Yadda ake sarrafawa PCB impedance?

Without impedance control, considerable signal reflection and distortion will be caused, resulting in design failure. Alamu na yau da kullun, kamar bas na PCI, bas na PCI-E, USB, Ethernet, ƙwaƙwalwar DDR, siginar LVDS, da sauransu, duk suna buƙatar sarrafa rashin ƙarfi. A ƙarshe ana buƙatar aiwatar da sarrafa rashin ƙarfi ta hanyar ƙirar PCB, wanda kuma yana gabatar da buƙatu mafi girma don fasahar hukumar PCB. Bayan sadarwa tare da masana’antar PCB kuma haɗe tare da amfani da software na EDA, ana sarrafa ƙoshin wayoyi gwargwadon buƙatun amincin sigina.

Za’a iya lissafin hanyoyin wayoyi daban -daban don samun ƙimar impedance daidai.

Microstrip lines

• Ya kunshi tsiri na waya tare da jirgin kasa da na’urar lantarki a tsakiya. Idan madaidaiciyar madaidaiciyar wuta, faɗin layin, da nisan ta daga jirgin ƙasa ana iya sarrafa su, to halayen sa na iya sarrafawa, kuma daidaiton zai kasance cikin ± 5%.

What is impedance control how to perform impedance control on PCB

Tsiri

Layin kirtani shine tsinken tagulla a tsakiyar wutar lantarki tsakanin jirage biyu masu gudanar da aiki. Idan kauri da faɗin layin, madaidaiciyar madaidaiciyar madaidaiciya, da tazara tsakanin jiragen ƙasa na yadudduka biyu ana iya sarrafa su, ƙimar halayyar layin tana da iko, kuma daidaiton yana cikin 10%.

What is impedance control how to perform impedance control on PCB

The structure of multi-layer board:

Domin sarrafa rashin daidaiton PCB da kyau, ya zama dole a fahimci tsarin PCB:

Yawancin lokaci abin da muke kira allon multilayer ya ƙunshi babban farantin karfe da takardar da aka ƙulla tare da juna. Core board yana da kauri, takamaiman kauri, farantin jan karfe biyu na burodi, wanda shine ainihin kayan da aka buga. 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.

Yawanci mafi ƙarancin filayen mutuƙar lantarki guda biyu na multilayer sune jikakken yadudduka, kuma ana amfani da yadudduka daban -daban na jan ƙarfe a waje na waɗannan yadudduka biyu azaman murfin jan ƙarfe na waje. Ƙayyadaddun kauri na bangon jan ƙarfe na waje da bango na jan ƙarfe gabaɗaya shine 0.5oz, 1OZ, 2OZ (1OZ kusan 35um ko 1.4mil), amma bayan jerin jiyya na farfajiya, kaurin ƙarshe na bangon jan ƙarfe zai ƙaru da kusan 1 OZ. Fushin jan ƙarfe na ciki shine murfin jan ƙarfe a ɓangarorin biyu na farantin. Kauri na ƙarshe ya bambanta kaɗan da kaurin asali, amma galibi ana rage shi da yawa saboda tsinkewa.

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.

Lokacin da aka yi wani kauri na allon da aka buga, a gefe guda, ana buƙatar zaɓin zaɓi na sigogi na kayan abu, a gefe guda, kaurin ƙarshe na takardar da aka warkar da shi zai zama ƙarami fiye da kaurin farko. Abubuwan da ke biyowa sune tsarin laminated 6-Layer:

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 jan karfe:

There are three thicknesses of copper foil that can be used: 12um, 18um and 35um. Kauri na ƙarshe bayan kammalawa shine kusan 44um, 50um da 67um.

Babban farantin: S1141A, daidaitaccen FR-4, faranti na jan karfe biyu da aka yi amfani da su ana yawan amfani da su. Za’a iya ƙayyade ƙayyadaddun zaɓi ta hanyar tuntuɓar masana’anta.

Semi-cured tablet:

Bayanai (kaurin asali) sune 7628 (0.185mm), 2116 (0.105mm), 1080 (0.075mm), 3313 (0.095mm). Ainihin kauri bayan latsa yawanci kusan 10-15um ƙasa da ƙimar asali. Za a iya amfani da mafi girman allunan 3 da aka warkar da su don faɗuwar ɓarna ɗaya, kuma kaurin allunan 3 da aka warkar da su ba za su zama iri ɗaya ba, aƙalla ana iya amfani da allunan warkar da rabi, amma wasu masana’antun dole ne su yi amfani da aƙalla biyu . Idan kaurin yanki mai warkarwa bai isa ba, za a iya kashe takardar jan ƙarfe a ɓangarorin biyu na babban farantin, sannan za a iya ɗaure sashin da aka warkar da shi a ɓangarorin biyu, ta yadda za a iya yin kaurin kaurin kauri. cimma.

Resistance waldi Layer:

A kauri daga solder tsayayya Layer a kan jan karfe ne C2≈8-10um. A kauri daga cikin solder tsayayya Layer a farfajiya ba tare da takardar jan ƙarfe shine C1, wanda ya bambanta da kaurin jan ƙarfe akan farfajiya. Lokacin kaurin tagulla a saman shine 45um, C1≈13-15um, kuma lokacin kaurin tagulla a saman shine 70um, C1≈17-18um.

Sashen ƙetare:

Za mu yi tunanin cewa ɓangaren giciye na waya madaidaici ne, amma a zahiri trapezoid ne. Layeraukar matakin TOP a matsayin misali, lokacin da kaurin murfin jan ƙarfe ya zama 1OZ, babban gefen ƙasa na trapezoid ya fi guntu 1MIL fiye da ƙaramar ƙasa. Misali, idan faɗin layin ya kai 5MIL, to, saman da ƙasan kusan 4MIL ne kuma gefen ƙasa da ƙasa kusan 5MIL ne. Bambanci tsakanin gefuna na sama da na ƙasa yana da alaƙa da kaurin jan ƙarfe. Tebur mai zuwa yana nuna alaƙar da ke tsakanin saman da ƙasa na trapezoid a ƙarƙashin yanayi daban -daban.

What is impedance control how to perform impedance control on PCB

Izini: Izini na zanen gado mai warkewa yana da alaƙa da kauri. Teburin mai zuwa yana nuna kauri da sigogi na izini na nau’ikan fakiti masu warkewa daban-daban:

What is impedance control how to perform impedance control on PCB

A dielectric m na farantin yana da alaka da guduro abu amfani. Daidaitaccen mutuƙar farantin FR4 shine 4.2 – 4.7, kuma yana raguwa tare da haɓaka mita.

Matsalar asarar Dielectric: kayan dielectric a ƙarƙashin aikin canza wutar lantarki, saboda zafi da yawan kuzarin da ake kira asarar wutar lantarki, galibi ana bayyana shi ta hanyar hasarar dielectric Tan δ. Babban darajar S1141A shine 0.015.

Mafi ƙarancin faɗin layi da tazarar layi don tabbatar da injin: 4mil/4mil.

Gabatar da kayan aikin lissafin impedance:

Lokacin da muka fahimci tsarin allon multilayer kuma muka mallaki sigogin da ake buƙata, zamu iya lissafin impedance ta software EDA. Kuna iya amfani da Allegro don yin wannan, amma ina ba da shawarar Polar SI9000, wanda shine kayan aiki mai kyau don ƙididdige ƙarancin halaye kuma yawancin masana’antun PCB suna amfani dashi yanzu.

Lokacin lissafin ƙalubalen halayyar siginar ciki na duka layin bambanci da layin tashar guda ɗaya, zaku sami ɗan bambanci kaɗan tsakanin Polar SI9000 da Allegro saboda wasu cikakkun bayanai, kamar siffar ɓangaren giciye na waya. Koyaya, idan don ƙididdige ƙuntataccen halayyar siginar Surface, Ina ba da shawarar ku zaɓi ƙirar da aka Rufe maimakon ƙirar Surface, saboda irin waɗannan samfuran suna la’akari da wanzuwar layin juriya, don haka sakamakon zai zama mafi inganci. Abin da ke biyowa shine sashin sikirin bangare na farfajiyar layin bambancin farfajiya wanda aka lissafa tare da Polar SI9000 la’akari da matakin juriya na siyarwa:

What is impedance control how to perform impedance control on PCB

Tun da kaurin garkuwar garkuwar garkuwar ba ta da sauƙin sarrafawa, ana iya amfani da ƙimar kusanci, kamar yadda mai ƙera jirgin ya ba da shawarar: cire takamaiman ƙima daga lissafin ƙirar Surface. Ana ba da shawarar cewa bambancin bambancin ya kasance ya rage 8 ohms kuma ƙarancin ƙarancin ƙarshen ya zama rabe 2 ohms.

Bukatun PCB daban -daban don wayoyi

(1) Ƙayyade yanayin wayoyi, sigogi da lissafin impedance. Akwai nau’ikan bambance -bambancen iri biyu don jigilar layin: yanayin bambancin layin microstrip na waje da yanayin bambancin layin tsiri na ciki. Ana iya ƙididdige ƙalubalen ta software mai alaƙa da lissafin impedance (kamar POLAR-SI9000) ko tsarin lissafin impedance ta hanyar saitin ma’auni mai dacewa.

(2) Layin layikan isometric. Ƙayyade faɗin layin da tazara, kuma ku bi ƙimar layin da aka ƙididdige da tazara yayin yin tuƙi. Tazara tsakanin layuka biyu dole ne ya kasance koyaushe bai canza ba, wato don ci gaba da daidaitawa. 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. Gabaɗaya ku guji yin amfani da siginar bambanci tsakanin yadudduka, wato saboda a cikin ainihin aikin PCB a cikin aiwatarwa, saboda daidaiton daidaiton daidaiton ƙasa ya yi ƙasa da abin da aka bayar tsakanin daidaitaccen etching, kuma a cikin aiwatar da laminated dielectric asarar, ba zai iya ba da tabbacin bambancin layin layi daidai yake da kauri na mai kashe wutar lantarki na interlayer, zai haifar da bambanci tsakanin yadudduka na bambancin canjin rashin ƙarfi. Ana ba da shawarar yin amfani da bambancin da ke tsakanin layin ɗaya gwargwadon iko.