The features comparison for various measurement of Organic Solderability Preservatives (OSP) thickness and discussion for copper roughness effect caused by various type micro-etching solutions

With the electronics industry rapidly moving to lead-free soldering and requirements for long term reliability of the assembly becoming more critical, fabricators and OEM´s must determine the most cost effective and reliable means of achieving bare board solderability and component attachment. OSP´s have long provided a reliable and inexpensive means of satisfying these requirements. Compare with the other final finish (ENIG, immersion Ag, immersion Tim...etc.), the OSP´s get more features and potentials except for thickness measurement. This paper will show the various measurement methods for OSP thickness, and to compare the features include UV, EDS, FIB and optical metrology (OSPrey 800). The OSP user and PCB/SMT shops can select the applicable and reliable method on mass production line testing and trouble shooting via this paper. The Optical metrology (OSPrey 800) seems to provide a quick and non-destructive measurement. However, the linear and reasonable data depends on the topography of the copper surface. The different roughness seems the key point to determine the slope of the thickness calibration and thickness precision. Therefore the roughness effect caused by various types micro-etching solutions is also discussed in this paper.