With the increasing speed of PCB ịgbanwere mgbaama, ndị nrụpụta PCB taa kwesịrị ịghọta ma chịkwaa impedance nke 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.

Otu esi ejikwa impedance PCB

Na omume, ọ dị mkpa ijikwa impedance trace mgbe oke ọnụọgụ dijitalụ gafere 1ns ma ọ bụ ugboro analog gafere 300Mhz. Otu akụkụ nke akara PCB bụ njiri mara njiri mara ya (oke nke voltaji ka ọ dị ugbu a ka ebili mmiri na -aga n’ahịrị nnyefe mgbaàmà). Njirimara njiri mara nke waya na bọọdụ sekit e biri ebi bụ ndepụta dị mkpa nke nhazi bọọdụ sekit, ọkachasị na imebe PCB nke sekit ugboro ugboro, a ga -atụlerịrị ma njiri mara waya ọ dabara na njiri mara nke ngwaọrụ ma ọ bụ akara chọrọ. This involves two concepts: impedance control and impedance matching. This paper focuses on impedance control and lamination design.

Njikwa impedance

Njikwa EImpedance, onye na -eduzi na bọọdụ sekit ga -enwe ụdị nnyefe mgbaama niile, iji meziwanye nnyefe nnyefe na ọ ga -abawanye ugboro ya, ma ọ bụrụ na ahịrị n’onwe ya n’ihi etching, ọkpụrụkpụ stacking, obosara waya na ihe ndị ọzọ dị iche iche, ga -akpata. mgbanwe impedance mgbanwe, mgbagha mgbama. Yabụ, ekwesịrị ijikwa uru impedance nke onye na-eduzi na bọọdụ sekit dị elu n’ime oke ụfọdụ, nke a maara dị ka “njikwa impedance”.

The impedance of a PCB trace will be determined by its inductive and capacitive inductance, resistance, and conductivity coefficient. Isi ihe na -emetụta impedance nke wiwi PCB bụ: obosara nke waya ọla kọpa, ọkpụrụkpụ nke eriri ọla kọpa, ọnụnọ nke dielectric nke ọkara, ọkpụrụkpụ nke ọkara, ọkpụrụkpụ pad, ụzọ nke waya ala, wiring gburugburu wiring. , wdg. Mgbochi PCB sitere na 25 ruo 120 ohm.

Na omume, ahịrị nnyefe PCB na -enwekarị akara, otu ma ọ bụ karịa, na ihe mkpuchi. Akara na akwa na -etolite impedance nchịkwa. PCBS ga-abụkarị ọkwa dị iche iche, a ga-arụkwa impedance nchịkwa n’ọtụtụ ụzọ. However, whatever method is used, the impedance value will be determined by its physical structure and the electrical properties of the insulating material:

Obosara na ọkpụrụkpụ nke Chọpụta mgbaàmà

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

Nhazi nke Chọpụta na efere

Insulation constants of core and prefilled materials

Usoro nnyefe PCB na -abịa n’ụdị abụọ: Microstrip na Stripline.

Microstrip:

Ahịrị microstrip bụ onye na -eduzi warara nwere ụgbọ elu ntụnyere n’otu akụkụ, nke elu na akụkụ kpughere n’ikuku (ma ọ bụ kpuchie ya), n’elu mkpuchi mkpuchi bọọdụ sekit Er mgbe niile, yana ike ma ọ bụ ịdọrọ ala. Dị ka e gosiri n’okpuru:

Note: In actual PCB manufacturing, the board manufacturer usually coats the surface of the PCB with a layer of green oil, so in actual impedance calculation, the model shown below is usually used for surface microstrip line calculation:

Ahịrị

Ahịrị rịbọn bụ rịbọn nke edobere n’etiti ụgbọ elu ntụaka abụọ, dị ka egosiri na eserese dị n’okpuru. Ogwe ọnụọgụ nke dielectric nke H1 na H2 nọchiri anya ya nwere ike ịdị iche.

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. Were gabazie.

A na -eji SI9000 gbakọọ ma ezuru ihe nchịkwa impedance:

Buru ụzọ gbakọọ njikwa impedance otu njedebe nke ahịrị data DDR:

TOP layer: 0.5oz copper thickness, 5MIL wire width, 3.8mil distance from the reference plane, dielectric constant 4.2. Họrọ ihe nlereanya, dochie na paramita ahụ, wee họrọ Ngụkọta Lossless, dị ka egosiri na ọnụ ọgụgụ a:

CoaTIng pụtara coaTIng, ma ọ bụrụ na enweghị coaTIng, jupụta 0 na ọkpụrụkpụ na 1 na dielectric (dielectric joogto) (ikuku).

Substrate na-anọchite akwa oyi akwa, ya bụ, oyi akwa dielectric, na-ejikarị fr-4, ọkpụrụkpụ gbakọọ site na ngụkọta ngụkọ ngụkọta ngwanrọ, 4.2 ugboro ugboro (ugboro ole erughị 1GHz).

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

9. Prepreg/Isi echiche nke mkpuchi oyi akwa:

PP (Prepreg) bụ ụdị ihe ọkụ eletrik, nke nwere eriri iko na resin epoxy. Core bụ n’ezie ụdị PP, mana ejiri foil ọla kpuchie akụkụ ya abụọ, ebe PP abụghị. Mgbe ị na -eme bọọdụ multilayer, a na -ejikọkarị isi na PP ọnụ, a na -ejikwa PP ijikọ n’etiti isi na isi.

10. Ihe chọrọ nlebara anya na imebe PCB lamination

(1) Nsogbu mgbasa ozi

Nhazi nke PCB kwesịrị ịdị nhata, ya bụ, ọkpụrụkpụ nke ọkara oyi akwa na akwa ọla kọpa nke akwa ọ bụla kwesịrị ịdị nhata. Were akwa isii dịka ọmụmaatụ, ọkpụrụkpụ nke elu-GND na ọkara ike kwesịrị ịdị ka ọkpụrụkpụ ọla kọpa, NA nke GND-L2 na L3-POWER kwesịrị ịdị ka ọkpụrụkpụ ọla kọpa. Nke a agaghị ekwe omume mgbe laminating.

(2) Ekwesịrị ijikọ akwa mgbaama na ụgbọ elu ntụnyere aka (ya bụ, ọkara ọkpụrụkpụ n’etiti akwa mgbaama na akwa mkpuchi ọla kọpa dị n’akụkụ kwesịrị ịdị obere); Ekwesịrị ijikọ mgbakwasa ọla kọpa na mgbakwasa ọla kọpa.

(3) N’ọnọdụ oke ọsọ, enwere ike ịgbakwunye akwa ọzọ iji kewapụ akara ngosi, mana a na -atụ aro ka ị ghara ikewapụ ọtụtụ ike ike, nke nwere ike ibute ndabichi mkpọtụ na -enweghị isi.

(4) A na -egosi nkesa nke ahịrị eji emebe laminated na tebụl na -esonụ:

(5) Ụkpụrụ niile nke nhazi oyi akwa:

N’okpuru elu akụrụngwa (oyi akwa nke abụọ) bụ ụgbọ elu ala, nke na -enye akwa mkpuchi ngwaọrụ yana ụgbọ elu maka ntụnye maka eriri elu dị n’elu;

Akara ngosi niile dị n’akụkụ ụgbọ elu ala ka o kwere mee.

Zere ịdị nso kpọmkwem n’agbata ọkwa abụọ dị ka o kwere mee;

Isi ike ọkụ kwesịrị ịdị n’akụkụ ka o kwere mee;

A na -echebara Symmetry nke usoro laminate echiche.

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

(Maka ọnọdụ dị n’okpuru 50MHZ, biko rụtụ aka na ya wee zuo ike n’ụzọ kwesịrị ekwesị), a na -atụ aro ụkpụrụ okirikiri nhọrọ ukwuu:

Akụkụ akụrụngwa na elu ịgbado ọkụ bụ ụgbọ elu ala zuru oke (ọta);

Ọ dịghị n’akụkụ yiri wiring oyi akwa;

Akara ngosi niile dị n’akụkụ ụgbọ elu ala ka o kwere mee.

Mgbama igodo dị n’akụkụ nhazi ahụ, ọ naghị agafe mpaghara nkewa.