Circuit board potting process technology

one. What is potting?

Potting (glue filling) is to pour polyurethane potting glue, silicone potting glue, and epoxy resin potting glue into devices equipped with electronic components and circuits by equipment or manual methods, and cure them at room temperature or heating conditions into thermosetting polymer insulating materials with excellent performance, so as to achieve the purpose of bonding, sealing, potting and coating protection.

two: The main role of potting?

The main functions of potting are: 1) to strengthen the integrity of electronic devices and improve the resistance to external shocks and vibration; 2) To improve the insulation between internal components and the circuit, which is conducive to the miniaturization and lightweight of the device; 3) To avoid direct exposure of components and circuits, and improve the waterproof, dustproof, and moisture-proof properties of the device; 5) heat transfer and thermal conductivity；

three: The advantages and disadvantages of the three potting adhesives?

1) Epoxy resin potting glue

Epoxy resin potting glue is mostly hard, almost as hard as stone after curing, it is difficult to remove, and has a good confidentiality function, but a small part is soft. Ordinary temperature resistance is about 100℃, the temperature resistance of heating and curing is about 150℃, and there are also those with temperature resistance above 300℃. It has the characteristics of fixing, insulation, waterproof, oil-proof, dust-proof, anti-theft, corrosion-resistant, aging-resistant, and hot and cold shock-resistant. Common epoxy potting adhesives are: flame-retardant, thermally conductive, low-viscosity, high-temperature resistant, etc.

Advantages: Good adhesion to hard materials, excellent high temperature resistance and electrical insulation ability, simple operation, very stable before and after curing, and excellent adhesion to a variety of metal substrates and porous substrates.

Disadvantages: The ability to resist changes in heat and cold is weak, and cracks are prone to occur after being hit by heat and cold, causing water vapor to penetrate from the cracks into the electronic components, and the moisture-proof ability is poor. And after curing, the colloid has high hardness and brittleness, which is easy to strain electronic components, and cannot be opened after potting, and the repair is not good.

Scope of application: Epoxy resin potting glue can easily penetrate into the gap of the product. It is suitable for potting small and medium-sized electronic components at room temperature and without special requirements for environmental mechanical properties, such as automobile and motorcycle igniters, LED drive power supplies, sensors, ring transformers, capacitors, triggers, LED waterproof lights, circuit board confidentiality, insulation, moisture-proof (water) potting.

2) Silicone potting glue

After the silicone electronic potting glue is cured, it is mostly soft and elastic and can be repaired. It is referred to as soft glue and has poor adhesion. Its color can generally be adjusted as needed, either transparent or non-transparent or colored. Two-component silicone potting adhesives are the most common. These types of adhesives include two types of condensing and additive agents. Generally, the condensed type has poor adhesion to components and potting cavities, and volatile low-molecular substances will be produced during the curing process, and there will be a more obvious shrinkage rate after curing; the molded (also known as silicone gel) has a very small shrinkage rate, and no volatile low-molecular substances will be produced during the curing process, which can be heated and cured quickly.

Advantages: Strong anti-aging ability, good weather resistance, and excellent impact resistance; it has excellent resistance to cold and heat changes and thermal conductivity, can be used in a wide operating temperature range, can maintain elasticity in the temperature range of -60℃~200℃, does not crack, can be used for a long time at 250℃, the heating and curing type has higher temperature resistance, excellent electrical properties and insulation capabilities, better insulation properties than epoxy resins, and can withstand voltages above 10,000V.After potting, it effectively improves the insulation of internal components and circuits, and improves the stability of electronic components; it is not corrosive to electronic components and does not produce any by-products in the curing reaction; it has excellent rework ability, which can quickly and easily remove the sealed components for repair and replacement; it has excellent thermal conductivity and flame retardant ability, which effectively improves the heat dissipation capacity and safety factor of electronic components; low viscosity, good fluidity, can penetrate into small voids and components; can be cured at room temperature or temperature, good self-defoaming, and more convenient to use; curing shrinkage rate is small, and it has excellent waterproof properties. And seismic resistance.

Disadvantages: High price and poor adhesion.

Scope of application: Suitable for potting various electronic components that work in harsh environments.

What are the advantages of organic electronic potting adhesives over other potting adhesives?

Advantage 1: Long-term protection of sensitive circuits or electronic components, and long-term and effective protection of electronic modules and devices, whether they are simple or complex structures and shapes.

Advantage 2: It has stable dielectric insulation properties and is an effective barrier to prevent environmental pollution. After curing, a soft elastomer is formed to eliminate the stress caused by shock and vibration within a large temperature and humidity range.

Advantage 3: It can maintain its original physical and electrical properties in various working environments, resist the degradation of ozone and ultraviolet rays, and have good chemical stability.

Advantage 4: It is easy to clean up and dismantle after potting, so that electronic components can be repaired, and new potting glue can be re-injected into the repaired parts.

3) Polyurethane potting glue

Polyurethane potting glue, also known as PU potting glue, is mostly soft and elastic after curing and can be repaired. It is referred to as soft glue. The adhesion is between epoxy and silicone, and the temperature resistance is generally not more than 100℃. There are more bubbles after potting. The potting conditions must be under vacuum, and the adhesion is between epoxy and silicone.

Advantages: Good low temperature resistance and shock resistance are the best of the three. It has the characteristics of low hardness, moderate strength, good elasticity, water resistance, mildew resistance, shock resistance and transparency, excellent electrical insulation and flammability, no corrosion to electrical components, and good adhesion to steel, aluminum, copper, tin and other metals, as well as rubber, plastic, wood and other materials.

Disadvantages: The high temperature resistance is poor, the surface of the colloid is not smooth and the toughness is poor after curing, the anti-aging ability and UV resistance are very weak, and the colloid is easy to change color.

Scope of application: It is suitable for potting indoor electrical components with low heat generation. It can protect the installed and debugged electronic components and circuits from vibration, corrosion, moisture and dust. It is an ideal potting material for moisture-proof and anti-corrosion treatment of electronic and electrical parts.

Fourth, the issues that should be considered when choosing potting materials?

1) Performance requirements after potting: operating temperature, alternating hot and cold conditions, internal stress of components, outdoor use or indoor use, force conditions, whether flame retardant and thermal conductivity are required, color requirements, etc.；

2) Potting process: manual or automatic, room temperature or heating, complete curing time, solidification time of glue after mixing, etc.；

3) Cost: The proportion of potting materials varies greatly. We must look at the actual cost after potting, rather than simply looking at the price of the material.

The adhesives used for potting are classified according to their functions as thermally conductive potting glue, adhesive potting glue, and waterproof potting glue; according to the material classification, there are polyurethane potting glue, silicone potting glue, and epoxy resin potting glue. For choosing soft glue or hard glue, both can be potted, waterproof and insulated at that time. If high temperature resistance and thermal conductivity are required, it is recommended to use silicone soft glue; if low temperature resistance is required, then it is recommended to use polyurethane soft glue; if there is no requirement, it is recommended to use epoxy hard glue, because epoxy hard glue has a faster curing time than silicone.

Epoxy resin potting glue has a wide range of applications, technical requirements vary widely, and there are many varieties. From the curing conditions, there are two types of curing at room temperature and heating curing; from the dosage form, there are two types of two-component and one-component. There is also room temperature curing epoxy potting glue, which is generally two-component. Its advantage is that it can be cured without heating after potting. The equipment requirements are not high, and it is easy to use. The defect is that the glue mixture has a large viscosity, poor infiltration, short application period, and the heat resistance and electrical properties of the cured material are not very high. It is generally used for potting low-voltage electronic devices or occasions where it is not suitable for heating and curing.

Five, potting process

The quality of potting products is mainly closely related to product design, component selection, assembly and potting materials used, and the potting process is also a factor that cannot be ignored. There are two potting processes for epoxy potting, normal and vacuum.

Epoxy resin. Amine curing potting materials at room temperature are generally used in low-voltage electrical appliances, and more normal potting is used.

Epoxy resin. Acid anhydride heating and curing potting material is generally used for potting high-voltage electronic devices, and vacuum potting technology is mostly used.

At present, there are two common methods of manual vacuum potting and mechanical vacuum potting, and mechanical vacuum potting can be divided into two situations: A and B components are mixed and defoamed first, and then potted and mixed after defoaming separately. There are three methods of operation：

The first type: one-component electronic potting glue, direct use, can be used to grab or directly pour；

The second type: two-component condensed electronic potting glue, curing agent 2%-3% or other proportions, stirring-vacuuming, defoaming-perfusion；

The third type: add molding electronic potting glue, curing agent 1:1, 10:1；

The process flow is as follows：

(1) Manual vacuum potting process

(2) Mechanical vacuum potting process

1) Measurement: Accurately weigh component A and component B (curing agent). 2) Mixing: mixing the components; 3) Defoaming: natural defoaming and vacuum defoaming; 4) Perfusion: the rubber should be perfused within the operating time, otherwise it will affect the leveling; 5) Curing: heating or curing at room temperature, the potted product is cured at room temperature, and after the initial solidification, it can enter the next process. It takes 8 to 24 hours to completely cure.If the temperature is high in summer, the curing will be faster; if the temperature is low in winter, the curing will be slower.

(3) Precautions: a. The surface of the potted product must be cleaned before potting! B. Pay attention to stirring the A and B components thoroughly before weighing, so that the pigments (or fillers) that sink to the bottom are dispersed into the glue.C. The primer should not be directly mixed with the rubber material. The primer should be used first. After the primer is dry, the rubber material should be used for potting.D. The curing speed of the rubber has a certain relationship with the temperature, and the curing will be slower when the temperature is low. In contrast, mechanical vacuum potting has large equipment investment and high maintenance costs, but it is significantly better than manual vacuum potting in terms of product consistency and reliability. No matter what kind of potting method, the set process conditions should be strictly observed, otherwise it is difficult to get satisfactory products.

six. Analysis of common problems and causes of potting products

(1) The starting voltage of partial discharge is low, and the high-voltage electronic products such as televisions, monitor output transformers, automobiles, motorcycle igniters, etc. are ignited or penetrated between the lines. Due to improper potting technology, partial discharge (arc), ignition or breakdown between the lines will occur during work. The wire diameter of the high-voltage coil of this type of product is very small, generally only 0.02~0.04mm, and the potting material fails to completely penetrate the turns, leaving gaps between the turns of the coil. Since the dielectric constant of the void is much smaller than that of the epoxy potting material, under alternating high voltage conditions, an uneven electric field will be generated, causing partial discharge at the interface, aging and decomposing the material, and causing insulation damage.

From the perspective of process analysis, there are two reasons for the gap between the lines:：

1) The degree of vacuum is not high enough during potting, and the air between them cannot be completely eliminated, so that the material cannot be completely infiltrated.

2) The preheating temperature of the glue or product before potting is not enough, and the viscosity cannot be reduced quickly, which affects the infiltration.

For manual potting or vacuum potting after mixing and defoaming, the material mixing and defoaming temperature is high, the operating time is long or exceeds the applicable period of the material, and the product does not enter the heating and curing process in time after potting, which will cause the viscosity of the material to increase, affecting the infiltration of the coil. Previously, according to relevant experts, the higher the starting temperature of the thermosetting epoxy potting material complex, the smaller the viscosity, and the faster the viscosity increases over time. Therefore, in order to make the material have good permeability to the coil, the following points should be paid attention to in operation：

1) The potting material complex should be kept within a given temperature range and used within the applicable period.

2) Before potting, the product should be heated to the specified temperature, and the heating and curing procedure should be entered in time after potting is completed.

3) The vacuum degree of potting should meet the requirements of technical specifications.

(2) Shrinkage, local depression, and cracking on the surface of the potting material. During the heating and curing process, the potting material will produce two kinds of shrinkage, namely chemical shrinkage during the phase transition from liquid to solid state and physical shrinkage during cooling.

Further analysis shows that there are two more processes of chemical change and shrinkage in the curing process, from the heating chemical crosslinking reaction after potting to the shrinkage of the microscopic mesh structure in the initial formation stage, which we call the gel pre-curing shrinkage. The shrinkage from the gel to the fully cured stage is called post-cured shrinkage.The amount of shrinkage of these two processes is different. During the transformation of the former from a liquid state to a mesh structure, the physical state mutates, the consumption of reactive groups is greater than that of the latter, and the volume shrinkage is higher than that of the latter. The epoxy loss in the pre-curing stage of the gel (75℃/3h) is greater than that in the post-curing stage (110℃/3h). The results of differential thermal analysis also prove this. The curing degree of the sample after 750℃/3h treatment is 53%.

If we take a high-temperature curing of the potted product, the two stages of the curing process are too close, and the gel pre-curing and post-curing are completed almost at the same time. This will not only cause excessive exothermic peaks, damage the components, but also cause huge internal stress on the potted parts, causing defects in the interior and appearance of the product. in order to obtain a good product, we must focus on the matching of the curing speed of the potting material (that is, the gel time of the A and B complexes) and the curing conditions when designing the potting material formula and the curing process. The method usually used is: the process of curing according to different temperature zones according to the nature and use of the potting material. According to experts, the potting of color TV output transformers is divided into curing procedures and internal exothermic curves according to different temperature zones. In the pre-curing temperature section of the gel, the curing reaction of the potting material is carried out slowly, the reaction heat is gradually released, the viscosity of the material increases and the volume shrinkage is carried out smoothly. When the material is in a fluid state at this stage, the volume shrinkage is manifested as a decrease in the liquid level until the gel is formed, which can completely eliminate the internal stress of the volume shrinkage at this stage. From the pre-curing to post-curing stage of the gel, the heating should also be gentle. After the curing is completed, the potting parts should slowly cool down in sync with the heating equipment, so as to reduce and adjust the stress distribution in the product in many ways, so as to avoid shrinkage, depression and even cracking on the surface of the product. Phenomenon.

For the formulation of the curing conditions of the potting material, it is necessary to refer to the arrangement of the embedded components in the potting product, the degree of fullness, the size and shape of the product, and the amount of single potting. For a single potting volume is large and there are fewer embedded components, it is completely necessary to appropriately reduce the gel pre-curing temperature and extend the time.

(3) The phenomenon of poor surface or partial non-curing of the cured object is also mostly related to the curing process.

The main reason is：

1) The metering or mixing device fails, and the production personnel make mistakes in operation.

2) Component A is stored for a long time and precipitates, and it is not sufficiently stirred evenly before use, resulting in an imbalance in the actual ratio of resin and curing agent.

3) Component B is stored in the open for a long time and fails to absorb moisture. 4) In the wet season, the potting parts do not enter the curing process in time, and the surface of the object absorbs moisture.

In short, to obtain a good potting product, the potting and curing process is indeed an issue worthy of high attention.

Common problems with electronic glue filling

1) How to solve the poisoning and non-curing of electronic potting glue?

Silicone poisoning generally occurs on the addition of molded electronic potting glue. After poisoning, the silicone will not cure. Therefore, when using the addition of molded potting glue, it should avoid contact with organic compounds containing phosphorus, sulfur, and nitrogen, or use polyurethane, epoxy resin, unsaturated polyester, condensed room temperature vulcanized silicone rubber and other products at the same time as the addition of molded silicone to prevent poisoning and non-curing.

2) What can be used to clean the electronic potting glue that is accidentally glued to it?

The commonly used silicone cleaning agents are mainly alcohol, acetone, liquor, etc. , Remember to dilute and apply when using them.

3) What should I do if the electronic potting glue can't dry in winter?

Due to the very low temperature in winter, the electronic potting glue will cure very slowly or even not for a long time after mixing. Therefore, we can increase the curing temperature and put the glued product in a 25℃ oven to cure.

Epoxy resin potting material, its process and common problems

1. There have been two major changes in the field of electronic packaging technology.

The first change appeared in the first half of the 1970s, characterized by the transition from pin plug-in mounting technology (such as DIP) to surface mount technology (such as QFP) in four-sided flat packaging; the second change occurred in the mid-1990s, which was marked by the emergence of solder ball arrays and BGA-type packaging. The corresponding surface mount technology and semiconductor integrated circuit technology together span the 21st century.With the development of technology, many new packaging technologies and packaging forms have emerged, such as chip direct bonding, potted plastic solder ball array (CD-PBGA), flip chip plastic solder ball array (Fc-PBGA), chip size packaging (CSP) and multi-chip components (MCM), etc. In these packages, a considerable part of the liquid epoxy material packaging technology is used.Potting is to mechanically or manually pour a liquid epoxy resin complex into a device equipped with electronic components and circuits, and cure it at room temperature or heating conditions to become a thermoplastic polymer insulating material with excellent performance.

2. Product performance requirements

The potting material should meet the following basic requirements: good performance, long application period, suitable for large-scale automatic production line operations; small viscosity, strong permeability, can fill components and inter-line; in the potting and curing process, the powder components such as fillers have small sedimentation and are not layered; the curing exothermic peak is low, and the curing shrinkage is small; the cured material has excellent electrical and mechanical properties, good heat resistance, good adhesion to a variety of materials, water absorption and linear expansion coefficient are small; in some cases, the potting material is also required to have properties such as flame-retardant, weather-resistant, thermal conductivity, and resistance to high and low temperature alternation. .

In specific semiconductor packaging, since the material must be in direct contact with the chip and the substrate, in addition to meeting the above requirements, the product must also have the same purity as the chip mounting material. In the potting of flip chips, due to the small gap between the chip and the substrate, the viscosity of the potting material is required to be extremely low. In order to reduce the stress generated between the chip and the packaging material, the modulus of the packaging material should not be too high. Moreover, in order to prevent moisture penetration at the interface, the packaging material should have good bonding properties between the chip and the substrate.

3. The main components and functions of potting material

The role of potting material is to strengthen the integrity of electronic devices and improve the resistance to external shocks and vibration; improve the insulation between internal components and circuits, which is conducive to the miniaturization and lightweight of the device; avoid direct exposure of components and circuits, and improve the waterproof and moisture-proof properties of the device.

Epoxy resin potting material is a multi-component composite system, consisting of resin, curing agent, toughening agent, filler, etc. For the viscosity, reactivity, service life, heat release, etc. of the system, it is necessary to make a comprehensive design in terms of formula, process, casting size structure, etc., to achieve a comprehensive balance.

3.1 Epoxy resin

Epoxy resin potting materials generally use low molecular weight liquid bisphenol A epoxy resin, which has a small viscosity and high epoxy value. Commonly used are E-54, E-51, E-44, and E-42. In the potting filled under the flip chip, due to the small gap between the chip and the substrate, the viscosity of the liquid packaging material is required to be extremely low. Therefore, the use of bisphenol A epoxy resin alone cannot meet the product requirements. in order to reduce product viscosity and meet product performance requirements, we can use combination resins: such as adding low-viscosity bisphenol F-type epoxy resins, glycidyl ester resins, and resin epoxides with high heat resistance, electrical insulation and weather resistance. Epoxides. Among them, the resin cyclic epoxide itself also has the effect of an active diluent.

3.2 Curing agent

The curing agent is an important component in the formula of epoxy potting material, and the performance of the curing material depends to a large extent on the structure of the curing agent.

(1) Aliphatic polyamines are generally used as curing agents for curing at room temperature, but such curing agents are highly toxic, irritating, and exothermic, and they are easy to oxidize during curing and use. Therefore, it is necessary to modify polyamines. For example, the use of active hydrogen on the amine group of polyamines, part of the synthesis with epoxy to hydroxyalkylation and part of the synthesis with acrylonitrile to cyanoethylation of the comprehensive modification, the curing agent can achieve low viscosity, low toxicity, low melting point, room temperature curing and a certain toughness of the comprehensive modification effect.

(2) Acid anhydride curing agent is the most important curing agent for two-component heating curing epoxy potting material. Commonly used curing agents are liquid methyltetrahydrophthalic anhydride, liquid methyl hexahydro phthalic anhydride, and hexahydro phthalic anhydride.

Anhydride, methylnadicic anhydride, etc.This kind of curing agent has a small viscosity and a large amount of dosage. It can play a dual role in curing and dilution in the potting material formula, and the curing exothermic is eased, and the overall performance of the cured material is excellent.

3.3 Curing accelerator

The two-component epoxy monoacid anhydride potting material generally needs to be heated for a long time at about 140℃ to cure. Such curing conditions not only cause a waste of energy, but also the components and skeleton housings in most electronic devices are unbearable. Adding accelerator components to the formula can effectively reduce the curing temperature and shorten the curing time. Commonly used accelerators are: Bian-based diamines, DMP-30 and other tertiary amines. You can also use imidazole compounds and metal salts of carboxylic acids, such as 2-ethyl-4-methylimidazole, 2-methylimidazole and the like.

3.4 Coupling agent

In order to increase the adhesion between silica and epoxy resin, a silane coupling agent needs to be added. Coupling agents can improve the adhesion and moisture resistance of materials. Commonly used silane coupling agents suitable for epoxy resins are glycidyl oxygen, propyltrioxysilane (KH-560), aniline methyltriethoxysilane, α-chloropropyltrimethoxysilane, α-mercaptopropyltrimethoxysilane, aniline methyltrimethoxysilane, diethylene diamine propyltrimethoxysilane and so on.

3.5 Active thinner

Using epoxy resin alone, the viscosity increases significantly after adding inorganic fillers, which is not conducive to operation and defoaming. It is often necessary to add a certain amount of diluent to increase its fluidity and permeability, and extend the service life. The diluent is divided into active and inactive. Inactive diluents do not participate in the curing reaction, and excessive amounts are added, which can easily cause the shrinkage rate of the product to increase, reducing the mechanical properties and thermal deformation of the product. The participation of the active diluent in the curing reaction increases the viscosity of the reactant and has little effect on the properties of the cured substance. The active diluent is selected in the potting material. The commonly used ones are: n-butyl glycidyl ether, allyl glycidyl ether, diethylhexyl glycidyl ether, and phenyl glycidyl ether.

3.6 Filler

The addition of fillers in the potting material has obvious effects on improving certain physical properties and reducing costs of epoxy resin products. Its addition can not only reduce costs, but also reduce the coefficient of thermal expansion, shrinkage and increase thermal conductivity of the cured material.The fillers commonly used in epoxy potting materials are silica, alumina, silicon nitride, boron nitride and other materials. Silica is divided into crystalline, fused angular and spherical silica. In the potting material for electronic packaging, molten spherical silica is preferred due to product requirements.

3.7 Defoamer

In order to solve the problem of air bubbles on the surface of the liquid packaging material after curing, a defoamer can be added. Commonly used are emulsified silicone oil emulsifiers.

3.8 Toughening agent

Toughening agents play an important role in potting materials. The toughening modification of epoxy resins mainly improves their toughness by adding toughening agents, plasticizers, etc. There are two types of toughening agents: active and inert. The active toughening agent can participate in the reaction with the epoxy resin to increase the viscosity of the reactant, thereby increasing the toughness of the cured product. Generally, liquid nitrile rubber with a decarboxylating agent is selected to form a toughened "island structure" in the system to increase the impact toughness and heat-resistant impact properties of the material.

3.9 Other components

In order to meet the specific technical and technological requirements of potting parts, other components can also be added to the formula.For example, flame retardant can improve the processability of the material; colorant is used to meet the appearance requirements of the product, etc.

4. Potting process Epoxy resin potting has two processes: normal and vacuum. Figure 1 shows the manual vacuum potting process flow.

5. Common problems and solutions

5.1 Discharge, inter-line ignition or breakdown phenomenon

Due to improper potting process, the device will produce discharge, inter-wire ignition or breakdown during operation. This is because the wire diameter of the high-voltage coil of this type of product is very small (generally only 0.5%).02mm～0．04mm), the potting material failed to completely penetrate between the turns, causing gaps between the turns of the coil.Since the dielectric constant of the void is much smaller than that of the epoxy potting material, an uneven electric field will be generated under alternating high voltage conditions, causing partial discharge, causing the material to age and decompose, causing insulation damage. From the perspective of technology, there are two reasons for the gap between the lines.：

(1) The degree of vacuum is not high enough during potting, and the air in the line cannot be completely eliminated, so that the material cannot be completely infiltrated.；

(2) The preheating temperature of the product before potting is not enough, and the viscosity of the material poured into the product cannot be reduced rapidly, which affects the infiltration. For manual potting or vacuum potting after mixing and defoaming, the material mixing and defoaming temperature is high, the operating time is long or exceeds the applicable period of the material, and the product does not enter the heating and curing process in time after potting, which will cause the viscosity of the material to increase, affecting the infiltration of the coil. The higher the starting temperature of the thermoplastic epoxy potting material complex, the smaller the viscosity, and the faster the viscosity increases over time. Therefore, in order for the material to have good permeability to the coil, care should be taken in operation to ensure that the potting material complex should be kept within a suitable temperature range and used within the applicable period. The product should be heated to the specified temperature before potting, and the heating and curing procedure should be entered in time after potting is completed, and the vacuum degree of potting should meet the requirements of the technical specifications.

5.2 Shrinkage, local depression, and cracking on the surface of the device

The potting material will produce two kinds of shrinkage during the heating and curing process: chemical shrinkage during the phase transition from liquid to solid state and physical shrinkage during cooling. There are two more processes of chemical change and shrinkage in the curing process: from the beginning of the heating chemical crosslinking reaction after potting to the initial formation of the microscopic mesh structure, the shrinkage is called the gel pre-curing shrinkage; the shrinkage from the gel to the complete curing stage is called the post-curing shrinkage. The shrinkage of these two processes is not the same. The physical state of the former changes from a liquid state to a mesh structure. The consumption of reactive groups is greater than that of the latter, and the volume shrinkage is higher than that of the latter. If the potting product is cured at a high temperature, the two stages of the curing process are too close, and the gel pre-curing and post-curing are completed almost at the same time. This will not only cause excessive exothermic peaks and damage the components, but also cause the potting parts to produce huge internal stress, causing defects in the interior and appearance of the product. In order to obtain a good product, it is necessary to pay attention to the matching of the curing speed of the potting material and the curing conditions when designing the potting material formula and the curing process. The method usually used is to cure the potting material in different temperature zones according to the nature and purpose of the potting material. In the pre-curing temperature section, the curing reaction of the potting material is carried out slowly, the reaction heat is gradually released, and the viscosity of the material increases and the volume shrinkage is carried out smoothly. When the material is in a fluid state at this stage, the volume shrinkage is manifested as the liquid level drops until it solidifies, which can completely eliminate the internal stress of the volume shrinkage at this stage. From the pre-curing stage of the gel to the post-curing stage, the heating should be gentle, and the potting parts should be cooled slowly in sync with the heating equipment after curing, so as to reduce and adjust the stress distribution in the product in many ways, so as to avoid shrinkage, depression and even cracking on the surface of the product. Phenomenon. For the formulation of the curing conditions of the potting material, it is necessary to refer to the arrangement of the components in the potting device, the degree of fullness, the size, shape, and the amount of potting per unit. For a single potting volume is large and there are fewer embedded components, it is completely necessary to appropriately reduce the gel pre-curing temperature and extend the time.

5.3 The surface of the cured object is poor or partially uncured

The phenomenon of poor surface or partial non-curing of the cured object is also mostly related to the curing process. Experts from the China Epoxy Resin Industry Association said that the main reasons are the failure of the metering or mixing device and the operation errors of the production personnel; the precipitation of component A after long-term storage, and the failure to stir well before use, resulting in the actual ratio of resin and curing agent is out of balance, and component B is stored in the open for a long time, and the moisture absorption fails; the potted seal does not enter the curing process in time during the wet season, and the surface of the object absorbs moisture. In short, to obtain a good potting and curing process is indeed an issue worthy of great attention.

seven, two-component glue filling process case

When filling the product with glue, put it next to the assembly line, manually put the product under the glue outlet head, press the start switch, and the machine will automatically fill the glue, and the glue will stop automatically after the glue is filled. Then the operator can put the glued product on the assembly line. The semi-automatic glue filling machine is suitable for all kinds of PCBA products, regardless of size.

2. Automatic glue filling machine

If they are mostly small products, the glue filling method is also very simple. Put the product in a fixture, then put the fixture on the countertop of the glue filling machine, click to start, and the machine will start filling glue. After all the glue filling is completed, it will automatically stop, and then the operator will remove the fixture from the countertop, and then put another fixture with the product installed, press start, in this cycle, all the operator has to do is put the fixture and press the start button.

3. Fully automatic glue filling line

Put the fixture containing the product on the transmission line, the machine automatically fills the glue, and automatically feeds the material to the oven for the oven, saving labor and efficient operation.

The above are the three methods of automatic glue filling. The use of automatic glue filling equipment can better save labor and improve production efficiency.