Sierra Circuits | Printed Circuit Board (PCB) Manufacturing & Assembly

Better DFM: Technical details, Hints and Do's and Don'ts

Currently we support the upload of 274X Gerber files. All Gerber files will have a Magnifying Glass next to them. If you do not see a Magnifying glass on any of your layers, this means that none of your files are in a valid 274X Gerber format.
You can Click on the Magnifying Glass icon to view the Gerber files (at this time, features like thermals and special apertures will not be displayed). You can also click on the file name to display the contents.

Once you upload your zip file you will be presented with a view showing it's contents. Each file will be represented on a row. The following describes the items of interest for each layer...

File Type:
Set the "File Type" field from the pull down list provided for any layers that are to be analyzed. Only the files that have the Magnifying Glass need to be set; all other layers except for the Excellon Drill files should be left as "Not Set". Any artwork layers that are not copper, solder mask, silk screen, or drill (ie. Fab Drawings and Solder Paste layers) should be set as "Drawing/Other".

Data Polarity:
Set the polarity for the copper artwork layers. Typically, the polarity is positive for all layers.

IMPORTANT NOTE ABOUT Soldermask Polarity: It is important that you understand that the polarity of Soldermask is almost always POSITIVE from a manufacturing perspective. There is some confusion in the industry about this because during design stage and in many design software these may be referred to as negative, but from a PCB manufacturing perspective, these are called positive.

Here is how you can understand how PCB manufacturers interpret polarity in a soldermask:
If your soldermask data represents the "absence of soldermask" then the data is in POSITIVE polarity.
In other words: if your data shows the places which you WANT TO SOLDER, then your soldermask layer is in POSITIVE format.

So when you are in the layer assignment screen on our website, it is most likely that soldermask should be assigned as positive polarity.

COPPER LAYERS: generally copper layers are also positive. But please note that in some copper layers the polarity may be negative, particularly if the copper layer is a plane layer.

The most common example of setting a negative polarity is when you have negative plane layers.

A negative plane layer can be identified when the data is made up of thermals, anti-pads, splits, etc. In this case the actual copper is the absence of data. These are negative planes. Correspondingly, a positive plane is when the actual copper is the data and the anti-pads, splits, thermals are the absence of data. A graphical example below will illustrate...


Negative plane shown above	Positive plane shown above

Layer Number:
Enter "Layer Number" field for Inner Copper layers only. You do not need to set this field for Outer and Non-Copper layers. The Layer Numbers entered will be used as the layer stack-up to manufacture your boards.
Drill Information Page:
Please note that on the DRIL INFO page the finished hole sizes must be specified in Mils (NOT in inches) Also be careful to identify which holes are plated and which ones are non-plated.
Drill File Examples:
################################
Example 1
################################
M48
R,T
VER,1
FMAT,2
INCH,TZ
TCST,OFF
ICI,OFF
ATC,ON
T1C0.0350
T2C0.0550
T3C0.0650
T4C0.1300
%
M47,OrCAD PCB Drill V2.01
M47,Holes between Component Layer and Solder Layer
G05
T1
X002595Y000895
X003057Y000897
X003860Y003810
X003905Y004495
X004395Y007910
X005500Y019500
X005500Y030000
X005650Y005260
X005920Y004340
T2
X013350Y038500
################################
Example 2
################################

%
T1C0.0350F200S100
X002595Y000895
X003057Y000897
X003860Y003810
X003905Y004495
X004395Y007910
X005500Y019500
X005500Y030000
X005650Y005260
X005920Y004340
T2C0.0550F200S100
X013350Y038500

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