背钻 backdrill
如果PCB的层数超过4层，PCB的走线从其中的某两层走线（除从表层到表层外），总会产生类似于下图这种情形的stub：产生多余的镀铜部分，当电路信号的频率增加到一定高度后，多余的镀铜就相当于天线一样，产生信号辐射对周围的其他信号造成干扰，严重时将影响到线路系统的正常工作，Backdrill的作用就是将多余的镀铜用钻孔的方式钻掉，从而消除此类EMI问题。其操作步骤和注意事项如下：<IMG alt=给net设定Backdrill src="http://pagesadmin.ednchina.com/images/article/0427846e-8d62-4c99-8081-c35c88091f98/1.jpg" _max_pth_stub属性>
1.给net设定Backdrill_max_pth_stub属性
Property BACKDRILL_MAX_PTH_STUB
Purpose Identificationofnetstargetedforbackdrilling
Usage Required
Value Maxallowablestubinlength(databaseunits)
Objects Nets
Backdrillanalysisflag S
2.给net设定Backdrill_min_pin_pth属性，Backdrill_min_pin_pth考虑可靠性,必须保证BACKDRILL去掉多余镀铜后,保证一定剩余一定长度.
<IMG alt=给net设定Backdrill src="http://pagesadmin.ednchina.com/images/article/0427846e-8d62-4c99-8081-c35c88091f98/2.jpg" _min_pin_pth属性>
Property BACKDRILL_MIN_PIN_PTH
Purpose Ensuresminimumpinplatingdepthisnotcompromised
Usage Optional
Value Length
Objects Symbols,pins
Backdrillanalysisflag P
3.压接的接插件backdrill：要保证良好的接触,必须保证下面的值：
http://pagesadmin.ednchina.com/images/article/0427846e-8d62-4c99-8081-c35c88091f98/3.jpg
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>wherevalues=pincontactrange;thisvaluemustbeobtainedfromthemanufacturer
Objects Symbols
Backdrillanalysisflag n/a
4.有些场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 Excludesobjectsfrombackdrillingeventhoughstubmaybepresent
Usage Optional
Value Boolean(true/false)
Objects Symbols,pins,vias
Backdrillanalysisflag X
背钻与否，不仅取决于数据速率还取决于板厚，下面简单的公式
: B# ?: O. `! u. L: Po2 e/ P板厚（mil）<300/数据速率，不需要背钻；
9 g, T$ n0 L0 k" V, l& Z6 q300/数据速率<板厚（mil）<600/数据速率，根据具体情况决定是否背钻；
, r; a! {3 k8 U5 |b- l0 L板厚（mil）>600/数据速率，必须背钻。
补充一下，backdrill工艺已经比较成熟，成品率也能够达到要求，只是采用backdrill会增加10%~20%的成本 ddddddddddddddddddddddddddddd 顶上去！！！！！
页:
[1]
