Ag labhairt di ar PCB bord, 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.

Is féidir bord PCB a roinnt ina bhord aon chiseal, bord ciseal dúbailte agus bord ilchiseal. Tá comhpháirteanna leictreonacha comhtháite sa PCB. Ar PCB bunúsach aon chiseal, tá na comhpháirteanna dírithe ar thaobh amháin agus tá na sreanga dírithe ar an taobh eile. Mar sin caithfimid poill a dhéanamh sa chlár ionas gur féidir leis na bioráin dul tríd an gclár go dtí an taobh eile, ionas go mbeidh bioráin na gcodanna táthaithe go dtí an taobh eile. 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. Uaireanta is gá sreang amháin a nascadh ó thaobh amháin go dtí an taobh eile den chlár trí pholl treorach (via). Is poill bheaga iad poill treorach sa PCB atá líonta nó brataithe le miotail is féidir a nascadh le sreanga ar an dá thaobh. Anois tá go leor máthairchláir ríomhaire ag úsáid 4 nó fiú 6 shraith de bhord PCB, agus go ginearálta úsáideann cártaí grafaicí 6 shraith de bhord PCB. Úsáideann go leor cártaí grafaicí ard-deireadh mar shraith nVIDIAGeForce4Ti 8 gciseal de bhord PCB, ar a dtugtar bord PCB ilchiseal. The problem of connecting lines between layers is also encountered on multi-layer PCBS, which can also be achieved through guide holes.

Toisc gur PCB ilchiseal é, uaireanta ní gá do na poill treorach an PCB iomlán a threá. Tugtar Buriedvias agus Blindvias ar phoill treorach den sórt sin toisc nach dtéann siad isteach ach cúpla sraitheanna. Ceanglaíonn poill dall roinnt sraitheanna de PCBS inmheánach le dromchla PCBS gan dul tríd an gclár iomlán. Níl poill adhlactha ceangailte ach leis an PCB inmheánach, mar sin níl solas le feiceáil ón dromchla. I PCB multilayer, tá an ciseal iomlán ceangailte go díreach leis an sreang talún agus leis an soláthar cumhachta. Mar sin déanaimid na sraitheanna a rangú mar Chomhartha, Cumhacht nó Talún. Má theastaíonn soláthairtí cumhachta éagsúla ó na codanna ar an PCB, de ghnáth bíonn níos mó ná dhá shraith chumhachta agus sreinge acu. 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. Is é 4 shraith PCB an phríomhchláir den chuid is mó. Nuair a dhéantar iad a mhonarú, déantar an dá shraith lár a rolladh, a ghearradh, a eitseáil, a ocsaídiú agus a leictreaphlátáil faoi seach. Is iad na ceithre shraith dromchla comhpháirteanna, ciseal cumhachta, stratum agus lannú solder faoi seach. The four layers are then pressed together to form a PCB for the main board. Then the holes were punched and made. After cleaning, the outer two layers of the line is printed, copper, etching, testing, welding resistance layer, screen printing. Faoi dheireadh, stampáiltear an PCB iomlán (lena n-áirítear go leor máthairchlár) i PCB gach máthairchláir, agus ansin déantar pacáistiú folúis tar éis an tástáil a rith. 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. The trick is to spread a thin layer of copper foil over the entire surface and remove any excess. Is modh eile nach n-úsáidtear ach aistriú a chur i gceangal, is é sin sreang copair a chur i bhfeidhm ach amháin nuair a bhíonn sí ag teastáil, ach ní bheimid ag caint faoi anseo.

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. Níl sa chochall ach teimpléad chun sraitheanna PCB a dhéanamh. Coscann cochall a chlúdaíonn an fótachóipeálaí ar an PCB roinnt réimsí den fhotoresist a nochtadh go dtí go mbeidh an fótoresist nochtaithe do solas UV. These areas, which are covered with photoresist, will become wiring. Other bare copper parts to be etched after photoresist development. The etching process may involve dipping the board into the etching solvent or spraying the solvent onto the board. Úsáidtear go ginearálta mar thuaslagóir eitseála ag baint úsáide as clóiríd ferric srl. After etching, remove the remaining photoresist.

1. Wiring width and current

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).

Nuair a bhíonn tiús an scragall copair thart ar 50um, is é leithead na sreinge 1 ~ 1.5mm (60mil) = 2A

The common ground is generally 80mil, especially for applications with microprocessors.

2. Cé chomh hard is atá minicíocht an bhoird ardluais?

Nuair a bhíonn ardú / titim an ama comhartha “3 ~ 6 oiread an ama tarchuir comhartha, meastar gur comhartha ardluais é.

Maidir le ciorcaid dhigiteacha, is í an eochair féachaint ar géire imeall an chomhartha, an t-am a thógann sé chun ardú agus titim,

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! – – – – – – eadhon! 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.PCB ag cruachadh agus ag leagan

The four – layer plate has the following stacking sequence. Mínítear thíos na buntáistí agus na míbhuntáistí a bhaineann le lannú éagsúil:

Ba chóir go mbeadh an chéad chás ar an gceann is fearr de na ceithre shraith. 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. Mar sin féin, ní féidir an chéad chás a úsáid nuair a bhíonn dlús an bhoird réasúnta ard. Because then, the integrity of the first layer is not guaranteed, and the second layer signal is worse. In addition, this structure can not be used in the case of large power consumption of the whole board.

The second case is the one we usually use the most. Ó struchtúr an bhoird, níl sé oiriúnach do dhearadh ciorcad digiteach ardluais. Tá sé deacair impedance ísealchumhachta a choinneáil sa struchtúr seo. Take a plate 2 mm as an example: Z0=50ohm. To line width of 8mil. Copper foil thickness is 35цm. Mar sin is é 0.14mm an ciseal comhartha agus lár an fhoirmithe. 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. Sciath EMI. 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. Meaitseáil impedance

Cinntear aimplitiúid an chomhartha voltais fhrithchaite de réir chomhéifeacht frithchaithimh na foinse ρ S agus an chomhéifeacht frithchaithimh ualaigh ρL

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

In the above equation, if RL=Z0, the load reflection coefficient ρL=0. If RS=Z0 source-end reflection coefficient ρS=0.

Because the ordinary transmission line impedance Z0 should usually meet the requirements of 50 ω 50 ω, and the load impedance is usually in thousands of ohms to tens of thousands of ohms. Dá bhrí sin, tá sé deacair meaitseáil impedance a bhaint amach ag taobh an ualaigh. However, because the signal source (output) impedance is usually relatively small, roughly in the tens of ohms. Dá bhrí sin tá sé i bhfad níos éasca meaitseáil impedance a chur i bhfeidhm ag an bhfoinse. If a resistor is connected at the load end, the resistor will absorb part of the signal to the detriment of transmission (my understanding). When the TTL/CMOS standard 24mA drive current is selected, its output impedance is approximately 13 ω. If the transmission line impedance Z0=50 ω, then a 33 ω source-end matching resistor should be added. 13 ω +33 ω =46 ω (approximately 50 ω, weak underdamping helps signal setup time)

When other transmission standards and drive currents are selected, the matching impedance can be different. In high-speed logic and circuit design, for some key signals, such as clock, control signals, we recommend that the source matching resistor must be added.

In this way, the connected signal will be reflected back from the load side, because the source impedance matches, the reflected signal will not be reflected back.