I-Via ingenye yezingxenye ezibalulekile ze-PCB enezingqimba eziningi, futhi izindleko zokumba ngokuvamile zibalelwa ku-30% kuya ku-40% wezindleko zebhodi le-PCB. Kalula nje, yonke imbobo ku-PCB ingabizwa ngokuthi i-via.
Umqondo oyisisekelo we- via:
Ngokombono wokusebenza, i-via ingahlukaniswa ngezigaba ezimbili: eyodwa isetshenziswa njengoxhumano lukagesi phakathi kwezendlalelo, kanti enye isetshenziswa njengendlela yokulungisa noma yokumisa idivayisi. Uma kusukela kunqubo, lezi zimbobo ngokuvamile zihlukaniswa izigaba ezintathu, okuyizimbobo ezingaboni, imigodi egqitshiwe kanye nemigodi.
Izimbobo eziyizimpumputhe zitholakala phezulu nangaphansi kwebhodi lesifunda eliphrintiwe futhi zibe nokujula okuthile kokuxhumeka kwe-surface circuit kanye nesifunda sangaphakathi esingezansi, futhi ukujula kwemigodi ngokuvamile akudluli isilinganiso esithile (i-aperture).
Umgodi ongcwatshiwe ubhekisela emgodini wokuxhuma otholakala engxenyeni yangaphakathi yebhodi lesifunda eliphrintiwe, elingadlulisi ebusweni bebhodi. Lezi zinhlobo ezimbili ezingenhla zezimbobo zitholakala kungqimba lwangaphakathi lwebhodi lesifunda, oluphothulwa yinqubo yokubumba imbobo ngaphambi kokuba i-lamination, futhi izingqimba eziningana zangaphakathi zingase zigqitshwe ngesikhathi kwakhiwa imbobo.
Uhlobo lwesithathu lubizwa ngokuthi yi- through-holes , edlula kulo lonke ibhodi lesifunda futhi lungasetshenziswa ukufeza ukuxhumana kwangaphakathi noma njengezimbobo zokubeka izingxenye zezingxenye. Ngenxa yokuthi kulula ukufeza imbobo kule nqubo futhi nezindleko ziphansi, iningi lamabhodi esekethe aphrintiwe ayisebenzisayo, kunalawa amabili ngokusebenzisa izimbobo. Izimbobo ezilandelayo, ngaphandle kwemiyalelo ekhethekile, zibhekwa njengezimbobo.
Ngokombono wokuklama, i-via ngokuyinhloko yakhiwe izingxenye ezimbili, enye imaphakathi nembobo yokubhoboza, kanti enye iyindawo yokushisela ezungeze umgodi wokubhoboza. Ubukhulu balezi zingxenye ezimbili bunquma ubukhulu be-via.
Ngokusobala, ekwakhiweni kwe-PCB enesivinini esikhulu, ephezulu kwabantu, abaklami bahlala befuna imbobo ibe mncane ngangokunokwenzeka, ukuze kushiywe isikhala esiningi sezintambo, ngaphezu kwalokho, i-via encane, i-parasitic capacitance yayo incane, ifaneleka kakhulu. kumasekhethi anesivinini esikhulu.
Kodwa-ke, ukuncishiswa kosayizi we-via nakho kuletha ukwanda kwezindleko, futhi ubukhulu bembobo abukwazi ukuncishiswa unomphela, bunqunyelwe ukubhoboza nobuchwepheshe be-electroplating: imbobo encane, uma kuthatha isikhathi eside ukumba, kuba lula ukuchezuka phakathi nendawo; Lapho ukujula komgodi kungaphezu kwezikhathi ezingu-6 ububanzi bomgodi, akunakwenzeka ukuqinisekisa ukuthi udonga lwembobo lungafakwa ngokulinganayo ngethusi.
Isibonelo, uma ukushuba (ngokujula kwembobo) kwebhodi le-PCB elinezingqimba ezi-6 ezijwayelekile kungu-50Mil, khona-ke ububanzi obuncane bokubhoboza obungahlinzekwa abakhiqizi be-PCB ngaphansi kwezimo ezijwayelekile bungafinyelela kuphela ku-8Mil. Ngokuthuthukiswa kobuchwepheshe bokugaya nge-laser, ubukhulu bokubhola bungaba buncane futhi bube buncane, futhi ububanzi bomgodi ngokuvamile bungaphansi noma bulingana no-6Mils, sibizwa ngokuthi ama-microholes.
Ama-Microholes avame ukusetshenziswa ekwakhiweni kwe-HDI (high density interconnect structure), futhi ubuchwepheshe be-microhole bungavumela imbobo ukuthi ibhojwe ngokuqondile ku-pad, okuthuthukisa kakhulu ukusebenza kwesifunda futhi igcine isikhala sezintambo. I-via ibonakala njengendawo yokunqamuka kokunqanyulwa komugqa wokudlulisela, okubangela ukubonakaliswa kwesignali. Ngokuvamile, ukuvinjelwa okulingana kwembobo cishe kungaphansi ngo-12% kunolayini wokudlulisela, isibonelo, ukuvinjelwa kolayini wokudlulisela ongu-50 ohms kuzoncishiswa ngo-6 ohms uma udlula emgodini (ikakhulukazi kanye nosayizi we-via, ukushuba kwepuleti nakho kuhlobene, hhayi ukuncishiswa ngokuphelele).
Kodwa-ke, ukuboniswa okudalwe ukungaqhubeki kokuvinjwa nge-impedance empeleni kuncane kakhulu, futhi i-coefficient yayo yokubonisa kuphela:
(44-50)/(44 + 50) = 0.06
Izinkinga ezivela ku-via zigxile kakhulu emiphumeleni ye-parasitic capacitance kanye ne-inductance.
I-Via's Parasitic capacitance kanye ne-Inductance
Kukhona i-parasitic stray capacitance ku-via ngokwayo. Uma ububanzi bendawo yokumelana ne-solder kungqimba olubekiwe kungu-D2, ububanzi bephedi ye-solder buyi-D1, ubukhulu bebhodi le-PCB bungu-T, kanti i-dielectric constant ye-substrate ingu-ε, amandla e-parasitic we- through hole. cishe:
C=1.41εTD1/(D2-D1)
Umphumela oyinhloko we-capacitance ye-parasitic kumjikelezo ukwandisa isikhathi sokukhuphuka kwesignali nokunciphisa isivinini sesifunda.
Isibonelo, kwi-PCB enogqinsi oluyi-50Mil, uma ububanzi be-via pad ingu-20Mil (ububanzi bembobo yokubhoboza buyi-10Mils) nobubanzi bendawo yokumelana ne-solder bungama-40Mil, khona-ke singakwazi ukulinganisa amandla e-parasitic ngefomula engenhla:
C=1.41x4.4x0.050x0.020/(0.040-0.020)=0.31pF
Inani lokushintsha kwesikhathi sokukhuphuka okubangelwa yile ngxenye yamandla cishe:
T10-90=2.2C(Z0/2)=2.2x0.31x(50/2)=17.05ps
Kungabonakala kulawa manani ukuthi nakuba ukusetshenziswa kokulibaziseka kokukhuphuka okubangelwa amandla e-parasitic wendlela eyodwa kungabonakali kahle, uma i-via isetshenziswa izikhathi ezimbalwa emugqeni ukushintsha phakathi kwezingqimba, kuzosetshenziswa izimbobo eziningi, futhi umklamo kufanele ucatshangelwe ngokucophelela. Emklamo wangempela, i-capacitance ye-parasitic ingancishiswa ngokukhulisa ibanga phakathi komgodi nendawo yethusi (i-Anti-pad) noma ukunciphisa ububanzi bepadi.
Ekwakhiweni kwamasekhethi edijithali anesivinini esikhulu, ukulimala okubangelwa i-inductance ye-parasitic ngokuvamile kukhulu kunethonya le-parasitic capacitance. Uchungechunge lwayo lwe-parasitic inductance luzokwenza buthaka umnikelo we-bypass capacitor futhi lwenze buthaka ukusebenza kahle kokuhlunga kwalo lonke uhlelo lwamandla.
Singasebenzisa le fomula yobufakazi ukuze simane sibale ukungeniswa kwe-parasitic kwe- through-hole approximation:
L=5.08h[ln(4h/d)+1]
Lapho u-L ebhekisela ekungeneni kwe-via, u-h ubude be-via, futhi u-d uwububanzi bembobo emaphakathi. Kungabonakala kufomula ukuthi ububanzi be-via bunomthelela omncane ekungeneni, kuyilapho ubude be-via bunomthelela omkhulu kakhulu ku-inductance. Usasebenzisa isibonelo esingenhla, i-out-of-hole inductance ingabalwa ngokuthi:
L=5.08x0.050[ln(4x0.050/0.010)+1]=1.015nH
Uma isikhathi sokukhuphuka kwesignali singu-1ns, khona-ke usayizi olinganayo we-impedance uthi:
XL=πL/T10-90=3.19Ω
I-impedance enjalo ayikwazi ukunakwa phambi kwe-high-frequency current ngokusebenzisa, ikakhulukazi, phawula ukuthi i-bypass capacitor idinga ukudlula izimbobo ezimbili lapho ixhuma ungqimba lwamandla kanye nokwakheka, ukuze i-inductance ye-parasitic yembobo izokwandiswa.
Indlela yokusebenzisa i-via?
Ngokuhlaziywa okungenhla kwezici ze-parasitic zembobo, singabona ukuthi ekwakhiweni kwe-PCB enesivinini esikhulu, izimbobo ezibonakala zilula zivame ukuletha imiphumela emibi kakhulu ekwakhiweni kwesekethe. Ukuze unciphise imiphumela emibi ebangelwa umphumela we-parasitic wembobo, umklamo ungaba ngangokunokwenzeka:
Ezicini ezimbili zezindleko nekhwalithi yesignali, khetha usayizi ozwakalayo we- via size. Uma kunesidingo, ungacabangela ukusebenzisa amasayizi ahlukene we-vias, njengamandla kagesi noma izimbobo zezintambo eziphansi, ungacabangela ukusebenzisa usayizi omkhulu ukuze unciphise i-impedance, futhi ukuze uthole izintambo zesignali, ungasebenzisa i-diaper encane. Yebo, njengoba usayizi we-via wehla, izindleko ezihambisanayo nazo zizokhuphuka
Amafomula amabili okukhulunywe ngawo ngenhla angaphethwa ngokuthi ukusetshenziswa kwebhodi elincanyana le-PCB kusiza ekwehliseni amapharamitha amabili angama-parasitic we-via.
Izintambo zesignali ebhodini le-PCB akufanele zishintshwe ngangokunokwenzeka, okusho ukuthi, zama ukungasebenzisi i-vias engadingekile.
I-Vias kumele ibhojwe ezikhonkwaneni zamandla kagesi kanye nomhlabathi. Uma umthofi emfushane phakathi kwamaphini kanye ne-vias, kungcono. Izimbobo eziningi zingabhojwa ngokuhambisana ukuze kuncishiswe i-inductance efanayo.
Beka izimbobo ezithile ezisekelwe phansi eduze nezimbobo zokushintsha kwesignali ukuze unikeze iluphu eseduze yesiginali. Ungakwazi ngisho nokubeka izimbobo zomhlabathi ngokweqile ebhodini le-PCB.
Kumabhodi e-PCB anesivinini esikhulu anokuminyana okuphezulu, ungacabangela ukusebenzisa izimbobo ezincane.