IPC Material

6.3 Electrical Clearance

Spacing between conductors on individual layers should be maximized whenever possible. The minimum spacing between conductors, between conductive patterns, layer to layer conductive spaces (z=axis), and between conductive materials,such as conductive markings or mounting hardware, and conductors shall be in accordance with Table 6-1, and defined on the master drawing. For additional information on process allowances effecting electrical clearance, see Section 10.

When mixed voltages appear on the same board and they require separate electrical testing, the specific areas shall be identified on the master drawing or appropriate test specification. When employing high voltages and especially AC and pulsed voltages greater than 200 volts potential, the dielectric constant and capacitive division effect of the material must be considered in conjunction with the recommended spacing.

For voltages greater than 500V, the (per volt) table values must be added to the 500V values. For example, the electrical spacing for a Type B1 board with 600V is calculated as:

600V - 500V = 100V

0.25 mm + (100V x 0.0025 mm)

= 0.50 mm clearance

When, due to the criticality of the design, the use of other conductor spacing is being considered, the conductor spacing on individual layers (same plane) shall be made larger than the minimum spacing required by Table 6-1 whenever possible. Board layout should be planned to allow for the maximum spacing between external layer conductive areas associated with high impedance or high voltage circuits. This will minimize electrical leakage problems resulting from condensed moisture or high humidity.
Voltage Between Conductors (DC or AC Peaks) Minimum Spacing
  Bare Board Assembly
B1 B2 B3 B4 A5 A6 A7
0-15 0.05 mm 0.1 mm 0.1 mm 0.05 mm 0.13 mm 0.13 mm 0.13 mm
16-30 0.05 mm 0.1 mm 0.1 mm 0.05 mm 0.13 mm 0.25 mm 0.13 mm
31-50 0.1 mm 0.6 mm 0.6 mm 0.13 mm 0.13 mm 0.4 mm 0.13 mm
51-100 0.1 mm 0.6 mm 1.5 mm 0.13 mm 0.13 mm 0.5 mm 0.13 mm
101-150 0.2 mm 0.6 mm 3.2 mm 0.4 mm 0.4 mm 0.8 mm 0.4 mm
151-170 0.2 mm 1.25 mm 3.2 mm 0.4 mm 0.4 mm 0.8 mm 0.4 mm
171-250 0.2 mm 1.25 mm 6.4 mm 0.4 mm 0.4 mm 0.8 mm 0.4 mm
251-300 0.2 mm 1.25 mm 12.5 mm 0.4 mm 0.4 mm 0.8 mm 0.8 mm
301-500 0.25 mm 2.5 mm 12.5 mm 0.8 mm 0.8 mm 1.5 mm 0.8 mm
> 500

See 6.3 for calculation.

 0.0025 mm/volt 0.005 mm/volt 0.025 mm/volt 0.00305 mm/volt 0.00305 mm/volt 0.00305 mm/volt 0.00305 mm/volt
  • B1 - Internal Conductors
  • B2 - External Conductors, uncoated, sea level to 3050 m
  • B3 - External Conductors, uncoated, over 3050 m
  • B4 - External Conductors, with permanent polymer coating (any elevation)
  • A5 - External Conductors, with conformal coating over assembly (any elevation)
  • A6 - External Component lead/termination, uncoated
  • A7 - External Component lead/termination, with conformal coating (any elevation)

6.3.1 B1 - Internal Conductors

Internal conductor-to-conductor and conductor-to-PTH (plated-through-hole) electrical clearance requirements at any elevation.

6.3.2 B2 - External Conductors, Uncoated, Sea Level to 3050 m

Electrical clearance requirements for uncoated external conductors are significantly greater than for conductors that will be protected from external contaminants with conformal coating. If the assembled end product is not intended to be conformably coated, the bare board conductor spacing shall require the spacing specified in this category for applications from sea level to an elevation of 3050 m.

6.3.3 B3 - External Conductors, Uncoated, Over 3050 m

External conductors on uncoated bare board applications over 3050 m require even greater electrical spacing than those identified in category B2.

6.3.4 B4-External Conductors, with Permanent Polymer Coating (Any Elevation)

When the final assembled board will not be conformably coated, a permanent polymer coating over the conductors on the bare board will allow for conductor spacing less than that of the uncoated boards defined by category B2 and B3. The assembly electrical clearances of lands and leads that are not conformably coated require the electrical clearance requirements stated in category A6. This configuration is not applicable for any application requiring protection from harsh, humid, contaminated environments.

Typical applications are computers, office equipment, and communication equipment, bare boards operating in controlled environments in which the bare boards have a permanent polymer coating on both sides. After they are assembled and soldered boards are not conformal coated, leave the solder joint and soldered land uncoated.
Note: All conductors, except for soldering lands, must be completely coated in order to ensure the electrical clearance requirements in this category for coated conductors.

6.3.5 A5 - External Conductors, with Conformal Coating Over Assembly (Any Elevation)

External conductors that are intended to be conformal coated in the final assembled configuration, for applications at any elevation, will require the electrical clearances specified in this category.

Typical applications are military products where the entire final assembly will be conformal coated. Permanent polymer coatings are not normally used, except for possible use as a solder resist. However, the compatibility of polymer coating and conformal coating must be considered, if used in combination.

6.3.6 A6 - External Component Lead/Termination, Uncoated

External component leads and terminations, that are not conformal coated, require electrical clearances stated in this category.

Typical applications are as previously stated in category B4. The B4/A6 combination is most commonly used in commercial, non-harsh environment applications in order to obtain the benefit of high conductor density protected with permanent polymer coating (also solder resist), or where the accessibility to components for rework and repair is not required.

6.3.7 A7 - External Component Lead/Termination, with Conformal Coating (Any Elevation)

As in exposed conductors versus coated conductors on bare board, the electrical clearances used on coated component leads and terminations are less than for uncoated leads and terminations.