Printed Circuit Design & Fab - May 2008 - (Page 31)

6.20 6.18 6.16 Dk @ 10 GHz 6.14 6.12 6.1 6.08 6.06 0 10 20 30 40 50 60 70 80 TC600 Competitor A Competitor B FIGURE 4. a) The maximum temperature reached at constant wattage was 82˚C for the conventional material. b) The maximum temperature reached at constant wattage was 73˚C for the thermally enhanced material. Temperature (˚C) FIGURE 3. Significantly reduced TCEr (thermal coefficient of dielectric constant) improves signal stability in any temperature fluctuation range. pendicular and in-plane) to reduce heat generation Maintaining laminate integrity in terms of key properties such as copper peel adhesion and low water absorption. The specific target products were to produced as 6.15 and 3.50 Dk materials to meet the predominant industry demand for RF amplifier designs. TABLE 1 compares the key properties of two standard and two thermally enhanced conductive materials. The unique chemistry of the engineered laminate material includes a significantly reduced TCEr (thermal coefficient of dielectric constant) as seen in FIGURE 3. This translates into a more stable signal within any range of temperature fluctuation. The improvements of this thermally enhanced material include: ■ Temperature insensitive materials help amplifier and antenna designers minimize dead bandwidth, which is lost to dielectric constant drift as operating temperature changes ■ For antenna designs, a significant shift in resonance frequency and bandwidth roll off at specific frequencies, results in lower gain performance, and ■ Thermal stability is critical to phase sensitive devices, such as impedance network transformers, utilized for matching networks of power amplifiers To illustrate the impact of thermal conductivity both in the perpendicular direction, as indicated by reduced temperatures measured at the active device, and in-plane, as determined by the degree of heat spreading, a sample circuit based on an RF power field effect transistor was developed and thermograms obtained using thermally conductive laminate and a standard material with a thermal conductivity of 0.46. The results were significant both in terms of the heat reduction at the top surface and the spreading of the heat in the plane of the board. The resulting thermograms dramatically illustrate the effect of increased thermal conductivity. The maximum temperature reached at constant wattage was 82˚C for the conventional material, 73˚C for the thermally enhanced material, a reduction of 10% and more importantly, a reduction of 9˚C that could be the difference between life and death for sensitive junctions. (FIGURES 4a and 4b). ■ or impact on signal integrity. These materials can provide improved component reliability as a result of improved solder joint reliability. There is less work hardening, less thermal expansion from lower retained heat and the materials have an inherently lower CTE. Products designed with these materials will see improved power handling, and these new thermally enhanced laminates complement other more traditional thermal management tools. While designed to meet the demands of RF circuits, these materials can also be used as a replacement for traditional high performance FR-4 substrates where thermal management is a critical design constraint. PCD&F RUSS HORNUNG is technical marketing manager at Arlon; rhornung@arlon-med.com. MIKE SMITH is VP of marketing and R&D, also with Arlon, and can be reached at msmith@ arlon-med.com. CHET GUILES is an Arlon retiree and industry consultant, and can be reached at cguiles@arlon-med.com. Making back to school plans? Mark your calendars for New time of year! September 14-19 Marriott Santa Clara Santa Clara, CA www.pcbwest.com PRINTED CIRCUIT DESIGN & FAB 31 Summary Traditional laminates provide the greatest resistance (insulation) to heat transfer. Increasing thermal conductivity of the base materials is a new approach to thermal management in RF designs, with negligible expected cost implications MAY 2008 http://www.pcbwest.com http://www.pcbwest.com

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Printed Circuit Design & Fab - May 2008 Contents Our Line Market Watch Around the World Happenings ROI EMC For the Real World PCB East Conference Brochure Positive Plating Don't Let your Signals Stub Their Toes Improve PCB Layout With Skill Utility Programs The Next Generation Design Tool Challenge Thermally Conductive Microwave Materials PCB Dielectric Degradation in Lead-Free Assembly Applications A Tale of Two Trade Shows Eliminating Board Defects Off the Shelf Marketplace Ad Index BGA Bulletin

Printed Circuit Design & Fab - May 2008

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