Ib. Basic tswvyim ntawm vias

Via yog ib qho ntawm cov khoom tseem ceeb ntawm Multilayer PCB, thiab tus nqi ntawm drilling feem ntau yog 30% mus rau 40% ntawm PCB raug nqi. Yooj yim muab, txhua qhov ntawm PCB tuaj yeem hu ua viav vias.

Los ntawm qhov pom ntawm kev ua haujlwm, vias tuaj yeem muab faib ua ob pawg: ib qho yog siv rau kev sib txuas hluav taws xob ntawm txheej txheej; lwm qhov yog siv los kho lossis tso cov khoom siv.

Nyob rau hauv cov nqe lus ntawm cov txheej txheem, cov vias no feem ntau muab faib ua peb pawg, uas yog dig muag vias, faus vias thiab vias. Qhov qhov muag tsis pom kev nyob rau saum thiab hauv qab ntawm cov ntawv luam tawm Circuit Board thiab muaj qhov tob. Lawv yog siv los txuas cov kab saum npoo thiab cov kab hauv qab. Qhov tob ntawm lub qhov feem ntau tsis tshaj ib qho piv txwv (aperture). Lub qhov faus yog hais txog qhov sib txuas nyob rau hauv txheej txheej ntawm lub rooj tsav xwm luam tawm, uas tsis txuas mus rau qhov chaw ntawm lub rooj tsav xwm Circuit Court. Ob lub qhov uas tau hais los saum toj no yog nyob rau hauv txheej txheej ntawm lub rooj tsav xwm hauv Circuit Court, thiab ua tiav los ntawm kev sib sau ntawm lub qhov ua ntej lamination, thiab ob peb txheej txheej sab hauv tuaj yeem sib tshooj thaum tsim cov viav vias. Qhov thib peb yog hu ua ib tug los ntawm lub qhov, uas nkag mus rau tag nrho cov Circuit Court board thiab yuav siv tau rau sab hauv interconnection los yog raws li ib tug tivthaiv mounting positioning qhov. Vim tias qhov dhau los ntawm qhov yooj yim dua rau kev siv hauv cov txheej txheem thiab tus nqi qis dua, feem ntau cov ntawv luam tawm Circuit boards siv nws es tsis txhob siv ob hom ntawm lub qhov. Cov nram qab no ntawm qhov, tshwj tsis yog tias tau teev tseg, raug suav hais tias yog ntawm qhov.

Los ntawm tus qauv tsim ntawm qhov pom, ib qho ntawm feem ntau yog tsim los ntawm ob ntu, ib qho yog qhov laum hauv nruab nrab, thiab lwm qhov yog qhov chaw ncoo nyob ib ncig ntawm lub qhov laum. Qhov loj ntawm ob ntu no txiav txim siab qhov loj ntawm cov viav vias. Obviously, nyob rau hauv high-ceev, high-density PCB tsim, designers yeej ib txwm cia siab hais tias qhov me me ntawm lub qhov yog, qhov zoo dua, yog li ntawd ntau wiring qhov chaw nyob rau hauv lub rooj tsavxwm. Tsis tas li ntawd, qhov me me ntawm lub qhov, cov kab mob parasitic capacitance ntawm nws tus kheej. Qhov me me, nws yog qhov tsim nyog rau high-speed circuits. Txawm li cas los xij, qhov kev txo qis ntawm qhov loj me kuj ua rau tus nqi nce ntxiv, thiab qhov loj ntawm lub viav vias tsis tuaj yeem txo qis mus ib txhis. Nws raug txwv los ntawm cov txheej txheem thev naus laus zis xws li drilling thiab plating: qhov me me ntawm lub qhov, qhov xyaum siv lub qhov ntev, qhov yooj yim dua nws yog deviate los ntawm qhov chaw nruab nrab; thiab thaum qhov tob ntawm lub qhov siab tshaj 6 npaug ntawm txoj kab uas hla ntawm lub qhov drilled, nws tsis tuaj yeem lav tias lub qhov phab ntsa tuaj yeem ua tau zoo sib xws nrog tooj liab. Piv txwv li, lub thickness (los ntawm qhov tob) ntawm ib txwm 6-txheej PCB board yog hais txog 50Mil, yog li qhov tsawg kawg nkaus drilling txoj kab uas hla PCB manufacturers tuaj yeem muab tau tsuas yog 8Mil.

Qhov thib ob, tus kab mob parasitic capacitance ntawm lub via

Lub vias nws tus kheej muaj tus kab mob parasitic rau hauv av. Yog tias nws paub tias txoj kab uas hla ntawm qhov kev sib cais ntawm qhov av txheej ntawm qhov yog D2, txoj kab uas hla ntawm lub ncoo yog D1, lub thickness ntawm lub PCB board yog T, thiab lub dielectric qhov tsis tu ncua ntawm lub board substrate yog ε, Qhov luaj li cas ntawm tus kab mob parasitic capacitance ntawm lub via yog kwv yees li: C = 1.41εTD1 / (D2-D1) Cov kab mob parasitic capacitance ntawm lub viav vias yuav ua rau lub voj voog kom ntev lub sij hawm nce ntawm lub teeb liab thiab txo qhov ceev ntawm lub voj voog. Piv txwv li, rau ib tug PCB nrog ib tug tuab ntawm 50Mil, yog hais tias ib tug viav vias nrog ib tug puab txoj kab uas hla ntawm 10Mil thiab ib tug ncoo txoj kab uas hla ntawm 20Mil, thiab qhov kev ncua deb ntawm lub ncoo thiab hauv av tooj liab cheeb tsam yog 32Mil, ces peb muaj peev xwm kwv yees li ntawm ntawm. siv cov qauv saum toj no Cov kab mob parasitic capacitance yog kwv yees li: C = 1.41 × 4.4 × 0.050 × 0.020 / (0.032-0.020) = 0.517pF, lub sij hawm nce siab tshwm sim los ntawm qhov no ntawm lub capacitance yog: T10-90 = 2.2C(Z0 /2) = 2.2 x 0.517x(55/2) = 31.28 ps. Nws tuaj yeem pom los ntawm cov txiaj ntsig no tias txawm hais tias qhov cuam tshuam ntawm qhov nce qeeb tshwm sim los ntawm parasitic capacitance ntawm ib qho ntawm ib qho tsis pom tseeb, yog tias cov viav vias siv ntau zaus hauv cov kab los hloov ntawm cov khaubncaws sab nraud povtseg, tus tsim qauv yuav tsum tseem xav txog. ua tib zoo.

Thib peb, parasitic inductance ntawm lub via

Ib yam li ntawd, muaj cov kab mob parasitic inductance nrog rau cov kab mob parasitic capacitance ntawm lub vias. Nyob rau hauv kev tsim ntawm high-ceev digital circuits, qhov teeb meem tshwm sim los ntawm parasitic inductance ntawm lub vias yog feem ntau ntau dua li qhov cuam tshuam ntawm parasitic capacitance. Nws cov kab mob parasitic inductance yuav ua rau tsis muaj zog rau kev koom tes ntawm bypass capacitor thiab ua rau tsis muaj zog lim dej ntawm tag nrho lub zog. Peb tuaj yeem xam qhov kwv yees kwv yees tus kab mob parasitic inductance ntawm ib ntawm nrog cov qauv hauv qab no: L = 5.08h [ln(4h / d) + 1] qhov twg L yog hais txog qhov inductance ntawm lub via, h yog qhov ntev ntawm qhov, thiab d yog qhov nruab nrab Qhov txoj kab uas hla ntawm lub qhov. Nws tuaj yeem pom los ntawm cov qauv hais tias txoj kab uas hla ntawm lub viav vias muaj qhov cuam tshuam me me ntawm qhov inductance, thiab 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 inductance ntawm qhov tuaj yeem suav tau raws li: L = 5.08 × 0.050 [ln(4 × 0.050 / 0.010) + 1] = 1.015nH. Yog tias lub sijhawm nce ntawm lub teeb liab yog 1ns, ces nws qhov sib npaug impedance yog: XL = πL / T10-90 = 3.19Ω. Xws li impedance yuav tsis raug ignored thaum high-frequency tam sim no dhau. Kev saib xyuas tshwj xeeb yuav tsum tau them rau qhov tseeb tias lub bypass capacitor yuav tsum dhau los ntawm ob lub vias thaum txuas lub dav hlau fais fab thiab lub dav hlau hauv av, kom cov kab mob parasitic inductance ntawm vias yuav nce exponentially.

Plaub, ntawm kev tsim hauv high-speed PCB

Los ntawm kev soj ntsuam saum toj no ntawm cov yam ntxwv parasitic ntawm vias, peb tuaj yeem pom tias nyob rau hauv high-speed PCB tsim, seemingly yooj yim vias feem ntau coj zoo tsis zoo rau Circuit Court tsim. Txhawm rau txo qhov tsis zoo tshwm sim los ntawm cov kab mob parasitic ntawm lub vias, cov hauv qab no tuaj yeem ua tiav hauv kev tsim:

1. Los ntawm qhov kev xav ntawm tus nqi thiab teeb liab zoo, xaiv qhov tsim nyog loj ntawm. Piv txwv li, rau 6-10 txheej nco module PCB tsim, nws yog qhov zoo dua los siv 10/20Mil (drilled/pad) vias. Rau qee qhov loj me me ntawm cov laug cam, koj tuaj yeem sim siv 8/18Mil. qhov. Raws li cov txheej txheem tam sim no, nws nyuaj rau siv cov vias me me. Rau lub zog lossis hauv av vias, koj tuaj yeem xav siv qhov loj dua los txo qhov impedance.

2. Ob qho qauv uas tau hais los saum toj no tuaj yeem txiav txim siab tias kev siv lub PCB thinner yog qhov tsim nyog rau kev txo qis cov kab mob parasitic ntawm ob.

3. Sim tsis txhob hloov cov khaubncaws sab nraud povtseg ntawm cov teeb liab ntawm lub rooj tsavxwm PCB, uas yog hais tias, sim tsis txhob siv cov vias tsis tsim nyog.

4. Lub hwj chim thiab hauv av pins yuav tsum tau drilled nyob ze, thiab cov hlau lead ntawm lub viav vias thiab tus pin yuav tsum yog luv li sai tau, vim hais tias lawv yuav ua rau kom inductance. Nyob rau tib lub sij hawm, lub hwj chim thiab av leads yuav tsum tuab li sai tau los txo impedance.

5. Muab ib co grounded vias ze ntawm vias ntawm lub teeb liab txheej kom muab lub voj ze tshaj plaws rau lub teeb liab. Nws tseem muaj peev xwm tso tau ntau qhov tsis txaus ntseeg hauv av vias ntawm PCB pawg thawj coj saib. Ntawm chav kawm, tus tsim yuav tsum hloov tau. Cov qauv ntawm kev sib tham ua ntej yog rooj plaub uas muaj cov ntaub qhwv ntawm txhua txheej. Qee zaum, peb tuaj yeem txo lossis txawm tias tshem cov ntaub qhwv ntawm qee cov khaubncaws sab nraud povtseg. Tshwj xeeb tshaj yog thaum qhov ceev ntawm vias yog siab heev, nws yuav ua rau tsim ib qho kev tawg zawj uas cais lub voj nyob rau hauv txheej tooj liab. Yuav kom daws tau qhov teeb meem no, ntxiv rau kev txav txoj hauj lwm ntawm lub viav vias, peb tseem tuaj yeem txiav txim siab tso cov viav vias ntawm cov txheej tooj liab. Lub ncoo loj yog txo.