Measuring Gas Phase Thermal Boundary Dynamics across Unequal Copper Density Substrates
Vapor phase reflow eliminates thermal deltas across unequal copper density substrates by transferring latent condensation energy at constant fluid temperatures.
Thermal Relief Pad
Geometric Pattern
Trace connections designed with thin spokes of copper between a mounting pad and a large plane restrict heat flow during assembly operations. Using a thermal relief pad allows hand-soldering irons or reflow ovens to heat the joint quickly by preventing the massive copper plane from acting as a heat sink. This pattern typically consists of a circular pad surrounded by a gap, bridged by three or four narrow metal lines.
Solderability Improvement
Without these narrow copper spokes, the large plane draws heat away from the solder joint so rapidly that the solder paste may never reach its melting point. In assembly lines, a thermal relief pad ensures that leaded or multi-pin parts connected to ground planes receive sufficient localized heat to form strong metallic bonds. Cold joints or tombstoning occur much less frequently when pads are thermally isolated from thick continuous copper sheets.
This isolation also reduces the time and temperature needed for manual rework, protecting the board substrate and adjacent components from heat damage.
Current Capacity
While narrow spokes improve solderability, they also reduce the electrical cross-section of the connection. Designing a thermal relief pad requires balancing the needs of heat isolation against the current-carrying demands of power circuits.