Characterization of thin layers in microelectronic packaging using acoustic microscopy

Some of the transducer and image related issues involved in characterizing thin layers in microelectronic packaging are discussed here. Specifically, the cases of Parylene N on stainless steel and thinned silicon wafers are described. For the case of the Parylene coating, it is shown how a thin layer can distort the pulse reflected from the interface to the extent that a well bonded coating appears delaminated. The experimental data are explained using a model that is capable of predicting pulse shapes. For the case of the silicon wafer, issues related to transducer selection and the limits of thickness estimation are discussed.