Filler-reinforced polymer composites demonstrate pervasive applications due to their strengthened performances, multi-degree tunability, and ease of manufacturing. In thermal management field, polymer composites reinforced with thermally conductive fillers are widely adopted as thermal interface materials (TIMs). However, the three dimensional (3D)-stacked heterogenous integration of electronic devices has posed the problem that high-density heat sources are spatially distributed in the package. This situation puts forward new requirements for TIMs, where efficient heat dissipation channels must be established according to the specific distribution of discrete heat sources. To address this challenge, a 3D printing-assisted streamline orientation (3D-PSO) method was proposed to fabricate composite thermal materials with 3D programmable microstructures and orientations of fillers, which combines the shape-design capability of 3D printing and oriented control ability of fluid. The mechanism of fluid-based filler orientation control along streamlines was revealed by mechanical analysis of fillers in matrix. Thanks to the designed heat dissipation channels, composites showed better thermal and mechanical properties in comparison to random composites. Specifically, the thermal conductivity of 3D mesh-shape polydimethylsiloxane/liquid metal (PDMS/LM) composite was 5.8 times that of random PDMS/LM composite under filler loading of 34.8 vol%. The thermal conductivity enhancement efficiency of 3D mesh-shape PDMS/carbon fibers composite reached 101.05% under filler loading of 5.2 vol%. In the heat dissipation application of 3D-stacked chips, the highest chip temperature with 3D-PSO composite was 42.14 °C lower than that with random composites. This is mainly attributed to the locally aggregated and oriented fillers’ microstructure in fluid channels, which contributes to thermal percolation phenomena. The 3D-PSO method exhibits excellent programmable design capabilities to adopt versatile distributions of heat sources, paving a new way to solve the complicated heat dissipation issue in 3D-stacked chips integration application.

Direct ink writing (DIW) holds enormous potential in fabricating multiscale and multi-functional architectures by virtue of its wide range of printable materials, simple operation, and ease of rapid prototyping. Although it is well known that ink rheology and processing parameters have a direct impact on the resolution and shape of the printed objects, the underlying mechanisms of these key factors on the printability and quality of DIW technique remain poorly understood. To tackle this issue, we systematically analyzed the printability and quality through extrusion mechanism modeling and experimental validating. Hybrid non-Newtonian fluid inks were first prepared, and their rheological properties were measured. Then, finite element analysis of the whole DIW process was conducted to reveal the flow dynamics of these inks. The obtained optimal process parameters (ink rheology, applied pressure, printing speed, etc) were also validated by experiments where high-resolution (<100 μm) patterns were fabricated rapidly (>70 mm s⁻¹). Finally, as a process research demonstration, we printed a series of microstructures and circuit systems with hybrid inks and silver inks, showing the suitability of the printable process parameters. This study provides a strong quantitative illustration of the use of DIW for the high-speed preparation of high-resolution, high-precision samples.