Ko že govorimo o PCB plošča, 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.

PCB ploščo lahko razdelimo na enoslojno ploščo, dvoslojno ploščo in večplastno ploščo. Elektronske komponente so integrirane v tiskano vezje. Na osnovnem enoslojnem tiskanem vezju so komponente koncentrirane na eni strani, žice pa na drugi. Zato moramo v plošči narediti luknje, tako da lahko zatiči gredo skozi desko na drugo stran, zato so zatiči delov varjeni na drugo stran. 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. Včasih je potrebno eno vodilo z ene strani na drugo stran plošče povezati skozi vodilno luknjo (preko). Vodilne luknje so majhne luknje na tiskanem vezju, napolnjene ali prevlečene s kovino, ki jih je mogoče priključiti na žice na obeh straneh. Zdaj mnoge računalniške matične plošče uporabljajo 4 ali celo 6 slojev PCB plošč, medtem ko grafične kartice običajno uporabljajo 6 plasti PCB plošče. Mnoge vrhunske grafične kartice, kot je serija nVIDIAGeForce4Ti, uporabljajo 8 slojev PCB plošče, ki se imenuje večplastna PCB plošča. The problem of connecting lines between layers is also encountered on multi-layer PCBS, which can also be achieved through guide holes.

Ker gre za večplastno tiskano vezje, včasih ni treba, da vodilne luknje prodrejo skozi celotno tiskano vezje. Takšne vodilne luknje se imenujejo Buriedvias in Blindvias, ker prodrejo le v nekaj plasti. Slepe luknje povezujejo več plasti notranjega PCBS s površinskim PCBS, ne da bi prodrle skozi celotno ploščo. Zakopane luknje so povezane samo z notranjim tiskanim vezjem, zato svetloba ni vidna s površine. V večplastnem tiskanem vezju je celotna plast neposredno povezana z ozemljitveno žico in napajalnikom. Tako plasti razvrščamo kot signalne, napajalne ali talne. Če deli na tiskanem vezju potrebujejo različne napajalnike, imajo običajno več kot dve napajalni in žični plasti. 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. PCB glavne plošče je večinoma 4 plasti. Med proizvodnjo se srednji dve plasti valjata, režeta, jedkata, oksidirata in galvanizirata. Štiri plasti so sestavna površina, plast moči, plast in spajkanje. Štiri plasti se nato stisnejo skupaj, da tvorijo tiskano vezje za glavno ploščo. Then the holes were punched and made. Po čiščenju se natisneta dve zunanji plasti linije, baker, jedkanje, preskušanje, plast odpornosti proti varjenju, sitotisk. Nazadnje je celotno tiskano vezje (vključno z mnogimi matičnimi ploščami) vtisnjeno v tiskano vezje vsake matične plošče, nato pa se po opravljenem testu izvede vakuumsko pakiranje. 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. Trik je v tem, da tanko plast bakrene folije razporedite po celotni površini in odstranite odvečno. Dodajanje prenosa je še ena manj uporabljena metoda, in sicer uporaba bakrene žice le tam, kjer je to potrebno, vendar o tem tukaj ne bomo govorili.

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. Pokrov je samo predloga za izdelavo plasti PCB. Pokrov, ki pokriva fotorezist na tiskanem vezju, preprečuje izpostavljenost nekaterih področij fotorezistata, dokler fotorezist ni izpostavljen UV -svetlobi. 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. Na splošno se uporablja kot topilo za jedkanje z uporabo železovega klorida itd. After etching, remove the remaining photoresist.

1. Širina in tok ožičenja

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).

Ko je debelina bakrene folije približno 50um, je širina žice 1 ~ 1.5mm (60mil) = 2A

Skupna osnova je običajno 80 mil, zlasti za aplikacije z mikroprocesorji.

2. Kako visoka je frekvenca plošče za visoke hitrosti?

Ko je čas porasta/padca signala “3-6 -kratnik časa prenosa signala, se to šteje za signal visoke hitrosti.

Pri digitalnih vezjih je ključnega pomena, da pogledamo strmost roba signala, čas, potreben za vzpon in padec,

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! – – – – – – – namreč! 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. Zlaganje in plastenje PCB

The four – layer plate has the following stacking sequence. Spodaj so pojasnjene prednosti in slabosti različnih laminacij:

Prvi primer bi moral biti najboljši od štirih plasti. 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. Vendar pa prvega primera ni mogoče uporabiti, če je gostota plošč relativno visoka. Ker potem celovitost prvega sloja ni zagotovljena, signal drugega sloja pa slabši. 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. Po strukturi plošče ni primeren za oblikovanje digitalnih vezij za visoke hitrosti. V tej strukturi je težko vzdrževati nizko impedanco moči. Take a plate 2 mm as an example: Z0=50ohm. To line width of 8mil. Copper foil thickness is 35цm. Torej je signalna plast in sredina formacije 0.14 mm. 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. EMI zaščita. 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. Ujemanje impedance

Amplituda odbitega signala napetosti je določena s koeficientom odboja vira ρ S in koeficientom odboja bremena ρL

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

V zgornji enačbi, če je RL = Z0, je koeficient odboja obremenitve ρL = 0. Če je RS = Z0 koeficient odboja na koncu vira ρS = 0.

Ker mora navadna impedanca daljnovoda Z0 običajno izpolnjevati zahteve 50 ω 50 ω, impedanca obremenitve pa je običajno v tisočih ohmih do več deset tisoč ohmov. Zato je težko uresničiti ujemanje impedance na strani obremenitve. However, because the signal source (output) impedance is usually relatively small, roughly in the tens of ohms. Zato je veliko lažje izvesti ujemanje impedance pri viru. If a resistor is connected at the load end, the resistor will absorb part of the signal to the detriment of transmission (my understanding). Ko je izbran standardni pogonski tok TTL/CMOS 24 mA, je njegova izhodna impedanca približno 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)

Ko so izbrani drugi standardi prenosa in pogonski tokovi, je lahko ujemajoča se impedanca drugačna. Pri hitri logiki in zasnovi vezja za nekatere ključne signale, na primer uro, krmilne signale, priporočamo, da dodate vir ujemanja z virom.

Na ta način se bo priključeni signal odbijal nazaj s strani obremenitve, ker se impedanca vira ujema, odsevni signal se ne bo odbil nazaj.