Effect of lead-free soldering on key material properties of FR-4 printed circuit board laminates

Abstract

The transition to lead-free soldering of printed circuit boards (PCBs) using solder alloys such as Sn/Ag/Cu has resulted in higher temperature exposures during assembly compared with traditional eutectic Sn/Pb solders. Variations, if any, in laminate material properties before and after board assembly should be considered in the selection of appropriate laminates. This paper provides guidelines for laminate selection that are arrived by assessing key material properties (glass transition temperature (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> ), coefficient of thermal expansion (CTE), decomposition temperature (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> ), time-to-delamination (T-260), and water absorption), and their responses to lead-free soldering assembly conditions. A range of commercially available FR-4 PCB laminate materials, classified on the basis of glass transition temperature (high, mid and low), curing agents (dicyandiamide (DICY) and phenolic), flame retardants (halogenated and halogen-free), and presence of fillers are studied. The laminate material properties under investigation are measured in accordance with IPC-TM-650 test standards before and after exposure to multiple lead-free soldering cycles.