How to design a PCB( Printed Circuit Board ) ?

WDF-FPC-M-37,4 layer,wonderfulpcb.com

Initially PCBs were designed manually by creating a photomask on a clear mylar sheet, usually at two or four times the true size. Starting from the schematic diagram the component pin pads were laid out on the mylar and then traces were routed to connect the pads. Rub-on dry transfers of common component footprints increased efficiency. Traces were made with self-adhesive tape. Pre-printed non-reproducing grids on the mylar assisted in layout. To fabricate the board, the finished photomask was photolithographically reproduced onto a photoresist coated on the blank copper-clad boards.

Nowadays PCBs are designed with dedicated layout software, generally in the following steps:

1.Schematic capture through an electronic design automation (EDA) tool.

2.Card dimensions and template are decided based on required circuitry and case of the PCB.

3.The positions of the components and heat sinks are determined.

4.Layer stack of the PCB is decided, with one to tens of layers depending on complexity. Ground and power planes are decided. A power plane is the counterpart to a ground plane and behaves as an AC signal ground while providing DC power to the circuits mounted on the PCB. Signal interconnections are traced on signal planes. Signal planes can be on the outer as well as inner layers. For optimal EMI performance high frequency signals are routed in internal layers between power or ground planes.

5.Line impedance is determined using dielectric layer thickness, routing copper thickness and trace-width. Trace separation is also taken into account in case of differential signals. Microstrip, stripline or dual stripline can be used to route signals.

6.Components are placed. Thermal considerations and geometry are taken into account. Vias and lands are marked.

7.Signal traces are routed. Electronic design automation tools usually create clearances and connections in power and ground planes automatically.

8.Gerber files are generated for manufacturing.

For further detailes, please contact wonderful09@wonderfulpcb.com.

Concept to PCB copy

1、Precision of PCB material copy
To copy board accuracy problem, depends on two links, one is the accuracy of software, one is the original image accuracy, for precision of software using 32-bit precision floating-point representation can say there is no limit, so the main depends on the original scanning image accuracy, for example, if with pictures of 1 million pixels making can wash 5 inch photos, but if you want to wash it into 20 inches of photographs that simply can't see clearly, is the same reason, so for a high precision circuit board, to take out very high precision PCB diagram, be about to choose when scanning high DPI.
  
The significance of DPI is how many points per inch.That is scanned by the distance between every two points on the image is 1000 / DPI, unit mil.

If is 400 DPI, then the distance between two points on image is 1000/400 = 2.5 mil, that is to say at this time the accuracy is 2.5 mil.   
This is the basis of the most scientific, so someone said that the precision can reach 1 mil, it is a prerequisite.Actually copy plate precision mainly depends on the original scan precision.

To sum up, when scanning the board set DPI is based on the actual boards on the required accuracy, if the accuracy requirement, such as mobile phone board spacing under 1 mil, then you need to scan DPI should be set in more than 1000 DPI.Currently on the market the scanner can satisfy this condition.

The higher the DPI, and clear images, the accuracy is higher, but the disadvantage is that the picture is too big, higher requirements for hardware, so according to particular case is particular Settings.400 dpi commonly used for the average accuracy of the board is very good, such as mobile phone board can be set in more than 1000 dpi.   

2、PCB copy board type
Some proposed can copy the board that in a moment, it sounds more dangerous, in fact as long as copy board software can open and save PROTEL PCB file directly, all placed element attribute fully supports the PROTEL format, including placement, can take out any type of boards.
  
3、PCB copy board software selection  
Copy board software quality mainly depends on the function is complete, it is best to copy all work on board in the software to do it, so efficiency is high, including the placement of components for best support PROTEL99SE, currently 99 se components library is very rich, can be downloaded to the Internet.This is also a key thing, depend on the era of handmade element is in the past, as many as there are as many as hundreds of BGP components encapsulation of elements, by hand and then to build components cost too much.To design a circuit to circuit is stable and reliable, usually copper mass and power or ground connection, which can reduce the noise and interference circuit.So involve the issue of network spread of copper, for complex circuit board, copper above there are a lot of the shop is to connect also has many is isolated, so bad if solve this problem, the shop copper will not be able to realize, so it must define the network to spread copper (" connected to the same network, different network isolation "), simply fill in all the copper sheet that is the end of the road.This is also a key problem of measuring copy board software.  

4、The grinding plate
For sandwich plate, the middle layer is not directly scanning, to copy the sandwich plate must be grinding layers, so copy profes sional bound to scrap a board.  

Current methods is the best way to use good grinding machine and manual grinding with yarn paper, using the latter method is one of the lowest cost method, sand paper is everywhere on the market can buy ordinary sandpaper, remember to sandpaper, grinding fine sand paper is difficult to move.      

Method is simple, the board according to the level of good use sand paper to grind hard, if there is a large piece of copper available forceps can pull off directly, or use flat fell a few times of grinding hard grind, then use sand paper to grind material.

Grinding plate isn't any technical content, are purely empirical, grinding a piece of sandwich plate.