JP2021009928A - Rigid/flex multilayer printed board - Google Patents

Abstract

To provide a rigid/flex multilayer printed board that has excellent connection reliability for a plating through hole and does not cause a crack in a plating film due to sagging of a cover film.SOLUTION: A rigid/flex multilayer printed board includes a flexible base board, a wiring pattern formed on the flexible base board, a flexible board consisting of a coverlay that protects the wiring pattern, a rigid board on the flexible board, which is composed of an insulating resin layer and the wiring pattern laminated so as to expose a part of the flexible board, and a plating through hole that connects the flexible board and the wiring pattern formed on the rigid board, and the surface of the plating film constituting the plating through hole is coated with a reinforcing metal film having hardness higher than that of the plating film.SELECTED DRAWING: Figure 1

Description

The present invention relates to a rigid flex multilayer printed wiring board, and more particularly to a rigid flex multilayer printed wiring board having excellent connection reliability of through-hole plating through holes.

In recent years, the automatic control of automobiles has been progressing more and more, and the number of parts and various sensors mounted on them has become extremely large. As a result, in printed wiring boards used for parts and sensors, there is an increasing demand for rigid flex multilayer printed wiring boards that can contribute to the high degree of freedom of installation in equipment and the miniaturization of equipment.

As shown in FIG. 9, the rigid flex multilayer printed wiring board pw generally has a flexible substrate 6 arranged in a central portion and a flexible region F that can be bent is partially exposed. A configuration in which a rigid substrate 17 is laminated on the front and back surfaces of No. 6 (the portion where the flexible substrate 6 and the rigid substrate 17 overlap is referred to as a "rigid region R" in which components can be mounted) is often adopted. When forming a through-plating through hole that connects the wiring patterns in the directions, an adhesive for attaching the rigid substrate 17 is interposed on the flexible substrate 6, so that the wall surface of the through hole drilled by drilling is smooth. There was a problem that it was not finished and plating defects were likely to occur.

As a means for solving such a problem, for example, the following is known (see Patent Document 1).
FIG. 10A shows an enlarged cross-sectional view of a main part of the through-plating through hole 15 provided in the rigid region R, and the rigid substrate 17 is laminated on the front and back surfaces of the flexible substrate 6 via an adhesive 3a. A metal foil 20a (for example, a copper foil or an aluminum foil) having excellent ductility and heat dissipation is provided on the side surface of the rigid substrate 17 on which the adhesive 3a is arranged and where the through-hole plating through hole 15 is formed. It is provided. The inner wall of the through hole 15a is smoothly finished by the metal foil 20a.

That is, when the adhesive layer 3a is softened by the frictional heat of the drill, as shown in FIG. 10B, the through hole end portion 15c of the rigid substrate 17 is chipped or cracked due to the advancing and retracting operations of the drill. In addition, since the adhesive 3a is scraped off, a pocket portion 25 may be formed in the plating film 15b. However, the durability and the function of radiating the frictional heat of the drill are combined with the strength improving function of the through hole end portion 15c. The above problem is solved by providing the metal foil 20a having excellent heat dissipation.

By the way, in the current rigid flex multilayer printed wiring board, the adhesive 3a shown in FIG. 10 is also a material in which the same reinforcing base material such as glass cloth as the rigid substrate 17 is impregnated with a thermosetting resin such as epoxy resin ( Prepreg) is used, and in addition, the entry board used for drilling (the backing plate placed on the board during drilling) is not the aluminum plate used for drilling the rigid board 17, but the drill. Since the configuration and processing method have been improved, such as by using an aluminum plate with a resin that suppresses frictional heat, the plating film 15b as shown in FIG. 10B can be formed without providing the metal foil 20a having excellent ductility and heat dissipation. The dent that is large enough to generate the pocket portion 25 no longer occurs.
However, as shown in FIG. 11, even in the current configuration and processing method, the coverlay 5 (specifically, the polyimide constituting the coverlay 5) that protects the wiring pattern 2 formed on the flexible base substrate 1 is used. There was a problem that the sagging (elongation) of the cover film 4) into the plating film 15b could not be completely eliminated (note that reference numeral 3 shown in FIG. 11 indicates “adhesion” constituting the coverlay 5. Agent ".).

This is because the drill used for drilling holes in rigid flex multilayer printed wiring boards does not emphasize wear resistance like general drills used for drilling holes in rigid substrates, but rather sharpness for flexible materials. Originally, it wears faster than general drills because it is emphasized, but in recent years, halogen-free materials containing a large amount of filler in the resin have been used as the insulating resin layer used for rigid substrates. This is because the drill has been worn more quickly, and even if the time for refreshing (polishing) or replacing the drill is set for each product, it cannot be completely prevented.
Therefore, it is almost impossible to eliminate the sagging of the cover film 4 into the plating film 15b caused by the advancing and retreating operations of the drill in the production lot. In other words, the sagging portion of the cover film 4. It is inevitable that the product in which 4a bites into the plating film 15b is mixed in the production lot.

Here, a problem will be described when the sagging portion 4a of the coverlay 4 bites into the plating film 15b.
First, in the case of a rigid flex multilayer printed wiring board, if the sagging portion 4a of the cover film 4 bites into the plating film 15b of the through-hole plating through hole 15, cracks 26 are likely to occur starting from the sagging portion 4a. (See FIG. 11).
The reason is that in the structure of the rigid flex multilayer printed wiring board, the flexible substrate 6 is arranged at the center of the substrate which receives the largest stress, that is, there is a sagging portion 4a of the cover film 4.
Even in the case of a rigid flex multilayer printed wiring board showing such a tendency, in the case of a general specification product, if the thickness of the plating film 15b is 20 μm, a reliability test {for example, plate thickness 0.6 mm, temperature Cycle test conditions: -65 ° C (30 minutes) ⇔ 125 ° C (30 minutes), 100 cycles} There is a high possibility that it will pass, so it does not matter so much, but in the case of in-vehicle specifications, general specifications In addition to being often thicker than (ie, susceptible to greater stress), reliability tests {eg, plate thickness 1.2 mm, temperature cycle test conditions: -65 ° C (30 minutes) ⇔ 125 ° C (30 minutes), 1000 cycles} also requires considerably stricter conditions than general specification products, so there is a high possibility that the reliability test cannot be passed, that is, starting from the sagging portion 4a of the cover film 4, it is easy to use. There is a problem that the risk of occurrence of 26 increases.

Incidentally, if the plating film 15b is thickened (for example, 35 μm or more), it is possible to avoid the risk of crack 26 being generated, but the plating film deposited on the outer layer is also thickened, which hinders high-density wiring. Therefore, it was difficult to hire them.

Japanese Unexamined Patent Publication No. 6-204625

The present invention has been made in view of the above-mentioned conventional problems and actual conditions, and is a rigid with excellent connection reliability of through-hole plating through holes, which does not cause cracks in the plating film due to sagging of the cover film. -The challenge is to provide a flex multi-layer printed wiring board.

As a result of conducting various studies to solve the above problems, the present inventor obtains extremely good results if the plating film constituting the through-plating through hole is coated with a reinforcing metal film having a hardness higher than that of the plating film. We have found that it can be obtained and have completed the present invention.

That is, the present invention comprises a flexible base substrate, a flexible substrate composed of a wiring pattern formed on the flexible base substrate, and a coverlay that protects the wiring pattern; the flexible substrate on the flexible substrate. A rigid substrate composed of an insulating resin layer laminated so as to expose a part of the substrate and a wiring pattern; and a rigid flex provided with a through-plated through hole for connecting the flexible substrate and the wiring pattern formed on the rigid substrate. A rigid flex multilayer printed wiring board, which is a multilayer printed wiring board, wherein the surface of a plating film constituting the through-plated through hole is covered with a reinforcing metal film having a hardness higher than that of the plating film. This solves the above-mentioned problems.

According to the present invention, even when the sagging portion of the cover film bites into the plating film of the through-plating through hole, the plating film is covered with a reinforcing metal film having a higher hardness, so that the plating film can be formed. A rigid flex multilayer printed wiring board with excellent connection reliability of through-plated through holes that does not cause cracks can be obtained.

(A) is a schematic cross-sectional explanatory view showing an embodiment of the rigid flex multilayer printed wiring board of the present invention, and (b) is an enlarged cross-sectional view of a main part of the circled portion of (a). (A) to (d) are schematic cross-sectional process charts showing a manufacturing example of the rigid flex multilayer printed wiring board of the present invention. (E) to (g) are schematic cross-sectional process diagrams following the process of FIG. (H) to (j) are schematic cross-sectional process charts following the process of FIG. (K) to (m) are schematic cross-sectional process diagrams following the process of FIG. (N) to (p) are schematic cross-sectional process diagrams following the process of FIG. (Q) to (s) are schematic cross-sectional process charts following the process of FIG. The schematic cross-sectional explanatory view which shows the other embodiment of the rigid flex multilayer printed wiring board of this invention. Schematic cross-sectional explanatory view showing the structure of a general rigid flex multilayer printed wiring board. (A) is an enlarged cross-sectional view of a main part of a through-plated through hole of a conventional rigid flex multilayer printed wiring board. (B) is an enlarged cross-sectional view of a main part for explaining a pocket portion of a plating film generated by a forward and backward operation of a drill. An enlarged cross-sectional view of a main part of a rigid flex multilayer printed wiring board for explaining the sagging of the cover film into the plating film caused by the advancement and retreat of the drill.

Hereinafter, embodiments of the rigid flex multilayer printed wiring board of the present invention will be described with reference to FIGS. 1 (a) and 1 (b). In this embodiment, a rigid flex multilayer layer provided with a thickness adjusting layer made of a core substrate having a thickness of 100 μm or more on the inner layer side, which is suitable for in-vehicle specification products requiring high rigidity and high-density wiring. The drawings of the printed wiring board are used, and the same parts as those in the prior art are designated by the same reference numerals.

In FIG. 1A, the PW is a rigid flex multilayer printed wiring board, and the rigid flex multilayer printed wiring board PW has a flexible substrate 6 arranged in a central portion and a flexible region F which is partially bendable. It is composed of a rigid substrate 17 laminated on the front and back surfaces of the flexible substrate 6 in an exposed form. The portion where the flexible substrate 6 and the rigid substrate 17 overlap is a "rigid region R" on which components can be mounted.
Specifically, the flexible substrate 6 covers the flexible base substrate 1, the first wiring pattern 2 formed on the front and back surfaces of the flexible base substrate 1, and the adhesive 3 that protects the first wiring pattern 2. It is composed of a coverlay 5 composed of a film 4.
On the other hand, the rigid substrate 17 is formed on the first insulating resin layer 7 arranged on the flexible substrate 6, the thickness adjusting layer 8 made of a core base material having a thickness of 100 μm or more, and the thickness adjusting layer 8. It is composed of a second insulating resin layer 9 and a second wiring pattern 10, and a third insulating resin layer 12 and a third wiring pattern 13 in which three layers are alternately laminated on the forming layer of the second wiring pattern 10. There is.

Then, in the rigid region R, a second wiring pattern 10 formed on both sides of the flexible substrate 6 and a wiring pattern located between the forming layers of the second wiring pattern 10 (here, "first wiring pattern"). 2 ”and“ second wiring pattern 10 ”) are connected to the belled hole 11, between the second wiring pattern 10 and the third wiring pattern 13, and between the third wiring patterns 13 adjacent in the vertical direction. A wiring pattern located between the blind via hole 14, the third wiring pattern 13 of the outer layer laminated on both sides of the flexible substrate 6 and the formation layer of the third wiring pattern 13 of the outer layer (here, "first wiring pattern"). A through-plated through hole 15 for connecting (corresponding to 2), “second wiring pattern 10”, and “third wiring pattern 13 for inner and outer layers” and a solder resist 16 for protecting the third wiring pattern 13 for the outer layer are formed. ..
As shown in FIG. 1B, the surface of the plating film 15b constituting the through-plating through hole 15 is covered with a reinforcing metal film 18 having a hardness higher than that of the plating film 15b. As a result, even when the sagging portion 4a of the cover film 4 bites into the plating film 15b, it is possible to prevent the occurrence of cracks starting from the sagging portion 4a, and the connection reliability of the through-hole plating through hole 15 can be prevented. Can be secured.

Subsequently, a method of manufacturing the rigid flex multilayer printed wiring board PW of the present invention will be described with reference to FIGS. 2 to 7.
The "insulating adhesive layer" that appears in the text is actually a cured "insulating resin layer" rather than a semi-cured adhesive after being cured by heating and laminating press. However, for convenience of explanation, the explanation will proceed with the expression "insulating adhesive layer" regardless of before and after curing.

First, the first wiring pattern 2 is formed by etching a metal foil (for example, "copper foil") having a thickness of 9 to 18 μm on both sides of a flexible base substrate 1 having a thickness of about 25 to 100 μm. Then, by laminating a coverlay 5 (for example, a coverlay having a thickness of about 25 to 70 μm composed of an adhesive 3 and a cover film 4 such as a polyimide film) that protects the first wiring pattern 2, the figure is shown. The flexible substrate 6 shown in 2 (a) is obtained.

Next, the thickness of the core base material 8a having a thickness of 100 μm or more (for example, an insulating substrate in which a reinforcing base material such as glass cloth is impregnated with a thermosetting resin such as epoxy resin) has a thickness of 35 to 105 μm or more. A double-sided metal foil-covered laminated board on which the conductor layer 19a (for example, "copper foil") is laminated is prepared (see FIG. 2 (b1)), and the double-sided metal foil-covered laminated board is etched to be flexible later. A thickness adjusting layer 8 having a solid dummy pattern 19 corresponding to a portion of the substrate 6 to be a flexible region F is obtained (see FIG. 2 (b2)).

Next, the first insulating adhesive layer 7a (for example, a reinforcing base material such as glass cloth) impregnated with a thermosetting resin such as epoxy resin to bond the flexible substrate 6 and the thickness adjusting layer 8 on which the dummy pattern 19 is formed. Prepare a semi-cured prepreg, etc. (see FIG. 2 (c1)), and make a slightly larger opening 7b at the location corresponding to the dummy pattern 19 by router processing, punching press processing, etc. Form (see FIG. 2 (c2)).

Here, it is desirable that the thickness of the first insulating adhesive layer 7a is the same as that of the dummy pattern 19, or that the thickness of the first insulating adhesive layer 7a is about 5 to 10 μm thinner than that of the dummy pattern 19.
The reason is that the resin flowing out from the first insulating adhesive layer 7a can be suppressed from flowing to the dummy pattern 19 side during the heating / laminating press, and the dummy pattern 19 is firmly adhered by the resin. This is because the layers can be laminated without (that is, the resin does not penetrate between the flexible substrate 6 and the dummy pattern 19) (that is, the step of removing the unnecessary portion 21 which is performed later can be easily performed). ..

Next, as shown in FIG. 2D, a first insulating adhesive layer 7a having an opening 7b formed on the front and back surfaces of the flexible substrate 6, a thickness adjusting layer 8 having a dummy pattern 19 formed, and a third layer. (Ii) Insulating adhesive layer 9a (for example, a semi-cured prepreg having a thickness of 20 to 60 μm obtained by impregnating a reinforcing base material such as glass cloth with a thermosetting resin such as epoxy resin), metal foil 20 (for example). For example, copper foils having a thickness of 9 to 18 μm) are arranged in this order, and then heated and laminated pressed to integrally form the constituent members (see FIG. 3E).

Here, in the present embodiment, an example in which only the dummy pattern 19 is formed on the thickness adjusting layer 8 is shown, but of course, a wiring pattern is also formed on the surface opposite to the formation surface of the dummy pattern 19. It is possible. In this case, if the thickness of the conductor layer 19a laminated on the core base material 8a is about 35 μm, it may be formed by etching as it is, and if it is as thick as 70 to 105 μm, the conductor layer 19a may be down-etched once. May be thinned and then formed by etching.

Next, as shown in FIG. 3 (f), after drilling a through hole 11a (for example, a through hole having a hole diameter of 150 to 300 μm) by drilling, a sodium permanganate solution, a potassium permanganate solution, or the like is prepared. By cleaning the inner wall of the through hole 11a by a wet desmear treatment or a dry desmear treatment such as plasma, and then sequentially performing a non-electrolytic plating treatment and an electrolytic plating treatment, the entire surface of the substrate including the through hole 11a is plated film 11b. (For example, a "copper plating film" having a set film thickness of 20 μm) is deposited (see FIG. 3 (g)).

Next, as shown in FIG. 4H, after filling the through hole 11a in which the plating film 11b is deposited with the hole-filling resin 11c, a well-known photoetching process {conductor layer (here, the metal foil 20 and the metal foil 20) A photosensitive etching resist is laminated on the conductor layer to which the plating film 11b is added), and then exposed and developed (for example, developed with a sodium carbonate solution of about 1%) to form an etching resist pattern. Then, after removing the conductor layer exposed from the etching resist pattern by an etching treatment (for example, an etching treatment with a ferric chloride solution or a cupric chloride solution), the unnecessary etching resist pattern is peeled off (for example,). By performing the step (peeling with a sodium hydroxide solution of about 3%)}, the second wiring pattern 10 is formed, and between the second wiring pattern 10 formed on both sides and the forming layer of the second wiring pattern 10. A belled hole 11 is formed to connect the first wiring pattern 2 to be located (see FIG. 4 (i)).

Next, as shown in FIG. 4 (j), a reinforcing group such as a third insulating adhesive layer 12a (for example, a glass cloth or the like) is placed on the second insulating adhesive layer 9a on which the second wiring pattern 10 is formed. A semi-cured prepreg having a thickness of 20 to 60 μm, which is impregnated with a heat-curable resin such as an epoxy resin, and a metal foil 20 (for example, a copper foil having a thickness of 9 to 18 μm) are sequentially laminated. After that, non-through hole 14a (for example, top diameter is 100 to 200 μm, bottom diameter is 100 to 200 μm, bottom diameter) that exposes the second wiring pattern 10 in the lower layer by performing laser processing such as the conformal method, the large window method, and the copper direct method. Formed a non-through hole (80 to 180 μm) (see FIG. 5 (k)), and then the inside of the non-through hole 14a was cleaned by desmear treatment, followed by electrolytic plating treatment and electrolytic plating treatment (plating for filled vias). By sequentially performing electrolytic plating treatment using a liquid), the non-through holes 14a are filled with plating 14b (for example, copper plating) (see FIG. 5 (l)).

Next, a photoetching process was performed on the conductor layer (a metal foil 20 and a plating film composed of a part of the plating 14b deposited on the metal foil 20) of the substrate shown in FIG. 5 (l). A wiring pattern 13 is formed, and a blind via hole 14 connecting the third wiring pattern 13 and the second wiring pattern 10 is formed (see FIG. 5 (m)).

Next, the same steps as in FIGS. 4 (j) to 5 (m) are performed once, and then the same steps as in FIGS. 4 (j) to 5 (l) are performed, as shown in FIG. 6 (n). Then, in the same manner as in the formation of the belly hole 11, the through hole 15a (for example, a through hole having a hole diameter of 200 to 800 μm) and the plating film 15b (for example, the set film thickness was set to 20 μm) were formed. A plating film) is formed (see FIG. 6 (o)).

Next, by performing a photo-etching process, the third wiring pattern 13 of the outer layer is formed, and the third wiring pattern 13 of the outer layer formed on both sides is located between the forming layers of the third wiring pattern 13 of the outer layer. After forming the through-plated through hole 15 connecting the first to third wiring patterns, the solder resist 16 that protects the third wiring pattern 13 of the outer layer is formed. Next, the surface of the plating film 15b (for example, copper plating film) constituting the through-plating through hole 15 is made of a metal having a hardness higher than this, for example, iron, cobalt, palladium, nickel, rhodium, platinum, chromium, or the like. By coating with a reinforcing metal film (not shown here, but corresponding to the “reinforcing metal film 18” shown in FIG. 1 (b)), the intermediate substrate MPW shown in FIG. 6 (p) is obtained.

Here, the configuration of the reinforcing metal film 18 is not particularly limited and may be arbitrarily selected, but a nickel plating film (for example, 3 to 5 μm) and a gold plating film deposited on the nickel plating film (for example, 0. A two-layer structure of 03 to 0.5 μm), a nickel plating film (for example, 1 to 5 μm), a palladium plating film (for example, 0.1 to 2 μm), and a gold plating film (0.03 to 0.5 μm). If the three-layer structure is deposited in this order, it can be formed at the same time during the nickel / gold plating treatment and the nickel / palladium / gold plating treatment performed as the surface treatment of the third wiring pattern 13 exposed to the outer layer. Therefore, it is preferable in order to simplify the manufacturing process and reduce the cost.

Next, router processing is performed on one surface A of the intermediate substrate MPW shown in FIG. 6 (p), and a slit 22 is formed along the outer circumference of the dummy pattern 19 (see FIG. 7 (q)). ), After removing the unnecessary portion 21a located on the flexible region F (see FIG. 7 (r)), the unnecessary portion 21b on the other surface B side of the intermediate substrate MPW is removed by the same means, and then the router. The rigid flex multilayer printed wiring board PW of the present invention shown in FIG. 7 (s) is obtained by performing outer shape processing by processing or punching.

In explaining the present invention, a rigid flex multilayer structure in which a thickness adjusting layer made of a core substrate having a thickness of 100 μm or more is arranged on the inner layer side, which can be suitably used for an in-vehicle specification product having a plate thickness of 0.8 mm or more. Although the description has been given using the example of the printed wiring board PW, the configuration of the present invention is not limited to this, and the insulating resin layer 23 in which the opening 23a is provided in advance in the portion corresponding to the flexible region F as shown in FIG. It may be a rigid flex multilayer printed wiring board having a structure in which wiring patterns 24 are alternately stacked. Further, the present invention can be applied to other configurations as long as it does not deviate from the present invention, and the plate thickness, the number of layers, the material, etc. can be changed within the scope of the present invention. is there.

Further, in using the present invention, it can be said that it is most effective to use it for an in-vehicle specification product in which cracks are likely to occur, but even for a general specification product whose reliability test is not so strict, the plate thickness is 1.0 mm or more. In this case, a higher stress is applied to the central layer on which the flexible substrate is arranged than in the upper and lower layers, and there is a high possibility that cracks in the through-plating through holes starting from the sagging portion of the cover film will occur. It can be said that it is desirable to use it not only for in-vehicle specification products but also for general specification products where cracks may occur.

1: Flexible base substrate 2: First wiring pattern 3, 3a: Adhesive 4: Cover film 4a: Dripping part 5: Coverlay 6: Flexible substrate 7: First insulating resin layer 7a: First insulating adhesive layer 7b : Opening 8: Thickness adjusting layer 8a: Core base material 9: Second insulating resin layer 9a: Second insulating adhesive layer 10: Second wiring pattern 11: Belid hole 11a: Through hole 11b: Plating film 11c: Hole Filling resin 12: Third insulating resin layer 12a: Third insulating adhesive layer 13: Third wiring pattern 14: Blind via hole 14a: Non-through hole 14b: Plating 15: Through plating Through hole 15a: Through hole 15b: Plating film 15c : Through hole end 16: Solder resist 17: Rigid substrate 18: Reinforcing metal film 19: Dummy pattern 19a: Conductor layers 20, 20a: Metal foil 21a, 21b: Unnecessary part 22: Slit 23: Insulating resin layer 23a: Opening 24: Wiring pattern 25: Pocket part 26: Crack F: Flexible area R: Rigid area MPW: Intermediate board PW, pw: Rigid flex multilayer printed wiring board

Claims (2)

A flexible base substrate, a flexible substrate composed of a wiring pattern formed on the flexible base substrate and a coverlay that protects the wiring pattern; a part of the flexible substrate is exposed on the flexible substrate. A rigid flex multilayer printed wiring board provided with a rigid substrate composed of an insulating resin layer and a wiring pattern laminated in such a manner; and a through-plated through hole for connecting the flexible substrate and the wiring pattern formed on the rigid substrate. A rigid flex multilayer printed wiring board, characterized in that the surface of a plating film constituting the through-plated through hole is coated with a reinforcing metal film having a hardness higher than that of the plating film. The reinforcing metal film has a two-layer structure consisting of a nickel plating film and a gold plating film deposited on the nickel plating film, or a three-layer structure in which a nickel plating film, a palladium plating film, and a gold plating film are deposited in this order. The rigid flex multilayer printed wiring board according to claim 1.