Bii o ṣe le ṣakoso PCB ikọjujasi?

Without impedance control, considerable signal reflection and distortion will be caused, resulting in design failure. Awọn ifihan agbara ti o wọpọ, bii ọkọ akero PCI, ọkọ akero PCI-E, USB, Ethernet, iranti DDR, ifihan LVDS, ati bẹbẹ lọ, gbogbo wọn nilo iṣakoso ikọlu. Iṣakoso ikọlu nikẹhin nilo lati ni imuse nipasẹ apẹrẹ PCB, eyiti o tun fi awọn ibeere ti o ga siwaju siwaju fun imọ -ẹrọ igbimọ PCB. Lẹhin ibaraẹnisọrọ pẹlu ile -iṣẹ PCB ati ni idapo pẹlu lilo sọfitiwia EDA, ikọlu ti wiwaba wa ni iṣakoso ni ibamu si awọn ibeere ti iduroṣinṣin ifihan.

Awọn ọna wiwọn oriṣiriṣi le ṣe iṣiro lati gba iye ikọlu ti o baamu.

Microstrip lines

• O ni okun okun waya pẹlu ọkọ ofurufu ilẹ ati aisi -itanna ni aarin. Ti ibakan aisi -itanna, iwọn ila, ati ijinna rẹ lati ọkọ ofurufu ilẹ jẹ iṣakoso, lẹhinna ikọlu abuda rẹ jẹ iṣakoso, ati pe deede yoo wa laarin ± 5%.

What is impedance control how to perform impedance control on PCB

Ipele

Laini tẹẹrẹ kan jẹ ṣiṣan idẹ ni aarin ti aisi -itanna laarin awọn ọkọ ofurufu meji ti n ṣakoso. 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:

Lati le ṣakoso ikọlu PCB daradara, o jẹ dandan lati ni oye igbekalẹ ti PCB:

Maa ohun ti a pe multilayer ọkọ ni ṣe soke ti mojuto awo ati ologbele-solidified dì laminated pọ pẹlu kọọkan miiran. Igbimọ mojuto jẹ lile, sisanra kan pato, awo akara idẹ meji, eyiti o jẹ ohun elo ipilẹ ti igbimọ ti a tẹjade. 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.

Nigbagbogbo awọn fẹlẹfẹlẹ apọju meji ti apọju pupọ jẹ awọn fẹlẹfẹlẹ tutu, ati awọn fẹlẹfẹlẹ bankanje lọtọ ni a lo ni ita ti awọn fẹlẹfẹlẹ meji wọnyi bi bankanje idẹ ti ita. Awọn sipesifikesonu sisanra atilẹba ti bankanje Ejò lode ati bankanje idẹ ti inu jẹ gbogbo 0.5oz, 1OZ, 2OZ (1OZ jẹ nipa 35um tabi 1.4mil), ṣugbọn lẹhin lẹsẹsẹ itọju oju ilẹ, sisanra ikẹhin ti bankanje Ejò ita yoo pọ si ni gbogbogbo nipa 1OZ. Bọtini idẹ ti inu jẹ ibora ti idẹ ni ẹgbẹ mejeeji ti awo mojuto. Awọn sisanra ikẹhin yatọ diẹ si sisanra atilẹba, ṣugbọn o dinku ni gbogbogbo nipasẹ ọpọlọpọ um nitori etching.

Ipele ita ti igbimọ multilayer jẹ Layer resistance alurinmorin, eyiti o jẹ ohun ti a sọ nigbagbogbo “epo alawọ”, nitoribẹẹ, o tun le jẹ ofeefee tabi awọn awọ miiran. 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. Atẹle naa jẹ ipilẹ ti a fi laminated fẹlẹfẹlẹ 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:

Bankan Ejò dada:

There are three thicknesses of copper foil that can be used: 12um, 18um and 35um. Awọn sisanra ikẹhin lẹhin ipari jẹ nipa 44um, 50um ati 67um.

Awo mojuto: S1141A, boṣewa FR-4, awọn abọ idẹ meji ti o jẹ akara ni a lo nigbagbogbo. Awọn pato yiyan le jẹ ipinnu nipa kikan si olupese.

Semi-cured tablet:

Awọn pato (sisanra atilẹba) jẹ 7628 (0.185mm), 2116 (0.105mm), 1080 (0.075mm), 3313 (0.095mm). Awọn sisanra gangan lẹhin titẹ jẹ igbagbogbo nipa 10-15um kere ju iye atilẹba. Iwọn ti awọn tabulẹti ti o ni itọju mẹta 3 le ṣee lo fun fẹlẹfẹlẹ idawọle kanna, ati sisanra ti awọn tabulẹti ologbele-3 ko le jẹ kanna, o kere ju idaji awọn tabulẹti ti a mu larada le ṣee lo, ṣugbọn diẹ ninu awọn aṣelọpọ gbọdọ lo o kere ju meji . Ti sisanra ti nkan ti o ni imularada ko to, bankanje idẹ ni ẹgbẹ mejeeji ti awo mojuto le ti wa ni pipa, ati lẹhinna nkan ti o ni imularada le ni asopọ ni ẹgbẹ mejeeji, ki fẹlẹfẹlẹ ti o nipọn ti o nipọn le jẹ ti ṣaṣeyọri.

Resistance alurinmorin Layer:

Awọn sisanra ti solder koju Layer lori bankanje Ejò ni C2≈8-10um. Awọn sisanra ti awọn solder koju Layer lori dada lai Ejò bankanje ni C1, eyi ti o yatọ pẹlu awọn sisanra ti Ejò lori dada. Nigbati sisanra ti idẹ lori dada jẹ 45um, C1≈13-15um, ati nigbati sisanra ti idẹ lori dada jẹ 70um, C1≈17-18um.

Ipa ọna:

A yoo ro pe apakan agbelebu ti okun waya jẹ onigun mẹta, ṣugbọn o jẹ trapezoid gangan. Gbigba ipele TOP bi apẹẹrẹ, nigbati sisanra ti bankanje idẹ jẹ 1OZ, eti isalẹ isalẹ ti trapezoid jẹ 1MIL kikuru ju eti isalẹ isalẹ. Fun apẹẹrẹ, ti iwọn ila naa ba jẹ 5MIL, lẹhinna awọn apa oke ati isalẹ jẹ nipa 4MIL ati awọn ẹgbẹ isalẹ ati isalẹ jẹ nipa 5MIL. Iyato laarin awọn ẹgbẹ oke ati isalẹ jẹ ibatan si sisanra idẹ. Tabili atẹle n fihan ibatan laarin oke ati isalẹ ti trapezoid labẹ awọn ipo oriṣiriṣi.

What is impedance control how to perform impedance control on PCB

Iyọọda: Iyọọda ti awọn iwe-itọju ti o ni itọju jẹ ibatan si sisanra. Tabili ti o tẹle n fihan sisanra ati awọn aye iyọọda ti awọn oriṣi oriṣiriṣi ti awọn iwe-itọju alabọde:

What is impedance control how to perform impedance control on PCB

Awọn aisi -itanna ibakan ti awo ni ibatan si awọn ohun elo resini ti a lo. Iwọn aisi -itanna ti awo FR4 jẹ 4.2 – 4.7, ati dinku pẹlu ilosoke igbohunsafẹfẹ.

Ifosiwewe pipadanu aisi -itanna: awọn ohun elo aisi -itanna labẹ iṣe ti iyipo ina mọnamọna, nitori ooru ati agbara agbara ni a pe ni pipadanu aisi -itanna, nigbagbogbo ṣafihan nipasẹ ifosiwewe pipadanu aisi -itanna Tan δ. Iye aṣoju fun S1141A jẹ 0.015.

Iwọn laini ti o kere julọ ati aye laini lati rii daju ẹrọ: 4mil/4mil.

Ifilọlẹ ohun elo iṣiro iṣiro impedance:

Nigba ti a ba loye igbekalẹ ti igbimọ multilayer ati Titunto si awọn iwọn ti a beere, a le ṣe iṣiro ikọlu nipasẹ sọfitiwia EDA. O le lo Allegro lati ṣe eyi, ṣugbọn Mo ṣeduro Polar SI9000, eyiti o jẹ ọpa ti o dara fun iṣiro iṣiro ikọlu ati pe o lo bayi nipasẹ ọpọlọpọ awọn ile -iṣelọpọ PCB.

Nigbati o ba n ṣe iṣiro ikọlu abuda ti ifihan inu ti mejeeji laini iyatọ ati laini ebute nikan, iwọ yoo rii iyatọ diẹ laarin Polar SI9000 ati Allegro nitori awọn alaye diẹ, gẹgẹbi apẹrẹ apakan agbelebu ti okun waya. Bibẹẹkọ, ti o ba jẹ lati ṣe iṣiro ikọlu abuda ti ami ifihan dada, Mo daba pe ki o yan awoṣe ti a bo dipo awoṣe Ilẹ, nitori iru awọn awoṣe ṣe akiyesi aye ti fẹlẹfẹlẹ resistance, nitorina awọn abajade yoo jẹ deede diẹ sii. Awọn atẹle jẹ sikirinifoto apa kan ti ikọlu laini iyatọ dada ti a ṣe iṣiro pẹlu Polar SI9000 ti n ṣakiyesi Layer resistance solder:

What is impedance control how to perform impedance control on PCB

Niwọn igba ti sisanra ti fẹẹrẹ fẹẹrẹ fẹẹrẹ ko ni iṣakoso ni rọọrun, ọna isunmọ tun le ṣee lo, bi a ti ṣeduro nipasẹ olupese ọkọ: yọkuro iye kan pato lati iṣiro awoṣe dada. A ṣe iṣeduro pe ikọlu iyatọ jẹ iyokuro 8 ohms ati idiwọ ikọja-ọkan jẹ iyokuro 2 ohms.

Awọn ibeere PCB iyatọ fun wiwa

(1) Pinnu ipo wiwa, awọn aye ati iṣiro ikọlu. Awọn ipo iyatọ meji lo wa fun ipa ọna laini: ipo iyatọ laini microstrip laini ita ati ipo iyatọ laini rinhoho inu. Idena le ṣe iṣiro nipasẹ sọfitiwia iṣiro iṣiro ikọlu ti o jọmọ (bii POLAR-SI9000) tabi agbekalẹ iṣiro ikọlu nipasẹ eto paramita ti o peye.

(2) Awọn laini isometric ti o jọra. Pinnu iwọn ila ati aye, ki o tẹle muna iwọn ila laini iṣiro ati aye nigba lilọ kiri. Aaye laarin awọn laini meji gbọdọ wa ni aiyipada nigbagbogbo, iyẹn ni, lati tọju ni afiwe. 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. Ni gbogbogbo gbiyanju lati yago fun lilo ami iyasọtọ laarin awọn fẹlẹfẹlẹ, eyun nitori ninu sisẹ gangan ti PCB ninu ilana, nitori titọ titete laminated jẹ iwọn kekere ju ti a pese laarin titọ etching, ati ninu ilana ti pipadanu aisi -itanna ti a ti laminated, ko le ṣe iṣeduro aaye laini iyatọ jẹ dọgba si sisanra ti aisi -itanna interlayer, yoo fa iyatọ laarin awọn fẹlẹfẹlẹ ti iyatọ ti iyipada impedance. A ṣe iṣeduro lati lo iyatọ laarin fẹlẹfẹlẹ kanna bi o ti ṣee.