With the increasing speed of PCB sauya siginar, masu zanen PCB na yau suna buƙatar fahimta da sarrafa ƙarancin abubuwan PCB. Ya dace da gajeriyar lokutan watsa siginar da ƙimar agogo mafi girma na da’irar dijital na zamani, alamun PCB ba su da alaƙa masu sauƙi, amma layin watsawa.

Yadda za a sarrafa impedance PCB

A aikace, ya zama tilas a sarrafa ƙarancin ganowa yayin da saurin ƙarancin dijital ya wuce 1ns ko mitar analog ya wuce 300Mhz. Ofaya daga cikin mahimman sigogi na alamar PCB shine ƙarancin halayen sa (ragin ƙarfin lantarki zuwa na yanzu yayin da igiyar ke tafiya tare da layin watsa siginar). Halayen halayyar waya a kan allon da’irar da aka buga alama ce mai mahimmanci na ƙirar allon kewaye, musamman a ƙirar PCB na madaidaicin madaidaiciya, dole ne a yi la’akari da ko ƙuntatawa ta waya ta yi daidai da halayen da ake buƙata ta na’urar ko sigina. This involves two concepts: impedance control and impedance matching. This paper focuses on impedance control and lamination design.

Rashin ikon sarrafawa

Sarrafa EImpedance, mai gudanarwa a cikin allon da’irar zai sami kowane nau’in siginar siginar, don haɓaka ƙimar watsawa kuma dole ne ya ƙara yawan mitar sa, idan layin da kanta saboda etching, stacking kauri, faɗin waya da sauran dalilai daban -daban, zai haifar canjin ƙimar impedance, murdiyar siginar. Sabili da haka, ƙimar impedance na mai gudanarwa akan babban allon kewayawa yakamata a sarrafa shi a cikin takamaiman fanni, wanda aka sani da “ikon hanawa”.

The impedance of a PCB trace will be determined by its inductive and capacitive inductance, resistance, and conductivity coefficient. Manyan abubuwan da ke shafar rashin hanawar wayoyin PCB sune: faɗin waya na jan ƙarfe, kaurin waya na jan ƙarfe, madaidaicin madaidaicin matsakaici, kaurin matsakaici, kaurin kushin, hanyar waya ta ƙasa, wayoyi a kusa da wayoyi , da dai sauransu. Matsakaicin PCB ya kasance daga 25 zuwa 120 ohm.

A aikace, layin watsawa na PCB yawanci yana ƙunshe da alama, ɗaya ko fiye yadudduka, da kayan rufi. Dabaru da yadudduka sune ke haifar da ƙarancin ikon sarrafawa. PCBS sau da yawa za su kasance masu yawa, kuma ana iya gina matsalar hana sarrafawa ta hanyoyi da yawa. However, whatever method is used, the impedance value will be determined by its physical structure and the electrical properties of the insulating material:

Nisa da kauri alamar alama

A tsawo daga cikin core ko prefill abu a kan ko dai gefen alama

Kanfigareshi na alama da farantin

Insulation constants of core and prefilled materials

Layin watsa PCB ya zo cikin manyan sifofi guda biyu: Microstrip da Stripline.

Microstrip:

Layin microstrip shine madubin tsiri tare da jirgin sama mai tunani a gefe ɗaya kawai, tare da saman da ɓangarorin da aka fallasa su cikin iska (ko mai rufi), sama da saman rufin da’irar Er ɗin dindindin, tare da samar da wutar lantarki ko ƙasa a matsayin abin tunani. Kamar yadda aka nuna a kasa:

Lura: A cikin masana’antar PCB na ainihi, masana’antun kwamiti galibi suna rufe saman PCB tare da rufin koren mai, don haka a cikin ainihin ƙididdigar rashin ƙarfi, ƙirar da aka nuna a ƙasa galibi ana amfani da ita don lissafin layin microstrip:

Layin layi:

Layin kirtani shi ne kintinkiri na waya da aka sanya tsakanin jirage guda biyu, kamar yadda aka nuna a adadi na ƙasa. Ƙididdigar zafin jiki na dielectric wanda H1 da H2 ke wakilta na iya zama daban.

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. Da sauransu.

Ana amfani da SI9000 don ƙididdige ko an cika buƙatun kulawar rashin ƙarfi:

Da farko lissafin ikon hanawa na ƙarshe na layin bayanan DDR:

TOP Layer: 0.5oz kauri na jan ƙarfe, faɗin waya na 5MIL, nisan mil 3.8 daga jirgin da ake magana, madaidaicin 4.2. Zaɓi ƙirar, musanya a cikin sigogi, kuma zaɓi Lissafi marasa asara, kamar yadda aka nuna a cikin adadi:

CoaTIng yana nufin coaTIng, kuma idan babu daidaituwa, cika 0 a kauri da 1 a cikin dielectric (dielectric akai) (iska).

Substrate yana tsaye ne don substrate Layer, wato, Layer dielectric, gabaɗaya ta amfani da fr-4, kauri da aka lissafa ta software na ƙididdigar rashin ƙarfi, madaidaicin 4.2 (mitar ƙasa da 1GHz).

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

9. Prepreg/Core ra’ayi na rufi Layer:

PP (Prepreg) wani nau’in kayan dielectric ne, wanda ya ƙunshi fiber gilashi da resin epoxy. Haƙiƙa Core ainihin nau’in PP ne, amma ɓangarorinsa biyu an rufe su da jan ƙarfe, yayin da PP ba. Lokacin yin allon multilayer, yawanci da PP galibi ana amfani dasu tare, kuma ana amfani da PP don haɗawa tsakanin cibi da cibiya.

10. Abubuwan da ke buƙatar kulawa a ƙirar lamination na PCB

(1) Matsalar yaƙi

Tsarin Layer na PCB yakamata ya zama daidaitacce, wato, kaurin matsakaicin Layer da jan ƙarfe na kowane Layer ya zama daidaitacce. Layersauki yadudduka shida alal misali, kaurin saman-GND da matsakaiciyar ƙarfin ƙasa ya zama daidai da kaurin jan ƙarfe, DA na GND-L2 da L3-POWER matsakaici ya zama daidai da kaurin jan ƙarfe. Wannan ba zai dame lokacin laminating.

(2) Layer siginar yakamata a haɗe tare da jirgin da ke kusa (wato, kaurin matsakaici tsakanin siginar siginar da murfin murfin jan ƙarfe kusa ya zama ƙarami); Ƙarfin ƙarfin jan ƙarfe da suturar jan ƙarfe ya kamata a haɗa su sosai.

(3) A cikin yanayin saurin sauri, ana iya ƙara ƙarin yadudduka don ware layin siginar, amma ana ba da shawarar kada a ware yadudduka masu ƙarfi da yawa, wanda na iya haifar da tsoma bakin hayaniya.

(4) Ana nuna rabe -raben laminated zane yadudduka a cikin tebur mai zuwa:

(5) Gabaɗayan ƙa’idodin tsarin Layer:

A ƙarƙashin farfajiyar ɓangaren (Layer na biyu) shine jirgin sama na ƙasa, wanda ke ba da garkuwar garkuwar na’urar da jirgin bincike don saman wayoyin saman;

Duk siginar siginar suna kusa da jirgin ƙasa gwargwadon iko.

Guji kusanci kai tsaye tsakanin yadudduka sigina biyu gwargwadon iko;

Babban wutar lantarki yakamata ya kasance kusa da mai yiwuwa;

Ana ɗaukar alamar tsarin laminate.

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

(Don yanayin da ke ƙasa da 50MHZ, da fatan za a koma zuwa gare shi kuma a kwantar da shi yadda ya dace), an ba da shawarar ƙa’idar shimfidar:

Bangaren sashi da farfajiyar walda sune cikakken jirgin ƙasa (garkuwa);

Babu m layi daya wayoyi Layer;

Duk siginar siginar suna kusa da jirgin ƙasa gwargwadon iko.

Alamar maɓalli tana kusa da samuwar kuma baya ƙetare yankin rarrabuwa.