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Eurocircuits PCB blog

Mi foglal le jelenleg minket az Eurocircuits-nél, projektek amiken jelenleg dolgozunk, új ötletek, háttér információk és egy hely ahol ön bekapcsolódhat, elmondhatja véleményét és megoszthatja velünk mi a lényeges ön számára mint elektronikai fejlesztő.

Milling, slots and cut-outs – hints and tips.

One of the most frequent questions we get asked via our support services is “how to I define slots in my PCB?”.  Slots and cut-outs also generate many exceptions, which may lead to delivery delays.  Some exceptions occur because the definition of the slots is not clear; others because slots and cut-outs are in the data but not in the order.

Terminology

“Routing” describes the cutting of the board profile, outline or contour.  We use a 2 mm cutter for this.  Any feature which can be cut with the 2 mm cutter is part of the profile.

“Milling” refers to any slots or cut-outs inside the PCB, but also to any slots in the profile of the PCB which can’t be cut with a 2 mm cutter.

How do I define my slots?

Gerber mechanical layer.

The safest and clearest way is in a Gerber mechanical layer which shows the slots/cut-outs and the profile of the PCB. Two possible ways forward:

  1. Use draws and/or flashes with the correct end size of the slot/cut-out
  2. Draw the slots/cut-outs with a 0.50 mm line.  It has the advantage that at the same time the line helps you to visually check the clearance of any copper to the board edge. Our engineers will take the centre of the line as the edge of the slot.

Combine your definition of the slots/cut-outs with the PCB contour (outline) into one Gerber file. This layer should line up with the copper layers, but to be as safe as possible make sure that the copper layers also include the PCB outline.

Different systems have different names for the mechanical layer (for instance in EAGLE it is layer Milling - layer 46).  Provided that you have included milling in your order (see below) our engineers will find the right file.

If there is no mechanical layer, you may have to adapt another layer.  If there could be any doubt which is the right file, point to it in a README file.

Avoid defining slots only in a copper layer or in a legend layer, as they are then very easy to overlook or misunderstand.  You can indicate large cut-outs in a copper or legend layer, but make sure that there is a clear outline, and put text CUTOUT in the middle.

Drill file.

Some CAD systems allow you to define slots in the drill file.  This is also safe and clear.  But they must be defined as slots with an X & Y dimension, not as a row of overlapping holes.

Plated/non-plated.

We take slots with copper on top and bottom to be plated.  Give the dimension of the finished slot size.  We will make the necessary adjustments for the plating.

Slots with no copper on top and/or bottom layer are non-plated.  If you need non-plated slots through copper pads, indicate this clearly in the mechanical layer or in a separate drill file.

Example:

This pictures shows the customer data:

 
customer file
  • an outline file containing some cut-outs (contour file, drawn with a 0.50mm line) - yellow
  • a drill file containing all drill holes and large round cut-outs defined as flashed hole - blue
  • a routing layer containing all slots defined as tracks with the correct slot sizes - red
 
PCB top view

The result shown on the final board. Note also the difference between the plated slot and the non-plated cut-out.

How do I order my slots?

In the Price calculator menu go to the section headed PCB definition and then to the Milling box.  There is a choice of 3 cutters: 2 mm, 1.2 mm and 0.50 mm.  Select the one which is the same size as, or smaller than, your smallest slot size.  Note that you cannot use a 0.5 mm cutter on board thicknesses greater than 2.00 mm.

If your board has slots or cut-outs, make sure that you fill in the Milling box.  It alerts our engineers that your board need milling.

1.2 mm and 0.5 mm cutters are cost-options.  If they have not been selected, we will need to increase the price of the PCB so our engineers will raise an exception.  There is no charge for the 2.00 mm cutter as it will cut the slots at the same time as it cuts the profile – but still complete the box so that we know that you need slots or cut-outs.

How do I check my slots?

PCB Visualizer is an automatic Gerber pre-production analyser.  Gerber is a pure vector format with, at present, no built-in attributes.  So PCB Visualizer cannot always detect structures like slots and cut-outs. What is possible at the moment:

  1. Your slots/cut-outs are defined using flashes and/or draws, placed in a separate mechanical layer and this layer lines up perfectly with all other layers => PCB Visualizer has no troubles recognizing all slots/cut-outs and displays them correctly.
  2. Your slots/cut-outs are drawn with a line (0.50mm). PCB Visualizer will display the line but the material inside the line will not be removed from the image. Our engineers will find and define them when they prepare the tooling for the PCB. Once this is done, you can view the prepared data in PCB Visualizer as the “Production data” rather than the “Customer data”.

If you want to check that the slots and cut-outs are correct before the board goes into production, set up pre-production approval by clicking the "Request pre-production approval box" under Running orders.  The job will then be halted after tool data preparation for you to check.

If you have any questions, contact our Live Chat support.

 
 
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Készítette: Patrick Martin
Téma:
PCB Design
Közzétéve:
16 Jun 2014
Megtekintés:
5838

Copper and the board edge.

There are three options under our Advanced options heading which may be confusing:

  1. Copper up to board edge
  2. PTH on the board edge
  3. Round-edge plating.

Here’s how to sort them out.

Copper up to board edge.

To avoid damage to the copper during the profiling operation we normally ask for a minimum distance between the copper features and the edge of the PCB.  This distance is:

  • 0.25 mm on outer layers with breakrouting
  • 0.40 mm on inner layers with breakrouting
  • 0.45 mm on all layers with V-cut scoring.

These figures are needed to accommodate industry-standard manufacturing and machining tolerances.  For V-cut scoring it is also necessary to accommodate the V of the cutter.

Sometimes it is necessary to run a copper plane up to the board edge.  In this case select “Copper to board edge”.  There is no extra charge for this but it alerts our engineers to set up a different cutter speed.

“Copper to board edge” should normally only be used for planes and large copper areas where any slight damage to the copper will not impact on the performance of the PCB.

Tracks must not be placed within the minimum distance of the board edge where they could be damaged.  Our engineers will raise an exception whenever they find tracks within the exclusion zone.

If we find pads within the minimum distance of the board edge, we will clip them back to restore the minimum copper-free space unless:

  • the pads are part of an edge connector (usually with a bevelled edge)
  • the pads are marked as "up to the board edge" in a separate mechanical layer
  • the clipping is more than 25% of the pad surface in which case we will send an exception to the customer.

NOTE.

Copper to board edge cannot be combined with V-cut scoring.

TIP.

We will always cut inner layer planes back by 0.40 mm to avoid any risk of shorting.

PTH on board edge.

Also called “castellated holes”.

  
    

These are plated holes cut through on the board edge and used to join two PCBs either by direct soldering or via a connector.  As the process requires extra steps, plated holes on the board edge are a cost-option.

Your data should clearly show the holes and the profile.  Ideally include the information in a mechanical layer.

TIPS.

  1. There must be enough spare space on the edge of the PCB for us to hold the PCB in the production panel during manufacture.  If you need castellated holes on all 4 sides, email us your design or proposed profile as early in the design process as possible.  We can then confirm that it is manufacturable or suggest any necessary changes.
  2. You must have pads on top and bottom layer (and on inner layers where possible) to anchor the plating securely to the PCB.
  3. As a general rule the holes should be as large as possible to ensure good soldering to the mother PCB.  We recommends 0.80 mm and above.
  4. All surface finishes are possible but our preference is for selective gold over nickel for the smaller sizes.

Round edge plating.

This means that most or part of the edge of a PCB or a cut-out is plated from the top side to the bottom side.

  

This may be to ensure a good ground to a metal casing or for shielding purposes.

To manufacture a board with round-edge plating we rout the board profile where the edge plating is required before the through-hole plating process.  This involves extra process steps so round-edge plating is a cost option.

TIPS.

  1. There needs to be a band of copper on each side for the plating to connect to.
  2. As we need to hold the circuit within the production panel during processing we cannot plate round 100% of the edge.  There must be some gaps so that we can place rout tabs.  If you need a very high percentage of edge-plating, email us your design or proposed profile as early in the design process as possible.  We can then confirm that it is manufacturable or suggest any necessary changes.
  3. Indicate clearly in a mechanical layer where you need round-edge plating.
  4. Selective chemical nickel-gold is the only surface finish suitable for round-edge plating.

 

 

 
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Készítette: Dirk stans
Téma:
PCB Design
Közzétéve:
19 Jun 2014
Megtekintés:
5713