Gerber past, present and future

More than 95% of all PCB designs produced worldwide are transferred from designer to fabricator as Gerber files. On most CAD systems the Gerber files are output automatically. It is only rarely the designers have to concern themselves about how a Gerber file represents their data. This in itself is a good measure of the power and ubiquity of the format, but occasionally an issue arises where some background knowledge may be helpful – and there are developments being planned for the format which will make it even more useful in future.

Gerber past:

Why “Gerber”?

Joe Gerber (1924 – 1996) was a US inventor who had fled from Austria to the US in 1940. Right from his student days he was interested in accurate data plotting, and during the 1950’s he developed the digital XY co-ordinate table which became the core of his future business, Gerber Scientific. The first product he launched using the new table was one of the world’s first digital drafting machines. Among later products was automatic cloth cutting machinery which is still widely used in the world’s garment industry. In the ‘80s he developed computerised equipment for machining spectacle lenses, again still used today.

In the 1960s Joe Gerber found another use for his XY table. He introduced the world’s first NC photoplotter to generate the phototools used to produce PCBs. It worked by first moving an optical head containing a light source to the correct location over the film on the bed of the plotter. A circular wheel with different sized/shaped holes in it (apertures) was then rotated so that the correct aperture was under the light source. For a pad the light-source was flashed on and off, exposing the pad on the film. For a track the light was left on while the head moved, drawing the track on the film. Hence we still talk about “aperture tables”, and, less often these days, “flashes” and “draws”. The plotters were known as vector plotters as the head followed the actual pattern of the PCB. The actual drive format was based on a pre-existing format, RS-274-D, developed by the US Electronic Industries Association (EIA) to drive any NC machine. The data was loaded into the very first Gerber photoplotters on punched cards.

RS-274-D becomes RS 274X

By the early 1980s PCB Computer-Aided Design (CAD) systems were becoming more common, replacing the old hand-taped 2:1 artworks. CAD systems could output drive data directly to a photoplotter to generate the phototools. At that time most photoplotters were Gerber plotters. Other vendors moved into the photoplotter market, but as Gerber had published a full specification of their format in 1980, Gerber RS-274-D became the de facto standard.

As a vehicle for transferring PCB layer images, the format had one critical limitation: the size, shape and number of the apertures was limited by the physical aperture wheel. This worked (more or less) for designs using conventional through-hole components with round or square pads, but it couldn’t handle the new surface-mount components which used a wide variety of mainly rectangular pad sizes. Using RS-274-D the only solution was to “paint” the pads with tiny draws. Similarly, a simple plane layer could be plotted in reverse, that is, the clearance holes in the plane are plotted black and the board manufacturer reverses the polarity either in his front-end CAM system or physically by contact printing. But this won’t work for mixed plane layers or planes on signal layers. These had to be filled with draws. A large image with SMDs and planes could take up to 24 hours to plot on this type of plotter.

The solution was a new type of photo-plotter and a new format. The raster photo-plotter used a light source, typically a laser, to raster-scan the film in a continuous pattern. The image was built up by a sequence of laser on, laser off commands. Now any shape could be plotted, built up of raster pixels. Today this is the standard industry tool for photo-imaging PCBs, with laser photo-plotters using up to 48 independently-switched simultaneous beams plotting at resolutions down to 50,000 dots per inch or more.

Now it was possible to make the Gerber format more flexible and more suited to the requirements of the PCB designer. RS-274X or Extended Gerber was launched in 1991. This allowed the user to define and image any shape, as a pad, a track or a polygon (plane). The aperture definitions no longer depended on a physical wheel and so they could be derived automatically from the CAD job and included in the file as part of the output.

Gerber today.

RS-274X is the standard PCB layer image data transfer format used today. It is clear, unambiguous, and, if any questions arise, man-readable. Each file is complete and allows you to draw any pad-shape or copper area that you want.

The old Standard Gerber RS-274-D still lingers on, despite its drawbacks. It is very limited; it needs a separate aperture table which often seems to go missing; it produces huge and unwieldy files; the output may require the merging of positive and negative images which at best requires extensive clean-up and at worst generates hard-to-spot errors.

Eurocircuits can still accept the older format if needed, e.g. for old jobs, though it does not work with PCB Visualizer. However, Extended Gerber, RS-274X is our preferred format as it has none of the limitations of RS-274-D and as each file is complete including the embedded aperture definition it works with PCB Visualizer, offering you all the benefits of our advanced data checking technology. All current generation and most older CAD systems generate RS-274X output. If your CAD system is still outputting the old-style Gerber RS-274-D, look into the output settings. Sometimes it is possible to switch from RS-274-D to RS-274X. There may be different terminology used on different systems. If you are in doubt, ask us.

For more advice on input formats, go to our PCB Design Guidelines

Gerber tomorrow.

Extended Gerber, RS-274X, provides an exact and unambiguous image of the layers of a PCB, but there is still some layer information which is necessary for fabrication (especially for automated data preparation) but is not included in the format.

Examples include:

  • What is the function of this layer: top copper, top solder mask, etc.?
  • Does the image show a single PCB or a delivery panel?
  • What is the function of this object: is it a SMD pad or a via pad, fiducial etc.?
  • What is the board profile? Automatic recognition software like PCB Visualizer can recognize rectangular profiles but not complex shapes.
  • What are the drill tolerances on this hole? For example, it may be a press-fit hole.
  • Which are the impedance-controlled tracks?
  • Which vias need to be filled?

The next step is to incorporate this type of information into the data transfer format. Any such further extension of the format has to be compatible with the existing format and with existing CAD systems. Although other formats have been proposed which can include non-image information, Gerber is so widely used and so effective in operation, that, like the QWERTY, QWERTZ and AZERTY keyboards, it cannot be easily replaced.

The Gerber format today is maintained and developed by the Belgian company Ucamco which bought the PCB Division of Gerber Scientific in 1997. Ucamco have recently published the blueprint for the next generation of RS-274X, Gerber RS-274X2. This adds attributes into the format which convey the information listed above.

This new development is further explained in our technical blog on Gerber X2. Eurocircuits are working closely with Ucamco on the new format as part of their drive to provide better tools for the European and global PCB design community. As the new attributes are implemented into CAD systems, we will add new functionality into our data input and validation procedures to handle them. Of course, we will also continue to accept the older Gerber formats.

Extend Extended Gerber – Gerber X2

Gerber”s new attributes set to transform CAD to CAM communication

With the support of Eurocircuits,, LPKF and AT&S, Ucamco drafted a new specification for a ground-breaking second extension to the Gerber format. This offers an unequivocal standard for non-image data that is just as simple, practical and universally accessible as the well-known Gerber image data format it now supports.

Ucamco“s Managing Director Karel Tavernier comments: “CAD/CAM professionals need to transmit data in a robust, reliable and cost-effective way, something the Gerber image format has been doing for years. It”s freely available, simple and to the point. It can be used by everybody, no matter how big or small the CAD or CAM operation is. It”s the most practical image description format out there, and by far the most used by our industry – every single day thousands of perfect PCB layer images are reliably transferred all over the world thanks to Gerber”.

Indeed, with Gerber, CAD/CAM professionals know that the most critical and fragile part of their archives – the image data – is secure and accurate. But there is another part of the PCB design that images cannot convey. This non-image data includes information about layer order and function, the differentiation between objects like SMD and via pads, and a raft of further information that, together with the image data, helps to translate designers” intentions into high performance products.

The problem is that there is currently no Gerber standard for transferring non-image data, leaving designers to decide for themselves how best to communicate with their manufacturing partners. They might add text files or drawings to their Gerber archive, or they might not, putting the onus on CAM engineers to search for the necessary information, or contact the designer if it”s missing. These are error-prone, time-consuming tasks that can end up affecting quality and deadlines, which can translate disastrously into loss of orders, clients and future business, especially in the time-critical context of prototypes and quick-turn boards. Thus whether you are a designer, customer or manufacturer of PCBs, data quality and clarity should be a top priority for you.

This is why Ucamco has developed its Gerber X2 format. X2 offers a series of attributes that provide a standard for describing non-image data – some might rather grandly say that they add intelligence to the image data. Applicable either to a whole file or to individual graphic objects, Gerber”s standard attributes can now be used to define

  • Gerber file function: top copper layer, top solder mask, etc.
  • Part: single PCB, customer panel etc.
  • Object function: SMD pad, via pad etc
  • PCB profile
  • Drill tolerances
  • Locations of impedance-controlled tracks
  • Filled vias
  • An MD5 checksum for added security

The attributes have been purposely crafted, from scratch with the sole aim of supporting the transfer of PCB data from design to manufacturing. They are essential, simple and focused rather than a casual smorgasbord of “nice to haves” with unnecessary complexity, not to mention potential bugs. There is no overhead of manufacturing specific attributes as are found in CAM formats. X2 is simple and clean.

The attributes intentionally do not cover all possible non-image data. Ucamco refrained from adding the netlist to X2 as there is a simple and well-established format adequately describing netlists: IPC-356-A. Materials were not added as they are not linked to images and can be handled by a subset of IPC-2581 as soon as 2581 is opened up to partial implementations. In this way X2 delivers the best of all worlds: accessibility, simplicity, performance, and tried and tested formats that work for everybody. It”s a great combination that gives designers a clear and simple method for ensuring that their manufacturing partners have all the data necessary for efficient, reliable manufacture. And it eliminates the need to adopt complex new formats wholesale, which is a blessing, as Ucamco R&D engineer Thomas Weyn explains: “Imaging software, notoriously hard to implement, takes forever to debug and field test, especially for images as complex as PCBs. Here, errors are fiendishly difficult to detect and almost inevitably lead to scrap, so it is far preferable to keep what we know works (the Gerber image format) and support it, without disrupting it, with what is missing”.

A prime design goal of X2 is ease of adoption and of implementation. To fully exploit the productivity jump that X2 can bring, CAD and CAM software only requires quite minor updates. Given that the imaging model remains unchanged, it only requires adding a few extra lines with the attributes when writing a Gerber file – it could hardly be simpler. The payback for this is a more versatile product and greater competitivity for systems vendors. The attributes” use is not mandatory: they can be used wholesale, partially or not at all, whichever suits the implementation best. Most importantly, systems that have not been updated will still generate the correct image as Gerber X2 is upward compatible with previous versions of the format as the image is not affected by the attributes. Existing workflows are not broken by introducing X2.

Before the final version goes live, Ucamco encourages CAD and CAM professionals to look at it and in particular at the Attributes in Section 5, and participate in its fine-tuning by sending comments to gerber@ucamco.com

In order to make X2 happen, Ucamco need CAD software vendors to buy in to X2. As X2 is easy to implement, it makes a chance. But they need your support. Please write to Ucamco at gerber@ucamco.com and let them know that you support the Gerber X2 format, and that youy would implement it in your workflows when it is available.

The draft Gerber X2 second extension is available at www.ucamco.com/downloads and a brief press release describes the rationale for its development.

Your optimum PCB Design flow

Achieve the ideal PCB Design flow by using Eurocircuits’ smart menus

In support of our Design engineering customer community, we have created smart menus and PCB visualization tools. These will help designers to follow the best PCB layout flow possible and thus save time, avoid communication problems and achieve the best price and reliability for their PCB.

Smart menus.

The Eurocircuits calculator is based upon the technology of our PCB Configurator software which is part of the PCB Visualization tools of our website. However this calculator can work without attaching data to it. You will have the complete service scope of Eurocircuits at your finger tips including all technical validation rules that apply when choosing different technical options for your board.

We therefore call it “smart menus”. They contain:

  • Build-up wizard: more than 700 predefined build ups including blind and buried combinations can be chosen.
  • Technical validation: around 300 rules are built into the smart menus helping you to choose only those combinations of options that are viable. All violation are explained and possible corrections advised. If none are clear or what you had in mind, calling operator assistance through “launch inquiry” is always possible.
  • Classification wizard: our classification aide shows you the possible pattern and drill classes in function of the chosen base copper foils.
  • Price guidance: on every option you choose, the smart menu informs you if there will be a slight cost increase or if the board is no longer poolable and the cost will be calculated based on production panels. All prices are always calculated including alternatives based upon other more favourable quantities and delivery terms. Also a full customer definable price matrix is possible.

Visualization tools

After you have finished your PCB Layout based upon the PCB design parameters you defined using our smart menus , you can load your PCB data into the shopping basket of your account. Our PCB Visualizer software will start analysing your data and will come up with a reply some minutes later. Your board is now viewable. What can you discover?

  • PCB Visualizer: see your input data and if necessary map an individual data file to another function on the board. You can view the board base upon the chosen order details or the default details in case you choose analyse my data. Going through all order details, you can view all comments and possible violation.
  • PCB Checker: shows the result of the design rule check of your data against the order details of the basket item. You can consult all possible errors individually and evaluate.
  • PCB Configurator: this tool allows you to change the order details and bring them in accordance with the content of your data.

Presentation “share our knowledge”

In this presentation we go through the PCB Design flow with the emphasis on the Eurocircuits smart menus and PCB Visualization tools and how they can help you gain time, avoid misunderstandings and save costs.

View the Presentation – click here

The presentation is best viewed when you open the speaker notes and view them on a second screen. This can be controlled from the option button in the bottom left corner.

The Smallest Possible Distance Between Two Holes

What is the smallest possible distance between plated through holes?

A. The holes are a part of different electrical nets?

Plated through holes that belong to a different electrical net, need at least 0.25mm base material between their hole walls. To calculate this, you will need to count with the manufacturing tool size which is 0.10mm larger than the end diameter.


A 1.00mm PTH finished hole size, is drilled with a 1.10mm tool. So to leave 0.25mm of base material between two holes of 1.00mm their centre coordinates need to be 1.35mm apart. Or in other words: two PTH holes from a different electrical net need to be 0.35mm from each other, measured on the finished holes size (end diameter).

Why do we need this distance?

Smaller than 0.25mm drill to drill distances will create micro cracks along the glass fibre walls. The chemicals used in the galvanic line can intrude these cracks and create small shorts between the hole walls. The resistance of these shorts is typically larger than 1 MOhm.

Why could we use a smaller distance in the past?

In the past (before 2006) the distance could be smaller because we used only base material for leaded PCB technology. The materials for lead-free PCB technology are more brittle and thus more sensitive to cracks and moisture intrusion.

B. The holes are a part of the same electrical net?

When the plated through holes are part of the same electrical net, the PCB designer may decide that the possible shorts described under point A above are not causing any problems. In that case we are able to produce these neighbouring PTH holes with a distance drill to drill of 0.15mm. Or in other words: 0.25mm between the finished holes size diameters.

Why do we need this distance?

If the distance between the hole walls becomes smaller than 0.15 mm than this will result in bad drilling causing the base material to be damaged en drill bits to be broken. It results into an avoidable cost increase.

What is the smallest possible distance between non-plated through holes?

Between the non-plated through holes we also have to keep a 0.15 mm drill to drill distance. For NPTH holes the tool diameter is equal to the end size diameter Or in other words: we need 0.15mm between the finished holes size diameters.

Why do we need this distance?

The reason was explained under point B. above. If the distance between the hole walls becomes smaller than 0.15 mm than this will result in bad drilling causing the base material to be damaged en drill bits to be broken. It results into an avoidable cost increase.

new CadSoft EAGLE DRU files for EAGLE V6

New as from 18/09/2017.

EAGLE dru files have been adapted to our new service definition and PCB classification effective September 18, 2017 : Eurocircuits-EAGLE_dru_18-09-17.zip

We provide DRU files for the following Eurocircuits services :

New in EAGLE Version 6

In the new EAGLE Version 6 format, the EAGLE brd-file is saved in XML format. Also new in EAGLE version 6 is that the used Design Rules Settings (used DRU-file) are embedded and saved in the EAGLE board file (EAGLE brd-file).

In the previously released EAGLE design rules of Eurocircuits (eC-EAGLE-design-rules-24-06-2011.zip) the DRU file description contained quote-characters (“), which are not supported as such in the XML format.

Using these “old” eC-EAGLE-design-rules in EAGLE Version 6 will lead to errors when trying to load a Version 6 EAGLE brd-file which has been saved with the “old” eC-EAGLE-design-rules. The eC-EAGLE-design-rules have been updated to correct this problem:

Eurocircuits-EAGLE_dru_18-09-17.zip

When you downloaded the eC-EAGLE design rules earlier and you did not upgrade to version 6 yet, you do not need to install these new DRU files. When you upgraded to version 6 of EAGLE we advise to use these new design rule files.

Design Rules


During the design of a PCB and certainly at the end of the PCB design, it is imperative that you check your layout against some technology rules in order to be sure that you design a producible PCB layout.

The basic items to check in a design are related to the “copper image” of the PCB, these are:

  • the track widths
  • the isolation distance between different tracks and/or component/via pads
  • and the annular ring (or restring) on component/via pads.

Next to these basic items, other items that can be checked are for instance related to:

  • soldermask (eg Soldermaskpad oversize),
  • items related to the mechanical outline of the PCB (eg distance of copper to the PCB contour),etc…

All these different checks to be made we call the “Design Rules”.

“Design rules” can be specified in most of the CAD-PCB design software. In some they arevery basic, in other the possible settings are more extended.

For CadSoft EAGLE we have made different “Design Rule Settings” (DRU-files) which contain the specific minimum design rules for a specific service of Eurocircuits.

Front-end data preparation – white paper (2012)

“What do PCB fabricators do with my data before they make my PCB?”

 

“Why can’t they use my data just as I sent it in?” “Why do I need to know? I’m an electronics engineer and they are the board fabricators?”. Our new white paper, “Front-end data preparation”, answers these questions.

An understanding of the front-end data preparation process is important for two reasons, speed and cost. PCBs for time-critical applications need to be delivered fast and on time. If information is missing from the data set supplied or if it is ambiguous or unclear we lose time while the issues are sorted out. The new white paper explains how we verify that the data is complete and clear, to make sure that we deliver the board that you want. Above all, it contains tips on how to present clear and unambiguous data and avoid some of the common traps which can delay deliveries.

Our pooling services have been developed to deliver prototype and small batch PCBs cost-effectively as well as fast and on time. The specifications of each service are based on a choice of base material and on a robust level of manufacturability to ensure the quality of the finished product. The white paper outlines how we check that each design fits the specification of the chosen service. If it doesn’t, we report back the data issues (raise an exception). Are there simple steps which you as a designer or we as fabricators can take to avoid having to use a more expensive option? If so we will propose them. Are there repairs we can make to bring the board back within specification and improve its manufacturability? In many cases we can make these repairs as part of the data preparation process and the white paper has links to more detailed information. Design for manufacturability tips highlight some critical areas. The white paper also links to the free design rule sets which can be uploaded form our website into EAGLE and Altium CAD systems to help ensure that your design meets the specifications of the most cost-effective pooling service.

Although the white paper follows our internal procedures and includes the names of our front-end data preparation stages, our data preparation process follows industry best-practice. So throughout we relate what we do and our design tips to the wider PCB fabrication world. Our goal is to provide a broad set of technical information which will benefit not just our users but also the wider electronics engineering community across Europe.

Download the Eurocircuits-frontend data preparation white paper in PDF format.

To preserve the environment and to make use of the many embedded links to articles on our web site, we recommended that you read this white paper in its digital form.

Eurocircuits production data – what’s in it?

To produce your board we use your design data in Gerber or EAGLE format and first perform the necessary front end actions as described in our white paper: “What do PCB fabricators do with your data before they make your PCBs?“.

When this is done and your board is ready for production, we save your board’s production data in your account. This data we call the job’s “single image” data. “Single image” means the data we load onto our order-pooling production multi-panels, so it may refer to a single circuit image or to a delivery panel if this is what you have ordered. This is the data that is visualized in the PCB image. You can download the full set from within your customer account.

 


The download of the single image production data from the Eurocircuits site has been possible since we launched our e-business platform more than 10 years ago. This open business policy has convinced customers over the years to come to us for their prototypes and small series even if they planned to have their large series produced in the Far East. We offer a fast and convenient way to calculate prices and place orders, a thorough data verification and manufacturability analysis and highly professional production processes. Combine this with the possibility to download the verified data and use it for production wherever else you want, and you have the best possible start for the life cycle of your products.

The single image files are name coded by Eurocircuits. But this is no secret either. Let us explain what the files are and what their names stand for.

file name convention.docx

 

The format of the files is mainly DPF. This is the internal format for UCAM, the front-end data preparation or CAM (Computer Aided Manufacturing) system we use designed and developed by Ucamco. The paste files can also be downloaded as Gerber data. To read DPF files as well as Gerber data and Excellon drill files we recommend GC-Prevue, available as a free download from www.graphicode.com.

We are sometimes asked if it possible to reload the single image data back into a CAD system. This is totally dependent on the CAD system. We have only input and processed manufacturing data. Other PCB manufacturers can use it for production through their own CAM systems. However the manufacturing data doesn’t contain any component information like foot-print coordinates or a functional net-list where nets are linked to component pin numbers and are described as power, ground, data line, etc… A successful reload of DPF or Gerber production data into a CAD system depends entirely on the functionality available in the CAD-system and should be investigated there.

Our team will gladly answer any queries you may have. Contact us on euro@eurocircuits.com.

Eurocircuits Data preparation – Make production panels

By now your job has already been through two of the three front-end data preparation stages :

Stage 3 – Make production panels and production tools

We now have a stack of orders that are ready to go into production.

Our business model is based on “order pooling”. We make our production more efficient by processing several different orders on the same production panel. More efficient production means lower prices for our customers, especially for prototype and small batch orders. Which orders can be pooled together? This depends on a lot of factors, and finding the right balance is our daily challenge.

We need to consider:

  • Delivery term : we separate rush orders from standard delivery orders. If we put both on the same production panel we could find that all panels have rush orders on them. If every job becomes urgent, production efficiency goes down and our delivery performance is affected.
  • Order size : we keep large and small orders apart. The higher the number of panels in a job, the longer it takes to process. Production planning becomes less flexible and again we risk deliveries.
  • Copper distribution : we discussed this already in our earlier blogs about our new plating simulation tool and the Elsyca Intellitool Matrix plating project. We need to be sure that the designs we pool together don’t reduce each other’s plating quality.
  • Classification/complexity of the boards : combining complex jobs with simpler jobs means that the final panel is more complex than it need be and so more expensive to produce. That’s why we have two different pooling services ‘STANDARD pool” for standard boards and “TECH pool” for more complex boards.
  • Technology: some technology options clearly can’t be combined with each other, for example different materials, copper weights and build-ups. In other cases combinations might reduce production efficiency or quality. For example we could in theory combine boards with different legend colors on a single production panel. In practice this would need two printing processes and two curing stages. We would lose time at the print stage and risk the quality if the panel went through too many heating/cooling cycles.

The final decision day by day on which orders are combined on which panel is made by highly skilled and experienced engineers. They have a growing number of software tools to help them to make the best decisions, and we are investing a lot of manpower and resources to develop even more powerful tools for the future.

Once the engineer has chosen the orders for the panel, how do we make it ready for production?


Panel preparation for production

Most of the steps below are fully automated processes

  • Run a Drill Tool Reduction: on pooling panels we remap all drill sizes larger than 1.00 mm to new tool sizes with a step of 0.10 mm rather than 0.05 mm – provided, of course, that we can still maintain the tolerance specifications of the finished hole size. This can reduce the number of different drill sizes needed by up to 60%, which in turn reduces total drilling times and so cuts cost of your PCB.
  • Add any customer-specified markings to the boards on the panel, for example UL markings or customer-specific date-codes.
  • Add different test coupons to the panel for inline quality checking. Together these coupons contain specific features which allow us to check all process steps and make sure that the panel meets all production specifications during and after the production.
  • Add specific galvanic compensation patterns (“robber/thieving bars”) to the open panel areas. This optimizes the final plating results and ensures that after plating the copper thickness in the holes and on the tracks is within the production specifications.
  • Add etch-compensation to meet the panel and production specifications. When we etch down into the copper the nature of the process means that we also etch away a small amount of copper to each side (“under-cut”). Etch compensation makes a small increase in all copper features so that after any under-cutting the feature size is as designed. This is especially important to maintain correct track widths.
  • Calculate the other data we are going to need for panel checking and manufacture, like the total copper surface area or the copper distribution, information which we will need for calculating plating currents.

Panel checking and optimization

  • Perform a galvanic plating simulation to ensure a uniform layer of plated copper over the entire panel within the production specifications. At this stage our engineers may move the circuits around on the panel or change the galvanic compensation patterns to get the best possible plating result.
  • Drill optimization. For each separate drill run on the panel, the complete drill path – the order in which all the holes are drilled – is automatically optimized to get the lowest possible drill time.
  • Routing optimization. For each routing operation on the panel, the complete rout path is optimized. Here we rely on experienced production engineers to get the best possible combination of edge finish, mechanical stability of the panel during routing, and shortest routing time.


Panel plating image samples:

  • Bad copper distribution
  • Good copper distribution

Panel output generation

  • Drill output: we generate drill output files for each drill operation required on the panel (plated, non-plated, blind, buried). These output files will drive our various drilling machines.
  • Rout output: rout output files for all the routing and milling operations needed (board profiling, slots, internal cut-outs). The output files drive the routing machines.
  • Plotter output: plot-files for our laser film plotters for all layers produced by photo-imaging (copper layers and soldermasks).
  • Legend output: for legend (“component ident” or “silk-screen”) printing we use digital ink-jet printers. As well as the legend pattern the output files can contain an instruction that prints a unique barcode on each individual PCB. When tests are completed this will give our customers who want it the ultimate in traceability.
  • Electrical test files for our different electrical test machines. Production panels are electrically tested before the single images are routed out. If needed a single board can also be electrically tested after final board profile routing.
  • AOI (Automated Optical Inspection) output generation. AOI testing is an automated optical comparison between the digital data supplied for the PCB and the actual copper layer we have produced. We AOI test all inner layers to detect shorts, opens and other faults which cannot be rectified once the board is bonded. We also AOI test some outer layers depending on the technology level of the panel.
  • Other information needed for manufacture such as:
    • the surface area and density calculations for copper layers, soldermask layers, plating layers, etc
    • panel images
    • drilling, routing and scoring drawings etc…

To production

The complete production panel job and all generated output data are packed together in a structured zip container and uploaded to the system.

The production panel is now ready for manufacture. Our production planners decide which production unit is going to actually make the panel (Eurocircuits Kft in Hungary or Eurocircuits Aachen in Germany). The decision is based on the technology required, the size of the job, the delivery term and available capacity.

Which Surface Finish fits your Design

Surface Finishes on Printed Circuit Boards

Then finally, you have finished your design and the moment has come to order the PCB. You have considered all the important aspects. The DRC check is done and you are relieved: no errors remaining.

The online calculator shows you the default pooling options and offers you the possibility to adjust some of them to your specific need. En there you bump onto the Surface Finish. What is Surface Finish and how to make the right choice?

Since all finishes have advantages and disadvantages, it is important to stand still by their application and to check how your boards will be treated during assembly. The different finishes we offer are Lead-free HAL, Electroless Nickel/Immersion Gold (known as ENIG) and Immersion Silver (ImAg). All of these are Lead-free and can be used for a RoHS design but also in a SnPb assembly. Edge connectors can be covered with hard Gold (electroplated Ni/Au).


Leadfree-HAL

The use of HAL as a finish results in PCBs with the highest level of solderability and solderability robustness with regards to multi-step assembly and storage and all this for a reasonable price. On the other hand, the HAL process requires the submerging of the complete PCB in liquid solder and is responsible for extra thermal load on the PCB. For that reason, it isn’t the best choice if your board requires small via holes or the board exceeds a normal thickness (when the aspect ratio is high). Another aspect is the less flat surface it may create. Although we try to achieve a flat surface, the variety of the amount of solder present on the solder-pads can make this finish less suitable for small sized components with small pad sizes.

ENIG (chem. Ni/Au)

Many customers choose this finish because of the flat surface, the good solderability and the acceptable shelf live, but also because they are already familiar with this finish from before the introduction of the Lead-free assembly. At least, this parameter could remain unchanged and gave at that time some confidence. However, the ENIG process is a complicated one with a higher risk of defects (skip plating, black pad or interface embrittlement). When using ENIG, the solder-joint is formed between the solder and the Ni layer of the NiAu surface, not with the underlying Cu. The Au is completely dissolved in the solder-joint. This interface is considerably more brittle than a SnCu interface and therefore not recommended for applications where shock, bending or strong vibrations are part of the picture. And last, but not least: it is the most expensive surface finish of the list. For some applications, like key pads or wire bonding, it is the better choice.

Immersion Silver (chem. Ag)

This surface finish is often a bone of contention, some love this finish, and some hate it. It offers a flat surface, a very good solderability and a long shelf life. The solder-joint is created with the underlying Cu, since the Ag is dissolved during soldering. Sounds good, but the ImAg is susceptible to sulferdioxide (SO²) which tarnishes the surface and creates the AgS² layer. This layer affects adversely the surface solderability. To avoid this tarnish, we pack the PCBs in silver saving paper and require hermetic sealing to avoid moisture and atmosphere SO² coming in. In case of multi step assembly, the partially assembled boards should better be stored in a sulfur-free atmosphere. If all this handling is not a problem and taken into account, it is the best choice and… the cheapest.

Any Lead Free

If you don’t choose a finish, your board will be produced on a production panel where the finish is lead-free HAL or chem. Ag or chem. NiAu. The choice is defined by other PCBs appearing on the same panel.

Gold for Edge Connectors

Due to the need of abrasive resistance of edge connectors we can finish these connectors with a layer of electroplated NiAu (hard gold). This finish is processed in a special sized bath construction and only used for these connectors. It is not possible to have this hard gold processed on other locations of the PCB.

Carbon

Carbon combines a high mechanical strength with a good electrical conductivity and can often be used as a substitute for gold on contacts. It is applied directly on the Cu and used for switch contacts, foil keyboards and can enable the creation of cross-over conductors. It is resistant to HAL and soldering processes without showing practically any change in resistance. Carbon is printed (conductive ink) and the accuracy in position and image is therefore limited by the printing process.

Summary Table

Eurocircuits data preparation – Single Image (part II) – other layers and outputs

Have you ever wondered what we are doing to your data when the order status is Single Image? Here is the answer based on the instructions we give to our data preparation engineers. Many of the steps described below are automated for speed and accuracy but we have ignored this to make a clearer presentation. More information on our requirements can be found on the home page under “Technology Guidelines”.

Stage 2 – Single Image data preparation (Single Image and Single Image Cross Check)

We covered before :

  • Eurocircuits data preparation – Analysis : the initial stage, checking if the data are complete and no obvious problems are there to fulfill the order.
  • Eurocircuits data preparation – Single Image (part I) – drill data and copper layers. : Verify and clean up the drill data and the outer and inner-layers.

This current article, Eurocircuits data preparation – Single Image (part II) – other layers and outputs, is our third article in a series about frontend engineering and is about the preparation of Soldermask, Silk screen (legend), coding on PCB”s, making customer panels, machine outputs: “drill layer, rout layer, V-cut layer”, SMD paste layers and optional other layers.

Solder-mask preparation

  • Replace any painted pads and areas with proper flash pads and polygons as for copper layers
  • Check for missing soldermask pads on component holes or fiducials
  • Check and add soldermask clearance pads on all non-plated holes
  • Check and correct the cover between the edge of the soldermask and the adjacent copper tracks or planes (= Mask Overlap Clearance or MOC) depending on the specification of the pattern class
  • Check and correct the clearance between the copper pad and the edge of the soldermask (=Mask Annular Ring or MAR) depending on the specification of the pattern class
  • Check and correct the minimum width of the solder-mask bridge between adjacent soldermask pads (=Mask Segment or MSM) depending on the specification of the pattern class
  • Save job


Silk-screen (Legend) preparation

  • Check and clip clearance to the board outline
  • Check and correct minimum text width to 0.17 mm
  • Clip the silk-screen data to ensure that there is no ink on component pads
    • As standard clip back 0.10 mm from the soldermask
    • If there is no soldermask clip against the copper pads, plus drill holes, plus rout layer
    • If there is no copper clip again the drill holes, plus rout layer
  • Save job

PCB coding

  • Add the Eurocircuits order number on the top or bottom silk-screen layer as specified
  • Add UL marking indication and any customer-special marking indication as ordered
  • Add Barcode coding (for traceability) as per specification
  • Save job

Drill drawing preparation

  • Assign standard hole-size symbols to the drill holes and provide the key
  • Check that all required dimensions and tolerances are indicated
    • For slots, indicate width, length, plated or non-plated
  • Add any additional information required:
    • Special routing or depth routing
    • Press fit holes
    • Other useful information
  • Save job

Rout layer preparation

  • Copy outline to rout layer
  • Check for any customer special instructions for board profile and prepare accordingly
    • Special rout shapes and tolerances
    • Non standard tooling (radius, …)
    • Specific requirements for a customer panel
    • Separate outer (profile) routing from inner routing (cut-outs and slots) and apply proper tool sizes and numbering
  • Convert drill holes larger than 10 mm into inner routing
  • Check and set rout directions
  • Apply tool compensation
  • Add break tabs according to specifications
  • Check and set correct tool sequences for pre-drills, routing stage drills, inner/outer routings
  • Save job

V-cut ( scoring) layer preparation

  • Create V-cut layer with 0.90 mm V-cut draws as per specifications
  • Save job

Paste layer preparation

  • If solder paste data is supplied by the customer use it without modifications
    • convert any painted pads to flash pads.
  • If no solder paste is supplied prepare the paste layer from the board data. Select all non-drilled, flashed pads that are free of soldermask and copy to a paste layer.
  • Save job

Special layers preparation

These layers will be prepared only when ordered.

  • Gold Finger Layer Preparation
    • Create the gold finger connections according the specifications
    • Add specific routing for the gold edge-connectors
    • Check the connections widths and positions and the bus bar width and position against the modified mechanical layers

  • Peel-off Layer Preparation
    • Create the peel-off layer as specified by the customer
    • Check that it is conform to our production requirements and resolve any errors.
  • Via-Fill Layer Preparation
    • Create the via-fill layer as specified by the customer
    • Check that via-fill is only applied on 1 side of the PCB. This cannot be the side with any BGA on it
    • Check that the via-fill layer is conform to our production requirements and resolve any errors
  • Carbon Layer Preparation
    • Create the carbon layer as specified by the customer
    • Check that it is conform to our production requirements and resolve any errors

Make a customer panel

The Single Image (the “deliverable”) may be a customer-specified panel or array. There are three options here:

  • Panelisation done by Eurocircuits according to the Eurocircuits standard panel rules
    • Create a Eurocircuits standard panel using automated panelisation routines in accordance with the order details:
      • Step X and Y
      • Panel border width
      • Distance between the individual circuits
    • Check for panel stability
      • Check routing or V-cut positions
      • Check break-tab positions and add more if needed for panel stability
  • Panelisation done by Eurocircuits to the customer’s specification
    • Prepare the panel to the customer’s panel drawing
    • Check for panel stability
      • Check routing or V-cut positions
      • Check break-tab positions and add more if needed for panel stability
  • Panelisation done by the Customer
    • the customer supplies fully panelised Gerber data
      • Check for panel stability
      • Check routing or V-cut positions
      • Check break-tab positions and add more if needed for panel stability
  • Save job

Final Check

  • Build a new netlist from the current data and check it against the reference netlist saved immediatly after the customer data was loaded.
  • If there are any differences between the two netlists, find the reason for it and correct when necessary.
  • Check each copper layer against its original data
  • Some differences are caused by our actions to make the board easier to produce, ignore them and find out where all other difference originate from and repair if needed.
  • If there are no more errors:
    • zip the job data
    • upload it to the system to allow for the next stage in the preparation process to begin

A second engineer now runs a series of checks to confirm that the production data matches:

  • the customer’s order and his other instructions
  • the specifications of the chosen Eurocircuits service

If there are any errors, these must be corrected. When the data is confirmed as correct, it is passed on to the next stage where it will be placed on a production pooling panel. We will bring this story shortly.