I presume that you are asking about the i9-9900 (there is no i5-9900) and whether this part uses TIM or solder to dissipate heat from its silicon to its heat spreader. The answer is yes, the part utilizes solder. In fact, all of the 9th gen. i5/i7/i9 processors use solder.
Intel's formal statement (see here) is "Unlocked 9th Gen Intel® Core™ i5, Intel® Core™ i7 and Intel® Core™ i9 processors are built using Solder Thermal Interface Material (STIM)". I presume from this that locked SKUs will retain TIM.