PCB layout is the finest
techniques with the highest limitation in the design process. Even the wire
cloth engineers with over ten-year experience would feel poor in wiring. Having
faced all kinds of problems, he knows the result for each wiring, which makes
him have no idea on the wiring. But the master is still there. They have very rational
knowledge, but also with some feelings of self-creation to wiring, which makes
the wire have beautiful artistic sense.
Followings are some good tips
and points:
First of all, it comes to a basic introduction, PCB
layers can be divided into single, double and multi-layer. Single-layer is now
basically eliminated. Two-layer board with a lot of sound systems now was used
generally as a power amplifier board. Multi-layer refers to four layers and 4 layers
above the plate, in general 4-layer density components for less demanding It
will suffice. From the perspective of hole, it can be divided into the
through-hole, blind hole, and buried hole. Through-hole is a hole is straight
from the top to the bottom through; the blind hole is worn from the top or
bottom of the hole to the middle layer, then do not continue to wear, this
advantage is not the position of the through-hole from the beginning to the end
of the block, other layers in the upper position of the hole can still trace;
buried hole. Buried hole is the middle layer to the middle layer, which was
buried and the surface is completely invisible. FIG details are as follows
Before automatic wiring, interactive requirements in
advance with relatively high for wiring, input and output terminals of adjacent
edges should be parallel, which can avoid reflection interference. When
necessary, plus ground isolation is needed and the wiring of two adjacent layers
are perpendicular to each other, because the parallel more prone to parasitic
coupling. Automatic routing depends on good layout, can be pre-set routing
rules, such as the number of tracks, the number of holes, step number and so
bent. Generally the first to explore cabling, rapid short-term connectivity,
and through the labyrinth wiring, the wiring should be global routing fabric
path optimization, it can disconnect the line has cloth as needed and try to
re-wiring, thereby improving the overall effect of the wiring.
For the layout, it is a principle of separate digital and
analog possible to make a principle is not slow and fast approaching. The basic
principle is to separate digital ground and analog ground, digital ground as
are the switching device, the current in the switch of the moment are great, do
not move when they very small, so the digital ground and analog ground can not
be mixed together. A recommended layout can be as shown below.
1 Notices on Wiring between power supply and ground
(1)It must add decoupling capacitors between power supply
and ground. Be sure to power through again after decoupling capacitors
connected to the chip's pins in the figure below lists the wrong connection of
several laws and a proper connection method, we refer to the following facing.
Have you ever made such kind of mistake? Decoupling capacitors in general has
two functions, one is to provide instant high-current chips, the second is to
remove the power supply noise, on the one hand is to make the power supply to
minimize noise impact chips, on the other hand is the noise generated by the
chip will not affect the power supply.
(2)Try to widen the power supply and the ground, which is
better than the power ground line width. The relationship is: Ground> power
cables> Signal line
(3)
You can use a large area of copper layer as the ground
and put in place on the PCB where is not used to connect the ground, for ground use, or made of multi-layer,
power, ground floor of the occupation.
2 Solutions tomixed digital circuits and analog circuits ?
Now, many of PCB circuit is no longer a single function,
but rather by the digital and analog circuits mixed composition, so when the
wiring on the need to consider mutual interference between them, especially to
line noise.
Due to the high frequency digital circuits, analog
circuits strong sensitivity of the signal line, the high-frequency signal lines
should be as far as possible away from the sensitive analog circuit devices,
but it is for the entire PCB, PCB ground node only to the outside world, and it
is necessary to issue the PCB internal processing resolution digital circuits
and analog circuits common ground, but in an internal circuit board, and analog
circuits to digital circuits are physically separate, but connected with the
outside world in PCB the interface (such as plugs, etc.). And analog circuits
to a digital circuit is a little short, please note that only one connection
point, and there are no common ground on the PCB, which is determined by the
system design.
3 Dealing with line corner
Typically there will be at the corner of the line
thickness changes, but when the diameter line thickness changes, will be some
reflection of the phenomenon. Corner the way for changes in the thickness of
the line, at right angles to the worst, 45-degree angle is better, the fillet
is the best. But rounded on the PCB design in terms of handling more trouble,
it is generally look at the sensitivity of the signal, and generally the signal
can be a 45-degree angle, and only those who are very sensitive to the line
only need to use the fillet.
4 Checking design rules after wiring
Whatever you do, after the completion of every
inspection, just like when we test if there is time remaining to be our answer
to be checked, which is an important way for us to get a high score, as we draw
PCB board, too. So that we can be more sure that we draw out the circuit board
is qualified products. We generally check the following aspects:
(1) Between the lines, the line and the
component pad, wire and through hole component pads and the through-hole,
through-hole and through hole , are their distances reasonable and meet
production requirements?
(2)Is the width
between power line and ground appropriate? If it is tightly coupled (low
impedance) between the power supply and ground, whether there can make the PCB
ground widened place.
(3)Have you taken
the best practices for critical signal cable, such as the length of the
shortest line added protection, input lines and output lines are clearly
separated.
(4)For analog and digital circuit, is there separate ground
wire.
(5)whether the PCB
after adding the pattern (as shown, graphing) may cause short-circuit signal.
(6)Modification to some unfavorable linear
(7)Whether the PCB plus a processing line, solder meets the
requirements of the production process, solder size is appropriate, the
character flag is pressure pads on the device, so as not to affect the quality
of electrical equipment.
(8)For the multilayer, the frame edge of power formation is
reduced, such as power strata exposed copper-board likely to cause a short
circuit.
In short, the above techniques and methods are essentials from experience, it
is worth learning from the drawing board when the PCB, PCB diagram in painting
process in addition to proficiency drawing tools, but also have a solid
theoretical knowledge and extensive practical experience, which can help you
quickly and efficiently complete your PCB Fig. But there is very important that
must be careful, whether it is the wiring or the overall layout very carefully
every step seriously, because of a small mistake you may cause your final
product becomes waste, and also look for not what went wrong, so we'd rather
spend more time drawing process of careful checking the details of a problem
are reluctant to go back to check, so it may take more time. In short, the
process of drawing, we should pay attention to the details of PCB.
Attn: If you need pcb design, pcb manufacture, pcb assembly service, plz feel free to contact me. Email: contact@hampoo.com. Website:http://ems.hampoo.com
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