Modulation of dielectric properties of bismaleimide laminates by hyperbranched polyimides with different structures

5G communications offer high-speed transmission, low latency and high interconnect density, which requires widely used 5G devices fabricated with low dielectric constant, low loss at high frequency, high thermal conductivity, good heat resistance and high reliability, among other characteristics. In this work, hyperbranched polyimide (HBPI) was prepared by a one-step process using hexamethylenediisocyanate trimer (HDI) and toluene diisocyanate trimer (TDI) as cores and coated with methylnaldehyde. A new type of laminate was prepared using a hyperbranched polyimide resin modified with bismaleimide as the matrix resin. The hyperbranched structure of HBPI was characterised by nuclear magnetic resonance and FT-IR techniques. Dielectric property tests showed that HBPI can reduce the dielectric constant (Dk) and dielectric loss of the laminate. At 10⁷ Hz, the dielectric constant of BMI-HBPI (HDI) laminate is 3.349 and the dielectric loss is 0.0018; the dielectric constant of BMI-HBPI (TDI) laminate is 3.501 and the dielectric loss is 0.00119. The reduction of Dk is achieved by increasing the free volume fraction in the system or reducing the content of polarisable functional groups in the system. Insulation and mechanical tests showed that the laminate has good performance characteristics, and its breakdown field strength, bending strength and fire resistance meet the requirements for copper-clad laminate of electronic class.