The determination of the machining parameters of PTFE pipes usually depends on the following factors: the type of material (braided, non-braided or ceramic filled, etc.), the ratio of plate thickness to aperture, the glue content of the substrate, the geometric parameters of the drill bit, etc. .
Glass cloth reinforced PTFE sheet is the most commonly used of many PTFE sheets, and it is also the most troublesome material to machine. The hardness of the FR-4 sheet itself supports the glass fiber bundles and prevents the fiber bundles from being pushed into the substrate by the drill bit. The PTFE resin is relatively soft. When the drill bit is not sharp enough or the cutting speed is not correct, not only will it cause drilling dirt, burrs and cause entanglement, but also the glass fiber bundle may be embedded in the substrate or cause fiber tearing, resulting in metal cavity in the hole.
The teflon pipe usually uses a carbide drill with a top angle of 1300C for FR-4 printed boards, which is completely suitable for teflon copper clad laminates or composite teflon multilayer boards, and new drills should be used for drilling. , Generally, the drill bit that has been turned should not be used, and the drill bit should be changed every 1,000-2,000 holes. The typical values of feed and speed for drilling a φ1.0mm hole are: 41mm/sec and 37,000RPM, respectively, and the withdrawal speed is 750in/min. According to experience, lower feed and speed can get better drilling quality, but the size of the aperture, the glue content of the substrate and whether it is wrapped around the knife should also be considered comprehensively.
The upper backing board can be made of 0.3-0.5mm thick phenolic cardboard, and the lower backing board can be 2.3-3.2mm thick phenolic fiberboard. When teflon copper clad laminates are drilled, knife wrapping often occurs. Pay attention to observe the wrapping of each hole diameter, and adjust the dust suction level and drilling speed appropriately. High-quality drill holes should be free of smudges and have very small burrs on both sides of the board. In short, the deburring process can be completely eliminated after optimizing the drilling feed, rotation speed, withdrawal speed, pressure of the presser foot, dust suction level and appropriate upper and lower backing plates. The typical process parameters for profile milling of composite PTFE multi-layer boards are: the feed is 60mm/sec, the speed is 20,000RPM, the upper pad is 0.3-0.5mm thick phenolic cardboard, and the bottom pad is extremely 2.3-3.2mm thick The phenolic fiberboard is milled counterclockwise, and a stack of 1-4 pieces is selected according to the thickness of the printed board.
The shape milling of PTFE sheets often produces burrs. To avoid burrs, in addition to adjusting the process parameters, the correct stacking method is also very important. The surface of the printed board after outline milling should be clean, and there should be no obvious melting burrs on the edge. Otherwise, it should be scraped off with a sharp knife. Be careful not to cut off the copper foil on the substrate and the edge. The microwave circuit has very strict requirements on the accuracy of the wire and the shape. The PTFE tube is a non-polar molecule and has special hydrophobicity. The hydrophobicity makes the material itself not easy to wet, which brings considerable difficulty to decontamination and pitting. There are usually two treatment methods, the first is plasma treatment and the second is chemical solution treatment.
The former requires special equipment, the latter is easier and less expensive, but less effective. We investigated both methods. First of all, it is necessary to use ordinary rigid multi-layer board to wash holes, use alkaline potassium permanganate series solution to clean drill stains, and then use special sensitization and roughening solutions developed by our center for treatment. After the untreated PTFE material of the PTFE pipe is holed according to the conventional hole metallization process, through the hole inspection microscope, we will find that not only the copper cannot be deposited on the pure PTFE material, but it is exposed in the hole. Electroless copper layers also cannot be deposited on the glass fiber heads and glass fiber bundles of the walls. Occasionally, the copper layer will peel off after repeated rework, and the bonding force is not strong. In order to roughen the surface of glass fiber to improve its surface wettability, we developed a new type of roughening treatment solution. To verify the coarsening effect, we conducted a set of comparative experiments.