Initial Heating Slope Selection in Convection Reflow Profiling
Selecting initial reflow heating slopes between 1.0 and 2.0 °C per second prevents solder spattering and flux exhaustion across high-density SMT assemblies.
Board Copper Weight
Nominal Thickness
Measurement of mass per unit area determines the finished thickness of conductive layers on a printed circuit. Specifying a board copper weight ensures that traces provide sufficient electrical conductivity and heat dissipation for the intended application. This value is traditionally expressed in ounces per square foot, where one ounce equates to a thickness of approximately 35 microns.
Designers select this value based on the power requirements of the circuit and the space available for routing.
Thermal Demand
Thicker deposits require more energy to reach soldering temperatures during the assembly process. Large planes of board copper weight act as heat sinks that pull thermal energy away from pads, potentially leading to cold solder joints or poor wetting. Reflow profiles must be adjusted to account for this mass by extending preheat times or increasing peak temperatures.
Variations in thickness across the panel can cause uneven heating if the distribution is not balanced. Fabrication houses often apply a tolerance to this value, meaning the actual thickness may vary slightly from the theoretical one ounce or two ounce target. Etching rates also differ depending on the height of the metal being removed.
This variance impacts the final impedance of high speed signals.
Current Capacity
The cross sectional area of a trace dictates the maximum amperage it can carry without exceeding a specific temperature rise. Standard charts facilitate these calculations. High current paths often demand two or three ounce copper to remain within safe operating margins.
This property also impacts the minimum spacing and width achievable through etching.