How to control packing and viscosity with bimodal hBN particle size distribution

Problem

Selecting hBN requires a system-level thermal decision. Filler conductivity alone does not predict compound viscosity, particle packing, bond-line thickness, contact resistance, electrical insulation, or reliability.

Mechanism

Heat moves through particle contacts and interfaces in the cured or solid composite. Particle size, morphology, orientation, loading, wetting, voids, pressure, and thickness determine whether the filler forms a useful thermal path.

Tradeoff

Increasing hBN loading can improve thermal transport while increasing viscosity, torque, brittleness, sedimentation risk, dispensing force, or interfacial defects. The best formulation meets the system thermal-resistance target inside the available processing window.

Material Strategy

Use the following decision sequence to define the host system, compare candidate materials, establish a process window, and confirm the final part. The guidance is method-conditioned and does not replace grade-specific data or application testing.

key answers

Bonghyung Lee hBN Comparison of product names or supplier representative figures alone is not sufficient in a practical review of particle size combination selection. First, the required functions of the final part or film, acceptable appearance and processing range, and actual test conditions must be defined. Then, candidate materials must be compared under the same base material, thickness, process, and conditioning conditions to obtain meaningful conclusions.

This page does not claim that any particular grade is superior to all systems. The function of the material depends on the resin or binder, particle dispersion, addition amount, shape, process and measurement method. Before purchasing, you must check what composition, test specimen, and method the values ​​in the technical data were obtained from, and conduct an evaluation that reflects actual mass production conditions.

Large particle skeleton and small particle filling

The ‘large particle framework and small particle packing’ item should be treated as an independent decision-making criterion for the selection of the bimodal hBN particle size combination. First, target values, measurement methods, allowable deviations, and failure criteria are documented and then candidate materials are compared. If conditions are not fixed, it is difficult to distinguish between material differences and test deviations.

Evaluation results include not only average values but also repeated measurements and ranges. When the goal is not met, the cause is identified by separating additives, base material, dispersion, process, specimen shape, and measurement conditions in that order.

Viscosity cost of excessive fines

The ‘viscosity cost of excessive fines’ item should be treated as an independent decision-making criterion for the selection of the bimodal hBN particle size combination. First, target values, measurement methods, allowable deviations, and failure criteria are documented and then candidate materials are compared. If conditions are not fixed, it is difficult to distinguish between material differences and test deviations.

Evaluation results include not only average values but also repeated measurements and ranges. When the goal is not met, the cause is identified by separating additives, base material, dispersion, process, specimen shape, and measurement conditions in that order.

Mix ratio screening

The ‘mixing ratio screening’ item is a key process variable that determines the final performance. Do not judge the dispersibility solely based on the primary particle size of the powder, but also review the actual aggregate size, surface treatment, and compatibility of the dispersant, resin, or solvent. Even if the concentrate appears stable, it can reagglomerate during binder addition, dilution, curing, or storage.

In comparative tests, the dosing sequence, mixing energy, temperature, time and batch size are fixed. Viscosity, particle size or filter residue, as well as functional values ​​of the final coating or molded part, must be measured to determine if the dispersion process has actually improved.

Determination of actual aggregate size

The item ‘Confirmation of actual aggregate size’ should be treated as an independent decision-making criterion for the selection of the bimodal hBN particle size combination. First, target values, measurement methods, allowable deviations, and failure criteria are documented and then candidate materials are compared. If conditions are not fixed, it is difficult to distinguish between material differences and test deviations.

Evaluation results include not only average values but also repeated measurements and ranges. When the goal is not met, the cause is identified by separating additives, base material, dispersion, process, specimen shape, and measurement conditions in that order.

Simultaneous determination of heat, flow, and sedimentation

In the ‘simultaneous determination of heat, flow, and sedimentation’, the bulk thermal conductivity of the filler data sheet and the thermal resistance of the completed system must be distinguished. Heat transfer in composites is limited by packing amount, particle contact, orientation, interface, cell, bond line thickness and contact pressure. High material thermal conductivity does not automatically guarantee low thermal resistance of the actual part.

The thickness, pressure, surface roughness, and curing state of the test piece are fixed, and the thermal conductivity and thermal resistance are selected according to the purpose. Check not only the initial values, but also interfacial delamination, pump-out, cracks, and performance changes after thermal cycling.

Recommended Evaluation Procedure

1. Target functions and failure conditions are defined by numerical or observation criteria.
2. A standard specimen is created using the base material, additive package, and substrate that will be used in mass production.
3. Rather than changing all variables at once, compare material types, addition amounts and key process conditions step by step.
4. In addition to initial functionality, appearance, processability, mechanical or adhesive properties and required durability are measured.
5. The optimal conditions are repeated on different raw material lots, on different dates, and in actual production facilities to confirm the process window.

The test report includes the name of raw materials, lot, mixing, specimen thickness and shape, equipment, temperature, time, speed, conditioning, and measurement method. Without this information, it is difficult to fairly compare results between suppliers or between lab and mass production.

Information to provide to suppliers

• Exact type and grade of base resin, binder or substrate
• Target function value, measurement method and tolerance range
• Limitations on color, transparency, surface, viscosity or mechanical properties
• Mixing, extrusion, injection, application, drying or curing conditions
• Thickness, shape and usage environment of specimens and final parts
• Required TDS, SDS, regulatory documentation and change management level
• Evaluation sample quantity, development schedule and expected mass production scale

Frequently Asked Questions

Can I select a grade based solely on representative values from the datasheet?

Representative values are useful for narrowing down candidates, but are insufficient as a basis for final selection. If the test composition, method, thickness and conditions are different from the actual system, the same results cannot be expected.

Is the highest dosage safest?

Not really. Higher additions may increase functionality but may worsen viscosity, torque, brittleness, color, haze, surface or cost. We need to find the minimum range that reliably satisfies the goal.

Can laboratory results be directly applied to series production?

Equipment size, shear, residence time, heat history and part geometry will vary and should not be applied without confirmation. It must be re-verified step by step in pilot and mass production facilities.

Request evaluation samples and technical reviews

Request particle size combination testing by sending us your maximum particle limit and viscosity limit. Please include the above input information with your request. The more specific the information, the faster you can narrow down the appropriate supply form - powder, masterbatch, or dispersion - and reduce unnecessary repetitive testing.

Recommended Architectures

• Use a matched baseline with the intended host resin, binder, substrate, color package, thickness, and geometry.
• Screen supplied form, loading, dispersion, and process variables in a bounded matrix.
• Advance only candidates that meet functional, processing, appearance, mechanical, and durability requirements together.
• Repeat the accepted window on production-relevant equipment and multiple raw-material lots.

Related Products

• hBN

Related Applications

• Thermally Conductive Electrically Insulating Polymers

Downloads & Engineering Support

Review the related Dispersion Engineering Overview Video, then request an application-specific technical review.