JP2016042540A - Manufacturing method of multilayer circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method subjecting a multilayer circuit board including a thermoplastic liquid crystal polymer film to perforation.SOLUTION: A manufacturing method of a multilayer circuit board is a manufacturing method in which a multilayer circuit board using a film as an insulation layer is subjected to perforation, the film being made of a thermoplastic polymer capable of forming an optically anisotropic molten layer. In the manufacturing method, a boring tool for use in the perforation has a web thickness taper of 0.015 or more and less than 0.075, and an entry board having a layer made of a resin material is used as an entry board in performing perforation.SELECTED DRAWING: None

Description

  The present invention relates to a manufacturing method for perforating a multilayer circuit board using a thermoplastic liquid crystal polymer film as an insulating layer.

  In recent years, there has been remarkable progress in technology in the field of microelectronics, and the demand for miniaturization and weight reduction of portable electronic devices such as mobile communication has become stronger, and the expectation for high-density mounting has further increased. Along with this, processing techniques for printed wiring boards that can withstand higher integration, such as multilayer wiring boards, narrowing of wiring pitches, and miniaturization of through holes, are being studied.

  Among the processing techniques for printed wiring boards, drilling for interlayer conduction of multilayer circuit boards is particularly important, and drilling using a drill as a drilling tool is generally performed.

  With the recent miniaturization of through-holes, the holes to be drilled have become smaller in diameter, resulting in worse hole position accuracy. Also, due to the deterioration of cutting waste dischargeability, drill breakage, and the inner wall of the drilled hole (smear) Is a problem. When drilling a printed wiring board with a drill, when the drill returns after drilling, the top metal foil layered on the printed wiring board may be lifted to cause burr. This burr is suppressed. However, a jig plate is generally used for the purpose of protecting the metal foil surface from being wrinkled. This jig board is placed in the uppermost layer of the printed wiring board to be drilled, and is divided into two types: the entry board used on the drill entry side and the backup board placed in the lowermost layer of the printed wiring board. Entry boards and backup boards with a layer made of a resin material that acts as a lubricant may be used to prevent problems such as drill breakage due to deterioration in hole position accuracy and chip evacuation. is there.

  For example, in Patent Document 1 (Japanese Patent Laid-Open No. 7-328996), the number of holes perforated in the inner layer material of a multilayer substrate is gradually increasing to 0.5 mmφ or less. There is a problem that fuzz called smear occurs on the inner wall, and there is a problem that insulation failure occurs in the subsequent plating process, or that the circuit board is likely to be defective due to breakage of the drill, and aluminum foil and resin having a specific hardness are described. A drilling method using an entry board for circuit board drilling formed by combining impregnated paper with a curable adhesive is disclosed.

  Further, in Patent Document 2 (Japanese Patent Laid-Open No. 10-335780), if the hole diameter is reduced to less than 0.35 mm in the drilling process of the printed wiring board, the effect of preventing drill heat generation is insufficient, and the inner wall of the hole in the printed wiring board. Describes the problem of smearing or drill breakage, and as an entry board for drilling printed wiring boards, a film-forming resin and a lubricity-imparting material are applied to the surface of the clad made of aluminum. An entry board is disclosed which is provided with a film formed by applying and baking a water-soluble solid lubricant containing

  Also, in the drilling process of printed wiring boards, from the viewpoint of productivity and cost reduction, a plurality of multilayer circuit boards are stacked and drilled. There is a problem that the hole becomes longer, the amount of cutting by the drill becomes larger, the frictional heat generated when the through hole is formed, the occurrence of smear increases, and the hole position accuracy deteriorates.

  For example, in Patent Document 3 (Japanese Patent Laid-Open No. 7-164228), a printed circuit board manufactured by laminating a glass fiber in a woven state and a copper foil forming a conductor with a resin such as epoxy is 0.4 mm or less. In drilling holes, small-diameter deep holes with a substantial aspect ratio (ratio of thickness to hole diameter) with several printed circuit boards piled up have the effect of hole bending as the drill advances. It describes the problem that the hole position accuracy deteriorates and leads to defective printed circuit boards. The reason why the hole position accuracy deteriorates is not only due to the decrease in the rigidity of the drill itself due to the reduction in diameter, but also the chisel part biting and centripetal effect when the drill enters the woven fabric of glass fiber, A method for improving the biting accuracy of a glass fiber to a woven fabric by using a drill having a specific shape and improving the hole position accuracy by reducing the bending of the hole is disclosed.

  As described above, in the conventional printed wiring board perforation processing technology, it is generally performed to use an entry board having a layer made of a resin material. There are various conditions besides the conditions such as backup board conditions, drill rotation speed, feed speed, tip load, drill shape (tip angle, twist angle, clearance angle, groove length, core thickness, core) Thick taper, etc.) and the presence or absence of cycle machining influences good drilling.

  In Patent Document 4 (Japanese Patent Application Laid-Open No. 2000-349413), in drilling a printed wiring board using an insulating substrate made of a glass epoxy resin not containing a halide, an entry board having a layer made of a resin material is used, and a drill is used. Has disclosed a method of drilling with high-speed rotation and low-speed feed, and by using this method, the smoothness of the inner wall surface of the through-hole can be improved and plating can be performed satisfactorily. It is described that thermal deformation of a printed wiring board due to frictional heat at the time can be prevented.

In the perforating process of a printed wiring board using a film made of a thermoplastic polymer capable of forming an optically anisotropic melt phase (hereinafter referred to as a thermoplastic liquid crystal polymer film) as an insulating substrate, The present invention relates to a manufacturing method for performing a drilling process with excellent positional accuracy and reduced inner surface roughness of a hole, and having a good cutting waste discharging property during drilling.
Furthermore, the present invention can perform a good drilling process even when drilling a small diameter hole having a diameter of 0.3 mm or less, and can perform a good drilling process even when performing a drilling process in which a plurality of multilayer circuit boards are stacked. The present invention relates to a manufacturing method that makes possible.

JP 7-328996 A JP-A-10-335780 JP-A-7-164228 JP 2000-349413 A

  The present inventors have a film made of a thermoplastic polymer that can form an optically anisotropic molten phase having a low dielectric constant and a low dielectric loss tangent (hereinafter, referred to as the following), which can suppress signal transmission loss even in a high frequency band. This is referred to as a thermoplastic liquid crystal polymer film). Using this thermoplastic liquid crystal polymer film as an insulating substrate, a multilayer circuit board formed by laminating this thermoplastic liquid crystal polymer film substrate and a conductor layer is used. The processing conditions for drilling were examined.

  As a result of the study by the present inventors, drilling by a drill using an entry board having a layer made of a resin material as an entry board can be performed on a multilayer circuit board using a thermoplastic liquid crystal polymer film as an insulating layer. The position accuracy of the hole formed as a result of the drilling process is poor, the roughness of the inner wall of the hole is large, the drill life is short, and the drill breaks during the drilling process. all right.

  Also, drill conditions during drilling are examined, and the hole position accuracy is high and the inner wall of the hole is roughened even if conditions such as the number of rotations of the drill, feed speed, ascending speed, number of stacked sheets, and whether or not cycle machining is performed are examined. It was not possible to carry out the drilling process with suppressed.

  When perforating a multilayer circuit board using such a thermoplastic liquid crystal polymer film, since the film is thermoplastic, the liquid crystal polymer resin is melted by the heat generated during drilling, and the molten resin becomes a hole. Adhering to the inner wall and solidifying causes the cause of poor conduction (smear). As a method of treating such smear, there is a method of dissolving and removing the resin adhering to the inner wall of the hole with a chemical solution, but there are limited chemical solutions that can treat smear made of a liquid crystal polymer having excellent chemical resistance. A chemical solution having a high smear processing capability has a problem of destroying a circuit board and the process becomes complicated.

  Furthermore, the above-mentioned problems become particularly prominent when the diameter of the hole to be machined is reduced to, for example, 0.3 mm or less, and deterioration of the hole position accuracy, roughening of the inner wall of the hole, occurrence of smear, breakage of the drill, etc. are likely to occur. Become.

  In addition, even when a plurality of multilayer circuit boards are stacked and drilled, and the through-hole becomes substantially long, the hole position accuracy deteriorates, the inner wall of the hole becomes rough, smear occurs, and the drill breaks easily. .

  An object of the present invention is a manufacturing method for perforating a multilayer circuit board including a thermoplastic liquid crystal polymer film, wherein the hole position accuracy is high, roughening of the inner wall of the hole is suppressed, smear is generated, and cutting scraps on the drill are generated. An object of the present invention is to provide a manufacturing method for perforating a multilayer circuit board, which can perform perforation with less winding.

  For multi-layer circuit boards using thermoplastic liquid crystal polymer film as an insulating layer, the drill after drilling was observed in order to find out why the conventional method could not perform good drilling. It was found that the generated cutting waste was wrapped around, and the cutting waste was not discharged well.

From the above, the reason why the multilayer circuit board using the thermoplastic liquid crystal polymer film as the insulating layer cannot be satisfactorily perforated was considered as follows.
Since the thermoplastic liquid crystal polymer film is thermoplastic, it is easily melted by the heat generated during the drilling process. In addition, the thermoplastic liquid crystal polymer film itself has a layered structure. It seems that the tendency to become a long and slender string becomes particularly remarkable. It was thought that such string-like cutting scraps were easily wound around the drill and caused problems such as breakage of the drill, deterioration of hole position accuracy, and roughening of the inner wall of the hole.

  Machining conditions when drilling a multilayer circuit board include entry board, backup board, drill rotation speed, feed speed, tip load, drill shape (tip angle, twist angle, clearance angle, groove length) , Core thickness, taper thickness, etc.) and the presence or absence of cycle machining, and these conditions are related to the evacuation of cutting waste during drilling and the positional accuracy of holes formed as a result of drilling ing. By combining a specific drill shape and a specific entry board from among these various conditions, the present inventors have successfully performed perforation processing of a multilayer circuit board using a thermoplastic liquid crystal polymer film as an insulating layer. The headline, the present invention has been reached.

  That is, the present invention is a manufacturing method in which a multilayer circuit board using a thermoplastic liquid crystal polymer film as an insulating layer is subjected to a punching process, and the core thickness taper of the drilling tool used for the punching process is 0.015 / mm or more and 0. A method for producing a multilayer circuit board, characterized in that an entry board having a layer made of a resin material is used as an entry board during drilling, which is a drilling tool of less than 0.075 / mm.

  According to the present invention, in drilling a multilayer circuit board using a thermoplastic liquid crystal polymer film as an insulating layer, the hole position accuracy is high, the cutting chip discharge is excellent, the roughness of the inner wall of the hole is suppressed, and the occurrence of smear is suppressed. In addition, drilling with a longer drill life is possible. In addition, small holes, for example, small holes with a diameter of 0.3 mm or less can be drilled well, and drilling can be performed with multiple multilayer circuit boards stacked, resulting in lower productivity and lower costs. It is possible to perform drilling with excellent resistance.

It is a photograph which shows the external appearance of the hole formed as a result of drilling a multilayer circuit board of the present invention, (a) is a photograph showing the result of Example 2, and (b) is a photograph showing the result of Comparative Example 4. . It is a photograph which shows the grade of the winding of the cutting waste to the drill used for the drilling process after giving a drilling process of the multilayer circuit board of this invention, (a) is the result of Example 2, (b) These are photographs showing the results of Comparative Example 4.

  An embodiment for carrying out the present invention is a manufacturing method in which a multilayer circuit board using a thermoplastic liquid crystal polymer film as an insulating layer is subjected to drilling, and the core thickness taper of the drilling tool used for the drilling is 0.015. The drill is less than 0.075, and an entry board having a layer made of a resin material is used as an entry board at the time of drilling.

(Thermoplastic liquid crystal polymer film)
The thermoplastic liquid crystal polymer film is formed from a liquid crystal polymer that can be melt-molded. The thermoplastic liquid crystal polymer is not particularly limited as long as it is a liquid crystalline polymer that can be melt-molded. For example, a thermoplastic liquid crystal polyester or a thermoplastic having an amide bond introduced therein is used. Examples thereof include liquid crystal polyester amide.

  The thermoplastic liquid crystal polymer may be a polymer in which an isocyanate-derived bond such as an imide bond, a carbonate bond, a carbodiimide bond, or an isocyanurate bond is further introduced into an aromatic polyester or an aromatic polyester amide.

  Specific examples of the thermoplastic liquid crystal polymer used in the present invention include known thermoplastic liquid crystal polyesters and thermoplastic liquid crystal polyester amides derived from the compounds (1) to (4) listed below and derivatives thereof. Can be mentioned. However, it goes without saying that there is an appropriate range of combinations of various raw material compounds in order to form a polymer capable of forming an optically anisotropic melt phase.

(1) Aromatic or aliphatic dihydroxy compounds (see Table 1 for typical examples)

(2) Aromatic or aliphatic dicarboxylic acids (see Table 2 for typical examples)

(3) Aromatic hydroxycarboxylic acids (see Table 3 for typical examples)

(4) Aromatic diamine, aromatic hydroxyamine or aromatic aminocarboxylic acid (see Table 4 for typical examples)

Representative examples of the liquid crystal polymer obtained from these raw material compounds include copolymers having the structural units shown in Tables 5 and 6.

  Among these copolymers, a polymer containing at least p-hydroxybenzoic acid and / or 6-hydroxy-2-naphthoic acid as a repeating unit is preferable. In particular, (i) p-hydroxybenzoic acid and 6-hydroxy- A polymer containing a repeating unit with 2-naphthoic acid, (ii) at least one aromatic hydroxycarboxylic acid selected from the group consisting of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid, and 4,4 ′ A repeating unit of at least one aromatic diol selected from the group consisting of dihydroxybiphenyl and hydroquinone and at least one aromatic dicarboxylic acid selected from the group consisting of terephthalic acid, isophthalic acid and 2,6-naphthalenedicarboxylic acid Polymers containing are preferred.

  For example, in the polymer (i), when the thermoplastic liquid crystal polymer contains at least repeating units of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid, p-hydroxybenzoic acid of the repeating unit (A) And the molar ratio (A) / (B) of the repeating unit (B) to 6-hydroxy-2-naphthoic acid is about (A) / (B) = 10/90 to 90/10 in the liquid crystal polymer. Desirably, it is desirable that (A) / (B) = about 50/50 to 85/15, and more preferably (A) / (B) = 60/40 to 80/20. It may be a degree.

  In the case of the polymer (ii), at least one aromatic hydroxycarboxylic acid (C) selected from the group consisting of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid, and 4,4′-dihydroxy At least one aromatic diol (D) selected from the group consisting of biphenyl and hydroquinone, and at least one aromatic dicarboxylic acid (E) selected from the group consisting of terephthalic acid, isophthalic acid and 2,6-naphthalenedicarboxylic acid. The molar ratio of each repeating unit in the liquid crystal polymer is about aromatic hydroxycarboxylic acid (C): aromatic diol (D): aromatic dicarboxylic acid (E) = about 30-80: 35-10: 35-10. More preferably, (C) :( D) :( E) = 35 to 75: 32.5 to 12.5: 3 May be about .5～12.5, more preferably, (C) :( D) :( E) = 40~70: it may be about 30 to 15: 30-15.

  Moreover, it is preferable that the molar ratio of the repeating structural unit derived from aromatic dicarboxylic acid and the repeating structural unit derived from aromatic diol is (D) / (E) = 95 / 100-100 / 95. Outside this range, the degree of polymerization does not increase and the mechanical strength tends to decrease.

  The optical anisotropy at the time of melting referred to in the present invention can be recognized by, for example, placing a sample on a hot stage, heating and heating in a nitrogen atmosphere, and observing the transmitted light of the sample.

  The thermoplastic liquid crystal polymer preferably has a melting point (hereinafter referred to as Mp) in the range of 260 to 360 ° C, more preferably Mp of 270 to 350 ° C. Mp is determined by measuring the temperature at which the main endothermic peak appears with a differential scanning calorimeter (Shimadzu Corporation DSC).

  The thermoplastic liquid crystal polymer may be a thermoplastic polymer such as polyethylene terephthalate, modified polyethylene terephthalate, polyolefin, polycarbonate, polyarylate, polyamide, polyphenylene sulfide, polyether ether ketone, and fluororesin within a range not impairing the effects of the present invention. Various additives may be added, and a filler may be added as necessary.

  The thermoplastic liquid crystal polymer film used in the present invention is obtained by extrusion molding of a thermoplastic liquid crystal polymer. Any extrusion molding method can be applied as long as the direction of the rigid rod-like molecules of the thermoplastic liquid crystal polymer can be controlled, but the known T-die method, laminate stretching method, inflation method and the like are industrially advantageous. In particular, in the inflation method and the laminate stretching method, stress is applied not only in the film machining direction (hereinafter abbreviated as MD direction) but also in the direction perpendicular thereto (hereinafter abbreviated as TD direction). A film with controlled dielectric properties in the TD direction is obtained.

  In extrusion molding, it is preferable to accompany a stretching process in order to control the orientation. For example, in extrusion molding by the T-die method, the melt sheet extruded from the T-die is not only in the MD direction of the film but also in the TD. The melt sheet extruded from the T-die may be stretched in the MD direction and then stretched in the TD direction.

  In addition, in the extrusion molding by the inflation method, a predetermined draw ratio (corresponding to a stretching ratio in the MD direction) and a blow ratio (corresponding to a stretching ratio in the TD direction) with respect to a cylindrical sheet melt-extruded from a ring die. May be stretched.

  The thermoplastic liquid crystal polymer film may be stretched as necessary after extrusion. The stretching method itself is known, and either biaxial stretching or uniaxial stretching may be adopted, but biaxial stretching is preferred because it is easier to control the degree of molecular orientation. For stretching, a known uniaxial stretching machine, simultaneous biaxial stretching machine, sequential biaxial stretching machine or the like can be used.

  Further, if necessary, known or conventional heat treatment may be performed to adjust the melting point and / or the thermal expansion coefficient of the thermoplastic liquid crystal polymer film. The heat treatment conditions can be appropriately set according to the purpose, for example, by heating for several hours at a melting point (Mp) of the liquid crystal polymer of −10 ° C. or higher (for example, about Mp−10 to Mp + 30 ° C., preferably about Mp to Mp + 20 ° C.). The melting point of the thermoplastic liquid crystal polymer film may be increased.

  The thermoplastic liquid crystal polymer film of the present invention thus obtained can be suitably used as a circuit board material because it has excellent dielectric properties and low hygroscopicity.

The thermoplastic liquid crystal polymer film, its derived from rigid structure, generally high melt viscosity at low shear regions, e.g., the melt viscosity of the thermoplastic liquid crystal polymer film at 300 ° C. (shear rate 1000 sec ^{- 1} ) may be, for example, 100 Pa · s or more, preferably about 200 to 100,000 Pa · s (for example, about 150 to 100,000 Pa · s), more preferably about 200 to 10,000 Pa · s. There may be. The melt viscosity can be measured using a viscoelastic rheometer (for example, AR 2000 manufactured by TA Instrucment Japan) under the conditions of a heating rate of 3 ° C./min, a frequency of 1 Hz, a strain of 0.1%, and a normal stress of 5N. it can.

  The melting point (Mp) of the thermoplastic liquid crystal polymer film can be selected within a range of about 200 to 400 ° C., preferably about 250 to 360 ° C., for the purpose of obtaining the desired heat resistance and processability of the film. Preferably it may be about 260-340 degreeC. The melting point of the film can be obtained by observing the thermal behavior of the film using a differential scanning calorimeter. That is, after the sample film was heated at a rate of 20 ° C./min to be completely melted, the melt was rapidly cooled to 50 ° C. at a rate of 50 ° C./min, and then again heated at a rate of 20 ° C./min. The position of the endothermic peak that appears later may be recorded as the melting point of the film.

  The thermoplastic liquid crystal polymer film used in the present invention may have any thickness, and includes a plate or sheet having a thickness of 5 mm or less. However, when used for a high-frequency transmission line, the transmission loss decreases as the thickness increases, so it is preferable to increase the thickness as much as possible. When a thermoplastic liquid crystal polymer film is used as the electrical insulating layer, the thickness of the film is preferably in the range of 10 to 500 μm, and more preferably in the range of 15 to 200 μm. When the thickness of the film is too thin, the rigidity and strength of the film are reduced. Therefore, a method of obtaining an arbitrary thickness by laminating films having a film thickness in the range of 10 to 200 μm may be used.

(Multilayer circuit board)
The thermoplastic liquid crystal polymer film used in the present invention can be bonded to a metal foil such as copper foil as a conductive material by thermal bonding or thermosetting adhesive to form a laminate. A wiring circuit can also be formed by forming a wiring circuit on one metal foil of the prepared laminate. Further, it may be formed on a multilayer substrate. In such a laminated body or printed circuit board, the thickness of the film is preferably in the range of 20 to 150 μm, more preferably in the range of 20 to 50 μm. If the film thickness is too thin, the rigidity and strength of the film will be reduced, so when mounting electronic components on the resulting printed circuit board, it will be deformed by pressure, resulting in poor wiring position accuracy. Cause.

  In addition, thermoplastic liquid crystal polymer films include other electrically insulating materials such as composites with ceramic powder such as aluminum oxide, multiple types of thermoplastic liquid crystal polymers, polyarylate, polyetherketone, polyamide, poly Composites or polymer alloys with ether sulfone, polyether imide, polyimide, polycarbonate, polytetrafluoroethylene, tetrafluoroethylene / hexafluoropropylene copolymer, polyvinyl fluoride, polyvinylidene fluoride, polytrifluoroethylene chloride, etc. It can also be used. In addition, additives, such as a lubricant and antioxidant, may be mix | blended with the raw material film.

In order to further improve the stability of the electrical resistance in the heat cycle test for checking the connection reliability of the above-mentioned wired circuit board, the thermal expansion coefficient of the conductor formed on the thermoplastic liquid crystal polymer film is set to P × 10 ^−6. when a cm / cm / ℃, thermal expansion coefficient of the thermotropic liquid crystal polymer film, (P-10) × 10 - 6 cm / cm / ℃ from ^{(P + 10) × 10 -} 6 cm / cm / ℃ range It is preferable to adjust so that it becomes inward. When it deviates from this range, the occurrence of interfacial peeling between the conductor and the thermoplastic liquid crystal polymer film increases. Here, P values of typical conductors such as copper and aluminum are 11 to 30.

(Drill shape)
[Heart thickness]
Generally, when the core thickness is increased, the rigidity of the drill is improved and the hole position accuracy is also improved, but the groove capacity is reduced by that amount, and the chip discharging performance is deteriorated. The core thickness of the drill used in the present invention is not particularly limited, but is preferably in the range of 0.07 to 0.093 in view of the balance between the hole position accuracy and the cutting waste dischargeability.

[Core thickness taper]
The core thickness taper is one of the factors that determine the hole position accuracy. Generally, as the drill core thickness taper increases, the drill rigidity increases and the hole position accuracy increases, while the groove capacity decreases. As a result, the dischargeability of the cutting waste is deteriorated, and the inner wall of the hole is roughened by the cutting waste. When the drill's core thickness taper is reduced, the rigidity of the drill is lowered and the hole position accuracy is deteriorated, but the groove capacity is increased, so that the cutting waste is improved. As described above, although the influence on the hole position accuracy and the chip dischargeability due to the increase / decrease in the taper of the thickness of the core is contrary to each other, it is used for the drilling of the multilayer circuit using the thermoplastic liquid crystal polymer film in the present invention. It is important that the core thickness taper of the drill is less than 0.075 / mm. In drilling a multilayer circuit board using thermoplastic liquid crystal polymer film, when using a drill with a core thickness taper of less than 0.075 / mm, with emphasis on chip discharge, hole position accuracy, Drilling with excellent discharge performance can be performed. This is presumably due to the following properties specific to thermoplastic liquid crystal polymer films.
(I) Since the thermoplastic liquid crystal polymer film is thermoplastic, it is easily melted by the heat generated during drilling, and the molten resin adheres to the drill and tends to hinder the discharge of cutting waste.
(Ii) Since the thermoplastic liquid crystal polymer film has a layered structure, the cutting waste generated when the thermoplastic liquid crystal polymer film is drilled easily takes a string-like shape, and the string-like cutting waste easily winds around the drill. .
(Iii) Since the thermoplastic liquid crystal polymer film is a soft material, even if it is processed with a drill having a small center thickness taper and low rigidity, hole position displacement due to the low rigidity of the drill hardly occurs.
For the reasons of (i) and (ii) above, when a multilayer circuit board using a thermoplastic liquid crystal polymer film is drilled, cutting waste generated during the drilling process is easily wound around the drill. In the hole position accuracy in the drilling process of the used multilayer circuit board, it is considered that the chip discharging property is a larger factor than the generally called rigidity of the drill. Therefore, it is considered that the hole position accuracy can be improved by using a drill with a small taper taper that emphasizes cutting waste dischargeability. Further, for the reason of (iii) above, since the degree of hole position deviation is not large even with a drill having a small thickness taper and low rigidity, the deviation of the large hole position accuracy as generally said does not occur, and it is good. It is thought that drilling can be performed with hole position accuracy. Further, when the core thickness taper is less than 0.015 / mm, the degree of deviation of the hole position accuracy due to the decrease in the rigidity of the drill becomes large. Therefore, it is important that the core thickness taper is 0.015 / mm or more. .
The range of the core thickness taper is preferably 0.015 / mm to 0.050 / mm, more preferably 0.015 / mm to 0.030 / mm, and still more preferably 0.020 / mm. -0.025 / mm.
Further, if the drill includes at least one portion having a thickness taper of 0.015 or more and less than 0.075 / mm from the distal end portion to the proximal end portion, from the distal end portion of the drill to the proximal end portion of the drill. The value of the core thickness taper may change.

[Helix angle]
Generally, if the twist angle of the drill is increased, the groove capacity is increased, so that the discharging performance at the time of drilling is good, but the shape of the cutting waste tends to be long and easy to wind around the drill. The twist angle of the drill used in the present invention is not particularly limited, but the twist angle may be in the range of 30 ° to 60 ° in view of the balance between the dischargeability of the cutting waste and the ease of winding the cutting waste on the drill. Preferably it may be 35 ° to 50 °, more preferably 40 ° to 45 °. Further, the twist angle may change from the drill tip to the drill base end.

(Drilling speed)
In this drilling process, the rotation speed of the drill is not particularly limited. However, in conventional drilling processes, generally, if the rotation speed is large, the frictional heat between the inner wall and the drill increases, so that melting of the liquid crystal polymer is prevented. From this point of view, it is advantageous that the rotational speed is small. On the other hand, when the rotational speed is extremely small, the discharging performance of the cutting waste is affected, so that it is preferably 50000 rpm or more, more preferably 65000 rpm or more, and further preferably 80000 rpm or more and 160000 rpm or less.

(Chip load)
The feed rate per minute (m / min) is obtained by multiplying the tip load (μm / rev) by the number of revolutions (rpm) and represents the machining efficiency. In general, when the chip load is high, the machining efficiency increases, but the load on the drill increases, so that the drill is easily broken. On the other hand, if the tip load is too slow, the wear of the drill is increased, the cutting waste becomes longer, and it is easy to wrap around the drill and the cutting waste discharge property is deteriorated, so that the drill breaks and the hole position accuracy deteriorates.
In the drilling process of the present invention, the value of the chip load is not particularly limited, but is preferably 6.25 μm / rev to 12.5 μm / rev in view of the balance between the load on the drill and the chip dischargeability. 8.00 μm / rev to 11.0 μm / rev is more preferable, and 9.00 μm / rev to 10.0 μm / rev is even more preferable.

(Entry boat)
As the entry board used in the present invention, it is important to use an entry board having a layer made of a resin material. The material of the entry board is not particularly limited, but may be a bake plate or an aluminum plate.

  In addition, the entry board having a layer made of a resin material may be one in which the entry board surface is lubricated or the entry board surface is laminated with a lubricating resin. By having a layer made of a resin material on the entry board surface that hits the intruding part of the drill during drilling, the biting part of the drill becomes a soft resin, improving the self-centering of the drill and improving the hole position accuracy . Further, the layer made of the resin material is melted by heat generated during the drilling process, and plays a role as a lubricant by coating the drill surface with a resin during the drilling process. This effect provides lubricity to the drill surface, reduces the frictional force generated between the multilayer circuit board and the drill during drilling, suppresses the generation of frictional heat, and melts the film contained in the multilayer circuit board. By suppressing the film, it is possible to prevent the film from fusing to the inner wall of the hole, and to suppress the roughening of the inner wall of the hole and the occurrence of smear. Moreover, since the lubricity is imparted to the drill surface, the slipperiness of the drill surface is increased, so that the cutting waste discharging effect can be enhanced.

  The composition of the resin material is not particularly limited. For example, the resin material may contain a water-soluble lubricant, and the water-soluble lubricant includes polyethylene glycol, polyoxyethylene monoether, polyoxyethylene ester, polyoxyethylene sorbitan. The monoester, polyoxyethylenepropylene block polymer, and polyglycerin monostearate may contain at least one kind.

(Hole diameter)
Although the hole diameter processed in the present invention is not particularly limited, for example, in the drilling of a small diameter of 0.3 mm or less, the hole position accuracy is high, the occurrence of smear of the hole inner wall is reduced, and the roughness of the hole inner wall is suppressed. , There is little wrapping of cutting swarf around the drill, good swarf discharge performance, excellent drill life can be performed, and even with a small diameter of 0.25 mm or less, the hole position accuracy is high, Generation of smears on the inner wall is reduced, roughening of the inner wall of the hole is suppressed, cutting scraps are not wound around the drill, cutting waste is excellent, and drilling can be performed with excellent drill life. Even with a small diameter of 0.20 mm or less, the hole position accuracy is high, the occurrence of smearing on the inner wall of the hole is reduced, the roughening of the inner wall of the hole is suppressed, and there is less wrapping of cutting swarf on the drill, resulting in better swarf discharging performance. And Dori It can perform machining with excellent life, and even with small diameters of 0.12 mm or less, the hole position accuracy is high, the occurrence of smear on the inner wall of the hole is reduced, and the roughening of the inner wall of the hole is suppressed, so that the cutting scraps on the drill are reduced. There are few windings, and the discharge | emission property of a cutting waste is favorable, and the process which was excellent in the drill life can be performed.

(Number of stacked multilayer circuit boards)
The number of stacked multilayer circuit boards in the drilling process of the present invention is not particularly limited, but from the viewpoint of productivity and cost reduction, it is preferable that the number of stacked sheets is large, and the number of stacked sheets is preferably 4 or more, more preferably 6 or more. 10 or more are more preferable.

In the perforation processing of a multilayer circuit board using the thermoplastic liquid crystal polymer film as an insulating layer in the present invention, an entry board having a layer made of a resin material is used, and the core thickness taper is 0.015, which is excellent in discharging performance. It is important to use a drill of at least / mm and less than 0.075 / mm. When this condition is met, the hole position accuracy is high, the drilling swarf discharge performance is good, the drill life is long, and the same drill can be repeatedly processed, the roughness of the inner wall of the hole is suppressed, and the occurrence of smear is suppressed. Good drilling can be performed.
When this condition is not satisfied, for example, an entry board having a layer made of a resin material is used, and when a drill having a core thickness taper of 0.075 or more is used, the hole position accuracy is poor, and the cutting waste discharging performance of the drill is poor. The drill life is short, the inner wall of the hole becomes rough, and problems such as smear occur.
In addition, for example, using an entry board that does not have a layer made of a resin material and does not impart lubricity to the drill, when using a drill having a taper of taper thickness of 0.015 / mm or more and less than 0.075 / mm, The hole position accuracy is poor, the drilling chip dischargeability is poor, the drill life is short, the inner wall of the hole is roughened, and smearing occurs.
In addition, for example, when using a drill having a core thickness taper of 0.075 or more using an entry board that does not have a layer made of a resin material and does not impart lubricity to the drill, the hole position accuracy is poor, There are problems such as poor chip discharge, short drill life, rough inner wall of the hole, and smear.

  In perforating a multilayer circuit board using the thermoplastic liquid crystal polymer film as an insulating layer in the present invention, an entry board having a layer made of a resin material is used, and the core thickness taper is 0.015 / By using a drill with a diameter of not less than 0.05 / mm and less than 0.075 / mm, for example, a small-diameter drilling with a hole diameter of 0.3 mm or less can be processed satisfactorily. Even when perforated by stacking multiple multilayer circuit boards, the hole position accuracy is high, the drill cutting waste is good, the drill life is long and the same drill can be repeatedly processed, and the inner wall of the hole is rough Therefore, it is possible to perform a good drilling process in which generation of smear is suppressed.

[Hole position accuracy]
For the evaluation of the hole position accuracy, the hole position deviation amount on the back side of the lowermost substrate of the multilayer circuit board subjected to perforation processing was measured by the gravity center correction method. “Position accuracy (Max) (μm)”, which is the maximum deviation from the target coordinates, was evaluated with a set hit count of 1000 hits. The evaluation criteria were evaluated as good when “positional accuracy (Max) (μm)” was 50 μm or less, and evaluated as bad when it exceeded 50 μm.

[Cutting waste discharge]
As for the chip evacuation property, the wrapping of the cutting swarf around the drill after drilling is photographed with a digital microscope, ○ when no cutting swarf is attached to the drill tip, and the cutting swarf is attached to the drill tip. Things were recorded as Δ or ×.

[Processing appearance]
The processed holes on the front and back surfaces of the first, third, and sixth sheets were photographed in the vicinity of 1000, 5000, and 10000 hits in each processing condition. A sample in which no burr was generated was indicated by ○, and a sample having a burr was indicated by ×.

[Processing defect rate]
The state of 360 holes on the entry board overlaid on the uppermost layer of the multilayer circuit board on which the drilling process was performed was confirmed, and the ratio of the number of holes where no burr was generated was defined as the processing defect rate.

[Drill life]
In drilling a multilayer circuit board, drilling was repeatedly performed using the same drill, and the drilling life was defined as the number of drills when the drill breakage broke. It was stopped at 10,000 hits.

[Example 1]
Copper foil (BHYX-T-12 made by JX Nippon Mining & Metals), thermoplastic liquid crystal polymer film (CTZ-100 made by Kuraray), thermoplastic liquid crystal polymer film (CTF-25 made by Kuraray), copper foil (JX Nippon Mining) A multilayer circuit board in which BHYX-T-12) manufactured by Nisseki Metal Co., Ltd., a plastic liquid crystal polymer film (CTZ-100 manufactured by Kuraray Co., Ltd.) and a copper foil (BHYX-T-12 manufactured by JX Nippon Mining & Metals Co., Ltd.) are laminated in this order. Prepared. The thickness of one multilayer circuit board was 0.26 mm.

  In the state where six multilayer circuit boards are stacked in the previous period, an aluminum board (LE812F3 manufactured by Mitsubishi Gas Chemical Co., Ltd.) having a layer made of a resin material as an entry board is used as the uppermost layer of the multilayer circuit board on the drill entry side. A bake board (SPB-W manufactured by Nippon Decorax Co., Ltd.) was installed as a backup board in the lowermost layer of the multilayer circuit board. The drilling machine used was ND-1V manufactured by Via Mechanics. As a drill used as a drilling tool, a drill having a twist angle of 45 °, a core thickness of 0.07 mm, and a core thickness taper of 0.020 / mm (FX L350CW manufactured by Union Tool Co., Ltd.) is used. Drilling with a hole diameter of 0.20 mm was performed under the conditions of 80000 rpm, a feed rate of 0.8 m / min, and a chip load of 10 μm / rev. In the drilling process, a cycle process was performed, and the ascending speed of the drill was set to 25.4 m / min. The results are summarized in Table 7.

[Example 2]
Drilling was carried out in the same manner as in Example 1 except that the drilling conditions during drilling were 120,000 rpm and the feed rate was 1.2 m / min. The results are summarized in Table 7.

[Example 3]
Drilling was performed in the same manner as in Example 1 except that the drilling conditions during drilling were 160000 rpm and the feed rate was 1.6 m / min. The results are summarized in Table 7.

[Example 4]
Drilling was carried out in the same manner as in Example 2 except that a drill having a twist angle of 45 °, a core thickness of 0.093 mm, and a core thickness taper of 0.022 / mm (FX L350CW manufactured by Union Tool Co., Ltd.) was used. . The results are summarized in Table 7.

[Example 5]
Drilling was performed in the same manner as in Example 2 except that a drill having a twist angle of 40 °, a core thickness of 0.093 mm, and a core thickness taper of 0.020 / mm (MC L173AW manufactured by Union Tool Co., Ltd.) was used. . The results are summarized in Table 7.

[Comparative Example 1]
Excavation processing was performed in the same manner as in Example 1 except that an aluminum plate having no resin layer was used as the entry board. The results are summarized in Table 7.

[Comparative Example 2]
Excavation processing was performed in the same manner as in Example 2 except that an aluminum plate having no resin layer was used as the entry board. The results are summarized in Table 7.

[Comparative Example 3]
Excavation processing was performed in the same manner as in Example 3 except that an aluminum plate having no resin material layer was used as the entry board. The results are summarized in Table 7.

[Comparative Example 4]
Drilling was performed in the same manner as in Example 2 except that a drill having a twist angle of 40 °, a core thickness of 0.09 mm, and a core thickness taper of 0.075 / mm (MCV L604W manufactured by Union Tool Co., Ltd.) was used. The results are summarized in Table 7.

[Comparative Example 5]
Bake board (SPB-W made by Nippon Decorax Co., Ltd.) without a layer made of resin material is used as an entry board, and a drill used as a drilling tool has a twist angle of 40 °, a core thickness of 0.09 mm, and a core thickness taper of 0 A drill of 075 / mm (MCV L604W manufactured by Union Tool Co., Ltd.) was used except that the drilling conditions during drilling were 50000 rpm, feed rate 0.6 m / min, and tip load 12.0 μm / rev. Drilling was performed in the same manner as in Example 1. The results are summarized in Table 7.

[Comparative Example 6]
Drilling was performed in the same manner as in Comparative Example 5 except that the drilling conditions during drilling were the conditions of a rotational speed of 65000 rpm, a feed rate of 0.8 m / min, and a tip load of 12.3 μm / rev. The results are summarized in Table 7.

[Comparative Example 7]
Drilling was performed in the same manner as in Comparative Example 5 except that the drilling conditions during drilling were the conditions of a rotational speed of 80000 rpm, a feed rate of 1.0 m / min, and a tip load of 12.5 μm / rev. The results are summarized in Table 7.

In Example 2, since a drill having a core thickness taper of 0.020 / mm is used and an entry board having a layer made of a resin material is used, all of the hole position accuracy, cutting waste discharging performance, and machining appearance are good. The result is obtained and the drill life is durable up to 10000 hits. On the other hand, in Comparative Example 2, a drill having a heart thickness taper of 0.020 / mm is used, but since an entry board that does not have a layer made of a resin material is used, the hole position accuracy, cutting waste discharging property, No good results can be obtained in any of the processed appearances, and the drill life is about 266 hits. In Comparative Example 4, an entry board having a layer made of a resin material is used. However, since a drill having a core thickness taper of 0.075 / mm is used, all of the hole position accuracy, cutting waste discharging performance, and machining appearance are good. The result is not obtained. Also, in Comparative Examples 5 to 7 in which processing was performed using an entry board having a core thickness taper of 0.075 / mm and not having a layer made of a resin material, good drilling was not performed. Absent.
For example, as shown in FIG. 1 (a), it can be seen that the hole formed as a result of the drilling process of Example 2 does not show resin adhesion to the hole wall surface and has less smear. On the other hand, as shown in FIG. 1 (b), it can be seen that in the holes formed as a result of the drilling process of Comparative Example 4, the adhesion of the resin to the hole wall surface was observed in some holes, and the smear was large.
Further, for example, as shown in FIG. 2A, it can be seen that the drill used for drilling after the drilling of Example 2 has little winding of cutting waste. On the other hand, as shown in FIG. 2 (b), it can be seen that the drill used for drilling after the drilling of Comparative Example 4 has a lot of winding of cutting waste.

  From the results of Examples 1 to 3, if a drill with a heart thickness taper of 0.020 / mm is used and an entry board having a layer made of a resin material is used, good even if the number of rotations and feed rate of the drill are different It can be seen that a simple drilling process can be performed.

  From the results of Comparative Examples 1 to 3, when using a drill with a core thickness taper of 0.020 / mm and using an entry board without laminating resin, it is good even if the drill speed and feed rate are changed. It turns out that the result is not obtained.

  From the results of Comparative Examples 5 to 7, when using a drill having a core thickness taper of 0.075 / mm and using an entry board that does not have a layer made of a resin material, the number of rotations of the drill, the feed speed, and the chip load It can be seen that good results cannot be obtained in terms of hole position accuracy, cutting waste discharge performance, machining appearance, and drill life even when changing.

  From the results of Example 2 and Example 4, when a drill with a core thickness taper of 0.020 / mm was used and an entry board having a layer made of a resin material was used, even if the core thickness was different, the processing It can be seen that good results are obtained in both positional accuracy and cutting waste dischargeability. Further, from the results of Example 4 and Example 5, when using a drill having a core thickness taper of 0.020 / mm and using an entry board having a layer made of a resin material, the twist angle of the drill is different. Even in this case, it can be seen that good results can be obtained in the processing position accuracy and the cutting waste dischargeability.

Claims (1)

A manufacturing method for perforating a multilayer circuit board using a film made of a thermoplastic polymer capable of forming an optically anisotropic melt phase as an insulating layer, the core thickness taper of a drilling tool used for the perforating process A multi-layer circuit board, characterized in that an entry board having a layer made of a resin material is used as an entry board at the time of drilling, and a drilling tool having a diameter of 0.015 / mm or more and less than 0.075 / mm Manufacturing method.