PCB News - PCB design should be paid attention to in the 7 steps of board making

1. Make physical borders

The closed physical border is a basic platform for subsequent component PCB layout and wiring, as well as a constraint on automatic layout, otherwise components coming from the schematic will be overwhelmed. But here must pay attention to, otherwise later installation problems can be big trouble. Still have namely corner place uses circular arc, can avoid sharp horn to scratch worker on one hand, can reduce stress action again at the same time. In the past, a product was always in the process of transportation in some machine surface shell PCB board fracture, after the use of arc is good.

2. Introduction of components and networks

It should be easy to draw components and networks into a drawn border, but this often leads to problems, so be careful to follow the prompts one by one, otherwise it will take more effort later. The problems here are generally as follows:

Component package form not found, component network problems, unused components or pins, these problems can be

quickly resolved.

3. Layout of components

The layout and wiring of components have great influence on the life, stability and electromagnetic compatibility of products, which should be paid special attention to. In general, the following principles should be followed:

3.1. Placement sequence

First place components with fixed positions related to the structure, such as power sockets, indicators, switches, connectors and so on. After these components are placed, LOCK them with the software LOCK function, so that they will not be moved by mistake in the future. Then place special components and large components on the line, such as heating elements, transformers, IC and so on. Place small devices.

3.2. Pay attention to heat dissipation

Component layout should pay special attention to heat dissipation. For high-power circuits, the heating elements

such as power tubes and transformers should be placed as far as possible on the side of the scattered layout, so as to facilitate heat emission, do not concentrate in one place, nor do not high capacitance too close to avoid premature aging of the electrolyte.

4. Wiring

The wiring principle

The knowledge of walking a line is very advanced, everyone will have their own experience, but there are some general principles.

◆ High frequency digital circuit wiring thinner, shorter better

Mixer high current signals, should pay attention to the isolation between high voltage signals and small signal (distance between related to bear pressure, usually on the 2 kv board is 2 mm distance, on top of this ratio is also increased, for example, if you want to bear the pressure test of 3 kv, is the distance between the high and low voltage lines should be above 3.5 mm, in many cases to avoid creepage, It also slots between high and low voltage on the printed circuit board.)

◆ When wiring two panels, the wires on both sides should be perpendicular, oblique or bent to each other, avoid parallel to each other, in order to reduce parasitic coupling; Printed wires used as circuit input and output should be as far as possible to avoid adjacent parallel rabbits, so as to avoid feedback, grounding wires should be added between these wires.

◆ The line corner as far as possible greater than 90 degrees, put an end to 90 degrees below the corner, also as little as possible with 90 degrees corner

◆ The same as the address line or data line, the difference in the length of the line should not be too large, otherwise the short line part should be artificially bent for compensation

Try to walk on the welding surface, especially PCB with through-hole process

◆ Use holes and jumpers as little as possible

◆ Single panel pad must be big, the line connecting the pad must be thick, can put tears put tears, the general single panel manufacturer quality will not be very good, otherwise there will be problems for welding and re-work

◆ Large area copper to use grid, in order to prevent wave welding board bubble and because of thermal stress and bending, but in special occasions to consider the direction of GND, size, can not simply fill with copper foil, but need to go to the wire

◆ Components and wiring can not be placed too far to the side, the general single panel is mostly paper board, easy to fracture after stress, if the edge of the connection or components will be affected

◆ The convenience of production, debugging and maintenance must be considered

It is important for analog circuits to deal with ground noise, which is often unpredictable but can cause great trouble and should be avoided. For the power amplifier circuit, the slightest ground noise will have a significant impact on the sound quality because of the amplification of the rear stage; In high A/D conversion circuit, the presence of high frequency components on the ground will produce A certain temperature drift, which will affect the work of the amplifier. At this time can be in the 4 corners of the board add back coupling capacitor, a foot and the board on the ground connection, a foot connected to the mounting hole (through the screw and shell connection), so that this component can be considered, and the amplifier and AD will be stable.

In addition, electromagnetic compatibility problems in the current environmental protection products more attention to the situation appears more important. Generally speaking, electromagnetic signal has 3: signal source, radiation, transmission line. Crystal oscillator is a common high frequency signal source. The energy value of each harmonic wave of crystal o

scillator is obviously higher than the average value in the power spectrum. The feasible way is to control the amplitude of the signal, grounding the crystal shell, shielding the interference signal, and using special filter circuits and devices.

Need special note is the snake line, because the application of different role is different, in the computer motherboard used in some clock signal, such as PCIClk, AGP-CLK, its role has two points: 1, impedance matching 2, filter inductance.

For some important signals, such as HUBLink in INTELHUB architecture, a total of 13 signals, frequency up to 233MHZ, must be strictly equal length, in order to eliminate the hidden trouble caused by time delay, at this time, the serpentine route is the solution.

Generally speaking, the line spacing of the serpentine line is > = 2 times the line width; If in the common PCB board, in addition to the role of filter inductor, but also as a radio antenna inductance coil and so on.

5. Adjust and improve

After finishing wiring, what should do is to be right character, individual element, go a line to do some of adjustment and apply copper (this job should not be too early, can affect speed otherwise, bring trouble to wiring again), it is to facilitate to undertake production likewise, debug, maintain.

Copper coating usually refers to a large area of copper foil to fill the wiring left blank area, you can shop GND copper foil, also can shop VCC copper foil (but this once the short circuit is easy to burn devices, grounding, unless have to increase the conduction area of the power supply, in order to withstand a larger current to VCC). To wrap the ground usually means to wrap two ground wires (TRAC) around a bunch of signal wires with special requirements to prevent it from being disturbed or interfering with others.

If copper is used instead of ground wire, attention must be paid to whether the whole ground is connected, current size, flow direction and whether there are special requirements to ensure that unnecessary errors are reduced.

6. Check the network

Sometimes, due to misoperation or negligence, the network relationship of the board drawn is different from the schematic diagram, so it is necessary to check. So after painting must not be rushed to the plate manufacturer, should be checked first, and then follow-up work.

7. Use simulation

Once this is done, software simulations can be performed if time permits. Especially high frequency digital circuit, so that some problems can be found in advance, greatly reduce the later debugging workload.