| Gerber format
What does it mean, why is it important for us to carry all the information and why you need as engineer to know at least the basics?
Since several decades, several engineer and developer work together, where work is concerned, it allows me in this presentation to discuse the theme only limited.
The photoplotter, as its name suggests, is no more than a plotter, plotter that uses light to write.
To the plotters have to say:
- How to use tool,
- When and when not to use the tool,
- Where to go next,
- When time and go straight or along the arc
2.1 Vector plotters:
It is no longer used plotter type, except the currently used laser-plotters. This are vectors and Gerber plotter hybrids. The laser plotters due to the current market leader Barco Graphics takes the lead new format, which is called DPF format. It can not be the subject of the presentation, but if desired, we can talk about it.
2.2 Gerber plotters:
Optical, fusing discs using plotters. In plotters fixed light source is used for the design development, thereby creating the final circuit design of the printed circuit board.
Let see, how works a Gerber plotter:
As you can see, the fixed light source reaches the surface of the film through optics and a single disc to reach the needed later forms.
- The aperture wheel include 24-70 different cut-outs, apertures. Above this required number of aperture the plotters contains automatically switched multiple wheels.
- The plotter moves the film below the fixed lens on the XY table.
Let's see the realization of the design:
As shown in the table is tilted, the use of different control codes to the plotter creates the design on the film according to the program.
- The table thus moving the film does not require a separate hearing in my opinion, because everyone knows the possibilities of the XY movement. However, you may note that in this case, a high-precision stepping motor controller is involved.
- The control codes, but only limited will be discussed in the chapter 4.
Let's see a summary of the most commonly used aperture types:
Until what is full-filled circular aperture.
Their shape depends on the parts you have to solder, depend on the occupied layer. In this case, I deliberately distinguish between components and layers. The cause, see below.
Unique, fusing, hard on the disk realizable forms.
This aperture type mainly for drawing and through-hole components, develop test points used.
Pads to accommodate surface-mount and through-hole components.
- Name for the same page sizes SQUARE
- Name for different sizes RECTANGLE
These apertures are truly multi-user, multi-user function.
- Fix traditional PTH or, less frequently, surface mount SMT components.
- With its shape, naturally without holes, can serve as test targets.
I will discuss only one from the Special apertures, the thermal pads.
This is a multilayer pad, used for the electrical connection of the inner layers of multilayer circuits. The connecting bridge is to minimize the thermal load of soldering.
Drew, polygon apertures:
The implementation of these apertures projected onto the disc would be difficult or the aperture is so unique that it would be uneconomical therefore then separately, later don’t useddiscs to create.
In this case, with use of existing apertures let to draw the bench, was necessary.
A drawing done by one or more apertures, depending on the desired contour.
It should be noted that the use of CAD systems such as Eagle, PCAD, OrCAD, etc.. can be used in real aperture only when these apertures the designer predefinedforward to the system.
In the absence of it a system can an already simple apertures replace with a default aperture drawn.
This fact makes it difficult to manufacture the case of the empty DRC control circuit, respectively. our case, we need to create an offer inspection.
In this case, prior to the check drawn on the apertures must be changed in real apertures!
The Gerber code, it differs from the traditional NC codes, that contains codes for selection of tool too.
The organization of the data in blocks. These blocks include the following:
- Tool selection
- EOB characters that follow a combination of the foregoing.
Codes D, G, H, X, Y, I, or J codes, followed by a numerical value.
So let's properly report merely lists the codes:
* – EOB characters, closing statements. In some systems, this code is '$'
D – Aperture selection and selecting use of aperture
X – X movement
Y – Y movement
G – Setup, setup codes
M – Control codes
I – Arc center relative position of X
J – Arc center relative position of Y
The Gerber files as well as the NC programs carry the key information that indicates the format. As the format of the structure of the information shown in the following image.
The meaning of each of the codes are listed below.
L - leading zero suppression
T - trailing zero suppression
D - without zero suppression
A - absolute coordinates
I - incremental coordinates
Nn - sequence, where n is the number digits (rarely used)
Gg - preparatory function code (rarely used)
Xa - input data size (up to 5.5)
Yb - input data format
Zb - input data format (Z rarely or never used)
Dn - drawing code
Mn - mixed code
In the past the operator have to observed the film polarity, these days special instructions given the plotters for it.
Let see, how it looks like:
%IPPOS*% - positive (left) %IPNEG*% - negative (right)
command appear as follows: command appear as follows:
The utilities have been designed to visualize by CAD designed and Gerber format converted files.
Instead of the PCGERBER I suggest the free GC-Prevue program.
This program with its capability can everything that we need, but because of the amount of knowledge we need another training.
As the basis of the foregoing, I think it turned out a part of the Gerber format we use can greatly more. Basically mainly used the capabilities of the blank PCB manufacturing firms.