Pali njira zambiri zothetsera mavuto a EMI. Masiku ano EMI kupondereza njira monga: ntchito EMI kupondereza zokutira, kusankha yoyenera EMI kupondereza mbali, ndi EMI kayeseleledwe kayeseleledwe. Kuyambira zofunika kwambiri PCB masanjidwe, nkhaniyi ikufotokoza za ntchito ndi njira zamapangidwe a PCB wosanjikiza powongolera ma radiation a EMI.

Kuyika moyenerera ma capacitor amphamvu yoyenerera pafupi ndi mapini amagetsi a IC kungapangitse kuti IC lituluke voteji kudumpha mwachangu. Komabe, vuto silikuthera apa. Chifukwa cha kuyankha kwafupipafupi kwa ma capacitor, izi zimapangitsa kuti ma capacitor asathe kupanga mphamvu ya harmonic yofunikira kuyendetsa kutulutsa kwa IC mwaukhondo mu gulu lonse la frequency. Kuphatikiza apo, voteji yosakhalitsa yomwe imapangidwa pabasi yamagetsi ipanga kutsika kwamagetsi pa inductor ya njira yolumikizira. Ma voltages osakhalitsa awa ndiye njira yayikulu yolumikizira EMI. Kodi mavutowa tiyenera kuwathetsa bwanji?

Ponena za IC pa bolodi yathu yozungulira, mphamvu yosanjikiza yozungulira IC imatha kuwonedwa ngati capacitor yapamwamba kwambiri, yomwe imatha kusonkhanitsa gawo la mphamvu zomwe zidatsitsidwa ndi discrete capacitor yomwe imapereka mphamvu zapamwamba kwambiri zoyeretsa. zotuluka. Kuphatikiza apo, inductance ya mphamvu yosanjikiza bwino iyenera kukhala yaying’ono, kotero chizindikiro chaching’ono chopangidwa ndi inductance chimakhalanso chaching’ono, potero kuchepetsa wamba EMI.

Zoonadi, kugwirizana pakati pa gawo la mphamvu ndi pini ya mphamvu ya IC kuyenera kukhala kwaufupi momwe zingathere, chifukwa kukwera m’mphepete mwa chizindikiro cha digito kukukula mofulumira komanso mofulumira, ndipo ndibwino kuti mugwirizane ndi pad kumene mphamvu ya IC pin ilipo. Izi ziyenera kukambidwa mosiyana.

Kuti muwongolere ma EMI wamba, ndege yamagetsi iyenera kuthandizira kutsitsa ndikukhala ndi inductance yotsika mokwanira. Ndege yamagetsi iyi iyenera kukhala yopangidwa bwino ndi ndege zamagetsi. Wina angafunse kuti, zabwino ndi zabwino bwanji? Yankho la funso limadalira kusanjika kwa magetsi, zipangizo pakati pa zigawo, ndi maulendo ogwiritsira ntchito (ndiko kuti, ntchito ya nthawi yowuka ya IC). Nthawi zambiri, masinthidwe a gawo lamagetsi ndi 6mil, ndipo cholumikizira ndi FR4, mphamvu yofananira ya gawo lamagetsi pa inchi imodzi ndi pafupifupi 75pF. Mwachiwonekere, malo ang’onoang’ono ang’onoang’ono, amatha kukhala ndi capacitance.

Palibe zida zambiri zokhala ndi nthawi yokwera ya 100 mpaka 300 ps, ​​koma malinga ndi liwiro lachitukuko cha IC, zida zokhala ndi nthawi yokwera pakati pa 100 mpaka 300 ps zitenga gawo lalikulu. Kwa mabwalo okhala ndi nthawi yokwera ya 100 mpaka 300ps, mtunda wa 3mil wosanjikiza sudzakhalanso woyenera kugwiritsa ntchito zambiri. Panthawiyo, kunali koyenera kugwiritsa ntchito ukadaulo wosanjikiza wokhala ndi masitayilo osakwana 1 mil, ndikusintha zida za dielectric za FR4 ndi zida zokhala ndi ma dielectric okhazikika. Tsopano, zoumba ndi mapulasitiki a ceramic amatha kukwaniritsa zofunikira za mapangidwe a 100 mpaka 300 ps kuwuka kwa nthawi.

Ngakhale zida zatsopano ndi njira zatsopano zitha kugwiritsidwa ntchito m’tsogolomu, masiku ano 1 mpaka 3ns amawuka mabwalo anthawi, 3 mpaka 6mil wosanjikiza masitayilo ndi zida za dielectric za FR4, nthawi zambiri zimakhala zokwanira kuthana ndi ma harmonics apamwamba ndikupangitsa kuti siginecha yocheperako ikhale yochepa mokwanira. , ndiye kuti, Common mode EMI ikhoza kuchepetsedwa kwambiri. Zitsanzo za mapangidwe a PCB osanjikiza omwe aperekedwa m’nkhaniyi atenga mtunda wa 3 mpaka 6 mils.

Electromagnetic shielding

Kuchokera pakuwona zizindikiro za zizindikiro, njira yabwino yosanjikiza iyenera kukhala yoyika zizindikiro zonse pamagulu amodzi kapena angapo, zigawozi zili pafupi ndi mphamvu yamagetsi kapena pansi. Kwa magetsi, njira yabwino yopangira magetsi iyenera kukhala kuti mphamvu yowonjezera ili pafupi ndi nthaka, ndipo mtunda wapakati pa mphamvu ya mphamvu ndi nthaka ndi yochepa kwambiri. Izi ndi zomwe timatcha njira ya “layer”.

Zithunzi za PCB

Ndi njira yanji ya stacking yomwe ingathandize kuteteza ndi kupondereza EMI? Chiwembu chotsatira cha stacking chimaganiza kuti mphamvu zamagetsi zimayenda pamtunda umodzi, ndipo magetsi amodzi kapena maulendo angapo amagawidwa m’madera osiyanasiyana a gawo limodzi. Nkhani ya magawo angapo amphamvu idzakambidwa pambuyo pake.

4-wosanjikiza bolodi

Pali zovuta zingapo zomwe zingatheke ndi mapangidwe a 4-layer board. Choyamba, gulu lachikhalidwe chamagulu anayi okhala ndi makulidwe a 62 mils, ngakhale chizindikirocho chili pamtunda wakunja, ndipo zigawo za mphamvu ndi nthaka zili pamtunda wamkati, mtunda wa pakati pa mphamvu ndi nthaka. akadali wamkulu kwambiri.

Ngati mtengo wofunikira ndi woyamba, mutha kuganizira njira ziwiri zotsatirazi pa bolodi yamitundu 4. Mayankho awiriwa amatha kuwongolera magwiridwe antchito a EMI kuponderezana, koma amangoyenera kugwiritsa ntchito pomwe kachulukidwe kagawo pa bolodi ndi otsika mokwanira ndipo pali malo okwanira kuzungulira zigawozo (ikani gawo lofunikira la mkuwa).

Njira yoyamba ndiyo kusankha koyamba. Zigawo zakunja za PCB ndi zigawo zonse zapansi, ndipo zigawo ziwiri zapakati ndi zizindikiro / mphamvu. Mphamvu yamagetsi pa chizindikiro chosanjikiza imayendetsedwa ndi mzere waukulu, womwe ungapangitse kuti njira yolepheretsa mphamvu yamagetsi ikhale yotsika, ndipo kulepheretsa kwa njira ya microstrip kumakhala kochepa. Kuchokera pakuwona kuwongolera kwa EMI, iyi ndiye mawonekedwe abwino kwambiri a 4-wosanjikiza PCB omwe alipo. Pachiwembu chachiwiri, chingwe chakunja chimagwiritsa ntchito mphamvu ndi nthaka, ndipo zigawo ziwiri zapakati zimagwiritsa ntchito zizindikiro. Poyerekeza ndi bolodi lachikale la 4-wosanjikiza, kuwongolerako ndi kwakung’ono, ndipo interlayer impedance ndi yosauka ngati bolodi yamitundu 4.

Ngati mukufuna kulamulira trace impedance, pamwamba stacking chiwembu ayenera kusamala kwambiri kukonza kuda pansi pa mphamvu ndi pansi mkuwa zilumba. Kuonjezera apo, zilumba zamkuwa zomwe zili pamagetsi kapena pansi ziyenera kulumikizidwa momwe zingathere kuti zitsimikizire kuti DC ndi yotsika kwambiri.

6-wosanjikiza bolodi

Ngati kachulukidwe ka zigawo pa bolodi 4-wosanjikiza ndi mkulu, 6-wosanjikiza bolodi ndi bwino. Komabe, ma ziwembu ena a stacking mu kapangidwe ka 6-layer board siabwino mokwanira kutchingira ma elekitiromagineti, ndipo ali ndi mphamvu zochepa pakuchepetsa chizindikiro chokhalitsa cha basi yamagetsi. Zitsanzo ziwiri zikukambidwa pansipa.

Poyamba, magetsi ndi nthaka zimayikidwa pazigawo za 2 ndi 5 motsatira. Chifukwa cha ❖ kuyanika kwakukulu kwa ❖ kuyanika kwa mkuwa wamagetsi, ndikovuta kwambiri kuwongolera ma radiation wamba a EMI. Komabe, pakuwona kuwongolera kwamphamvu kwa chizindikiro, njira iyi ndi yolondola kwambiri.