1. IPC-2221 6.2 Conductive Material Requirements The minimum width and thickness of conductors on the finished board shall be determined primarily on the basis of the current-carrying capacity required, and the maximum permissible conductor temperature rise. The minimum conductor width and thickness shall be in accordance with Figure 6-4 for conductors on external and internal layers of the printed board.

2. IPC-2221 6.2 Conductive Material Requirements The conductor's permissible temperature rise is defined as the difference between the maximum safe operating temperature of the printed board laminate material and maximum temperature of the thermal environment to which the printed board will be subjected. For convection-cooled printed board assemblies, the thermal environment is the maximum ambient temperature where the printed board will be used.

3. IPC-2221 6.2 Conductive Material Requirements For conduction-cooled printed board assemblies in a convection environment, the temperature rise is caused by the dissipated power of the conduction-cooled parts and the temperature rise through the printed board and/or heatsink to the cold plate should also be considered.

4. IPC-2221 6.2 Conductive Material Requirements For conduction-cooled printed board assemblies in a vacuum environment, the thermal environment is the temperature rise caused by the dissipated power of the parts and the temperature rise through the printed board and/or heatsink to the cold plate. In a vacuum environment, the effects of radiation heat transfer between the parts, the printed board assembly and the cold plate should also be considered.

5. IPC-2221 6.2 Conductive Material Requirements For internal layers, the conductor thickness is the copper foil thickness of the base laminate unless blind/buried vias are used in which case the copper foil thickness includes copper process plating. For external layers, the conductor thickness also includes the thickness of plated copper deposited during the plated-through hole process, but should not include the thickness of solder coating, tin-lead plating, or secondary platings.

6. IPC-2221 6.2 Conductive Material Requirements It should be noted that the foil thickness specified by the standard drawing noted for the preferred printed board materials are nominal thickness values which can generally vary by as much as ± 10%. For external layers, the total copper thickness will also vary due to processing prior to plating which may reduce the thickness of base copper.

7. IPC-2221 6.2 Conductive Material Requirements Furthermore, since the thickness of plated copper is controlled by the requirement for the thickness of copper required in the barrel of the plated-through hole, the associated amount of copper on the external layers may not be the same thickness as the plating in the barrels of the plated-through holes (see 10.1.1). Therefore, if conductor thickness is critical, a minimum finished board conductor thickness should be specified on the master drawing.

8. IPC-2221 6.2 Conductive Material Requirements For ease of manufacture and durability in usage, these parameters should be optimized while maintaining the minimum recommended spacing requirements. To maintain finished conductor widths, as on the master drawing, conductor widths on the production master may require compensation for process allowances as defined in Section 10.