Me yasa layuka masu mahimmanci a PCB gefuna masu saurin tsoma bakin ESD?

Sake saita tsarin ya faru lokacin da aka gwada benci na ƙasa ta amfani da fitowar lamba ta ESD na 6KV a tashar ƙasa. Yayin gwajin, Y capacitor ɗin da aka haɗa da tashar jirgin ƙasa kuma an yanke aikin aikin dijital na ciki, kuma sakamakon gwajin bai inganta sosai ba.

Tsoma bakin ESD yana shiga cikin kewayon samfurin a cikin nau’ikan daban -daban. Don samfuran da aka gwada a wannan yanayin, wurin gwajin shine maƙasudin ƙasa, mafi yawan kuzarin katsalandan na ESD zai gudana daga layin ƙasa, wato, ESD na yanzu baya gudana kai tsaye zuwa cikin kewayen samfurin, amma , a cikin IEC61000-4-2 daidaitaccen yanayin gwajin ESD a cikin wannan kayan aikin tebur, tsawon layin ƙasa a cikin kusan 1m, Layin ƙasa zai samar da babban rashi na gubar (ana iya amfani da shi don kimanta 1 u H/m), tsangwamar fitowar wutar lantarki yana faruwa (adadi 1 sauyawa K) lokacin da aka rufe, madaidaicin mita (ƙasa da 1 ns yana tashi tare da fitowar electrostatic yanzu ba sa samfuran da aka gwada sun dace da rukunin yanar gizo na lantarki (FIG. 1 G point voltage in K ba sifili bane lokacin rufewa). Wannan wutar lantarki ba sifili a tashar ƙasa za ta ƙara shiga cikin kewayon samfurin. Hoto 1 ya ba da ƙirar ƙirar ƙimar ESD a cikin PCB a cikin samfurin.

FIG. 1 Tsarin zane na tsangwama na ESD yana shiga PCB a cikin samfurin

Hakanan ana iya ganin shi daga Hoto na 1 cewa CP1 (parasitic capacitance tsakanin fitarwa da GND), Cp2 (parasitic capacitance tsakanin PCB board da reference grounding floor), wurin aiki na PCB board (GND) da electrostatic sallama gun (ciki har da grounding waya na gun fitowar wutar lantarki) tare suna samar da hanyar kutse, kuma tsangwama na yanzu shine ICM. A cikin wannan hanyar kutse, allon PCB yana tsakiyar, kuma a bayyane PCB ke damun ta da fitowar wutar lantarki a wannan lokacin. Idan akwai wasu igiyoyi a cikin samfurin, tsangwama zai fi tsanani.

Ta yaya tsangwama ya kai ga sake saita samfurin da aka gwada? Bayan binciken PCB na samfurin da aka gwada, an gano cewa an sanya layin sarrafa saiti na CPU a cikin PCB a gefen PCB kuma a waje da jirgin GND, kamar yadda aka nuna a hoto 2.

Don bayyana dalilin da yasa layukan da aka buga a gefen PCB suna da saukin kutsawa, fara da ƙarfin parasitic tsakanin layin da aka buga a cikin PCB da farantin ƙasa. Akwai ƙarfin parasitic tsakanin layin da aka buga da farantin ƙasa, wanda zai dame layin siginar da aka buga a cikin allon PCB. An nuna zane -zanen ƙirar katsalandan na yanayin yau da kullun da ke tsangwama layin da aka buga a cikin PCB a cikin Hoto 3.

Hoto na 3 yana nuna cewa lokacin da tsangwama na yau da kullun (ƙarfin tsangwama na yau da kullun dangane da bene mai faɗi) ya shiga GND, za a samar da ƙarfin tsangwama tsakanin layin da aka buga a cikin allon PCB da GND. Wannan ƙarfin wutar tsangwama yana da alaƙa ba kawai don rashin daidaituwa tsakanin layin da aka buga da GND na allon PCB (Z a cikin Hoto na 3) amma har da ƙarfin parasitic tsakanin layin da aka buga da farantin ƙasa mai tushe a cikin PCB.

Tunanin cewa rashin daidaiton Z tsakanin layin da aka buga da allon PCB GND ba canzawa ba, lokacin da ƙarfin parasitic tsakanin layin da aka buga da bene mai faɗi ya fi girma, tsangwama na Vi tsakanin layin da aka buga da allon PCB GND ya fi girma. An haɗa wannan ƙarfin lantarki tare da ƙarfin aiki na al’ada a cikin PCB kuma zai shafi madaidaicin aiki a cikin PCB.

FIG. 2 Zane na ainihi na rabe -raben PCB na samfurin da aka gwada

FIG. 3 Halin katsalandan na yanayin yanayin katsalandan PCB da aka buga zane -zane

Dangane da dabara 1 don ƙididdige ƙarfin parasitic tsakanin layin da aka buga da farantin ƙasa na ƙasa, ƙarfin parasitic tsakanin layin da aka buga da farantin ƙasa na fa’ida ya dogara da nisa tsakanin layin da aka buga da farantin ƙasa (H a Tsarin 1) da kuma yanki daidai da filin wutar lantarki da aka kafa tsakanin layin da aka buga da farantin ƙasa mai nuni

A bayyane yake, don ƙirar da’irar a cikin wannan yanayin, layin siginar sake saitawa a cikin PCB an shirya shi a gefen allon PCB kuma ya faɗi a waje da jirgin GND, don haka layin siginar sake saiti zai shiga cikin matsala sosai, wanda ke haifar da sabon saiti na tsarin yayin ESD gwaji.