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PCB外(wai)派駐場工程師如何(he)設計抗(kang)靜電設計“放電針”

time : 2023-04-11 14:53       作者:凡億pcb

靜電(dian)(dian)(dian)(dian)對(dui)電(dian)(dian)(dian)(dian)路的(de)(de)(de)危害(hai)很大(da)(da),靜電(dian)(dian)(dian)(dian)的(de)(de)(de)瞬間(jian)電(dian)(dian)(dian)(dian)壓(ya)為幾(ji)千伏到幾(ji)十萬伏,冬天人體靜電(dian)(dian)(dian)(dian)至少(shao)在幾(ji)萬伏以上,如此(ci)大(da)(da)的(de)(de)(de)靜電(dian)(dian)(dian)(dian)進入電(dian)(dian)(dian)(dian)路后(hou)會對(dui)電(dian)(dian)(dian)(dian)路中較弱的(de)(de)(de)元器件(jian)如芯片等造成(cheng)(cheng)致命損傷,因(yin)此(ci)電(dian)(dian)(dian)(dian)路靜電(dian)(dian)(dian)(dian)保(bao)護(hu)(hu)一直是(shi)電(dian)(dian)(dian)(dian)路設(she)計不可缺少(shao)的(de)(de)(de)環(huan)節。常規方案是(shi)用快速二(er)極(ji)管(guan)、氣體放電(dian)(dian)(dian)(dian)管(guan)、保(bao)險(xian)絲等組合(he)成(cheng)(cheng)保(bao)護(hu)(hu)電(dian)(dian)(dian)(dian)路實現(xian)對(dui)靜電(dian)(dian)(dian)(dian)的(de)(de)(de)消(xiao)除,達到保(bao)護(hu)(hu)電(dian)(dian)(dian)(dian)路元器件(jian)的(de)(de)(de)目的(de)(de)(de)。但(dan)是(shi)該保(bao)護(hu)(hu)方案大(da)(da)幅度增加(jia)了電(dian)(dian)(dian)(dian)路成(cheng)(cheng)本(ben),擴大(da)(da)了PCB板的(de)(de)(de)使用面積(ji),不利于產品小型化(hua)低成(cheng)(cheng)本(ben)設(she)計。
 
一(yi)般(ban)情況下(xia),使干燥(zao)空氣擊穿的(de)(de)電(dian)(dian)(dian)(dian)場強度(du)約為(wei) 3 × 10^6 V/m,將(jiang)該量記為(wei)E,靜電(dian)(dian)(dian)(dian)壓(ya)記為(wei)U(單(dan)位(wei)為(wei)伏(fu)),放(fang)(fang)電(dian)(dian)(dian)(dian)距離記為(wei)S(單(dan)位(wei)為(wei)米),則有(you)S=U/E,若靜電(dian)(dian)(dian)(dian)壓(ya)為(wei)3000V,則尖端放(fang)(fang)電(dian)(dian)(dian)(dian)間距約為(wei)1mm;根據這種放(fang)(fang)電(dian)(dian)(dian)(dian)特性(xing),可(ke)在(zai)受保(bao)(bao)護器(qi)件的(de)(de)電(dian)(dian)(dian)(dian)路中加入(ru)一(yi)個(ge)呈鋸齒狀(zhuang)的(de)(de)尖端放(fang)(fang)電(dian)(dian)(dian)(dian)對,該放(fang)(fang)電(dian)(dian)(dian)(dian)對是在(zai)PCB板上的(de)(de)兩個(ge)鋸齒形銅皮,銅皮不能蓋油。鋸齒狀(zhuang)尖端放(fang)(fang)電(dian)(dian)(dian)(dian)對的(de)(de)一(yi)半在(zai)信(xin)號電(dian)(dian)(dian)(dian)路中,另一(yi)半在(zai)電(dian)(dian)(dian)(dian)路板電(dian)(dian)(dian)(dian)源地上,尖端間距為(wei)1mm,這樣可(ke)實現3000V以上的(de)(de)靜電(dian)(dian)(dian)(dian)放(fang)(fang)電(dian)(dian)(dian)(dian),達到保(bao)(bao)護元(yuan)器(qi)件的(de)(de)目的(de)(de),降低(di)了產品成(cheng)本(ben)和(he)PCB板需求(qiu)面積。
 
PCB外(wai)派設(she)(she)計工程師在實(shi)際設(she)(she)計時,可(ke)(ke)(ke)在某一個保護器件上并排(pai)放(fang)(fang)置(zhi)多個尖(jian)端(duan)放(fang)(fang)電(dian)(dian)(dian)(dian)對(dui),以(yi)實(shi)現徹(che)底干凈的消除靜電(dian)(dian)(dian)(dian),尖(jian)端(duan)間距可(ke)(ke)(ke)設(she)(she)置(zhi)為0.4mm。在電(dian)(dian)(dian)(dian)路接口處,信(xin)號線位置(zhi)(高(gao)壓(ya)(ya)信(xin)號線除外(wai)),低(di)壓(ya)(ya)電(dian)(dian)(dian)(dian)源處均(jun)可(ke)(ke)(ke)放(fang)(fang)置(zhi),尖(jian)端(duan)放(fang)(fang)電(dian)(dian)(dian)(dian)對(dui)附近及上方不要(yao)有(you)導線等其他易燃體,因(yin)為尖(jian)端(duan)放(fang)(fang)電(dian)(dian)(dian)(dian)會有(you)瞬間電(dian)(dian)(dian)(dian)火花產生,在一些特殊情(qing)況下(xia)可(ke)(ke)(ke)以(yi)采(cai)用此方法(fa)去較好地(di)消除靜電(dian)(dian)(dian)(dian)威(wei)脅(xie)。具體設(she)(she)計參考如下(xia)圖:
 


在實際PCB設計制造中,要保持放電針的阻焊開窗和且保留焊盤尖端,防止加工加工后的成品無法實現放電功能!