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Milling Prototype PC Boards with Roland’s EGX-350 Desktop Engraver Review by Mauro Grassi We take Roland’s EGX-350 CNC milling machine on a test run making fast prototype PC boards. We found it surprisingly good – it can route, drill and cut out a complete PC board quickly, without using chemicals. It lets you move from concept to working prototype in a matter of hours. 18  Silicon Chip siliconchip.com.au When that high-speed bit starts attacking the blank PC board, bits of swarf fly everywhere. Not only for this reason, the Roland has interlocks on the cover to make sure it stays closed – and you stay protected. T here are several options when it comes to making prototype PC boards, whether at professional designer level or in a school, college – or even an advanced hobbyist. One is to send the artwork to a specialist PC board prototyping house and pay for it to be done. While relatively expensive, for many that’s a completely viable option (and one we’ve used here at SILICON CHIP), even though the turnaround will normally be at least 3-5 days. A big advantage of this method is that the board will (usually) be returned to you with all holes drilled, perhaps with a “conformal” protective coating on the copper and solder mask; sometimes even with a silk-screen component overlay. Another option is to etch your own PC boards, using perhaps a photoresist pre-sensitised board and a UV light exposure box. The results can be good but you have to use chemicals and drill the holes manually, neither of which is particularly pleasant. The chemicals are somewhat hazardous and must siliconchip.com.au be disposed of properly. However, the quickest, most hassle free method, is to use a CNC (Computer Numerically Controlled) milling machine. A CNC machine’s head can be controlled precisely using a computer. It functions very much like a plotter but has a spinning head containing either a milling (or engraving) “bit” or a drill. How does it do it? Blank PC board consists of a nonconductive base layer, usually of fibreglass or a resin-bonded paper, onto which is laminated a very thin sheet of copper. In the normal “etched” board, the pads and tracks are protected by “resist” while the areas between them are chemically dissolved away, leaving the tracks electrically isolated from each other. Milling a PC board achieves a similar result but instead of etching, the areas between the tracks are mechanically milled or engraved away, down to the base layer, under the control of a computer. In fact, the software used to create the PC board pattern is usually able to produce the file which can control the CNC milling machine. The CNC milling machine can also drill the holes and cut out the board, even in arbitrary patterns: nonrectangular boards with shaped edges and cut-outs can be made in this way. In this case, it is simply a matter of instructing the bit to cut deeper, right through both the copper and the base layers. The Roland EGX-350 Although normally marketed as a general engraving CNC machine for making signs, panels and the like (which it does well), the Roland EGX350 is adept at making fast prototype PC boards. It is also one of the most affordable CNC milling machines on the market. However, to produce PC boards you will need special software, as the supplied Roland “Engrave Studio” is geared towards general engraving tasks and not PC board manufacture. Although there are cheaper CNC machines on the market, few are suitable for milling PC boards. To be suitable, November 2009  19 Specifications at a glance: Table (work) size:.................. 305(W) x 230(D) mm XYZ-axes travels:................. 305(X) x 230(Y) x 40(Z) mm XYZ-axes drive system:........ Stepping motor – 3-axis simultaneous control Operating speed: X and Y axes: ............... 0.1 to 60mm/second Z axis: .......................... 0.1 to 30mm/second Software resolution:.............. 0.01mm/step or 0.025 mm/step Mechanical resolution: X and Y axes: ............... 0.0025 mm/step Z axis: .......................... 0.00125 mm/step Spindle motor:...................... Brushless DC motor - maximum 50W Spindle speed:...................... 5000 to 20000 RPM Dimensions:.......................... 616(W) x 591(D) x 393(H) mm Weight:................................. 34kg a milling machine with good Z-depth control, mechanical resolution and repeatability is required. Repeatability refers to how accurate the positioning is over many movements. To some extent, contactless laser cutters overcome the problem of having to have good Z-depth regulation – though these are prohibitively expensive. Z-depth control is critical if the milling bit does not have a square section head – if it is conical, for example, a thin track may be cut too much and disappear altogether. Resolution and Backlash The resolution of a CNC machine refers to smallest step the head can move in each of its axes. Good resolutions – of a fraction of a millimetre – can be obtained by using stepper motors, mechanical gears and linear screws (the screw assemblies that convert the rotational motion from a motor into linear motion, such as lead screws or ball screws). As you can see in the specifications panel, the Roland EGX-350 has impressive resolution figures for its price. The repeatability can be adversely affected by backlash. Backlash refers to the unwanted movement in response to a reversal in direction along an axis – it leads to inaccuracies in the head position and can be a problem where high precision is required, as when milling PC boards. This machine uses a proprietary anti-backlash mechanism developed by Roland. Plated-through holes Although it is possible, given some care with placement, to mill doublesided PC boards there is still the 20  Silicon Chip problem of how to connect the two layers together. Naturally, producing plated-through-holes, or “vias”, cannot be achieved by a milling machine. The simplest way around this is to use small (conductive) pins soldered on both sides. This is relatively easy but labour intensive, because each pin needs to be soldered individually. It is therefore more suitable for PC boards with relatively few inter-layer connections. Work area At 393 x 616 x 591mm, the Roland EGX-350 does not take up too much space on a desk. When it comes to making PC boards with a milling machine, you are restricted by the size of the area over which the cutting head runs. In this case, the work area is 305mm by 230mm, which represents quite a substantial PC board. In any case, you can sometimes overcome this problem by breaking up a big design into separate PC board modules. Connections The connections to the Roland EGX350 are accessible at the back, on two sides. Mains power connection is via an IEC socket on the right hand side. The serial, USB and hand controller connections are on the left hand side. The serial or USB connections can be used to connect the Roland EGX-350 to your PC. The hand controller The Roland EGX-350 can be controlled manually using the supplied hand controller. This has a 16 x 2 line LCD display that shows the X, Y and Z coordinates in machine units, as well as a simple menu system. You select a menu and use the arrow keys to navigate through different sub menus. There is also a digital click wheel that can be used to vary the spindle speed between 5000 and 20000 RPM. Every detail seems to have been well thought out in the design of this machine – for example, the hand controller contains no gaps between buttons, so no dust can fall into it. Safety features The Roland EGX-350 has a number of welcome safety features that make it a particularly good choice. The work area is completely enclosed by a durable transparent cover, with microswitches which detect when the cover opens and automatically cut power to the motors. It is possible to manually override the switches with the cover open; for this reason, where required for certain applications (eg schools), the machine can be delivered with tamper-proof micro-switches. The machine also incorporates internal over-current protection which activates if the motors lock up (for example, if you drill into some hard material and the bit becomes stuck). In that case, the current through the motor will rise steeply, which is detected by the driving electronics and the supply to the motor is stopped. You will get a failure message on the hand controller and the only way to proceed is to then reset the machine by turning the power off. The other safety feature is the red kill switch – pressing it immediately cuts all mains power to the machine. This can be used in an emergency to stop the machine instantly. Apart from those features, any running job can be either paused or cancelled using the hand controller. Setting up a job For general engraving work, the machine comes with the Roland Engraving Studio software but as we mentioned earlier, for making PC boards you will need additional PC software – the one we tried is called CopperCAM from Intellecta (see www. galaad.net/coppercam). This Windows software is normally an option but Intellecta will be including it with any Roland EGX-350 purchased from them as a result of this siliconchip.com.au review (make sure you tell them you saw it in SILICON CHIP!) Producing Gerber plots Gerber plots have been traditionally used to control plotters – they are almost universally accepted by PC-board-making houses. For that reason, most PC board design software such as Protel, Altium and Eagle have the facility to produce these and other CAM files. You will need Gerber plots (for each layer) as well as the Excellon drill file. CopperCAM Using CopperCAM, you can import the Gerber plots and the Excellon drill file. You select the layer and compute the contour paths. The drilling coordinates are aligned to the copper tracks by selecting a reference pad on both. You then select ‘adjust to reference pad’ to align the two ‘layers’. Tools You can maintain a tool library for the different tools under CopperCAM. As a minimum, you will need an engraving bit and a drill bit. Each tool will have its own plunge speed and depth. The top speed of the machine is quite fast (see the specifications). But the milling speed affects the quality of the cut: too fast and there will be noticeable burring of the edges along the cut and you may also damage the tool bit. Too slow a speed may well mean a slowly-made board. Different materials and tools have natural milling speeds that are adequate for that application. For making PC boards, Intellecta recommended using paper phenolic PC boards, as these are softer than the typical fibreglass board, and therefore more forgiving on the engraving bit. The engraving bit is made from tungsten carbide, which is a very hard composite but is expensive. The tools will wear out over time and they should be reasonably sharp to obtain a clean cut – especially if many thin tracks, of the order of 15 thou, are on the PC board. It is also possible for the tool bit to break in the middle of an engraving job – the costs of tool replacement can quickly accumulate but experience to some extent circumvents this. The guaranteed life of the tool bit is siliconchip.com.au Part of a PC board milled with the Roland EGX-350 CNC Desktop Engraver – one of many boards we produced. It looks a little different to conventionally etched PC boards because the cuts between tracks actually go a few thou into the base. measured in metres, and therefore it depends on the complexity of the PC boards being milled as to how many such boards can be made with the same tool bit. Setting the Z depth Setting the reference Z depth is particularly important for milling PC boards. The reference Z depth will affect how deep the cut is made into the copper, because the depth set in CopperCAM is relative to the reference depth (which is the point of contact between tool bit and board). The uniformity of the Z depth is especially important for those boards with fine tracks of the order of 15 thou or so (this was the smallest track we were able to route consistently in our testing). You can purchase accessories for this machine including a vacuum table and a T-slot table that may help in achieving this uniformity. But we found that we could get quite good results simply by attaching the board to the supplied base using doublesided tape. Tool Changes Unlike more expensive milling machines with automatic tool changers, tool (bit) change is manual. While automatic changers are convenient, they add substantial cost and are not strictly necessary, especially for prototyping PC boards. CopperCAM allows you to mill each layer separately, then the engraving bit can be changed to a drill bit and the holes drilled. Drilling the Holes Drilling is particularly easy, with various options in CopperCAM. You can select one drill bit for all holes – irrespective of the hole sizes embedded in the drill file. This is a good option to minimise the number of tool changes, which is time consuming and delicate, as the Z depth needs to be set every time a tool is changed. If you do not wish to use different tool bits for differently sized holes, CopperCAM also has an option to use a single drill bit to make different hole sizes by circular boring. This is where the machine makes the hole by moving the head around the centre of the hole. However, this can lead to many broken drill bits if not set up properly and is obviously harsher on the drill bits. In any case, for many PC boards, the best way is to use a single drill bit for all holes and enlarge the holes manually as the need arises. This is the method we preferred, using a single 0.7mm drill bit. Most standard components such as resistors, capacitors, transistors, diodes and integrated circuits will usually fit through this size hole. Larger hole sizes, like those for TO-220 packages can then be drilled manually using a drill press. Isolation Rub-outs The quickest way to engrave the PC board is if the software creates a minimum isolation path around tracks – in other words, it leaves as much “dead copper” (copper which is not connected to the circuit) on the board as possible. There may be legitimate reasons for removing the ‘dead’ copper, however, such as electrical considerations, ground planes, inter-track capacitance or perhaps simply to make assembly easier. November 2009  21 This shot shows the large piece of MDF we used as a base (complete with drill holes from an earlier produced board). It’s very important that the blank PC board is flat and level due to the tight tolerances used in milling and drilling. It is not hard to get solder bridges between a pad and an adjacent area when the only isolation is a single thin strip of missing copper. Rub outs, although more time consuming and causing greater wear on the tool bits, help reduce the chances of solder bridges. Conclusion We tried this machine over a period of days. In that time we were able to manufacture a number of PC boards with consistently good results. We were able to go from the electronic concept conceived in the morning to having a finished and working PC board by late afternoon – this involved not only designing the PC board on computer but also writing firmware, as the designs used a microcontroller. Using a milling machine to manufacture PC boards, especially singlesided PC boards, is by far the most convenient and quickest method of production. However, convenience costs: milling machines are not cheap. This one, however, should certainly be affordable for designers but also fit within the budgets of educational institutions and perhaps even for ad22  Silicon Chip vanced hobby use – especially when you consider that it can do much more than produce PC boards. Admittedly, the outlay involved in purchasing a machine such as this could buy you many PC boards from your local board maker. However, it is the convenience of a very short turnaround, coupled with the ability to test concepts on-the-go that make a milling machine attractive for situations that may require several iterations of boards. Of course, apart from the initial capital outlay to purchase the machine, there is the ongoing cost of consumables. This includes the tungsten carbide engraving tool bits, the collets, the drilling bits and the blank copper board. The bits wear out over time and will need regular replacement. They sometimes break too! But if you chose the alternative photo-etching route, you’d also be up for the cost of pre-sensitised PC board, the chemicals required, drills and so on. And you’d certainly take a lot longer coming up with a finished board. Simply put, we believe the Roland EGX-350 is one of the best CNC ma- chines for making PC boards in its price range. Price The Roland EGX-350 costs $8795 (inc. GST) and can be purchased direct from Intellecta Technologies. Intellecta Technologies supply the engraving tools for PC boards as well as drill bits, collets and services of interest to the education sector, specifically relating to PC board prototyping, including the CopperCAM software. Acknowledgement Our thanks to Dr Tony Pugatschew from Intellecta Technologies and Roland DG Australia for their technical assistance in this review. Contacts Intellecta Technologies 51 George Street Thebarton SA 5031 Phone: (08) 8351 8288. Website: www.intellecta.net Roland DG Australia Unit 14, 25 Frenchs Forest Road Frenchs Forest NSW 2086 Phone: (02) 9975 0000 Website: www.rolanddg.com.au SC siliconchip.com.au