如果PCB的層數(shù)超過4層，PCB的走線從其中的某兩層走線（除從表層到表層外），總會產(chǎn)生類似于下圖這種情形的stub：產(chǎn)生多余的鍍銅部分，當電路信號的頻率增加到一定高度后，多余的鍍銅就相當于天線一樣，產(chǎn)生信號輻射對周圍的其他信號造成干擾，嚴重時將影響到線路系統(tǒng)的正常工作，Backdrill的作用就是將多余的鍍銅用鉆孔的方式鉆掉，從而消除此類EMI問題。其操作步驟和注意事項如下：
1.給net設定Backdrill_max_pth_stub屬性
Property | BACKDRILL_MAX_PTH_STUB |
Purpose | Identification of nets targeted for backdrilling |
Usage | Required |
Value | Max allowable stub in length (database units) |
Objects | Nets |
Backdrill analysis flag | S |
2.給net設定Backdrill_min_pin_pth屬性， Backdrill_min_pin_pth 考慮可靠性, 必須保證BACKDRILL去掉多余鍍銅 后, 保證一定剩余一定長度.
Property | BACKDRILL_MIN_PIN_PTH |
Purpose | Ensures minimum pin plating depth is not compromised |
Usage | Optional |
Value | Length |
Objects | Symbols, pins |
Backdrill analysis flag | P |
3.壓接的接插件backdrill：要保證良好的接觸, 必須保證下面的值：
Property | BACKDRILL_PRESSFIT_CONNECTOR |
Purpose | Use on pressfit connectors to permit backdrilling from both sides of the board. Backdrill depth will not protrude into contact range as defined by the property string. |
Usage | Optional |
Value | <value1:value2> where values = pin contact range; this value must be obtained from the manufacturer |
Objects | Symbols |
Backdrill analysis flag | n/a |
4.有些場合不能用此功能的可以用下面的命令排除.
Exclusions
It may be necessary to exclude certain objects from backdrilling even though stub violations are present. The BACKDRILL_EXCLUDE property can be applied to symbols, pins or vias at both the library and design level using Edit - Property. Common examples might include solder tail connectors or a dense pin escape pattern in BGA areas. The PCB designer should consult with a manufacturing engineer before assuming all pin/via objects are suitable for backdrilling.
Property | BACKDRILL_EXCLUDE |
Purpose | Excludes objects from backdrilling even though stub may be present |
Usage | Optional |
Value | Boolean (true/false) |
Objects | Symbols, pins, vias |
Backdrill analysis flag | X |
5.定義層（可選）
User Overrides
In most cases, the backdrill layer ranges defined in the Backdrill Setup and Analysis user interface satisfy your requirements to manage stubs. The BACKDRILL_OVERRIDE property allows user-specified control of layer ranges for any pin or via and from ether side of the board or both. This is done regardless of violations that may result, such as testpoint conflicts or backdrilling through a connection. The override property was considered for the design of test coupons where the OEM wishes to evaluate the performance of the board fabricator with respect to the adherence of depth ranges. The designer may override the "to" layer to effectively drill out the layer where the trace connects the pin/via. The expected usage of this property is limited; please exercise caution to prevent accidental over-drilling.
Property | BACKDRILL_OVERRIDE |
Purpose | User-specified backdrill range |
Usage | Optional: special circumstances |
Value | TOP:<layer_name>:BOTTOM:<layer_name> |
Objects | Pins, Vias |
Backdrill analysis flag | O or W (warning) |
定義方法：在Manufacture>NC …Backdrill setup and analysis
6.NC>DRILLLENGEND，輸出鉆孔表，注意要選擇 Include backdrill
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7.產(chǎn)生鉆孔文件，輸出鉆孔文件，也要s Include backdrill
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