With the increasing integration and high-performance development of electronic components, potting adhesive, as a key protective material, is becoming more and more widely used in fields such as power modules, sensors, motors, PCB circuit boards, etc. Encapsulation not only improves the weather resistance, waterproofing, chemical resistance, and heat dissipation performance of devices, but also plays an important role in enhancing product stability and extending service life.
However, in practical applications, many engineers and technicians still have doubts about the curing conditions, expansion control, and removal methods of the sealant. This article will provide you with a comprehensive understanding of the entire process of using sealant from usage to problem-solving.
1、 Analysis of the curing mechanism of sealant
According to the different material systems, there are mainly several types of sealing adhesives, such as epoxy resin, organosilicon, polyurethane, acrylic ester, etc. Their curing methods are slightly different:
- Classification of curing methods
Characteristics of material system curing methods
Epoxy resin has high hardness and strong adhesion after heating curing/room temperature curing
Organic silicon room temperature condensation/addition molding is soft, elastic, and has excellent resistance to high and low temperatures
Polyurethane moisture curing/two-component reaction with good flexibility, suitable for outdoor sealing
Acrylic free radical induced light/heat curing for rapid curing, suitable for automated production lines - Reason for abnormal solidification: poisoning without solidification
Especially when using addition molding silicone sealant, the problem of “poisoning without curing” is often encountered, manifested as the surface not drying for a long time and the overall colloid collapsing. This is because colloids come into contact with certain substances containing tin, amines, sulfur, phosphorus, and alkynes, inhibiting the reaction of platinum catalysts and leading to non solidification.
✅ ** Solution suggestion: * * Avoid using unwashed metal shells, sulfur-containing rubber, and plastics with excessive plasticizers. If necessary, conduct compatibility testing
2、 Analysis and Response to the Expansion Problem of Sealing Adhesive
Reason for expansion:
During the curing or use process, there may be abnormal changes in the volume of the sealant, mainly due to:
Excessive coefficient of thermal expansion (CTE)
The difference in CTE between the sealing material and the sealed component (such as metal or ceramic) is significant, and the component will expand and crack when heated.
swelling
Some polyurethane colloids are prone to moisture absorption and may expand and bubble in high humidity environments.
Release of reactive gases
Some fast curing adhesives release trace amounts of gas during the reaction process, forming bubbles or bulges.
Control method:
Choose low CTE and moisture resistant potting adhesive (such as filler reinforced epoxy adhesive, organic silicone).
Using vacuum sealing technology to remove bubbles.
Optimize the curing process: pre cure at room temperature first, and then cure at high temperature.
3、 Methods for removing different types of sealant
Once the sealant is cured, it becomes difficult to disassemble if there is a need for maintenance or replacement. The following is a summary of removal techniques for different materials: - Method for removing silicone sealant
Organic silicone is soft and elastic, chemically stable, and difficult to dissolve in most solvents.
Soft silicone potting adhesive (such as gel):
➤ Use a blade to make a cut along the edge and manually peel it off.
➤ Try to keep the entire piece removed to avoid cutting into the circuit board.
Hardened silicone gel:
➤ It can be softened with a blade and a hot air gun, but it is not recommended to use strong corrosive solvents as they can cause significant damage to the circuit board.
⚠️ Attention: Forcefully prying off may damage PCB components, and the dismantling operation should be carried out with great caution. - Removal method of epoxy resin sealant
After curing, epoxy sealant forms a hard material that is extremely difficult to remove.
When not cured: can be wiped and cleaned with alcohol or acetone;
After solidification:
Conventional solvents such as alcohol, acetone, and acetic acid are ineffective;
Usually requires high-temperature baking (>150 ℃)+mechanical methods (grinding, crushing);
If design errors are found after sealing, they can only be destroyed and scrapped.
❗ Suggestion: In the design and selection stage, evaluate in advance whether rework is necessary to avoid maintenance difficulties in the later stage. - Removal method of polyurethane sealant
Polyurethane adhesive has good moisture and corrosion resistance, strong electrolyte resistance, and is commonly used in components such as batteries and sensors.
Removal method:
Using its “alkali sensitive” characteristic, soak it in concentrated alkali solution, soften it, and then mechanically remove it;
If it has been fully crosslinked, you can try soaking it in ketone or ester organic solvents for a long time to make it swell and soften, and then remove it with tools.
⚠️ During the dismantling process, it is necessary to avoid liquid infiltration into the circuit to prevent short circuits or corrosion.
4、 Factors affecting the smoothness of the sealing adhesive surface
Whether the surface of the sealing adhesive is smooth and flat not only affects the appearance, but also relates to the waterproof, insulation, and product grade. But in practical applications, many people will find that:
Why do I always have bubbles, dents, orange peel, or waves on the surface of the glue I seal
Common causes of uneven surfaces:
Reason category, specific problem solution
Insufficient defoaming and failure to promptly remove bubbles after mixing. Use a vacuum defoamer and let it stand before sealing
The curing speed is too fast, and the surface tension of the colloid cannot flow smoothly. Control the curing temperature to avoid excessive catalyst
The viscosity is too high and the colloid has poor fluidity, making it difficult to self level. It is recommended to heat it appropriately to reduce viscosity or choose a low viscosity adhesive
If the environmental humidity is too high, the surface will absorb moisture and become white or rough. Control the environmental humidity (preferably 40-60%)
Improper mixing method generates microbubbles, forming an “orange peel” effect. Slowly stir to avoid severe vortices
Uneven sealing speed causes surface fluctuations. Maintain a constant injection speed to avoid intermittent flow
Tip:
If you pursue a mirror effect, you can use hot air to gently sweep the surface before curing to promote leveling.
When the surface roughness is severe, surface repair glue or sandpaper can be used for polishing treatment.
Craftsmanship determines quality, details determine success or failure
Although sealant is only one part of the material system, it has a decisive impact on the performance and lifespan of electronic products. By scientifically controlling the curing process, avoiding expansion issues, mastering removal methods, and improving surface quality, you will significantly enhance product stability, maintenance convenience, and overall grade.
Used well, it is a protective shield;
If not used properly, it is a ‘source of disaster’.
The world of sealant is worth exploring together with you and me.
📌 Tip Summary:
⚠ Remember to evacuate and remove bubbles before curing;
⚠ Different adhesives have different shelf lives, so do not use them beyond their expiration date;
⚠ During the curing process, a buffer zone should be left to avoid thermal expansion causing the shell to open;
⚠ Before sealing, it is recommended to conduct a small trial before launching in bulk.
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📩 If you have any questions about sealing adhesive selection, technical specifications, or material recommendations, please feel free to comment and exchange!
Tags: Sealing glue · Curing of sealing glue · Reasons for uneven surface of sealing glue
