High-performance laminates feature high mechanical and thermal characteristics. They are suitable for demanding applications, providing good dimensional stability during thermo-cycles or lead-free soldering. And excellent electrical properties are required for high-frequency applications. Many high-Tg laminates (filled or unfilled) show a higher degree of brittleness because of their high cross-linking density, which also leads to lower copper-peel strength. Dow Chemical recently launched its LDk-HTd, a low Dk and high-Tg resin which has low dielectric constants over a wide range of frequencies and reportedly superior toughness and thermal stability. The material is flame retardant according to UL94 V-0, and the toughened laminate is not prone to delamination. Very good copper adhesion is achieved when the LDk-HTd resin is used in combination with the Gould copper foil type JTCHTEAB (IPC-4562, grade 3). An optimized foil treatment (mechanical bond) combined with a special adhesion promoter (chemical bond) results in enhanced bonding properties. In case of cohesive defect, the crack does not propagate at the copper/resin interface but instead into the resin matrix. The adhesion to copper foil is strong enough. The rough surface of the resin matrix with typical fan-shape structures indicates a sufficient level of resin ductility. The resin toughness and the bonding strength of the copper foil are optimized.
EPP EUROPE 433
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