As an electronics engineer designing the circuit is an essential hard effort , I summarize some of the following should be noted PCB design places , hoping to inspire you . We focus on the system board to discuss specific program issues.
1 . Making physical borders
Closed the border for subsequent physical component layout, alignment is a basic platform, but also plays a binding effect on the automatic layout , otherwise , coming from the schematic component overwhelmed . But here we must pay attention to the exact , or after installation problems occur in big trouble . There is a corner where the best arc , on the one hand to avoid sharp corners scratched workers , but they can reduce the stress . I used to always have a product of individual machines PCB board surface shell case appears broken , like the arc after the switch in the transport process .
Introducing 2 and the network element
The introduction of elements and network -drawn border should be very simple , but there is often a problem , be sure to follow the prompts to resolve the errors one by one carefully , otherwise back to spend more effort. The problem here in general are the following :
Can not find the package components , component network problems, there are elements or pins unused controls suggesting that these problems can be quickly buttoned .
3 layout elements
Layout and trace elements of the product life, stability , electromagnetic compatibility has great influence , should pay special attention to the place . Should have the following general principles :
( 1 ) Place the order
First place fixed position and structure -related components, such as electrical outlets , lights , switches , connectors and the like, these devices are placed after a good software LOCK function to lock it , so that he would not be moved by mistake . Then place a special element lines and large components, such as heating elements , transformers , IC and so on. Finally, place a small device .
( 2 ) Note that the heat
Component placement special attention to heat issues . For high-power circuits should be such that the heating element power tubes , transformers, etc. Try to place aside dispersed layout , easy heat dissipation , not concentrated in one place , nor too high capacitance to avoid premature aging of the electrolyte .
4 . Wiring
Wiring principles
Traces of knowledge is very profound , will each have their own experience , but still some prevailing principles.
◆ High-frequency digital circuits traces carefully, some good short
◆ between the large current signal , and the high voltage signal should be noted that small signal isolation ( separation distance and pressure to bear on , the board is usually the case when the required distance 2KV 2mm, on top of this base also increase the ratio of for example, to withstand the pressure test 3KV , the distance between the high and low voltage lines should be 3.5mm or more, in many cases in order to avoid creepage , still slotted between the high and low pressure on the PCB . )
◆ When two panel wiring , both sides of the wire should be perpendicular , oblique or curved alignment, avoiding parallel to each other , in order to reduce the parasitic coupling ; as input and output circuits printed conductors should be avoided adjacent parallel rabbit to avoid feedback between these wires plus ground wire is best .
◆ traces corner as greater than 90 degrees , 90 degrees or less to prevent the corner , but also minimize the use of 90 -degree corners
◆ with the address lines or data lines, trace length difference not too much, otherwise the short-term portion of curved lines to compensate people go
◆ traces walking in the welding surface , especially PCB through-hole technology
◆ hole used as little as possible , jumper
◆ single panel pads must be large , the line must be connected to the pads thick, able to put to put teardrop teardrop , generally single- panel manufacturers quality is not very good , otherwise the welding and RE-WORK will have problems
◆ use a large copper grid , in order to prevent bubbles and wave soldering board because heat stress and bending , but in special occasions to consider GND flow , size, not simply filled with copper trouble , but need to go line
◆ components and traces can not be too put aside , in general , mostly single- panel paper board, easily broken by the force , or if the connection is put on the edge components will be affected
◆ must consider the production , commissioning and maintenance convenience
Analog circuits for processing in question is very important, the noise floor is often inconvenient expected to produce , but once produced will bring great trouble , it should not rain silk. For the amplifier circuit, the noise will be tiny because the level of amplification have a significant impact on the sound quality ; in high-precision A / D converter circuit, if there is a high frequency component to the online presence will have some drift, impact amplifier operation . Then you can be connected to the four corners of the board plus decoupling capacitors, and the board foot , one foot is connected to the mounting holes up ( connected by screws and chassis ) , which can consider this component to the amplifier and AD also stabilizes .
In addition, the electromagnetic compatibility problems in the current circumstances it doubly concerned for environmentally friendly products even more important. Electromagnetic signal sources are generally three : a signal source , the radiation , the transmission line . A high frequency oscillator is a common signal source , the energy value of the harmonic power spectrum will be significantly higher than the average crystal . Feasible approach is to control the signal amplitude , crystal shell grounding , shielding against interfering signals , using a special filter circuits and devices.
Of particular note is the serpentine traces , because different applications and its role is different, the computer's motherboard used in the some clock signals, such as PCIClk, AGP-Clk, it does two things: one , impedance matching 2, the filter inductor .
Some important signals, such as INTELHUB architecture HUBLink, a total of 13 , the frequency up to 233MHZ, requirements must be strictly equal length , to eliminate hidden dangers caused by time lag , then, serpentine traces is the only solution .
In general , the serpentine trace line from > = 2 times the width ; if ordinary PCB board , in addition to having a filter inductance effect , but also as a radio antenna coil inductance and so forth.
5 Adjust the sound
Upon completion of wiring to do is to text, the individual components , traces some adjustments and copper ( this work should not be too early , otherwise it will affect the speed , and gave the wiring trouble ) , the same is to facilitate production, commissioning and maintenance.
Copper usually refers to a large area of white space after the copper wiring left to fill , you can shop GND copper foil , copper foil can also be spread VCC ( but so easy to burn once the short circuit devices , the best ground , unless forced by to increase the power conduction area to withstand large current was connected to VCC). Package usually refers to the ground by two (TRAC) to wrap a handful have special requirements for signal lines , to prevent it from interference by others or interfere with others.
If instead of using copper ground wire must pay attention to whether the whole connectivity , the current size , flow and any special requirements in order to ensure the reduction of unnecessary mistakes .
6 Check the check network
Sometimes, because of misuse or negligence painted board network relationship diagram is different, then it is necessary to check the prosecution . So after unfinished must not rush to the plate manufacturers, should first check , and then follow up .
7 Using simulation function
After completing these tasks, if time permits can also be software emulation . Especially the high-frequency digital circuits , so you can find some of the problems in advance , greatly reducing the workload for subsequent commissioning .
