Substrate and electronic device

Abstract

The invention provides a substrate and an electronic device which can cope with narrower pitch of solder bumps, reduce the amount of solder used, and ensure a desired solder bump height. A substrate according to an embodiment includes: a base material; a wiring pattern provided on the base material; an insulating member covering the substrate and the wiring pattern and having an opening corresponding to a bump forming portion of the wiring pattern; and a covering portion which is formed of a material having a larger solder contact angle than the bump forming portion at the opening portion, and which covers a part of the bump forming portion.

Description

Technical Field

[0001] Embodiments of the present invention relate to a substrate and an electronic device. Background Art

[0002] In recent years, high-density mounting technology corresponding to increased capacity has been required for printed circuit boards mounted on hard disk drives (HDDs).

[0003] In particular, the shape of the flexible printed circuit board (FPC) that electrically connects the magnetic head to a printed circuit board equipped with a control circuit or a drive circuit and carries a preamplifier IC that amplifies the signal from the magnetic head is strictly restricted. Due to the multi-pin and large-scale preamplifier IC, the difficulty of installation becomes higher.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 9-283908

[0007] Patent Document 2: Japanese Patent Application Laid-Open No. 2-140936 Summary of the invention

[0008] Problems to be solved by the invention

[0009] Therefore, it is desired to realize high reliability while taking into consideration manufacturing quality, mountability, and the like for flexible printed circuit boards.

[0010] More specifically, a plurality of solder bumps for electrically connecting a magnetic head are formed on a flexible printed circuit board, and it is desired to suppress short circuits between adjacent solder bumps, reduce the amount of solder used, and ensure a desired solder bump height in response to narrowing of pitches.

[0011] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a substrate and an electronic device that can cope with narrower pitches of solder bumps while reducing the amount of solder used and ensuring a desired solder bump height.

[0012] Means for solving problems

[0013] The substrate of the embodiment comprises: a base material; a wiring pattern arranged on the base material; an insulating component covering the base material and the wiring pattern and having an opening corresponding to a bump forming portion of the wiring pattern; and a covering portion, which is formed at the opening by a material having a larger contact angle of solder than that of the bump forming portion and covers a portion of the bump forming portion. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1It is an explanatory diagram of a flexible substrate assembly for HDD according to an embodiment.

[0015] Figure 2 This is a schematic perspective view of the appearance of a solder bump portion.

[0016] Figure 3 This is an explanatory diagram of solder bump formation (part 1).

[0017] Figure 4 This is an explanatory diagram of solder bump formation (part 2). DETAILED DESCRIPTION

[0018] Next, embodiments will be described in detail with reference to the drawings.

[0019] Here, before explaining the embodiment, conventional problems will be explained.

[0020] Conventionally, HDDs have been designed with optimized designs and then verified for reliability, resulting in high-density, high-reliability substrates.

[0021] The flexible substrate used in HDD is equipped with multiple CPUs, SoC (System on a Chip) embedded with signal processing circuits for analog signals read from multiple magnetic heads, host interface circuits, storage devices such as DRAM, and motor driver ICs for driving spindle motors and voice coil motors.

[0022] Furthermore, a preamplifier IC that is connected to the magnetic head and performs writing and reading of data by the magnetic head is mounted on the flexible substrate.

[0023] Furthermore, the flexible substrate is required to have good flexibility and durability against repeated bending operations caused by seek operations of a high-speed HDD, and cleanability to prevent dust from being emitted.

[0024] In recent years, in order to achieve further large-capacity HDDs, from the perspective of increasing the number of disks and heads, embedding TDMR (Two Dimensional Magnetic Recording) and microwave assisted recording (MAMR) technologies, it is hoped to further suppress short circuits between adjacent solder bumps, reduce the amount of solder used, and ensure the desired solder bump height in response to narrowing of pitches.

[0025] Figure 1 It is an explanatory diagram of a flexible substrate assembly for HDD according to an embodiment.

[0026] Figure 1 (A) is a front view of the flexible substrate assembly. Figure 1 (B) is a rear view of the flexible substrate assembly.

[0027] The flexible substrate assembly 10 includes a flexible substrate 11 , a first support plate 12 , a second support plate 13 , and a third support plate 14 .

[0028] In this structure, the first support plate 12 is fixed at a predetermined position near the magnetic head in the HDD housing, the second support plate 13 is arranged at a predetermined position in the HDD housing, and the third support plate 14 is fixed at a predetermined position near the controller substrate of the HDD.

[0029] The flexible substrate 11 includes a head portion 11 - 1 , a wiring pattern portion 11 - 2 , and a base portion 11 - 3 .

[0030] The head 11 - 1 includes an amplifier connection terminal portion 21 where a preamplifier IC is arranged, and a solder bump forming portion 22 where a plurality of solder bumps are formed to connect a terminal group of connection cables of a plurality of magnetic heads.

[0031] More specifically, the solder bump forming portion 22 has a number corresponding to the number of magnetic heads that can be connected (in Figure 1 In the example, 20) corresponding to the terminal group 25. Figure 1 In the example of FIG. 1 , the terminal groups 25 extend in the vertical direction, and each terminal group 25 has solder bump portions (terminal portions) 26 whose number corresponds to the number of functions of the magnetic head.

[0032] For example, each of the terminal groups 25 has ten solder bump portions 26 .

[0033] The wiring pattern portion 11 - 2 is arranged by covering a wiring pattern (not shown) formed of copper foil with a cover film, and electrically connects the wiring pattern of the head portion 11 - 1 and the wiring pattern of the base portion 11 - 3 .

[0034] The base portion 11 - 3 is provided with connection terminals (not shown) for a controller substrate of the HDD device and the like.

[0035] Figure 2 This is a schematic perspective view of the appearance of a solder bump portion.

[0036] like Figure 1 As shown, the solder bump portion 26 is formed on the flexible substrate 11 .

[0037] Specifically, the solder bump portion 26 is provided with a base material 11A constituting the flexible substrate 11 and a wiring pattern 11B constituted of a copper foil or the like on the base material 11A.

[0038] As a material of the base material 11A, a resin film such as a polyimide film or a PET film is used.

[0039] A base film 11C as an insulating member is provided on the substrate 11A.

[0040] The base film 11C covers the substrate 11A and the wiring pattern 11B, and has openings 11C1 formed therein corresponding to the bump forming portions 11B1 of the wiring pattern 11B.

[0041] As a material of the base film 11C, a resin film such as a polyimide film or a PET film is used.

[0042] The wiring pattern 11B uses, for example, a copper thin film as a conductor.

[0043] Furthermore, the portion of the wiring pattern 11B other than the opening portion 11C1 and a portion of the base film 11C have a covering film 11D that functions as a covering portion 11D1 that covers a portion of the bump forming portion 11B1, and the covering film 11D is formed of a material having a larger contact angle of solder than the bump forming portion 11B1 (a material having lower wettability of solder than the bump forming portion 11B1), that is, a material having a larger contact angle (lower wettability) than the material of the wiring pattern 11B.

[0044] exist Figure 2 In the embodiment, the bump forming portion 11B1 has a rectangular shape when viewed from above. In addition, a portion of the cover film 11D functions as a cover portion 11D1 and is provided at both ends of the bump forming portion 11B1 in the longitudinal direction (in the Figure 2 In the example of FIG. 1 , it is the upper left portion and the lower right portion of the bump forming portion 11B1).

[0045] Furthermore, the covering portion 11D1 has a convex shape from both ends in the longitudinal direction of the bump forming portion 11B1 toward the center of the bump forming portion 11B1.

[0046] exist Figure 2 In the example shown in FIG. 1 , the planar shape of the covering portion 11D1 is a triangle.

[0047] The cover portion 11D1 may be formed by punching the cover film 11D or cutting it with a cutter before attaching the cover film 11D, or by cutting the cover film with a laser cutting device.

[0048] Here, the planar shape of the covering portion 11D1 is not limited to any shape as long as it has a convex shape protruding from both ends of the bump forming portion 11B1 in the longitudinal direction toward the center of the bump forming portion 11B1. Figure 2 The triangle shown may take various shapes such as a polygonal shape, a semicircular shape, or a semi-elliptical shape.

[0049] In addition, in the above description, the covering portion 11D1 is formed integrally with the covering film 11D as an insulating component, but it can also be composed of a material different from the covering film 11D as an insulating component or a separate body from the covering film 11D with the same material, and the material is a material with a larger contact angle with respect to the solder (lower wettability) than the wiring pattern 11B.

[0050] Here, formation of solder bumps will be described.

[0051] Figure 3 This is an explanatory diagram of solder bump formation (part 1).

[0052] Figure 3 (A) is a top view of the solder paste during solder bump formation according to the embodiment. Figure 3 (B) is Figure 3 AA cross-sectional view of (A). In addition, Figure 3 (C) is a top view of the conventional solder bump formation when applying solder paste.

[0053] The formation of the solder bumps is performed by a screen printing method.

[0054] More specifically, solder paste SP is supplied to a metal mask (printing mask), and the mask is lifted, as shown in FIG. Figure 3 (A) and Figure 3 As shown in FIG. 1B , solder paste SP is formed on the bump formation portion 11B1 of the flexible substrate 11 .

[0055] In this case, if Figure 3 As shown in (B), the solder paste SP is applied to the cover portion 11D1 at the portion where the cover portion 11D1 is formed, as shown in FIG. Figure 3 This is different from the case where the conventional solder paste SP shown in (C) is applied to the entire area on the wiring pattern constituting the bump formation portion 11B1.

[0056] Then, a reflow oven is used to form solder bumps.

[0057] In this case, examples of the heating method in the reflow furnace include hot air heating, infrared heating, steam heating, and the like. In order to maintain the temperature uniformity in the furnace and prevent excessive temperature rise, a plurality of heating methods may be combined.

[0058] More specifically, in the reflow furnace, the temperature is raised while the solvent contained in the solder paste is volatilized, and preheating is performed to maintain the flux (solder auxiliary agent) at a certain temperature at which it is easily activated.

[0059] Figure 4 This is an explanatory diagram of solder bump formation (part 2).

[0060] Figure 4(A) is a top view of the solder bump portion of the embodiment when it is formed. Figure 4 (B) is Figure 4 AA cross-section of (A).

[0061] After the preheating, main heating is performed to raise the temperature of the flexible substrate and the mounted components to a temperature at which the solder melts while raising the temperature uniformly.

[0062] Thereby, the solder paste SP is completely liquefied, and the liquefied solder gradually becomes a spherical shape due to surface tension.

[0063] In this case, if Figure 3 As described in (C), in the past, solder paste SP was applied to the entire area on the wiring pattern constituting the bump forming portion 11B1, so the contact angle of the area coated with solder paste SP with respect to the solder was the same. Therefore, the solder bump was formed simply according to the contact angle of the wiring pattern constituting the bump forming portion 11B1 of the solder.

[0064] On the other hand, according to the embodiment, the contact angle of the cover portion 11D1 which is a part of the cover film 11D is larger than the contact angle of the wiring pattern 11B. Therefore, when the solder paste SP applied to the cover portion 11D1 melts, the solder is more repelled.

[0065] That is, the molten solder moves toward the center of the bump forming portion 11B1 and further upward from the bump forming portion 11B1, and the height of the solder bump SB is formed higher when the amount of solder paste SP is the same as when the cover portion 11D1 is not provided.

[0066] In this case, if the height of the solder bump SB is made the same as that in the related art, the amount of solder used can be further reduced compared to the related art solder bump forming method.

[0067] Then, after the solder bump is formed into a desired shape, it is cooled by blowing air.

[0068] Furthermore, once the formation of the solder bumps is completed, it is not preferable from the viewpoint of reliability that flux residues remain on the flexible substrate, and therefore flux cleaning is performed to remove the flux.

[0069] As a result, it is possible to cope with the narrowing of the solder bump pitch and reduce the amount of solder used, thereby forming a solder bump capable of ensuring a desired solder bump height.

[0070] The above description is a qualitative description of the formation of the solder bump, and the effects of the embodiment will be described in more detail.

[0071] In order to explain the effects of the embodiment, the results of simulations of solder bump formation will be described below.

[0072] In this case, the simulation model used is as follows.

[0073] The composition of the solder was set to Sn-3.0Ag-0.5Cu.

[0074] The density of solder is 7400[g / m 3 ].

[0075] The surface tension of solder is 500 [mN / m].

[0076] The thickness of the solder paste was 108.5 μm, and the transfer rate thereof was 100%.

[0077] The thickness of the wiring pattern (conductive material) was 12 μm, and the contact angle was 10 [deg.].

[0078] The thickness of the coating film was 12.5 μm and the contact angle thereof was 160 [deg.].

[0079] The thickness of the substrate film was 12.5 μm, and the contact angle thereof was 160 [deg.].

[0080] The thickness of the adhesive layer was 15 μm, and the contact angle thereof was 160 [deg.].

[0081] (First simulation)

[0082] First, a simulation was performed to determine whether the method of the embodiment can form a solder bump with a higher height than that of the conventional example when the mounting area of ​​the solder bump is the same (first simulation).

[0083] In the first simulation, Figure 3 As shown in (C), the shape of the conventional (comparative) solder bump forming portion is a rectangular shape with a size of 0.1463 mm×0.382 mm and an area of ​​0.0559 mm 2 .

[0084] In addition, the shape of the solder bump forming portion of the embodiment is as follows: Figure 3 As shown in (A), the two ends of the long side direction of the rectangular shape are cut into an isosceles triangle shape corresponding to the covering part (a drum shape in which the short bases of two trapezoids of the same shape are abutted), the length of the long base of the trapezoid is 0.450 mm, the height of the isosceles triangle (cut height) is 0.068 mm, and its area is 0.0559 mm 2 .

[0085] The solder bumps obtained as a result of the simulation are as follows.

[0086] (Conventional solder bump)

[0087] Metal solder volume: 9.766×10 -12 mm 3

[0088] Bump height: 188μm

[0089] Bump width: 243μm

[0090] (Solder Bump of Embodiment)

[0091] Metal solder volume: 9.753×10 -12 mm 3

[0092] Bump height: 191μm

[0093] Bump width: 244μm

[0094] That is, according to the embodiment, a solder bump having a higher height can be formed with the same mounting area compared with the conventional solder bump forming method.

[0095] (Second simulation)

[0096] In the first simulation, the shape of the covering portion was set to a triangular shape, but in the second simulation, the shape of the covering portion was set to a semicircular shape.

[0097] In the second simulation, the shape of the conventional (comparative) solder bump forming portion is a rectangular shape with a size of 0.1463 mm×0.396 mm and an area of ​​0.058 mm. 2 .

[0098] In addition, the shape of the solder bump forming portion of the embodiment is a shape in which both ends of the long side direction of the rectangular shape are cut into a semicircular shape (winding shape) equivalent to the covering portion, the length of the bottom side of the solder bump forming portion is 0.450 mm, the radius of the semicircle (cut height) is set to 0.038 mm, and its area is 0.058 mm 2 .

[0099] The solder bumps obtained as a result of the simulation are as follows.

[0100] (Conventional solder bump)

[0101] Metal solder volume: 9.817×10 -12 mm 3

[0102] Bump height: 183μm

[0103] Bump width: 240μm

[0104] (Solder Bump of Embodiment)

[0105] Metal solder volume: 9.800×10 -12 mm 3

[0106] Bump height: 186μm

[0107] Bump width: 242μm

[0108] That is, it can be seen that according to the embodiment, a solder bump having a higher height can be formed with the same mounting area compared with the conventional solder bump forming method.

[0109] As described above, according to the present embodiment, it is possible to provide a substrate and an electronic device that can cope with narrower pitches of solder bumps while reducing the amount of solder used and ensuring a desired solder bump height.

[0110] Several embodiments of the present invention have been described, but these embodiments are presented as examples and are not intended to limit the scope of the invention. These new embodiments can be implemented in various other ways, and various omissions, substitutions, and changes can be made without departing from the scope of the subject matter of the invention. These embodiments and their variations are included in the scope and subject matter of the invention, and are included in the invention described in the claims and the scope of their equivalents.

[0111] Description of symbols

[0112] 10 Flexible substrate assembly

[0113] 11. Flexible Substrate

[0114] 11-1 Head

[0115] 11-2 Wiring pattern

[0116] 11-3 Base part

[0117] 11A Base material

[0118] 11B Wiring pattern

[0119] 11B1 Bump formation section

[0120] 11C Base film

[0121] 11D Covering Film

[0122] 11D1 Covering

[0123] 12 First support plate

[0124] 13 Second support plate

[0125] 14 Third support plate

[0126] 21 Amplifier connection terminal

[0127] 22 Solder bump forming section

[0128] 25 Terminal Group

[0129] 26 Solder bump part

[0130] 11C1 Opening

[0131] SB Solder Bump

[0132] SP Solder Paste

Claims

1. A substrate comprising: Base material; A wiring pattern is disposed on the substrate; an insulating member covering the substrate and the wiring pattern and having an opening corresponding to a bump forming portion of the wiring pattern; as well as The covering portion is formed of a material having a larger contact angle of solder than that of the bump forming portion in the opening portion, and covers a portion of the bump forming portion.

2. The substrate according to claim 1, wherein The bump forming portion has a rectangular shape, The covering portion is provided at both ends of the bump forming portion in the longitudinal direction.

3. The substrate according to claim 2, wherein The covering portion has a convex shape from the end portion toward a center portion of the bump forming portion.

4. The substrate according to claim 3, wherein A planar shape of a portion of the covering portion covering the bump forming portion is a triangular shape, a polygonal shape, or a semicircular shape.

5. The substrate according to claim 1, wherein The covering portion is formed integrally with the insulating member from the same material as that of the insulating member.

6. The substrate according to claim 1, wherein The cover portion is formed of a material different from that of the insulating member.

7. An electronic device comprising: The substrate according to any one of claims 1 to 3; and An electronic component is connected to the solder bump formed on the bump forming portion.

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