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Milling of PCBs?
I wonder if anyone here has experience of milling PCBs using
CNC rather than etching them, and if so, what pitfalls and pratfalls were encountered? |
#2
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Milling of PCBs?
On Wed, 27 May 2015, gareth wrote:
I wonder if anyone here has experience of milling PCBs using CNC rather than etching them, and if so, what pitfalls and pratfalls were encountered? No, but I have done boards at times using a Dremel tool and a cutting bit. It worked better for discrete components than ICs, it being easier to make larger "pads", and I'm not certain just building over the circuit board is all that worse. You have to use a light touch, press too hard and maybe you cut through the board, don't press hard enough and you may not isolate the "pad" enough. Obviously if you have a CNC, you can do much finer work. I don't really see why subtracting via cutting is all that different from subtracting via etching, though if making multiple boards, you make the layout and can etch the boards at the same time, while with a CNC, you have to do one at a time. Michael |
#3
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Milling of PCBs?
On 5/27/2015 7:29 AM, gareth wrote:
I wonder if anyone here has experience of milling PCBs using CNC rather than etching them, and if so, what pitfalls and pratfalls were encountered? Years ago a place I worked had one of the machines that cost a few thousand. It wasn't great as they hadn't provided a good base so the board could be inserted multiple times with the same registration or easily flipped for double sided. The bits were conical rather than flat tipped and tended to break easily. In the end the company went belly up and we were stuck with proprietary software that was no longer maintained. The only people who really used it much were the RF guys... Some in s.e.d use a mounting technique of soldering bits of double sided PCB onto a board of copper clad as soldering islands. No etching needed. Not the greatest appearance, but it is very fast and simple to make and you do have a decent ground plane even if you don't have good impedance controlled runs... maybe. I expect you could find a wire with the appropriate thickness insulation for a given impedance and glue it to the copper clad. Think microstrip. -- Rick |
#4
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Milling of PCBs?
In article , rickman wrote:
On 5/27/2015 7:29 AM, gareth wrote: I wonder if anyone here has experience of milling PCBs using CNC rather than etching them, and if so, what pitfalls and pratfalls were encountered? Years ago a place I worked had one of the machines that cost a few thousand. It wasn't great as they hadn't provided a good base so the board could be inserted multiple times with the same registration or easily flipped for double sided. The bits were conical rather than flat tipped and tended to break easily. In the end the company went belly up and we were stuck with proprietary software that was no longer maintained. The only people who really used it much were the RF guys... There are still fast-prototyping PCB milling machines which do this. They don't seem to have a really big market - "quick turn" fabrication houses are plentiful and are usually quick enough. In-house milling seems to be mostly for "We've gotta have this *today*" applications, or for the occasional situation where one is too afraid of having the details of the PCB "leak" to a competitor before the product comes out. From what I've heard, one of the problems with this approach is that milling the copper off of the PCB isn't a trivial problem. Copper is soft and flexible enough that it can tend to clog the bit, or stretch-and-tear rather than milling off of the substrate cleanly. Some hobbyists do it with (e.g.) Zen CNC systems, or Dremel-based CNCs, etc. I know there's software out there which can read in a Gerber file, and produce a file of G-code commands which will mill out an isolation zone around each trace or area plotted by the Gerber. As with an etched PCB, you'd want to fill as much as possible of the unused space with ground plane (or unconnected fill zones) so that you don't end up having to mill away lots of copper. Using carbide bits would (I think) be essential - high-speed steel probably won't stand up to FR4 for very long. |
#5
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Milling of PCBs?
On 27.5.2015 14:29, gareth wrote:
I wonder if anyone here has experience of milling PCBs using CNC rather than etching them, and if so, what pitfalls and pratfalls were encountered? I have experimented some pcb milling, using desktop CNC with working area slighly larger than A4-paper. Smallest SMD components were 0603 size, using v-shaped engraving bits of 0.1mm tip diameter. Needs two softwares, first one to design the pcb and second phase is to convert this to cnc code. This takes some time as the cutting procedures are adjustable to each line on pcb desing. The need to adjust hole sizes, viases, layers, line widths depend on pcb, more complex designs take more time also preparing time for cut and transfer to individual cutting files with different tools used. Some re-design is needed sometimes between pcb-design and cnc-prepare as cutting width is constant. This two-phase is one way to do all, some sw packages do both phases internally and the pcb design is directly what is actually cut, this may sometimes be less optimized for cutting time spend. So software selections need some evaluation depending on the actual needs. Third sw is needed to finally control the cnc-cut described in the tool path files prepared in two previous phases. Most difficulties are keeping pcb material exactly flat on milling base plate, use of vacuum plates might benefit, but this needs extra accessories like vacuum pump etc. so this isn't choice for occasional use. CNC machines are like cars, some of them have automatic tool changers, some don't, some automation speeds much the time spent on tool changing between cuts, though by increased price level of the cnc-mill. CNC is ok for prototyping or limited small amount of pcb's, as pcb markings and specific solder layers are not simple to add to milled plate. Commercial processing is done using more sophisticated means and machinery so all these comments don't apply to them. To sum briefly, most of the time around 50..70% of time is spent on describing pcb-files and preparing them to cnc code. Actual cut is 10...20% of time used. |
#6
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Resolving AM and FM if a very narrow Xtal filter
Ian Jackson wrote on 2/2/2014 3:46 PM:
On 5/27/2015 7:29 AM, gareth wrote: I wonder if anyone here has experience of milling PCBs using CNC rather than etching them, and if so, what pitfalls and pratfalls were encountered? Years ago a place I worked had one of the machines that cost a few thousand. It wasn't great as they hadn't provided a good base so the board could be inserted multiple times with the same registration or easily flipped for double sided. The bits were conical rather than flat tipped and tended to break easily. In the end the company went belly up and we were stuck with proprietary software that was no longer maintained. The only people who really used it much were the RF guys... Yeah, a place I worked had one of these, likely the same company as theirs went belly up too. RF guys use double sided often if not always. Digital stuff often needs more layers. The island breadboard approach is even more limited being effectively single sided and entirely unsuitable for any type of high density packages. So again, mostly used for RF type of designs. -- Rick C Viewed the eclipse at Wintercrest Farms, on the centerline of totality since 1998 |
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