With the increasing speed of PCB signalni almashtirish, bugungi kunda PCB dizaynerlari PCB izlarining impedansini tushunishi va boshqarishi kerak. Corresponding to the shorter signal transmission times and higher clock rates of modern digital circuits, PCB traces are no longer simple connections, but transmission lines.

PCB impedansini qanday nazorat qilish kerak

Amalda, raqamli chegaraviy tezlik 1ns dan oshganda yoki analog chastotasi 300 MGts dan oshganda iz empedansini nazorat qilish zarur. PCB izining asosiy parametrlaridan biri uning xarakterli empedansidir (to’lqin signal uzatish liniyasi bo’ylab harakatlanayotganda kuchlanishning tokga nisbati). The characteristic impedance of wire on printed circuit board is an important index of circuit board design, especially in PCB design of high frequency circuit, it must be considered whether the characteristic impedance of wire is consistent with the characteristic impedance required by device or signal. This involves two concepts: impedance control and impedance matching. This paper focuses on impedance control and lamination design.

Empedansni boshqarish

Elektr o’tkazuvchanligini nazorat qilish, elektron kartadagi o’tkazgich uzatish tezligini yaxshilash uchun signal uzatishning barcha turlariga ega bo’ladi va agar uning o’zi chizish, yig’ish qalinligi, simning kengligi va boshqa omillarga bog’liq bo’lsa, uning chastotasini oshirish kerak. impedans qiymatining o’zgarishi, signalning buzilishi. Shuning uchun, yuqori tezlikli elektron platadagi o’tkazgichning impedans qiymati ma’lum bir diapazonda nazorat qilinishi kerak, bu “impedans nazorati” deb nomlanadi.

The impedance of a PCB trace will be determined by its inductive and capacitive inductance, resistance, and conductivity coefficient. The main factors affecting the impedance of PCB wiring are: the width of copper wire, the thickness of copper wire, the dielectric constant of medium, the thickness of medium, the thickness of pad, the path of ground wire, the wiring around the wiring, etc. PCB empedansi 25 dan 120 ohmgacha.

Amalda, tenglikni uzatish liniyasi odatda iz, bir yoki bir nechta mos yozuvlar qatlamlari va izolyatsion materiallardan iborat. Izlar va qatlamlar boshqaruv impedansini hosil qiladi. PCBS ko’pincha ko’p qatlamli bo’ladi va boshqaruv impedansi turli yo’llar bilan qurilishi mumkin. However, whatever method is used, the impedance value will be determined by its physical structure and the electrical properties of the insulating material:

Width and thickness of signal trace

The height of the core or prefill material on either side of the trace

Iz va plastinka konfiguratsiyasi

Insulation constants of core and prefilled materials

PCB uzatish liniyalari ikkita asosiy shaklda bo’ladi: Microstrip va Stripline.

Microstrip:

Mikrostripli chiziq – bu faqat bir tomonida mos yozuvlar tekisligi bo’lgan, yuqori va yon tomonlari havo bilan qoplangan (yoki qoplangan), izolyatsiyalanuvchi doimiy Er platasining sirtidan yuqorida, quvvat manbai yoki topraklama mos yozuvlar sifatida. Quyida ko’rsatilganidek:

Eslatma: Haqiqiy tenglikni ishlab chiqarishda, taxta ishlab chiqaruvchisi odatda tenglikni sirtini yashil yog ‘qatlami bilan qoplaydi, shuning uchun haqiqiy empedansni hisoblashda quyida ko’rsatilgan model odatda sirt mikrostripli chiziqlarni hisoblash uchun ishlatiladi:

Stripline:

Tasma chizig’i – bu quyidagi rasmda ko’rsatilgandek, ikkita mos yozuvlar tekisligi orasiga qo’yilgan simli lenta. H1 va H2 bilan ko’rsatilgan dielektrikning dielektrik konstantalari boshqacha bo’lishi mumkin.

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:

Dielektrik doimiy Er, simlar kengligi W1, W2 (trapezoid), simlar qalinligi T va izolyatsiya qatlami qalinligi H.

W1, W2:

The calculated value must be within the red box. Va hokazo.

SI9000 is used to calculate whether the impedance control requirements are met:

First calculate the single-end impedance control of DDR data line:

TOP layer: 0.5oz copper thickness, 5MIL wire width, 3.8mil distance from the reference plane, dielectric constant 4.2. Modelni tanlang, parametrlarni o’rnating va rasmda ko’rsatilgandek Yo’qotishsiz hisobni tanlang:

CoaTIng – bu qo’shilish degan ma’noni anglatadi va agar u bo’lmasa, qalinligi 0 va dielektrik (dielektrik doimiy) (havo) bilan 1 to’ldiring.

Substrat substrat qatlamini, ya’ni dielektrik qatlamini anglatadi, odatda fr-4 yordamida, qalinligi impedans hisoblash dasturi bilan hisoblangan, dielektrik doimiy 4.2 (chastotasi 1 GGts dan kam).

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

9. Yalıtım qatlamining Prepreg/Core tushunchasi:

PP (Prepreg) – shisha tolasi va epoksi qatronidan tashkil topgan dielektrik materialning bir turi. Yadro aslida PP muhiti turidir, lekin uning ikki tomoni mis folga bilan qoplangan, PP esa unday emas. Ko’p qavatli taxtalarni yasashda odatda yadro va PP birgalikda ishlatiladi va PP yadro va yadro o’rtasida bog’lanish uchun ishlatiladi.

10. PCB laminatsiyasini loyihalashda e’tiborga muhtoj masalalar

(1) Warpage muammosi

PCB qatlam dizayni nosimmetrik bo’lishi kerak, ya’ni har bir qatlamning o’rta qatlami va mis qatlamining qalinligi nosimmetrik bo’lishi kerak. Masalan, oltita qatlamni olaylik, yuqori GND va pastki quvvatli muhitning qalinligi mis qalinligiga mos kelishi kerak, GND-L2 va L3-POWER muhitining qalinligi esa mis qalinligiga mos kelishi kerak. Laminatsiyalash paytida bu buzilmaydi.

(2) Signal qatlami qo’shni mos yozuvlar tekisligi bilan mahkam bog’langan bo’lishi kerak (ya’ni signal qatlami bilan qo’shni mis qoplamali qatlam orasidagi o’rta qalinlik juda kichik bo’lishi kerak); Quvurli mis va erga solingan mis birikmalari mahkam bog’langan bo’lishi kerak.

(3) juda yuqori tezlikda, signal qatlamini ajratish uchun qo’shimcha qatlamlar qo’shilishi mumkin, lekin keraksiz shovqin aralashuviga olib kelishi mumkin bo’lgan bir nechta quvvat qatlamlarini ajratmaslik tavsiya etiladi.

(4) Odatda laminatlangan dizayn qatlamlarining taqsimlanishi quyidagi jadvalda ko’rsatilgan:

(5) qatlamlarni joylashtirishning umumiy tamoyillari:

Komponent yuzasi ostida (ikkinchi qavat) yer tekisligi joylashgan bo’lib, u qurilmaning ekranlovchi qatlamini va yuqori qavat simlari uchun mos yozuvlar tekisligini ta’minlaydi;

Barcha signal qatlamlari iloji boricha er tekisligiga ulashgan.

Iloji boricha ikkita signal qatlami o’rtasida to’g’ridan -to’g’ri qo’shni bo’lishdan saqlaning;

Asosiy quvvat manbai iloji boricha qo’shni bo’lishi kerak;

Laminat strukturaning simmetriyasi hisobga olinadi.

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

(50 MGts dan past bo’lgan sharoitda, iltimos, unga murojaat qiling va uni mos ravishda bo’shating), tartib printsipi taklif qilinadi:

Komponent yuzasi va payvandlash yuzasi to’liq er tekisligi (qalqon);

Qo’shni parallel simi qatlami yo’q;

Barcha signal qatlamlari iloji boricha er tekisligiga ulashgan.

Kalit signal shakllanishiga ulashgan va segmentatsiya zonasini kesib o’tmaydi.