gapirganda PCB kartasi, many friends will think that it can be seen everywhere around us, from all household appliances, all kinds of accessories in the computer, to all kinds of digital products, as long as electronic products almost all use PCB board, so what is PCB board? A PCB is a PrintedCircuitBlock, which is a printed circuit board for electronic components to be inserted. A copperplated base plate is printed and etched out of the etching circuit.

PCB kartasini bir qatlamli, ikki qavatli va ko’p qatlamli taxtalarga bo’lish mumkin. Elektron komponentlar PCBga o’rnatilgan. Bir qatlamli asosiy PCBda komponentlar bir tomonga, simlar esa boshqa tomonga jamlangan. Shunday qilib, biz taxtada teshiklar qilishimiz kerak, shunda pinlar taxtadan boshqa tomonga o’tishi mumkin, shuning uchun qismlarning pinlari boshqa tomonga payvandlanadi. Because of this, the positive and negative sides of such PCB are respectively called ComponentSide and SolderSide.

A double-layer board can be seen as two single-layer boards glued together, with electronic components and wiring on both sides of the board. Ba’zan bitta simni taxtaning boshqa tomoniga hidoyat teshigi (orqali) orqali ulash kerak bo’ladi. Qo’llanma teshiklari – bu har ikki tomondan simlarga ulanadigan metall bilan qoplangan yoki qoplangan tenglikni kichik teshiklari. Hozirda ko’pgina kompyuter anakartlari 4 yoki hatto 6 qatlamli tenglikni kartasidan foydalanmoqda, grafik kartalarda odatda 6 qatlamli tenglikni kartasi ishlatiladi. NVIDIAGeForce4Ti seriyasi kabi ko’plab yuqori darajali grafik kartalar ko’p qatlamli tenglik kartasi deb nomlangan tenglikni kartochkasining 8 qatlamidan foydalanadi. The problem of connecting lines between layers is also encountered on multi-layer PCBS, which can also be achieved through guide holes.

Bu ko’p qatlamli PCB bo’lgani uchun, ba’zida hidoyat teshiklari butun PCBga kirishi shart emas. Bunday ko’rsatma teshiklari Buriedvias va Blindvias deb ataladi, chunki ular faqat bir necha qatlamlarga kirib boradi. Yopiq teshiklar bir necha qatlamli ichki PCBS qatlamlarini butun taxtaga kirmasdan PCBS yuzasiga ulaydi. Ko’milgan teshiklar faqat ichki PCB bilan bog’langan, shuning uchun yorug’lik sirtdan ko’rinmaydi. Ko’p qatlamli PCBda butun qatlam to’g’ridan -to’g’ri er simiga va quvvat manbaiga ulanadi. Shunday qilib, biz qatlamlarni Signal, Quvvat yoki Ground deb tasniflaymiz. Agar tenglikni qismlari har xil quvvat manbalarini talab qilsa, ular odatda ikkidan ortiq quvvat va simli qatlamlarga ega. The more layers you use, the higher the cost. Of course, the use of more layers of PCB board to provide signal stability is very helpful.

The process of making a professional PCB board is quite complicated. Take a 4-layer PCB board for example. Asosiy kartaning tengligi asosan 4 qatlamdan iborat. Ishlab chiqarishda o’rta ikkita qatlam mos ravishda o’raladi, kesiladi, ishlanadi, oksidlanadi va elektrolizlanadi. To’rt qatlam – mos ravishda komponentlar yuzasi, quvvat qatlami, qatlam va lehim laminatsiyasi. Keyin to’rtta qatlam bir -biriga bosilib, asosiy karta uchun tenglikni hosil qiladi. Then the holes were punched and made. Tozalashdan so’ng, chiziqning tashqi ikki qatlami bosiladi, mis, gravitatsiya, sinov, payvandlash qarshiligi qatlami, ekranli bosib chiqarish. Nihoyat, barcha tenglikni (shu jumladan ko’plab anakartlarni) har bir anakartning tenglikni kartochkasiga muhrlanadi, so’ngra sinovdan o’tganidan keyin vakuumli qadoqlash amalga oshiriladi. If the copper skin is not well coated in THE process of PCB production, there will be poor adhesion phenomenon, easy to imply short circuit or capacitance effect (easy to cause interference). The holes on PCB must also be taken care of. If the hole is punched not in the middle, but on one side, it will result in uneven matching or easy contact with the power supply layer or formation in the middle, resulting in potential short-circuiting or bad grounding factors.

Copper wiring process

The first step in fabrication is to establish an online wiring between parts. We use negative transfer to express the working negative on a metal conductor. Hiyla shundaki, mis folga yupqa qatlamini butun yuzaga yoyib, uning ortiqcha qismini olib tashlash kerak. O’tkazish – bu mis simni faqat kerakli joyda qo’llash, lekin biz bu erda bu haqda gapirmaymiz.

Positive photoresists are made from photosensitizers that dissolve under illumination. There are many ways to treat photoresist on copper, but the most common way is to heat it and roll it over a surface containing photoresist. It can also be sprayed in liquid form, but the dry film provides higher resolution and allows for thinner wires. Kaput – bu PCB qatlamlarini tayyorlash uchun shablon. PCBda fotorezistni yopuvchi qopqoq, fotorezistni UV nurlari ta’sir qilmaguncha, fotorezistning ba’zi joylari ta’sirlanishini oldini oladi. These areas, which are covered with photoresist, will become wiring. Boshqa yalang’och mis qismlari fotorezistni ishlab chiqqandan so’ng qirib tashlanishi kerak. The etching process may involve dipping the board into the etching solvent or spraying the solvent onto the board. Odatda temir xlorid va boshqalar yordamida erituvchi erituvchi sifatida ishlatiladi. After etching, remove the remaining photoresist.

1. Simlarning kengligi va oqimi

General width should not be less than 0.2mm (8mil)

On high density and high precision PCBS, pitch and line width are generally 0.3mm (12mil).

Mis folga qalinligi taxminan 50um bo’lganda, simning kengligi 1 ~ 1.5mm (60mil) = 2A

Umumiy ma’lumot umumiy 80 mil, ayniqsa, mikroprotsessorli ilovalar uchun.

2. Yuqori tezlikli taxtaning chastotasi qanchalik baland?

Signal vaqtining “signal uzatish vaqtining 3 ~ 6 barobariga” ko’tarilishi/pasayishi yuqori tezlikdagi signal hisoblanadi.

Raqamli kontaktlarning zanglashiga olib keladigan bo’lsak, asosiysi – signalning balandligiga, ko’tarilish va tushish vaqtiga,

According to a very classic book “High Speed Digtal Design” theory, the signal from 10% to 90% of the time is less than 6 times the wire delay, is high-speed signal! – – – – – – aynan! Even 8KHz square wave signals, as long as the edges are steep enough, are still high-speed signals, and transmission line theory needs to be used in wiring

3. PCBni yig’ish va qatlamlash

The four – layer plate has the following stacking sequence. Turli xil laminatsiyaning afzalliklari va kamchiliklari quyida keltirilgan.

Birinchi holat to’rt qatlamning eng yaxshisi bo’lishi kerak. Because the outer layer is the stratum, it has a shielding effect on EMI. Meanwhile, the power supply layer is reliable and close to the stratum, which makes the internal resistance of the power supply smaller and achieves the best suburbs. Biroq, taxtaning zichligi nisbatan yuqori bo’lganda birinchi holatni ishlatish mumkin emas. Chunki u holda, birinchi qavatning yaxlitligi kafolatlanmaydi, ikkinchi qavatdagi signal esa yomonroq bo’ladi. Bunga qo’shimcha ravishda, butun taxtaning katta quvvat sarfi bo’lsa, bu tuzilmadan foydalanish mumkin emas.

The second case is the one we usually use the most. Kengash tuzilishidan, u yuqori tezlikli raqamli elektron dizayn uchun mos emas. Bu strukturada kam quvvatli impedansni saqlab qolish qiyin. Take a plate 2 mm as an example: Z0=50ohm. To line width of 8mil. Copper foil thickness is 35цm. Shunday qilib, signal qatlami va qatlamning o’rtasi 0.14 mm. The formation and power layer are 1.58mm. This greatly increases the internal resistance of the power supply. In this kind of structure, because the radiation is to the space, shielding plate is needed to reduce EMI.

In the third case, the signal line on layer S1 has the best quality. S2. EMI himoyasi. But the power supply impedance is large. This board can be used when the power consumption of the whole board is high and the board is an interference source or adjacent to the interference source.

4. Impedance matching

Ko’rsatilgan kuchlanish signalining amplitudasi manbaning aks ettirish koeffitsienti ρ S va yukni aks ettirish koeffitsienti ρL bilan belgilanadi.

ρL = (RL-z0)/(RL + Z0) and ρS = (rS-z0)/(RS + Z0)

Yuqoridagi tenglamada, agar RL = Z0 bo’lsa, yukni aks ettirish koeffitsienti DL = 0. Agar RS = Z0 manba oxiridagi aks ettirish koeffitsienti DS = 0 bo’lsa.

Chunki oddiy elektr uzatish liniyasining impedansi Z0 odatda 50 ω 50 ω talablariga javob berishi kerak va yuk empedansi odatda ming ohmdan o’n minglab ohmgacha bo’ladi. Shuning uchun yuk tomonida impedans mos kelishini sezish qiyin. Biroq, signal manbai (chiqish) empedansi odatda nisbatan kichik bo’lgani uchun, taxminan o’nlab ohmlarda. Shuning uchun manbada impedans mosligini amalga oshirish ancha oson. Agar yuk uchida qarshilik ulangan bo’lsa, rezistor signalning bir qismini uzatish zarariga singdiradi (mening tushunishimcha). TTL/CMOS standart 24mA haydovchi oqimi tanlansa, uning chiqish empedansi taxminan 13 ω ni tashkil qiladi. Agar elektr uzatish liniyasining impedansi Z0 = 50 ω bo’lsa, 33 ω manbali mos keladigan qarshilik qo’shilishi kerak. 13 ω +33 ω = 46 ω (taxminan 50 ω, zaif namlanish signalni sozlash vaqtiga yordam beradi)

Boshqa uzatish standartlari va haydovchi oqimlari tanlansa, mos keladigan empedans boshqacha bo’lishi mumkin. Yuqori tezlikdagi mantiq va sxemani loyihalashda, masalan, soat, nazorat signallari kabi ba’zi kalit signallari uchun manba mos keladigan rezistorni qo’shish tavsiya etiladi.

Shunday qilib, ulangan signal yuk tomondan qaytariladi, chunki manba impedansi mos keladi, aks ettirilgan signal qaytarilmaydi.