We now take the clean data and modify it to build the production tooling.
Prepare the job data.
1. Make security copies.
The first operation is to make a security copy of the data. We will use this later to check that we haven’t made any mistakes during data preparation. We build and save a netlist from the Gerber data as well as a copy of the layers.
If your CAD system allows you to output a netlist in IPC format include it in your data package. We can use it to check for any errors in the Gerber data supplied.
2. Add the material information
We attach the files to the standard build for the order. This imports the correct material thickness, copper thickness, solder-mask and legend colour etc. If the job needs a special build the engineer will make the build now.
Prepare the mechanical data for board manufacture.
1. Drill data.
We need to modify the hole size so that the hole after plating meets the customer’s specified size and tolerances. See here for the details .
Always specify finished hole sizes. Different board manufacturers use different rules for calculating the oversize, so if you oversize at the design stage the figures you use may not suit your chosen supplier.
Where possible specify standard drill tolerances +/- 0.1 mm for component holes and +0.1/0.3 mm for via holes. Tighter tolerances are possible but increase the cost of the finished circuit as they are not allowed in the pooling services.
2. Profile and internal cut-out/slot data.
Our engineers convert your board’s profile and cut-out information into a path for the router cutter. We use a standard 2 mm cutter for the profile and if required smaller cutters for internal slots and cut-outs (internal milling). If you have asked for the boards to be delivered in a panel the engineers add break-out tabs to hold the circuits in place during transport and assembly. The tabs are patterned to combine a secure hold with a clean snap-off.
There is no need to include a cutter path in your data. It is time-consuming for you to construct and in any case different manufacturers use different diameter cutters for profiling. And it will be incomplete as it doesn’t include start and end points and for a panel the order in which each cut will be made. Each manufacturer will optimise the cutter path in his own way. More info in our dedicated paragraph on mechanical operations.
The alternative to profile routing for a customer’s delivery panel is V-cut or scoring. We make a V-shaped cut in each side of the PCB leaving about 1/3 of the material to hold the panel together. Scoring can only be used for straight cuts across the panel, but it can be combined with routing for more complex profiles. As the circuits abut each other it is more economical of space but
!!! the V-shaped cut means that there can be no copper within 0.40 mm of the edge of the board.
3. Mechanical drawings.
Although our drilling and profiling machines are driven by digital data we still need drawings for tool set-ups and for quality checks. These drawings showing a complete set of dimensions and hole and slot sizes are also available to our users as an online PDF, part of our visual feedback policy.
Prepare copper, solder-mask, silkscreen (legend) and paste layers.
1. Outer layers
We “clean” the outer layer data and carry out the repairs we identified earlier. Cleaning means converting any drawn/painted features into proper pads and polygons and removing minor copper defects (pinholes, slivers and peelables). These minor defects can cause shorts and opens in production if small pieces of etch/plating resist or copper break off the circuit and stick back in the wrong place. More information .
Avoid drawn and painted features wherever possible. In RS274X you can define any pad or polygon you need. Slivers and pinholes are a common by-product of copper flood procedures but we can clean them automatically.
2. Inner layers.
As well as cleaning and repairing the data as for outer layers we also remove all non-functional pads and make sure that all thermal pads are properly connected (more information). We remove non-functional pads to reduce the risk of internal shorts and to increase the reliability of the plated hole.
There is often a trade-off here between a good clearance between the solder-mask window and the pad and good coverage over adjacent copper. For the details see “PCB Design Guidelines – Soldermask and our blog.
You can deliver the solder-mask windows at the same size as the pads and we will make the necessary adjustments.
4. Silk-screen (legend)
CAD systems often place component labels over pads. To ensure good solderability we cut the legend back to 0.1 mm from the edge of the soldermask window. The software tidies the remaining text to give a clean image.
5. Paste layers.
If the customer has supplied a solder-paste layer we check it against the copper data. If there is no solder-paste layer supplied we build one by selecting all the surface-mount component pads. If the customer has asked for a delivery panel the paste layer is stepped and repeated at the same time as the other layers. It is then available for download to make third-party stencils.
Add identification codes
Users often need to know who made a PCB, when it was made, and whether it meets certain safety standards. We screen our internal order number unobtrusively onto the board. You can then look this up on our website to see when the board was made, what materials were used and what inspection stages it passed. This information may also be stored on the board as a barcode. Where a board has to meet UL flammability standards we add our UL marking as well.
Prepare special layers
These include data for hard-gold plated edge connector fingers, peelable solder-mask, via-fill and carbon pads. There is more information on these in our PCB Design Guidelines and in our blog.
Make the delivery panel
If the customer has asked us to put the boards into a delivery panel we do this when we have prepared all the data for the individual circuits. For the different options see our PCB panel guidelines.
You can also supply your own panelised data. More information and tips
1. The engineer finally verifies his completed production data against the reference layers and reference netlist that he saved at the beginning of the process.
2. A second engineer then cross-checks the data for a second time against the customer’s order, any customer instructions, and the specifications of the chosen service.