With its 9th generation Core processor family, Intel introduced STIM (soldered thermal interface material) to transfer heat between the processor die and the metal integrated heatspreader (IHS), as opposed to fluid thermal pastes. Enthusiasts prefer soldered IHS for their superior heat-transfer characteristics. It was known since the series launch that STIM will be restricted to the unlocked "K" SKUs, such as the i9-9900K and i7-9700K, while locked SKUs would retain thermal pastes. PC enthusiast @momomo_us (Twitter handle) de-lidded a Core i5-9400F sample to confirm this.