Copper is starting to hit its limits in advanced packaging.
Pure Cu is ~400 W/m·K, while at Semicon Taiwan there are debut of Cu/diamond composites reaching ~800 W/m·K, helping spread heat faster and reduce local hotspots. They can also reduce warpage: silicon is ~3 ppm/K CTE vs copper at ~17 ppm/K, while Cu/diamond can be tuned closer to ~6–10 ppm/K.
The challenge is the Cu/diamond interface. Copper does not naturally bond well with diamond, so Ti, Cr, Mo, or W are often added to form a carbide bonding layer. But too much carbide hurts thermal conductivity, making interface thickness critical. Compared with simply alloying Cu, the industry is working on pre-coating diamond particles using PVD or CVD giving much tighter control.