Printed circuit board 5 methods that dependability devises

Right choice sheet nods ground connection and many bits of ground connection to be in low frequency circuit, the working frequency of signal is less than 1MHz, the inductance influence between its wiring and parts of an apparatus is minor, and what ground connection circuit forms is circumfluent bigger to disturbing influence, should use a bit ground contact consequently. When signal job frequency is more than 10MHz, ground wire impedance becomes very big, answer to reduce ground wire impedance as far as possible right now, should use ground contact of nearby much spot. It is when working frequency when 1 ～ 10MHz, if use a bit ground contact, length of its ground wire should not exceed the 1/20 of wavelengh, should use method of many bits of ground connection otherwise. 2.

digital circuit and imitate circuit departure. There is circuit of high speed logic already on circuit board, have linear circuit again, should make they part as far as possible, and both ground wire does not want interblend, carry ground wire to be linked together with power source respectively. Want to increase the contact area of linear circuit as far as possible. 3.

If ground wire is very fine,add thick ground wire as far as possible, ground connection potential follows voltaic change and change, the time signal n that causes electronic equipment is flabby, fight noise function addle. Should add ground wire as far as possible accordingly thick, make it can be passed 3 be located in printed circuit board allow electric current. Be like likely, the width of ground wire should be more than 3mm.

4.

The printed circuit that makes ground wire design of closed circuit road be comprised by digital circuit only board when ground wire system, closed circuit of ground wire make it the road can enhance power of the sound energy that fight a confusion of voices apparently. Its reason depends on: Printed circuit board on have element of a lot of integrated circuit, when encountering the component with much report having waste time especially, because accept the restriction of ground wire degree of finish, bigger voltage can arise on knot, cause force of the sound energy that fight a confusion of voices to drop, if become ground connection structure annulus way, can narrow voltage is worth, increase the capacity of the voice that fight a confusion of voices of electronic equipment. 2, compatibility of electromagnetism of electromagnetism compatibility design is to show electronic equipment is in all sorts of electromagnetism environments the capacity that still can have the job effectively. The purpose that electromagnetism compatibility designs is to make electronic equipment can restrain all sorts of foreign interference already, make electronic equipment can work normally in specific electromagnetism environment, can reduce electronic equipment itself to be disturbed to the electromagnetism of other electron equipment again at the same time. 1.

Choose reasonable lead width. Because twinkling changes,electric current is disturbed in the concussion that prints generation of the place on line basically is caused by the inductance composition that prints lead, because this answers,reduce the inductance that prints lead to measure as far as possible. The inductance quantity that prints lead and its length become direct ratio, with its width becomes inverse ratio, short and the lead of essence of life is consequently right restraining interference is advantageous. The line of driver of clock down-lead, travel or bus line driver often carries great very short time to change electric current, print lead to want as far as possible short. To discrete element circuit, print lead width to be in 1.

When 5mm is controlled, can satisfy requirement; completely to integrated circuit, print lead width to be able to be in 0.

2 ～ 1.

Choose between 0mm. 2.

Use right wiring strategy. Use equality to walk along a line to be able to reduce lead inductance, but the mutual inductance between lead increases with distributinging capacitance, if layout allows, had better use well glyph meshy wiring structure, the one side that particular way is printed board is transverse wiring, another fore-and-aft wiring, use plated through hole to be linked together in alternate aperture place next. To restrain string of faze between printed board lead, the equality that should avoid Sunday run as far as possible when designing wiring takes a line, pull open the distance between line and line as far as possible, line and ground wire and power supply cord as far as possible not across. What a ground connection installs between very sensitive line is disturb to print a line in a few pairs, restrain string of faze effectively. Make the electromagnetism radiate of the generation when lead through imprinting to avoid high frequency signal, in printed circuit board when wiring, still should notice the following: ● reduces the discontinuous sex that prints lead as far as possible, for example lead width is not choppy, the corner of lead should be more than 90 degrees to prohibit cricoid walk along a line to wait. Down-lead of ● clock signal produces electromagnetism radiate the most easily to disturb, when taking a line, should stand by with photograph of ground wire loop, driver should be tightened be next to connector. Driver of ● bus line should be endured closely its desire the bus line of drive. Leave printed circuit to those board down-lead, driver should be next to connector closely. The wiring of ● data bus line should place ground wire of a signal between every two line. Had better be to be next to main least of all address catalyst to set ground return closely, because latter Chang Zai has high frequency electricity. ● decorates high speed, middling speed and low speed logic in printed board when circuit, should arrange parts of an apparatus 3.

Restrain reflection to disturb. To restrain a reflex that prints line terminal now to disturb, besides special need, should shorten as far as possible the length that prints a line and use slow fast circuit. Can add terminal to match when necessary, mix rightly in the extreme of transmission line namely power source end adds those who receive value of a same block to match resistor each. According to experience, faster to average rate TTL circuit, its print line to grow to should use terminal to match measure at 10cm above. Match the block value of resistor to answer according to the output of integrated circuit drive electric current and the maximum that absorb electric current decide. 3, go Ou capacitance configuration is in loop of direct current source, laden change can cause power source noise. It is for example in digital circuit, from a condition when circuit changeover is another kind of condition when, can produce a very big aiguille electricity on power supply cord, form transient noise voltage. Configure the noise that goes because load changes,Ou capacitance can be restrained and arising, it is printed circuit board a kind of groovy way that dependability devises, configuration principle is as follows: Input of ● power source carries bond of 100uF of a 10 ～ electroanalysis capacitor, if printed circuit board the position allows, those who use 100uF above electroanalysis the interference rejection effect of capacitor will be better. ● configures for chip of every integrated circuit 0.

The capacitor of pottery and porcelain of 01uF. If encounter printed circuit board the space is little and do not install when falling, but 10 chip configure every 4 ～ Tantalum of 10uF of a 1 ～ electroanalysises capacitor, the high frequency impedance of this kind of parts of an apparatus is particularly small, inside limits of 500kHz ～ 20MHz impedance is less than 1 Ω , and leakage current is very small (0.

5uA is the following) . The parts of an apparatus with big change of the weak to noise ability, electric current when closing mixes ● the memory such as ROM, RAM parts of an apparatus, should be in the power supply cord of chip (Vcc) with ground wire (GND) receive directly go Ou capacitance. ● goes the down-lead of Ou capacitance cannot grow too, especially capacitance of high frequency bypass cannot take lead 4, printed circuit board of dimension and parts of an apparatus decorate printed circuit board size wants moderate, too big when print line to grow, impedance increases, fight noise ability to drop not only, cost is high also; Too small, come loose heat is bad, at the same time close line disturbs Yi Shoulin. Like respect and other logic circuit are being decorated in parts of an apparatus, should put the parts of an apparatus that concerns each other so that stand by as far as possible some, it is better to can be obtained so defy noise result. If pursue,2 are shown. Plant when generator, brilliant brace up produce noise easily with the clock input end of CPU, should stand by each other some. Circuit of circuit of easy the parts of an apparatus or appliance that produces noise, small electric current, big electric current should be far from logistic circuit as far as possible, be like likely, answer to do circuit board additionally, this are very important. 5, hot design from be helpful for coming loose hot angle sets out imprint plate making had better be erect installation, board with board the distance between should not be less than 2cm commonly, and parts of an apparatus is imprinting the it is certain to arrange means to should abide by regulation on plate making: Sort the equipment with cool air to using freedom to be opposite, had better be integrated circuit (or other parts of an apparatus) arrange by lengthwise means, the equipment with compulsive to using cool air, had better be integrated circuit (or other parts of an apparatus) arrange by horizontal long way. The parts of an apparatus that goes up with a printed board should give out heat by its as far as possible quantity size and medicinal powder hot degree partition is arranged, calorific quantity the parts of an apparatus with small or poor hear resistance (like small signal transistor, miniature integrated circuit, electroanalysis capacitance) those who be put in cooling air current is the most genteel (the entrance is in) , calorific quantity the parts of an apparatus with big or good hear resistance (wait like circuit of power transistor, large scale integration) put in cooling air current the most downstream. On horizontal way, high-power parts of an apparatus stands by printed board edge to decorate as far as possible, so that shrink,; of short pass hot method is on perpendicular direction, high-power parts of an apparatus stands by printed board upper part to decorate as far as possible, so that reduce the to temperature of other parts of an apparatus effect when jobs of these parts of an apparatus. Compare sensitive parts of an apparatus to temperature, had better find a place for the area in temperature lowest (the bottom that is like equipment) , must not put it in calorific parts of an apparatus upper part, many parts of an apparatus had better be complex overall arrangement is handed in in horizontal. Of the printed board inside equipment medicinal powder air of hot main support flows, want to study air flow way when the design so, reasonable configuration parts of an apparatus or printed circuit board. Incline to always is when air flows at obstruction little place flows, be in so printed circuit board on when configuring parts of an apparatus, should avoid to stay in a certain area have bigger airspace. Overall in many printed circuit board configuration also should note same question. Many practice experience makes clear, use reasonable parts of an apparatus to range way, reduce the temperature rise of printed circuit effectively, the fault rate that makes parts of an apparatus reachs device thereby drops apparently above place is narrated is printed circuit only board a few general principles that dependability designs, printed circuit board dependability and specific circuit are having close relationship, still do not need to undertake corresponding processing according to specific circuit in the design, ability assures printed circuit to the greastest extent board dependability. CNC Milling CNC Machining