Surface Mount International Conference Proceedings


Author: Mats Lindgren
Company: IVF
Date Published: 4/28/1997   Conference: Surface Mount International

Abstract: This paper presents the some of the results from an evaluation of sequential build-up (SBU) boards from six different PWB manufacturers using in total four different dielectrics. Three of these manufacturers started their manufacturing of SBU using photo sensitive dielectric during the evaluation. The three other manufacturers were already in full production of SBU boards. These manufacturers used photo sensitive dielectric and plasma etching respectively. In order to evaluate the SBU technology a special test board was designed and manufactured. Visible inspection and cross sectioning of the boards showed that there are many space saving and reliable solutions with SBU boards compared to ordinary epoxy laminates. Measurements on surface insulation resistance and bulk resistance showed that the SBU boards manufactured in this project have comparable values to ordinary PWB technology with Ni/Au finish. However, there are differences between different dielectric materials and solder masks. The ionic contamination on the boards were low. The results from peel strength tests of copper in the top layer and shear tests of passives were comparable to standard PWB substrates. Delamination between large copper planes and the underlying dielectric occurred after reflow soldering for all photo sensitive dielectrics, Due to the problem with delamination between the copper and the dielectric material large copper planes must be avoided. This could be solved by meshing the copper planes.

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