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30 PCB007 MAGAZINE I SEPTEMBER 2018 Low etch surface preparation aids with dry film adhesion, novel resist strippers are needed to en- sure no film residues, while controlled etch pro- cesses must be able to form the final patterns without excessive undercut or track width loss Improved Layer Bonding With finer patterns, higher track densities and the push for higher operating frequencies, SLP processes must minimize copper removal and maximize signal integrity through low surface roughness where possible. High-Resolution Surface Finish With finer features across the SLP, the fi- nal finish must also ensure compatibility, and in most cases this means no extraneous plat- ing (nickel foot). This, in combination with en- hanced corrosion resistance and controlled gold thickness , makes the new generation of ENIG chemistries the preferred solution for high-end PCB applications. Summary With more mobile device designers looking to utilize the benefits of FOWLP and other direct at- tach package types, a new generation of HDI PCBs is already in the market. Targeting <30 mm fea- tures and based on mSAP techniques, these sub- strate-like PCBs make use of the latest high-end manufacturing processes and materials, to enable the next evolution in advanced HDI boards. Chemical and material suppliers are realigning processes and products from the packaging in- dustry and adjusting them to fit into this new S LP sector, while prospective SLPs producers are re- viewing their existing processes and deciding if the y should invest. As some will inevitably de- cide against the investment, will we risk a limit in the futur e numbers of players in the SLP sup- ply chain? Only time will tell, but the advanced HDI mark et is again facing a new challenge, but one we can surely rise to meet. PCB007 Roger Massey is technical marketing manager at Atotech GmbH. The Electronic Transistor You've Been Waiting For How do you pack more power into an electric car? The answer may be electronic transistors made of gallium oxide, which could enable auto- makers to boost energy output while keeping vehi- cles lightweight and streamlined in design. A recent advancement—reported in the Sep- tember issue of the journal IEEE Electron Device Letters—illustrates how this evolving technology could play a key role improving electric vehicles, solar power and other forms of renewable energy. "To advance these technologies, we need new electrical components with greater and more ef- ficient power-handling capabilities," says the study's lead author Uttam Singisetti, PhD, asso- ciate professor of electrical engineering in UB's School of Engineering and Applied Sciences. "Gal- lium oxide opens new possibilities that we cannot achieve with existing semiconductors." The most widely used semiconducting materi- al is silicon. For years, scientists have relied upon it to manipulate greater amounts of power in elec- tronic devices. But scientists are running out of ways to maximize silicon as semiconductor, which is why they're exploring other materials such as silicon carbide, gallium nitride and gallium oxide. While gallium oxide has poor thermal conductiv- ity, its bandgap (about 4.8 electron volts) exceeds that of silicon carbide, gallium nitride, and silicon. Bandgap measures how much energy is re- quired to jolt an electron into a conducting state. Systems made with high-bandgap material can be thinner, lighter and handle more power than sys- tems consisting of materials with lower bandgaps. (Source: University at Buffalo)

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