With the increasing speed of PCB ngoper sinyal, perancang PCB saiki kudu ngerti lan ngontrol impedansi tilak PCB. 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.

Cara ngontrol impedansi PCB

Ing prakteke, kudu ngontrol impedansi tilak nalika kacepetan marginal digital ngluwihi 1n utawa frekuensi analog ngluwihi 300Mhz. Salah sawijining paramèter utama tilak PCB yaiku impedansi karakteristik (rasio voltase nganti saiki nalika gelombang mlaku sajrone garis transmisi sinyal). 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.

Kontrol imppedansi

Kontrol EImpedansi, konduktor ing papan sirkuit bakal duwe kabeh jinis transmisi sinyal, supaya bisa ningkatake tingkat transmisi lan kudu nambah frekuensi, yen garis kasebut amarga etching, kekandelan tumpukan, jembar kawat lan faktor liyane, bakal nyebabake pangowahan nilai impedansi, distorsi sinyal. Mula, nilai impedansi konduktor ing papan sirkuit kecepatan tinggi kudu dikendhaleni ing kisaran tartamtu, sing diarani “kontrol impedansi”.

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. Impedansi PCB antara 25 nganti 120 ohm.

Ing prakteke, garis transmisi PCB biasane kalebu tilak, siji utawa luwih lapisan referensi, lan bahan insulasi. Ngambah lan lapisan mbentuk impedansi kontrol. PCBS bakal asring multi-lapisan, lan impedansi kontrol bisa dibangun kanthi macem-macem cara. 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

Konfigurasi tilak lan piring

Insulation constants of core and prefilled materials

Saluran transmisi PCB ana rong bentuk utama: Mikrostrip lan Stripline.

Microstrip:

Garis mikrostrip yaiku konduktor strip kanthi bidang referensi mung ing siji sisih, kanthi sisih ndhuwur lan sisih kasebut kena hawa (utawa dilapisi), ing ndhuwur permukaan papan sirkuit Er terisolasi isolasi, kanthi pasokan listrik utawa grounding minangka referensi. Kaya sing dituduhake ing ngisor iki:

Cathetan: Ing pabrikan PCB nyata, pabrikan dewan biasane nutupi permukaan PCB kanthi lapisan minyak ijo, mula ing petungan impedansi nyata, model sing ditampilake ing ngisor iki biasane digunakake kanggo pitungan garis mikrostrip permukaan:

Garis garis:

Garis pita yaiku pita kawat sing diselehake ing antarane rong bidang referensi, kaya sing dituduhake ing gambar ing ngisor iki. Konstanta dielektrik saka dielektrik sing diwakili dening H1 lan H2 bisa beda.

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:

Konstanta listrik dielektrik, jembaré kabel W1, W2 (trapezoid), kekandelan kabel T lan kekandelan lapisan insulasi H.

W1, W2:

The calculated value must be within the red box. Lan liyane.

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

Ngitung dhisik kontrol impedansi siji-baris garis data DDR:

TOP layer: 0.5oz copper thickness, 5MIL wire width, 3.8mil distance from the reference plane, dielectric constant 4.2. Pilih model, ganti paramèter, banjur pilih Itungan Tanpa Rugi, kaya sing dituduhake ing gambar:

CoaTIng tegese coaTIng, lan yen ora ana coaTIng, isi kekandelan 0 lan 1 ing dielektrik (konstanta dielektrik) (udara).

Substrat tegese lapisan substrat, yaiku lapisan dielektrik, umume nggunakake fr-4, kekandelan sing diwilang dening piranti lunak pitungan impedansi, konstanta dielektrik 4.2 (frekuensi kurang saka 1GHz).

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

9. Konsep prepreg / Inti lapisan jampel:

PP (Prepreg) minangka salah sawijining jinis bahan dielektrik, kasusun saka serat kaca lan resin epoksi. Inti sejatine JENIS medium PP, nanging loro-lorone ditutupi foil tembaga, dene PP ora. Nalika nggawe papan multilayer, inti lan PP biasane digunakake bebarengan, lan PP digunakake kanggo ikatan antarane inti lan inti.

10. Prakara sing perlu digatekake ing desain laminasi PCB

(1) Masalah Warpage

Desain lapisan PCB kudu simetris, yaiku kekandelan lapisan medium lan lapisan tembaga saben lapisan kudu simetris. Contone, njupuk enem lapisan, kekandelan medium ndhuwur-GND lan kekuatan ngisor kudu konsisten karo kekandelan tembaga, lan medium GND-L2 lan L3-POWER kudu konsisten karo kekandelan tembaga. Iki ora bakal mlengkung nalika laminasi.

(2) Lapisan sinyal kudu dipasang kanthi erat karo bidang referensi jejer (yaiku, kekandelan medium antarane lapisan sinyal lan lapisan nutupi tembaga jejer kudu cilik banget); Klamben tembaga sing kuat lan klamben tembaga lemah kudu dikencengi.

(3) Yen kacepetan dhuwur banget, lapisan ekstra bisa ditambahake kanggo ngisolasi lapisan sinyal, nanging disaranake ora ngisolasi sawetara lapisan listrik, sing bisa nyebabake gangguan swara sing ora perlu.

(4) Distribusi lapisan desain laminasi khas ditampilake ing tabel ing ngisor iki:

(5) Prinsip umum susunan lapisan:

Ing ngisor permukaan komponen (lapisan nomer loro) ana pesawat dhasar, sing nyedhiyakake lapisan tameng piranti lan bidang referensi kanggo kabel lapisan ndhuwur;

Kabeh lapisan sinyal jejer karo bidang lemah sing paling adoh.

Aja cedhak langsung ing antarane rong lapisan sinyal nganti bisa;

Pasokan listrik utama mesthine kudu jejer;

Simetri struktur laminasi dianggep.

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

(Kanggo kahanan ing ngisor 50MHZ, delengen lan santai kanthi tepat), prinsip tata letak disaranake:

Permukaan komponen lan permukaan las minangka pesawat dhasar (tameng);

Ora ana lapisan kabel paralel sing jejer;

Kabeh lapisan sinyal jejer karo bidang lemah sing paling adoh.

Sinyal tombol jejer karo formasi lan ora nyebrang zona segmentasi.