Anyone familiar with high-frequency and microwave-printed circuits understands the sensitive design considerations each requires. Occasionally, you may need to reduce the width of a circuit or conductor when a pad or conductor violates space requirements.
This type of modification is an extremely delicate operation that requires not only the hands of a surgeon but also the use of customized tools specifically designed for the application.
Recently, we faced such a challenge. We were asked to remove a pad section to provide the specified separation between the pad and a nearby conductor.
We normally make such a cut with a standard carbide cutter and a milling machine, but controlling the milling depth would have been difficult on this particular project.
We used a common precision knife to cut and remove the section, but with a twist. We modified the knife blade and placed it into a milling machine. (See Figure 1).
A special fixture to support the board was developed. The modified blade was placed in the knife, and the knife was installed into the collet of the milling machine.
The milling machine was never turned on; it was used to precisely control the knife's movement. You might expect we would cut completely through the entire pad depth on the first pass - not so! If we did, we might have cut too deep, causing a "crazing" of the baseboard material and, thus, damage. Even the slightest penetration of the base material beyond the pad's depth may have caused damage.
Thus, the milling system was set to cut three-fourths of the pad thickness. The final pad material was removed by hand, allowing a more controlled removal without damaging the remaining pad's adhesion. Modifying standard knife blades is not difficult and can be accomplished using grinders and files.
This is a special modification that requires specialized tools and fixtures. A milling machine or similar precision coordinate system is also needed.
