Abstract
IoT (Internet of things) society will be coming in the near future, and everything will be connected by the Internet. Consequently, data traffic will be increased, and so will the demand to improve the performance of communication devices. Currently, plastics and ceramics are commonly used as insulating materials for communication components, but they are getting close to the limit in terms of material properties, because the next generation high performance communication devices require signal frequency of 20GHz and beyond. Therefore, further improvements in the properties of the insulating materials as well as in the performance of electronic devices are being demanded.
Copper conformal metallization on glass provides many opportunities for high frequency electronic devices. The most obvious advantage is given by the material properties. The glass substrate was chosen for low conductivity and low dielectric loss for high frequency application, and for its scalability to the larger area panels with low cost. While applications require strong interfacial adhesion between copper film and glass substrate, glass is often inferior as compared to metal-to metal adhesion. Direct copper metallization on glass is conventionally a difficult task, and it usually does not provide enough peeling strength either. Therefore, forming Ni and Ti seed layers by sputtering and precursors deposited by sol-gel method are being studied. However, these processes have been limitedly used or not been used in mass production, because creation of vias and simultaneous formation of seed layers on both sides by sputtering is difficult to undertake. The Sol-gel method does not provide stable peel strength and it takes a long process. This additional process requirement to add a layer to promote the adhesion of Cu to glass burdens the factories in a couple of ways: 1) enlarging the glass substrate is difficult due to the limitation in equipment size, 2) forming the film inside the through holes is also difficult due to high-aspect ratio via requirements, and 3) high cost due to slow processing speed.
In an earlier reports, we presented evidence that we have successfully demonstrated direct copper plating on glass, showing the adhesion strength of 0.42kN/m between glass and copper seed layer. In the present work, we are reporting wet plating process which enables easy and uniform film formation on large glass substrates and inside through holes. This low cost wet plating process enables forming copper film directly on glass without adhesion layer and enhancing the adhesion strength without degrading glass properties and copper conductivity.
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