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Decreasing the dielectric constant and water uptake by introducing hydrophobic cross-linked networks into co-polyimide flms
Decreasing the dielectric constant and water uptake by introducing hydrophobic cross-linked networks into co-polyimide flms
The high durability of low-k value is the key parameter for the low dielectric materials especially used under humid conditions, because the k value is very sensitive to moisture. Here, to decrease the dielectric constant and improve the water resistance, a series of novel co-polyimides are successfully prepared based on cross-linkable diamine monomer by a two-step pathway combining polymerization and crosslinking reaction. It is intriguingly found that with the gradual increase content of cross-linkable group, the dielectric properties, water resistance as well as thermal and mechanical properties of those co-polyimides can be fnely tuned. After cross-linking, the dielectric properties are signifcantly enhanced and the flm surface changed from hydrophilic (78.7–89.2°) to hydrophobic (93.0–104.2°), which endow the cross-linked flms with superior water resistance and high durability of low-k value. The best performance is obtained for cross-linked co-polyimide (CL-Co-PI-4) containing 30% cross-linkable group. The CL-Co-PI-4 exhibits low dielectric constant of 2.32 and dielectric loss of 0.016 at 1 MHz. Excitingly, the CL-Co-PI-4 demonstrates an extremely low water uptake of 0.051 ± 0.010%, which represents the best water resistance for the reported polyimides. After exposing to di?erent humidity conditions for 12 h, the increasing percentage of k value is very low and below 0.84%. The CL-Co-PI-4 still keep its k value below 2.35 after equilibrating at 75% R.H. for 14 days. The excellent moisture resistance and overall performance make the CL-Co-PI-4 a good candidate for dielectric material under both dry and humid conditions.
