Isolation Milling vs. Etching
Isolation Milling Statement
Please consider the following as an open minded statement that shall help you at the true starting point to decide how to make your in-house prototype PCBs.
The Bungard CCD was introduced in 1991 to fill the gap of (hand-) drilling, milling and routing of PCBs and Aluminium front panels in prototype labs, but was soon compared to machines from LPKF or T-Tech in terms of “quick” prototyping by isolation milling.
No doubt, this machine is well suited for that technique, and we developped it further to meet particular issues of that application. Anyhow, we do not consider this way of making prototypes to be a professional standard. We say: Only in-house wet processing allows to create circuit boards that really match industry standards.
As a proven matter of fact, even though our machine is one of the fastes of that kind in the world, isolation milling is many times slower and much more expensive than chemical etching. Even more, data preparation and machine operation require that engineers instead of executive staff invest their valuable time.
On the other hand, isolation milling creates boards that differ heavily in their electrical / RF performance, as compared to etched PCBs. This is an important aspect that RF designers do have to consider – and that cannot be overcome with even the highest priced, extremly short living special mill tools.
To say it sharply to the point, isolation milling is a slow, expensive, almost 30 years old attempt to be different by someone who had a paranoia against chemical etching. This technique indeed created strong public interest (and a hand full of competing suppliers), but has never reached industrial acceptance.
I repeat, the machine is well suited for isolation milling, and the cons of that technique are general, not particular to us. Only it seems we are one of the few suppliers in the world that allow you a choice, so we need to inform you that there is a choice!
At any time, you may start making prototypes with the Bungard CCD, but at any time you feel the above statement becomes true for you, please remember: The name Bungard stands for Professional Prototyping by wet processing.
Can I make RF / Microwave circuits by isolation milling?
Yes, you can, but these prototypes will show heavily differentelectrical properties than an industry-made PCB.
Can I use a CNC plotter to create multilayered PCBs?
That is not possible for sure. The inner layers of such a board are too thin (0.2mm). They will be destroyed by the penetration of the isolation milling tool. The air inclusions in the milling channels will cause delamination of the layers under the smallest thermal stress, i. e. during soldering. Why else has this technique never found any acceptance in industry?
Can I do through-hole plating with just the CNC plotter?
That is again big nonsense. We know what you might have been told, but here comes the truth: conductive pastes have a too high electrical resistance. They cannot be soldered, as they decompose under application of heat, and they are mechanically too weak. We understood that LPKF stopped promoting this technique in Europe. Of course, we have optional accessories to use our machine for dispense application, but what we mean there is for example to apply solder creams or SMT adhesives.
Can I place rivets for vias or multilayer PCBs?
No. To connect the inner layers, rivets or pins will not work, as they do not establish the necessary electrical contact to the very thin lateral edges of the 35 µm copper pads.
With the BUNGARD CCD, can I cut a PCB in any shape without using a seperate shear?
Yes, that is one of the applications that we designed it for. You can also mill / route aluminium or other material like plastics or even wood. And please ask our competitors if they have a motor driven Z axis that would allow a defined depth and stroke speed.
How do I mount the boards on the machine?
The Bungard CCD comes with a universal clamp fixture system where you can put your board or your ready-cut front panel in a predefined Zero position. Secondly you are free to prepare any drill base sheet with two or more fixing holes that you may use with reference pins. This way of mounting the boards is essential if you have to mount a board on the machine more than once or if you have to turn it over for double side milling.
Motor driven versus electro-magnetic / pneumatic Z axis
Only with a motor driven Z axis you have control over the actual penetration depth and Z stroke speed, which are both indispensible parameters if you want more than stamping the holes in the board. We understood that LPKF machines cannot even drill / cut deeper than 2 mm, and in absence of a defined drill speed
, we even heard about problems with PTH due to poor wall quality of the drill holes. With our motor driven Z axis you have an active stroke length of more than 30 mm, and the board penetration depth is limited only by the type of tool being used. And if we tell our software to cut 3.0 mm deep with 5 m/min stroke speed, (maybe in 3 iterations of 1.0 mm per turn) then it will cut exactly this depth at that speed, without fiddeling around on mechanical adjustment screws…