PCBgogo

I saw some basic knowledge about PCB, today I summarized it and I want to share with you now.

1. Definitions:
For standard board, it is the combination of bare board and components on it. While for bare board PCB, it is called printed wiring board. We usually call it PWB.

(1) Traces:
The base material of PCB is comprised of dielectric, heat insulation, uneasy to bend materials. On its surface, we can see thin traces, its material is copper. Originally the copper covered the whole PCB. Parts of it were etched during the process of production. Those parts left become net-like thin traces, which are called conductor pattern, and are used to provide circuit connection for components on PCB.

(2) Name of two side:
On most common single sided PCB, components are on one side, conductor pattern is on the other side. Then we would need to drill holes on the board, so that pins can put through the board to the other side. Therefore, the both sides of PCB are called component side and solder side.

(3) Gold finger:
Gold finger is functioned to connect two PCBs. We usually insert the gold finger of one PCB to the proper slot of the other PCB.

(4) Solder mask and silk screen:
The green or white oil on PCB is called solder mask, which is functioned as dielectric protective layer, can protects copper traces and also can prevent components to be soldered at incorrect place.

On the dielectric layer, a layer of silk screen will be printed. Some words will be printed to show the position of those components. It is also called legend.

2. The classification of PCB

(1) Single sided PCB
Single sided board means the conductor pattern appears only on one side. Because single sided PCB has many strict limits. On trace design, only circuit at early stage use this kind of boards.

(2) Double sided PCB
Double sided board means the conductor patterns appear on both sides of the board. However if we use the conductor patterns on both sides, there should be proper circuit to connect two sides. The bridge between the circuits is called via. Those vias are plated with metal, such as tin, copper, gold, etc. Because the area of double sided PCB is two fold of the area of single sided, and the conductor pattern can cross with each other, so it suits to be used on more complex circuits.

(3) Multi-layer boards
In order to enlarge the area of conductor pattern, multilayer PCB uses more single or double boards. It uses several piece of double sided boards, and a dielectric layer is put between every layer of boards. The layers of one PCB represent the layer of conductor patterns. The amount of the layers is always even number. Technically we can make PCBs up to 100 layers.

For via, if we use it on double sided PCB, the whole boards will be drilled. While on multilayer PCB, if you just want to connect some traces, via may will waste trace space of some layers. Then we use buried vias and blind vias to solve this problem, because they are only drilled through several layers.

a. Buried vias only connect inner PCBs, so we cant see them from the surface.

b. Blind vias connects several layers PCB with surface PCB.

In multilayer PCB, the whole board directly connects the ground line and power (used for preventing affection of the transmission signals on the signal). So we divide layers into signal, power, or ground. If the components on PCB need different power supply, this kind of PCB would have more than two layers of power and wire layers.

3. Components encapsulation technology

(1) Through hole technology
It means we mount components on one side, and solder the pins on the other. The disadvantage of it is space consuming. In fact, theirs pins take up space of both sides. While the advantage of it is good construction, which can bear pressure.

(2) Surface mounted technology
it means pins are soldered on the same side as components. We dont have to drill holes on PCB and dont have to solder every pin. The advantage of SMT is that the components are more compact and cheaper than those in THT.

4. Gerber files:
Usually it comprises the layout plan of signal, ground, power, solder mask, silk screen, and drilling layout plan, etc.

5. Manufacture steps
choose base material, then use subtractive transfer to show the artwork on metal conductor.