应用可靠性6_PCB设计_部分2

36CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6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）6.6PCB布局微电子器件在整机中的位置CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6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6.6PCB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37CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6经常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6.6PCB布局SMD元件的布局CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.66.6PCB布局波峰焊SMD的安全间距相同类型器件38CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.66.6PCB布局波峰焊SMD的安全间距(续)不同类型器件CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.66.7PCB接地电源线与地线尽量靠近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强度会相互抵消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39CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6网状地线：高频数字电路梳状地线：低频模拟电路6.7PCB接地地线的走法CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6NoisyAnalogDigital6.7PCB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)40CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.66.7PCB接地数模混合电路:分板CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.66.7PCB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41CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.66.7PCB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CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.66.7PCB接地PCB接口的排布(续)差昀好（但减少了信号线的数目）42CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6湖泽式多点接地单面PCB多点接地双面PCB多点接地6.7PCB接地多点接地方式:PCB内部CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.66.7PCB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λ/20（64MHz信号的λ/20=23.4cm）43CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.66.7PCB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CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6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6.7PCB接地保护环和填充地44CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6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6.7PCB接地时钟产生电路的局部屏蔽CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.66.7PCB接地时钟产生电路的局部屏蔽(续)45CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6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λ/20，典型值为0.5inch（1.27cm）6.7PCB接地地线网格CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6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6.7PCB接地焊盘的接地方式46CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.66.7PCB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CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.66.7PCB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47CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6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6.7PCB接地20H原则:规则CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.66.7PCB接地20H原则:实例4层PCB板20H原则应用实例48CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.66.7PCB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CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.66.7PCB接地在地平面开槽的影响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尽量不开槽，在槽上不走或不跨信号线信号线不要跨越地平面或电源平面内的间隙49CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.66.7PCB接地信号线不要跨越隔离槽错误正确CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.66.7PCB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的变化50CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.66.7PCB接地在地平面开过孔的影响与开槽的影响类似CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6接地面上尽量少开过孔，空隙也要尽可能地少6.7PCB接地过孔导致的信号环路好差51CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.66.7PCB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好差CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6不要出现悬浮的导电岛，若为散热与屏蔽，应接地6.7PCB接地导电岛(Island)52CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.6CopyrightbyYiqiZhuang2009V4.66.7PCB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昀差：输入信号接到