JP3464049B2 - Aluminum alloy backing plate for drilling through-hole printed circuit boards - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal plate suitable as a backing plate used for drilling a through-hole printed circuit board with a drill. In the present invention, the size of the intermetallic compound means an equivalent diameter obtained by converting the area into a circle. 2. Description of the Related Art There are various types of printed circuit boards used for electric and electronic equipment. Through-hole printed circuit boards which enable high-density mounting by using both sides of the board have been actively used in recent years. ing. For through-hole printed circuit boards, paste copper foil on both sides of the insulating resin, form circuits on the copper foil on both sides, then drill holes in the plane so that they penetrate the upper and lower surfaces, apply conductive plating in the holes , To connect the circuits on both sides. [0003] Drilling is performed by stacking several to several tens of printed circuit boards on a discarded plate, stacking a contact plate on top of the printed circuit board, pressing the printed circuit board, and performing precision drilling. . Drilling of this through-hole printed circuit board is often done without lubrication for the simplicity of post-processing, and the drill has an undercut type neck that is thinner than the tip to prevent the generation of frictional heat Things are used. However, since the drill generates vibration during rotation, when returning the drill after drilling, the tip of the drill contacts the copper foil of the first printed circuit board, lifts the copper foil, and causes a return. In a through-hole printed circuit board, plating is applied to the inner surface of the hole to form an energizing circuit. However, if there is a return in the copper foil, the plating thickness will be uneven at the return portion, and a spark will be generated at the time of energization, making it unusable. Therefore, the return height H is 7 μm or less, and the return inclination angle y (y = tan)
θ) must be regulated to 0.83 or less. In order to prevent the return of the copper foil on the upper surface of the uppermost printed circuit board, and to improve the bite at the tip of the drill and secure the hole positioning accuracy, a backing plate is placed on the printed circuit board and drilled. Processing has been done. [0005] Conventionally, a bakelite plate has been used as the backing plate. However, the bakelite plate is made by impregnating paper or cloth with phenolic resin and heating it, so it has excellent properties as a backing plate to prevent the return of the printed circuit board. There was a disadvantage that the position accuracy was poor.
Also, it is difficult to reuse the used bakelite patch,
It is unsuitable for recycling, and wastes resources and costs are expensive. On the other hand, when an aluminum plate is used as a backing plate, it is lightweight, easy to handle, and can be reused at low cost. Also, the drill accuracy is good because the drill tip slides and vibrates little. However, there is a problem that the aluminum plate material has a higher extensibility than the bakelite plate material, and it is easy to cause a return at the copper foil hole edge of the uppermost printed circuit board. SUMMARY OF THE INVENTION It is an object of the present invention to provide a backing plate having a hole precision equal to or higher than that of a conventional aluminum plate and having a small return equivalent to or more than a bakelite plate. That is, according to the present invention, there are provided 0 or less intermetallic compounds having a breaking elongation of 5% or less and a ratio of the size of the intermetallic compound to the plate thickness of 10/150 or more. / 15
0 to less than 10/150 intermetallic compounds 15/0.
An aluminum alloy backing plate for drilling a through-hole printed circuit board having a diameter of ² mm ² or less. Hereinafter, the present invention will be described. [0010] When the elongation at break of the aluminum plate material exceeds 5%, the cutting powder remains continuous without being pulverized and is wound around a drill. When drilling, there is no problem if it is wound around the drill, but when the drill is returned, the swarf wrapped around the drill hits the backing plate or printed circuit board, and irregularly deforms the backing plate and the copper foil on the surface of the printed circuit board. Deformation of the copper foil may result in depression, but often returns. However, if the breaking elongation is 5% or less, the cutting powder is finely cut, so that it does not wind around the drill, so that deformation of the contact plate and return of the printed circuit board do not occur. Therefore, the elongation at break of the aluminum plate material is set to 5% or less. [0011] Intermetallic compounds such as crystals and precipitates, for example, Al (Fe) n, A generated in aluminum alloy sheet material
l (Mg, Si) n, Al (Mn, Fe) n, AL (F
e, Si) n, etc. are generally hard and have poor machinability. Therefore, in the present invention, the ratio of the size of the intermetallic compound to the thickness of the backing plate is 10 /
0 for 150 or more, 5/150 or more for 10/150
By setting the number of particles less than 15 / 0.2 mm ² or less, the influence of the intermetallic compound on generation of return is reduced. When there is a huge intermetallic compound having a ratio of the size of the intermetallic compound to the thickness of the backing plate of 10/150 or more, the drill blade cuts the intermetallic compound during drilling. , Because the intermetallic compound is hard,
The reaction gives a circumferential rotational force and a force in the plate thickness direction to the aluminum base material of the backing plate. This force causes the caul plate to buckle and generate concave wrinkles concentric with the drill hole diameter.
In general, when the drill returns, when the copper foil on the top of the top printed circuit board and the tip of the drill come into contact with the undercut due to vibration, a force is applied in the direction that causes the copper foil to return, but wrinkles occur on the backing plate. As a result, the printed circuit board cannot be sufficiently held down, and the copper foil returns. But,
If there is no intermetallic compound having a size ratio of 10/150 or more, such a phenomenon does not occur, and thus no return occurs. Therefore, the number of intermetallic compounds having a ratio of the size of the intermetallic compound to the thickness of the backing plate of 10/150 or more is zero. The ratio of the size of the intermetallic compound to the thickness of the backing plate is 5/150 or more and less than 10/150.
When it exceeds 0.2 / 0.2 mm ² , it does not generate wrinkles on the backing plate, but when cutting an intermetallic compound having poor machinability, the intermetallic compound is elastically pushed into the aluminum base material, and It is considered that the aluminum base material also has elastically widened holes. Then, when the drill returns, the undercut at the tip of the drill comes into contact with the intermetallic compound that is popping out of the hole wall by elastic return, giving a force in the return direction to the backing plate, causing the copper foil to return elastically. I can't hold it down. However, if the ratio of the size of the intermetallic compound to the thickness of the backing plate is 5/150 or more and less than 10/150 is 15 / 0.2 mm ² or less, such a phenomenon does not occur, and therefore, the return No occurrence. The type of the aluminum alloy is not particularly limited. However, in order to reduce the amount of the intermetallic compound so as to fall within the regulation range of the present invention, a pure aluminum type (1000 type) such as JIS1050 or JIS1100 or an Al-Mn type ( 3000
System) aluminum alloys are preferred. The tempering of the aluminum plate material is not particularly limited, either, but in order to satisfy the condition of elongation at break of the present invention, a hard plate hardened by work hardening such as H material, particularly H18 material is preferable. Although the thickness of the backing plate is not particularly limited, it is usually preferably 0.05 to 1.0 mm, more preferably 0.15 to 0.3 mm. Embodiments of the present invention will be described below. A plate having a thickness shown in Table 2 was prepared using an alloy having a composition shown in Table 1. Here, Invention Examples 1-4 are H18 materials work-hardened by final cold rolling, Comparative Example 1 is H24 material annealed by final annealing after cold rolling, and Comparative Examples 2 and 3 are inappropriate in alloy composition. Those having many intermetallic compounds and Comparative Examples 4 to 6 are those of a conventionally used bakelite plate. For these, elongation at break was measured by a tensile test, and the structure was observed with a microscope to determine the number of intermetallic compounds. Table 2 shows the results. Table 2
"10 or more" in the column of "intermetallic compound" means the number of intermetallic compounds having a size of 10/150 or more as a ratio of the size of the intermetallic compound to the thickness of the backing plate, and "5-10 "Means that the ratio of the size of the intermetallic compound to the thickness of the backing plate is 5/150.
It means the number of objects that are not less than 10/150. [Table 1] [Table 2] Drilling was performed using these plates, and the occurrence of return and the accuracy of the hole position were measured. Table 3 shows the results. Drilling conditions: Drill: 0.4 mmφ UC type • Number of revolutions: 70,000 rpm • Feed: 20 μm / rev • Printed circuit board: 1.6 mm × 3 • Discard plate: Bakelite 1.5 mmt • Number of drilled holes: 1000 Measurement of return height and return inclination angle Object: Processing order of printed circuit board side printed circuit board 991 to 100
Observation method: Observation of one cross section by the cross section method: Measurement: Maximum value measured with a microscope of 500 times. Measurement of hole position. Object: Processing order of the abutment plate and discarded plate. 5
20, 961 to 1000 120 holes. Measurement: Measure and display the position with a coordinate measuring machine.
Indicated / Standard: JIS5011 x + 3σ <± 50 μm Judgment of reusability (recyclability) ・ When reusable ○ ○ In the case of incineration or burial × × [Table 3] As shown in Table 3, each of the invention examples satisfies the condition that the return height of the printed circuit board is 7 μm or less, the return inclination angle is 0.83 or less, and the hole position accuracy is also standard. The accuracy satisfies x + 3σ <50 μm. In addition, since it is made of an aluminum alloy, it is excellent in reusability. Therefore, it can be judged comprehensively that it is excellent as a backing plate when drilling a through-hole printed circuit board with a drill. On the other hand, Comparative Example 1
Is H24 material by the final annealing, the elongation is out of the range of the present invention, and therefore, the cutting powder is continuous without breaking at the time of drilling. The result is a large return, and the tilt angle has deviated from the regulation value. In Comparative Example 2, the number of intermetallic compounds was out of the range of the present invention because the alloy components were changed. As a result, concentric deformation occurred due to the cutting resistance of the intermetallic compounds, and the mechanism as described above was used. This causes a large return on the printed circuit board. Comparative Example 3 was the same as Comparative Example 2, except that the rolling conditions were changed to reduce the sheet thickness, so that there was no large intermetallic compound, but the number of medium-sized intermetallic compounds was out of the range of the present invention. In addition, due to the thinness of the plate, buckling is apt to occur, which results in large deformation at the time of drilling. Therefore, the height of the return generated on the printed circuit board is large and the inclination angle is large. In Comparative Examples 4 to 6, the use of a conventional bakelite plate was used, and although the occurrence of return was small, the accuracy of the hole position was extremely poor. As described in detail above, the elongation at break of the present invention is 5%
And the ratio between the size of the intermetallic compound and the plate thickness is 10 /
0 or more intermetallic compounds of 150 or more, 5/150 or more 10
In the drilling of a through-hole printed circuit board using a plate material for drilling a through-hole printed circuit board with less than 15 / 0.2 mm ² or less intermetallic compound less than / 150, the swarf was cut because the swarf was cut finely. As a result, the cutting resistance is small because hard intermetallic compounds are restricted, so that no extra force is applied to the backing plate or the printed board. As a result, when drilling with a drill, a hole with less return of the hole edge, more specifically, a return height of less than 7 μm,
Further, it is possible to form a hole having a gentle return with a return inclination angle y (y = tan θ) of 0.83 or less. Therefore, it is possible to obtain a high-quality printed circuit board which is free from obstacles due to return and which does not generate a spark when energized due to uniform plating. In addition, there is little slip at the tip of the drill and vibration of the drill, and the hole accuracy is better than that of a conventional drilling process using a bakelite plate as a backing plate. Furthermore, the aluminum plate material has only a small area with a hole, and the weight loss is less than several percent,
Since the adhesion of copper foil chips is negligibly small, it can be remelted and used as the same alloy, so that it has excellent recyclability. Also, it is much cheaper and more economical to use aluminum by re-dissolving scrap than to use aluminum.

Claims (1)

(57) Claims 1. No intermetallic compound having an elongation at break of 5% or less and a ratio of the size of the intermetallic compound to the plate thickness of 10/150 or more, 5/150 or more An aluminum alloy patch for drilling a through-hole printed circuit board, wherein the number of intermetallic compounds of less than 10/150 is 15 / 0.2 mm ² or less.