JP2007048999A - Rigid-flex multilayer board or multilayer flexible wiring board manufacturing method and rigid-flex multilayer board or multilayer flexible wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To find a laser processing condition suitable for manufacturing a rigid flex multilayer substrate or a multilayer flexible wiring board, and to form a via hole having a good shape and excellent reliability.
Laser processing conditions for producing a via hole 32 used for interlayer connection are a pulse energy of 1 to 20 mJ, a pulse width of 1 to 30 μs, and a shot number of 1 to 10 times. Provided is a method for producing a rigid-flex multilayer board or multilayer flexible wiring board. In the present invention, it is preferable to form a multilayer board 30 by laminating a plurality of copper-clad laminates 10 and 20, and to form an opening 23 for a via hole 32 by laser processing in the state of the multilayer board 30.
[Selection] Figure 1

Description

  The present invention relates to a manufacturing method of a rigid flex multilayer board or a multilayer flexible wiring board, and a rigid flex multilayer board or a multilayer flexible wiring board.

  Conventionally, multilayer printed wiring boards having two or more layers of circuits have been widely used as circuit boards used inside electrical and electronic devices. The multilayer printed wiring board includes a rigid rigid wiring board (multilayer RPC) composed only of a rigid wiring board (RPC), and a rigid flex multilayer board in which a flexible wiring board (FPC) and a rigid wiring board (RPC) are combined. R-F wiring board) is well known. Multilayer rigid wiring boards are used in electronic devices such as personal computer motherboards. Rigid flex multilayer substrates are used in electronic devices such as digital cameras. Furthermore, in recent years, from the viewpoint of reducing the weight and thickness of electrical and electronic devices, the adoption of multilayer flexible wiring boards (multilayer FPC), which is composed entirely of FPCs, is also progressing.

FIG. 5 shows a method for manufacturing a multilayer FPC having a four-layer circuit as an example of a method for manufacturing a general multilayer printed wiring board. FIG. 5 shows the copper foil 12 and the single-sided copper-clad laminate 20 of the inner layer FPC 10 only on one side (upper circuit two layers), and the other side (lower circuit two layers) is omitted for simplicity. is doing.
(1) A via hole forming opening 23 is formed in a single-sided copper-clad laminate 20 (see FIG. 5A) having a copper foil 22 on one side of an insulating substrate 21 (see FIG. 5B).
(2) As shown in FIG. 5 (c), the single-sided copper clad laminate 20 having the openings 23 and the inner layer FPC 10 are laminated with an adhesive 31. The inner layer FPC 10 is obtained by forming circuits on the copper foils 12 (only one side is shown) on both surfaces of the insulating base material 21 before lamination.
(3) As shown in FIG. 5D, the via hole forming opening 23 is filled with a conductor 33 by electrolytic copper plating or the like, and a via hole 32 for establishing conduction between layers is formed.
(4) A surface resist (not shown) is formed to protect the circuit formed on the copper foil 22 of the single-sided copper clad laminate 20.

Patent Document 1 proposes an optimum laser processing condition for a printed wiring board using a prepreg as an insulating substrate.
JP 2000-232268 A

The opening for forming a via hole is generally formed by laser processing using a carbon dioxide laser. However, it is not necessary to irradiate the laser indiscriminately, and it is obvious to carry out under the optimum laser processing conditions. When deviating from the optimum region, the following phenomenon occurs.
(1) Damage to the metal layer due to laser (2) Adhesive layer on the inner wall surface of the via hole, unevenness of the insulating substrate, and plating failure (3) Abnormal deposition of plating in the via hole (4) Residual carbide

  When such a phenomenon occurs, the yield in manufacturing a printed wiring board is lowered, and the reliability as an industrial product is impaired. As a result, a continuity failure or the like may occur in an electric device or an electronic device in which a printed wiring board is used, and the electrical reliability may be significantly reduced.

  The proposal described in Patent Document 1 is limited to the case where prepreg is used as the insulating base material, and is not appropriate when polyimide is used. That is, Patent Document 1 is a proposal only for a multilayer RPC, and cannot be applied to an R-F wiring board in which FPC and RPC are combined, or a multilayer FPC configured only by FPC. This is because the object to be irradiated with the laser is different, and the optimum region of the laser processing conditions is also different.

  Moreover, the method described in Patent Document 1 is a manufacturing method in which a via hole is formed in a single-sided circuit board and the core layer is laminated to form a multilayer printed wiring board. However, in such a method, as shown in FIG. 6, there is a possibility that displacement occurs when the via hole forming opening 23 is formed by laser processing after being stacked. The portion 24 where the circuit 12 of the inner layer FPC 10 does not exist at the bottom of the opening 23 is not provided with the plating 33, and there is a problem of poor conduction as shown in FIG. For this reason, it is necessary to design in consideration of positional deviation, and it is necessary to increase the land diameter, so that there is a problem that it is not suitable for circuit refinement.

  Further, Patent Document 1 only clearly shows laser processing conditions for a single-sided printed wiring board, and does not specify laser processing conditions for a multilayer substrate.

  The present invention has been made in view of the above circumstances, finds a laser processing condition suitable for manufacturing a rigid-flex multilayer board or a multilayer flexible wiring board, and forms a via hole having a good shape and excellent electrical reliability. It is an object of the present invention to provide a method for producing a rigid flex multilayer substrate or a multilayer flexible wiring board, and a rigid flex multilayer substrate or a multilayer flexible wiring board.

In order to solve the above-mentioned problems, the present invention provides a laser processing condition for producing a via hole used for interlayer connection, wherein the pulse energy is 1 to 20 mJ, the pulse width is 1 to 30 μs, and the number of shots is 1 to 10 times. A method for producing a rigid-flex multilayer board or multilayer flexible wiring board is provided.
In the present invention, it is preferable to laminate a plurality of copper-clad laminates to form a multilayer board, and perform laser processing of the via hole in the state of the multilayer board.
As the laser used for the laser processing, a carbon dioxide laser is preferable.
As the insulating substrate on which the via hole is formed, it is preferable to use a substrate formed from a polyimide composite material having a thickness of 5 to 50 μm.
The thickness of the copper foil of the copper clad laminate is preferably 3 to 50 μm.
The diameter of the via hole is preferably 5 to 300 μm.

According to the present invention, a rigid flex is characterized in that a via hole formed under laser processing conditions with a pulse energy of 1 to 20 mJ, a pulse width of 1 to 30 μs, and a shot number of 1 to 10 is used for interlayer connection. A multilayer substrate or a multilayer flexible wiring board is provided.
The insulating base material having the via hole is preferably formed from a polyimide composite material having a thickness of 5 to 50 μm.
The thickness of the copper foil of the copper clad laminate is preferably 3 to 50 μm.
The hole diameter of the via hole is preferably 5 to 300 μm.

According to the present invention, a laser processing condition for forming an opening for forming a via hole is optimized for a rigid flex multilayer substrate or a multilayer flexible wiring board, and a via hole having a good shape and excellent electrical reliability is obtained. It is possible to form.
When a multilayer board is formed by laminating a plurality of copper-clad laminates and laser processing of via holes is performed in the state of the multilayer board, since there is no positional shift due to the lamination, the density can be increased. Moreover, IVH can be formed in the state of a multilayer board.

The present invention will be described below with reference to the drawings based on the best mode. FIG. 1 is a sectional process diagram for explaining an example of a method for forming a via hole in a multilayer printed wiring board using the present invention.
In the method for manufacturing a multilayer printed wiring board according to this embodiment, first, as shown in FIG. 1A, a plurality of copper-clad laminates 10 and 20 are laminated to form a multilayer board 30. Here, the copper-clad laminate 10 (hereinafter referred to as “first copper-clad laminate 10” for distinction) positioned on the inner side during laser processing is either one side of the insulating substrate 11 or Copper foil 12 is laminated on both sides (FIG. 1 shows copper foil 12 only on one side). Further, a copper clad laminate 20 (hereinafter referred to as a “second copper clad laminate 20” for distinction) positioned outside during laser processing is formed on one surface of the insulating substrate 21 with copper. This is a single-sided copper-clad laminate in which a foil 22 is laminated.

  Prior to lamination, a circuit is formed on the copper foil 12 of the first copper-clad laminate 10. In the case where the first copper-clad laminate 10 is a double-sided copper-clad laminate, plating through holes and the like are formed in order to establish conduction between the circuits on both sides. Between the copper foil 12 of the first copper clad laminate 10 and the second copper clad laminate 20, an adhesive layer 31 for adhering them is laminated. Needless to say, generally used adhesives such as epoxy and acrylic are applicable to the adhesive layer 31, but are not particularly limited in the present invention.

  As the insulating base materials 11 and 21 of the copper-clad laminates 10 and 20, polyimide and a polyimide composite material are used. The thickness of the insulating base materials 11 and 21 is not particularly limited as long as it is in the range of about 5 to 50 μm. The thickness of the copper foils 12 and 22 is not particularly limited as long as it is in a range of about 3 to 50 μm that is generally used. By using a carbon dioxide laser, the copper foil 12 of the first copper-clad laminate 10 does not penetrate during laser processing.

  After the lamination of the copper clad laminates 10 and 20, as shown in FIG. 1 (b), the copper foil 22 of the second copper clad laminate 20 is at a position where via holes 32 are formed prior to laser processing. Opening 22a is formed. The position of the opening 22a is at a predetermined position on the conductor pattern of the copper foil 12 so that the plating layer 33 formed in the via hole 32 can be connected to the copper foil 12 of the first copper-clad laminate 10 satisfactorily. Aligned with respect to. The alignment between the layers can be performed with reference to an alignment hole (not shown) or an alignment mark.

  In order to form the via hole 32 in the state of the multilayer board 30, as shown in FIG. 1 (c), the insulating base material 21 of the second copper-clad laminate 20 exposed from the opening 22a and its lower side 1 is formed by drilling the adhesive material layer 31 located on the surface by laser irradiation to form a via hole forming opening 23 and removing a smear such as carbides (desmear). Then, as shown in FIG. The opening 23 is filled with a conductor (plating layer) 33 by plating or the like. The plating layer 33 can be formed by electrolytic or electroless plating such as copper. After forming a circuit and a via hole in the second copper clad laminate 20, it is preferable to laminate a cover lay (CL) or a surface resist (not shown) for circuit protection or the like. Moreover, you may perform protection processes, such as a rust prevention process.

  The insulating base material 21 of the second copper clad laminate 20 in which the opening 23 of the via hole 32 is formed is preferably made of a polyimide composite material having a thickness of 5 to 50 μm. The reason is that if the thickness of the insulating substrate 21 is less than 5 μm, the strength is lowered and handling is difficult, and conversely if it exceeds 50 μm, formation of fine via holes and filling of a conductive substance becomes difficult. The diameter (hole diameter) of the opening 23 of the via hole 32 is not particularly limited as long as it is a size generally processed with a carbon dioxide laser (5 to 300 μm).

In the present invention, the following conditions (1) to (3) are adopted as laser processing conditions when opening the via hole forming opening 23 in the insulating base material 21.
(1) The pulse energy is 1 to 20 mJ, more preferably 2 to 10 mJ.
(2) The pulse width is 1 to 30 μs, more preferably 3 to 10 μs.
(3) The number of shots is 1 to 10 times, more preferably 3 to 7 times.

  The laser used for processing is preferably a carbon dioxide laser. The laser pulse interval is preferably 2 ms or more.

The reason why the laser processing conditions (1) to (3) are used is as follows.
When the pulse energy is low and / or the number of shots is small, carbides may remain or abnormal deposition of the plating layer 33 may occur. In particular, when the pulse energy is low and the number of shots is small, the opening 23 may not exist. On the contrary, when the pulse energy is high and / or the number of shots is large, damage to the copper foils 12 and 22 around the opening 23 or the bottom of the opening 23 is large, and the adhesive on the inner wall surface of the opening 23 is large. Concavities and convexities on the surface of the layer 31 and the insulating substrate 21 are also increased, which causes a decrease in electrical reliability. In addition, when the pulse width is short, the thermal influence on the resin is increased, and the unevenness on the surfaces of the adhesive layer 31 and the insulating substrate 21 is also increased.

  That is, if the pulse energy is lowered, the pulse width is lowered, and the number of shots is increased, the shape of the via hole forming opening 23 is good, but the productivity is lowered and the cost is increased. Conversely, the higher the pulse energy, the longer the pulse width, and the smaller the number of shots, the higher the productivity, but the shape of the via hole forming opening 23 deteriorates. Therefore, by performing laser processing within the conditions described in (1) to (3) above, the via hole 32 having a good shape and excellent electrical reliability can be formed. In particular, it is preferable to use the conditions more preferable in the above (1) to (3).

In other words, the laser processing conditions must take into account electrical reliability and productivity, and parameters for laser processing such as “pulse energy”, “pulse width”, and “number of shots” are optimal regions. That is why.
The present invention is not a laser processing condition for a single-sided copper-clad laminate or a prepreg described in Patent Document 1, but a laser processing condition for a copper-clad laminate using polyimide. That is, among the multilayer printed wiring boards, a rigid flex multilayer board (R-F wiring board) in which a flexible wiring board (FPC) and a rigid wiring board (RPC) are combined, and a multilayer flexible wiring board composed only of FPC. Only (multi-layer FPC) is targeted.

As described above, according to the present invention, the laser processing conditions for forming the opening 23 for the via hole 32 are optimized for a rigid-flex multilayer board or multilayer flexible wiring board, and have a good shape and electrical properties. It is possible to form the via hole 32 having excellent mechanical reliability.
When a multilayer board 30 is formed by laminating a plurality of copper clad laminates 10 and 20, and laser processing of the via hole 32 is performed in the state of the multilayer board 30, it is possible to form a circuit by correcting misalignment during lamination. , Position shift can be prevented and high density can be achieved. Moreover, IVH can be formed in the state of the multilayer board 30.

Hereinafter, the present invention will be specifically described with reference to examples. In addition, this invention is not limited only to these Examples.
In the following examples, a four-layer flexible wiring board (substrate size: 300 × 300 mm) was produced in which one single-sided copper-clad laminate was laminated on each side of a double-sided copper-clad laminate.

<Constituent materials>
As the double-sided copper-clad laminate (double-sided CCL) serving as the inner layer substrate, a laminate of 18 μm thick copper foils on both sides of 25 μm thick polyimide (PI) was used.
As the single-sided copper-clad laminate (single-sided CCL) to be the outer layer substrate, one obtained by laminating a 18 μm thick copper foil on one side of a 25 μm thick polyimide (PI) was used.
As the coverlay (CL), a laminate of 25 μm thick adhesive material on one side of 25 μm thick polyimide (PI) was used.
As the interlayer adhesive, an adhesive having a thickness of 40 μm was used.

<Manufacturing method>
(1) A required wiring pattern is produced on the inner layer CCL to form an inner layer FPC.
(2) Single-sided CCL is laminated on both sides of the inner layer FPC. At this time, an interlayer adhesive is interposed between the inner layer FPC and each single-sided CCL.
(3) An opening for forming a via hole (via diameter φ50 μm) is opened using a carbon dioxide laser.
(4) After desmearing the inside of the opening, electrolytic copper plating is performed to achieve interlayer conduction.
(5) A required wiring pattern is formed on the outer layer substrate to form an outer layer FPC.
(6) A coverlay (CL) is laminated on the surface of the outer layer FPC to complete a multilayer FPC.

<Laser processing conditions>
The laser processing conditions shown in (1), (2), and (3) of Table 1 were used as laser processing conditions when opening a hole for forming a via hole using a carbon dioxide laser.

Under the laser processing conditions of (1) in Table 1, the pulse width was fixed to 7 μs, the number of shots was fixed to 7 times, and the pulse energy was changed in 9 ways in the range of 1 to 50 mJ.
Under the laser processing conditions of (2) in Table 1, the pulse energy was fixed to 5 mJ, the number of shots was fixed to 5 times, and the pulse width was changed to 10 in the range of 1 to 50 μs.
In the laser processing conditions of (3) in Table 1, the pulse energy was fixed to 4 mJ, the pulse width was fixed to 4 μs, and the number of shots was changed to 10 in the range of 1 to 50 times.

<Test method>
In order to test the interlayer connection reliability of the sample, a vapor phase heat shock test (vapor phase thermal shock test) generally performed as an evaluation of a printed wiring board was performed. The test conditions were set to -25 ° C / 30 minutes to 125 ° C / 30 minutes (using a low temperature bath of -25 ° C and a high temperature bath of 125 ° C and replacing them in alternate tanks in 60 minutes per cycle). Then, the conductor resistance of the via hole was continuously measured, and the number of cycles until disconnection (until the resistance value reached a predetermined value or more) was counted.

<Test results>
The results of tests conducted on the laser processing conditions (1), (2), and (3) in Table 1 are shown in FIGS. 2, 3, and 4, respectively.

  As shown in FIG. 2, the number of cycles decreases as the pulse energy increases in the laser processing condition (1). This is because the laser was irradiated more than necessary, "damage of the metal layer by laser", "unevenness of the adhesive layer and insulating substrate on the inner wall of the via hole", "abnormal deposition of plating in the via hole", "carbide It is probable that the “deterioration of plating due to residual” occurred.

  From FIG. 3, the number of cycles decreases as the pulse width increases in the laser processing condition (2). This is because the laser was irradiated more than necessary, "damage of the metal layer by laser", "unevenness of the adhesive layer and insulating substrate on the inner wall of the via hole", "abnormal deposition of plating in the via hole", "carbide It is probable that the “deterioration of plating due to residual” occurred.

  From FIG. 4, the cycle number decreases as the number of shots increases under the laser processing condition (3). This is because the laser was irradiated more than necessary, "damage of the metal layer by laser", "unevenness of the adhesive layer and insulating substrate on the inner wall of the via hole", "abnormal deposition of plating in the via hole", "carbide It is probable that the “deterioration of plating due to residual” occurred.

  In the gas phase heat shock test, it is judged that the electrical reliability is better as the number of cycles until disconnection is larger. If the cycle number is absolutely large (if it is above a certain value), it is considered that the reliability as a printed wiring board can be secured. Is different. Therefore, it is preferable to select the one having a relatively high cycle number from the dependence on the parameters of laser processing conditions such as pulse energy, pulse width, and number of shots.

From FIG. 2, the pulse energy for obtaining the number of cycles of 1000 times or more is 1 to 20 mJ, and the pulse energy for obtaining the number of cycles of 1500 times or more is 2 to 10 mJ.
From FIG. 3, the pulse width for obtaining the number of cycles of 1000 times or more is 1 to 30 μs, and the pulse width for obtaining the number of cycles of 1500 times or more is 3 to 10 μs.
From FIG. 4, the number of shots that can obtain 1000 or more cycles is 1 to 10 times, and the number of shots that can obtain 1500 or more cycles is 3 to 7 times.
In the present invention, it was determined that the number of cycles of 1000 times or more can be used as suitable laser processing conditions. More preferably, the number of cycles was determined to be 1500 times or more. Based on this determination, it can be seen that the above laser processing conditions are suitable.
The pulse width is not particularly limited as long as it is 2 ms or more.

  The present invention can be used for manufacturing a rigid-flex multilayer board and a multilayer flexible wiring board.

(A)-(d) It is sectional process drawing explaining an example of the method of forming a via hole in a multilayer printed wiring board using this invention. It is a graph which shows the relationship between the pulse energy and cycle number by an Example. It is a graph which shows the relationship between the pulse width and cycle number by an Example. It is a graph which shows the relationship between the shot number and cycle number by an Example. (A)-(d) It is sectional process drawing explaining an example of the method of forming a via hole in a multilayer printed wiring board using a conventional method. It is sectional drawing explaining an example of the state which the position shift produced in the copper foil of inner layer FPC, and the opening of outer layer CCL. FIG. 7 is a cross-sectional view illustrating a problem when plating is performed on the multilayer substrate in which the positional shift of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... 1st copper clad laminated board (inner layer FPC), 11 ... Insulating base material, 12 ... Copper foil (circuit), 20 ... 2nd copper clad laminated board (single-sided copper clad laminated board), 21 ... Insulating Substrate, 22 ... copper foil (circuit), 23 ... opening for via hole formation, 30 ... multilayer board (multilayer printed wiring board), 32 ... via hole.

Claims (10)

  Rigid-flex multilayer substrate characterized in that laser processing conditions for producing via holes used for interlayer connection are conditions of pulse energy of 1 to 20 mJ, pulse width of 1 to 30 μs, and number of shots of 1 to 10 times Or the manufacturing method of a multilayer flexible wiring board.   The rigid-flex multilayer board or multilayer flexible wiring board according to claim 1, wherein a multilayer board is formed by laminating a plurality of copper-clad laminates, and via holes are laser processed in the state of the multilayer board. Method.   The method for manufacturing a rigid-flex multilayer board or multilayer flexible wiring board according to claim 1 or 2, wherein the laser used in the laser processing is a carbon dioxide gas laser.   The rigid-flex multilayer substrate according to any one of claims 1 to 3, wherein the insulating base material on which the via hole is formed is formed of a polyimide composite material having a thickness of 5 to 50 µm. Multilayer flexible wiring board.   The method for producing a rigid-flex multilayer board or multilayer flexible wiring board according to any one of claims 1 to 4, wherein the copper foil of the copper-clad laminate has a thickness of 3 to 50 µm.   6. The method of manufacturing a rigid-flex multilayer board or multilayer flexible wiring board according to claim 1, wherein the via hole has a diameter of 5 to 300 [mu] m.   Rigid flex multilayer substrate or multilayer flexible characterized in that via holes formed under laser processing conditions with pulse energy of 1 to 20 mJ, pulse width of 1 to 30 μs, and number of shots of 1 to 10 are used for interlayer connection Wiring board.   The rigid-flex multilayer substrate or multilayer flexible wiring board according to claim 7, wherein the insulating base material having the via hole is formed of a polyimide composite material having a thickness of 5 to 50 µm.   9. The rigid-flex multilayer board or multilayer flexible wiring board according to claim 7, wherein the copper-clad laminate has a copper foil thickness of 3 to 50 [mu] m.   The rigid-flex multilayer board or multilayer flexible wiring board according to any one of claims 7 to 9, wherein the via hole has a hole diameter of 5 to 300 µm.

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