Mar a chumas tu smachd PCB bacadh?

Without impedance control, considerable signal reflection and distortion will be caused, resulting in design failure. Feumaidh comharran cumanta, leithid bus PCI, bus PCI-E, USB, Ethernet, cuimhne DDR, comharra LVDS, msaa, uile smachd impedance. Impedance control ultimately needs to be realized through PCB design, which also puts forward higher requirements for PCB board technology. After communication with PCB factory and combined with the use of EDA software, the impedance of wiring is controlled according to the requirements of signal integrity.

Faodar diofar dhòighean wiridh obrachadh a-mach gus an luach impedance co-fhreagarrach fhaighinn.

Microstrip lines

• Tha e air a dhèanamh suas de stiall de uèir leis a ’phlèana talmhainn agus dielectric sa mheadhan. Ma tha smachd air an seasmhach dielectric, leud na loidhne, agus an astar bhon phlèana talmhainn, tha smachd air a bhacadh sònraichte, agus bidh an cruinneas taobh a-staigh ± 5%.

What is impedance control how to perform impedance control on PCB

Stripline

Tha loidhne rioban na stiall de chopar ann am meadhan an dielectric eadar dà phlèana giùlain. If the thickness and width of the line, the dielectric constant of the medium, and the distance between the ground planes of the two layers are controllable, the characteristic impedance of the line is controllable, and the accuracy is within 10%.

What is impedance control how to perform impedance control on PCB

The structure of multi-layer board:

Gus smachd a chumail air bacadh PCB gu math, feumar structar PCB a thuigsinn:

Mar as trice tha an rud ris an can sinn bòrd multilayer air a dhèanamh suas de phlàta bunaiteach agus duilleag leth-chruaidh lannaichte còmhla ri chèile. Tha bòrd bunaiteach na thiugh cruaidh, sònraichte, dà phlàta copair arain, a tha na stuth bunaiteach den bhòrd clò-bhuailte. And the semi-cured piece constitutes the so-called infiltration layer, plays the role of bonding the core plate, although there is a certain initial thickness, but in the process of pressing its thickness will occur some changes.

Mar as trice is e sreathan fliuch a th ’anns an dà shreath dielectric as fhaide a-muigh, agus tha sreathan foil copair air an cleachdadh air taobh a-muigh an dà shreath sin mar am foil copair a-muigh. Tha an sònrachadh tiugh tùsail de foil copair a-muigh agus foil copair a-staigh sa chumantas 0.5oz, 1OZ, 2OZ (tha 1OZ timcheall air 35um no 1.4mil), ach às deidh sreath de làimhseachadh uachdar, mar as trice bidh an tighead deireannach de foil copair a-muigh ag àrdachadh le timcheall air 1OZ. Is e am foil copar a-staigh an còmhdach copair air gach taobh den phrìomh phlàta. Chan eil an tighead mu dheireadh glè eadar-dhealaichte bhon tighead tùsail, ach mar as trice tha e air a lughdachadh le grunn um mar thoradh air searbhag.

Is e an ìre as iomallaiche den bhòrd multilayer an ìre dìon tàthaidh, agus is e sin a chanas sinn gu tric “ola uaine”, gu dearbh, faodaidh e a bhith buidhe no dathan eile cuideachd. The thickness of the solder resistance layer is generally not easy to determine accurately. The area without copper foil on the surface is slightly thicker than the area with copper foil, but because of the lack of copper foil thickness, so the copper foil is still more prominent, when we touch the printed board surface with our fingers can feel.

When a particular thickness of the printed board is made, on the one hand, reasonable choice of material parameters is required, on the other hand, the final thickness of the semi-cured sheet will be smaller than the initial thickness. Tha na leanas mar structar lannaichte àbhaisteach 6-ìre:

What is impedance control how to perform impedance control on PCB

PCB parameters:

Different PCB plants have slight differences in PCB parameters. Through communication with circuit board plant technical support, we obtained some parameter data of the plant:

Foill copair uachdar:

There are three thicknesses of copper foil that can be used: 12um, 18um and 35um. Tha an tighead mu dheireadh an dèidh crìochnachadh mu 44um, 50um agus 67um.

Plàta bunaiteach: S1141A, FR-4 àbhaisteach, dà phlàta copair arain air an cleachdadh gu cumanta. Faodar na mion-chomharrachaidhean roghainneil a dhearbhadh le bhith a ’cur fios chun neach-dèanamh.

Semi-cured tablet:

Is e sònrachaidhean (tiugh tùsail) 7628 (0.185mm), 2116 (0.105mm), 1080 (0.075mm), 3313 (0.095mm). Tha an fhìor thiugh an dèidh brùthadh mar as trice timcheall air 10-15um nas lugha na an luach tùsail. Faodar 3 tablaidean leth-leigheasach a chleachdadh aig a ’char as àirde airson an aon fhilleadh in-shìoladh, agus chan urrainn do thiugh 3 tablaidean leth-leigheas a bhith co-ionann, faodar co-dhiù aon leth-chlàr leigheis a chleachdadh, ach feumaidh cuid de luchd-saothrachaidh co-dhiù dhà a chleachdadh . If the thickness of the semi-cured piece is not enough, the copper foil on both sides of the core plate can be etched off, and then the semi-cured piece can be bonded on both sides, so that a thicker infiltration layer can be achieved.

Còmhdach tàthaidh an aghaidh:

The thickness of the solder resist layer on the copper foil is C2≈8-10um. The thickness of the solder resist layer on the surface without copper foil is C1, which varies with the thickness of copper on the surface. When the thickness of copper on the surface is 45um, C1≈13-15um, and when the thickness of copper on the surface is 70um, C1≈17-18um.

Earrann tarsainn:

Bhiodh sinn a ’smaoineachadh gur e ceart-cheàrnach a th’ ann an crois-earrann de uèir, ach gu dearbh is e trapezoid a th ’ann. A ’gabhail an ìre TOP mar eisimpleir, nuair a tha tiugh foil copair 1OZ, tha an oir ìosal as àirde de trapezoid 1MIL nas giorra na an oir ìosal as ìsle. Mar eisimpleir, ma tha leud na loidhne 5MIL, tha na taobhan àrda is ìosal mu 4MIL agus tha na taobhan ìosal is ìosal mu 5MIL. The difference between top and bottom edges is related to copper thickness. The following table shows the relationship between top and bottom of trapezoid under different conditions.

What is impedance control how to perform impedance control on PCB

Ceadaidheachd: Tha ceadachd dhuilleagan leth-leigheasach co-cheangailte ri tiugh. Tha an clàr a leanas a ’sealltainn paramadairean tiugh is ceadachd diofar sheòrsaichean de dhuilleagan leth-leigheasach:

What is impedance control how to perform impedance control on PCB

The dielectric constant of the plate is related to the resin material used. The dielectric constant of FR4 plate is 4.2 — 4.7, and decreases with the increase of frequency.

Factar call dielectric: is e call dielectric a chanar ri stuthan dielectric fo ghnìomh achadh dealain eile, mar thoradh air caitheamh teas is lùth, mar as trice air a chuir an cèill le factar call dielectric Tan δ. Is e an luach àbhaisteach airson S1141A 0.015.

Leud loidhne as ìsle agus farsaingeachd loidhne gus dèanamh cinnteach à innealachadh: 4mil / 4mil.

Ro-ràdh inneal àireamhachaidh bacadh:

Nuair a thuigeas sinn structar a ’bhùird ioma-inneal agus maighstireachd na paramadairean a tha a dhìth, is urrainn dhuinn tomhas a dhèanamh air a’ bhacadh tro bhathar-bog EDA. Faodaidh tu Allegro a chleachdadh gus seo a dhèanamh, ach tha mi a ’moladh Polar SI9000, a tha na inneal math airson a bhith a’ tomhas bacadh caractar agus a tha a-nis air a chleachdadh le mòran fhactaraidhean PCB.

Nuair a bhios tu a ’tomhas buaidh caractar an comharra a-staigh an dà chuid an loidhne eadar-dhealaichte agus an loidhne crìochnachaidh singilte, chan fhaigh thu ach beagan eadar-dhealachaidh eadar Polar SI9000 agus Allegro air sgàth cuid de mhion-fhiosrachadh, leithid cumadh crois-earrann na h-uèir. Ach, ma tha e gu bhith a ’tomhas buaidh caractar an comharra Surface, tha mi a’ moladh dhut am modal Coated a thaghadh an àite a ’mhodail Surface, oir tha modailean mar sin a’ toirt aire do bhith an sàs ann an còmhdach solder, agus mar sin bidh na toraidhean nas cruinne. Tha na leanas mar phàirt de dhealbh-sgrìn den bhacadh loidhne diofraichte uachdar air a thomhas le Polar SI9000 a ’beachdachadh air an ìre dìon solder:

What is impedance control how to perform impedance control on PCB

Leis nach eil tiugh an t-sreath resister solder furasta a smachdachadh, faodar dòigh tuairmseach a chleachdadh cuideachd, mar a mhol neach-dèanamh a ’bhùird: thoir air falbh luach sònraichte bho àireamhachadh modail Surface. Thathas a ’moladh gum bi am bacadh eadar-dhealaichte nas lugha na 8 ohms agus gum bi an casg aon-cheann nas lugha na 2 ohms.

Riatanasan PCB eadar-dhealaichte airson uèirleadh

(1) Obraich a-mach am modh wiring, paramadairean agus àireamhachadh impedance. Tha dà sheòrsa de mhodhan eadar-dhealachaidh ann airson slighe loidhne: modh eadar-dhealachaidh loidhne microstrip còmhdach a-muigh agus modh eadar-dhealachaidh loidhne stiall còmhdach a-staigh. Faodar bacadh a thomhas le bathar-bog àireamhachaidh impedance co-cheangailte (leithid POLAR-SI9000) no foirmle àireamhachaidh impedance tro shuidheachadh paramadair reusanta.

(2) Loidhnichean isometric co-shìnte. Obraich a-mach leud is farsaingeachd na loidhne, agus lean gu teann an leud loidhne a tha air a thomhas agus farsaingeachd nuair a bhios tu a ’dol. Feumaidh an farsaingeachd eadar dà loidhne fuireach gun atharrachadh, is e sin, gus cumail co-shìnte. There are two ways of parallelism: one is that the two lines walk in the same side-by-side layer, and the other is that the two lines walk in the over-under layer. San fharsaingeachd feuch ri bhith a ’seachnadh a bhith a’ cleachdadh an comharra eadar-dhealachaidh eadar na sreathan, is e sin air sgàth gu bheil fìor ghiullachd PCB sa phròiseas, air sgàth gu bheil cruinneas co-thaobhadh lannaichte mòran nas ìsle na tha air a sholarachadh eadar an cruinneas searbhachaidh, agus ann am pròiseas call dielectric lannaichte, chan urrainn gealltainn gu bheil farsaingeachd loidhne eadar-dhealachaidh co-ionann ri tiugh an dielectric interlayer, ag adhbhrachadh an eadar-dhealachadh eadar na sreathan de dh ’eadar-dhealachadh atharrachadh impedance. Thathas a ’moladh an eadar-dhealachadh a chleachdadh taobh a-staigh an aon fhilleadh cho mòr‘ s a ghabhas.