to ensure that the thermal silica gel is in a solid or liquid state. If the temperature is too high, the volume of the thermal adhesive fluid will expand, the distance between molecules will be stretched, the interaction will be weakened, and the viscosity will decrease; the temperature will drop, the volume of the fluid will shrink, and the distance between molecules will shrink. The interaction is enhanced and the viscosity rises, both of which are not conducive to heat dissipation. If the withstand temperature is around 100°C, then epoxy resin and polyurethane are both acceptable, while silicone can withstand high and low temperatures from -60°C to 200°C; the ability to resist cold and heat changes, silicone is the best, followed by is polyurethane, epoxy is the worst;
5) Other considerations, such as the internal stress of the components, whether it is used outdoors or indoors, the stress, whether flame retardancy is required, color requirements, manual or automatic potting, etc.
The potting process can be divided into two types according to the electrical insulation treatment methods: mold forming and moldless forming; mold forming is divided into general pouring and vacuum pouring. Vacuum perfusion is generally used when other conditions are the same. The general potting process flow is shown in the figure below.
Common problems in potting
Mold design, silicone rubber is fluid when used, in order to prevent the rubber material from leaking everywhere, causing waste of rubber material and polluting the environment, the design of the mold is very critical. The mold design generally needs to achieve the following points: easy to assemble, disassemble, and demould; tight fit to prevent rubber leakage; flat support bottom surface to ensure that the thickness of each part of the adhesive layer is basically the same during the drying process, and it is convenient to control the potting height.(Lithium - Ion Battery Equipment)
Bubbles, after the bubbles are mixed in the rubber, not only affect the appearance quality of the product, but more importantly, affect the electrical and mechanical properties of the product. For silicone rubber, due to its good toughness, air bubbles mainly affect the electrical properties of the product. The main reasons for the generation of air bubbles are: low molecular weight or volatile components produced during the reaction process; air bubbles brought in by mechanical agitation; moisture brought in by fillers that are not completely dried; hole. For two-component silicone rubber, the rubber must be fully stirred when mixing. Using a vacuum drying oven to carry out vacuum degassing treatment can significantly improve the quality of the adhesive layer, and simultaneously improve the strength and toughness.
Adhesiveness between the rubber material and the electronic device, and the potting compound makes the electronic device a whole, thereby improving the shock resistance of the electronic device. In order to improve its bonding strength, in addition to choosing a rubber with good bonding performance, attention should also be paid to workpiece cleaning, surface treatment and demoulding during operation.
Polyurethane
Polyurethane potting material has high insulation resistance and bonding strength, so it is an ideal potting material. Polyurethane potting materials are used for the preparation of sealing castings, for electronic products such as circuit boards, electronic components, plug socket potting, and can also be used as adhesives and coatings.
Polyurethane potting process
Surface treatment: If the surface treatment is not good, it will lead to debonding of the potting parts. Some potting parts have low water absorption, and no surface treatment is required. Metal potting parts need surface treatment. After surface treatment, the potting parts generally need to be potted within 24-48 hours.
Water removal: The potted parts will absorb moisture in the air, and need to be dried to remove water. Can be 60~10. ℃ heating 10min to several hours to remove water. It depends on how much water the potting parts absorb and how difficult it is to remove water.
Preheating: material B is preheated to 50-60°C; material A is preheated to 30°C
Blistering: put material A and material B into a vacuum-capable airtight container according to the measured weight ratio, and stir for 1-5 minutes to vacuum, the vacuum degree is lower than 20mm Hg. Stop stirring.
Pouring: Pouring in one direction with minimal shaking.
Curing temperature and time: to choose the appropriate curing temperature and time. Curing at room temperature to 10°C for 3-24 hours, depending on the curing speed. For reactants cured at room temperature, it usually takes 1 to 2 weeks to cure completely.
The above mixing temperature and curing temperature can be adjusted according to requirements. The mixing temperature should ensure that the reactants are transparent or translucent, so that they are in a homogeneous phase. The curing temperature should ensure that the reactants do not separate phases and the reaction is close to complete.
What should be paid attention to in the selection of thermal conductive potting glue?
1) Thermal conductivity, the unit of thermal conductivity is W/m.K, which means the thermal conduction power of a column with a cross-sectional area of 1 square meter and a temperature difference of 1 meter along the axial direction when the temperature difference is 1 Kelvin (K=℃+273.15). The larger the value, the faster the heat passing rate of the material and the better the thermal conductivity.
The thermal conductivity varies greatly, and the basic reason is that there are differences in the thermal conductivity mechanisms of different substances. Normally, metals have the highest thermal conductivity, followed by non-metals and liquids, and gases have the smallest thermal conductivity. Silver has a thermal conductivity of 420, copper is 383, aluminum is 204, and water has a thermal conductivity of 0.58. At present, the thermal conductivity of mainstream thermal silica gel is greater than 1W/m.K, and the high-quality ones can reach more than 6W/m.K.
2) Viscosity. Viscosity is a measure of fluid viscosity. It refers to the resistance of the fluid against movement. It is expressed by the ratio of the shear stress to the shear rate of the fluid. There are many ways to measure viscosity, such as energy viscosity The unit is Poise or Pa. Seconds.
The thermally conductive adhesive has good flatness, and can be easily spread around the surface of the chip under a certain pressure, and guarantees a certain viscosity, so that the excess glue will not overflow after extrusion.
3) Dielectric constant, the dielectric constant is used to measure the performance of the insulator to store electric energy, which refers to the capacitance between two metal plates when the insulating material is used as the medium and the capacitance between the same two plates when the air is used as the medium or vacuum ratio of capacitance.
The dielectric constant represents the polarization level of the dielectric, that is, the ability to restrain the charge. The larger the dielectric constant, the stronger the ability to restrain the charge.
4) Working temperature range, due to the characteristics of thermal conductive adhesive itself, its working temperature range is very wide. The working temperature is an important parameter to ensure that the thermal silica gel is in a solid or liquid state. If the temperature is too high, the volume of the thermal adhesive fluid will expand, the distance between molecules will be stretched, the interaction will be weakened, and the viscosity will decrease; the temperature will drop, the volume of the fluid will shrink, and the distance between molecules will shrink. The interaction is enhanced and the viscosity rises, both of which are not conducive to heat dissipation. If the withstand temperature is around 100°C, then epoxy resin and polyurethane are both acceptable, while silicone can withstand high and low temperatures from -60°C to 200°C; the ability to resist cold and heat changes, silicone is the best, followed by is polyurethane, epoxy is the worst;
5) Other considerations, such as the internal stress of the components, whether it is used outdoors or indoors, the stress, whether flame retardancy is required, color requirements, manual or automatic potting, etc.
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