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34 The PCB Magazine • April 2014 to damage. That is not to say that robust PWBs cannot be made, but there is a challenge in pro- ducing them. One must test the interconnect and the material in order to confirm robustness in a given application. PCB HDI PWB RELIABILITY continues researchers are working to develop optical chips, where light can be controlled with nano- structures to be used for future circuits based on photonics instead of electronics. But it has proved to be impossible to achieve per- fect photonic nanostructures: they are inevitably a little bit imperfect. now researchers at the niels Bohr institute in collabora- tion with dtu have discovered that imperfect nanostructures can offer entirely new functionalities. they have shown that imper- fect optical chips can be used to produce "nanolas- ers," which is an ultimately compact and energy- efficient light source. the results are published in the scientific journal nature nanotechnology. the nanolaser is based on the disorder in the pattern of holes in the photonic crystal. the light source is built into the clear-as-glass photonic crystal, and light is reflected and channeled into the crys- tal's middle lane, then thrown back and forth. due to im- perfections is intensified and spontaneously turns into laser light. Unavoidable Disorder Used to Build Nanolaser Figure 10: adhesive delamination. Figure 12: crazing with a caF failure. Figure 11: cohesive crack. paul reid's career in pcB fabrica- tion and reliability testing spans 35 years. one of his specialties is producing technical animations of failure modes induced by thermal excursions, giving him insight into the mecha- nisms of circuit board failure. reid is now re- tired. to contact the author, click here.

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