Thermal conductivity tester for measuring the thermal conductivity of adhesive

Adhesive, as a bridge connecting material, is widely used in fields such as electronic packaging, aerospace, and automotive manufacturing. Its thermal conductivity directly affects the heat dissipation efficiency, bonding reliability, and long-term stability of the product. For example, high thermal conductivity adhesive is required in electronic devices to dissipate chip heat and avoid performance failure due to local overheating; Low temperature scenarios, such as cold chain transportation, may require low thermal conductivity adhesives to reduce heat transfer. Therefore, accurate measurement of the thermal conductivity of adhesive is crucial for its formulation optimization, quality control, and engineering applications.

1、 Experimental principle

1. Transient heat source method

The transient heat source method injects a constant heat flux into the sample through a flat probe (circular or square), measures the temperature rise of the probe surface over time, and inverts the thermal conductivity and thermal diffusivity of the material.

2、 Experimental steps

1. Measurement equipment: DZDR-AS thermal conductivity tester

2. Sample preparation

Epoxy resin adhesive: Mix evenly according to the ratio (epoxy resin: curing agent=3:1), apply it between two clean aluminum plates (size 50mm × 50mm × 1mm), with a thickness controlled at 1.0mm. After vacuum defoaming, place it in a 25 ℃ oven for 24 hours of curing;

Silicone sealant: Squeeze directly into the gap of the aluminum plate (thickness 1.5mm), scrape the surface flat, and leave it at room temperature for 24 hours to complete vulcanization;

Aluminum based thermal conductive adhesive: Mix aluminum powder (particle size 20 μ m, filling amount 60wt%) and silicone resin in proportion, coat between aluminum plates (thickness 1.2mm), cure at 80 ℃ for 1 hour, and then cure at 150 ℃ for 1 hour.

3. Testing process

Fix the cured adhesive sample on the sample stage, ensuring that the sample is in close contact with the probe and avoiding air gaps;

Set test parameters: heating power P=0.2W (to avoid sample overheating and decomposition), test time t=160s (covering the linear growth stage of temperature rise);

Start the test and the instrument automatically records the temperature rise curve of the probe surface over time

Each sample is tested 5 times and the average is taken to reduce random errors.

4. Data Processing and Results

By comparing with the standard sample (acrylic sheet), the instrument measurement value (0.21 ± 0.005W/(m · K)) has an error of less than 3% compared to the theoretical value (0.21W/(m · K)), indicating that the transient plane heat source method is reliable and accurate under the instrument conditions.

5. Analysis of Factors Affecting the Thermal Conductivity of Adhesive

Molecular structure and polarity: Epoxy resin adhesive (A) is a polar polymer with strong hydrogen bonding between molecular chains and significant phonon scattering, resulting in a low thermal conductivity (≈ 0.31W/(m · K)); Silicone adhesive (B) has high molecular chain flexibility, abundant free volume, and lower thermal conductivity (≈ 0.20W/(m · K)).

Filler modification: Aluminum based thermal conductive adhesive (C) significantly improves overall thermal conductivity (≈ 2.20W/(m · K)) by adding high thermal conductivity aluminum powder (λ≈ 200W/(m * K)), but uneven dispersion of fillers may lead to local thermal resistance, resulting in slightly larger test standard deviation.

Curing degree: If the epoxy resin adhesive is not fully cured (such as insufficient time), the molecular chain cross-linking density is low, the free volume is large, and the thermal conductivity will decrease by about 15%~20% (in this experiment, sufficient cross-linking was achieved after 24 hours of curing).

3、 Experimental conclusion

The transient planar heat source method can quickly and accurately measure the thermal conductivity of adhesives (with a single test time of 160 seconds and an error of less than 3%), and is suitable for small-sized, soft adhesive samples; The thermal conductivity of adhesive is mainly determined by its molecular structure (polarity, free volume) and filler content. Aluminum based thermal conductive adhesive can significantly improve its thermal conductivity through filler modification; During the testing process, it is necessary to control the sample thickness, contact pressure, and curing degree to reduce errors.