WO2008072930A2

WO2008072930A2 - Sheets for drilling

Info

Publication number: WO2008072930A2
Application number: PCT/KR2007/006545
Authority: WO
Inventors: Bu Jin Hong; Seung Bong Chae
Original assignee: Bu Jin Hong; Seung Bong Chae
Priority date: 2006-12-15
Filing date: 2007-12-14
Publication date: 2008-06-19
Also published as: WO2008072930A3

Abstract

Disclosed is a sheet for drilling suitable for use as a cover sheet for efficiently realizing a high-quality product upon drilling in the process of fabricating a printed circuit board. In the sheet including an organic material layer for imparting a lubricating function and a metal layer in contact with the organic material layer, the surface of the metal layer opposite the surface in contact with the organic material layer is controlled to have tan? of a predetermined value or more according to a slippage testing method. Thus, when the sheet is placed on a blank board during the drilling of a printed circuit board, it has increased adhesiveness to the board and therefore an air layer is not formed between the sheet for drilling and the board, thus preventing the slippage of a drill and decreasing the vibration thereof, resulting in improved drill straightness. Wear resistance of the drill is maintained, thus increasing the drill replacement period, thereby realizing high-quality sheets for drilling.

Description

[DESCRIPTION]

[invention Title]

SHEETS FOR DRIIiLING

[Technical Field] The present invention relates in general to sheets for drilling, and more particularly, to a sheet suitable for use as a cover sheet for efficiently realizing a high- quality product in the course of drilling, which is one of the processes for fabricating a printed circuit board.

[Background Art]

A printed circuit board (PCB) plays a role in electrically connecting electronic parts mounted thereon, and is regarded as a very important inner part of an electrical product. The fabrication of the PCB includes placing a blank board in the form of a laminate of a plurality of layers on a backup board, disposing an entry board on the uppermost blank board, and forming through holes downward in the entry board and simultaneously drilling the entire blank board in that state, thereby forming small holes in the blank board for a PCB.

As the entry board, typically useful is a pure aluminum sheet having no lubricating layer, for example, an AlOOO aluminum sheet. This has been mainly used so that, in the drilling of the blank board for a PCB, the breakage of the blank board is prevented, the formation of burrs is decreased, and hole position accuracy is improved. In recent years, as electronic parts are mounted at high densities on the PCB, circuit line width and interval are decreased, the drilling speed is increased, and the number of layers of the board is increased. Accordingly, small holes having a diameter of 0.35 mm or less must be formed.

However, the use of the pure aluminum sheet having no lubricating layer as the entry board incurs problems related to hole position accuracy and the breakage of a drill bit. In the case where the aluminum sheet is used, the end of the drill bit frequently breaks or the drill bit itself is broken, thus making it impossible to increase the number of layers of the blank board, which is to be drilled in order to fabricate a PCB, resulting in poor efficiency. Further, because the end of the drill bit skids on the surface of the board, there is a problem in which the small hole is not formed at an accurate position. Furthermore, the inner surface of the small hole is roughened, undesirably causing problems in a subsequent plating process . Therefore, in order to solve the above problems, prevent the breakage of the end of the drill bit, prevent the roughening of the inner surface of the small hole, and improve the accuracy of the position at which the small hole is formed in the blank board, a resin-coated metal sheet provided with a lubricating layer on at least one surface thereof by attaching a lubricating sheet to one or more surfaces thereof is proposed.

For example, Korean Unexamined Patent Publication No. 2002-0018984 discloses a lubricant sheet for drilling a PCB, comprising a metal foil 5-500 μm thick and an organic material layer 2~300 μm thick formed on one surface of the metal foil. Specifically, the organic material layer of the lubricant sheet for drilling a PCB is composed of a mixture comprising polyether ester, a solid water-soluble lubricant, and polyethylene glycol; or a mixture comprising polyether ester, a solid water-soluble lubricant, and a liquid water-soluble lubricant.

In addition, Korean Unexamined Patent Publication No. 2003-0036041 discloses an entry sheet, which comprises a water-soluble resin and a water-insoluble lubricant and has a metal foil formed on one surface thereof.

In addition, Korean Unexamined Patent Publication No. 2005-0056149 discloses a resin-coated metal sheet, in which at least one surface of the metal sheet is coated with a thermoplastic resin. In this disclosure, the thermoplastic resin is substantially water-insoluble and has a melting peak temperature ranging from 60^°C to 120^"C according to JIS K7121, and the melt viscosity of the thermoplastic resin, which is melted at 150°C, ranges from 1 x 10³ poise to 1 x 10⁴ poise under conditions of a shear rate of 200 mm/sec, and also, under conditions of 3000 mm/sec, ranges from 5 x 10² poise to 5 x 10³ poise, and furthermore, the thermoplastic resin has a durometer D hardness in a range of 20 to 45 according to JIS K7125.

The sheets according to the above techniques have a structure in which the organic material layer for imparting a lubricating function, that is, the lubricating layer, is formed on at least one surface of the metal layer.

Hence, in the drilling of the PCB, the upper surface of the copper foil, which is a blank board, is brought into contact with the metal layer. When the metal layer of the sheet for drilling is brought into contact with the upper surface of the copper foil, which is a blank board, adhesiveness between the copper foil and the sheet is decreased and thus an air layer is formed in the space therebetween, and furthermore, rotation vibration of the drill is not absorbed, undesirably entailing a slight slippage phenomenon, with the result that the drill may slip when drilling is conducted. Thereby, the drilled board chips are mixed with the lubricant material of the lubricating layer and are not efficiently discharged upon suction (chip suction) , and thus, a phenomenon in which the chips are re-attached to the surface of the sheet for drilling in contact with the board, occurs, undesirably causing erroneous operation of the drill. Consequently, it is impossible to conduct hole processing according to a design.

[Disclosure]

[Technical Problem]

Accordingly, the present invention provides a sheet for drilling, which is able to increase adhesiveness to a board in the drilling of a PCB, thus efficiently realizing high quality.

In addition, the present invention provides a sheet for drilling, which is able to be prevented from slipping on a board in the drilling of a PCB.

In addition, the present invention provides a sheet for drilling, which is able to improve straightness of a drill in the drilling of a PCB.

In addition, the present invention provides a sheet for drilling, which enables the maintenance of wear resistance of a drill. In addition, the present invention provides a sheet for drilling, which is able to decrease smearing in the hole of the drilled board.

[Technical Solution]

According to the present invention, a sheet for drilling may comprise an organic material layer for imparting a lubricating function and a metal layer, wherein the surface of the metal layer opposite the surface in contact with the organic material layer has tanθ of 20° or more at the time of beginning to slip on a glass surface in an inclination test according to a slippage testing method using a slip tester.

In the sheet for drilling, the surface of the metal layer opposite the surface in contact with the organic material layer may have a non-slip layer composed of a resin having a composition which is same as or different from that of the organic material layer.

The non-slip layer may be a film layer composed of a polymer or a copolymer obtained from at least one monomer selected from the group consisting of ethylene, ethylene vinyl acetate, ethyl acrylic acid, and ethyl methacrylic acid. In the sheet for drilling, any one layer selected from among the organic material layer and the non-slip layer may further have a color layer on one surface thereof.

In the sheet for drilling, the surface of the metal layer opposite the surface in contact with the organic material layer may be processed through chemical treatment or physical treatment.

The surface of the metal layer opposite the surface in contact with the organic material layer may have surface roughness (Ra) of 0.3 μm or more.

[Advantageous Effects] According to the present invention, in a sheet for drilling, comprising an organic material layer for imparting a lubricating function and a metal layer, the surface of the metal layer opposite the surface in contact with the lubricating layer is controlled to have tanθ of a predetermined value or more with respect to a glass surface according to a slippage testing method, thereby improving adhesiveness to a board to thus prevent the formation of an air layer between the board and the sheet. Therefore, in the drilling, as the straightness of a drill may be improved and the vibration of the drill may be decreased, wear resistance of the drill may be maintained, and the drill replacement period may be prolonged. Further, the chips, which are to be discharged, are prevented from being introduced into the board and the metal layer, thus eliminating the danger of erroneous operation of the drill .

[Best Mode]

Hereinafter, a detailed description will be given of the present invention. According to the present invention, a sheet for drilling comprises a metal layer, one surface of which has an organic material layer for imparting a lubricating function, that is, a lubricating layer, and the other surface of which has tanθ of 20° or more at the time of beginning to slip on a glass surface in an inclination test according to a slippage testing method using a slip tester.

In the case where the surface of the metal layer opposite the surface in contact with the lubricating layer has tanθ of 20° or more at the time of beginning to slip on a glass surface in an inclination test according to a slippage testing method, friction force with the surface of a board, such as a copper foil, is satisfactory, and thus hole position accuracy may be improved upon drilling. That is, a predetermined process capability index, represented by Cpk, may be satisfied. Specifically, in the case where the surface of the metal layer opposite the surface in contact with the lubricating layer has tanθ of 20° or more at the time of beginning to slip on a glass surface in an inclination test according to a slippage testing method, the process capability index, represented by Cpk, measured using the finally obtained sheet for drilling, is about 2.1 to about 2.4, which shows good hole position accuracy.

The value of tanθ means increased friction force relative to the inherent friction force of a metal layer, for example, an aluminum metal, to a copper foil. In the case where the surface of the metal layer opposite the surface in contact with the lubricating layer has a value smaller than 20° in tanθ which is obtained with respect to a glass surface according to a slippage testing method, the sheet for drilling is not prevented from slipping on a board, such as a copper foil . In order to achieve the technical spirit of the present invention, in the sheet for drilling comprising the metal layer and the lubricating layer thereon, methods for satisfying the range of the tanθ of one surface of the metal layer according to a slippage testing method are not particularly limited. As an example thereof, there is proposed a method of additionally forming a resin layer on the surface of the metal layer opposite the surface in contact with the lubricating layer, or of processing the surface of the metal layer opposite the surface that is in contact with the lubricating layer.

In the case where the resin layer is additionally formed on the surface of the metal layer opposite the surface in contact with the lubricating layer, the composition for the resin layer is not particularly limited, as long as the value of tanθ is realized in the aforementioned range. The resin layer is preferably adjusted to have a composition able to achieve predetermined adhesiveness, and may be a resin layer (which is referred to as a "non-slip layer", in the present invention) having the same or a different composition as that of the lubricating layer.

Generally, in the sheet for drilling, the organic material layer for imparting a lubricating function, that is, the lubricating layer, includes a polymer, which is water-soluble or water-insoluble, and a lubricant, which is water-soluble or water-insoluble.

Specifically, in the case of being water-soluble, the organic material layer may be composed of a mixture comprising polyether ester, a solid water-soluble lubricant, and polyethylene glycol having a number average molecular weight ranging from 200 to 600, or a mixture comprising polyether ester, a solid water-soluble lubricant, and a liquid water-soluble lubricant.

Preferably, the organic material layer is water- insoluble. In the case of the water-soluble resin, adhesiveness between the resin and the metal layer is poor and the difference in absorption with the metal is increased, and thus the metal sheet itself may warp. Hence, it is preferred that the organic material layer be substantially water-insoluble, whether the matrix resin portion thereof is water-insoluble or slightly water- soluble .

The lubricating layer preferably has a thickness of

20 μm to 300 μm. If the lubricating layer is too thin, it does not function as a lubricant upon drilling and does not satisfactorily realize the discharge of cutting remnants.

On the other hand, if the lubricating layer is too thick, the accuracy of drilling is deteriorated or a drill may break down. In the sheet for drilling according to the present invention, in the case where the non-slip layer has the same composition as that of the lubricating layer, it preferably has a water-insoluble composition, as in the lubricating layer, the preferable composition of which is water-insoluble . The non-slip layer functions to increase adhesiveness between the sheet and the board and functions as a cushioning layer to thus decrease the vibration of a drill, ultimately improving the straightness of the drill. When the straightness of the drill is improved, re-attachment of chips to the board during drilling, that is, smearing, may be decreased, thereby increasing the quality of the drilled board. Upon drilling, this layer plays a role as a cushioning layer and thus can decrease the wear of the drill . The non-slip layer preferably has a thickness of 50 μm or less in terms of hole workability.

Preferably, the resin layer may be composed of a polymer or a copolymer obtained from an ethyl acrylate monomer or an ethyl methacrylate monomer. When the sheet for drilling according to the present invention is manufactured, the metal layer, the lubricating layer, and the non-slip layer are adhered using any one method selected from among dry lamination, wet lamination, and high-temperature lamination. Alternatively, the use of a known adhesive is possible. For example, the adhesive for dry lamination includes acryl, urethane, and ester, and the adhesive for high-temperature lamination includes ethylene- vinyl acetate copolymer resin, olefin, and rubber. The exemplified adhesives may be used alone, or may be used in combinations thereof. When the sheet for drilling according to the present invention has a structure in which the resin layer is formed on both surfaces of the metal layer, in the case where the lubricating layer and the non-slip layer have different compositions, the upper and lower surfaces of the sheet should be distinguished from each other in order to conduct the drilling process. For ease of distinction, a color layer may be additionally provided on one surface of either the lubricating layer or the non-slip layer.

Also, antistatic performance may be imparted into the composition of the resin layer, thus preventing the attachment of fine dust due to static electricity or erroneous operation of a drill .

In addition, as another example of the method for satisfying the range of the tanθ of one surface of the metal layer, there is provided a method of physically or chemically processing the surface of the metal layer opposite the surface in contact with the lubricating layer, without the addition of the resin layer.

Examples of the physical treatment include, but are not limited to, patterning and embossing, and examples of the chemical treatment include, but are not limited, surface processing using an acid treatment. In the case where the surface of the metal layer opposite the surface in contact with the lubricating layer is treated through a physical method or a chemical method, the surface roughness of the treated surface should be 0.3 μm or more . When the surface roughness is less than 0.3 μm, the surface of the metal layer opposite the surface in contact with the lubricating layer cannot have the above range of tanθ at the time of beginning to slip on a glass surface in an inclination test according to a slippage testing method.

Herein, the term "surface roughness" indicates a surface roughness value measured using a surface roughness meter (Kosaka, SE-30C) .

The metal layer included in the sheet for drilling is preferably composed of aluminum, and more preferably pure aluminum having a purity of 99.0%. The thickness of the metal layer ranges from 5 μm to 500 μm, preferably 30 μm to 300 μm, and more preferably 50 μm to 200 μm.

[Mode for Invention] A better understanding of the present invention may be obtained through the following examples, which are set forth to illustrate, but are not to be construed as the limit of the present invention.

Preparative Example 1: Formation of Non-Slip Layer A film having a thickness of 30 μm was extruded at 170°C using a blown extruder with the use of HanHwa LLDPE 3120 and SamSung Total EVA E120A.

Preparative Example 2 : Formation of Non-Slip Layer

A film having a thickness of 30 μm was extruded at 150°C using a blown extruder with the use of Dow Chemical Affinity PL 1840.

Preparative Example 3: Non-Slip through Surface Treatment of Al Foil

Either or both surfaces of an aluminum sheet having a purity of 99% or more and a thickness of 130 μm were subjected to surface treatment using a work roll which was embossed upon rolling of the aluminum sheet in order to be roughened, thus forming an aluminum foil having surface roughness of 0.30 μm or more.

Example 1 As a lubricating layer, a film having a thickness of 35 μm, obtained using an ethylene-methacrylic acid copolymer resin (Dupont, Nucrel 0910) , and the film having a thickness of 30 μm, obtained in Preparative Example 1, were sequentially placed on both surfaces of a pure aluminum sheet having a thickness of 130 μm, and were then laminated using an adhesive, thus manufacturing a sheet for drilling, in which the lubricating layer and the non-slip layer were formed on both surfaces of the metal layer.

Example 2 A sheet for drilling was manufactured in the same manner as in Example 1, with the exception that the film obtained in Preparative Example 2 was used as the non-slip layer, and was then laminated using an adhesive.

Example 3

An aluminum foil was formed in the same manner as in Preparative Example 3, after which the lubricating layer of Example 1 was laminated thereon, thus manufacturing a metal sheet for drilling.

Example 4

A sheet for drilling was manufactured in the same manner as in Example 2, with the exception that a lubricating layer composed of a mixture comprising ethylene-vinyl acetate copolymer resin and ethylene-acrylic acid copolymer resin was used.

Example 5

A sheet for drilling was manufactured in the same manner as in Example 1, with the exception that a non-slip layer having the same composition as that of the lubricating layer was used.

Example 6

A sheet for drilling was manufactured in the same manner as in Example 2, with the exception that a non-slip layer having the same composition as that of the lubricating layer was used.

Comparative Example 1 A sheet for drilling was manufactured in the same manner as in Example 1, with the exception that the non- slip layer was not provided, but only the lubricating layer was provided.

Comparative Example 2

A sheet for drilling was manufactured in the same manner as in Example 4, with the exception that the non- slip layer was not provided, but only the lubricating layer was provided.

In order to evaluate the friction force of the sheets for drilling, obtained in Examples 1 to 6 and Comparative Examples 1 and 2, tanθ of the sheets at the time of beginning to slip on a glass surface in an inclination test according to a slippage testing method using a slip tester (Dae Sung Tester, YX-219) was measured. The results are shown in Table 1 below. The reason why the measurement at the time of beginning to slip is conducted with respect to the glass surface is attributed to experimental limitation, in which the glass plate provided in the available slip tester is not replaced with a copper foil. However, because the glass plate is more slippery than copper foil, it is possible to estimate the friction force of the sheets for drilling of Examples 1 to 6 and Comparative Examples 1 and 2 to the copper foil .

Specifically, the slippage testing method was conducted by placing each sheet sample, having a size of 100 mm x 100 mm, on a flat and clear glass plate of the slip tester and measuring the inclined angle of the glass plate at the time at which the sheet sample begins to slip from the glass plate while tilting the glass plate at a rate of 800 ± 80 mm/min. The inclined angle of the glass plate at the time at which the sheet sample begins to slip is tanθ.

TABLE 1

Experimental Example The sheets for drilling of Examples 1 to 6 and Comparative Examples 1 and 2 were subjected to drilling, thus evaluating hole position accuracy, inner wall roughness, drill breakage, and hole smearing. For the drilling, in the sheets of Examples 1 to 6, the non-slip layer 13, and in the sheets of Comparative Examples 1 to 3, the metal layer 1 were disposed to come into contact with the upper surface of a double-sided copper PCB (FR-4, copper foil 18 μm thick) having a thickness of 0.4 mm. Seven PCBs were overlaid, beneath which a backup board composed of a bakelite sheet having a thickness of 1.5 mm was disposed, thus conducting the drilling of the PCB.

The drilling process was conducted under the following conditions .

Drill bit: diameter 0.25 mm Number of rotations: 125,000 rpm Transfer rate: 2.5 m/min

Distances between centers of adjacent holes: 0.5 mm Number of drill bits: 5000 hit

(1) The hole position accuracy was determined with respect to the lowermost board (7^th board) among the seven

PCBs, which were overlaid and subjected to 5000 hit

(drilling) . That is, in the lowermost board, the errors from the centers of hit 5000 holes were measured, and the maximum thereof was calculated. The case where the maximum was less than 50 μm is indicated by ®, the case where the maximum was between 50 μm and less than 70 μm is indicated by O, the case where the maximum was between 70 μm and 100 μm is indicated by Δ, and the case where the maximum was 100 μm or more is indicated by X.

(2) The inner wall roughness was determined with respect to the 5^th board downward. The inner wall roughness values of opposite wall surfaces in the drilled hole at the 4000^th hit and two front and rear holes thereof were measured and averaged. The case where the average was less than 5.0 μm is indicated by ®, the case where the average was less than 7.0 μm is indicated by O, the case where the average was less than 10 μm is indicated by Δ, and the case where the average was 10 μm or more is indicated by X. (3) The smearing of the drilled hole was observed.

Insufficient diffusion of friction heat resulted in a smearing phenomenon, in which the temperature of the drill bit was increased and the resin portion of the chip was softened and melted and thus re-attached to the cross- section of the copper foil in the hole. After washing, the cross-sections of the 20 holes were observed using a microscope. The case where no smearing was observed is indicated by 10, the case where smear was slightly observed is indicated by 5, and the case where smear was entirely observed is indicated by 0.

The results of (1) to (3) are shown in Table 2 below. TABLE 2

As is apparent from Table 2, when the non-slip layer was additionally provided, the accuracy of the hole was further improved and the inner wall roughness was improved. However, in the case where the metal layer was in contact with the surface of the board, it can be seen that adhesiveness to the board was decreased, the hole position accuracy was slightly decreased, and the surface roughness of the hole was deteriorated.

Claims

[CLAIMS]

[Claim l]

A sheet for drilling, comprising an organic material layer for imparting a lubricating function and a metal layer, wherein a surface of the metal layer opposite a surface in contact with the organic material layer has tanθ of 20° or more at a time of beginning to slip on a glass surface in an inclination test through a slippage testing method using a slip tester.

[Claim 2]

The sheet for drilling according to claim 1, wherein the surface of the metal layer opposite the surface in contact with the organic material layer has a non-slip layer formed of a resin having a composition which is same as or different from that of the organic material layer.

[Claim 3]

The sheet for drilling according to claim 2, wherein the non-slip layer is a film layer formed of a polymer or a copolymer obtained from at least one monomer selected from a group consisting of ethylene, ethylene vinyl acetate, ethyl acrylate, and ethyl methacrylate.

[Claim 4]

The sheet for drilling according to claim 2, wherein any one layer selected from among the organic material layer and the non-slip layer further has a color layer on one surface thereof.

[Claim 5]

The sheet for drilling according to claim 1, wherein the surface of the metal layer opposite the surface in contact with the organic material layer is processed through chemical treatment or physical treatment.

[Claim 6]

The sheet for drilling according to claim 5, wherein the surface of the metal layer opposite the surface in contact with the organic material layer has surface roughness (Ra) of 0.3 μm or more.