Silicon Micro-powder for Thermal Conductive Encapsulant

Silicon Micro-powder for Thermal Conductive Encapsulant

It is widely recognized that incorporating fillers into epoxy potting compounds significantly enhances specific physical properties while reducing production costs. These additives not only lower expenses but also increase thermal conductivity, as well as decrease the thermal expansion coefficient and shrinkage rate of cured products. Commonly used thermal conductive fillers in epoxy potting compounds include alumina, magnesium oxide, zinc oxide, aluminum nitride, boron nitride, and silicon carbide, with micron-sized alumina and silicon micropowder being the predominant components.

The silicon micropowder series for thermal conductive potting compounds features high purity, reliability, thermal conductivity, solder resistance, adhesive strength, low stress, and low thermal expansion. As a filler in potting materials, it effectively dissipates heat generated by circuits, prevents heat concentration and temperature rise in traces, thereby extending the lifespan of electronic components. The low thermal expansion coefficient of silicon micropowder in thermal conductive potting compounds reduces stress during encapsulation, effectively preventing component cracking. Its excellent fluidity ensures smooth molding processes without incomplete encapsulation, significantly improving yield rates. Additionally, it enhances filler distribution in resin, contributing to cost reduction.

2. Characteristics of Silicon Micro-powder for Thermal Conductive Encapsulant:

First, let's analyze the reasons for agglomeration of ultrafine powder particles such as silicon micropowder:

1: Particle aggregation caused by intermolecular forces, hydrogen bonds, and electrostatic interactions.

2. The particles are easy to interact and aggregate through the interface due to the quantum tunneling effect, charge transfer and the coupling of the interface atoms.

3. Because the specific surface area of the ultrafine powder is huge, it is easy to adsorb gas, medium or lose the original surface property after contact with air or various media, leading to adhesion and agglomeration.

4. The surface energy is very high and the contact interface is large, which makes the grain growth speed is accelerated, and the grain size is difficult to keep constant.

The above analysis shows that the molecular force between the surface of the silicon powder and the tackifier in the thermal conductive filler directly affects the performance of the tackifier in the potting compound. At present, the effective method to reduce the molecular force between the two is to carry out scientific and reasonable surface treatment on the silicon powder, so as to reduce the polarity of the silicon powder surface.

The thermal conductive filler in potting compounds is typically an inorganic powder. The incorporation of silicon micropowder enhances the thermal conductivity of epoxy potting compounds, reduces curing shrinkage, improves dimensional stability, decreases internal stress, effectively prevents cracking, minimizes heat release during curing, and improves the material's heat resistance, dielectric properties, and thermal conductivity, thereby reducing production costs. The silicon micropowder series for thermal conductive potting compounds exhibits the following characteristics:

1. It can eliminate the stress caused by impact and vibration in a wide range of temperature and humidity;

2. No by-products are generated during curing, no solvent is used, and deep curing can be achieved;

3. The product features high purity with minimal impurities and excellent electrical insulation properties.

4. Excellent dielectric properties, thermal conductivity, and flame retardancy;

5. Excellent adhesion performance to prolong product lifespan.

III. Our company's product specifications:

4. Analysis of the thermal conductivity, viscosity, mechanical properties and electrical properties of the thermal conductive potting compound with quartz powder:

1.1 Effect of Quartz Powder Content on Thermal Conductivity of Thermal Conductive Encapsulant

As the amount of quartz powder increases, the thermal conductivity of the potting compound gradually rises. This occurs because higher quartz powder content increases its volume fraction in the compound, reducing particle spacing and decreasing thermal resistance, which leads to a rapid initial increase in thermal conductivity. However, once the quartz powder reaches a certain level, an effective thermal conduction network forms within the system. At this stage, further increases in quartz powder content result in a slower growth rate of the potting compound's thermal conductivity.

1.2 Effect of Quartz Powder Content on Viscosity of Thermal Conductive Encapsulant

With the increase of the amount of quartz powder, the viscosity of the potting compound increases continuously, because the surface of quartz powder has active hydroxyl and the particle size is small, and the chemical bonding and physical adsorption between the quartz powder and the silicone rubber in the potting compound increase. With the increase of the amount of quartz powder, the interaction force between the quartz powder and the silicone rubber also increases, which leads to the continuous increase of the viscosity of the potting compound.

1.3 Effect of Quartz Powder Content on Mechanical Properties of Thermal Conductive Encapsulant

The tensile strength of potting compound exhibits an initial increase followed by a decline as quartz powder dosage increases. This occurs because quartz powder acts as a semi-reinforcing material for silicone rubber. When its dosage increases, the interaction between quartz powder and silicone rubber intensifies, thereby enhancing the compound's tensile strength. However, excessive viscosity of the potting compound may cause uneven dispersion of quartz powder, leading to localized agglomeration and subsequent reduction in tensile strength. Additionally, the elongation at break of the potting compound decreases with increasing quartz powder dosage. This phenomenon results from the enhanced interaction between quartz powder and silicone rubber, which restricts the free sliding of polysiloxane polymer chains.

1.4 Effect of Quartz Powder Content on Electrical Properties of Thermal Conductive Encapsulant

As the quartz powder content increases, the relative permittivity of the potting compound gradually rises. This is attributed to the high polarity of quartz powder, whose relative permittivity exceeds that of silicone rubber. Consequently, the potting compound's relative permittivity increases with higher quartz powder content. Simultaneously, the volume resistivity of the potting compound decreases, as quartz powder exhibits lower volume resistivity than silicone rubber. When the quartz powder content remains constant, the volume resistivity of potting compound A, B, and C increases sequentially. This occurs because the coupling agent treatment enhances interfacial adhesion between the filler and matrix, reducing chain segment mobility. This process increases intermolecular forces in polysiloxanes, decreases free volume, and consequently lowers ion carrier mobility, thereby diminishing conductivity and increasing volume resistivity.

5. Common filler names and their functions:

The filler serves to enhance certain product properties and improve heat dissipation during resin curing. Its use also reduces epoxy resin consumption, thereby lowering production costs. Different fillers can be selected based on application requirements, with dosage determined by specific needs. Below is a brief introduction to commonly used fillers:

In addition, according to the data, the addition of appropriate amount (27-35%) of P, AS, Sb, Bi, Ge, Sn, and Pb oxides to the resin can maintain its bonding properties under high temperature and pressure.