Glue Filling (Potting) Process Introduction
Tortai’s potting and encapsulation systems provide superior protection for printed circuit boards and electrical equipment. Used in today’s most challenging environments, such as automotive and aerospace, where thermal conductivity and operating temperature extremes are the norm, potting materials offer enhanced mechanical strength, provide electrical insulation and improve thermal reliability. Electronic potting is an ideal solution for electronic assemblies, providing strong, flexible mechanical protection for precision components and wiring. Electronic assemblies need to be potted with high quality materials that can withstand harsh conditions. This ensures that electronic assemblies can be used in applications where standard component protection is not sufficient.
Our professional configuration of automatic potting machine, can help customers to achieve PCBA encapsulation one-stop service, with potting technology are experienced engineers, on the potting process there is blistering, moulding is not beautiful such as surface shrinkage holes, depressions and other aspects of the control especially have unique experience.
The purpose of PBCA circuit boards to do potting (potting) is to protect the board from the external environment and also for confidentiality reasons. Potting provides protection in the following ways:
|Moisture and dust resistance||Gluing blocks the entry of air, moisture and dust and prevents the board from moisture, contamination and corrosion.|
|Mechanical Protection||Gluing can increase the mechanical strength of the circuit board, reduce the vibration and shock damage to the circuit board, and improve the shock resistance and reliability of the circuit board.|
|Dielectric Protection||Potting provides an electrically insulating layer that prevents short circuits and leakage between circuit boards and improves the board’s voltage resistance.|
|Thermal Management||The potting material can have good thermal conductivity to help dissipate heat from the board, keep the board’s operating temperature in the proper range, and improve the board’s performance and reliability.|
|Resistant to Corrosion||Potting prevents corrosion of metal components on the board and extends the life of the board.|
|Confidentiality Requirements||By potting circuit boards, intellectual property and trade secrets can be protected by preventing unauthorised personnel from accessing design and layout information on the board. Potting increases the board’s tamper resistance and reduces the risk of information leakage.|
What is potting?
Potting (potting) is the polyurethane potting adhesive, silicone potting adhesive, epoxy resin potting adhesive with equipment or manual way into the device equipped with electronic components, lines, curing at room temperature or under the condition of heating to become a thermosetting polymer insulation material with excellent performance, so as to achieve the purpose of bonding, sealing, potting and coating protection. material, so as to achieve the purpose of bonding, sealing, potting and coating protection.
What are the types of potting compounds? What are the advantages and disadvantages of each? What is the scope of application?
English name: Potting of smidahk; used for electronic components bonding, sealing, potting and coating protection. Potting compound is liquid before curing, with fluidity, viscosity of the glue according to the material of the product, performance, production process and different. Potting compound completely cured to achieve its use value, after curing can play a waterproof moisture, dust, insulation, thermal conductivity, confidentiality, anti-corrosion, temperature resistance, shockproof role.
Electronic potting compound types are very many, from the type of material to points, the current use of the most common most of the three main types, namely, epoxy resin potting compound, silicone resin potting compound, polyurethane potting compound, and these three materials can be subdivided into several hundred different potting compound products.
|Category||Introduction||Advantages||Disadvantages||Scope of use|
|Epoxy Oxygen Tree resin Potting Sealing adhesive||Epoxy resin potting adhesive is mostly hard, after curing and stone almost hard, it is difficult to remove, with good confidentiality, but there are a small number of soft. Ordinary temperature resistance is about 100 ℃, temperature curing temperature resistance is about 150 ℃, there are also temperature resistance is more than 300 ℃. There are fixed, insulating, waterproof, oil, dust, anti-theft, corrosion resistance, aging resistance, resistance to hot and cold shock and other characteristics. Commonly available epoxy potting adhesive are: flame retardant, thermal conductivity, low viscosity type, high temperature type, and so on.||Good adhesion to hard materials, excellent high temperature resistance and electrical insulation ability, easy to operate, very stable before and after curing, excellent adhesion to a variety of metal substrates and porous substrates.||Weak resistance to hot and cold changes, easy to produce cracks after the impact of heat and cold, resulting in water vapour penetration from the cracks into the electronic components, poor moisture resistance. Moreover, the hardness of the cured colloid is high and brittle, which is easy to strain the electronic components, and it can’t be opened after potting, so the reparability is not good.||Epoxy resin potting adhesive is easy to penetrate into the gap of the product, suitable for potting at room temperature and no special requirements for the mechanical properties of the environment of small and medium-sized electronic components, such as automotive, motorbike ignition, LED drive power supply, sensors, toroidal transformers, capacitors, triggers, LED waterproof lamps, circuit boards, confidentiality, insulation, moisture-proof (water) potting.|
|Organic Silicon Potting Sealing adhesive||Silicone electronic potting adhesive cured mostly soft, flexible can be repaired, referred to as soft glue, poor adhesion. Its colour can generally be arbitrarily adjusted according to need, or transparent or non-transparent or coloured. Two-component silicone potting adhesive is the most common, this type of adhesive including condensation type and additive agent of the two categories. General shrinkage type of components and potting cavity adhesion is poor, the curing process will produce volatile low molecular substances, after curing there is a more pronounced shrinkage; add the moulding (also known as silicone gel) shrinkage is very small, the curing process will not produce volatile low molecular substances, can be heated to fast curing.||Strong aging resistance, good weather resistance, excellent impact resistance; excellent resistance to hot and cold changes and thermal conductivity, can be used in a wide range of operating temperatures, can be used in -60 ℃ ~ 200 ℃ temperature range to maintain the elasticity of non-cracking, can be used for a long period of time in the 250 ℃, heating curing type of resistance to higher temperatures, with excellent electrical properties and insulation capacity, insulation performance is better than the epoxy resin, can be withstand voltage More than 10000V. After potting, it can effectively improve the insulation between internal components and lines, and improve the stability of electronic components; it has no corrosion on electronic components and does not produce any by-products in the curing reaction; it has excellent repair ability, and can be quickly and conveniently taken out of the components after sealing to repair and replace them; it has excellent thermal conductivity and flame-retardant ability, and can effectively improve the heat dissipation ability and safety coefficient of electronic components; Low viscosity, good fluidity, able to penetrate into the small gaps and components below; can be cured at room temperature can also be heated curing, self-bubbling good, more convenient to use; curing shrinkage is small, with excellent waterproof performance and shock resistance.||High price and poor adhesion.||Suitable for potting all kinds of electronic components that work in harsh environments.|
|Polyurethane Ammonia Polyurethane Potting Sealing Adhesive||Polyurethane potting adhesive, also known as PU potting adhesive, cured more soft, elastic can be repaired, referred to as soft glue, adhesion between epoxy and silicone, temperature resistance is general, generally not more than 100 ℃, after the potting of vapour bubbles is more, the potting conditions must be in a vacuum, adhesion between epoxy and silicone.||It has good low-temperature resistance and the best anti-vibration performance among the three kinds. It has low hardness, moderate strength, good elasticity, water resistance, anti-mould, anti-vibration and transparency, etc. It has excellent electric insulation and flame retardant, no corrosion to electrical components, good adhesion to steel, aluminium, copper, tin and other metals, as well as rubber, plastic, wood and other materials.||High temperature resistance is poor, the surface of the cured colloid is not smooth and poor toughness, aging resistance and UV resistance are very weak, the colloid is easy to discolour.||Suitable for potting indoor electrical components that do not have high heat generation, it can make the installed and debugged electronic components and circuits not be affected by vibration, corrosion, humidity and dust, etc. It is the ideal potting material for the moisture-proof and corrosion-proof treatment of electronic and electrical parts.|
In addition to these three common sealants, there are two others that are relatively common:
Polyacrylate Potting Adhesives
Polyacrylate potting compounds are suitable for the protection of sensors and connection points that require high oil resistance and are commonly used in the automotive industry. Thanks to their excellent protection and fixation features, this formulation is highly sought after in the market, especially with the development of electric vehicles and ADAS systems.
Electronic Potting Gels
Electronic Potting Gel offers an innovative formulation for applications where traditional potting gels are not suitable. This new technology transparently pots components and assemblies with a soft, flexible cured surface and excellent dimensional stability.
What should be considered when selecting potting materials?
(1) Requirements of performance after potting: use temperature, hot and cold alternating conditions, components to withstand internal stress, outdoor use or indoor use, stress conditions, whether the requirements of flame retardant and thermal conductivity, colour requirements and so on;
(2) potting process: manual or automatic, room temperature or heating, complete curing time, the solidification time of the glue after mixing;
3) Cost: the specific gravity of the potting material varies greatly, we must look at the actual cost after potting, rather than simply look at the selling price of the material.
Adhesives used for potting, according to the functional classification of thermal conductivity potting adhesive, adhesive potting adhesive, waterproof potting adhesive; according to the material classification of polyurethane potting adhesive, silicone potting adhesive and epoxy resin potting adhesive, for the choice of soft or hard glue, when both can be potting, waterproof insulation, if the requirements of the high-temperature thermal conductivity, then it is recommended that the use of organosilicone soft adhesive; if the requirements of low-temperature resistance, it is recommended that the use of soft polyurethane adhesive; If there is no special requirements, it is recommended to use polyurethane adhesive If there is no special requirements, it is recommended to use epoxy hard glue, because epoxy hard glue is faster than silicone curing time.
Epoxy resin potting adhesive has a wide range of applications, technical requirements are very different, there are many varieties. From the curing conditions on the points of room temperature curing and heating curing two categories; and from the agent type on the points of two-component and one-component two categories, there is room temperature curing epoxy potting adhesive is generally two-component, its advantage lies in the potting does not need to be heated to curing, on the equipment requirements are not high, easy to use, there are defects is the glue mixture operation viscosity, poor immersion, short application period, and the cured material of the thermal and electrical properties are not very high, generally used for low-voltage electronics, and generally used for low-pressure electronic curing, the curing time is longer than that of silicone. High, generally used for low-pressure electronic device potting or should not be heated curing occasions.
Application Range of Glue Filling
|Electronic potting||Potting blocks protect sensitive electrical and electronic components from a variety of operating conditions, such as temperature fluctuations, humidity, vibration, etc.|
|Plug and cable potting||Potting compounds fill extremely small gaps in plug housings, connectors and power devices. Potting materials for plugs and cables are elastic, highly waterproof, mechanically stable and tear-resistant.|
|Optoelectronic potting||Optoelectronic potting provides high weather resistance, protects electronic equipment from environmental influences, and protects against moisture and dehumidification.|
|LED Potting||Transparent or opaque potting systems protect leds from water, dust, and other atmospheric influences for efficient packaging and optimal lighting for spotlights.|
|Filter Potting||The end caps are used to connect various filters, and the filters are glued to the filter frame and sealed to achieve a seamless seal of the filter frame, and the filtered air is cleaner. The foam potting material binds the filter medium to the filter frame, reducing cost and weight while also meeting high quality requirements. Thanks to the bubble structure, the amount of adhesive per filter can be reduced by up to 50%. The lower density reduces weight and makes it easier to handle parts.|
What are the different types of potting processes? What are the precautions to be taken?
The quality of potting products, mainly with product design, component selection, assembly and potting materials used are closely related to the potting process is also a factor that can not be ignored. Epoxy potting has two kinds of potting process: normal and vacuum.
Epoxy resin. Amine room temperature curing potting material, generally used for low-voltage electrical appliances, mostly using normal potting.
Epoxy resin. Acid anhydride heating curing potting material, generally used for high-voltage electronic devices potting, mostly using vacuum potting process.
At present, there are two common manual vacuum potting and mechanical vacuum potting, and mechanical vacuum potting can be divided into A, B components first mixed defoaming after potting and first separate defoaming after mixed potting two cases. There are three operation methods:
The first: single-component electronic potting adhesive, direct use, can be used to snatch the fight can also be directly infused;
The second type: two-component condensed electronic potting adhesive, curing agent 2% -3% or other proportion, mixing – vacuum defoaming – potting;
The third type: additive moulding electronic potting adhesive, 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 the A component and B component (curing agent).
(2) Mixing: mix the components;
(3) Defoaming: natural defoaming and vacuum defoaming;
(4) Filling: the adhesive should be filled within the operating time otherwise it will affect the levelling;
(5) curing: heating or room temperature curing, potting products at room temperature curing, after the initial solid can enter the next process, the full curing takes 8 to 24 hours. Summer temperature is high, the curing will be faster; winter temperature is low, the curing will be slower.
A、the surface of the product must be cleaned before sealing!
B、Note that before weighing, mix the A and B components well respectively, so that the pigment (or filler) which sinks to the bottom can be dispersed into the glue.
C、the primer must not be mixed directly with the adhesive, the primer should be used first, after the primer is dry, then the adhesive should be potted with this adhesive.
D、the curing speed of the adhesive has a certain relationship with the temperature, low temperature curing will be slower.
In contrast, mechanical vacuum potting, equipment investment, maintenance costs are high, but the consistency and reliability of the product is significantly better than the manual vacuum potting process. No matter what kind of potting method, should strictly comply with the set process conditions, otherwise it is difficult to get satisfactory products.
What are the common problems of potting products? Cause analysis.
Partial discharge starting voltage is low, the line between the fire or breakdown TV, monitor output transformer, car, motorbike ignition and other high-voltage electronic products, often due to improper potting process, there will be a partial discharge when the work (arc), between the line between the fire or breakdown phenomenon, is because of the high-voltage coils of such products is very small, generally only 0.02 ~ 0.04mm, potting material fails to completely saturate the turns, so that the coil between the turns Survival of the gap between the turns of the coil. Due to the gap dielectric constant is much smaller than the epoxy potting material, in the alternating high-voltage conditions, will produce an uneven electric field, caused by the interface of the partial discharge, so that the material aging decomposition, resulting in insulation damage.
From the process point of view of analysis, caused by the gap between the line has the following two reasons:
1)The vacuum degree is not high enough when potting, and the air between them is not completely excluded, so that the material can not be completely infiltrated.
2) Before potting glue or product preheating temperature is not enough, the viscosity can not be quickly reduced, affecting the infiltration.
For manual potting or first mixed defoaming after vacuum potting process, material mixing and defoaming temperature is high, long operating time or more than the material application period, as well as potting the product is not timely into the heating and curing process, will cause the material viscosity increases, affecting the infiltration of the coil. Previously, according to relevant experts, heat curing epoxy potting material complex, the higher the starting temperature, the lower the viscosity, with the extension of time, viscosity growth is also more rapid. Therefore, in order to make the material on the coil has good infiltration, operation should pay attention to the following points:
1)The potting compound should be kept within the given temperature range and used up within the applicable period.
2)Before potting, the product should be heated to the specified temperature, and the potting should be promptly entered into the heating and curing procedure.
3)The vacuum degree of potting should meet the requirements of technical specifications.
Potting surface shrinkage, local depression, cracking potting compound in the heating curing process, will produce two kinds of contraction, namely, from liquid to solid phase change process of chemical shrinkage and cooling process of physical shrinkage. Further analysis, the chemical change in the curing process contraction and there are two processes, from the beginning of the chemical cross-linking reaction after potting heating to the initial formation of the microscopic mesh structure stage of the contraction produced, we call the gel pre-curing contraction. The contraction from the gel to the complete curing stage is called post-curing contraction. The amount of shrinkage in these two processes is different. In the former process, the physical state of the gel changes abruptly from liquid to reticulated structure, and the amount of reactive groups consumed is greater than that of the latter, and the volume shrinkage is also higher than that of the latter. Gel pre-curing stage (75 ℃ / 3h) the disappearance of epoxy group is greater than the post-curing stage (110 ℃ / 3h), the results of the differential thermal analysis also proved this point, the specimen was treated by 750 ℃ / 3h curing degree of 53%.
If we take a high-temperature curing of the potting product, the two stages of the curing process are too close to each other, and the pre-curing and post-curing of the gel are nearly completed at the same time, which will not only cause too high an exothermic peak and damage the components, but also cause the potting part to produce a huge amount of internal stresses, resulting in the product’s internal and external defects. In order to obtain good products, we must be in the potting compound formulation design and curing process development, focusing on the potting compound curing speed (i.e., A, B complex gel time) and curing conditions to match the problem. The method usually used is: according to the nature of the potting material, the use of different temperature zones according to the segment curing process. According to experts, the colour TV output transformer potting according to different temperature zones segment curing procedures and product internal exothermic curve. In the gel pre-curing temperature section of the potting material curing reaction slowly, the reaction heat is gradually released, the viscosity of the material to increase and volume contraction is carried out gently. At this stage, the material is in the fluid state, then the volume contraction is manifested as a drop in the liquid level until the gel, which can completely eliminate the internal stress of volume contraction at this stage. From the gel pre-curing to post-curing stage, the temperature should also be gentle, curing is complete, potting should be synchronised with the heating equipment to slowly cool down, multi-faceted to reduce and regulate the distribution of internal stresses in the product, to avoid the surface of the product to produce shrinkage holes, depressions and even cracking phenomenon.
The formulation of the curing conditions of the potting material, but also with reference to the potting product embedded components of the layout, the degree of fullness and the size of the product, shape, single potting volume. For a single potting volume and embedded components less, appropriately reduce the gel pre-curing temperature and extend the time is completely necessary.
3、poor surface curing material or local non-curing phenomenon
Cured material surface bad or local non-curing these phenomena are also mostly related to the curing process. The main reasons are:
1) Measuring or mixing device failure, production personnel operating errors.
2) A component of the long storage of precipitation, not fully stirred before use, resulting in the actual ratio of resin and curing agent is out of proportion.
3) Component B is stored for a long time with open mouth, moisture absorption and failure.
4) During the high humidity season, the potting parts did not enter the curing process in time, and the surface of the object absorbed moisture.
It can be seen that to obtain a good potting product, the potting and curing process is indeed a problem that deserves great attention.
Frequently Asked Questions about Electronic Potting Adhesive
(1) How to solve the poisoning of electronic potting compound without curing?
Silicone poisoning generally occurs in the additive electronic potting gel, poisoning silicone will appear after the phenomenon of non-curing, so the use of additive sealant should be avoided with phosphorus, sulfur, nitrogen-containing organic compounds in contact, or with the additive silicone at the same time the use of polyurethane, epoxy resins, unsaturated polyester, condensed room temperature vulcanisation of silicone rubber and other products, to prevent the occurrence of poisoning does not cure the phenomenon.
(2) What can I use to clean the electronic potting gel that I accidentally stuck to?
Commonly used silicone cleaning agents are mainly alcohol, acetone, white spirit, etc., remember to dilute coated when used.
(3) winter electronic potting compound can not dry how to do?
Due to the winter temperature is very low, resulting in electronic potting adhesive in the mixing curing is very slow or even a long time does not cure, so we can improve the curing temperature, you can put the good glue products in the oven at 25 ℃ curing.
Epoxy resin potting compound and its process and common problems
1、in the field of electronic packaging technology there have been two major changes.
The first change appeared in the first half of the 1970s, which is characterised by the pin insertion mounting technology (such as DIP) to the transition to the surface mount technology of the four-sided flat package (such as QFP); the second shift occurred in the mid-1990s, which is marked by the emergence of the solder ball array, BGA-type packages, and this corresponds to the surface mount technology and semiconductor integrated circuit technology across the 21st century together. The corresponding surface mount technology and semiconductor integrated circuit technology together across the 21st century. With the development of technology, there are many new packaging technology and packaging forms, such as chip direct bonding, potting plastic solder ball array (CD-PBGA), flip-chip plastic solder ball array (Fc-PBGA), chip size packaging (CSP) and multi-chip components (MCM), etc., a considerable part of these packages use liquid epoxy material packaging technology. Potting, that is, the liquid epoxy resin compound with mechanical or manual way into the device equipped with electronic components, lines, curing at room temperature or heating conditions into a thermally isotropic polymer insulation material with excellent performance.
2、Product performance requirements
Potting compound should meet the following basic requirements: good performance, long application period, suitable for large quantities of automatic production line operations; viscosity is small, strong infiltration, can be filled with components and line between; in the potting and curing process, filler and other powder components settlement is small, non-delamination; curing exothermic peak is low, the curing contraction is small; curing of electrical properties and mechanical properties of cured material, good heat resistance, good adhesion to a variety of materials, water absorption and low coefficient of expansion; some occasions, but also excellent thermal isotropic polymer insulating material, the cured material should be used in a variety of applications. Coefficient of expansion is small; in some occasions also requires potting compound with flame retardant, weathering, thermal conductivity, resistance to high and low temperature alternation and other properties.
In the specific semiconductor package, because the material to be in direct contact with the chip, the substrate, in addition to meet the above requirements, but also requires that the product must have the same purity as the chip mounted materials. In the flip chip potting, because the gap between the chip and the substrate is very small, the viscosity of the potting material is required to be extremely low. In order to reduce the stress generated between the chip and the encapsulation material, the modulus of the encapsulation material cannot be too high. And in order to prevent the penetration of water at the interface, the encapsulation material should have good adhesive properties between the chip and the substrate.
Three methods of filling glue with PCBA
|Semi-automatic glue filling machine||In the product gluing, placed next to the assembly line, manually put the product into the gluing head below, press the start switch, the machine will be automatically gluing, gluing finished automatically stop. Then the operator will put the glued products on the assembly line. Semi-automatic gluing machine is suitable for all kinds of PCBA products, regardless of size.|
|Automatic Glue Filling Machine||If the majority of small products, the gluing method is also very simple, put the product into a jig, and then put the jig into the gluing machine table, press the start, the machine will start to fill the glue, and so on all the filling is completed, the automatic stop, and then the operator will be the jig off the table, and then put another loaded product jig, press the start, and so on, and so on, the operator has to do is to put the jig, and press the start button.|
|Fully Automatic Glue Filling Line||Put the fixtures with products on the transfer line, the machine will automatically fill the glue, and automatically feed the materials to the oven, saving labour and running efficiently.|
These are the 3 methods of automatic glue filling, the use of automatic glue filling equipment can better save labour and improve production efficiency.
Tortai Technologies Co., Ltd. can provide you with high quality electronic glue filling services to ensure that your circuit boards have excellent water, dust and shock resistance. Using state-of-the-art glue filling machines and their highly reliable processes, we provide you with customised solutions to ensure that every project receives the best quality and efficiency. Our dedicated team will ensure that tasks are completed within tight schedules and provide comprehensive after-sales support to ensure that our customers are satisfied with our services. Working with Tortai we are dedicated to serving you and doing our best to meet your needs, we look forward to working with you, thank you!