Wiring overview and principles
 With the rapid development of high-speed theory, pcb alignment can not be seen as a simple interconnection carrier, but from the transmission line theory to analyze the impact of various distribution parameters. The distributed parameter circuit is a circuit that must consider the distribution of circuit component parameters. The distribution of parameters refers to the circuit at the same moment the two adjacent potential and current are not the same. This shows that the voltage and current in the distributed parameter circuit are in addition to a function of time, or a function of spatial coordinates. At the same time pcb complexity and density are also increasing, from the copper through the hole design, to the micro-hole design, and then to the multi-stage buried blind hole design, there are buried resistance, buried, buried device design, High density to the pcb wiring with a great difficulty at the same time, also need pcb design engineers more in-depth understanding of pcb production process and its process parameters.
Wiring is divided into automatic routing and manual wiring, automatic wiring in many ways can not meet the requirements of high standards of hardware engineers, it is generally manual wiring to achieve.
 Firing of DFM requirements
1, hole
Mechanical drilling conventional recommended above 8mil, limit 6mil, try to ensure that the thickness ratio is generally in the 10: 1, the higher the thicker the more difficult to process. Device hole ring width of at least 8mil, through the hole ring width of at least 4mil, the processing company will automatically optimize the cam processing, solder mask window for the unilateral 50um.
The same network spacing can be 6mil. The spacing of the different network vias is 275um, and the spacing of the different network devices is 425um.
Production is the drill bit is generally larger than the original hole 150um, drill to 0.05mm increments, the larger drill, will be 0.1mm increments. And then through the hole, plating to meet the final finished aperture requirements.
Non-metallized drilling to the edge of the board edge of the 150um that is not broken holes, conventional border tolerance. Metallized drilling to the edge of the board at least 10 mil.
0.5oz copper thick, the smallest line width can be done 3mil, the minimum spacing of 2mil.
1oz copper thickness of the thinest line width 3.5mil, the minimum spacing of 4mil
2oz copper thickest line width 4mil, minimum spacing 5.5mil.
Internal layer to avoid copper at least 20mil.
Small discrete devices, both sides of the alignment to be symmetrical.
When the SMT pad pins need to be connected, they should be connected from the outside of the welding pin and are not allowed to be connected internally.
For the SMT pad in the large area of ​​copper need to wear pad connection.
ETCH line distribution evenly, to prevent warpage after processing.
Electrical characteristics in wiring
1, impedance control and impedance continuity
Avoid sharp angle, right angle alignment.
Key signal cabling minimizes the use of fewer vias.
High-speed signal line to consider the appropriate arc wiring
2, crosstalk or EMC and other interference control requirements
High-speed signal and low-speed signal to be layered partition wiring
Digital signal and analog signal on the 1st stratified partition wiring
Sensitive signal and interference signal hierarchical partitioning
The clock signal should take precedence over the inner layer
In the power inductors, transformers and other sensitive devices under the projection area do not shop copper. (Due to the parasitic capacitance between the coil, and its inductor to produce parallel resonance, so there will be SRF, and SRF and EPC, so EPC smaller the better, you can ensure that the more inductive frequency range, and SRF at least DC -DC Converter switching frequency of ten times, for example, if the switching frequency of 1.2MHz, the SRF at least 12MHZ. Therefore, Layout, the power below the power to dig out, do not have metal, to avoid additional EPC, resulting in inductive frequency Range reduction)
The key signal is to be distributed in the preferred layer to ground as the reference plane
Key signals are considered to be handled in packets.
Any signal, including the return path of the signal, must avoid the formation of a loop, which is one of the important principles of EMC design.
 High-speed cabling 3w principle
Topology and timing requirements
 Meet the timing requirements of the system can be the key to the normal stability of the work, delay control response to the pcb design is the alignment of the length of control, or even long and even have become a wiring engineer in the mouth of your term. Timing design is also very complex system requirements, pcb design engineers not only to be around the same length, but also a real understanding of the long behind the timing requirements.
Power supply and power signal wiring requirements
Power supply inlet circuit to do the principle of post-protection filtering
Chip and its filter capacitor pins should be as short as possible, storage capacitor to punch, reduce the wiring to install the inductance
Consider the safety requirements, the power supply network pressure is greater need to stay away from the high-voltage network plug-in pins and vias need to do hollowing out
Wiring in the heat to consider
Electronic design there is an important trend, that is, voltage drop, power upgrade, pcb cabling as an important part of the design of the plate, it becomes more important. When necessary, the need to use the relevant electrical and thermal simulation tools to assist in thermal design.
Strict calculation of the wiring channel to meet the current requirements.
But also concerned about the current carrying capacity of the hole, a reasonable number of holes and location planning.
Large heat under the chip can be a small location can be a large area plus ground copper, and add holes to strengthen the heat.
High-power heat of the device in the projection area, in all layers do not take high-speed lines and sensitive signal lines.
High current power supply, if its wiring path to make a long time, need to strengthen its wiring channel to reduce heat loss.
Has been added to the thermal pad of the heating device, in the heat pad to add holes to enhance the heat.
Wiring summary
PCB cabling is a system of engineering, design engineers need to have a comprehensive knowledge of multidisciplinary, but also have a strong analytical ability to deal with all aspects need to achieve a better balance.
PCB design is not myth, not a black box, there is no universal method, all reasonable norms, behind can find a real theoretical process, the usual work to think, ask, learn more, this is Become a master of the road.