PCB drill bits are mainly used for drilling and manufacturing printed boards. Generally, the types of drill bits of CNC drilling machines in PCB factories are as follows: straight shank twist drill bit, fixed shank twist drill bit and fixed shank shovel drill bit. Straight shank twist drills are mostly used in single head drilling machines to drill simple printed boards or single panels. Now they are rarely seen in large circuit board manufacturers, and their drilling depth can reach 10 times the diameter of the drill bit. When the substrate stack is not high, the use of drill sleeve can avoid drilling deviation. At present, most manufacturers use CNC drilling machines. CNC drilling machines use fixed shank bits of cemented carbide, which is characterized by automatic replacement of bits. High positioning accuracy, no need to use drill sleeve. Large helix angle, fast chip removal speed, suitable for high-speed cutting. Within the full length of the chip removal groove, the drill bit diameter is an inverted cone, the friction between the drill bit and the hole wall is small, and the drilling quality is high. Common drill shank diameters are 3.00mm and 3.175mm.
Good PCB drill bits are made of high-quality cemented carbide materials, which have excellent characteristics such as high rigidity, high hole position accuracy, good hole wall quality and long service life. Now let’s introduce the material of drill bits: drill bits for PCB drilling are generally made of cemented carbide, because epoxy glass cloth and copper foil wear the tools very fast. The so-called cemented carbide is made by pressing and sintering with tungsten carbide powder as the matrix and cobalt powder as the binder. It usually contains 94% tungsten carbide and 6% cobalt. Because of its high hardness, very wear-resistant and certain strength, it is suitable for high-speed cutting. However, the toughness is poor and very brittle. In order to improve the properties of cemented carbide, some use chemical vapor deposition of a layer of 5 ~ 7 micron extra hard titanium carbide (TIC) or titanium nitride (TIN) on the carbonized matrix to make it have higher hardness. Some use ion implantation technology to inject titanium, nitrogen and carbon into their matrix to a certain depth, which not only improves the hardness and strength, but also these implanted components can migrate inward during bit regrinding. In addition, a layer of diamond film is formed on the top of the bit by physical methods, which greatly improves the hardness and wear resistance of the bit. The hardness and strength of cemented carbide are related not only to the ratio of tungsten carbide and cobalt, but also to the particles of powder. The average grain size of tungsten carbide phase of ultra-fine cemented carbide bit is less than 1 micron. This kind of drill has not only high hardness, but also improved compressive and flexural strength. In order to save cost, many drill bits now adopt welded shank structure. The original drill bit is made of cemented carbide as a whole. Now the drill shank at the rear adopts stainless steel, which greatly reduces the cost. However, due to the use of different materials, its dynamic concentricity is less than that of the overall cemented carbide drill bit, especially in terms of small diameter.
Use of drill bit: 1. The drill bit shall be packed in a special packing box to avoid vibration and collision.
2. When in use, take out the drill bit from the packing box and install it into the spring collet of the spindle or the tool magazine for automatic replacement of the drill bit. Put it back in the packing box after use.
3. Non contact measuring instruments such as tool microscope shall be used to measure the drill bit diameter, so as to prevent the cutting edge from being bruised due to contact with the mechanical measuring instrument.
4. Some CNC drilling machines use locating rings, while some CNC drilling machines do not use locating rings. If locating rings are used, the depth positioning during installation must be accurate. If locating rings are not used, the elongation of the drill bit installed on the main shaft should be adjusted uniformly. Multi spindle drilling machines should pay more attention to this point to make the drilling depth of each main shaft consistent. If it is inconsistent, it may cause the drill bit to drill to the table or unable to drill through the circuit board, resulting in scrapping.
5. At ordinary times, 40 times stereo microscope can be used to check the wear of the cutting edge of the drill bit.
6。 The concentricity of the main shaft and the spring collet and the clamping force of the spring collet shall be checked frequently. Poor concentricity will cause the drill bit with small diameter to break and the hole diameter to be large. Poor clamping force will cause the actual speed to be inconsistent with the set speed, and the collet will slip with the drill bit.
7. The clamping length of the fixed shank drill bit on the spring collet is 4 ~ 5 times the diameter of the drill shank.
8. Always check the spindle presser foot. The contact surface of the presser foot shall be horizontal and perpendicular to the main shaft without shaking, so as to prevent drilling breakage and deviation during drilling.
9. The dust collection effect of the drilling machine is good. The dust collection air can reduce the temperature of the drill bit and take away the dust to reduce the high temperature caused by friction.
9. The base plate stack, including the upper and lower base plates, shall be firmly positioned and leveled in the one hole one slot positioning system on the worktable of the drilling machine. When using adhesive tape, it is necessary to prevent the drill bit from sticking chips on the tape, resulting in difficult chip removal and broken drill.
10. When ordering the drill bit from the manufacturer, spot check whether it 4% meets the requirements during incoming inspection. The notches, scratches and cracks were 100% examined with a 10 ~ 15 times microscope.
11. Timely regrinding of the bit can increase the use and regrinding times of the bit, prolong the service life of the bit and reduce the production cost and expense. Usually measured with a tool microscope, the wear depth within the full length of the two main cutting edges shall be less than 0.2mm. 0.25mm shall be removed during regrinding. The ordinary fixed shank bit can be reground 3 times, and the under cut bit can be reground 2 times. If the grinding is too much, the drilling quality and accuracy will be reduced, resulting in the scrapping of the finished circuit board. Excessive regrinding is counterproductive.
12. When the drill bit is worn and its wear diameter is reduced by 2% compared with the original, the drill bit shall be scrapped.
13. Setting of drill bit parameters in general, the manufacturer provides a parameter table of the drilling speed and down speed of the drill bit produced by the factory. This parameter is only a reference. The actual process personnel should obtain a drill bit speed and down speed parameter in line with the actual situation through actual use. Generally, the actual parameters are different from the reference parameters, but the difference is not too much.
At present, there are many manufacturers of drill bits, including domestic and imported. There is a slight gap between domestic products and foreign products. Of course, the price of imports is also slightly expensive. There are also bits produced in Taiwan and Hong Kong, and some bits produced in Taiwan to play American and European brands. In contrast, the quality of bits imported from Europe, America and Japan is stable. Although the price is slightly expensive, it is worth it for craftsmen, In the actual use process, the probability of bit quality problems is very small. For example, the product requirements are high. It is recommended to use imported bits. The hardness of bits in Europe and America is higher, while that in Japan is softer. Bits in Europe and America prefer to bend rather than bend. It is not easy to deviate from the hole in use, but the probability of breaking is higher, Japanese drill bits have good flexibility and are not easy to break, but drilling holes are prone to deviation, especially small drill bits. In the process of actual use, it can be selected according to needs.