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PCB fabrication terms & conditions

BGA's

All via holes under BGA's must be covered with solder resist. This prevents wicking of solder away from BGA pads whilst undergoing reflow. Failure to do this may make successful BGA placement difficult.

Blind & buried vias

Blind & buried via PCBs are not offered on the PCB Train service. We manufacture blind or buried via PCBs but not on the PCB Train service. Ask us for a specific quote. Blind & buried via techniques should only be used if all else fails to solve a tracking problem. A PCB with blind or buried vias will cost considerably more than a conventional 4 or 6 layer PCB. For smaller quantities it would normally be more cost effective to have an 8 layer PCB rather than a 4 layer PCB with blind vias.

Copper layers

We recommend that copper pattern density is balanced across each side of a PCB and between side 1 & side 2. This improves plating uniformity and reduces bow and twist problems. It is recommended to create all copper planes as solid rather than hatched copper areas. This applies to inners as well as outer layers. This is because copper fragments from the corners of copper features are formed after etching hatched copper areas. These fragments have the potential to cause short circuits. So hatched copper areas should be avoided.

Data files

Gerber files must be accompanied by an aperture-list, containing D-code-values and the shapes used. We recommend that Gerber files should be in Extended-Gerber-format with embedded apertures (RS274X). Use flashed pads as often as possible.

Use an aperture-list containing the same number of different apertures as there are used in your design.
Output "pads" as filled.
Indicate the used data-format.
Indicate readability of the layers (preferably from component side, or solder side).
Add a build-up drawing showing how all the layers "laminate" together.
Do not mirror any layers. Send all layers as seen from top-side.
Data files must contain only one type of PCB.
The PCB images may be step and repeated. We recommend that you zip your files with PKzip.
If you upload your files on our website pcbtrain.com, the files must be in *.zip file format.
All design notes must be placed in a .readme file and zipped up with the appropriate gerber data.

Drill files

The CAD design software default output should be satisfactory for CNC drilling. Ensure that finished hole sizes are included in the data. Do not make via holes unnecessarily small. A reasonable small size is 0.4mm although smaller ones are possible.

File name conventions

We recommend that file extensions are used to identify each Gerber file. Protel give this advice with which we broadly agree. When you generate the Gerber output a series of files are created, each one corresponding to one of the layers enabled in the Gerber set up. These files are then loaded into a Gerber photo plotter, which produces the necessary photo tools for PCB manufacture. Each Gerber file is given the name of the PCB document, with a unique extension that identifies that layer and plot type. For example, the Top layer Gerber file for a PCB called MyDesign will be saved as MyDesign.GTL, to indicate "Gerber Top Layer". Because each design normally generates numerous Gerber files, these extensions help identify each file. We recommend that this convention is followed. CAD design software normally generates similar extensions by default. The following table shows typical file extensions:

Top Overlay .GTO

Bottom Overlay .GBO

Top Layer .GTL

Bottom Layer .GBL

Mid Layer 1, etc. .G1, .G2, etc

Power Plane 1, etc. .GP1, GP2, etc

Mechanical Layer 1, etc. .GM1, .GM2, etc

Top Solder Mask .GTS

Bottom Solder Mask .GBS

Top Paste Mask .GTP

Bottom Paste Mask .GBP

Drill Drawing .GDD

Drill Drawing; Top to Mid 1, Mid2 to Mid 3, etc. .GD1, GD2, GD3, etc.

Drill Guide .GDG

Drill Guide; Top to Mid 1, Mid 2 to Mid 3, etc .GG1, GG2, GG3, etc.

Pad Master, Top .GPT

Pad Master, Bottom .GPB

Keep Out Layer .GKO

Gerber Panels .P01, .P02, etc.

Gold tags

Gold tags are not offered on the PCBTrain service. We manufacture PCBs with gold tags but do not offer this on the PCB train service. Send us your data for a quote.

Layer identification

Each PCB layer must be identified. Text may be placed on each side of a PCB to identify the nature of the layer. "Side 1" means a component side or top side. "Side 2" means a solder side or bottom side. Inner layers should be numbered starting from the inner layer adjacent to the component side. This would be inner layer 1. We recommend placing some text on every PCB layer (right reading when printed) to ensure correct orientation when printed.

Legends

For good quality assembly it is crucial to ensure there is no risk of legend ink being printed on pads. A clearance of at least 0.125 mm must be allowed between the legend and copper a pad. Legends will be shaved back if they do not meet the copper pad to legend clearance requirements. This may affect legibility.

Rout files

A CNC rout file is not required. However a profile cutting line is required within the gerber data. Draft this line with a "zero" width line. If a non-zero width line is used, our working assumption is that the centre line of the cutting line marks the outside dimensions of the finished PCB. Do not compensate for the router cutter diameter or for the "finite" width of the line use to draw the profile. Cut-outs and slots must also be specifically identified as such with text annotation on your drawings.

Minimum radius of an internal corner

Note that the minimum radius of an internal corner (1.0mm) will be half the diameter of the standard router used (normally 2.0mm.) The thinnest slot will also be limited by the size of the router used (normally 2.0mm). If thinner slots are required, ask us to quote.

Solder resist

Solder resist layers must be identified with appropriate text descriptions printed within the solder resist. The text should be right reading when viewed as printed on the PCB. Solder resist clearances will be increased if they do not meet the copper pad to solder resist clearance requirements.

Surface finishes

The standard and recommended PCB finish is I.S. (Immersion Silver) which is inherently lead free. Lead free HASL (Hot Air Solder Leveled) and Au/Ni (0.1 micron of immersion gold over 5 microns electroless nickel) are available on some services.

Symmetrical PCBs

We recommend that the design of perfectly symmetrical PCB is avoided because of the possibility of mirroring during production.

Testing

Test files are created from gerber data. Therefore pads and tracks erroneously left unconnected in the gerber data will test as good PCBs. Visually check that all required circuit connections are present and complete. We recommend that pads are created from "flashed" shapes rather than from "painted" lines. It is the "flashed" shape which identifies the net end.