Ziningi izindlela zokuxazulula izinkinga ze-EMI. Izindlela zesimanje zokucindezelwa kwe-EMI zifaka: ukusebenzisa i-EMI suppression coatings, ukukhetha izingxenye zokucindezela ze-EMI ezifanele, kanye nomklamo wokulingisa we-EMI. Kusukela kokuyisisekelo PCB isakhiwo, lesi sihloko sidingida indima nezindlela zokuklama zokupakishwa kwezingqimba ze-PCB ekulawuleni imisebe ye-EMI.

Ukubeka ama-capacitor omthamo ofanele eduze kwamaphini wokuphakela amandla we-IC kungenza i-IC output voltage yeqe ngokushesha. Nokho, inkinga ayigcini lapha. Ngenxa yempendulo yemvamisa elinganiselwe yama-capacitor, lokhu kwenza ama-capacitor angakwazi ukukhiqiza amandla e-harmonic adingekayo ukushayela okukhiphayo kwe-IC ngokuhlanzekile kubhendi yefrikhwensi egcwele. Ngaphezu kwalokho, i-voltage yesikhashana eyakhelwe kubha yebhasi yamandla izokwakha ukwehla kwamandla kagesi ku-inductor yendlela yokuxhuma. Lawa ma-voltage esikhashana ayimithombo yokuphazamiseka ye-EMI yemodi evamile. Kufanele sizixazulule kanjani lezi zinkinga?

Ngokuqondene ne-IC ebhodini lethu lesifunda, ungqimba lwamandla oluzungeze i-IC lungathathwa njenge-capacitor ephezulu kakhulu, engaqoqa ingxenye yamandla evuzwe yi-discrete capacitor ehlinzeka ngamandla aphezulu-frequency ukuze ahlanzeke. okukhiphayo. Ngaphezu kwalokho, ukufakwa kwesendlalelo esihle samandla kufanele kube kuncane, ngakho-ke isignali yesikhashana ehlanganiswe yi-inductance nayo incane, ngaleyo ndlela inciphisa imodi evamile ye-EMI.

Yiqiniso, ukuxhumana phakathi kwesendlalelo samandla kanye nephinikhodi yamandla e-IC kumele kube kufushane ngangokunokwenzeka, ngoba umkhawulo okhuphukayo wesiginali yedijithali uya ngokushesha futhi ngokushesha, futhi kungcono ukuwuxhuma ngqo ku-pad lapho amandla e-IC. pin itholakala. Lokhu kumele kuxoxwe ngokwehlukana.

Ukuze ulawule i-EMI yemodi evamile, indiza yamandla kufanele isize ekuhlukaniseni futhi ibe ne-inductance ephansi ngokwanele. Le ndiza esebenza ngogesi kufanele kube izindiza eziklanywe kahle eziklanywe kahle. Omunye angase abuze, ukuthi kuhle kangakanani? Impendulo yombuzo incike ekubekweni kwamandla kagesi, izinto ezisetshenziswayo phakathi kwezingqimba, kanye nemvamisa yokusebenza (okungukuthi, umsebenzi wesikhathi sokukhuphuka kwe-IC). Ngokuvamile, isikhala sesendlalelo samandla singu-6mil, futhi isiphambano siyinto engu-FR4, amandla alinganayo esendlalelo samandla iyintshi yesikwele cishe angu-75pF. Ngokusobala, isikhala esincane sesendlalelo, sikhulu amandla.

Awekho amadivaysi amaningi anesikhathi sokukhuphuka se-100 kuya ku-300 ps, ​​​​kodwa ngokuya ngesivinini samanje sokuthuthukiswa kwe-IC, amadivayisi anesikhathi sokukhuphuka ebangeni le-100 kuya ku-300 ps azothola ingxenye ephezulu. Kumasekhethi anesikhathi sokukhuphuka esingu-100 kuye ku-300ps, isikhala sesendlalelo esingu-3mil ngeke sisafaneleka ezinhlelweni eziningi zokusebenza. Ngaleso sikhathi, kwakudingeka kusetshenziswe ubuchwepheshe bokubeka ngezingqimba ezinezikhala ezingaphansi kwe-1 mil, futhi esikhundleni sezinto ze-dielectric ze-FR4 ngezinto ezinama-dielectric constants aphezulu. Manje, ama-ceramics namapulasitiki e-ceramic angahlangabezana nezidingo zokuklama zamasekhethi wesikhathi sokukhuphuka angu-100 kuya ku-300 ps.

Nakuba izinto ezintsha nezindlela ezintsha zingase zisetshenziswe esikhathini esizayo, kumasekhethi anamuhla avamile angu-1 kuya ku-3ns, isikhala sesendlalelo esingu-3 kuya ku-6mil kanye nezinto ze-dielectric ze-FR4, ngokuvamile kwanele ukuphatha ama-harmonics asezingeni eliphezulu nokwenza isiginali yesikhashana ibe phansi ngokwanele. , okusho ukuthi, Imodi evamile EMI ingancishiswa kakhulu. Izibonelo zedizayini zokunqwabelanisa ezinezingqimba ze-PCB ezinikezwe kulesi sihloko zizothatha isikhala sesendlalelo esingu-3 kuya ku-6 mils.

Electromagnetic shielding

Ngokombono wokulandela isignali, isu elihle lokubeka izingqimba kufanele kube ukubeka yonke iminonjana yesignali isendlalelo esisodwa noma eziningi, lezi zingqimba ziseduze nongqimba lwamandla noma ungqimba lomhlabathi. Ngokunikezwa kwamandla, isu elihle lokubeka izingqimba kufanele kube ukuthi ungqimba lwamandla luseduze nongqimba lomhlabathi, futhi ibanga phakathi kongqimba lwamandla kanye nongqimba lomhlabathi lincane ngangokunokwenzeka. Yilokhu esikubiza ngesu “lokwendlalela”.

PCB stacking

Iluphi uhlobo lwesu lokupakisha olungasiza ukuvikela nokucindezela i-EMI? Uhlelo olulandelayo lokunqwabelanisa olunezendlalelo luthatha ukuthi amandla akhona ageleza kusendlalelo esisodwa, futhi i-voltage eyodwa noma ama-voltage amaningi asatshalaliswa ezingxenyeni ezihlukene zesendlalelo esifanayo. Indaba yezendlalelo zamandla amaningi izoxoxwa kamuva.

4-ungqimba ibhodi

Kunezinkinga ezimbalwa ezingaba khona ngomklamo webhodi lezingqimba ezi-4. Okokuqala, ibhodi lendabuko elinezingqimba ezine elinobukhulu obungama-mils angu-62, noma ngabe ungqimba lwesignali luphezu koqweqwe lwangaphandle, futhi izingqimba zamandla nomhlabathi zingaphakathi kwesendlalelo sangaphakathi, ibanga phakathi kohlaka lwamandla kanye nongqimba lomhlabathi. isenkulu kakhulu.

Uma imfuneko yezindleko ingeyokuqala, ungacabangela izindlela ezimbili ezilandelayo ebhodini elingokwesiko lezendlalelo ezi-4. Lezi zixazululo ezimbili zingathuthukisa ukusebenza kokucindezelwa kwe-EMI, kodwa zifaneleka kuphela izinhlelo zokusebenza lapho ukuminyana kwengxenye ebhodini kuphansi ngokwanele futhi kunendawo eyanele ezungeze izingxenye (beka ungqimba lwethusi wamandla adingekayo).

Inketho yokuqala ukukhetha kokuqala. Izendlalelo zangaphandle ze-PCB zonke ziyizingqimba zomhlabathi, futhi izingqimba ezimbili ezimaphakathi ziyizingqimba zesignali/zamandla. Ukunikezwa kwamandla kwesendlalelo sesignali kuhanjiswa ngomugqa obanzi, ongenza ukuthi i-impedance yendlela yokunikezwa kwamandla ibe phansi, futhi ukuvinjelwa kwendlela yesignali ye-microstrip nakho kuphansi. Ngokombono wokulawula kwe-EMI, lesi yisakhiwo se-PCB esendlalelo esingcono kakhulu esingu-4 esitholakalayo. Ohlelweni lwesibili, ungqimba lwangaphandle lusebenzisa amandla nomhlabathi, kanti izingqimba ezimbili ezimaphakathi zisebenzisa amasignali. Uma kuqhathaniswa nebhodi lendabuko elinezingqimba ezi-4, ukuthuthukiswa kuncane, futhi i-interlayer impedance impofu njengebhodi lendabuko elinezingqimba ezi-4.

Uma ufuna ukulawula i-trace impedance, uhlelo lokupakisha olungenhla kufanele luqaphele kakhulu ukuhlela imikhondo ngaphansi kwamandla kanye neziqhingi zethusi zomhlabathi. Ukwengeza, iziqhingi zethusi ekunikezeni amandla noma ungqimba lomhlabathi kufanele zixhunywe ngangokunokwenzeka ukuze kuqinisekiswe i-DC kanye nokuxhumeka kwe-low-frequency.

6-ungqimba ibhodi

Uma ukuminyana kwezingxenye ebhodini le-4-layer liphakeme kakhulu, ibhodi le-6-layer lingcono kakhulu. Nokho, ezinye izikimu zokunqwabelanisa ekwakhiweni kwebhodi lezingqimba eziyisi-6 azilungile ngokwanele ukuvikela inkambu kazibuthe, futhi zinomthelela omncane ekwehlisweni kwesignali yesikhashana yebhasi lamandla. Izibonelo ezimbili kuxoxwa ngazo ngezansi.

Esimweni sokuqala, ukunikezwa kwamandla kanye nomhlabathi kubekwe phezu kwezingqimba ze-2 ne-5 ngokulandelanayo. Ngenxa ye-impedance ephezulu yokunamathela kwethusi kokunikezwa kwamandla, akukuhle kakhulu ukulawula imisebe ye-EMI yemodi evamile. Nokho, ngokombono wokulawula isignali impedance, le ndlela ilungile kakhulu.