Berbicara Papan 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.

Papan PCB dapat dibagi menjadi papan lapisan tunggal, papan lapisan ganda dan papan multi lapisan. Komponen elektronik terintegrasi ke dalam PCB. Pada PCB satu lapis dasar, komponen terkonsentrasi di satu sisi dan kabel terkonsentrasi di sisi lain. Jadi kita perlu membuat lubang di papan agar pin dapat melewati papan ke sisi lain, sehingga pin bagian dilas ke sisi lain. 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. Terkadang perlu untuk menghubungkan satu kabel dari satu sisi ke sisi lain papan melalui lubang pemandu (via). Lubang pemandu adalah lubang kecil pada PCB yang diisi atau dilapisi logam yang dapat dihubungkan dengan kabel di kedua sisinya. Saat ini motherboard komputer banyak yang menggunakan 4 atau bahkan 6 lapis papan PCB, sedangkan kartu grafis umumnya menggunakan 6 lapis papan PCB. Banyak kartu grafis kelas atas seperti seri nVIDIAGeForce4Ti menggunakan 8 lapis papan PCB, yang disebut papan PCB multi-lapis. The problem of connecting lines between layers is also encountered on multi-layer PCBS, which can also be achieved through guide holes.

Karena merupakan PCB multi-layer, terkadang lubang pemandu tidak perlu menembus seluruh PCB. Lubang pemandu semacam itu disebut Buriedvias dan Blindvias karena hanya menembus beberapa lapisan. Lubang buta menghubungkan beberapa lapisan PCB internal ke permukaan PCB tanpa menembus seluruh papan. Lubang yang terkubur hanya terhubung ke PCB internal, sehingga cahaya tidak terlihat dari permukaan. Dalam PCB multilayer, seluruh lapisan terhubung langsung ke kabel ground dan catu daya. Jadi kami mengklasifikasikan layer sebagai Signal, Power atau Ground. Jika bagian-bagian pada PCB membutuhkan catu daya yang berbeda, mereka biasanya memiliki lebih dari dua lapisan daya dan kawat. 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 papan utama sebagian besar 4 lapisan. Saat manufaktur, dua lapisan tengah digulung, dipotong, diukir, dioksidasi dan dilapisi masing-masing. Keempat lapisan tersebut masing-masing adalah permukaan komponen, lapisan daya, stratum dan laminasi solder. The four layers are then pressed together to form a PCB for the main board. Then the holes were punched and made. Setelah dibersihkan, dua lapisan luar garis dicetak, tembaga, etsa, pengujian, lapisan ketahanan las, sablon. Akhirnya, seluruh PCB (termasuk banyak motherboard) dicap ke PCB masing-masing motherboard, dan kemudian pengemasan vakum dilakukan setelah lulus tes. 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. Triknya adalah dengan menyebarkan lapisan tipis foil tembaga ke seluruh permukaan dan menghilangkan kelebihannya. Menambahkan transfer adalah metode lain yang jarang digunakan, yaitu menerapkan kawat tembaga hanya di tempat yang diperlukan, tetapi kita tidak akan membicarakannya di sini.

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. Tudung hanyalah template untuk membuat lapisan PCB. Tudung yang menutupi photoresist pada PCB mencegah beberapa area dari photoresist terekspos sampai photoresist terkena sinar 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. Umumnya digunakan sebagai pelarut etsa menggunakan besi klorida dll. After etching, remove the remaining photoresist.

1. Lebar dan arus kabel

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).

Ketika ketebalan foil tembaga sekitar 50um, lebar kawat adalah 1 ~ 1.5mm (60mil) = 2A

Persamaannya umumnya 80mil, terutama untuk aplikasi dengan mikroprosesor.

2. Seberapa tinggi frekuensi papan berkecepatan tinggi?

Ketika naik/turun waktu sinyal “3~6 kali waktu transmisi sinyal, itu dianggap sebagai sinyal kecepatan tinggi.

Untuk rangkaian digital, kuncinya adalah melihat kecuraman tepi sinyal, waktu yang dibutuhkan untuk naik turun,

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! — — — — — – yaitu! 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. Penumpukan dan pelapisan PCB

The four – layer plate has the following stacking sequence. Keuntungan dan kerugian dari laminasi yang berbeda dijelaskan di bawah ini:

Kasus pertama harus yang terbaik dari empat lapisan. 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. Namun, kasus pertama tidak dapat digunakan ketika kepadatan papan relatif tinggi. 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. Dari struktur papan, tidak cocok untuk desain sirkuit digital berkecepatan tinggi. Sulit untuk mempertahankan impedansi daya rendah dalam struktur ini. Take a plate 2 mm as an example: Z0=50ohm. To line width of 8mil. Copper foil thickness is 35цm. Jadi lapisan sinyal dan tengah formasi adalah 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. pelindung 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. Pencocokan impedansi

Amplitudo sinyal tegangan pantul ditentukan oleh koefisien pantul sumber S dan koefisien pantul beban L

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

Pada persamaan di atas, jika RL=Z0, koefisien refleksi beban L=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. Oleh karena itu, sulit untuk mewujudkan pencocokan impedansi pada sisi beban. However, because the signal source (output) impedance is usually relatively small, roughly in the tens of ohms. Oleh karena itu jauh lebih mudah untuk menerapkan pencocokan impedansi pada sumbernya. If a resistor is connected at the load end, the resistor will absorb part of the signal to the detriment of transmission (my understanding). Ketika arus penggerak 24mA standar TTL/CMOS dipilih, impedansi keluarannya kira-kira 13 . 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.