Backdrill相關設置及Backdrill文檔輸出方法

如果PCB的層數超過4層，PCB的走線從其中的某兩層走線（除從表層到表層外），總會產生類似于下圖這種情形的stub：產生多余的鍍銅部分，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
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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.
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3.壓接的接插件backdrill：要保證良好的接觸,? 必須保證下面的值：
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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.

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.
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定義方法：在Manufacture>NC …Backdrill setup and analysis
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6.NC>DRILLLENGEND，輸出鉆孔表，注意要選擇 Include backdrill
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7.產生鉆孔文件，輸出鉆孔文件，也要s Include backdrill
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