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7 Common Mistakes Made with Gerber Files, and How to Avoid CAM Hold

The most effective way to avoid having your order go on CAM hold is to take advantage of FreeDFM.com. You will get the following benefits:

  • Free PCB design file check for manufacturability
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  • You get a graphical report, delivered in minutes, showing any potential issues with detail as to their nature and location
  • Reduces possibility of CAM Hold issues after order placement
  • Enables 48% faster total thru-put from order placement to shipment
  • Also provides a price quote with your choice of turntimes

Creating Gerber files that accurately reflect what you want manufactured is a challenge no matter how long you have been a PCB designer. However, by learning from others and avoiding the most common mistakes, you can speed up the turnaround time, reduce the chance of orders placed on hold, and complete your projects faster. The following list reviews the top seven most common mistakes made with Gerber files and how you can avoid them.

1. Missing Aperture List

Your Gerber files specify what to do and where. Your aperture list specifies what tool to use. A single comprehensive aperture list for all layers should be sent with your gerber files, rather than a separate aperture list for each layer. Please note: An aperture list does not need to be sent with 274X format files. If you send 274D format, we use your aperture list in combination with your gerber files to create your artwork.

Requirements: One comprehensive aperture list for all layers, English Units. Please do not modify the aperture list your software outputs. An aperture list does not need to be sent with 274X format files.

Resolution: All layout packages which output 274D also output an aperture list. Common extensions include .rep, .apt, and .apr. If you have difficulty outputting an aperture list, please send 274X format.

2. Missing Excellon Drill File

Excellon drill files are used to determine what size holes to drill and where. Plated and non-plated holes need to be included in one drill file, with plated and non-plated holes having different tool numbers.

Requirements: Excellon Format, ASCII Odd/ None, 2.4 Trailing Zero Suppression, English Units, No Step and Repeats.

Resolution: Nearly all layout packages will output an Excellon drill file. If you cannot generate one, we can in most cases create one from your fabrication drawing for an engineering fee.

3. Missing Tool List

A tool list is used in combination with your Excellon drill file to create your drill. Your drill file specifies where to place the holes. Your tool list specifies what tool to use. A tool list should be embedded in your Excellon drill file or sent as a separate text file. Using a tool list provided on a fabrication drawing is not preferable, as it eliminates many of the automatic verifications and makes data entry errors far more likely.

Requirements: Tool list embedded in Excellon drill file or sent as a separate text file.

Resolution: If your layout software will output an Excellon drill file, it will also output a tool list. Common extensions include .tol and .rep.

4. Missing Gerber Files

Believe it or not, many times people submit orders and forget to attach their Gerber files.

Requirements: Gerber 274X or 274D, English units are preferable.

Resolution: ODB++ files are acceptable; however, these files should be sent to This email address is being protected from spambots. You need JavaScript enabled to view it.. It is possible to convert many other file formats to Gerber. Please send your non-Gerber formats to This email address is being protected from spambots. You need JavaScript enabled to view it..

5. Insufficient Annular Ring

An annular ring is the donut ("annulus") created when your drill pierces a copper layer. It is defined as the radius of this donut. For example, a .030" pad with an .020" hole would have a .005" annular ring. This is required to allow for complete plating on vias, as well as solderability on component holes. Many times people do not allow for the proper annular ring requirements.

Requirements: A minimum of .005" annular ring for vias or a minimum of .007" for component holes is required for manufacturing.

Resolution: All layout packages provide this as a DFM check. Setting sufficient annular ring in your layout software is the preferred method in order to maintain proper copper spacing.

6. Insufficient Copper Trace Width/Spacing

Copper spacing is the minimum air gap between any two adjacent copper features. Trace width is the minimum width of a copper feature, usually traces.

Requirements: A minimum of .005" trace width/spacing is necessary. A premium is charged for trace width/spacing less than .007".

Resolution: All layout packages provide this as a DFM check. Setting sufficient trace width/ spacing in your layout software is the preferred method. Trace width and spacing push and pull against one another, so changing a problem area may require rerouting traces, adding vias, or moving components.

7. Insufficient Inner Clearances

Inner clearance is the minimum distance from the edge of a hole to any adjacent, unconnected, inner layer copper. Sufficient inner clearances help ensure that your drill does not cause shorts to your inner copper layers. This is important for both plated and non-plated holes, as non-plated holes may either cut into an adjacent trace or cause shorts during assembly.

Requirements: A minimum of .010" inner clearance is required and .015" is preferred.

Resolution: Most inner clearance issues can be resolved if negative image inners are provided, but it is preferred to not modify these. Setting these clearances in your layout software is the preferred method, as this will maintain intended connectivity. While most layout packages provide this as a DFM check, not all do. Those that do not can usually be manipulated to check for this violation by setting spacing and annular ring higher.

General guidelines: Spacing + Annular ring = Inner clearance. Another trick that can help resolve problem areas is to move the affected traces to outer copper layers, where this is not an issue.

020 Finished Thickness

The stackups pictured are our "typical" stackups for the layer count and finished thicknesses noted.  However, these stackups are not "Guaranteed" unless you so specify in your files used when placing your order.  Additionally, for these or any specific stackup that you require, be sure to order as "Custom" and select "Controlled Dielectric."

Rigid-PCBs-1

Advanced Circuits builds Single-Sided through 10 layer prototype and production circuit boards.  The stackups pictured are our "typical" stackups for the layer count and finished thicknesses noted.  However, these stackups are not "Guaranteed" unless you so specify in your files used when placing your order.  Additionally, for these or any specific stackup that you require, be sure to order as "Custom" and select "Controlled Dielectric".  We process four layer boards with final thickness of 0.020", 0.031", 0.040", 0.047", 0.062", 0.093" and 0.125". You may select ½, 1 or 2 ounce inner layer copper foil for your board.

While our 4, 6, and 8 layer boards are limited to 16X22 inches the 10 layer maximum size is 14x20.

We have several inner layer cores available using Isola's FR406 materials - they include 5, 8, 10, 14, 18, 21, 28, 35, 39, 59 and 93 mil cores.

-Six layer boards are produced in thickness of 0.031", 0.040", 0.047", 0.062", 0.093" and 0.125" with the same inner layer foil options.

-Both our eight and ten layer boards are available in finished thickness of 0.062", 0.093" and 0.125".

Advanced Circuits can supply you with a RoHS compliant multi-layer board using laminate materials that can be matched up with the exposure to high temperatures during your assembly processes. It is important to keep in mind that some lead free assembly processes will require the laminate base material to withstand temperatures in excess of 260 degrees C or 500 degrees F for extended periods of time. To resolve this, we have high temperature laminates in our inventory so that our customers will be able to meet the higher temperature cycling requirements of some lead free assembly applications.

In high temperature materials we currently stock Isola's 370HR in cores of 5, 8, 10, 14, 21, 28, 39, 59, 93 and 125 mils. Advanced Circuits has UL approval for processing high thermal capacity materials manufactured by Isola and Nelco among others in producing your multi-layer board. These materials met the UL testing for 130°C maximum operating temperature, solder limits of 288°C for 20 seconds, 94-V0 flame rating and direct support of current carrying parts. Each of these laminate systems meets the minimum requirements of IPC 4101B. Individual manufacturer's material types may exhibit variations in electrical, thermal and physical properties. Normally a single manufacturer's material will be stocked for use. If you have specific questions please contact your Advanced Circuits sales representative.

PCB Tolerances

Inner Layer Clearances

We require a minimum of 0.010" inner layer clearance.

Copper to Edge of Printed Circuit Board

Minimum of 0.010" (outer layers) and 0.015" for inner layers (0.020" preferred for inner layers). For scoring, minimum of .015 for outer layers and .020 for inner layers

Pad Size/Annular Ring

Pad size should be at least + 0.010" over finished hole size for vias and + 0.014" over finished hole size for component holes. This means the annular ring (radius of the pad) should be at least .005" for vias and a minimum of 0.007" for component holes.

Hole Size

+/- 0.005"  Standard Spec (applies to holes up to .250", larger holes will be routed, see Rout tolerances below)

+/- 0.005"  Custom Spec

+/- 0.003" Custom Spec upon request 1 oz and 2 oz finished copper weight and 3 oz finished copper weight (when starting with 2 oz foil) only.

If your hole tolerances are zero (see below), then Advanced Circuits will assume that you are OK with our default hole tolerance.  Our default hole tolerance is listed above.

Example: Customer Drill Chart with Zero Hole Tolerance

Rigid-PCBs-2

Our minimum finished hole size; 0.008". Call your salesperson if you required a finished hole size less than 0.008".

Printed Circuit Board Thickness:

Thickness tolerances may vary 10% (min.+/- 0.005")

Minimum Board Thickness
ThicknessDefaultFile Review Req.
2-Layer .020" .010"
4-Layer .020" .015"
6-Layer .031" .025"
8-Layer .047" .031"
10-Layer .062" .040"
 

PCB Inner Layer Thickness

Tolerances do not apply to the inner layers of prototypes.

Rout (Board Outline and Internal Cutouts)

The Outer Layer Tolerances on Standard Spec defined boards is +/- 0.010" (+/- 0.005" available for Custom Spec upon request)
Note: We rout to your board size using the center of the board outline on your mask layer.

Copper Trace Width/Spacing (Trace and space)

Copper spacing is the minimum air gap between any two adjacent copper features. Trace width is the minimum width of a copper feature, usually traces.

Requirements: A premium is charged for trace width/spacing less than .007".   
(We can process .004" for 1 oz. CU. finished (outer layers) and .5 oz. CU finished (inner layers).
For 1 oz. finished copper weight (inner layers), the minimum trace width/space is 0.005"
For 2 oz. finished copper weight (inner & outer), the minimum trace width/space is 0.006"
For 3 oz. finished copper weight (inner & outer), the minimum trace width/space is 0.010"
For 4 oz. finished copper weight (inner & outer), the minimum trace width/space is 0.012"
Note: Advanced Circuits does not offer weights such as 1.5 or 2.5 ounce finished on standard and custom spec orders.

Trace Width/Air Gap

The greater of +/- 20% or +/- 0.002"

Soldermask Swell

This is the expansion of mask relief over pad area. Our minimum is 0.005" over pad dimension or 0.0025" each side. Advanced Circuits will modify files to meet the minimum dimension.

Slot Width

Minimum 0.031" in width. For smaller width, call your salesperson for pricing and turntime.

Tab Rout Spacing

Please allow 0.100" spacing between your individual pcbs for tab rout spacing. When scoring there should be no spacing between boards.

Silkscreen (Legend)

0.005" minimum line width.

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