RE: Re: Plotters for application of Etch resist

I have made hundreds of single sided boards from 1 square inch to 48 square inches on my plotter. I have done this for almost 10 years. I am now in the process of considering other methods because of the time it takes, (however it is much easier than many other methods for making PC boards).

In my collection of Plotter board designs, I have 32 different power supplies, 6 computer parallel port interface drivers, a multitude of timers, relay drivers, alarm circuits, etc. I have done several double sided boards when the top layer is Ground (only). I must say, it has been an amazing tool and I have used it to the point of wearing it down to the nub.

I began developing this method around different kinds of pens. I built some special pen holders for my plotter so that I could put all sorts of pens in the plotter. I had some success, and might have found even more success if I had continued to improve on the types of pens and inks used, but I took a left turn and never went back. I have heard of some who have had success but was happy with my odd method. I also never needed to figure out the plotter commands necessary to make (full on) double sided boards on the plotter, but believe it can be done without a great deal of trouble.

I also have discovered that "machining thin sheets of copper in the plotter and etching out the shapes is a pretty cool way of making a great deal of other things, for instance small components for clocks. It is a fair way of making small slits for optical devices. As it turns out a plotter is pretty accurate and very repeatable. When making small parts in the plotter, I use a small basket in the etcher so that the small parts do not fall out into the acid in the etch tank.

The Method: I spray paint on the copper board (or thin sheet of copper). I let it dry.
I then install an 8-1/2" x 11" stiff piece of paper in the plotter.
I then install a plotter pen in the plotter and draw a board outline on the paper in the plotter.
I then tape the painted PC board or thin sheet of copper to the paper using the outline as reference.
Next I install a special holder, holding a scribe in the plotter pen holder.
In the PC Development programs I use, I have a special layer called "Scribe" which is in all of the pad stacks, and will draw a little drill punch mark in the center of each pad in the design. The acid will make enough of a mark so that the drill will center on every pad in the drilling process. After I complete the board layout, I draw 20 mill lines around the traces of the solder side of the board. When I write the plot file to disk, I turn off the the trace layers and turn on the "scribe" layer. What I get is 20 mill lines where I want to seperate conductors and drill marks to aid in the drilling process. I can make the line width as small as 10 mill, or as large as I want for high voltage clearance where required. The method doesn't waste much acid because I am scribing off a minimum of copper to get the job done.

In practice, I have found that sometimes to help in the soldering process, it is a good idea to scribe two lines near any hole which has so much copper around it that the soldering Iron can't heat up the area very quickly. It is also a good idea to either solder plate the raw copper or conformal coat the finished assembly to keep the copper from corrosion. To solder plate the copper, I put flux on the board and run a little solder on the iron around the board. There is a lot of copper, so I usually conformal coat the board after all componts are in place (especially with large boards).

The kind of paint and the thickness of paint used makes a big difference. Enamel paint is too hard. Lacquer paint works pretty well, but every year they make paint better and more envirnomental friendly, but for the most part it is not too crytical. In practive, I re-run the scribe step in the plotter a second or a third time if I don't see copper where I want to see copper. It helps to use black paint for this inspecition process. I have had sucess with clear coats, but it is difficult to see that a clear coat has been properly scribed off.

The scribe I use is carbide and I can adjust the height of the scribe in the adaper I built. It remains sharp over many boards. After 10 hours of use I grind a new point on it, but I have never had any trouble with it. If you set it too low in plotter it will trip over the board edge, but I built a gauge for setting the height and have never had any trouble. Essentially, whatever you want etched away, the scribe will expose it and the acid will eat it. It works very well... but I am ready to improve the method to see if I can eliminate a few steps.

This is why I am interested in wire edm. When I ask for peoples comments about wire edm, I got some interesting information, but no one described how wire edm might apply in a method where the wire itself is used in a "blind" hole, or is not supported on both ends of the wire. I think you know where I'm going with this. Edm works pretty well when it comes to removing copper, but under the copper is fiberglass, and feeding an 8 mill wire into fiberglass will bend it. The thickness of the copper is quite uniform, so the idea is that the smarts of the system need only manage the wire through one or two mills of copper, and by knowing where the copper starts, the consumption of the wire, and the other factors, it may be possible to make PC boards without Acid. Two sided boards should be easy enough.

Most of the CNC desktop PC mills take gerber files and make boards. A low end unit goes for about $15,000 and if you want tool changers it heads up in the area of $50,000. CNC desktop PC mills will drill all of the through holes for you. A wire edm will not drill holes in fibergalss, so you are stuck with a drilling operation. Naturally plated through holes are outside of all of this.

I wonder if a PC board prototype machine based on EDM could be built for a reasonable cost, since the machine does not need to be as heavy and rigid as a milling machine? The "smarts" are not expensive, and the spark power supply (modulator) is not as large as other EDM machines.

However, I am interested in other concepts for clean and simple ways of making boards. I know about the photo coppier method, but have not had much sucess with it. I will have a CNC mill later this year and wonder if anyone knows of a gerber to CNC mill package, which might allow anyone to make boards on any CNC mill from the Gerber file? Fun stuff.

David Howland








-----Original Message-----
From: Raynor Johnston [SMTP:rhj-rbj@...]
Sent: Monday, October 11, 1999 6:45 AM
To: CAD_CAM_EDM_DRO@onelist.com
Subject: [CAD_CAM_EDM_DRO] Re: Plotters for application of Etch resist

From: "Raynor Johnston" <rhj-rbj@...>

A little bit maybe off subject for this list but will try it anyway...
A number of people have over the years been experimenting by replacing
plotter pens with other pens (steadler lumocolor in particular), etch resist
pens, or simply putting etch ink into plotter pen bodies all in order to
apply artwork direct to metal substrates loaded onto plotter tables.
I have found an Australian fellow who is still doing it with a custom made
plotter he fabricated using hardware from other plotters.
My questions...has anyone on the list any recent experience of this activity
and what pens/inks/plotters etc they are using successfully.
What metals have they successfully worked on.
What etchants did they employ.
thanks
Raynor Johnston (NZ)

Welcome to CAD_CAM_EDM_DRO@...,an unmoderated list for the discussion of shop built systems in the above catagories.
To Unsubscribe, read archives, change to or from digest.
Go to: http://www.onelist.com/isregistered.cgi
Log on, and you will go to Member Center, and you can make changes there.
For the FAQ, go to http://www.ktmarketing.com/faq.html
bill,
List Manager