Taħdit ta ‘ Bord tal-PCB, 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.

Bord tal-PCB jista ‘jinqasam f’bord b’saff wieħed, bord b’saff doppju u bord b’ħafna saffi. Komponenti elettroniċi huma integrati fil-PCB. Fuq PCB bażiku b’saff wieħed, il-komponenti huma kkonċentrati fuq naħa waħda u l-wajers huma kkonċentrati fuq in-naħa l-oħra. Allura rridu nagħmlu toqob fil-bord sabiex il-brilli jkunu jistgħu jgħaddu mill-bord għan-naħa l-oħra, sabiex il-brilli tal-partijiet ikunu wweldjati man-naħa l-oħra. 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. Kultant huwa meħtieġ li tgħaqqad wajer wieħed minn naħa waħda għan-naħa l-oħra tal-bord minn toqba gwida (via). It-toqob tal-gwida huma toqob żgħar fil-PCB mimlija jew miksija b’metall li jistgħu jiġu mqabbda ma ‘wajers fuq iż-żewġ naħat. Issa ħafna motherboards tal-kompjuter qed jużaw 4 jew saħansitra 6 saffi ta ‘bord tal-PCB, filwaqt li l-kards tal-grafika ġeneralment jużaw 6 saffi ta’ bord tal-PCB. Ħafna karti grafiċi high-end bħas-serje nVIDIAGeForce4Ti jużaw 8 saffi ta ‘bord tal-PCB, li jissejjaħ bord tal-PCB b’ħafna saffi. The problem of connecting lines between layers is also encountered on multi-layer PCBS, which can also be achieved through guide holes.

Minħabba li huwa PCB b’ħafna saffi, xi drabi t-toqob tal-gwida m’għandhomx għalfejn jippenetraw il-PCB kollu. Toqob ta ‘gwida bħal dawn jissejħu Buriedvias u Blindvias għax jippenetraw biss ftit saffi. It-toqob għomja jgħaqqdu diversi saffi ta ‘PCBS interni mal-wiċċ tal-PCBS mingħajr ma jippenetraw il-bord kollu. It-toqob midfuna huma konnessi biss mal-PCB intern, għalhekk id-dawl ma jidhirx mill-wiċċ. F’BPK b’ħafna saffi, is-saff kollu huwa mqabbad direttament mal-wajer ta ‘l-art u l-provvista ta’ l-enerġija. Allura aħna nikklassifikaw is-saffi bħala Sinjal, Qawwa jew Art. Jekk il-partijiet fuq il-PCB jeħtieġu provvisti ta ‘enerġija differenti, ġeneralment ikollhom aktar minn żewġ saffi ta’ enerġija u wajer. 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. Il-PCB tal-bord prinċipali huwa l-aktar 4 saffi. Meta timmanifattura, iż-żewġ saffi tan-nofs jiġu rrumblati, maqtugħa, nċiżi, ossidizzati u electroplated rispettivament. L-erba ‘saffi huma l-wiċċ tal-komponent, is-saff tal-qawwa, l-istratum u l-laminazzjoni tal-istann rispettivament. L-erba ‘saffi huma mbagħad ippressati flimkien biex jiffurmaw PCB għall-bord prinċipali. Then the holes were punched and made. Wara t-tindif, iż-żewġ saffi ta ‘barra tal-linja huma stampati, ram, inċiżjoni, ittestjar, saff ta’ reżistenza għall-iwweldjar, stampar fuq skrin. Fl-aħħarnett, il-PCB kollu (inklużi bosta motherboards) huwa ttimbrat fil-PCB ta ‘kull motherboard, u mbagħad isir imballaġġ bil-vakwu wara li jgħaddi mit-test. 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. Il-trick huwa li tifrex saff irqiq ta ‘fojl tar-ram fuq il-wiċċ kollu u tneħħi kwalunkwe eċċess. It-trasferiment ta ‘l-appendiċi huwa metodu ieħor inqas użat, li huwa li napplikaw wajer tar-ram biss fejn hemm bżonnu, imma mhux se nitkellmu dwaru hawn.

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. Il-barnuża hija biss mudell biex isiru saffi tal-PCB. Barnuża li tkopri l-photoresist fuq il-PCB tipprevjeni li xi partijiet tal-photoresist jiġu esposti sakemm il-photoresist ikun espost għad-dawl 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. Ġeneralment użat bħala solvent ta ‘inċiżjoni bl-użu ta’ klorur ferriku eċċ. After etching, remove the remaining photoresist.

1. Wisa ‘u kurrent tal-wajers

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).

Meta l-ħxuna tal-fojl tar-ram hija ta ‘madwar 50um, il-wisa’ tal-wajer huwa 1 ~ 1.5mm (60mil) = 2A

L-art komuni hija ġeneralment 80mil, speċjalment għal applikazzjonijiet bi mikroproċessuri.

2. Kemm hi għolja l-frekwenza tal-bord ta ‘veloċità għolja?

Meta l-lok / waqgħa tal-ħin tas-sinjal “3 ~ 6 darbiet il-ħin tat-trasmissjoni tas-sinjal, huwa kkunsidrat bħala sinjal ta ‘veloċità għolja.

Għal ċirkuwiti diġitali, iċ-ċavetta hija li tħares lejn il-wieqaf tat-tarf tas-sinjal, il-ħin li tieħu biex jogħla u jaqa ‘,

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! – – – – – – jiġifieri! 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. Stivar u saffi tal-PCB

The four – layer plate has the following stacking sequence. Il-vantaġġi u l-iżvantaġġi ta ‘laminazzjoni differenti huma spjegati hawn taħt:

L-ewwel każ għandu jkun l-aħjar mill-erba ‘saffi. 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. Madankollu, l-ewwel każ ma jistax jintuża meta d-densità tal-bord hija relattivament għolja. 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. Mill-istruttura tal-bord, mhuwiex adattat għal disinn ta ‘ċirkwit diġitali b’veloċità għolja. Huwa diffiċli li tinżamm impedenza ta ‘enerġija baxxa f’din l-istruttura. Take a plate 2 mm as an example: Z0=50ohm. To line width of 8mil. Copper foil thickness is 35цm. Allura s-saff tas-sinjal u n-nofs tal-formazzjoni huwa 0.14mm. 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. Lqugħ 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. Tqabbil ta ‘impedenza

L-amplitudni tas-sinjal tal-vultaġġ rifless huwa determinat mill-koeffiċjent tar-riflessjoni tas-sors ρ S u l-koeffiċjent tar-riflessjoni tat-tagħbija ρL

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

Fl-ekwazzjoni ta ‘hawn fuq, jekk RL = Z0, il-koeffiċjent tar-riflessjoni tat-tagħbija ρL = 0. Jekk RS = Z0 koeffiċjent tar-riflessjoni tat-tarf tas-sors ρS = 0.

Minħabba li l-impedenza ordinarja tal-linja ta ‘trasmissjoni Z0 għandha ġeneralment tissodisfa r-rekwiżiti ta’ 50 ω 50 ω, u l-impedenza tat-tagħbija ġeneralment tkun f’eluf ta ‘ohms sa għexieren ta’ eluf ta ‘ohms. Għalhekk, huwa diffiċli li tirrealizza tqabbil ta ‘impedenza fuq in-naħa tat-tagħbija. However, because the signal source (output) impedance is usually relatively small, roughly in the tens of ohms. Għalhekk huwa ħafna iktar faċli li timplimenta t-tqabbil tal-impedenza fis-sors. If a resistor is connected at the load end, the resistor will absorb part of the signal to the detriment of transmission (my understanding). Meta l-kurrent tas-sewqan standard 24L ta ‘TTL / CMOS jintgħażel, l-impedenza tal-ħruġ tiegħu hija madwar 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.

B’dan il-mod, is-sinjal konness se jkun rifless lura min-naħa tat-tagħbija, minħabba li l-impedenza tas-sors taqbel, is-sinjal rifless ma jiġix rifless lura.