Under the right circumstances lasers are the perfect solution for cutting the shields precisely and reliably from shielded cables. Laser shield cutting works because fiber lasers emit near infra-red light that is strongly absorbed by metallic shields, but weakly interacts with polymer insulations and dielectrics. Fiber lasers come in a multitude of varieties, but the laser parameters have to be very carefully chosen for the laser to be suitable for shield cutting. The cutting depth is limited to a couple of thou (50 microns) and hence is not suited to thick shields as may be found on larger (>>30 AWG) cables. The technology works best for the following:
A common method to cut the shield of a micro-coax ribbon cable is to scribe the soldered shield. After the outer jacket is pulled back, the cable is dipped in solder so that the individual braided shields of the coaxial cables becomes a single solid piece of solder. A high speed laser spot is passed over the soldered shield. This removes a small depth of the shield and creates a weakness in the solid soldered shield. This is a robust method as the 1 micron laser light does not cut completely through the shield, meaning that the underlying layers cannot be damaged. The downside is that there is an additional step (soldering) in the process. The Gemini-2 and Gemini–4 are best suited for this method.
Many flat flexible cables (FFCs) are structured with a shielding layer laminated in the cable structure. Sometimes these shield layers are wrapped loosely around the FFC and can be easily cut off. However, in some cable constructions it is necessary to bond the shielding foil to the underlying cable insulation. In this case it is necessary to ablate the shield at high speed with the laser by passing it back and forth over the shield in a grid pattern. Gemini cable shield cutting machines are ideally suited for this application, being able to strip the shield from both sides without removing the cable. The system can also be configured with carbon dioxide laser technology within the same unit allowing the whole cable to be stripped in a single process. The Gemini-4 product is ideally suited to this application.
Foil shields are a popular way of shielding multi-conductor cables. They tend to be made from polyester (Mylar) tape which is sputtered with a metallic layer – usually aluminium. This offers a low cost foil shield that is lightweight and very tough. Such foils are very common in InfiniBand cables where each twin-ax pair is wrapped in this foil shield. The way the foil is wrapped around the cable determines the best stripping method. The foil is covered in metal on only one side. If the foil side faces the dielectric, so that the polyester backing is facing out – it is possible to cut the foil shield with a Mercury stripper. This is very advantageous as the same system can be used to cut the jacket and dielectric. The laser light cuts the polyester backing and reflects from the aluminium foil. This is very convenient as it means the inner dielectrics are protected. Because the metalized layer is very thin (just a few atoms thick) – the foil snaps directly at this cut point making it simple to mechanically peel off the shield.
Infiniband cable utilizes a large amount of shielding with each signal line being wrapped in a metalized Mylar film. For many InfiniBand cable constructions, the Mylar shield can be scribed with a carbon dioxide laser. However, some constructions have a heavier shielding layer. In these cases a 1 micron laser is used to scribe the shield to allow it to be snapped off.