This paper describes several techniques involving transmission line ma
trix modelling which can be used to locate and characterize inhomogene
ous features within a circuit package where the thermal response to he
ating of the underside is inspected at the top surface. These are used
to confirm a semi-empirical thermal non-destructive testing approach
to the determination of the lateral dimensions of a feature. The time
to maximum contrast is an important parameter which can be used to est
imate the depth of the same feature. This paper then describes our app
roach to the determination of feature thermal parameters and the influ
ence of measurement noise on overall accuracy of the estimate. (C) 199
8 Published by Elsevier Science Ltd. All rights reserved.