With the increasing speed of PCB signal switching, today’s PCB designers need to understand and control the impedance of PCB traces. 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.

Tsela ea ho laola PCB impedance

Ka ts’ebetso, ho hlokahala hore o laole leqheka la motlakase ha lebelo la marang-rang la digital le feta 1ns kapa maqhubu a analog a feta 300Mhz. E mong oa entsprechen senotlolo sa mosaletsa oa PCB ke impedance lona bath (karo-karolelano ea gagamalo ho jwale ha leqhubu le tsamaea hammoho le mola phetiso pontšo). 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.

Impedance control

EImpedance Controling, the conductor in the circuit board will have all kinds of signal transmission, in order to improve the transmission rate and must increase its frequency, if the line itself due to etching, stacking thickness, wire width and other different factors, will cause impedance value change, the signal distortion. Therefore, the impedance value of the conductor on the high-speed circuit board should be controlled within a certain range, known as “impedance control”.

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 impedance ranges ho tloha 25 ho ea ho 120 ohm.

Ts’ebetsong, mohala oa phetisetso ea PCB hangata o na le mosaletsa, karolo e le ‘ngoe kapa tse fetang tse ling, le lisebelisoa tsa ho kenya letsoho. Traces and layers form the control impedance. PCBS hangata e tla ba le mekhahlelo e mengata, ‘me taolo ea taolo e ka hahuoa ka mekhoa e fapaneng. 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

Tlhophiso ea mosaletsa le poleiti

Insulation constants of core and prefilled materials

Likhoele tsa phetisetso ea PCB li tla ka mefuta e ‘meli e meholo: Microstrip le Stripline.

Microstrip:

Mohala oa microstrip ke mokhanni oa marang-rang o nang le sefofane sa litšupiso ka lehlakoreng le le leng feela, ka holimo le mahlakore a pepesitsoeng moeeng (kapa a koahetsoeng), ka holim’a bokahare ba boto ea potoloho ea Er, e nang le phepelo ea motlakase kapa mobu e le sets’oants’o. Joalokaha ho bontšitsoe ka tlase:

Tlhokomeliso: Ka tlhahiso ea PCB ea ‘nete, moetsi oa boto hangata o apesa bokaholimo ba PCB ka lera la oli e tala, ka hona ka palo ea impedance ea’ nete, mohlala o bonts’itsoeng ka tlase hangata o sebelisoa bakeng sa palo ea microstrip line:

Stripline:

Mohala oa lente ke lente la terata le behiloeng lipakeng tsa lifofane tse peli tsa litšupiso, joalo ka ha ho bonts’itsoe setšoantšong se ka tlase. Mechini ea dielectric ea dielectric e emeloang ke H1 le H2 e ka fapana.

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. Joalo joalo.

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. Khetha ea mohlala, ka nkang sebaka ka entsprechen, ‘me khetha Lossless Calculation, joalo ka ha ho bonts’itsoe setšoantšong:

CoaTIng e bolela coaTIng, ‘me haeba ho se na coaTIng, tlatsa 0 ka botenya le 1 ka dielectric (dielectric constant) (moea).

Substrate e emetse substrate layer, ke hore, dielectric layer, ka kakaretso e sebelisa fr-4, botenya bo baloang ke software ea ho bala ea impedance, dielectric e sa fetoheng ea 4.2 (frequency e ka tlase ho 1GHz).

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

9. Khopolo ea Prepreg / Core ea lera la ho kenya:

Maq (Prepreg) ke mofuta oa thepa ea dielectric, e entsoeng ka fiber ea khalase le epoxy resin. Core ha e le hantle ke TYPE ea seaplane sa PP, empa mahlakore a eona a mabeli a koahetsoe ka foil ea koporo, ha PP e se joalo. Ha ho etsoa mapolanka multilayer, konokono le maq hangata sebediswa hammoho, ‘me maq e sebelisoa ho tlamahano pakeng tsa konokono le konokono.

10. Litaba tse hlokang tlhokomelo ka moralo oa lamination ea PCB

(1) Bothata ba warpage

Moralo lera la PCB e lokela ho ba setshwani, ke hore, botenya ba lera mahareng le lera koporo ea lera ka ‘ngoe e lokela ho ba ditshwani. Nka likarolo tse tšeletseng ka mohlala, botenya ba top-GND le tlase-tlase bohare bo lokela ho tsamaellana le botenya ba koporo, ‘Me ea GND-L2 le L3-POWER e bohareng e lokela ho lumellana le botenya ba koporo. Sena se ke ke sa ohla ha o lata.

(2) Lera la lets’oao le lokela ho hokahanngoa ka thata le sefofane sa litšupiso se haufi (ke hore, botenya bo mahareng lipakeng tsa lera la lets’oao le lera la koporo le haufi le lokela ho ba nyane haholo); Ho apara koporo ea matla le ho roala koporo ea fatše ho lokela ho kopanngoa ka thata.

(3) Tabeng ea lebelo le phahameng haholo, ho ka eketsoa likarolo tse ling ho arola lera la lets’oao, empa ho kgothaletswa hore o seke oa arola likarolo tse ngata tsa motlakase, tse ka bakang tšitiso ea lerata e sa hlokahaleng.

(4) Kabo ea likarolo tse tloaelehileng tsa moralo e entsoe ka tafole e latelang:

(5) Melao-motheo e akaretsang ea tlhophiso ea lera:

Ka tlasa karolo ea karolo (mokato oa bobeli) ke sefofane se fatše, se fanang ka sesebelisoa se sirelletsang sesebelisoa le sefofane sa litšupiso bakeng sa wiring e kaholimo;

Likarolo tsohle tsa matšoao li haufi le sefofane sa fatše ka hohle kamoo ho ka khonehang.

Qoba ho hokahana ka kotloloho lipakeng tsa likarolo tse peli tsa matšoao kamoo ho ka khonehang;

Phepelo e kholo ea motlakase e lokela ho ba haufi ha ho khoneha;

Ts’ebetso ea sebopeho sa laminate e tsotelloa.

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

(Bakeng sa maemo a ka tlase ho 50MHZ, ka kopo e fetisetse ho eona ‘me u phomole ka nepo).

Karolo e hahiloeng ka karolo le bokaholimo ba ho tjheseletsa ke sefofane se felletseng (thebe);

Ha ho haufi le wiring lera;

Likarolo tsohle tsa matšoao li haufi le sefofane sa fatše ka hohle kamoo ho ka khonehang.

Letšoao la senotlolo le haufi le sebopeho mme ha le tšele sebaka sa karohano.