Ukulawula kanjani PCB impedance?

Without impedance control, considerable signal reflection and distortion will be caused, resulting in design failure. Izimpawu ezijwayelekile, njengebhasi le-PCI, ibhasi le-PCI-E, i-USB, i-Ethernet, inkumbulo ye-DDR, isiginali ye-LVDS, njll., Konke kudinga ukulawulwa kwe-impedance. Ukulawulwa kwe-impedance ekugcineni kudinga ukutholakala ngokuklanywa kwe-PCB, okubeka nezidingo eziphakeme zobuchwepheshe bebhodi le-PCB. Ngemuva kokuxhumana nefektri ye-PCB futhi kuhlanganiswe nokusetshenziswa kwesoftware ye-EDA, impedance yezintambo ilawulwa ngokuya ngezidingo zobuqotho besiginali.

Izindlela ezahlukahlukene zokufaka izintambo zingabalwa ukuthola inani le-impedance elihambelanayo.

Microstrip lines

• Inomucu wocingo onendiza yaphansi ne-dielectric maphakathi. Uma i-dielectric engaguquki, ububanzi bomugqa, nebanga layo ukusuka endizeni yasemhlabeni kuyalawuleka, impedance yayo yesici iyalawuleka, futhi ukunemba kuzoba ngaphakathi kwe- ± 5%.

What is impedance control how to perform impedance control on PCB

I-Stripline

Umugqa weribhoni umucu wethusi phakathi kwe-dielectric phakathi kwezindiza ezimbili eziqhuba. If the thickness and width of the line, the dielectric constant of the medium, and the distance between the ground planes of the two layers are controllable, the characteristic impedance of the line is controllable, and the accuracy is within 10%.

What is impedance control how to perform impedance control on PCB

The structure of multi-layer board:

Ukuze ulawule kahle i-PCB impedance, kubalulekile ukuqonda ukwakheka kwe-PCB:

Imvamisa lokho esikubiza ngokuthi ibhodi ye-multilayer yakhiwa yipuleti eliyisisekelo neshidi eliqinile elihlanganiswe ndawonye. Ibhodi eliyinhloko liwubulukhuni obunzima, obucacile, ipuleti lethusi lesinkwa, okuyisisekelo sebhodi eliphrintiwe. And the semi-cured piece constitutes the so-called infiltration layer, plays the role of bonding the core plate, although there is a certain initial thickness, but in the process of pressing its thickness will occur some changes.

Imvamisa izingqimba zombili zedielectric ezingaphandle kakhulu zemigqa eminingana ziyizingqimba ezimanzi, bese kusetshenziswa izingqimba zefreyili ezihlukile ngaphandle kwalezi zingqimba ezimbili njengefreyimu yangaphandle yethusi. Ubuningi bokuqala bokucaciswa kwe-foil yangaphandle yethusi kanye ne-foil yangaphakathi yethusi imvamisa i-0.5oz, i-1OZ, i-2OZ (i-1OZ icishe ibe yi-35um noma i-1.4mil), kepha ngemuva kochungechunge lokwelashwa kwendawo, ubukhulu bokugcina bocingo lwethusi lwangaphandle luzokwanda cishe 1OZ. Ucwecwe lwangaphakathi lwethusi luyimbozo yethusi ezinhlangothini zombili zepuleti eliyisisekelo. Ubukhulu bokugcina buhlukile kancane kubukhulu bokuqala, kepha ngokujwayelekile bancishiswa ngo-um abaningana ngenxa yokudonswa.

Isendlalelo sangaphandle sebhodi le-multilayer ungqimba lokumelana nokushisela, okuyilokho esivame ukuthi “uwoyela oluhlaza”, kunjalo, lungaba luphuzi noma eminye imibala. The thickness of the solder resistance layer is generally not easy to determine accurately. The area without copper foil on the surface is slightly thicker than the area with copper foil, but because of the lack of copper foil thickness, so the copper foil is still more prominent, when we touch the printed board surface with our fingers can feel.

When a particular thickness of the printed board is made, on the one hand, reasonable choice of material parameters is required, on the other hand, the final thickness of the semi-cured sheet will be smaller than the initial thickness. Okulandelayo isakhiwo esijwayelekile esinezingqimba eziyi-6:

What is impedance control how to perform impedance control on PCB

PCB parameters:

Different PCB plants have slight differences in PCB parameters. Through communication with circuit board plant technical support, we obtained some parameter data of the plant:

Surface ucwecwe zethusi:

There are three thicknesses of copper foil that can be used: 12um, 18um and 35um. Ubukhulu bokugcina ngemuva kokuqeda cishe buba ngu-44um, 50um no-67um.

Ipuleti elingumongo: I-S1141A, i-FR-4 ejwayelekile, amapuleti amabili wethusi ayisinkwa asetshenziswa kakhulu. Ukucaciswa kokuzikhethela kunganqunywa ngokuxhumana nomkhiqizi.

Semi-cured tablet:

Imininingwane (ubukhulu bangempela) ingu-7628 (0.185mm), 2116 (0.105mm), 1080 (0.075mm), 3313 (0.095mm). Ubukhulu bangempela ngemuva kokucindezela imvamisa cishe bube ngu-10-15um ngaphansi kwenani langempela. Kungasetshenziswa amaphilisi ama-3 aphulukisiwe angaphansi kwesendlalelo esifanayo sokungena, futhi ukushuba kwamaphilisi amathathu aphulukisiwe akunakufana, okungenani kungasetshenziswa amaphilisi ayisithupha aphulukisiwe, kepha abanye abakhiqizi kufanele basebenzise okungenani amabili . Uma ukushuba kwesiqeshana eselaphekiwe kunganele, ucwecwe lwethusi ezinhlangothini zombili zepuleti lomgogodla lungasuswa, bese kuthi isiqeshana eselapheke kancane singahlanganiswa ezinhlangothini zombili, ukuze ungqimba lokungena olunamandla lube kufinyelelwe.

Ukumelana Welding ungqimba:

Ubukhulu besendlalelo se-solder resist on the foil yethusi ngu-C2≈-8-10um. Ubukhulu besendlalelo sokumelana ne-solder ebusweni ngaphandle kocwecwe lwethusi yi-C1, ehluka ngobukhulu bethusi ebusweni. Lapho ukushuba kwethusi ebusweni kungu-45um, C1≈13-15um, futhi lapho ukushuba kwethusi ebusweni kungu-70um, C1-17-18um.

Isigaba sokunqamula:

Singacabanga ukuthi ingxenye yesiphambano yocingo ingunxande, kepha empeleni iyi-trapezoid. Ukuthatha ungqimba we-TOP njengesibonelo, lapho ukushuba kocwecwe lwethusi kuyi-1OZ, umphetho ongaphezulu ongezansi we-trapezoid ngu-1MIL mfushane kunomphetho ongezansi ongezansi. Isibonelo, uma ububanzi bomugqa bungu-5MIL, khona-ke izinhlangothi eziphezulu nezingezansi zimayelana ne-4MIL kanti izinhlangothi ezingezansi nezingezansi zingaba ngu-5MIL. Umehluko phakathi kwemiphetho ephezulu neyaphansi uhlobene nokujiya kwethusi. Ithebula elilandelayo likhombisa ubudlelwane obuphakathi phezulu nangaphansi kwe-trapezoid ngaphansi kwezimo ezihlukile.

What is impedance control how to perform impedance control on PCB

Ukuvunyelwa: Ukuvunyelwa kwamashidi aphulukiswe kancane kuhlobene nokushuba. Ithebula elilandelayo likhombisa ukushuba nokuvunyelwa kwemingcele yezinhlobo ezahlukahlukene zamashidi aphulukisiwe:

What is impedance control how to perform impedance control on PCB

Ukuhlala kwe-dielectric kwepuleti kuhlobene nezinto ze-resin ezisetshenzisiwe. Ukuguquguquka kwedielectri kwepuleti le-FR4 kungu-4.2 – 4.7, futhi kuncipha ngokwanda kwemvamisa.

Isici sokulahleka kwe-dielectric: izinto zedielectric ngaphansi kwesenzo sokushintsha inkambu kagesi, ngenxa yokushisa namandla okusetshenziswa kubizwa ngokuthi ukulahleka kwe-dielectric, okuvame ukuvezwa nge-dielectric loss factor Tan δ. Inani elijwayelekile le-S1141A lingu-0.015.

Ubuncane bomugqa wobubanzi nokuhlukaniswa kwemigqa ukuqinisekisa ukusetshenziswa: 4mil / 4mil.

Isingeniso sethuluzi lokubala le-impedance:

Lapho siqonda ukwakheka kwebhodi le-multilayer futhi sazi imingcele edingekayo, singabala impedance nge-software ye-EDA. Ungasebenzisa i-Allegro ukwenza lokhu, kepha ngincoma iPolar SI9000, okuyithuluzi elihle lokubala impedance yesici futhi manje isetshenziswa amafemu amaningi e-PCB.

Lapho kubalwa impedance yesici sesiginali yangaphakathi yomugqa wokuhlukanisa nolayini owodwa wokugcina, uzothola umehluko omncane kuphela phakathi kwePolar SI9000 ne-Allegro ngenxa yeminye imininingwane, njengokuma kwengxenye yesiphambano setambo. Kodwa-ke, uma kuzobalwa i-impedance yesici sesiginali ye-Surface, ngiphakamisa ukuthi ukhethe imodeli Eboshwe esikhundleni semodeli ye-Surface, ngoba amamodeli anjalo abhekela ubukhona besendlalelo sokumelana nesoder, ngakho-ke imiphumela izoba nenembile. Okulandelayo isithombe-skrini esinqunyelwe se-impedance yomugqa wokwahlukaniswa komhlaba obalwe nePolar SI9000 kubhekwa ungqimba lokumelana ne-solder:

What is impedance control how to perform impedance control on PCB

Njengoba ukushuba kwesendlalelo se-solder resist kungalawulwa kalula, indlela eseduze nayo ingasetshenziswa, njengoba kunconyiwe ngumkhiqizi webhodi: khipha inani elithile kusibalo semodeli ye-Surface. Kunconywa ukuthi i-impedance umehluko ibe ngu-8 ohms kanye ne-single-end impedance ibe ngu-2 ohms.

Izidingo ezihlukile ze-PCB zezintambo

(1) Thola imodi yezintambo, amapharamitha nokubalwa kwe-impedance. Kunezinhlobo ezimbili zezindlela zokwehluka komugqa womzila: imodi yongqimba lwangaphandle lwe-microstrip mode kanye nemodi yomehluko womugqa wesendlalelo sangaphakathi. Impedance ingabalwa ngesoftware yokubala ehlobene ye-impedance (efana ne-POLAR-SI9000) noma ifomula yokubalwa kwe-impedance ngokuhlelwa kwepharamitha okufanelekile.

(2) Imigqa ehambisanayo ye-isometric. Thola ububanzi bomugqa nezikhala, bese ulandela ngokuqinile ububanzi bomugqa obaliwe nezikhala lapho kuhanjiswa umzila. Isikhala phakathi kwemigqa emibili kufanele sihlale singashintshi, okungukuthi, ukugcina ukufana. There are two ways of parallelism: one is that the two lines walk in the same side-by-side layer, and the other is that the two lines walk in the over-under layer. Ngokuvamile zama ukugwema ukusebenzisa isignali yomehluko phakathi kwezendlalelo, okungukuthi ngoba ekucutshungweni kwangempela kwe-PCB kunqubo, ngenxa yokunemba kokulungiswa kokulungiswa okune-laminated kuncane kakhulu kunalokho okuhlinzekwe phakathi kokunemba kwe-etching, nasenqubeni yokulahleka kuketshezi okunamathiselwe, akunakuqinisekisa ukuthi ukwehlukaniswa komugqa kuyalingana nobukhulu be-dielectric ye-interlayer, kuzodala umehluko phakathi kwezendlalelo zokwehluka koshintsho lwe-impedance. Kunconywa ukusebenzisa umehluko ngaphakathi kwesendlalelo esifanayo ngangokunokwenzeka.