With the increasing speed of PCB beddelidda signal, naqshadeeyayaasha PCB ee maanta waxay u baahan yihiin inay fahmaan oo ay xakameeyaan is -hortaagga raadadka PCB. U dhigma waqtiyada gudbinta signalada gaaban iyo heerka saacadaha sare ee wareegyada dhijitaalka ah ee casriga ah, raadadka PCB hadda ma aha isku xirnaan fudud, laakiin waa khadadka gudbinta.

Sida loo xakameeyo impedance PCB

Ficil ahaan, waxaa lagama maarmaan ah in la xakameeyo raad -raaca marka xawaaraha dhijitaalka ah ee dhijitaalka ah uu dhaafo 1ns ama inta jeer ee analoggu ka badan yahay 300Mhz. Mid ka mid ah halbeegyada muhiimka ah ee raad -raaca PCB -ga ayaa ah is -beddelkiisa dabeecadda (saamiga danab iyo kan hadda sida hirarku u socdo safka gudbinta signalada). Cillad -darrada dabeecadda ee siligga ee ku taal guddiga wareegga ee daabacan ayaa ah tilmaame muhiim u ah naqshadda guddiga wareegga, gaar ahaan naqshadeynta PCB ee wareegga soo noqnoqoshada sare, waa in la tixgeliyaa haddii is -xakamaynta dabeecadda ee siligga ay la jaanqaadayso is -beddelka dabeecadda ee ay u baahan tahay aaladda ama signalada. This involves two concepts: impedance control and impedance matching. This paper focuses on impedance control and lamination design.

Xakamaynta xakamaynta

Xakamaynta EImpedance, kaariyaha guddiga wareegga wuxuu lahaan doonaa dhammaan noocyada kala -gudbinta calaamadaha, si loo hagaajiyo heerka gudbinta oo waa inuu kordhiyaa soo noqnoqoshada, haddii khadka laftiisa ay sabab u tahay qashin -qubka, dhumucda xargaha, ballaca siligga iyo arrimo kale oo kala duwan, ayaa sababi doona isbeddelka qiimaha is -beddelka, dhalan -rogga signalada. Sidaa darteed, qiimaha impedance ee kaariyuhu ku leeyahay guddiga wareegga-xawaaraha sare waa in lagu xakameeyaa xayndaab gaar ah, oo loo yaqaan “xakamaynta impedance”.

The impedance of a PCB trace will be determined by its inductive and capacitive inductance, resistance, and conductivity coefficient. Waxyaabaha ugu waaweyn ee saameynaya carqaladaynta fiilooyinka PCB waa: ballaca siligga naxaas, dhumucda siligga naxaasta, joogteynta dielectric ee dhexdhexaadka, dhumucda dhexdhexaadka, dhumucda suufka, waddada siligga dhulka, fiilooyinka ku wareegsan fiilooyinka , iwm. Isbeddelka PCB wuxuu u dhexeeyaa 25 illaa 120 ohm.

Ficil ahaan, khadka gudbinta PCB caadi ahaan wuxuu ka kooban yahay raad, hal ama dhowr lakab oo tixraac ah, iyo qalabka dahaarka. Raad -raaca iyo lakabyada ayaa sameeya is -xakamaynta xakamaynta. PCBS-yada badiyaa waxay noqon doonaan lakabyo badan, iyo xakamaynta xakamaynta waxaa loo dhisi karaa siyaabo kala duwan. However, whatever method is used, the impedance value will be determined by its physical structure and the electrical properties of the insulating material:

Ballaca iyo dhumucda raadraaca signalada

Dhererka udub -dhexaadka ama walxaha prefill ee labada dhinac ee raadraaca

Qalabaynta raad iyo saxan

Insulation constants of core and prefilled materials

Khadadka gudbinta PCB waxay ku yimaadaan laba qaab oo waaweyn: Microstrip iyo Stripline.

Microstrip:

Khadka microstrip -ka waa xarig xarig leh oo leh diyaarad tixraac oo dhinac kaliya ah, oo dusha iyo dhinacyaduba u fidsan yihiin hawada (ama dahaarka leh), oo ka sarreysa dusha sare ee dahaarka guddiga wareegga Er ee joogtada ah, oo leh korontada ama saldhigga tixraac ahaan. Sida hoos ka muuqata:

Fiiro gaar ah: Wax -soo -saarka PCB -ga dhabta ah, soo -saaraha guddigu wuxuu inta badan ku dahaadhaa dusha PCB -ga lakab saliid cagaaran ah, sidaa darteed xisaabinta impedance -ka dhabta ah, moodalka hoos lagu muujiyey waxaa badanaa loo adeegsadaa xisaabinta khadka microstrip -ka:

Xariijin:

Xarriiqda xarig waa xarig silig ah oo la dhex dhigay laba diyaaradood oo tixraac ah, sida ka muuqata shaxda hoose. Jaangooyooyinka dielectric ee dielectric -ka ay matalaan H1 iyo H2 way kala duwanaan karaan.

The above two examples are only a typical demonstration of microstrip lines and ribbon lines. There are many kinds of specific microstrip lines and ribbon lines, such as coated microstrip lines, which are related to the specific laminated structure of PCB.

The equations used to calculate the characteristic impedances require complex mathematical calculations, usually using field solving methods, including boundary element analysis, so using the specialized impedance calculation software SI9000, all we need to do is control the parameters of the characteristic impedances:

Dielectric constant Er, wiring width W1, W2 (trapezoid), wiring thickness T and insulation layer thickness H.

W1, W2:

The calculated value must be within the red box. Iyo wixii la mid ah.

SI9000 waxaa loo isticmaalaa in lagu xisaabiyo in shuruudaha xakamaynta impedance la buuxiyey:

Marka hore xisaabi xakamaynta hal-dhamaadka impedance of line data DDR:

Lakabka TOP: 0.5oz dhumucda naxaasta, ballaca siligga 5MIL, masaafo 3.8mil u jirta diyaaradda tixraaca, 4.2. Dooro tusaalaha, ku beddel cabbirrada, oo dooro Xisaabinta Khasaaray, sida ku cad shaxanka:

CoaTIng micnaheedu waa isku -duubnaan, oo haddii aysan jirin isku -duubni, buuxi 0 dhumucdiisuna tahay 1 oo ah koronto -dhaliyaha (dielectric joogto ah) (hawo).

Substrate-ku wuxuu u taagan yahay lakabka substrate, taas oo ah, lakabka dielectric, guud ahaan iyadoo la adeegsanayo fr-4, dhumucda lagu xisaabiyay softiweerka xisaabinta impedance, 4.2 joogto ah (inta jeer ka yar 1GHz).

Click on Weight (oz) to set the thickness of the copper layer, which determines the thickness of the cable.

9. Diyaarinta/Fikradda Muhiimka ah ee lakabka dahaarka:

PP (Prepreg) waa nooc ka mid ah qalabka korontada ku shaqeeya, oo ka kooban fiber galaas iyo cusbi epoxy. Dhab ahaantii Core waa nooc ka mid ah dhexdhexaad PP, laakiin labadiisa dhinac waxaa lagu daboolay bireed naxaas ah, halka PP aysan ahayn. Marka la samaynayo looxyo badan, udub -dhexaadka iyo PP ayaa sida caadiga ah la wada isticmaalaa, PP -na waxaa loo isticmaalaa in lagu xidho xudunta iyo xudunta.

10. Arrimaha u baahan in fiiro gaar ah loo yeesho naqshadaynta dahaarka PCB

(1) Dhibaatada warpage

Naqshadaynta lakabka ee PCB waa inay ahaato mid siman, taas oo ah, dhumucda lakabka dhexdhexaadka ah iyo lakabka naxaasta ee lakab kasta waa inuu ahaadaa mid siman. Qaado lix lakab tusaale ahaan, dhumucda GND-da sare iyo dhexdhexaad-awoodda hoose waa inay la jaanqaaddaa dhumucda naxaasta, IYO ta GND-L2 iyo L3-POWER dhexdhexaadku waa inay la jaanqaaddaa dhumucda naxaasta. Tani ma dillaaci doonto marka la xirayo.

) Dharka naxaasta ee korontada ah iyo labiska naxaasta dhulka waa in si adag laysugu xidhaa.

(3) Markay tahay xawaare aad u sarreeya, lakabyo dheeri ah ayaa lagu dari karaa si loo go’doomiyo lakabka signalada, laakiin waxaa lagu talinayaa inaan la kala soocin lakabyo awood badan, oo sababi kara faragelin qaylo aan loo baahnayn.

(4) Qeybinta lakabyada naqshadeynta caadiga ah ee dahaarka leh ayaa lagu muujiyay shaxda soo socota:

(5) Mabaadiida guud ee habaynta lakabka:

Dusha sare ee qaybta (lakabka labaad) waa diyaaradda dhulka, taas oo bixisa lakabka gaashaanka qalabka iyo diyaaradda tixraaca ee fiilooyinka lakabka sare;

Dhammaan lakabyada calaamaduhu waxay ku dhegan yihiin diyaaradda dhulka intii suurtogal ah.

Ka fogow isu -dhowaanshaha tooska ah ee u dhexeeya laba lakab oo signal inta ugu badan ee suurtogalka ah;

Awoodda ugu weyn ee korontadu waa inay ahaataa mid u dhow sida ugu macquulsan;

Calaamadda qaab -dhismeedka dahaarka ayaa la tixgeliyaa.

For the layer layout of the motherboard, it is difficult for the existing motherboard to control the parallel long-distance wiring, and the working frequency of the board level is above 50MHZ

(Xaaladaha ka hooseeya 50MHZ, fadlan tixraac oo si habboon u dabci), mabda’a qaab -dhismeedka ayaa la soo jeediyay:

Dusha sare iyo dusha alxanka waa diyaarad dhulka oo dhameystiran (gaashaan);

Ma jiro lakab xarig oo isbarbar socda;

Dhammaan lakabyada calaamaduhu waxay ku dhegan yihiin diyaaradda dhulka intii suurtogal ah.

Calaamadda muhiimka ahi waxay ku dhegan tahay samayska mana dhaafto aagga kala -qaybinta.