Exploring the Cross-Linking Effect on Decreasing the Dielectric Constant and Dissipation Factor of Poly(ester imide)s at a High Frequency of 10–40 GHz

Abstract

Polyimides possess excellent thermal-mechanical stability and solution processability and can be widely used in the electronic industry. In particular, they can achieve a decent insulating property at a high frequency spanning the range 10–40 GHz via chemical structural design, so it is important to investigate the structure–dielectric relationship of polyimides. However, it is challenging to reach a low dielectric constant (D k) as well as a low dissipation factor (D f), simultaneously, owing to the trade-off between the free volume and rigidity of polyimides. Among them, poly­(ester imide)­s (PEIs) are well-known for their ultralow D f of 0.003 at 10 GHz; however, their high D k of 3.2 confines the insulating capability of PEIs. To overcome this difficulty, a cross-linking strategy is applied to PEIs to decrease their D k. In this research, the linear PEI is copolymerized with a series of aromatic cross-linkers comprising melamine, tris­(4-aminophenyl)­amine, 1,3,5-tris­(4-aminophenyl)­benzene, 1,3,5-tris­(4-aminophenoxy)­benzene, benzene-1,3,5-triyl tris­(4-aminobenzoate), and tris­(4-aminophenyl)­benzene-1,3,5-tricarboxylate. The functional groups of aromatic triamine cross-linkers including ether and ester groups strike the best balance between the polymer’s free volume and rigidity. The experimental results revealed that they maintain decent thermal stability with a glass transition point over 350 °C and enhance mechanical durability with strength/elongation at a break of 164 MPa and 22%. Notably, the cross-linked PEIs can reduce the D k to below 3.0 and maintain the D f at approximately 0.003 at a high frequency spanning the range of 10–40 GHz. This study provides an effective approach to control the dielectric properties of polyimides through manipulating the structure rigidity and free volume by using cross-linking.

Structural Design and Polymerization of High-Frequency Low Dielectric Benzoxazine Resins

“…At present, low f values of the matrix resins are highly demanded for PCB applications . In theory, the signal transmission rate is inversely proportional to the f value and the square root of the k value .…”

Polarization Analysis and Humidity Dependence of Dielectric Properties of Aromatic and Semialicyclic Polyimides Measured at 10 GHz

“…They showed that the anisotropy and local chain rigidity of PI chains represented by DoP correlate to electrical energy loss rather than the dipole moment. Many studies about the dielectric properties of PIs, such as low- D k / D f PIs with cross-linking structures, long triphenyl side chains, and bulky bis­(trifluoromethyl) biphenyl pendant groups, have been reported to date. However, no quantitative analysis of the anisotropic dielectric properties of PI films based on theoretical principles has been reported using reproducible experimental methods with variable humidity measurements for systematic molecular design of low- D k / D f PI.…”

Graft Architectured Poly(phenylene oxide)-Based Flexible Films with Superior Dielectric Properties for High-Frequency Communication Above 100 GHz

“…Up to now, various polymers including modified polyimide (mPI) and liquid crystal polymer (LCP) have been widely studied as polymeric substrates and dielectric layers for FCCL. − Despite significant progress being made on this front, achieving the aforementioned prerequisite properties still remains a major challenge. In detail, mPI, which has been widely used as electrical insulation layers, has high D f at high-frequency regimes and water uptake, limiting its usage in high-frequency applications. − While LCP demonstrates the potential for exceptional dielectric properties for FCCL in high-frequency regimes and reduced water absorption, the LCP film produced using traditional processing methods inherently showed anisotropic mechanical properties . Furthermore, the cost efficiency of LCP presents a hindrance to their widespread application. − Given these, developing new dielectric polymeric layers presenting low D k , low D f , thermal/mechanical stability, and low water uptake is an interesting issue.…”