Lead/halogen-free laminates and their effect on desmearing and metallisation

摘要

Purpose - This paper aims to show critical processing issues observed for the newer restriction of the use of hazardous substances compliant laminate materials. Design/methodology/approach - Several samples of the popular lead-free and halogen-free laminate materials were tested under laboratory conditions to ascertain their desmear characteristics in comparison to the standard FR4 and high T_g laminate materials available on the market. Literature searches and experiences in the field were used to give a supplier's point of view of the newer laminate materials. Findings - The new directives forcing the exclusion of solder and restricting the use of halogens means that newer laminate materials have significantly different chemical and physical properties to laminates previously considered standard. These differences have a drastic effect on the desmearing process in general, making it more difficult to get high weight losses and, for almost all lead-free materials, reducing the roughness that can be generated. This affects the copper/laminate bonding strength and so increases risks of blistering and hole wall pull away. Alternative approaches are required to improve this adhesion and one of these is to use a specifically designed low stress electroless copper with good adhesion properties. Research limitations/implications - Most of the work was performed under laboratory conditions and, although mainly substantiated in production lines, can only be used as a guide. Owing to the large amount of different laminate materials, applications and processing techniques it is difficult to predict the full effect for every PCB manufacturer. In-house testing should be performed by individual PCB manufacturers on each laminate material considered suitable for their technical requirements. Originality/value - The paper details the main areas to concentrate on when desmearing and metallising newer laminate materials and suggests alternative approaches to improve the processing of these materials.