Printed circuit board

PCB circuit board design basic steps

PCB design step one: PCB copy board copy of the preliminary work

1, the use of schematic design tools to draw schematics, and generate the corresponding network table. Of course, there are some special circumstances, such as the circuit version is relatively simple, there is already a network table and other cases can also be designed without schematics, directly into the PCB design system, in the PCB design system, you can directly take the parts package, manually generated network table.

2, manual changes to the network table will be some components with fixed pins and other pads on the schematic diagram is not defined to the network connected to it, without any physical connection can be defined to the ground or protection ground. Some schematics and PCB package library pin name inconsistencies in the pin name of the device to the same as the PCB package library, especially diodes, triodes, etc.

PCB design step two: draw their own definition of non-standard device packaging library
It is recommended to draw their own devices are put into a PCB library of their own established special design files.
PCB design step

3: set up the PCB design environment and draw the printed circuit board version of the frame including the middle of the hollow, etc.

1, the first step after entering the PCB copy system is to set the PCB design environment, including setting the size and type of grid points, cursor type, layer parameters, wiring parameters and so on. Most of the parameters can use the system defaults, and these parameters are set to meet personal habits, no need to modify later.

2, the planning of the printed circuit board, mainly to determine the board’s edge, including the size of the circuit board size, etc.. In the need to place a fixed hole where the appropriate size of the pad. For 3mm screws available 6.5 ~ 8mm outside diameter and 3.2 ~ 3.5mm inside diameter of the pad for standard boards can be transferred from other boards or PCB izard.

Note: Before drawing the board ground border, be sure to set the current layer to Keep Out layer, that is, the prohibition of wiring layer.
PCB design step

4: After opening all the PCB copy library files to be used, access to the network table file and modify the package of parts
This step is a very important part, the network table is the soul of PCB automatic wiring, but also the schematic design and the impression of the circuit version design interface, only after loading the network table, you can carry out the circuit version of the wiring.

In the process of schematic design, ERC check will not involve the packaging of parts. Therefore, the package of the part may be forgotten during schematic design, and the package of the part can be modified or supplemented according to the design when the network table is introduced.Of course, you can manually generate the network table directly in the PCB and specify the part package.

PCB design step

5: layout of circuit board copy parts package location, also known as parts layout
Protel99 can be used for automatic layout, or manual layout. If the automatic layout, run “Tools” under the “Auto Place”, with this command, you need to have enough patience. The key to wiring is layout, most designers use manual layout form. Protel99 has added some new techniques for layout. The new interactive layout options include auto-selection and auto-alignment. Using the auto-select method you can quickly collect similarly packaged components, then rotate, expand and organize them into groups that can be moved to the desired location on the board. When the simple layout is complete, use the Auto Align method to neatly expand or shrink a group of similarly packaged components.
Tip: In automatic selection, use Shift+X or Y and Ctrl+X or Y to expand and collapse the X and Y directions of the selected components.

Note: Parts layout, should be considered from the mechanical structure of heat dissipation, electromagnetic interference, future wiring convenience and other aspects. Layout the devices related to the mechanical size first and lock these devices, then the large position-occupying devices and core components of the circuit, and then the peripheral small components.
PCB copy of the sixth step: according to the situation and then make appropriate adjustments to lock all the devices

If the board space allows then you can put on the board some similar to the wiring area of the experimental board. For large boards, more fixing screw holes should be added in the middle. The board has heavy devices or larger connectors and other stressed devices on the side should also be fixed screw holes, if necessary, you can put some test pads in the appropriate location, preferably in the schematic to add. Will be too small pad over the hole to change the size of all fixed screw hole pad network definition to ground or protection ground, etc..
After the placement with VIEW3D function to see the actual effect, save the disk.

PCB design step seven: PCB rewiring rules set
Wiring rules is to set the wiring specifications (such as the use of the level, the width of each group of lines, over-hole spacing, wiring topology and other part of the rules, can be exported from other boards through the Design-Rules Menu, and then imported into this board) This step does not have to be set every time, according to personal habits, set once on.
PCB board heat dissipation: generally will take two solutions to reduce the problem of cell phone PCB board heat: one is the hardware heat dissipation, such as the use of graphite sheet or thermal grease heat dissipation, and one is the core optimization of heat dissipation.

Thermally conductive graphite sheet is graphene stacked into, graphene is a two-dimensional structure of carbon materials, thermal conductivity up to 1600 W/m-K, higher than carbon nanotubes and diamond. It conducts heat fast in the horizontal direction and acts as a heat in the vertical direction. So we see that today many, many electronic product brands are using graphite heat dissipation. For example, Apple and LG, Xiaomi cell phones, etc., all use graphite heat dissipation.

Thermal grease heat dissipation, thermal grease is toothpaste shaped, when using directly apply it, easy to use, thermal conductivity up to 500W/m-K, so that the CPU and heat sink good contact, so that the heat of the CPU timely transfer to the heat sink, and then through the heat sink emitted, so as to play the purpose of cooling the CPU.


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