Issue link: https://iconnect007.uberflip.com/i/1514189
JANUARY 2024 I DESIGN007 MAGAZINE 21 reinforcement makes this material particularly attractive for products with stringent high- temperature operating requirements. • Glass transition temp (Tg): 200°C minimum • Surface resistivity: 6 x 10 4 MΩ • Dielectric breakdown: 40kV Note: e moisture absorption rate for PI materials is relatively high when compared to the FR-4 and B-T composites. Special Application Laminates Alternative dielectric formulations have evolved that can address the technical needs of a wide range of special applications. High- frequency laminate products, for example, are better known for cores with better high- frequency properties, such as PTFE (Teflon®) that has a wider range of Dk values than FR-4 material. e PTFE composite is more expen- sive than fiberglass, but is better suited for high operational frequencies, making the laminate a good choice for RF circuit boards. • Low electrical signal and dielectric loss • Excellent thermal management characteristics • Broad range of Dk (dielectric constant) • Low out-gassing (ideal for space applications) • Enables improved impedance control Comparing the commercial FR-4 to the PTFE (Polytetrafluoroethylene), the material is less likely to experience a dielectric break- down when operating in extreme environmen- tal conditions. When selecting base materials for the circuit board, the designer must consider end-prod- uct safety. Government agencies, both domes- tic and international, have banned a number of elements considered a health hazard, for example, plating and soldering alloys that con- tain lead. Part two of this series will focus on PCB fabricator-recommended design guidelines for efficient circuit board fabrication process- ing. DESIGN007 Vern Solberg is an independent technical consultant, specializ- ing in SMT and microelectronics design and manufacturing tech- nology. To read past columns, click here.