Minco’s General Capabilities

Conductor width nomograph

The nomograph on the facing page will help you determine themaximum allowable current capacity (in amperes) of a conduc- tor. Reprinted from IPC-2221 (and MIL-STD-2118), the nomo- graph shows current for various conductor thicknesses, width, and temperature rises. A ss umption s
1.The nomograph is valid only for conductors with a polyimidecover layer — not exposed conductors.2.The conductor thickness includes copper plating. Be awarethat plating may add 0.0005" (13µm) to 0.0014" (36µm) of thickness. Selectively plated circuits do not have significant plating over conductors. The nomograph does not apply for plated metals other than copper.3.Derate current by 15% for conductor thicknesses greaterthan 3 oz. (0.0042”/75µm).4.The temperature rise curves only recognize heat generatedby the conductor itself. Heat from power dissipating compo- nents or nearby conductors on other layers is not included.5.It is assumed that conductor coverage is relatively small; i.e. there is enough free space between conductors for lateral heat dissipation. Groups of closely spaced parallel conduc- tors on the same layer can be treated as one large conductor. Add all the cross sectional areas together and all the currents together to determine the temperature rise.6.Current ratings are for still air environments. Forced air cool-ing will increase the maximum allowable current. Operating circuits in a vacuum will greatly decrease the maximum allowable current.Contact Minco for assistance in cases where the nomographdoes not apply. Also contact us if you have difficulty designing sufficient current capacity into the space available. We can sug- gest ideas to increase current capacity. U s in g th e nomo g r a ph
1.Locate the width of the conductor on the left side of the bottom chart.2.Move right horizontally, until you intersect the line of theappropriate conductor thickness. Move down vertically to the bottom of the chart to determine the cross-sectional area of the conductor.3.Move up vertically, until you intersect the line of the appro-priate allowable temperature rise. This is the increase in tem- perature of the current-carrying conductor. Conductor tem- perature should not exceed 105°C. For example, if the ambi- ent temperature might reach 80°C, the temperature rise above ambient of the conductor should be less than 25°C (105°C - 80°C). In this case use the 20°C curve.4.Move left horizontally to the left side of the chart to determine the maximum allowable current.Reverse the order of these steps to calculate required conduc-tor width for a given current. Conductor as p e ct r a tio
For best producibility, design conductors to be at least fivetimes as wide as they are thick. For example, with 2 oz. Copper (0.0028"/50µm) design the conductors to be 0.0140" (0.36mm) or wider. In tight situations Minco is successful in achieving 2.5:1 ratio conductor widths. ConductorWidthAdhesivePo T l yimide Ideal: Conductor width greaterthan 5x conductor thickness. 12