As an electronic engineer the designa circuit is a necessary masterly skill, but the principle design is again perfect, if the circuit wafer will design the unreasonable performance to sell at a discount greatly, will be serious when even cannot the normal work. According to mine experience, I summarize the place which below some PCB in the design should pay attention, hoped that can have the enlightenment to you.
No matter with any software, the PCB design has an approximate procedure, comes according to the order to be able time-saving to reduce effort, therefore I will introduce according to the manufacture flow. (because the protel contact surface style and the windows Windows is close, the operation custom is also close, and has the formidable simulation function, the use person are quite many, will give the explanation by this software. )
The schematic diagram design is the earlier period preparatory work, saw the beginner frequently, for convenient drew the PCB board directly, like this gain does not equal the loss, to simple board, if the skilled flow, might as well might jump over. But must certainly come regarding the beginner according to the flow, may form the good habit like this at the same time, on the other hand also only then like this can avoid to the complex electric circuit making a mistake.
When picture schematic diagram, when level design must pay attention to each document to connect finally is a whole, this has the important meaning similarly to the later work. Because, software’s difference some softwares can appear looked that resembles connected has not linked (in actually electrical specification) situation. If does not use the correlation detection tool examination, if had problems, and so on boards completed have only then discovered late. Therefore emphasized repeatedly makes the importance according to the order, hoped brings to everybody’s attention.
The schematic diagram is comes according to the design project, so long as electrical connection correct not any flattery. Below we discuss in the concrete system board procedure with emphasis the question.
l, manufacture physics frame
The seal physical frame to the later part layout, walked the line is a basic platform, also played to the automatic layout is restraining the role, otherwise, the part which came from the schematic diagram can feel helpless. But here must certainly pay attention precisely, otherwise later will appear installs the question troublesome to be possible to be big. Also has is the corner place easiest to use circular arc, on the one hand may avoid the acute angle scratching the worker, simultaneously may reduce the stress function. Before my product always has the individual machine in the transportation process to present the surface shell PCB board break the situation, after changing to the circular arc, was good.
2nd, part and network introduction
Make the human the part and the network to draw in the good frame to be very simple, but here will often have problems, certainly must solve one by one carefully according to the prompt mistake, otherwise behind will want an expense bigger strength. Here question generally speaking has following some:
Part’s seal form could not find, the part network question, did not have the use part or the base pin, the comparison prompts these questions to be possible to do very quickly decides.
3rd, part’s layout
Part’s layout with walks the line to the product life, stable, the electromagnetic compatibility to have the very tremendous influence, is should the special attention place. Generally speaking should have the following some principles:
3.l laying aside order
Lays aside and the structure related stationary position primary device first, like the power point., the indicating lamp, the switch, the bridge piece and so on, after these components lay aside, with software’s LOCK function its locking, will cause it later not to move by mistake. Again on laying aside line’s special part and big primary device, like heating element, transformer, IC and so on. Finally laying aside small component.
3.2 attention radiations
The part layout also wants the special attention radiation question. Regarding the high efficiency electric circuit, should these heating element like power tube, the transformer and so on keep to the side as far as possible the scattered layout laying aside, is advantageous for the thermal sending out, do not concentrate in a place, also does not want the high electric capacity too in order to avoid nearly causes the electrolyte premature aging.
4th, wiring
Wiring principle
Walks the line the knowledge is very profound, each person will have own experience, but somewhat general principle.
◆ the high frequency digital circuit walks the line thin some, short somewhat good
◆ between the big electric current signal, the high voltage signal and the small signal should pay attention isolate (isolate are away from with the pressure resistance which must withstand related, usually in situation when 2KV on the board must be away from 2mm, above this by the proportion calculated that must enlarge, for example, if withstands 3KV the pressure resistance test, then between the high and low pressure line’s distance should above 3.5mm, in many situations to avoid crawling the electricity, but also on between printed wiring board high and low pressure slot. )
when ◆ two kneading board wiring, the both sides wire suitable mutually perpendicular, oblique, or walks the line curving, avoids mutually parallel, reduces the parasitic coupling; The printed wiring which loses the human and the output uses should evade the rabbit neighboring as far as possible as the electric circuit parallel, in order to avoid occurs gives, is best between these wires affixes the grounding.
◆ walks the line corner to be bigger than 90 degrees as far as possible, ceases 90 degrees following corners, also as far as possible little uses 90 degrees corners
◆ with is the address wire or the data line, walks the line length difference not to be too big, otherwise the short line partial important people to walk the curved line to make the compensation
◆ walks the line to walk as far as possible in the face of weld, specially through hole craft PCB
◆ as far as possible little uses the hole, to jump the line
◆ the single kneading board welds the plate to probably be big, welds scrutinizes the company line certainly to be thick, can put the waterdrop to put the waterdrop, the one-sided lumber yard quality generally will not be good, otherwise the butt weld and RE-WORK will have the question
◆ the big area spreads the copper to need to use the grid shape, to prevent the wave welds when the board sparging and because of the thermal load function, but is curving, but under the special occasion must consider that GND flow direction, the size, cannot simple settle with the copper foil packing, but is needs to go to the line
◆ the primary device and walks the line not to be able too to keep to the side to put, the common single kneading board many are the paperboard, after the stress, easy to break, if or will put the primary device on the edge segment to come under the influence
◆ must consider the production, the debugging, the service conveniences
Processes the place to the analogous circuit the question is very important, ground produces the noise often inconveniently expected, but once will produce will bring the enormous trouble, should not rain silk fabrics. Regarding the power amplifier electric circuit, the extremely small place noise can, because, the level enlargement has the obvious influence to the acoustic fidelity; In high accuracy A/D switching circuit, if in the grounding will have the high frequency component existence certainly to produce floats warm, will interfere with amplifier’s work. By now might draw back the lotus root electric capacity in board 4 jiao Canada, on a foot and the board place company, a foot company arrives at the installment hole to come up (through bolt and cabinet continually), like this may ponder this component, the amplifier and AD also stabilized.
Moreover, electromagnetic compatibility question, in the present people pay attention doubly to the environmental protection product in the situation appeared is more important. Generally speaking the electromagnetism signal’s origin has 3: Supply oscillator, radiation, transmission line. The crystal oscillator is the common one kind of high frequency supply oscillator, the crystal oscillator various subharmonics energy content will be higher than the mean value obviously on the power spectrum. The feasible procedure is the control signal scope, the crystal oscillator case earth, carries on the shield to the unwanted signal, uses the special filter circuit and the component and so on.
Those who need the special explanation walks the line snake-shaped, because the application situation different its function is also different, uses in computer’s motherboard on some clock signal, like PCIClk, AGP-Clk, its function has two points: 1st, impedance matching 2, filter inductance.
To some important signals, like in INTELHUB construction HUBLink, altogether 13, the frequency may reach 233MHZ, the request must strict and so on be long, eliminates the hidden danger which the time lag creates, by now, walked the line was the only solution snake-shaped.
Generally speaking, walks the line snake-shaped line-spacing >=2 time of line width; If in the ordinary PCB boards, besides has the filter inductance function, but may also take radio antenna’s inductance coil and so on.
5th, the adjustment consummates
After completing the wiring, must do is to the writing, the individual part, walks the line to make an adjustment as well as to spread the copper (this work not to be suitable is too early, will otherwise affect speed, also will bring troublesome to wiring), similarly will be for ease of carries on the production, the debugging, the service.
The gap which after the big area’s copper foil spreads the copper usually to refer to fills wiring stays behind, may spread GND the copper foil, may also spread VCC the copper foil (, but once like this short-circuits easily to burn down component, best earth, only if has to use for to enlarge power source’s breakover area, relies on is only then met big electric current VCC). Wraps the place usually to refer to with two groundings (TRAC) wraps up one pinch to have the special request holding wire, prevents it or disturbs by others disturbance others.
If with spreads the copper tape certainly to pay attention for the grounding entire whether to connect, does the electric current size, whether there is flow with requests specially, guarantees the reduced nonessential fault.
6th, inspection checkup network
Because sometimes the misoperation or the negligence creates the board network relations which and the schematic diagram will draw is different, by now examined the checkup was very necessary. Will therefore draw later to cut cannot give the making lithograph plates factory eagerly, should make the checkup first, latter will carry on the following work again.
7th, use simulation function
After completing these work, if adequate time may also carry on the software simulation. Specially the high frequency digital circuit, like this may discover some questions ahead of time, reduces the later debugging work load greatly.
