Akizungumza ya PCB bodi, 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.

Bodi ya PCB inaweza kugawanywa katika bodi moja ya safu, bodi ya safu mbili na bodi nyingi za safu. Vipengele vya elektroniki vimejumuishwa kwenye PCB. Kwenye PCB ya msingi ya safu moja, vifaa vinajilimbikizia upande mmoja na waya zinajilimbikizia upande mwingine. Kwa hivyo tunahitaji kutengeneza mashimo kwenye ubao ili pini ziweze kupitia bodi kwenda upande mwingine, kwa hivyo pini za sehemu zimeunganishwa kwa upande mwingine. 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. Wakati mwingine ni muhimu kuunganisha waya moja kutoka upande mmoja hadi upande mwingine wa bodi kupitia shimo la mwongozo (kupitia). Mashimo ya mwongozo ni mashimo madogo kwenye PCB iliyojazwa au kufunikwa na chuma ambayo inaweza kushikamana na waya pande zote mbili. Sasa bodi nyingi za kompyuta za kompyuta zinatumia tabaka 4 au hata 6 za bodi ya PCB, wakati kadi za picha kwa ujumla hutumia tabaka 6 za bodi ya PCB. Kadi nyingi za michoro ya kiwango cha juu kama nVIDIAGeForce4Ti hutumia safu 8 za bodi ya PCB, ambayo inaitwa bodi ya PCB ya safu nyingi. The problem of connecting lines between layers is also encountered on multi-layer PCBS, which can also be achieved through guide holes.

Kwa sababu ni PCB yenye safu nyingi, wakati mwingine mashimo ya mwongozo hayaitaji kupenya PCB nzima. Mashimo kama hayo ya mwongozo huitwa Buriedvias na Blindvias kwa sababu hupenya tu kwenye tabaka chache. Mashimo ya kipofu huunganisha tabaka kadhaa za PCBS za ndani kwa PCBS za uso bila kupenya bodi nzima. Mashimo ya kuzikwa yameunganishwa tu na PCB ya ndani, kwa hivyo mwanga hauonekani kutoka juu. Katika PCB yenye safu nyingi, safu nzima imeunganishwa moja kwa moja na waya wa ardhini na usambazaji wa umeme. Kwa hivyo tunaainisha tabaka kama Signal, Power au Ground. Ikiwa sehemu kwenye PCB zinahitaji vifaa tofauti vya umeme, kawaida huwa na zaidi ya safu mbili za nguvu na waya. 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 ya bodi kuu ni tabaka 4. Wakati wa utengenezaji, tabaka mbili za kati zimevingirishwa, kukatwa, kuchapwa, kuoksidishwa na kuchapwa kwa mtiririko huo. Tabaka nne ni sehemu ya uso, safu ya nguvu, safu na utaftaji wa solder mtawaliwa. Tabaka hizo nne hukandamizwa pamoja kuunda PCB kwa bodi kuu. Then the holes were punched and made. Baada ya kusafisha, safu mbili za nje za mstari zimechapishwa, shaba, kuchoma, kupima, safu ya upinzani ya kulehemu, uchapishaji wa skrini. Mwishowe, PCB nzima (pamoja na bodi nyingi za mama) imewekwa ndani ya PCB ya kila ubao wa mama, halafu ufungaji wa utupu unafanywa baada ya kufaulu mtihani. 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. Ujanja ni kueneza safu nyembamba ya karatasi ya shaba juu ya uso wote na kuondoa ziada yoyote. Kuomba uhamishaji ni njia nyingine isiyotumiwa sana, ambayo ni kutumia waya wa shaba pale tu inapohitajika, lakini hatutazungumza hapa.

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. Hood ni templeti tu ya kutengeneza tabaka za PCB. Kofia inayofunika mtangazaji wa picha kwenye PCB inazuia baadhi ya maeneo ya mtaalamu wa picha asionekane hadi mpiga picha awekwe kwenye nuru ya 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. Inatumiwa kwa ujumla kama kutengenezea kwa kutumia kloridi ya feri nk. After etching, remove the remaining photoresist.

1. Wiring upana na sasa

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).

Wakati unene wa karatasi ya shaba iko karibu 50um, upana wa waya ni 1 ~ 1.5mm (60mil) = 2A

Sehemu ya kawaida kwa ujumla ni 80mil, haswa kwa matumizi na microprocessors.

2. Mzunguko wa bodi ya mwendo wa kasi uko juu kiasi gani?

Wakati kupanda / kushuka kwa wakati wa ishara “mara 3 ~ 6 wakati wa kupitisha ishara, inachukuliwa kama ishara ya kasi.

Kwa nyaya za dijiti, ufunguo ni kuangalia mwinuko wa ishara, wakati inachukua kuinuka na kushuka,

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! – – – – – – yaani! 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 kuweka na kuweka

The four – layer plate has the following stacking sequence. Faida na hasara za lamination tofauti zimeelezewa hapa chini:

Kesi ya kwanza inapaswa kuwa bora zaidi ya tabaka nne. 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. Walakini, kesi ya kwanza haiwezi kutumika wakati wiani wa bodi uko juu sana. Kwa sababu basi, uadilifu wa safu ya kwanza hauhakikishiwi, na ishara ya safu ya pili ni mbaya zaidi. 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. Kutoka kwa muundo wa bodi, haifai kwa muundo wa mzunguko wa dijiti wa kasi. Ni ngumu kudumisha impedance ya nguvu ndogo katika muundo huu. Take a plate 2 mm as an example: Z0=50ohm. To line width of 8mil. Copper foil thickness is 35цm. Kwa hivyo safu ya ishara na katikati ya malezi ni 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. Kulinda 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. Ufanisi unaofanana

Ukubwa wa ishara ya voltage inayoonyeshwa imedhamiriwa na mgawo wa kutafakari chanzo ρ S na mgawo wa kutafakari mzigo ρL

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

Katika equation hapo juu, ikiwa RL = Z0, mgawo wa kutafakari mzigo ρL = 0. Ikiwa RS = Z0 mgawo wa mwisho wa kutafakari chanzo ρS = 0.

Kwa sababu kawaida impedance ya laini ya usambazaji Z0 inapaswa kukidhi mahitaji ya 50 ω 50 ω, na impedance ya mzigo kawaida huwa katika maelfu ya ohms hadi makumi ya maelfu ya ohms. Kwa hivyo, ni ngumu kutambua kulinganisha kwa impedance upande wa mzigo. However, because the signal source (output) impedance is usually relatively small, roughly in the tens of ohms. Kwa hivyo ni rahisi sana kutekeleza kulinganisha impedance kwenye chanzo. If a resistor is connected at the load end, the resistor will absorb part of the signal to the detriment of transmission (my understanding). Wakati kiwango cha sasa cha TTL / CMOS cha 24mA kinachaguliwa, impedance yake ya pato ni takriban 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)

Wakati viwango vingine vya usafirishaji na mikondo ya gari imechaguliwa, impedance inayofanana inaweza kuwa tofauti. Kwa mantiki ya kasi na muundo wa mzunguko, kwa ishara kadhaa muhimu, kama saa, ishara za kudhibiti, tunapendekeza kontena inayolingana na chanzo lazima iongezwe.

Kwa njia hii, ishara iliyounganishwa itaonyeshwa nyuma kutoka upande wa mzigo, kwa sababu chanzo cha impedance kinalingana, ishara iliyoonyeshwa haitaonyeshwa tena.