Complete Shield

This item checks for a shielding ratio on design. Ground shielding should consider the effect on impedance change.

High speed design utilizes ground planes to stabilize signal transmission. However, use of solid ground planes is restricted in miniaturized and high-density designs, so use of partial ground plane and ground traces becomes common. Since a perfect shielding is impossible, designers should carefully consider these in their designs. In general, with considering pin and via usages, minimum of 80 percent shielding is recommended.
  • Item: Input item name.
  • Check Type: Define the shield checking method of net.
    • Separate Net: PollEx DFE detects existence of shielding net(s) within specific distance per every segment. The DFE regards only the portion of shielding net which is parallel with target net.


      Figure 1.
    • Merged Net: The DFE extends the searching area with the same amount of specific distance, then PollEx DFE detects existence of shielding net(s) within that region. This method is more accurate than Separate Net method, however it takes more time.


      Figure 2.
  • Net: Define net group for shielding.
  • Shield Net: High speed signal will be shielded with nets in this GND net group.
  • Component Keep IN/OUT: Define test region. For example, you can test inside or outside the breakout region of CPU with different test values.
    • Component Group: Select required component group which is used for defining the test region.
    • Range (COC+distance): Enter the distance value to define breakout range. The COC (Component Overlap Check) plus this distance value is considered the test range.
    • Region:
      • IN: DFE tests the inside of the breakout region of target component.
      • OUT: DFE tests the outside of the breakout region of target component.
    • Target Layer: Select the required test layer.
      • All Layer: Test all layers.
      • Component Place Layer: Test only component placement layer.
  • H-Shield Check: Option for horizontal shield check.
    • Shield Distance: Distances from nets in net group from ground nets in GND net group.
    • Use Width Value(W): The value in Shield Distance is considered as multiple of Pattern Width.
    • Max: Specify maximum distance from differential pair net to ground. The DFE searches shielding net within this range.
    • Min: Specify minimum clearance from net to ground. If shield net exists closer than this clearance, it reports fail.
    • Min Horizontal Shield Ratio(%): Minimum shielding net length ratio against total net. If the shielding ratio is smaller than the given value, it is reported as failed. (Ratio = The total length of shielded portion of net/Total length of net)
    • Shield Ratio Calculation Type: Determine shield ratio calculation method.
    • All Layer: Calculate shield ratio for total net.
    • Per Layer: Calculate shield ratio per each layer.
    • Inner Layer: Calculate shield ratio for internal layer only.
    • Pin Escape: Enter a radius of circular region around pins to be excluded for the rule check.
    • Via Escape: Enter a radius of circular region around vias to be excluded for the rule check.
    • Exclude Short Pattern: Exclude the short length trace shorter than this value.
    • Include trace corner: The ground shield length at which signal bend is always longer than signal trace length. This leads to results that are not accurate. In order to eliminate this problem, the DFE ignores the bending position. When this function is selected, the DFE is calculated including the bending position in the shield ratio.

Guard Via Distance Check

The DFE check maximum via distance of shielding net.
  • Guard Via Range: Define the maximum distance from trace edge within which guard via should be exist. The DFE considers only the vias within this range as a guard via.
  • Max Via Distance: If the via distance is greater than this value, it is reported as failed.
  • Except PAD: Exclude pin pad for testing.
  • Merge Result Via Count: PollEx DFE shows the merged result of all errors on the same display.

V-Shield Check

Option for vertical shield check.
  • Vertical Shield Ratio Check:
  • Shield Distance (Extended V-Shield Width): Specify minimum required GND width of upper/below layer.
  • Min Vertical Shield Ratio(%):Minimum ground shielding ratio. If the shielding ratio is smaller than the given value, it is reported as failed. (Ratio = Shield Area/Net Area)
  • Shield Ratio Calculation Type: Determine test layer.
    • All Layer: Calculate shield ratio for total net.
    • Per Layer: Calculate shield ratio per each layer.
    • Inner Layer: Calculate shield ratio for internal layer only.
  • Exclude/Include Option
    • Check Layer:
    • L1 Layer: check one layer above and below.
    • L2 Layer: check two layers above and below.
    • L2-Hop Layer: check two layers, one layer apart above and below.


      Figure 3. Check layer
    • Pin Escape: Enter a radius of circular region around pins to be excluded for the rule check.
    • Via Escape: Enter a radius of circular region around vias to be excluded for the rule check.
    • Exclude Short Pattern: Exclude the short length trace shorter than this value.
    • Consider both upper and lower direction: Upon selecting, above and below layer will be tested if not wider layer side will be checked (above or below)
High speed signal’s 100 percent ground shielding is perfect, but it is impossible. Over 80 percent and shielding for all routed layers are recommendation.


Figure 4.

If there are ground planes on adjacent layers, shielding ground on the signal layer may alter impedance when it is too close to the signal trace. The effect of ground shielding on impedance change needs to be carefully considered.

The shielding must be done at the same distance on both sides of signal trace. If there is a shielding ground only on one side, it may cause EMI problems.

Ground shielding not only provides solutions for EMI but also reduces return path.