应用可靠性6_PCB设计_部分2.pdf

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1、36Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6远离易出现高温或者高耗能的器件（大电阻、散热器等）远离易出现高压、高频和浪涌干扰的设备（电动机、变压器等）远离易积累灰尘、异物的区域远离易形成静电的地方（如操作人员可直接触摸到的地方，金属物体等）发热量大的器件尽可能靠近容易散热的表面尽量减少连线、接触点的数目（尽量不采用IC座，尽量采用SMT）6.6 PCB布局微电子器件在整机中的位置Copyright by Yiqi Zhuang 20

2、09 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6易碎元器件布局时尽量靠近传送边或受应力较小区域，其轴向尽量与进板方向平行6.6 PCB布局机械强度考虑大而重的元器件应安放在PCB固定支架附近，以提高PCB的固有频率及增加防振能力对称（差分，桥式）电路的元器件尽量对称排列，使分布参数对称37Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6经常

3、插拔器件或板边连接器周围3mm范围内尽量不布置SMD，以防止连接器插拔时产生的应力损坏器件任何钻孔需离板边1mm以上，以防破孔SMD与DIP的元件至少需有1mm的距离双面摆件时，背面SMD与DIP元件孔之间至少需有2mm的距离元件距离板边至少要有5mm以上的距离6.6 PCB布局SMD元件的布局Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.6 PCB布局波峰焊SMD的安全间距相同类型器件相同类型器件38Copyright by Yiq

4、i Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.6 PCB布局波峰焊SMD的安全间距(续)不同类型器件不同类型器件Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.7 PCB接地电源线与地线尽量靠近好处好处长距离平行的电源线与电线之间形成了去耦电容电源线与地线若承载着大小相近且方向相反的电流时，两者所产生的磁感应

5、强度会相互抵消方式方式电源线与地线要么并排平行地放在PCB的同一层上，要么放在相邻的两层电源线、地线要尽量的粗，大于正常线宽3倍以上较好较差39Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6网状地线：高频数字电路梳状地线：低频模拟电路网状地线：高频数字电路梳状地线：低频模拟电路6.7 PCB接地地线的走法Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6

6、Copyright by Yiqi Zhuang 2009 V4.6NoisyAnalogDigital6.7 PCB接地数模混合电路:分区高频多点接地低频单点接地全局单点接地在任意一个方向上,垂直地线与水平地线至少每隔6cm连接一次(双面板则搁一个过孔)40Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.7 PCB接地数模混合电路:分板Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiq

7、i Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.7 PCB接地复杂电路的地线电压、电流差别大的器件尽量远离，以避免产生干扰甚至打火41Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.7 PCB接地PCB接口的排布所有信号线与地线的间距不要超过13mm对于特别敏感且较长的信号线，应每隔一定间隔与其地线对调Copyright by Yiqi Zhuang 2009 V4.6Copy

8、right by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.7 PCB接地PCB接口的排布(续)差差最好（但减少了信号线的数目）最好（但减少了信号线的数目）42Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6湖泽式多点接地单面PCB多点接地双面PCB多点接地6.7 PCB接地多点接地方式:PCB内部Copyright by Yiqi Zhuang 2009 V4.6Co

9、pyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.7 PCB接地多点接地方式:PCB与机箱在任意方向上，PCB与机箱接地点之间的距离不能超过/20（64MHz信号的/20=23.4cm）43Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.7 PCB接地多点接地方式:PCB与机箱(续)PCB与机箱间多点接地实例：计算机主板与机箱间多点接地实例：计算机主板

10、Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6对于敏感元件和I/O端口使用保护环和填充地，保护环应单点接地6.7 PCB接地保护环和填充地44Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6在时钟产生电路铺设接地敷铜面，以减少对周边电路的电磁干扰6.7 PCB接地时钟产生电路的局部屏蔽

11、Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.7 PCB接地时钟产生电路的局部屏蔽(续)45Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6与大面积铜箔相比，铜箔网格的附着力更高，否则铜箔受热可能膨胀脱落，但需均匀分布对高频信号的接地效果比接地平面更好（考虑到趋肤效应）更加有利于散

12、热，占用板表面积比例低，有利于提高元件密度网格单元间距不应大于/20，典型值为0.5inch（1.27cm）6.7 PCB接地地线网格Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6好处是可防止产生虚焊点量，因为焊接时热量不会很快地被散发掉。缺点是增加了工作时的热阻，而且增加了地平面的不连续性，不利于电磁兼容6.7 PCB接地焊盘的接地方式46Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yi

13、qi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.7 PCB接地实例有利于减少集成电路引脚之间的分布电容及信号之间的串扰对敏感信号线的屏蔽保护Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.7 PCB接地芯片封装下的接地IC封装下的接地，可以减少IC自身产生的噪声影响47Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zh

14、uang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6电源层比地层内缩20H（H为电源层与地层之间的距离），可有效抑制边缘辐射（约可降低70左右）电源/地平面边缘附近的射频电流很强，易对周边形成辐射干扰6.7 PCB接地20H原则:规则Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.7 PCB接地20H原则:实例4层PCB板20H原则应用实例48Copyright by Yiqi Zhuang

15、2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.7 PCB接地信号回流方式依靠地线（地平面）的信号回流依靠电源线（电源平面）的信号回流Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.7 PCB接地在地平面开槽的影响问题问题信号回流线过长，易对其它信号产生干扰，且使本信号畸变增加了接地阻抗对策对策尽量不开槽，在槽上不走或不跨信号线

16、信号线不要跨越地平面或电源平面内的间隙49Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.7 PCB接地信号线不要跨越隔离槽错误正确错误正确Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.7 PCB接地高频信号利用电容通过隔离槽电容的容量必须选择合适，否则会导致信号相位发生不期望

17、的变化50Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.7 PCB接地在地平面开过孔的影响与开槽的影响类似Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6接地面上尽量少开过孔，空隙也要尽可能地少接地面上尽量少开过孔，空隙也要尽可能地少6.7 PCB接地过孔导致的信号环路好差51Co

18、pyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.7 PCB接地过孔导致的信号环路(续1)等效电路过孔布置的两种方案过孔布置的两种方案好差Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6不要出现悬浮的导电岛，若为散热与屏蔽，应接地6.7 PCB接地导电岛(Island)52Copyrigh

19、t by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.7 PCB接地放大器输入信号的接地:问题输入信号输入信号输入信号放大器板放大器板设备机壳放大器板设备机壳较差：输入信号地线接到放大器PCB板地线的任意一点差：输入信号接到设备机壳地最差：输入信号接到外部地Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6

20、6.7 PCB接地放大器输入信号的接地:对策输入信号放大器板输入信号地线接到放大器输入端地线采用差分方式放大，消除共模干扰输入信号放大器板53Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.7 PCB接地放大器输出信号的接地:问题放大器输出接地回路与输入接地回路之间有公共阻抗Rs放大器输入电压Vin放大器实际输入电压Vin=Vin-(IoutRs)Copyright by Yiqi Zhuang 2009 V4.6Copyright b

21、y Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.7 PCB接地放大器输出信号的接地:对策输出信号地线直接接到PCB的输入端地线，但仍然存在PCB到供电单元PSU的公共阻抗Rs，适合较大电流输出输出信号地线直接接到供电单元PSU的地线端，彻底消除公共阻抗Rs，适合很大电流输出54Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.8 PCB布线走线寄生效应:线阻抗对串扰的影

22、响PCB走线的特性阻抗越小，串扰越弱Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.8 PCB布线布线优先次序长度缩短优先原则长度缩短优先原则：布线设计的首要规则是极小化布线的长度，尤其是时钟振荡电路、快速开关电路和电流支路。布线越短，则干扰越小，寄生电抗越低，辐射也更少关键信号线优先原则关键信号线优先原则：电源、模拟小信号、高速信号、时钟信号和同步信号等关键信号优先布线密度优先原则密度优先原则：从单板上连接关系最复杂的器件着手布线，从

23、单板上连线最密集的区域开始布线尽量为时钟信号、高频信号、敏感信号等关键信号提供专门的布线层，并保证其最小的回路面积必要时应采取手工优先布线、屏蔽和加大安全间距等方法，来保证信号质量55Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6尽量缩短高频电路的连线（特别是时钟线）（短线规则）6.8 PCB布线长度控制规则对高频信号线，布线长度不得与其波长成整数倍关系，以免产生谐振现象。（谐振规则）Copyright by Yiqi Zhuang 20

24、09 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.8 PCB布线拐角规则:拐角带来的信号反射90度角，拐角反射大（、）45度角，拐角反射小（、）56Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.8 PCB布线拐角规则:直角或锐角带来的问题走线阻抗不连续（直角走线导致的阻抗变化约为720），导致信号的反射走线寄生电容上升（4mils宽

25、、介电常数4.3、特征阻抗50的传输线，一个直角带来的电容增加约为0.01pF），加大信号的延迟局部电场强度加大，产生高频信号的发射刻蚀时易形成局部走线变窄，阻碍大电流通过布线面积大于钝角Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.8 PCB布线拐角规则:对策走线避免急剧的弯曲和尖角采用45角取代90角，且拐角附近的线长不可过小（大于线宽的3倍）圆弧角更好，但对计算机的处理能力以及工艺实现能力要求高57Copyright by Yi

26、qi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6层间串扰往往比线间串扰更大，因此不同层的布线尽可能正交或大角度交叉6.8 PCB布线方向控制规则Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.8 PCB布线覆铜均匀化规则规则双面板：将总的覆铜量平均分配到电路板的两个面上多层板：将总的覆铜量平均分配到电路板的所有层

27、上如布线本身无法实现均匀化，可以将所有的空白出添铜，并使其接地或电源目的防止电路板各处所受张力不均匀，导致温度变化时产生龟裂等现象防止层叠不平整导致制造问题，例如影响电镀层的均匀性58Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.8 PCB布线禁止电源层重叠规则不同电源层在空间上要避免重叠。以便减少不同电源之间的干扰，特别是一些电压相差很大的电源之间，难以避免时可考虑中间隔地层。Copyright by Yiqi Zhuang 200

28、9 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.8 PCB布线走线闭环检查规则防止信号线在不同层间形成自环，以免引起辐射干扰59Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.8 PCB布线3W规则两根印制线的中心距大于3倍印制线的宽度，可保持70%的电场不互相干扰（若使用10W的间距，可保证98%的电场不互相干扰），对非高速线可不使

29、用该规则Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.8 PCB布线3W规则(续)信号线-信号线信号线-通孔-信号线信号线-时钟线-信号线边-信号线-差分线-差分线-信号线-边60Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6较差较好对于不得不走的高频平行长线，可以加接地线来进行

30、隔离6.8 PCB布线平行走线规则Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.8 PCB布线环路与分支回路：高频信号发射，对周边电路形成干扰；易感应来自周边的高频信号，对自身电路形成干扰分支：容易感应或接收来自外部的静电脉冲，也易形成高频辐射分支环路分支环路61Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Z

31、huang 2009 V4.6当交变电流通过闭合回路时，会在回路周围产生电磁场，从而形成干扰。电流频率越高，回路面积越大，则这种干扰就越大。因此，任何信号线（尤其是高频时钟线）都不要形成环路，如不可避免，环路面积应尽量小（环路最小规则）。6.8 PCB布线环路:问题的由来GNDISignalRadiated EmissionPCBCopyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.8 PCB布线环路:两点接地形成环路两点接地单点接地62Co

32、pyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.8 PCB布线环路:实例1Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.8 PCB布线环路:实例2较差较好63Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 200

33、9 V4.6Copyright by Yiqi Zhuang 2009 V4.66.8 PCB布线环路:实例3无交链面积，干扰小有交链面积，干扰较大有很大的交链面积，干扰最大Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6较好较差6.8 PCB布线环路:实例464Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhua

34、ng 2009 V4.6电源线紧靠地线，使电源线与地线形成的环路面积最小6.8 PCB布线环路:实例5Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6并联导线应合并6.8 PCB布线环路:实例665Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6较差较好多条电源及地线应连接成网络状6.8

35、 PCB布线环路:实例7Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6单点接地，单点接电源线，以避免电源环路和地线环路6.8 PCB布线环路:实例866Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.8 PCB布线环路:实例9采用接地平面和电源平面Copyright by Yiqi

36、 Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.8 PCB布线分支:产生高频辐射GND WirePCBI/O Cable1cmGND Plane or Grid67Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.5 PCB布线分支:导致波形畸变Copyright by Yiqi Zhuang 2009 V4.6C

37、opyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.8 PCB布线分支;改为一笔划布线分支布线：易产生高频辐射，同时特性阻抗被改变而导致反射一笔画布线：不易产生高频辐射，但线路的总长度增加68Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6减少分支一般不允许出现一端浮空的布线（Dangling Line)。（走线的开环检查规则）6.8 PCB布线分支:设计

38、实例Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.8 PCB布线分支:长度控制如不得不出现分支，也要尽量控制分支的长度，一般的要求是Tdelay=Trise/20 69Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6每个VLSI芯片的GND与VCC间应接去耦电容，以实现电源滤波与去

39、耦6.8 PCB布线去耦电容:作用Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.8 PCB布线去耦电容:接地层及电源层使用双面PCB情形使用多层PCB情形70Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.66.8 PCB布线去耦电容:电路图要明确安装位置较差较好最好Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6Copyright by Yiqi Zhuang 2009 V4.6去耦电容的位置应尽量靠近芯片，而且芯片与去耦电容之间的线应尽量短而粗，最好不要有过孔（与芯片在同一PCB层）较好较差6.8 PCB布线去耦电容:尽量靠近芯片