Lub viav vias yog ib qho tseem ceeb ntawm ntau txheej PCB, thiab tus nqi ntawm qhov drilling feem ntau yog 30% mus rau 40% ntawm tus nqi ntawm PCB board.Yooj yim muab, txhua qhov ntawm PCB tuaj yeem hu ua viav vias.
Basic tswvyim ntawm viav vias:
Los ntawm qhov pom ntawm kev ua haujlwm, qhov ntawm tuaj yeem muab faib ua ob pawg: ib qho yog siv los ua hluav taws xob sib txuas ntawm cov khaubncaws sab nraud povtseg, thiab lwm yam yog siv los kho lossis muab tso rau ntawm lub cuab yeej.Yog hais tias los ntawm cov txheej txheem, cov qhov no feem ntau muab faib ua peb pawg, xws li qhov muag tsis pom qhov, faus qhov thiab los ntawm qhov.
Qhov qhov muag tsis pom kev nyob rau sab saum toj thiab hauv qab ntawm lub rooj tsavxwm luam tawm thiab muaj qhov tob rau kev sib txuas ntawm cov kab hluav taws xob saum npoo thiab sab hauv Circuit Court hauv qab no, thiab qhov tob ntawm qhov feem ntau tsis tshaj ib qho piv txwv (aperture).
Lub qhov faus yog hais txog lub qhov sib txuas nyob rau hauv txheej txheej ntawm lub rooj tsav xwm luam tawm, uas tsis txuas mus rau saum npoo ntawm lub rooj tsavxwm.Qhov saum toj no ob hom ntawm qhov yog nyob rau hauv lub puab txheej ntawm lub rooj tsavxwm Circuit Court, uas yog ua tiav los ntawm lub qhov molding txheej txheem ua ntej lamination, thiab ob peb txheej sab hauv tej zaum yuav overlapped thaum lub sij hawm tsim los ntawm lub qhov.
Hom thib peb yog hu ua dhau-qhov, uas dhau los ntawm tag nrho lub rooj tsav xwm hauv Circuit Court thiab tuaj yeem siv los ua kom muaj kev sib txuas sab hauv lossis ua qhov chaw teeb tsa qhov chaw rau cov khoom siv.Vim tias qhov dhau los ntawm qhov yooj yim dua rau kev ua tiav hauv cov txheej txheem thiab tus nqi qis dua, feem ntau ntawm cov ntawv luam tawm hauv Circuit Court boards siv nws, es tsis yog ob qho tib si los ntawm qhov.Cov qhov hauv qab no, tsis muaj cov lus qhia tshwj xeeb, suav tias yog los ntawm qhov.
Los ntawm tus qauv tsim ntawm qhov pom, ib qho ntawm feem ntau yog tsim los ntawm ob ntu, ib qho yog nruab nrab ntawm lub qhov drilling, thiab lwm qhov yog qhov chaw vuam pad nyob ib ncig ntawm lub qhov drilling.Qhov loj ntawm ob ntu no txiav txim siab qhov loj ntawm via.
Obviously, nyob rau hauv high-ceev, high-density PCB tsim, cov designers yeej ib txwm xav kom lub qhov me me li sai tau, thiaj li hais tias ntau qhov chaw nyob yuav tsum tau sab laug, ntxiv rau, qhov me me ntawm, nws tus kheej parasitic capacitance yog me me, tsim nyog. rau high-speed circuits.
Txawm li cas los xij, kev txo qis ntawm qhov loj me kuj ua rau cov nqi nce ntxiv, thiab qhov loj ntawm lub qhov tsis tuaj yeem raug txo kom tsawg, nws raug txwv los ntawm kev siv tshuab drilling thiab electroplating: lub qhov me dua, qhov ntev dua qhov drilling, nws yooj yim dua. yog deviate los ntawm qhov chaw;Thaum qhov tob ntawm lub qhov yog ntau tshaj 6 npaug ntawm txoj kab uas hla ntawm lub qhov, nws yog tsis yooj yim sua kom paub meej tias lub qhov phab ntsa yuav tsum uniformly plated nrog tooj liab.
Piv txwv li, yog tias lub thickness (los ntawm qhov tob) ntawm ib txwm 6-txheej PCB pawg thawj coj saib yog 50Mil, ces qhov tsawg kawg nkaus drilling txoj kab uas hla PCB manufacturers muaj peev xwm muab tau nyob rau hauv ib txwm tej yam kev mob tsuas yog ncav cuag 8Mil.Nrog rau txoj kev loj hlob ntawm laser drilling tshuab, qhov luaj li cas ntawm lub drilling kuj yuav me me thiab me, thiab txoj kab uas hla ntawm lub qhov feem ntau tsawg dua los yog sib npaug zos rau 6Mils, peb hu ua microholes.
Microholes feem ntau siv nyob rau hauv HDI (high density interconnect structure) tsim, thiab microhole thev naus laus zis tuaj yeem tso cai rau lub qhov drilled ncaj qha rau ntawm lub ncoo, uas zoo heev txhim kho qhov kev ua haujlwm hauv Circuit Court thiab txuag qhov chaw txuas.Lub viav vias tshwm raws li qhov tawg ntawm impedance discontinuity ntawm cov kab sib kis, ua rau muaj kev cuam tshuam ntawm lub teeb liab.Feem ntau, qhov sib npaug impedance ntawm lub qhov yog kwv yees li 12% qis dua cov kab sib kis, piv txwv li, qhov impedance ntawm 50 ohms kis tau tus mob yuav raug txo los ntawm 6 ohms thaum nws dhau los ntawm lub qhov (tshwj xeeb thiab qhov loj ntawm qhov ntawm, lub phaj thickness kuj muaj feem xyuam nrog, tsis yog qhov txo qis).
Txawm li cas los xij, qhov kev xav tau tshwm sim los ntawm impedance discontinuity ntawm qhov tseeb yog qhov tsawg heev, thiab nws qhov kev xav coefficient tsuas yog:
(44-50)/(44+50) = 0.06
Cov teeb meem tshwm sim los ntawm cov viav vias yog ntau dua rau cov teebmeem ntawm cov kab mob parasitic capacitance thiab inductance.
Ntawm Parasitic capacitance thiab inductance
Muaj ib tug parasitic stray capacitance nyob rau hauv nws tus kheej.Yog hais tias lub cheeb ntawm lub solder kuj cheeb tsam ntawm lub nteg txheej yog D2, txoj kab uas hla ntawm lub solder ncoo yog D1, lub thickness ntawm lub PCB board yog T, thiab lub dielectric qhov tsis tu ncua ntawm lub substrate yog ε, parasitic capacitance ntawm lub qhov. yog kwv yees li:
C=1.41εTD1/(D2-D1)
Cov txiaj ntsig tseem ceeb ntawm cov kab mob parasitic capacitance ntawm lub voj voog yog kom ntev lub sij hawm nce ntawm lub teeb liab thiab txo qhov ceev ntawm Circuit Court.
Piv txwv li, rau PCB nrog lub thickness ntawm 50Mil, yog hais tias txoj kab uas hla ntawm lub ncoo yog 20Mil (txoj kab uas hla ntawm lub qhov drilling yog 10Mils) thiab txoj kab uas hla ntawm lub solder resistance cheeb tsam yog 40Mil, ces peb yuav kwv yees cov parasitic capacitance ntawm los ntawm cov qauv saum toj no:
C = 1.41x4.4x0.050x0.020/(0.040-0.020)=0.31pF
Tus nqi nce lub sij hawm hloov los ntawm qhov no ntawm lub capacitance yog kwv yees:
T10-90 = 2.2C(Z0/2) = 2.2x0.31x(50/2)=17.05ps
Nws tuaj yeem pom los ntawm cov txiaj ntsig no tias txawm hais tias qhov kev siv hluav taws xob nce qeeb los ntawm cov kab mob parasitic capacitance ntawm ib qho ntawm ib qho tsis pom tseeb, yog tias cov viav vias siv ob peb zaug hauv kab los hloov ntawm txheej, ntau qhov yuav siv tau, thiab tus tsim yuav tsum tau ua tib zoo xav txog.Hauv qhov tsim tiag tiag, cov kab mob cab tuaj yeem raug txo los ntawm kev nce qhov kev ncua deb ntawm lub qhov thiab thaj tsam tooj liab (Anti-pad) lossis txo txoj kab uas hla ntawm lub ncoo.
Nyob rau hauv kev tsim ntawm high-ceev digital circuits, qhov teeb meem tshwm sim los ntawm cov kab mob parasitic inductance feem ntau ntau dua li qhov cuam tshuam ntawm parasitic capacitance.Nws cov kab mob parasitic inductance yuav ua rau tsis muaj zog ntawm kev ua haujlwm ntawm bypass capacitor thiab ua rau tsis muaj zog lim dej ntawm tag nrho lub zog.
Peb tuaj yeem siv cov qauv hauv qab no kom yooj yim xam cov kab mob parasitic inductance ntawm qhov kwv yees los ntawm qhov:
L = 5.08h[ln(4h/d)+1]
Qhov twg L yog hais txog qhov inductance ntawm via, h yog qhov ntev ntawm via, thiab d yog txoj kab uas hla ntawm lub hauv paus qhov.Nws tuaj yeem pom los ntawm cov qauv hais tias txoj kab uas hla ntawm lub viav vias muaj kev cuam tshuam me ntsis ntawm qhov inductance, thaum qhov ntev ntawm cov viav vias muaj qhov cuam tshuam loj tshaj plaws ntawm qhov inductance.Tseem siv cov piv txwv saum toj no, qhov tawm ntawm qhov inductance tuaj yeem suav tau raws li:
L=5.08x0.050[ln(4x0.050/0.010)+1]=1.015nH
Yog tias lub sijhawm nce ntawm lub teeb liab yog 1ns, ces nws qhov sib npaug impedance loj yog:
XL = π L / T10-90 = 3.19Ω
Xws li impedance yuav tsis raug ignored nyob rau hauv lub xub ntiag ntawm high-frequency tam sim no los ntawm, tshwj xeeb, nco ntsoov tias lub bypass capacitor yuav tsum dhau los ntawm ob lub qhov thaum txuas lub hwj chim txheej thiab tsim, thiaj li hais tias tus parasitic inductance ntawm lub qhov yuav multiplied.
Yuav siv lub viav vias li cas?
Los ntawm kev soj ntsuam saum toj no ntawm cov yam ntxwv ntawm cov kab mob parasitic ntawm lub qhov, peb tuaj yeem pom tias nyob rau hauv high-speed PCB tsim, zoo li cov qhov yooj yim feem ntau ua rau muaj qhov tsis zoo rau kev tsim ntawm lub voj voog.Yuav kom txo tau cov kev tsis zoo tshwm sim los ntawm cov kab mob parasitic ntawm lub qhov, qhov tsim yuav ua tau kom deb li deb tau:
Los ntawm ob qho tib si ntawm tus nqi thiab cov teeb liab zoo, xaiv qhov tsim nyog ntawm qhov ntawm qhov loj me.Yog tias tsim nyog, koj tuaj yeem txiav txim siab siv ntau qhov sib txawv ntawm vias, xws li rau cov khoom siv hluav taws xob lossis hauv av xaim qhov, koj tuaj yeem txiav txim siab siv qhov loj dua los txo qhov impedance, thiab rau cov teeb liab xaim, koj tuaj yeem siv me me ntawm.Tau kawg, raws li qhov loj me ntawm qhov txo qis, tus nqi sib txuas kuj tseem yuav nce ntxiv
Ob lub qauv uas tau tham saum toj no tuaj yeem txiav txim siab tias kev siv lub rooj tsav xwm PCB thinner yog qhov tsim nyog los txo cov kab mob parasitic ntawm ob.
Lub teeb liab thaiv ntawm PCB pawg thawj coj saib yuav tsum tsis txhob hloov pauv kom deb li deb tau, uas yog hais tias, sim tsis txhob siv cov vias tsis tsim nyog.
Vias yuav tsum tau drilled rau hauv cov pins ntawm lub hwj chim mov thiab hauv av.Qhov luv luv ntawm cov hlau lead ntawm cov pins thiab lub vias, qhov zoo dua.Ntau lub qhov tuaj yeem drilled nyob rau hauv parallel kom txo tau qhov sib npaug inductance.
Muab qee qhov hauv av los ntawm-qhov nyob ze ntawm qhov dhau-qhov ntawm lub teeb liab hloov los muab lub voj ze tshaj plaws rau lub teeb liab.Koj tuaj yeem tso qee qhov av ntau dhau ntawm lub rooj tsavxwm PCB.
Rau kev kub ceev PCB boards nrog siab ceev, koj tuaj yeem xav txog siv micro-qhov.