PCB Design Software

All general discussions regarding PCB design should go here

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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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China's PCB industry has entered an era of stable development

Postby liuliying » Mon Mar 25, 2019 5:59 am

PCB is the support and electric connector of electronic components. The output value of PCB industry across the globe accounts for over one quarter in that of the electronic components, with the industry scale amounting to US$ 60 billion. Due to huge domestic demand in China, coupled with the advantages of low labor cost and comprehensive associated industries, the production capacity of PCB around the world has begun to shift to China since 2000 and China has surpassed Japan and become the largest PCB manufacturer across the globe since 2006.
The current development state of PCB industry seen from the top one hundred list
Seen from the list of the top one hundred PCB enterprises, the past decade has seen a rapid development in PCB’ production capacity in Chinese mainland. As is seen from the sales, there were only 28 enterprises whose sales exceeded RBM 0.1 billion in 2001 according to the ranking list published for the first time in 2002. Starting from 2005, enterprises who could be enlisted into the ranking list amounted to 100. In the ranking list published in 2016 which was the 15th time, enterprises in the comprehensive PCB industry whose business revenue reached RMB 0.1 billion amounted to 131, 4.7 times compared with the one published for the time. In terms of business revenue, Zhending Technology whose comprehensive ranking was in the first place has reached RMB 16.819 billion, 13 times higher than Guangzhou Litian who ranked first in the ranking list published for the first time 15 years ago. In terms of regional development, the top one hundred PCB enterprises are mainly located in Shenzhen, Huizhou, Suzhou, Shanghai, Kunshan, Taiwan, HK, etc..
Domestic PCB products are making advancements from the low end to the high one.
Currently, China’s PCB industry has stepped into a period of stable development, with the major products being centered on middle and low end PCB products which have comparative cost advantages. According to the market data organized by China’s Commercial Industry Research Academy, in China, the market share of hard plate and composite plate is 13.0% and 3.7% respectively, the four-layer laminate, six-layer laminate, eight-layer laminate, and 16-layer laminate is 19.1%, 13.5% and 10.4% respectively while the IC support plate and laminate of over 18 layers (including 18-layer laminate) account for a smaller market share, being 2.7% and 1.2% respectively. The market share of HDI plate and flexible plate in China is 16.5% and 17.1% respectively. With the technology of China’s PCB industry being continuous improved, products with high technology and high added value, such as, HDI plate, package substrate, flexible plate have witnessed a continuous increase in sales. http://www.pcbindex.com/
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Drilling is very important in the production process of printed circuit board

Postby liuliying » Tue Apr 02, 2019 6:29 am

The copper foil lines between conductive patterns in different layers of circuit boards are conducted or connected by such holes, but the copper plated holes of component lead legs or other reinforcing materials can not be inserted. Printed circuit boards (PCBs) are formed by stacking many copper foil layers. Copper foil layers can not communicate with each other because each layer of copper foil is covered with an insulating layer, so they need to rely on via for signal link between them, so they have the title of Chinese through hole.
The through hole of circuit board must pass through the plug hole to meet the customer's demand. In changing the traditional plug hole technology of aluminium sheet, the surface welding and plug hole of circuit board are completed by white mesh, which makes the production more stable, the quality more reliable and the application more perfect. With the rapid development of the electronic industry, higher requirements have been put forward for the fabrication process and surface mounting technology of printed circuit boards (PCB).

The plug hole technology of the through hole came into being at the historic moment. At the same time, it should meet the following requirements:

Only copper is needed in the hole, and the welding resistance can be plugged or not.

There must be tin and lead in the hole, with a certain thickness requirement (4um), so as to avoid the solder resistance ink entering the hole, resulting in tin beads hidden in the hole.

Conduction holes must have soldering ink plug holes, no light transmission, no tin rings and beads, must be flat and other requirements.

Blind hole is the connection between the outermost circuit of printed circuit board (PCB) and the adjacent inner layer by electroplating hole. It is called Blind Pass because it can not see the opposite. In order to increase the utilization of space between circuit layers, blind holes are used. Blind hole is also a through hole to the surface of PCB. http://www.pcbindex.com/
Blind holes are located on the top and bottom surfaces of circuit boards and have a certain depth. They are used to connect the surface circuit with the underlying inner circuit. The depth of holes generally has a prescribed ratio (aperture). Special attention should be paid to this method of production. The drilling depth must be just right. If you do not pay attention to it, it will cause difficulties in electroplating in the hole. So very few factories use this method. In fact, it is also possible to drill holes in individual circuit layers and then bond them together, but more precise positioning and alignment devices are needed.

Buried hole is the connection between any circuit layers in the printed circuit board (PCB), but it is not connected with the outer layer, that is, there is no meaning of through hole extending to the surface of the circuit board.
This production process can not be achieved by bonding circuit boards and then drilling. Drilling operations must be carried out at the time of individual circuit layers, first local bonding, then plating, and finally all bonding. Because the operation process is more laborious than the original through hole and blind hole, the price is also the most expensive. This process is usually used only for high-density circuit boards, increasing the space utilization of other circuit layers.

In the production process of printed circuit board (PCB), drilling is very important. A simple understanding of drilling is to drill the required holes in the copper clad laminate, with the function of providing electrical connections and fixing devices. If improper operation results in problems in the process of hole passing, the device can not be fixed on the circuit board, which will affect the use of the circuit board slightly, and the whole board will be scrapped heavily. Therefore, the drilling process is very important.
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Re: PCB Design Software

Postby pcbindex1 » Wed Apr 03, 2019 5:20 am

Before routing, you should make an analysis of the design and carefully set the tools and software, which will make the design meet standards more.

1. To determine the number of PCB layers

The size and number of routing layers of PCB should be determined in the preliminary stage of designing. The number of routing layers and ways of stack-up will directly influence routing and resistance of the printed wiring. Determining the size of the board will be beneficial to confirming the ways of stacking up so as to achieve the desired designing effect. At the current stage, the cost differences between different multi-layer boards. When designing, many circuit layers must be adopted and make the coating copper evenly spread.

2. The rules and limits of layout

To complete routing smoothly, routing tools need to operate in the correct rules and limited conditions. Each signal line should be classified in the order of priority based on specific requirements. The higher the level is; the stricter the rules are. The rules involve the width of printing wires, the maximum number of holes, depth of parallelism, interaction between the signal lines and limitations between different layers, which will have huge impact on the performance of routing tools.

3. Layout of the components:

In the process of optimizing assembling, the rule of DFM will limit the layout of the components. If the assembling department allows movement of components, circuits can be optimized to facilitate automatic routing. The rules and constraint conditions will also impact the design of distribution. Auto-routing tools can handle one signal at a time, however, the routing tools can handle routing like a designer through setting restraint conditions and layers of the routing signal.

For example, as for the layout of power lines:

1. In the layout of PCB, decoupling circuits of the power should be designed near the relevant circuits instead of the power part, or it will not only affect bypass, but also pulsating current will flow through the power circuits or ground circuits, leading to crosstalk.

2. As for direction of power inside the circuits, power supply should be from the final stage to the first stage and filter capacitor should be at the final stage.

3. As for some main current passages, if the current needs to be disconnected or measured in the process of adjusting or testing, there should be current gap in the printing wires in the layout.

Besides, regulated power supply should be installed separately on the printing boards. When power and circuits share the same printing boards, it should be avoided that regulated power supply and circuit components are mixed or power and circuits share the same ground wires, because this kind of routing will not only generate disturbance, also also makes it difficult to disconnect the load in maintenance. At that time, there is no other option but to cut part of the printing wires, which will damage the printing board.

But for the current stage, PCB Manufacturer surface treatment process hasn’t changed much and manufacturers seem to have a long way to go in pursuing the change, but it should be noted that a slow change in the long run will surely lead to tremendous changes. Under the circumstances of louder voice for environmental protection, PCB surface treatment technique will surely make great changes in the future.

The basic purpose of surface treatment is to ensure good weldability and electric performance. As copper tends to exists in the form of oxidizing materials in the nature, which is difficult to maintain in the state of the original copper, so copper needs special treatment. In the following assembling process, strong scaling powder needs to be used to remove the copper oxidizing material. Strong scaling powder is difficult to remove itself, therefore, it is seldom adopted in the industry.
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5G is expected to jumpstart exciting new capabilities in several markets including automotive

Postby liuliying » Wed Apr 10, 2019 3:26 am

5G is expected to jumpstart exciting new capabilities in several markets including automotive, mobile, and the IoT. The new wireless standard will provide orders of magnitude improvements in communication speed and latency, leaving systems companies to decide whether to process their data locally or in the cloud. The choice these companies make will, to a certain degree, determine semiconductor architecture decisions going forward, from processor and memory to power budgets and more. http://www.pcbindex.com/
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Re: PCB Design Software Reflections from Change in Line Width of PCB

Postby liuliying » Wed Apr 17, 2019 5:55 am

When performing PCB wiring, it often happens that when the alignment passes through a certain area, due to the limited wiring space in the area, finer lines have to be used. After passing through this area, the lines are restored to their original width. Changes in the width of the alignment cause impedance changes, so reflections occur and affect the signal. So in what circumstances can this impact be ignored, and in what circumstances must we consider its impact? Three factors are related to this effect: the size of the impedance change, the signal rise time, and the delay of the signal on the narrow line.
The size of the impedance change is discussed first. Many circuits are designed to reflect noise less than 5 % of the voltage swing(this is related to the noise budget on the signal). According to the coefficient of reflection formula: Hey =(Z2-Z1) /(Z2 + Z1) = <UNK> Z /(<UNK> Z +2 Z1) ≤ 5 %, the approximate rate of change of impedance can be calculated as: <UNK> Z/Z1 ≤ 10 %
As you may know, the typical indicator of impedance on a circuit board is + / -10 %, and that's why.
If the impedance change occurs only once, for example, after the line width changes from 8mil to 6mil, the 6mil width is maintained at all times. To meet the noise budget requirement that the signal reflection noise at the mutation does not exceed 5 % of the voltage swing, the impedance change must be less than 10 %. This is sometimes difficult to do. Take the microstrip line on the FR4 plate as an example. Let's calculate. If the line width is 8 mil, the thickness between the line and the reference plane is 4 mil, and the characteristic impedance is 46.5 ohms. After the line width changes to 6 mil, the characteristic impedance becomes 54.2 ohms, and the impedance change rate reaches 20 %. The range of reflection signals must be excessive. As for the effect on the signal, it is also related to the time delay of the signal rising time and the signal from the drive end to the reflection point. But at least it's a potential problem. Fortunately, the problem can be solved by impedance matching terminal connection. http://www.pcbindex.com/
If the impedance change twice, for example, after the line width changes from 8mil to 6mil, it will change back to 8mil after pulling out 2cm. Then the reflection will occur at the two ends of the 2cm long 6mil wide line, once the impedance becomes larger. Positive reflection occurs, and then the impedance becomes smaller and negative reflection occurs. If the interval between the two reflections is short enough, the two reflections may cancel each other out, thereby reducing the impact. Assuming the transmission signal is 1V, 0.2 V is reflected in the first positive reflection, 1.2 V continues to transmit forward, and -0.2 * 1.2 = 0.24 V is reflected back in the second reflection. Assuming that the 6mil line is extremely short in length and that the two reflections occur almost simultaneously, the total reflection voltage is only 0.04 V, which is less than 5 % of the noise budget requirement. Therefore, whether this reflection affects the signal, how much effect it has, is related to the delay at the impedance change and the signal rise time. Studies and experiments show that as long as the delay at the impedance change is less than 20 % of the signal rise time, the reflection signal will not cause problems. If the signal rises at 1 NS, the delay at the impedance change is less than 0.2 NS corresponding to 1.2 inches, and the reflection does not cause problems. That is to say, for this case, there is no problem with the length of the 6mil wide alignment as long as it is less than 3cm.
When the width of the PCB alignment changes, it is necessary to carefully analyze the actual situation and whether it affects it. There are three parameters to pay attention to: how large the impedance change, how long the signal rises, and how long the neck part of the line width changes. Make a rough estimate based on the above method and set aside a certain amount of margin. If possible, minimize the length of the neck.
It should be pointed out that in actual PCB processing, the parameters can not be as accurate as the theory. The theory can provide guidance for our design, but it can not copy the copy and can not be dogmatic. After all, this is a practical science. The estimated value should be revised according to the actual situation and applied to the design.

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