Circuit Connection Reliability Analysis of Laser-Drilled Blind Via Holes Using Data-Mining Method

The purpose of the present study is to analyze the circuit connection reliability of printed wiring boards (PWBs) with respect to thermal stresses on drilled hole walls. Micro-via drilling using laser technology has become the predominant method of machining smaller blind via holes. Moreover, a technique that uses copper foil in forming the circuit has been considered as a means of limiting the hole depth more accurately. After forming the blind via holes, copper plating must be used in order to maintain high reliability in circuit interconnectivity. In the present study, using the finite element method (FEM), we evaluated the effects of both the shape of the holes and the thickness of the copper plating on thermal stress occurring at the hole bottom. However, numerous factors are associated with the thermal stress, making the proper material composition and hole shape design difficult to determine. FEM must be applied to large amounts of data in order to identify quantitative tendencies. In addition, we applied a data-mining method to the thermal stress data, in an attempt to elucidate the factors that influence the reliability of blind via holes. The data-mining method revealed new factors that were hidden in the data; notably, the coefficient of thermal expansion in the thickness direction, despite the presence of other complex factors.