FENG EDWARD (CN)
| US5332341A | 1994-07-26 | |||
| EP0588244A2 | 1994-03-23 | |||
| US4529340A | 1985-07-16 | |||
| CN201552324U | 2010-08-18 | |||
| JPH033713A | 1991-01-09 | |||
| CN202087453U | 2011-12-28 |
| CLAIMS What is claimed is: 1. An apparatus for cooling a drill bit, comprising: a housing having an open ended chamber therein which extends through the housing for receiving the drill bit, a first passage for providing a cooling substance to the chamber to cool the drill bit, and an outlet in communication with the chamber and through which the drill bit can extend for drilling. 2. The apparatus of claim 1 , further comprising a pipe extending through the first passage for providing the cooling substance into the chamber. 3. The apparatus of claim 1 , further comprising a second passage in communication with the chamber for exhausting atmosphere and particulate matter from the chamber. 4. The apparatus of claim 3, further comprising an exhaust pipe in communication with the second passage. 5. The apparatus of claim 1 , further comprising a spacer member having a hole therethrough, the spacer member sized and shaped for being disposed adjacent the housing with the hole in registration with the outlet. 6. The apparatus of claim 5, wherein the spacer member is manufactured from a material selected from the group consisting of metal, plastic, and a composition having a hardness greater than a hardness of the housing. 7. The apparatus of claim 1 , wherein the cooling substance is selected from the group consisting of carbon dioxide (CO2), nitrogen (N2), and a combination of C02 and N2. 8. The apparatus of claim 2, further comprising a nozzle connected to an end of the pipe and positioned in the chamber for spraying the cooling substance to contact the drill bit. 9. The apparatus of claim 8, wherein the nozzle comprises an inner tube through which C02 is provided and an outer tube surrounding the inner tube and through which N2 is provided. 10. The apparatus of claim 9, wherein the inner and outer tubes are co-axial. 1 1 . The apparatus of claim 1 , further comprising a pump in fluid communication with the cooling substance for pulsing said cooling substance into the chamber. 12. The apparatus of claim 1 , wherein the housing is formed from a material selected from the group consisting of metals and plastics. 13. A method of cooling a drill bit, comprising: receiving the drill bit in a chamber of a housing; providing a cooling substance to the chamber for cooling the drill bit; and containing the cooling substance in the chamber. 14. The method of claim 13, wherein the providing the cooling substance occurs after drilling with the drill bit. 15. The method of claim 13, further comprising exhausting the cooling substance from the chamber. 16. The method of claim 13, wherein the providing the cooling substance comprises pulsing the cooling substance into the chamber at select intervals. 17. The method of claim 13, wherein the cooling substance is selected from the group consisting from C02, N2, and a combination of C02 and N2. 18. The method of claim 17, wherein providing the combination of C02 and N2 comprises providing a first stream of the C02 and a second stream of the N2 adjacent the first stream to the chamber. 19. The method of claim 18, wherein the first and second streams are co-axial. 20. The method of claim 13, wherein the containing the cooling substance comprises sealing the chamber of the housing from atmosphere external to the housing. |
CIRCUIT BOARDS
SPECIFICATION
[0001] The present embodiments relate to apparatus used to drill holes in printed circuit boards.
[0002] Most types of printed circuit board (PCBs) for the electronics industry consist of a plurality of layers, both resin layers and metal layers. Manufacturers of PCBs are required to drill a myriad of holes in each board. The holes are then copper plated at an interior thereof, and the copper functions as connectors between the plurality of layers of the board. During the drilling process, the resin layers of the PCB are heated and can be "smeared" over the copper layers in the holes, thereby preventing electrical contact among the layers after the copper plating. The resulting "smear" in the holes must therefore be removed before the plating process. This results in additional, unwanted processing time of the PCBs.
[0003] Heat is generated during the cutting and grinding process which occurs during PCB drilling. The temperature from the drilling can be as high as 300° Celsius. The smear that is produced from the drilling at all sides of the hole is caused by the hot drill bit melting the epoxy of the resin layers in the PCB material. In addition, the drill bit begins to wear out from repeated use and the worn bits have a tendency to worsen the smearing that occurs. One way to reduce the smearing is to correspondingly reduce the speed of the drill, but this reduces the efficiency and the effectiveness of the drilling and the assembly line process for the PCBs. Economies of scale dictate that drilling faster is more economical, even if it is required to remove the smear thereafter.
l [0004] It would therefore be desirable to have an apparatus which can be used with the drill to avoid the smearing, but does not sacrifice speed of the drilling process.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] For a more complete understanding of the present embodiments, reference may be had to the following description taken in conjunction with the drawing Figures, of which:
[0006] FIG. 1 shows an apparatus embodiment of the invention for cooling a drill bit; and
[0007] FIG. 2 shows a nozzle for the apparatus embodiment of FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
[0008] The apparatus embodiment shown in FIG. 1 is shown generally at 10 and is used in association with a drill for which a spindle 12 is shown.
[0009] Attached to a spindle 12 of a drill is a drill bit 14 used to drill holes in for example printed circuit boards (PCB) 16. It is understood that the drill bit 14 can be used to drill holes in other objects and articles of manufacture.
[0010] The apparatus 10 includes a pressure cover 18 or housing having a side wall 20 defining an open ended chamber 22 or space. The spindle 12 can be connected to the pressure cover 18 by mechanical fasteners such as screws for example. The pressure cover 18 may be manufactured from metal or plastic. The chamber 22 is open ended at two sides as shown in FIG. 1 , and is sized and shaped to receive the spindle 12 and the drill bit 14. As shown in FIG. 1 , the chamber 22 is constructed with a step 23 having a diameter less than that of the chamber to receive the spindle 12 to a certain depth within the chamber, the depth being commensurate with the portion of the drill bit 14 that will drill through and penetrate the PCB 16. In effect, the chamber 22 and a lower portion 24 of the cover 18 coact to restrict the downward movement of the spindle 12 in the open ended chamber 22. A lower portion 25 of the chamber 22 is sized and shaped to receive the drill bit 14 and to be positioned in registration with an area of the PCB 16 that is to be drilled.
[0011] A spacer member 26 or insert is disposed adjacent the housing and, as shown, between a bottom surface 28 of the side wall 20 and an upper surface 30 of the PCB 16. The spacer 26 may be formed as part of the pressure cover 18. During drilling the spacer 26 supports a head of the drill as the bit 14 drills through the PCB 16. During certain applications when the pressure cover 18 and the spacer 26 are positioned for drilling, the spacer can form a hermetic seal so that the chamber 22 is sealed off from the atmosphere external to the pressure cover and the PCB. The spacer 26 may be manufactured from metal or plastic, but usually from a material harder than the material from which the cover 18 is manufactured.
[0012] The pressure cover 18 includes ports or passages in the side wall 20. A first port 32 or passage in the side wall 20 is for introducing a cooling substance into the open ended chamber 22. A second port 34 or passage is for exhausting or venting the atmosphere and any particular matter from the chamber 22 through for example an exhaust hose 36.
[0013] Referring to the first port 32, a gas pipe 38 may be extended through the first port and include an end portion 40 terminating in the chamber 22 proximate the drill bit 14. Carbon dioxide (C0 2 ) 42 can be introduced from a remote source (not shown) through a pipe 44 which is connected to the gas pipe 38. A valve 46, flow meter 48 and a pressure meter 50 for the gas are in fluid communication with the pipe 44. The valve 46 is disposed upstream of the flow meter 48, and the flow meter is disposed upstream of the pressure meter 50, all of which are disposed upstream of the pipe 38.
[0014] The C0 2 42 is provided as liquid C0 2 so that it changes phase to gas and solid (dry ice) during its passage through the gas pipe 38 to be injected from the end portion 40 of the pipe. The C0 2 can be jetted or pulsed as a spray 45 into the chamber 22. The end portion may include a nozzle. With the pressure drop along the pipe 38, the liquid C0 2 will change to a mixture of gas and solid, and the solid will eventually change to gas as well. The C0 2 gas cools the drill bit 14. The spindle 12 rotates at a very high velocity in order to propel the drill bit 14 through the PCB 16. The cooling occurs during the period of time when the drill bit 14 is withdrawn or retracted from a hole it has just drilled in the PCB 16. This is because the drill bit 14 is exposed to the cooling gas in the chamber 22. The holes in the PCB are small and are drilled in a fraction of a second. That is, when the drill bit 14 is retracted or removed from the hole it just drilled in the PCB 16, the bit is immediately exposed to gaseous carbon dioxide to cool the bit so that it is at a reduced temperature for the next hole to be drilled, thereby reducing the chance that melting and smearing of the epoxy will occur in the resin layers. By way of example only, a temperature in the chamber 22 is from -10°C to 5°C due to use of the C0 2 .
[0015] The liquid carbon dioxide can be pulsed if necessary and the jet of coolant C0 2 aimed directly at the drill bit. In effect, the drill bit is cooled when it is withdrawn so that it is at a reduced temperature for the next drilling operation, thereby preventing frictional heat from building up to melt the epoxy of the resin board. Alternatively, the pulsing of the C0 2 to contact the drill bit 14 can occur as soon as the drill bit is withdrawn from the hole and until such time just before the drill bit commences drilling the next hole in the PCB 16. To provide the pulsing of the C0 2 , a pump 43 for the liquid C0 2 is used. The pump 43 is in fluid
communication with the pipe 44, and can be upstream of the valve 46. The pump 43 can be timed to provide pulsed bursts of the C0 2 to the chamber 22, or the pump can be controlled by a signal transmitted from the drill 12. That is, when the bit 14 is being retracted from the PCB 16 the drill can transmit or trigger a signal to the pump 43 to provide the C0 2 to the chamber 22. The C0 2 injection cycle can also begin with a pulse of liquid C0 2 commencing when the drill bit 14 contacts the PCB 16 and is stopped when the drill bit is withdrawn from the PCB.
[0016] Alternately, the spray 45 can be continuously provided as a spray, pulsed stream or jet, to the chamber 22. However, the drilling of the PCB 16 will usually prevent the C0 2 from entering the drilled hole to cool the bit 14, until such time as the bit is withdrawn from the hole. Therefore, providing the C0 2 to the chamber 22 may be done only when the bit 14 is not actually drilling the PCB 16 in order to conserve the C0 2 . That is, providing the C0 2 to the chamber 22 during the drilling is not detrimental to the drilling procedure or the PCB 16; but it will result in using more C0 2 .
[0017] Referring to FIG. 2, another type of nozzle 52 is shown to be mounted to the end portion 40 of the pipe 38. In this nozzle 52, also referred to as a coaxial tube nozzle, gas or liquid C0 2 54 is introduced into an inner tube 56, while nitrogen gas 58 (for example at 3 bar) is introduced into a pipe branch 60 which is in communication with an outer tube 62 or pipe for the nitrogen. The inner tube 56 is disposed within the outer tube 62. The C0 2 54 and nitrogen 58 flow along the nozzle 52 such that the nitrogen is external to and in certain
applications shrouds the carbon dioxide 54 when the gases exit the nozzle to be provided to the drill bit 14. The nitrogen will reduce the moisture condensation at the drill bit 14 and on the PCB 16. The inner tube 56 and outer tube may be coaxial. The pipe 38, the nozzle 40 and the co-axial nozzle 52 can be
manufactured from stainless steel.
[0018] The present embodiments reduce the smears which occur with known drilling apparatus and eliminate the subsequent de-smearing process which is necessary for same. The present embodiments also reduce wear of the drill bit 14 and prolong its working life. The surface of the holes drilled in the PCB 16 are rendered more smooth and drilling speed is increased because overheating of the drill bit and smearing is substantially reduced.
[0019] It will be understood that the embodiments described herein are merely exemplary, and that one skilled in the art may make variations and modifications without departing from the spirit and scope of the invention. All such variations and modifications are intended to be included within the scope of the invention as described and claimed herein. Further, all embodiments disclosed are not necessarily in the alternative, as various embodiments of the invention may be combined to provide the desired result.