Momwe mungayang’anire PCB impedance?

Without impedance control, considerable signal reflection and distortion will be caused, resulting in design failure. Zizindikiro wamba, monga basi ya PCI, basi ya PCI-E, USB, Ethernet, kukumbukira kwa DDR, siginecha ya LVDS, ndi zina zambiri, zonse zimafunikira kuwongolera ma impedance. Impedance control ultimately needs to be realized through PCB design, which also puts forward higher requirements for PCB board technology. After communication with PCB factory and combined with the use of EDA software, the impedance of wiring is controlled according to the requirements of signal integrity.

Njira zosiyanasiyana zolumikizira zingaperekedwe kuti muthe kupeza mtengo wolingana wa impedance.

Microstrip lines

• Ili ndi chingwe cha waya wokhala ndi ndege yapansi ndi ma dielectric pakati. Ngati nthawi zonse dielectric, m’lifupi mwake mzere, ndi mtunda wake kuchokera kumtunda wapansi ndizoyendetsedwa, ndiye kuti mawonekedwe ake amatha kuwongoleredwa, ndipo kulondola kwake kumakhala mkati mwa ± 5%.

What is impedance control how to perform impedance control on PCB

Mzere

Mzere wa riboni ndi mzere wamkuwa pakati pa dielectric pakati pa ndege ziwiri zoyendetsa. 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:

Pofuna kuwongolera bwino mpweya wa PCB, ndikofunikira kumvetsetsa kapangidwe ka PCB:

Kawirikawiri chimene timachitcha bolodi multilayer wapangidwa mbale pachimake ndi theka-solidified pepala laminated pamodzi ndi mzake. Kore board ndi yolimba, yolimba makulidwe, mbale ziwiri zamkuwa zamkuwa, zomwe ndizofunikira kwambiri pa bolodi losindikizidwa. 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.

Kawirikawiri zigawo zakumapeto kwa ma dielectric a multilayer ndizonyowa, ndipo zigawo za mkuwa zimagwiritsidwa ntchito kunja kwa zigawo ziwirizi ngati zojambulazo zamkuwa zakunja. The makulidwe choyambirira mfundo za zojambulazo akunja mkuwa ndi zojambulazo mkati mkuwa zojambulazo zambiri 0.5oz, 1OZ, 2OZ (1OZ ndi za 35um kapena 1.4mil), koma pambuyo pa mndandanda wa chithandizo chapamwamba, makulidwe omaliza a zojambulazo zamkuwa wakunja zimakulirakulira pafupifupi 1OZ. Chojambula chamkuwa chamkati ndichophimba chamkuwa mbali zonse ziwiri za mbale yayikulu. Makulidwe omaliza amasiyana pang’ono ndi makulidwe apachiyambi, koma nthawi zambiri amachepetsedwa ndi ma um angapo chifukwa chakuthwa.

The outermost layer of the multilayer board is the welding resistance layer, which is what we often say “green oil”, of course, it can also be yellow or other colors. 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.

Pakakhala makulidwe ena a bolodi losindikizidwa, mbali imodzi, kusankha koyenera kwa magawo azinthu kumafunika, komano, makulidwe omaliza a pepala lomwe lachiritsidwa azikhala laling’ono kuposa makulidwe oyambilira. Otsatirawa ndi mawonekedwe 6 osanjikiza:

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:

Pamwamba zojambulazo mkuwa:

There are three thicknesses of copper foil that can be used: 12um, 18um and 35um. Makulidwe omaliza atamaliza ndi pafupifupi 44um, 50um ndi 67um.

Mbale yachitsulo: S1141A, muyezo FR-4, mbale ziwiri zamkuwa zimagwiritsidwa ntchito kwambiri. Zomwe mungasankhe zitha kutsimikizika polumikizana ndi wopanga.

Semi-cured tablet:

Specifications (original thickness) are 7628 (0.185mm), 2116 (0.105mm), 1080 (0.075mm), 3313 (0.095mm). The actual thickness after pressing is usually about 10-15um less than the original value. Mapiritsi atatu otetezedwa pang’ono atha kugwiritsidwa ntchito polowererapo chimodzimodzi, ndipo makulidwe a mapiritsi atatu osachiritsidwa sangakhale ofanana, mapiritsi osachepera theka angagwiritsidwe ntchito, koma opanga ena ayenera kugwiritsa ntchito osachepera awiri . Ngati makulidwe a chidutswacho sichikwanira, zojambulazo zamkuwa mbali zonse ziwiri za mbaleyo zimatha kuzimitsidwa, kenako chidutswa chomwe chidachiritsidwa chimatha kulumikizidwa mbali zonse ziwiri, kuti cholowerera cholowera chikhale zakwaniritsidwa.

Kukana kuwotcherera wosanjikiza:

Kutalika kwa solder kukana wosanjikiza pazithunzi zamkuwa ndi C2≈-8-10um. Kutalika kwa solder kukana wosanjikiza pamwamba popanda zojambulazo zamkuwa ndi C1, zomwe zimasiyanasiyana ndi makulidwe amkuwa pamtunda. Pamene makulidwe amkuwa pamwamba ndi 45um, C≈1-13um, ndipo makulidwe amkuwa pamtunda ali 15um, C70≈1-17um.

Gawo loyenda:

Titha kuganiza kuti gawo lamtundu wa waya ndi laling’ono, koma kwenikweni ndi trapezoid. Kutenga TOP wosanjikiza monga chitsanzo, pamene makulidwe a zojambulazo zamkuwa ndi 1OZ, m’munsi chapamwamba m’mphepete mwa trapezoid ndi 1MIL wamfupi kuposa m’mphepete pansi. Mwachitsanzo, ngati mulifupi mulifupi ndi 5MIL, ndiye kuti mbali zakumtunda ndi zapansi zili pafupifupi 4MIL ndipo mbali zapansi ndi pansi zili pafupifupi 5MIL. The difference between top and bottom edges is related to copper thickness. The following table shows the relationship between top and bottom of trapezoid under different conditions.

What is impedance control how to perform impedance control on PCB

Kuloleza: Kololedwa kwa mapepala omwe amachiritsidwa ndikokhudzana ndi makulidwe. Tebulo lotsatirali likuwonetsa makulidwe ndi kuloleza magawo amitundu yosiyanasiyana yamankhwala ochiritsidwa:

What is impedance control how to perform impedance control on PCB

The dielectric constant of the plate is related to the resin material used. The dielectric constant of FR4 plate is 4.2 — 4.7, and decreases with the increase of frequency.

Kutaya kwa dielectric factor: zida zamagetsi zomwe zimasinthidwa ndikusintha magetsi, chifukwa cha kutentha ndi kugwiritsa ntchito mphamvu kumatchedwa kutaya kwa dielectric, komwe kumawonetsedwa ndi kutaya kwa dielectric factor Tan δ. Mtengo wofanana wa S1141A ndi 0.015.

Osachepera mzere m’lifupi ndi katayanitsidwe mzere kuonetsetsa Machining: 4mil / 4mil.

Kuwerengera chida chowerengera cha impedance:

Tikamvetsetsa kapangidwe ka bolodi yama multilayer ndikudziwa magawo oyenera, titha kuwerengera zosokoneza kudzera pulogalamu ya EDA. Mutha kugwiritsa ntchito Allegro kuti muchite izi, koma ndikupangira Polar SI9000, chomwe ndi chida chabwino chowerengera zosokoneza zomwe zikugwiritsidwa ntchito ndi mafakitale ambiri a PCB.

Powerengera kutsekemera kwamakina amkati amizere yonse ndi mzere umodzi wokha, mupeza kusiyana pang’ono pakati pa Polar SI9000 ndi Allegro chifukwa cha zina, monga mawonekedwe a mtanda wa waya. Komabe, ngati ikuyenera kuwerengetsa mawonekedwe amtundu wa Surface, ndikukuuzani kuti musankhe mtundu wokutira m’malo mwa mawonekedwe a Surface, chifukwa mitundu iyi imaganizira za kukhalapo kwa chosanjikiza cha solder, zotsatira zake zidzakhala zolondola kwambiri. Chotsatirachi ndichithunzi pang’ono cha mawonekedwe amtundu wosiyana owerengera owerengedwa ndi Polar SI9000 poganizira zosanjikiza za solder:

What is impedance control how to perform impedance control on PCB

Popeza makulidwe osanjikiza osungunuka sangawongoleredwe mosavuta, njira yofananira itha kugwiritsidwanso ntchito, monga ikulimbikitsidwa ndi wopanga bolodi: chotsani phindu linalake pakuwerengera kwa Surface. Ndikulimbikitsidwa kuti malire osiyanitsa akhale ochepera ma 8 ohms ndipo gawo limodzi lamapeto lisakhale 2 ohms.

Kusiyanitsa kwa PCB pakukonda

(1) Sankhani mawonekedwe a zingwe, magawidwe ake ndi kuwerengera kwa impedance. Pali mitundu iwiri yamitundu yosiyanitsira njira yolowera: mitundu yakunja yama microstrip mzere wosiyanitsa mitundu ndi mawonekedwe osiyanitsa mzere wosanjikiza. Impedance imatha kuwerengedwa ndi pulogalamu yofananira yowerengera ma impedance (monga POLAR-SI9000) kapena njira yowerengera ya impedance pogwiritsa ntchito magawo oyenera.

(2) Mizere yofanana yozungulira. Sankhani m’lifupi mwake ndi katayanitsidwe, ndipo tsatirani mosamalitsa mulitali ndi malo omwe anawerengedwa poyenda. Kusiyanitsa pakati pa mizere iwiri kuyenera kukhalabe kosasintha, ndiye kuti, kufanana. 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. Nthawi zambiri yesetsani kupewa kugwiritsa ntchito chizindikiro chosiyana pakati pa zigawozo, chifukwa chifukwa pokonza PCB pakadali pano, chifukwa cha kulondola kwa mayikidwe a laminated ndikotsika kwambiri kuposa momwe zimakhalira pakati pa utoto, komanso pakuwonongeka kwa ma dielectric, Sitingatsimikizire kuti kusiyanasiyana kwa mzere ndikofanana ndi makulidwe a dielectric yama interlayer, kungayambitse kusiyana pakati pa zigawo za kusiyana kwa impedance kusintha. Tikulimbikitsidwa kuti mugwiritse ntchito kusiyanasiyana momwe mungathere.