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Source:互联网Author:qyadmin Addtime:2019-11-13 16:39 Click:

Backup board pcb drill holes requirement and method


what is   PCB drill 

       PCB drill  holes can be divided into two categories, one is used for electrical connection between each layers; The other is used to fix or position the components.
 
       technology in PCB manufacturing. the holes are generally divided into three categories, which are blind vias. buried vias and through holes. Blind via located at the top layer and bottom layer surface of the printed circuit board. which used for the connection between surface layer and inner layer.  the depth of the hole is usually not exceed a certain ratio.

       Buried hole refers to connection hole. that located in inner layer of the printed circuit board. buried hole does not extend to the surface of the circuit board. Through holes drilled through the whole printed circuit board. which can used for internal electrical interconnection. or used as a positioning hole to assemble components. Because the through holes. are easier to achieve in the pcb manufacturing process with lower cost. so most of printed circuit boards choose to use it. rather than the other two holes (blind via and buried via).
 
      pcb design, the hole is consist of two parts. one is the drill hole in the center area, the other is the pad around the drill hole. The size of these two parts determine the hole size. in the design of a printed circuit board with high speed and high density. the designers always hope that the holes the smaller the better. so that it can leave more space for circuit layout.

        But the hole size decrease will bring the increase of the pcb fabrication cost, moreover. the hole size is impossible to decrease. because it's limited by the process of drilling and plating. The smaller hole size, the longer drill time required, and the easier off center position. When the depth of hole is more than 6 times of hole diameter. the copper plating process won't guarantee that the hole wall could plate copper . For example, a standard 6 layer PCB with thickness (depth of the hole) about 50 mil. so the PCB manufacturer can provide the smallest hole diameter to 8 mil.

pcb drill holes

Drill PCB Backup board development

       In the early 1990s, due to the low price, high stability, low drilling . and good heat resistance of wood fiberboard it used as a drilling pad. In the mid-to-late 1990s, the type of cover pad used in PCB drilling was also selected to use. another type of metal with a better thermal conductivity. At the beginning, ordinary soft aluminum used. The thermal conductivity of aluminum is much larger than that of resin.

       The largest temperature of the drill can reduced from 2 000 ° C to more than 1 000 ° C.  but its material is too soft. which is easy to cause scratches, which causes the drill to slip. There are abnormalities such as poor hole position accuracy and broken needles. As a result, alloy aluminum cover plates with better processing properties have emerged. and become one of the varieties of cover plates that are still in common use today.

       At the beginning of the 21st century. as the aperture diameter decreased (below 0.3 mm). and the requirements for drilling quality increased, the manufacturers of cover. and pad began to develop and improve the original phenolic resin paper pad products. , density, surface hardness, flatness, thickness uniformity, material, etc. are all improved. At the same time, to solve the problem. that the surface of the alloy aluminum cover plate is too hard and cause slippage. a lubricated aluminum piece has developed.
 
      Depending on the composition of the material. the cover is often divided into four categories: lubricated aluminum. plain aluminum, phenolic paper cover and epoxy glass cover. The bolsters divided into three categories: wooden slabs. wood slabs, and phenolic paper slabs. At present, the domestic use of the cover plate is aluminum, which accounts for 82.2%. the use of the pad is wood pulp board, which accounts for 59.1%.
 
       With the development of high-end, functional and specialization of PCB technology. the cover pad used as an auxiliary material for drilling of printed circuit boards. and is also becoming more refined, diversified and functionalized. The type and quality of the cover pad plays a crucial role in the hole quality. processing efficiency, yield, bit life. and final reliability of the printed circuit board.

Backup board for PCB micro hole drilling requirement

       The general structure when drilling micro-holes of printed circuit boards. that is, the uppermost layer is the cover plate. the middle is the PCB board, and the lower layer is the backing plate. In the modern printed circuit board processing process. to ensure the high drilling quality and drilling efficiency of the plate. the use and correct matching of the cover plate and the pad are particularly important.

      At present. the commonly used cover plates in the industry include: a variety of aluminum sheets. composite aluminum cover sheets, phenolic cover sheets. epoxy glass cloth sheets and cold-punched sheets. common pads include: high-density wood mats, phenolic wood mats Plate. melamine wood mat, phenolic paper mat. high-density fiberboard and aluminum foil composite wood mat.
 
       When drilling micro-holes of printed circuit boards. the pads used should meet the following requirements.  To have proper surface hardness, it can reduce the burrs on the hole surface. and avoid the wear of the drill bit due to excessive hardness. the resin is not included in the composition to avoid Produce drilling. have a large thermal conductivity to conduct drilling heat to. reduce the drilling temperature. have enough elasticity to reduce the resistance during drilling. so that the drill can positioned to improve hole accuracy. At the same time, the stiffness must ensured to avoid the vibration of the drill. So, choosing the right cover is critical to the drilling process.
 
       At the same time, the role of the pad is also crucial. In the PCB drilling process, the pad used located below the plate to machined to protect the plate. and the drill press, drill through the plate and improve the quality of the micropores. To ensure the quality of the hole processing. the backing plate should have good flatness and excellent dimensional tolerance. easy to cut. the surface required to be hard and flat, the inner hole surface. or the drill bit at high temperature, and the drilling should be fine and powdery, easy to discharge. 

PCB backup baord drilling method

 
       In the drilling of printed circuit boards to. provide apertures necessary for passing component leads therethrough. and for attaching the boards in place, a problem has encountered. in that a burr produced on the periphery of the aperture. where the drill exits from the copper-clad surface. Such a burr is unacceptable in view of the fact that it forms a dam-like condition during through hole. plating which can entrap contaminants or air. this often later resulting in cracking of the through hole plating. and a resultant electrical failure.

      Such burrs thus must removed, either by a separate sanding operation or prevented. by use of a suitable backup board. the latter approach being much more desirable in view of the fact that it is less costly and does not. increase the time needed for sanding.
 
      This prior art backup board. employs a core of hard pressed wood . which covered with outer layers of metallic foil (aluminum). While the backup board of my remove prior patent. is quite effective in eliminating burrs and provides cooling of the drill. the backup board of the backp board  provides some improvements thereover. , the backup board of the backup board, by employing a core having open spaces therein. between an upper and a lower foil sheet. further facilitates the cooling of the drill and printed circuit board workpiece. under the air flow provided through the core during the drilling.

     Further, these open spaces in the core can employed to ease the removal of. cuttings from the workpiece. Further, .the. cooling of the drill facilitated. after drilling through the workpiece in view of the fact. that the drill tip enters the open core after it penetrates the upper sheet. and does not penetrate the lower sheet. It is to noted that a vacuum system is generally employed by the drilling machine for removing. cuttings from the workpiece area. The core of the present invention facilitates the use of. such vacuum systems both for the removal of the cuttings. and for cooling of the printed circuit board workpiece and the drill.
 
      It is the object of this backup board to provide an improved backup-material. and method for use in drilling printed circuit boards. It is another object of this invention to provide an improved backup board. for use in drilling printed circuit boards. wherein improved means afforded for facilitating the removal of cuttings. and the cooling of the workpiece and drill


tags:
hole size. drill bit. drill size. copper pad. finished hole. drilling holes. drill press. laser drilling. drilled holes. harbor freight. pcb hole. 12 2019. ground plane. pcb manufacturer. hand drill. solder mask. lead diameter. via holes. larger size. annular ring. surface mount.