How much do you know about PCB Print Circuit Board Carbide Micro Drill Bits？
1.PCB drill bit types：
Drills for printed board drilling include straight shank twist drills, fixed shank twist drills and fixed undercut drills.
Straight shank twist drills are mostly used for single-head drilling machines. Drilling simple printed boards or single-sided boards.It is now rarely seen in large circuit board production plants,The drilling depth can be up to 10 times the drill diameter.
In the case where the substrate stack is not high, the use of the drill sleeve can avoid the deviation of the drill.At present, most manufacturers use CNC drilling machines, and CNC drilling machines use fixed shank drill bits of carbide, which is characterized by the ability to automatically replace the drill 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 flute, the diameter of the drill bit is an inverted cone, the friction with the hole wall during drilling is small, and the drilling quality is high. Common drill shank diameters are 3.00mm and 3.175mm
- PCB drill bit common nouns：
①Back Taper: refers to the constant reduction of the drill bit diameter along the length of the drill body.
②Band land clearance (Body Land Clearance): It means that the narrowed part of the blade belt diameter causes a gap behind the blade belt. The size of this depth is determined by the manufacturer
③Carry Out: refers to the rear section of the chip pocket, which is produced by the grinding wheel passing by
④Chamfer Angle: refers to the angle at the end of the drill shank with a diameter of 1/8in, which helps to load and unload the drill bit and reduce the wear of the drill shank on the drill fixture and sleeve
3.PCB drill bit main application:
PCB drills are mainly used for PCB manufacturing: PCB Printed circuit board, which are bonded together by several layers of resin materials, and use copper foil wiring inside.
There are 4, 6, and 8 layers. Drilling accounts for 30-40% of the cost of printed circuit boards, and mass production often requires special equipment and drill bits.A good PCB drill uses good quality cemented carbide materials, with high rigidity, high hole position accuracy, good hole wall quality, long life and other excellent characteristics.
PCB drill bit principle:
The pcb drill bit is a kind of cutting, so the principle is roughly the same as general cutting; generally speaking, there are two calculation formulas widely used in drilling:
1:R.P.M=（S.F.M*12）/π*D
2:I.P.M=R.P.M*Chipload
First introduce the units of the above two formulas:
•R.P.M=Drill rotation speed, revolution/minute, that is, how many revolutions per minute
- F.M=surface cutting speed, ruler/minute, that is, the cutting distance or length of the cutting edge of the drill pin on the board surface per minute
- D: diameter of drill bit
- P.M: Infeed knife speed, inch/minute, how many inches of depth per minute
- Chipload: Infeed amount, ㏕/revolution, how much the infeed depth per revolution is ㏕, and here is a brief introduction to the source of R.P.M=(S.F.M*12)/π*D
In drilling operations, the combination of rotation speed and infeed knife speed has a decisive factor on the quality of the hole wall，which affects the service life of the drill bit and the service life of the spindle spindle .
Generally speaking, from the slice condition of the hole wall, we can roughly see whether the rotation speed and the infeed knife speed are good or bad.If the combination of the two is not good, the hole wall will have roughness, smear, burr ,nail-head, but some factories do not have equipment for hole wall slicing. Is the setting appropriate? Here are some simple ways to distinguish:
- The temperature rise and fall during drilling can be roughly judged from the conditions of R.P.M and Chipload. Generally speaking, when the R.P.M increases, the increased kinetic energy will increase the heat generated by the friction between the drill bit and the wall of the hole. And when the chipload is reduced, the time that the drill bit stays in the hole wall is also increased (heat accumulation is the main factor for the formation of the smear)
- Whether the R.P.M and Chipload used are appropriate is determined from the wear of the drill bit:
- If the physical part of the sharpened WEB is excessively worn, it means that the Chipolad used is too high
- If the cutting lip is found to be excessively worn by the drill verifier, it means that the R.P.M used is too high. The general recommended conditions are as follows:
（1）For double-sided panels, S.F.M is approximately between 500 and 600.
（2）For multilayer boards, S.F.M is controlled between 550 and 600.
（3）Chipolad is set between 2㏕/rev and 4㏕/rev.
5.PCB drill bit characteristic:
①Large space for chip evacuation: small chip evacuation resistance, smooth chip evacuation, small calorific value in drilling, reducing drilling pollution;
②Excellent cutting edge sharpness: due to the use of nanotechnology and advanced grinding technology, the cutting edge of the drill bit is sharper than before, which can reduce the cutting force, reduce the rate of drill breakage, and improve the quality of the hole wall;
③Tools based on customer applications Design: A variety of drill bits can meet different application needs. All parameters of the drill bit, such as core thickness and core taper, have been carefully designed, and the actual effect is obvious;
④The cutting edge is strictly symmetrical: it is beneficial to efficient cutting and avoids drilling deviation.
6.PCB drill bit material:
Drill bits for printed board drilling are generally made of cemented carbide, because the epoxy glass cloth composite copper foil plate wears the tool particularly fast.
The so-called cemented carbide is made of tungsten carbide powder as the matrix, and cobalt powder is used as a binder to press and sinter. Usually contains 94% tungsten carbide. Because of its high hardness, it is very wear-resistant and has a certain strength, suitable for high-speed cutting. But the toughness is poor and very brittle. In order to improve the performance of cemented carbide, some use chemical vapor deposition of a layer of 5-7 microns of ultra-hard titanium carbide (TIC) or titanium nitride (TIN) on the carbonized substrate to make it Has a 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 migrates inwardly when the drill bit is reground.
There is also a physical method to generate a layer of diamond film on the top of the drill bit, which greatly improves the hardness and wear resistance of the drill bit.
The hardness and strength of cemented carbide are not only related to the ratio of tungsten carbide, but also to the particles of the powder.
The ultrafine particles of cemented carbide drills have an average size of tungsten carbide grains below 1 micron. This kind of drill has not only high hardness but also improved compressive and flexural strength.
In order to save costs, many drill bits now use a welded shank structure. The original drill bit is made of cemented carbide. The rear drill shank uses stainless steel. The cost is greatly reduced. However, due to the different materials, its dynamic concentricity is not as good as the overall hard. Alloy drill, especially in small diameter
Precautions:
1. The drill bit should be packed in a special packaging box to avoid vibration and collision.
2. When in use, the drill bit should be installed in the spring collet of the spindle or the tool magazine for automatic drill bit replacement when the drill bit is taken out of the packaging box. Put it back in the box immediately after use.
3. To measure the diameter of the drill, use a non-contact measuring instrument such as a tool microscope to prevent the cutting edge from contacting the mechanical measuring instrument and being scratched.
4. Some CNC drilling machines use a positioning ring. Some CNC drilling machines do not use a positioning ring. For example, the depth positioning when installing the positioning ring must be accurate. If the positioning bit is not used, the elongation of the drill bit to the main shaft must be adjusted. Consistent, multi-spindle drilling machine should pay more attention to this point, so that the drilling depth of each spindle should be consistent. If it is inconsistent, it may cause the drill bit to reach the table or fail to penetrate the circuit board and cause scrap.
5. Normally, you can use a 40x stereo microscope to check the wear of the cutting edge of the drill.
6. Always check the concentricity of the spindle and the spring chuck and the clamping force of the spring chuck. If the concentricity is not good, it will cause the drill with a small diameter to break and the hole diameter is large. If the clamping force is not good, the actual speed and The set speed does not match, and the chuck and the drill bit slip.
7. The clamping length of the fixed shank bit on the spring chuck is 4 to 5 times the diameter of the drill shank in order to clamp it firmly.
8. Always check the spindle presser foot. The contact surface of the presser foot must be horizontal and perpendicular to the main shaft, and should not be shaken to prevent drill breakage and deviation holes in the drilling.
9. The dust suction effect of the drilling machine is better. The dust suction air can reduce the temperature of the drill bit. Colleagues take away the dust to reduce friction and generate high temperature.
10. The substrate stack including upper and lower backing plates should be positioned and laid flat in a hole and slot positioning system on the workbench of the drilling machine. The use of adhesive tape is required to prevent the drill bit from sticking to the chip on the tape, which causes difficulty in chip removal and broken drill.
11. When ordering the manufacturer’s drill bit, it is necessary to randomly check whether 4% of it conforms to the regulations when entering the factory. And 100% with a microscope of 10 to 15 times to check for notches, scratches and cracks.
12. The drill bit is reground in time, which can increase the use and regrind times of the drill bit, extend the life of the drill bit, and reduce the production cost and expense. Usually measured with a tool microscope, within the total length of the two main cutting edges, the wear depth should be less than 0.2mm. When regrinding, 0.25mm should be ground away. The ordinary fixed shank drill can be reground 3 times, and the undercut The drill bit can be reground twice. Excessive re-grinding will reduce the quality and accuracy of drilling, which will cause the scrap of finished circuit boards. The effect of excessive refining is counterproductive.
13. When the wear diameter is reduced by 2% compared with the original due to wear, the drill bit is scrapped.