4. The design of PCB-- PCB design related concepts

6.PCB design related concepts

Juvtmall ( a company supply PCB Prototyping, PCBA service and sell kinds of components, modules and so on) 

Via holes:

Once selected, be sure to deal with the gap between it and the surrounding each entity especially easy to ignore the gap between the line not connected to via hole of each layer in the middle and via hole, if it is a automatic wiring, can be in "number Via minimization" (Via Minimiz8tion) in the sub menu select "on" to automatically solve.

The larger load flow required, the larger hole size required, such as the larger the hole in the power layer and the other layer.

Silk screen layer:

For the convenience of installation and maintenance of the circuit, etc., it needs printing logo and writing code on the upper and lower surface of the printing circuit, such as component label and nominal value, the profile of the component and the signs of the manufacturer, date of manufacture, etc. Many beginners to design related content of the silk printing layer, only pay attention to the text symbol to place neatly and aesthetically, ignore the PCB effect that actually produced.

The board of their design, character is blocked by component or invaded weld-aid area has been put on credit, and label be put on the adjacent components, such the design will bring great inconvenience to fitting and maintenance. The correct character layout principle of silk printing is: "no ambiguity, make use of every single space, beautiful and generous".

SMD package:

The Protel packaging library has a large number of SMD packages, namely surface welding devices. In addition to the compact size, the biggest feature of such devices is pin holes of single-sided distribution.

Therefore, the device should be selected the surface in order to avoid "Missing Plns". In addition, the relevant text of such component can only be placed according to the side of it.

Filling area:

Network filling area (External Plane) and filling area (Fill)

As the name suggests, the network filling area is large areas of copper foil made as network shape, the filling area is only the complete copper foil.

In the beginner's design process, there is often no difference between the both on the computer, in essence, as long as you enlarge the surface of the picture. It is usually not easy to tell the difference, so less attention to the distinction between the two when using, what need to stress is that the former has the strong function in the characteristic of the circuit to inhibit the action of the high frequency interference, is suitable for the place should be done large area filling, especially the areas as shielding area, divided area or high current is particularly appropriate when the power cord. The latter is used for the end of general line or the transition zone and so on needs small area to fill.

Bonding pad:

The bonding pad is the most common contact in PCB design and the most important concept, but beginners can easily ignore its selection and correction, always use circular welding disks in the design. 

The type of the pad to be selected should be considered in terms of shape, size, arrangement, vibration and heat condition, force direction, etc.

Protel gives a series of welding disks of different sizes and shapes in the package library, such as round, square, octagon, round square, and positioning, etc., but sometimes it is not enough, so it needs to be edited by yourself. For example, for fever and more stress, current larger pad, can be designed into "tears shape", in the design of output transformer pin bonding pad of PCB, many manufacturers adopt this form.

In general, the following principles should be considered in addition to the above mentioned principles:

(1) the size difference between the width of the wire and the specific length of the welding plate should be considered when the shape is inconsistent.

(2) it is necessary to choose the unsymmetrical soldering plate when the tracing between the pins of the component.

(3) the size of the hole should be edited and determined according to the size of the pins. The principle is that the hole is the size of the pin to the diameter of the pin is 0.2-0.4 mm.

All kinds of film:

These membranes are not only necessary for PB production process, but also necessary for the welding of components. According to the position and function of "film", it can be divided into two types: the TOp or Bottom and TOp or BottomPaste mask of component surface (or solder side).

As the name implies, the TOp or Bottom is coated on the solder plate, which improves the weldable performance of the film, which is the light spot on the green plate slightly larger than the welding disk.

TOp or BottomPaste mask is just the opposite, in order to adapt the wave soldering of the board , that require copper foil beside the bonding pad on board can't stick tin, so other parts except the welding plate should be coated with a layer of paint,in order to prevent these parts on the tin.

So these two fills are kind of complementary.

From this discussion, it is not difficult to ensure the setting of items such as "solder Mask En1argement" in the menu.

Two meanings of the flying thread:

When automatic wiring, network connection like a rubber band for observation after adds components through the network and makes a preliminary layout, using the Show command can see the layout under the condition of network connection cross, constantly adjust element position to make the cross at least, to achieve maximum automatic wiring completion rate.This step is important. In addition, the automatic wiring is finished, and which network has not yet wiring, can also be searched through this function. After finding out the network not wiring, the manual compensation can be used to make it possible to use the second meaning of "flying wire", which is to connect these networks with wires in the future printing plates. If the circuit board is produced by mass production of automatic line, it can be considered as a 0 resistance value and a resistance element with uniform weld spacing to design.

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