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Pad Diameter

Pad Diameter

All planes and pads should be maximized wherever feasible, consistent with good design practice and electrical clearance requirements. (see Spacing of Conductors for Various Voltages)The minimum pad size should be determined by the following formula:

                                 minimum pad size = a + 2b + c

                                 where:   a = hole diameter

                                              b = minimum annular ring requirement
                                                   (0.1mm for THP hole and 0.25mm for Non-THP hole)

                                              c = standard fabrication allowance
                                                   ( 0.25mm for Boards up to 300mm
                                                     0.45mm for Boards from 300mm to 450mm
                                                     0.55mm for Boards from 450mm to 600mm)

 

When eyelets or standoff terminals are used, the pads should be designed to have a minimum diameter of at least 0.5mm greater than the maximum diameter of the projection eyelet or solder terminal flange.

Annular Ring Requirements

An annular ring is required for all plated-through holes. The minimum annular ring is the minimum amount of copper (at the narrowest point) between the edge of the hole and the edge of the pad after plating the finished hole.

 

Spacing of Conductors for Various Voltages

In order to prevent a voltage breakdown (arcing) between adjacent conductors, the minimum space between the conductors, as set out in the table below, should be adhered to. Please note that the minimum spacing which can be manufactured is 0.13mm (0.005")

Voltage between Conductors (DC or AC Peak) Minimum Spacing
Bare Board Assembly
B1 B2 B3 B4 A5 A6 A7
0 - 15 V 0.1mm
(0.004")
0.64mm
(0.025")
0.64 mm
(0.025")
0.13 mm
(0.005")
0.13 mm
(0.005")
0.13 mm
(0.005")
0.13 mm
 (0.005")
16 - 30 V 0.1mm
(0.004")
0.64mm
(0.025")
0.64 mm
(0.025")
0.13 mm
(0.005")
0.13 mm
(0.005")
0.25 mm
(0.010")
0.13 mm
(0.005")
31 - 50 V 0.1mm
(0.004")
0.64mm
(0.025")
0.64 mm
(0.025")
0.13 mm
(0.005")
0.13 mm
(0.005")
0.38 mm
(0.015")
0.13 mm
(0.005")
51 - 100 V 0.1mm
(0.004")
0.64mm
(0.025")
1.5mm
(0.060")
0.13 mm
(0.005")
0.13 mm
(0.005")
0.50 mm
(0.020")
0.13 mm
(0.005")
101 - 150 V 0.2mm
(0.008")
0.64mm
(0.025")
3.18mm
(0.125")
0.38 mm
(0.015")
0.38 mm
(0.015")
0.75 mm
(0.030")
0.38 mm
(0.015")
151 - 170 V 0.2mm
(0.008")
1.27mm
(0.050")
3.18mm
(0.125")
0.38 mm
(0.015")
0.38 mm
(0.015")
0.75 mm
(0.030")
0.38 mm
(0.015")
171 - 250 V 0.2mm
(0.008")
1.27mm
(0.050")
6.4mm
(0.250")
0.38 mm
(0.015")
0.38 mm
(0.015")
0.75 mm
(0.030")
0.38 mm
(0.015")
251 - 300 V 0.2mm
(0.008")
1.27mm
(0.050")
12.7mm
(0.500")
0.38 mm
(0.015")
0.38 mm
(0.015")
0.75 mm
(0.030")
0.38 mm
(0.015")
301 - 500 V 0.25mm
(0.010")
2.54mm
(0.100")
12.7mm
(0.500")
0.75 mm
(0.030")
0.75 mm
(0.030")
1.5 mm
(0.060")
0.75 mm
(0.030")
Greater than 500 V 0.0025mm/V
(0.0001 "/V)
0.005mm/V
(0.0002 "/V)
0.0254mm/V
(0.001 "/V)
0.00305mm/V
(0.00012 "/V)
0.00305mm/V
(0.00012 "/V)
0.00305mm/V
(0.00012 "/V)
0.00305mm/V
(0.00012 "/V)

 

 B1 - Internal Conductors

 B2 - External Conductors, uncoated, sea level to 10 000 feet

 B3 - External Conductors, uncoated, over 10 000 feet
 B4 - External conductors with permanent polymer coating (any altitude)
 A5 - External Conductors with conformal coating over assembly (any altitude)
 A6 - External Component lead/termination, uncoated
 A7 - External Component lead/termination, with conformal coating (any altitude)

 

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