PCB Design Software

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PCB Design Software

Postby tutu10 » Fri Mar 08, 2019 9:01 am

Any recommendations?

Small simple and free (is always nice) or reasonably priced.

I'm a complete idiot on this stuff so am trying to learn... many thanks.
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Re: PCB Design Software

Postby Ramon » Fri Mar 08, 2019 11:04 am

A free solution, for smaller project is Autodesk Eagle: https://www.autodesk.com/products/eagle/free-download
For hobbyists and students there is a free version. Limits are the size of board and schematics and the fact that only 2-sided boards can be engineered.
Keep calm and focus on soldering
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What problems should PCB copper cladding deal with?

Postby liuliying » Tue Mar 12, 2019 2:55 am

Copper cladding refers to the use of idle space on PCB as a reference level and then filled with solid copper, which is also known as copper filling. The significance of copper cladding lies in reducing ground wire impedance and improving anti-interference ability, reducing voltage drop and improving power supply efficiency, and connecting with ground wire to reduce Ring Road area. If there are more PCBs, such as SGND, AGND, GND, etc., how to clad copper? My approach is that according to the different position of PCB plate, the most important "ground" is used as the reference to clad copper independently, and the copper is separated digitally and analogically. At the same time, before copper cladding, the corresponding power supply wiring should be roughened first: V5.0V, V3.6V, V3.3V (SD card power supply), and so on. In this way, a number of polymorphic structures with different shapes are formed.
Copper cladding needs to deal with several problems: one is the single point connection in different places; the other is the copper cladding near crystal oscillator. The crystal oscillator in the circuit is a high frequency emitter. The method is to deposit copper around crystal oscillator, and then the shell of crystal oscillator is grounded separately. Thirdly, the problem of isolated islands (dead zones), if it feels very big, it will not take much to define a place through the hole to add.

In addition, large area copper cladding or grid copper cladding is good, it is not good to generalize. Why? Large area copper cladding, if the wave soldering, the board may be warped, or even foamed. From this point of view, the grid has better heat dissipation. Usually the high frequency circuit has a high requirement of multi-purpose grid against interference, and the low frequency circuit has a large current circuit and other commonly used complete copper paving.

In digital circuits, especially those with MCU, the function of copper coating is to reduce the impedance of the whole ground surface. More specifically, I generally operate in this way: each core module (also digital circuit) will be partitioned with copper when allowed, and then connected with each copper coating by wire. The purpose of this is also to reduce the impact between all levels of circuits.

For mixed circuits of digital and analog circuits, the independent routing of ground wires, and the final summation to the power filter capacitor, it is clear to all. However, there is one thing: the ground wire distribution in analog circuits can not be simply covered with a piece of copper, because the analog circuit pays much attention to the interaction between the front and back stages, and the analog ground also requires a single point of grounding, so whether the analog copper coating can be applied has to be handled according to the actual situation. http://www.pcbindex.com/
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Analysis of PCB Raw Materials

Postby liuliying » Sat Mar 16, 2019 5:23 am

From the perspective of PCB industry chain, the upstream is the raw material for PCB production, mainly including copper clad laminate, copper foil, copper ball, semi-curing sheet, gold salt, ink, dry film and other chemical materials; the middle is the PCB manufacturing industry; the downstream is the terminal application market.
First, look at the direct cost composition of PCB. PCB cost mainly includes material cost and manual manufacturing cost. Among them, material cost mainly includes copper clad laminate, accounting for about 30%; copper foil, accounting for about 9%; material cost mainly consists of copper clad laminate and copper foil; and manual manufacturing cost, accounting for about 40%.

For the upstream main raw materials of copper clad laminate, the cost composition of copper clad laminate is many. Copper foil, fiberglass cloth, resin and other manufacturing costs (including labor, warehousing logistics, equipment depreciation, hydroelectric coal, etc.) account for roughly 39%, 18%, 18% and 25% of the total cost respectively. Copper foil, fiberglass cloth and resin account for more than 70% of the three raw materials. The price of raw materials is the key factor affecting the cost of copper clad laminates.

So as can be seen from the above two figures, the main cost of PCB lies in the material cost, accounting for about 50% - 60% of the total. The cost of PCB mainly consists of copper clad laminate and copper foil. For copper clad laminate, the cost mainly lies in the material cost, which accounts for about 70% of the total, mainly copper foil, fiberglass cloth and resin.

The price increase and transmission logic of materials is basically that the price change of materials mainly consisting of copper foil, fiberglass cloth and resin upstream causes the cost change of copper clad laminates, and the cost change of copper clad laminates affects the cost change of PCB laminates downstream. Therefore, to study the cost of PCB and copper clad laminate, we need to focus on the price changes of upstream copper foil, fiberglass cloth and resin. http://www.pcbindex.com/
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Generally, in PCB design, there are several reasons for signal equal length processing

Postby liuliying » Wed Mar 20, 2019 5:20 am

Equivalent length is generally used to satisfy the system's equivalence to the signal group, that is, to satisfy the time sequence of the signals in the group, the system's requirements must be satisfied. For example, for DDR, the data signal is processed by +/-25mil in a group of 8 bits. If the equal length of the signal is not within this tolerance range, the difference of the signal line length is too large, which will lead to a longer relative delay, and ultimately the DDR running speed is not high.

But when we design, we sometimes find that the DDR device is not equal in length, and its products can also run normally without any impact. The reason is that the system software has delayed processing of the signal, and the software has done timing control. For the stripline, the corresponding line length per PS delay is about 6 mil, so the general signal group length is 6 mil, and the total delay is 1 PS. Generally, we do not need to control the length of the design too small, control to +/-10mil or so is very good. +/- 10 mil equal length and +/-1 mil equal length, the difference in time is not more than 4 ps, the general IC signal margin is not more than 4 ps, so it is not necessary to control too small when doing equal length, which leads to the difficulty of their own design routing.

Differential signal (Differential signal analysis can see our public number past articles) is equal in length to meet the phase, a pair of differential signals phase difference 180 degrees, if the length difference is too large, will lead to its phase offset.

Design Time Equal Length Processing Method for 03PCB

When designing, we first need to look at the data manual of the device, according to which we can get the signal of the same length and its range. For conventional signals, such as DDR, network ports, HDMI signals and so on, the design experience can be used for equal length.

Before making equal length, we should first find the longest signal line in the signal group which needs to be made equal length, and find ways to shorten it so as to shorten the length of all signal lines in this group and the length of other signal lines needed to winding.

When dealing with equal length, we should take into account the winding of signals with smaller space. We should first remove the nearby signals, and then process this part of the signal, so as not to make the winding space insufficient and equal length.

When the length is equal, the distance between the edges of the serpentine line should be kept 3W, that is, 3x line width. If the space is limited, at least 2W should be achieved.
For differential signals, the equal-length error is generally controlled at +/-5mil. The position around the equal-length is at the end of the length error and the waveform around it is wavelet.

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