Kev tswj hwm impedance yog dab tsi thiab yuav ua li cas ua kev tswj hwm impedance ntawm PCBs

Hauv kev tsim cov khoom siv hluav taws xob niaj hnub no, PCBs ua lub luag haujlwm tseem ceeb. Kev ua tau zoo ntawm PCBs cuam tshuam ncaj qha rau kev ruaj khov, kev ntseeg siab thiab kev sib kis tau zoo ntawm tag nrho lub cev hluav taws xob. Ntawm lawv, kev tswj hwm impedance yog ib feem tseem ceeb ntawm kev tsim PCB. Vim tias cov voj voog digital niaj hnub muaj lub sijhawm xa cov teeb liab luv dua thiab cov nqi moos siab dua, cov kab PCB tsis yog kev sib txuas yooj yim lawm, tab sis cov kab xa xov sib xws. PCB impedance tswj yog hais txog kev tswj qhov ceev xa thiab impedance phim ntawm cov teeb liab ntawm PCB kom ntseeg tau tias qhov zoo thiab kev ruaj khov ntawm kev xa cov teeb liab.

Hauv cov xwm txheej ua tau zoo, nws yog qhov tsim nyog los tswj qhov impedance ntawm cov kab thaum lub zog digital marginal siab dua 1ns lossis qhov zaus analog tshaj 300MHz. Ib qho ntawm cov yam ntxwv tseem ceeb ntawm PCB trace yog nws cov yam ntxwv impedance (piv txwv li qhov sib piv ntawm voltage rau tam sim no thaum nthwv dej raug xa mus raws kab xa teeb liab). Qhov impedance ntawm cov xov hlau ntawm PCBs yog qhov qhia tseem ceeb ntawm kev tsim PCB. Tshwj xeeb tshaj yog hauv kev tsim PCB zaus siab, nws yog qhov tsim nyog los xav txog seb qhov impedance ntawm cov xov hlau puas sib xws lossis phim qhov impedance ntawm cov cuab yeej lossis teeb liab. Qhov no suav nrog 2 lub tswv yim: kev tswj impedance thiab kev sib phim impedance. Tsab xov xwm no tsom mus rau cov teeb meem ntawm kev tswj impedance thiab kev tsim pawg.

Muaj ntau yam teeb liab xa mus rau hauv cov hlau lead ntawm PCB. Yuav kom txhim kho nws qhov kev xa mus, nws qhov zaus yuav tsum tau nce ntxiv. Tus nqi impedance ntawm lub voj voog nws tus kheej txawv vim muaj ntau yam xws li etching, txheej tuab thiab hlau dav, thiab lwm yam, ua rau muaj kev cuam tshuam ntawm cov teeb liab. Yog li ntawd, tus nqi impedance ntawm cov hlau lead ntawm cov PCB ceev ceev yuav tsum tau tswj hwm hauv qee qhov ntau, uas hu ua "impedance control".

Qhov impedance ntawm cov kab ntawm PCB yog txiav txim siab los ntawm lawv cov inductive thiab capacitive inductance, resistance thiab conductivity coefficient. Cov yam uas cuam tshuam rau qhov impedance ntawm PCB wiring feem ntau suav nrog qhov dav thiab tuab ntawm cov hlau tooj liab, qhov dielectric tas mus li thiab tuab ntawm cov khoom nruab nrab, qhov tuab ntawm cov ntaub qhwv solder, txoj kev ntawm cov hlau av, thiab cov xov hlau nyob ib puag ncig cov xov hlau, thiab lwm yam. Qhov ntau ntawm PCB impedance yog 25 txog 120 ohms.

Hauv kev xyaum, cov kab xa hluav taws xob PCB feem ntau muaj cov xov hlau, ib lossis ntau txheej siv, thiab cov ntaub ntawv rwb thaiv tsev. Cov kab thiab txheej tsim cov impedance tswj. PCBs feem ntau siv cov qauv ntau txheej, thiab kev tswj impedance kuj tuaj yeem tsim tau ntau txoj hauv kev. Txawm li cas los xij, tsis hais txoj kev siv li cas los xij, tus nqi impedance yuav raug txiav txim siab los ntawm nws cov qauv lub cev thiab cov khoom siv hluav taws xob ntawm cov ntaub ntawv rwb thaiv tsev:

Ib daim microstrip yog ib daim hlau uas hais txog ib txoj kab xa hluav taws xob uas muaj ib sab xwb uas muaj lub dav hlau siv los ua piv txwv. Sab saud thiab sab nraud raug cua (lossis raug txheej) thiab nyob rau ntawm qhov chaw ntawm ib qho rwb thaiv tsev tas mus li Er PCB, nrog rau lub zog lossis txheej av ua piv txwv. Raws li pom hauv daim duab hauv qab no:

Lus Cim: Hauv kev tsim PCB tiag tiag, lub Hoobkas PCB feem ntau pleev ib txheej ntawm cov kua xim ntsuab rau ntawm qhov chaw ntawm PCB. Yog li ntawd, hauv kev xam impedance tiag tiag, tus qauv qhia hauv daim duab hauv qab no feem ntau yog siv rau cov kab microstrip saum npoo.

Ib txoj kab hlau yog ib txoj hlua hlau uas muab tso rau nruab nrab ntawm 2 lub dav hlau siv, raws li pom hauv daim duab hauv qab no. Cov dielectric constants ntawm dielectric uas sawv cev los ntawm H1 thiab H2 tuaj yeem sib txawv.

Ob qho xwm txheej saum toj no tsuas yog ib qho piv txwv ntawm microstrip thiab striplines, feem ntau yog siv rau kev kawm ntawm embedded IoT intelligent hardware thiab lwm yam systems. Muaj ntau hom microstrip thiab striplines tshwj xeeb, xws li coated microstrip, uas muaj feem cuam tshuam rau cov qauv stacking ntawm PCBs.

Cov qauv siv los xam cov yam ntxwv impedance xav tau kev suav lej nyuaj, feem ntau siv cov txheej txheem daws teeb meem teb, suav nrog kev tshuaj xyuas cov ciam teb. Yog li ntawd, nrog kev siv software xam impedance tshwj xeeb SI9000, txhua yam peb yuav tsum ua yog tswj cov kev teeb tsa ntawm cov yam ntxwv impedance:

Tus dielectric tas mus li Er ntawm cov txheej rwb thaiv tsev, qhov dav ntawm cov xov hlau W1 thiab W2 (trapezoidal), qhov tuab ntawm cov xov hlau T, thiab qhov tuab ntawm cov txheej rwb thaiv tsev H.

W - qhov dav ntawm kab tsim

A - kev poob ntawm etch (saib cov lus saum toj no)

Qhov laj thawj rau qhov dav tsis sib xws ntawm sab saud thiab hauv qab ntawm kab yog vim tias thaum lub sijhawm tsim cov PCBs, xeb tshwm sim los ntawm sab saud mus rau hauv qab, ua rau cov kab xeb zoo li trapezoidal.

Muaj kev sib raug zoo ntawm qhov tuab ntawm kab T thiab qhov tuab ntawm tooj liab ntawm cov txheej no, raws li nram no:

* Vim yog qhov cuam tshuam me me ntawm lub ntsej muag solder tuab ntawm impedance, nws xav tias yog tus nqi tas mus li ntawm 0.5mil.

Peb tuaj yeem ua tiav kev tswj hwm impedance los ntawm kev tswj cov kev ntsuas no. Siv Anwei's bottom PCB ua piv txwv, peb yuav piav qhia cov kauj ruam ntawm kev tswj hwm impedance thiab kev siv SI9000:

Txheej thib ob yog lub dav hlau hauv av, txheej thib tsib yog lub dav hlau fais fab, thiab cov txheej seem yog cov txheej teeb liab.

Kev Piav Qhia: Lub dielectric ntawm cov txheej nruab nrab yog FR-4, nrog rau dielectric tas mus li ntawm 4.2; Cov txheej sab saud thiab hauv qab yog cov txheej liab qab uas kov ncaj qha rau huab cua, thiab dielectric tas mus li ntawm huab cua yog 1.

Cov neeg tsim PCB tuaj yeem siv cov qauv hierarchical ntawm PCBs kom ua tiav kev tswj impedance. Los ntawm kev tso cov txheej teeb liab sib txawv rau hauv cov txheej sib txawv, interlayer capacitance thiab inductance tuaj yeem tswj tau zoo. Feem ntau hais lus, txheej sab hauv siv cov ntaub ntawv impedance siab thiab txheej sab nraud siv cov ntaub ntawv impedance qis los txo qhov cuam tshuam ntawm kev cuam tshuam thiab crosstalk.

Cov kab sib txawv ntawm kev xa cov teeb liab tuaj yeem muab kev tiv thaiv kev cuam tshuam zoo dua thiab txo qhov kev pheej hmoo ntawm kev sib tham. Cov kab sib txawv ntawm kev xa cov teeb liab yog ob txoj hlua sib luag nrog cov hluav taws xob sib txawv tab sis qhov loj sib npaug, uas tuaj yeem muab kev ncaj ncees ntawm cov teeb liab thiab kev tiv thaiv kev cuam tshuam zoo dua. Qhov impedance ntawm cov kab sib txawv ntawm kev xa cov teeb liab feem ntau yog tswj los ntawm kev xaiv ntawm qhov sib nrug ntawm kab, qhov dav thiab lub dav hlau hauv av.

Cov kev ntsuas geometric xws li PCB kab dav, qhov chaw thiab qhov layout kuj siv tau los tswj impedance. Rau cov kab microstrip feem ntau, qhov dav ntawm kab tuab dua thiab qhov chaw loj dua tuaj yeem txo qhov impedance. Rau cov kab coaxial, cov kab sab hauv me dua thiab cov kab sab nraud loj dua tuaj yeem ua rau impedance nce. Kev xaiv cov qauv geometry ntawm cov xov hlau xav tau kev ua kom zoo raws li qhov xav tau impedance thiab zaus teeb liab.

Qhov dielectric tas mus li ntawm cov ntaub ntawv PCB kuj cuam tshuam rau impedance. Kev xaiv cov ntaub ntawv uas muaj cov khoom dielectric ruaj khov yog ib feem ntawm kev tswj impedance. Hauv cov ntawv thov high-frequency thiab high-speed, cov ntaub ntawv siv feem ntau suav nrog FR-4 (iav fiber reinforced board), PTFE (polytetrafluoroethylene), thiab RF (xov tooj cua zaus) laminates.

Ua ntej tsim PCB, kev siv cov cuab yeej simulation thiab tsim qauv tuaj yeem pab cov neeg tsim qauv sai thiab raug txheeb xyuas thiab kho qhov impedance kom zoo. Cov cuab yeej no tuaj yeem simulate tus cwj pwm ntawm lub voj voog, kev poob ntawm cov teeb liab thiab kev sib cuam tshuam electromagnetic los txiav txim siab qhov zoo tshaj plaws ntawm PCB tsim qauv. Qee cov cuab yeej simulation feem ntau suav nrog CST Studio Suite, HyperLynx thiab ADS.

Kev tswj hwm PCB impedance ua lub luag haujlwm tseem ceeb hauv cov hluav taws xob digital thiab analog ceev ceev. Los ntawm kev tsim qauv hierarchical tsim nyog, kev siv cov kab sib txawv ntawm cov teeb liab kis, kev tswj hwm cov qauv ntawm cov xov hlau, kev xaiv cov ntaub ntawv PCB tsim nyog, thiab kev siv cov cuab yeej simulation thiab tsim qauv, tuaj yeem ua tiav kev tswj hwm impedance meej, yog li txhim kho kev ua haujlwm ntawm lub voj voog thiab kev ncaj ncees ntawm cov teeb liab.