For this study, the authors wanted to assess the impact of different solder mask options on under-component cleanliness. The solder mask specification for the substrates used in this study included SMD and NSMD, as well as NoSM, for comparative purposes. The solder mask used on the test vehicles employed for this study was a liquid photo-imageable (LPSM or LPI) solder mask. The test vehicles were populated with numerous chip cap components with four solder paste types: no-clean tin-lead solder paste (old generation), no-clean tin-lead solder paste (new generation), no-clean lead-free solder paste (old generation), and no-clean lead-free solder paste (new generation).