How to Properly Copy a PCB During Board fabrication
Copying a PCB during board fabrication and copying a pcb during stencil creation are two different concepts,requiring different copying types and software.I previously briefly introduced copying for PCB stencil creation.Today,I’ll explain how to copy a PCB during SMT board fabrication.
1.PCB Copy Accuracy
The accuracy of a PCB copy depends on two factors:software accuracy and the accuracy of the original image.For software accuracy,using 32-bit floating-point representation offers virtually no accuracy limitations.Therefore,the accuracy of the original scanned image is paramount.For example,a 1-megapixel image can be printed out as a 5-inch image,but a 20-inch image would be completely unreadable.The principle is the same.Therefore,for circuit boards requiring very high precision,a higher DPI(dpi)is essential when scanning to achieve a highly accurate copy.
DPI stands for dots per inch.This means the distance between each two points on the scanned image is 1000/DPI,measured in mils.
If the DPI is 400,then the distance between two points on the image is 1000/400=2.5mils,meaning the accuracy is 2.5mils.
This is the most scientific basis.So,while some claim accuracy can be below 1mil,that’s a premise.PCB copy accuracy primarily depends on the original scanning accuracy.
In summary,the DPI setting when scanning a board should be determined based on the required accuracy.However,the disadvantage is that the image is larger and the hardware requirements are higher,so the setting should be tailored to the specific situation.For boards of average accuracy,400 DPI is generally sufficient.For mobile phone board,1000 DPI or higher is recommended.
2.PCB copy Type
Some are suggesting that you can copy any type of board,which sounds far-fetched.In reality,as long as the PCB copying software can directly open and save PROTEL PCB files,and all placed element properties fully support the PROTEL format,including placement functionality,it can copy any type of board.
3.Choosing PCB copying Software
the quality of PCB copying software depends primarily on its comprehensive functionality.It’s best to perform all work within the software for maximum efficiency.Support for component placement,including PROTEL 99SE,is particularly good.99SE currently has a very extensive component library that can be downloaded online,This is crucial.The days of manually creating components are over,as many BGP component creation prohibitively expensive.
For circuit stability and reliability,circuit design generally requires large copper areas and power or ground connections to reduce noise and interference.This involves the issue of network copper placement,For complex PCBs,many copper layers need to be connected and many need to be isolated.If this issue isn’t addressed properly,copper placement won’t be possible.Therefore,it’s crucial to define networks for copper placement(connect the same network,isolate different networks”).Simply filling everything with copper will result in disconnected circuits.This is also a key consideration when evaluating PCB copying software.
4.Board Grinding
For multi-layer PCBs,the middle layers can’t be directly scanned.Copying a multi-layer PCB requires grinding out the layers,which inevitably results in a scrapped board.
Currently ,the best methods are using a good grinder and manually grinding with gauze paper.The latter is the least expensive.Sandpaper can be purchased from any common store.Remember to use coarse sandpaper;fine sandpaper is difficult to remove.
The method is simple:level the board and sand firmly with sandpaper.Large clumps of copper can be removed with pilers,or hard-to-grind areas can be removed with a flat file.Then, continue grrinding with sandpaper.
In fact,grinding the board does not require any technical content.It is purely an experience based thing.You will understand it by grinding a multi-layer PCB board.