Thermal TSV is a dedicated through-silicon via filled with copper that serves exclusively as a vertical heat conduction path rather than an electrical signal carrier — providing a low-thermal-resistance channel through stacked silicon dies to extract heat from buried layers in 3D-stacked packages, where the thermal conductivity of copper (400 W/mK) is 2.7× higher than silicon (148 W/mK), making thermal TSVs essential for managing hotspots and reducing peak temperatures in 3D ICs and HBM memory stacks.

What Is a Thermal TSV?

• Definition: A copper-filled via that passes through a silicon die from top to bottom, identical in fabrication to a signal TSV but not connected to any electrical circuit — its sole purpose is to conduct heat vertically from a hot region on one side of the die to a cooler surface or heat sink on the other side.
• Dummy Via: Thermal TSVs are sometimes called "dummy TSVs" because they carry no signal — they occupy silicon area that could otherwise be used for transistors or routing, representing a direct tradeoff between thermal performance and functional density.
• Array Placement: Thermal TSVs are typically placed in arrays directly above or below hotspot regions — a 10×10 array of 10 μm diameter TSVs at 50 μm pitch occupies 0.25 mm² but can reduce hotspot temperature by 10-15°C.
• Keep-Out Zone: Each TSV requires a keep-out zone (KOZ) around it where no transistors can be placed — due to mechanical stress from the copper-silicon CTE mismatch, the KOZ is typically 2-5 μm around each TSV, increasing the effective area cost.

Why Thermal TSVs Matter

• 3D Stack Cooling: In 3D-stacked dies, interior layers have no direct path to the heat sink — thermal TSVs create artificial heat pipes through the silicon stack, reducing the thermal resistance from buried dies to the package surface by 20-40%.
• Hotspot Management: Thermal TSVs placed under hotspot regions provide targeted cooling — reducing peak temperature more effectively than increasing overall cooling capacity, because the problem is localized heat concentration, not total heat.
• HBM Thermal Path: HBM memory stacks use thermal TSVs alongside signal TSVs — the copper-filled vias help conduct heat from interior DRAM dies (which have no direct contact with the heat sink) to the top of the stack where the heat spreader makes contact.
• Design Flexibility: Thermal TSVs can be added to existing designs without changing the circuit — they are placed in unused silicon area (white space) between functional blocks, providing thermal improvement with minimal design disruption.

Thermal TSV Design Parameters

Thermal TSV vs. Signal TSV

Thermal TSVs are the essential heat management tool for 3D-stacked semiconductors — providing dedicated copper heat pipes through silicon dies that reduce hotspot temperatures and thermal resistance in vertically integrated packages, enabling the high-power 3D stacking needed for HBM memory, stacked processors, and advanced heterogeneous integration.