How to Pot Electronic Components?

1. What Is Potting?

The term “potting” (glue-filling) is used to describe the pouring of polyurethane, silicone, or epoxy resin potting adhesive into electronic equipment with circuits and components. This can be done manually or by machine. There have been two significant transformations in electronics packaging technology since its debut. Beginning in the early 1970s, two fundamental shifts occurred within this sector. The first was the transition from pin-insertion installation to quad flat packages (such QFP). The second occurred in mid-1990s with the introduction of BGA and solder ball array type packaging. Surface mounting technology (SMT), semiconductor integrated circuits and their packaging all entered the 21st Century together. As technology has developed, new packaging technologies have been created, including direct chip bonding (CD-PBGA), potted plastics solder balls array (FCPBGA), and chip size packages (CSP). A large part of these packages use liquid epoxy packaging technology.

2. The Main Purpose of Potting

1) Strengthen the integrity of electronic devices and improve their resistance to external vibrations and impacts;

2) Improve the insulation between circuits and internal components, which allows for the miniaturization of equipment and the reduction of weight;

3) Avoid direct exposure to circuits and components, and improve their waterproof, dustproof, and moisture-proof performances;

4) Heat transfer and conduction.

3. Types of Potting Adhesives

1) Epoxy Resinsealanthas

The majority of epoxy resin potting is hard and almost as hard as a stone after curing. It is difficult to remove and provides good confidentiality, but there is a small amount that is soft. Temperature resistances are generally 100 degrees, 150 degrees for heating curing, and even higher temperatures. It is waterproof, oilproof, dustproof, antitheft, corrosion resistant, age-resistant and has cold and heat shock resistance. Epoxy potting adhesives are increasingly becoming the go-to choice, with thermal conductive glue being one of the more widely-used types, featuring low viscosity and high temperature resistance.

Advantages: Its user-friendliness, excellent electrical insulation properties and temperature resistance are just a few, plus adhesion with both porous and metal substrates is outstanding.

Disadvantages: It has poor resistance to heat and cold changes. Cracks are easily produced after cold shocks and can penetrate electronic components. The cured colloid can also be hard and brittle. This makes it difficult to repair and damage electronic components. It is also impossible to open after sealing.

Scope of application: Epoxy resin potting adhesive can penetrate easily into gaps between products. It is ideal for small and medium-sized electronics that do not require special mechanical properties for the environment under room temperature, such as LED driver power supply, sensors, toroidal transistors, capacitors and triggers.

2) Silicone Encapsulants

After curing silicone electronic potting adhesive is elastic, soft and repairable. It’s called soft glue. The color of the glue can be changed to suit your needs, whether it is transparent, opaque or colored. This type of silicone potting adhesive is usually two-component, and it comes in addition and condensation types. The shrinkage type is prone to poor adhesion with the components and potting cavity. It will also produce volatile low molecular substances during curing, and shrinkage after curing can be obvious. However, the addition type, which is sometimes called silicone gel, has a low shrinkage, produces no volatile low molecular substances during curing, and it can be heated quickly and cured.

Advantages: It has excellent thermal conductivity and resistance to heat and cold changes, and can be used at a range of temperatures. The heat-curing version has a higher temperature resistance and excellent electrical properties, as well as a better insulation capacity. It can also withstand voltages above 10000V. It improves electronic component stability and insulation after sealing. Likewise, it has good thermal conductivity, is flame retardant, and can easily be removed for repair or replacement.

Disadvantages: High price, poor adhesion.

Scope of application: Suitable for encapsulating electronic components in harsh environments.

What are the benefits of silicone electronic glue over other potting adhesives?

Advantage 1: Protection of electronic modules or equipment for a long time, regardless of their shape or size.

Advantage 2: A dielectric insulation with a stable performance. This is an effective barrier against environmental pollution. It cures to a soft elastomer which eliminates the stress caused by shocks and vibrations in a wide temperature and humidity range.

Advantage 3: It is able to maintain its original electrical and physical properties under different working conditions, resists degradation by ultraviolet and ozone rays and has good chemical resistance.

Advantage 4: After potting, it is easy to remove and clean. This allows electronic components to be repaired.

3) Polyurethane Sealant

Polyurethane glue for potting is also known as PU glue. Most of them become soft, elastic and repairable after curing. They are called soft glue. Adhesion occurs between silicone and epoxy resin. Temperature resistance is usually not more than 100. After potting there are bubbles, and the potting has to be done in vacuum conditions.

Advantages: The best shockproof performance and good low temperature resistance. It is transparent, has a low hardness and moderate strength. It also has good elasticity. Furthermore, it is non-corrosive to electrical components, has a good adhesion with metals like steel, aluminum and copper, as well as rubber, plastic and wood.

Disadvantages: The colloid has poor high temperature resistance. Its surface is not smooth, its toughness after curing is low, it is weak in UV and anti-aging resistance and is easily colored.

Scope of application: It can be used to pot indoor electrical components that generate low heat. It protects electronic components and circuits installed and debugged from vibration, corrosion and moisture, etc. It is a perfect potting material to protect electronic and electrical components from moisture and corrosion.

4. When Choosing Potting Material, What Should You Consider?

1) Performance requirements: Temperature of operation, hot and cool alternation, internal stresses, outdoor or indoor use and stress conditions, color requirements and flame retardant requirements.

2) Potting method: Automatic or manual, room temperature, heating, curing time and coagulation of glue mixed.

3) Cost: The cost of the potting material is affected by its specific gravity. The price of a material is not the only thing to consider. You should also look at how much it will cost you after potting.

Potting materials must meet the following requirements:

√ High performance, long application time, suitable for automatic production lines of large scale;

√ Low viscosity and strong impregnation;

√ Powder components, such as fillers, should have minimal sedimentation during the potting process and no stratification;

The material used in specific semiconductor packaging must not only meet the requirements above, but also be as pure as the mounting material. This is because the material will come into direct contact with both the chip and the substrate. The potting of flip-chips requires a very low viscosity potting material due to the small gap between the substrate and the chip. The packaging material’s modulus cannot be too high in order to reduce stress between the chip, and the packaging. To prevent moisture from penetrating the interface of the chip and the substrate, the packaging material must adhere well to both.

Soft glue and hard adhesive can both be potted and waterproofed. If high temperature resistance or thermal conductivity is needed, silicone soft glue is the best choice. Polyurethane soft adhesive is better for low temperature resistance. Epoxy potting adhesive is widely used with different types and technical requirements. In terms of curing conditions it can be classified into two types: heating curing or room temperature curing. It is also divided by dosage form, with two components or one component. Room temperature curing epoxy adhesive for potting is typically a two-component glue. The glue is easy to use, has low equipment requirements and can be heated after potting. The glue mixture is high in viscosity and has poor permeability. It also takes a short time to apply, and its heat resistance and electrical properties are low. It is used to pot low-voltage electronics or in areas where heating and curing would not be suitable.

5. Three Methods of PCBA Glue Filling

1) Semi-Automatic Glue Filling Machine

To fill glue into the product manually, place the product beneath the glue head and press the start button. The machine will fill glue automatically, and then stop itself after it has been filled. After the glue has been filled, the operator can place the product onto the assembly line. Semi-automatic glue machines are suitable for PCBA products of all sizes.

2) Automatic Glue Filling Machine

The method of filling glue is very easy if the majority of your products are small. The product is placed in a jig and then the jig is placed on the table of a glue filling machine. Press start and the machine starts filling. The machine will automatically stop after the glue has been filled. The operator will then remove the jig and place another one with the product and press start. This cycle is repeated. The operator only has to place the jig on the table and then press the start button.

3) Fully Automatic Glue Filling Line

The machine will automatically fill glue and feed material into the oven. This saves labor and runs efficiently.

These are three methods of automatic adhesive filling. Automated glue filling machines are a great tool to increase production and save time.

6. Potting Process

The design of the potted product, component selection and assembly, as well as the potting materials are all closely related to its quality. The potting process is very important. For epoxy potting, there are two different potting methods: vacuum potting and normal potting. Epoxy resin. Normal potting and amine room temperature curing materials are used primarily for low voltage electrical appliances. Epoxy resin. Vacuum potting and acid anhydride heating-curing potting materials are used most often for high voltage electronic device potting.

Manual vacuum potting is the most common process. Mechanical vacuum potting is also popular. Mechanical vacuum potting is divided into two scenarios: A and B components must be mixed and degassed prior to potting, or degassed separately and then mixed before potting. Three different operation methods are available:

The first one: use a one-component electronic potting glue that can be sprayed on or poured directly;

The second type is a two component electronic potting adhesive with a curing substance of 2% to 3%, or in other proportions. It involves stirring, vacuum degassing, and pouring;

The third type addition type electronic potting adhesive, curing agent 1:10, 1:1.

The flow of the process is shown below:

1) Measuring: Weigh component A (curing agent) and component B (component B).

2) Mixing: Combine the components;

3) Degassing: Vacuum degassing or natural degassing;

4) Pouring: The adhesive should be poured during the time of the operation, otherwise the leveling will be affected;

5) Curing: Heating/Room Temperature Curing, the product in the pot is heated to room temperature and then the next step can be performed. The cure takes between 8 and 24 hours. The curing process will be quicker in summer when the temperatures are high; slower during winter when the temperatures are low.

Notes:

√ Before encapsulation, the surface of the product must be cleaned!

√ Before weighing the components A and B, be sure to fully mix them to distribute the pigments (or fillers) that settle to the bottom.

√ You cannot mix primer and glue. The glue can be encapsulated after the primer has dried.

√ The temperature has an impact on curing speed. Lower temperatures slow down the curing process.

Mechanical vacuum-encapsulation requires large investments in equipment, and has high maintenance costs. However, it offers a superior product consistency and reliability compared to manual vacuum encapsulation. No matter which encapsulation technique is used, it’s important to strictly follow the process conditions. Otherwise, you may not get a satisfactory result.

7. Common Problems in Electronic Gluing

1) How to cure electronic potting adhesive that is poisoned and not curing?

Silicone poisoning is most common in electronic potting glues of the addition type. The silicone will not cure after poisoning. To prevent silicone poisoning, use addition-type potting adhesives that do not contain organic compounds with phosphorus and sulfur.

2) How can you remove the electronic potting adhesive that has accidentally been stuck?

Alcohol, acetone and white wine are the most common silicone cleaning agents. When using, remember to dilute them and apply.

3) What can I do if my electronic potting adhesive does not dry during winter?

The electronic potting adhesive cures slowly or does not cure at all in the winter due to the low temperatures. To cure glue, we must increase the temperature of our oven and place our product inside at 25-degrees Celsius.

8. Summary

As electronics technology evolves, small devices become ever more powerful while their functionality requirements continue to expand. The smaller electronic devices are, the more likely to be prone to problems and difficult to fix. The components are very easily damaged by water vapor or small vibrations. Potting glue is used to improve the performance and quality of electronic components. The majority of electronic products today are potted using silicone potting adhesive, polyurethane glue or epoxy glue. These three glues are suitable for a variety of products. It is very strong and has excellent adhesion.