Integrated Circuit Epoxy Outer Molding
I believe ICs use some kind of high temperature plastic, that survives 205C reflow soldering.  It melts when touched long enough by a hot soldering iron,  like 425F - which does not bother the solder mask, the copper on the PCB, or the PCB material itself.  I read a couple of Texas Instruments datasheets and didn't see anything on the IC body material, just "lead free" and "Green" notes, see page 3


  Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
  lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
  
  Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
  the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
  
  Green (RoHS &amp; no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
  in homogeneous material)