Definition
Trace current capacity, or ampacity, is the maximum current a PCB trace can carry before it heats up beyond an acceptable temperature rise. A trace has finite resistance, so current passing through it dissipates heat; the trace settles at whatever temperature lets it shed that heat to its surroundings. Capacity is therefore always quoted against a target temperature rise, such as 10C or 20C above ambient, not as a single hard limit.
How it is calculated
The governing reference is IPC-2152, published in 2009, which replaced the older formulas of IPC-2221 with charts derived from extensive real-board testing. It relates four variables: trace cross-sectional area (width times copper thickness), current, temperature rise, and whether the trace is on an external or internal layer. Internal traces generally run hotter because they are insulated by laminate, whereas external traces shed heat to air. IPC-2152 also accounts for nearby copper planes and vias that pull heat away, which the older standard ignored, so it often allows narrower traces than IPC-2221 for the same current.
Why it matters for mining hardware
Power-delivery traces on hashboards carry substantial current to the ASIC chains. A trace sized too narrow becomes a hot spot, accelerating laminate degradation and, in extreme cases, lifting or vaporizing copper. During repair, a jumper wire that bypasses a damaged trace must match the original current capacity; an undersized wire simply moves the failure rather than fixing it. Heavier copper or wider traces are the usual ways to raise capacity.
Current capacity scales directly with copper weight, and high-current return paths often rely on via stitching.
In Simple Terms
Trace current capacity, or ampacity, is the maximum current a PCB trace can carry before it heats up beyond an acceptable temperature rise. A trace…