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ECWC 2014: The Base Materials Session

The focus of the session turned to new base materials as Lin Lin, from the Technology Development Centre at Panasonic, introduced a newly-developed ultra-low-loss laminate for high-speed and high-frequency PCBs.

The exponential trend in information and communications technology, for example the projected 61% compound annual growth rate in global mobile data traffic, necessitating the high-speed transmission of large-volume data using the minimum of electrical energy, had created a demand for halogen-free low-loss laminates suitable for fabricating high layer count PCBs with high heat resistance, low CTE, high thickness accuracy, and suitability for lead-free soldering

Of the many laminates previously developed for use in high-speed and high-frequency applications, only woven-glass ceramic-filled PTFE materials had the right dielectric properties to meet performance requirements at GHz frequencies. But PTFE materials were difficult to laminate so their use was limited to low layer-count constructions, so Panasonic had set out to develop a new-generation material with equivalent dielectric properties but better heat resistance and processability, suitable for building high layer-count multilayers.

To achieve the desired dielectric loss characteristics, they had based their new material on a low-Df thermosetting polymer, a modified polyphenylene ether, with a low-Df, low-Dk hardener and a low-Df inorganic filler. The high crosslink density gave low CTE and good temperature resistance. When combined with a low-Dk glass cloth and a low- profile copper foil, the result was a novel high-performance material with excellent stability of dielectric properties within a wide frequency range, with ultra-low transmission loss and lower temperature drift than ceramic-filled PTFE. And the laminates and pre-pregs were eminently suitable for the fabrication of high layer-count HDI multilayer constructions. The new material was expected to be widely applied to next-generation high-speed and high-frequency applications such as network equipment, base stations and high frequency parts. The material had high Tg, low moisture absorption and good heat resistance, making it compatible with lead-free soldering processes.

Not all electronics-grade resins were used in laminate manufacture. The final presentation of the base materials session gave an insight into alternative applications of resins at the next level, in impregnating, encapsulating, and potting of transformers and modules. Jens Buerger from ELANTAS Beck, specialists in the protection of electronic components in the automotive, industrial, medical, and avionics sectors, reported the results of a study of the impact of linear coefficient of expansion on temperature shock resistance.

There were three main categories of electronic protection: thin-film coatings applied by dip or spray were mainly used for moisture protection of PCBs. Thick film coatings, typically applied by dam-and-fill, swirl or dip, were used for major protection of PCBs from chemical attack and vibration. Encapsulation or potting, by dispensing or vacuum potting, gave chemical, mechanical and vibration protection, as well as sealing the assembly.

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