1.Company information Based in Shenzhen, UNIWELL circuits cO., lTD. in design, development, manufacture and sales of high precision double-sided & multilayer PCBs (Printed Circuit Board) focusing on quick turn, prototype, medium and large volumes, also could provide: - PCB Contract...Send Inquiry
Board Thickness: 1.6 mm
Surface treatment: immersion silver.
Material: FR4 TG170.
Min line width/line distance:8/10mil
Uniwell provides single side board, double layer board ,multilayer boar (up to 32 layer),single side flex board, double side flex board and multilayer flex board, rigid-flex board etc.
The fast quick turn of prototype without sacrificing quality is the biggest character.
Based in Shenzhen, Uniwell circuits cO., lTD. in design, development, manufacture and sales of high precision double-sided & multilayer PCBs (Printed Circuit Board) focusing on quick turn, prototype, medium and large volumes, also could provide:
- PCB contract manufacturing
- PCB assembly Services
- PCB design and sale
- Component procurement & material management
- Product design
- Fast PCB&PCBA prototyping
- Cable and wire assemblies
- Plastics and molds
- AOI,X-Ray testing, other function testing service
3.High quality PCB design should take care of the inventory.
Component layout is a basic premise for designing high-quality PCB diagrams.The requirements for component layout include installation, stress, heating, signal and aesthetics.
Component layout is a basic premise for designing high-quality PCB diagrams.
The requirements for component layout include installation, stress, heating, signal and aesthetics.
Refers to the specific application situations, in order to install circuit board smoothly into the chassis, shell, slot, not space interference, such as short circuit accident, and make the specified connectors in a specified position on the chassis or enclosure and put forward a series of basic requirements.I won't go into that.
The circuit board shall be able to withstand all kinds of external forces and vibration during installation and operation.Therefore, the circuit board should have reasonable shape, and the position of various holes (screw holes and special-shaped holes) on the board should be arranged reasonably.Generally, the distance between the hole and the plate is greater than the diameter of the hole.At the same time, it should also be noted that the weakest sections of the plates caused by the special-shaped holes should also have sufficient bending strength.The connector on the board directly "extends" the equipment housing, especially to ensure the reliability of long-term use.
In the case of high power and heating devices, in addition to ensuring the heat dissipation conditions, it should be placed in the proper position.Especially in the precision simulation system, it is necessary to pay special attention to the adverse effects of the temperature field generated by these devices on the fragile preamplifier circuit.In general, a large part of the power should be separated into a module, and some thermal isolation measures should be taken with the signal processing circuit.
Signal interference is the most important factor to be considered in PCB layout design.Several basic aspects are: weak signal circuit and strong signal circuit separation or even isolation;The ac part is separated from the dc part;The high frequency part is separated from the low frequency part;Notice the direction of the signal line;The arrangement of ground lines;Appropriate shielding, filtering and other measures.These are a lot of arguments that have been emphasized over and over again, not repeated here.
Not only should you consider the neat and orderly placement of the components, but also consider the graceful flow of the line.As the general layman sometimes emphasizes the former, it is necessary to evaluate the advantages and disadvantages of the circuit design. In order to image the product, the former should be given priority when the performance is not demanding.However, in the case of high performance, if you have to use a double panel, and the circuit board is enclosed within it, you should give priority to the beauty of the walking line.The next section will discuss the "aesthetics" of wiring.
The following is a detailed introduction to some of the less common anti-interference measures in the literature.Considering the practical application, especially in the product trial, a large number of double panels are still used, and the following contents are mainly for double panels.
Avoid right angles when you turn, and try to make a transition with a diagonal or arc.
The line should be orderly and orderly, and arranged in different categories, which can not only avoid the mutual interference of different signals, but also facilitate inspection and modification.For digital system, signal lines of the same camp (e.g., data line, address line) between don't have to worry about the problem of interference, but like to read, write, clock control signal, it should be cool, best protected land line.
Large floor (will be further discussed below), the ground wire (it should be "face") and try to keep a reasonable equal distance between signal lines, on the premise of prevent short circuit, leakage near as much as possible.
For weak current systems, ground and power lines should be as close as possible.
Use the system of the component of the table, the signal line is as full as possible.
There is a lot of discussion on the importance and layout principle of the ground line in the literature, but there is still a lack of detailed and accurate introduction to the ground line layout in the actual PCB.My experience is that, in order to improve the reliability of the system (rather than just making an experimental prototype), the ground line cannot be overemphasized, especially in weak signal processing.To this end, we must spare no effort to implement the principle of "large area spread".
When paving the ground, it must be grid - like, unless it is fragmented by other lines.The thermal performance and high frequency conductivity of the grid are much better than that of the whole ground.In the double panel wiring, sometimes it is necessary to separate the ground wire in order to walk the signal line, which is extremely unfavorable for maintaining low enough ground resistance.For this reason, a series of "smart" means must be adopted to ensure the "smooth" of the current.These techniques include:
A large number of surface mount components are used to eliminate the "original" space occupied by welding holes.
Make full use of positive space: the extensive use of surface-mount components of occasions, to try to make the signal lines go top, as far as possible to ground to the bottom "selfless", it also involves numerous finely tips, I have my book in one of PCB skills: exchange pin has a recruit, there are many similar spells, will continue to write.
Reasonable arrangement of signal lines, will board in critical areas, especially the "heart" (here is related to the whole plate ground communication) "to" to the ground, as long as the careful design, it still can do it.
Negative and positive cooperation: sometimes one side on the plate, ground is "desperate", can try to make the two sides of the wiring coordinate with each other at this moment, "I can't stay here has its own place for ye", in the opposite position corresponding to the empty out a piece of turf ground laid enough, again through the number, location, reasonable enough via (considering hole has larger resistance), through this?Quot;"The bridge" will be forcibly divided by the lines of the signal lines that have been crossed, but they are reluctant to be attached, and hope that the unified two sides of the Taiwan straits will be integrated into a sufficient electric conductivity.
The number of the wall of the dog: it is very difficult to get out of the place and not willing to the huge ground line to be cut off by a single signal line, let this signal injustice a bit, walk across the wiring.Sometimes, I am not content to just pull a bare wire, the signal precisely and need to go through a resistor, or other "long legs", I can perfectly justifiable to extend the pin of the device, the position of part-time jumper, both through the signal, and avoid the jumper this unseemly names: - (in most cases, of course, I can always make such a signal from the right place to avoid ground by the cross, the only need is observation and imagination.
At the very least, the path of the ground current should be reasonable, and the large current and the weak signal current must not advance side by side.Sometimes, choosing a reasonable path, a row of ground lines is worth an unreasonably configured group.
Finally, by the way, there is a famous saying: "you can trust your mother, but never trust your land."In a very weak signal processing occasions (below microvolt), even by hook or by crook ensures the consistent of ground potential, on the key points of ground potential difference still wants more than processed signal amplitude, at least in the same order of magnitude, even though the static potential right, instantaneous potential difference may still be very big.For such an occasion, the first principle is to make the circuit work as independent of the ground potential as possible.
2.3.Power line layout and power filtering.
I don't agree with the general literature that the power line should be as thick as possible.Only in high power (1 seconds on average power supply current may reach 1 a), must ensure enough power cord width (my experience, 50 mil per 1 a current corresponding to meet the needs of most cases).The width of the power cord is not the key if only to prevent interference from the signal.Even, sometimes the finer power lines are better!The quality of the power supply is generally not in its absolute value, but in the fluctuation of power supply and the interference of superposition.The key to power interference is filter capacitance!If your application does have stringent requirements for power quality, don't skimp on the filter capacitor!When using the filter capacitance, note the following:
The whole circuit of the power input end there should be a "total" filtering measures, and various types of capacitors should match each other, "the same can't be little, at least not bad J for digital system should have at least 100 + 10 uF uF electrolytic tantalum + uF + 1 nf SMT patch 0.1.High frequency (100kHz)100uF electrolysis +10uF chip tantalum +0.47uF patch + 0.1uf patch.Ac simulation system: for dc and low-frequency analog systems: 1000uF|1000uF electrolysis +10uF tantalum +1uF patch +0.1uF patch.
There should be a "set" of filter capacitors around each important chip.For digital systems, a 0.1 uF patch is enough, general important or working current and larger chip should also be on a 10 uF chip tantalum or 1 uF patch, the highest working frequency chips (CPU, crystals) and 10 nf | 470 pf or a 1 nf.The capacitance should be as close as possible to the chip's power pin and as direct as possible, the smaller the closer.
For the chip filter capacitance, the inside (filter capacitance to the chip power tube foot) should be as thick as possible, preferably with multiple fine lines.Supplied with the filter capacitor is low (ac) impedance voltage source and suppress exchange coupling interference, outside condenser tube feet (from the main power to filter capacitance of a) the power cord is not so important, don't be too thick line width, at least to take up a lot of plate area.In some simulation systems, the power input is also required to use the RC filter network to further suppress the interference, while the smaller power line sometimes happens to have the effect of the resistor in the RC filter, which is beneficial.
For a system with a wide range of operating temperature, it is important to note that the aluminum electrolytic capacitor can reduce or even lose the filtering effect at low temperature, and the appropriate tantalum capacitors should be used instead.For example, use 100uF tantalum |1000uF aluminum instead of 470uF aluminum, or replace 100uF aluminum with 22uF chip tantalum.
Note that aluminum electrolytic capacitors should not be too close to high-power heating devices.
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