# Patent

## Title
Method of manufacturing a printed wiring board

## Abstract

A method for manufacturing a printed wiring board including providing a structure having a wiring substrate having a conductor circuit, a build-up multilayer structure formed over the wiring substrate and having an outermost conductor circuit and an outermost insulative resin layer, and a solder resist layer formed over the outermost conductor circuit and outermost insulative resin layer and having openings with an opening diameter D for mounting electronic elements, forming conductor pads with a pitch of about 200 pm or less on the outermost conductor circuit in the openings of the solder resist layer, respectively, and forming solder bumps with a height H from a surface of the solder resist layer on the conductor pads on the conductor pads, respectively, such that a ratio H/D is about 0.55 to about 1.0.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a divisional of and claims benefit of priority from U.S. application Ser. No. 12/713,274, filed Feb. 26, 2010, which is a continuation of and claims benefit of priority from U.S. application Ser. No. 11/476,557, filed Jun. 29, 2006, now U.S. Pat. No. 7,714,233, issued May 11, 2010, the entire contents of each of which are hereby incorporated by reference. U.S. application Ser. No. 11/476,557 claims priority of JP 2005-192862 filed with Japanese Patent Office on Jun. 30, 2005, and the disclosure of which is incorporated herein by reference in its entirety.


TECHNICAL FIELD
The present invention relates to a printed wiring board for mounting electronic parts such as capacitors, IC and the like on the outer layer, more particularly, a printed wiring board adaptable to narrow pitching of solder bump for mounting electronic parts.
BACKGROUND ART
Recent years, high performance is remarkable in electronics represented by portable telephones and communication terminals. And, for these electronics is used a printed wiring board having IC chips mounted thereon. As a method of mounting IC chips on a printed wiring board, a flip chip type of directly mounting IC chips on the surface of a printed wiring board is widely employed. As such a printed wiring board, there has been known the one comprising a core substrate, a build-up layer formed on the core substrate and connecting pads for mounting an IC chip through a solder bump on the surface of the build-up layer.
Here, as a printed wiring board, use are made of epoxy resin, BT (bismaleimide triazine) resin phenol resin and the like formed with reinforcement such as glass fiber or the like. The thermal expansion coefficient of these core substrates is about 12-20 ppm/° C. (30-200° C.) and about 4 times larger than that (about 3.5 ppm/° C.) of silicon of the IC chip package.
Therefore, the flip-chip type has, in case of repeating temperature change with heat generation, the possibility of destroying the solder bump due to differences in thermal expansion and heat contraction between the IC chip and the core substrate. For solving such problem, there is proposed a method of interposing an interposer having a thermal expansion coefficient between the printed wiring board and the IC (refer to Japanese unexamined patent application No. 59-996).
BRIEF SUMMARY OF THE INVENTION
According to one embodiment of the present invention, there is provided a printed wiring board comprising a wiring substrate provided with at least one conductor circuit, a solder resist layer formed on the surface of the wiring substrate, covering the at least one conductor circuit, conductor pads formed on a part of the at least one conductor circuit exposed from respective openings provided in the solder resist layer for mounting electronic parts, and solder bumps formed on the respective conductor pads, wherein the conductor pads are arranged with a pitch of about 200 μm or less and the ratio (H/D) of a height H of the solder bump from the surface of the solder resist layer to an opening diameter D of the opening is about 0.55 to about 1.0.
According to other embodiment of the present invention, there is provided a printed wiring board comprising a wiring substrate provided with at least one conductor circuit, a solder resist layer formed on the surface of the wiring substrate, covering the at least one conductor circuit, conductor pads formed on a part of the at least one conductor circuit exposed from the respective openings provided in the solder resist for mounting electronic parts, solder bumps formed on the respective conductor pads, and an under fill material or resin for sealing a gap or space defined between electronic parts mounted through the solder bumps and the solder resist layer, wherein the conductor pads are arranged with a pitch of about 200 μm or less and the ratio (H/D) of a height H of the solder bump from the surface of the solder resist layer to an opening diameter D of the opening is about 0.55 to about 1.0
In the embodiment of the present invention, the surface of the solder resist layer can be flattened at least in an electronic part mounting region, and it is desirable that maximum surface roughness (uneven amount) of the flattened surface (1st uneven face) is made about 0.8 μm to about 3.0 μm.
Further, in the embodiment of the present invention, the surface of the flattened solder resist layer can be further roughened, and it is desirable that surface roughness of the roughened surface (2nd uneven face) of the solder resist layer is smaller than the maximum surface roughness of the flattened surface and about 0.2 μm to about 0.5 μm at an arithmetic mean roughness (Ra).
Further, in the embodiment of the present invention, it is desirable that the conductor pad defined as a part of the conductor circuit exposed from the opening provided in the solder resist layer is formed in the form of a filled-via which is defined by a plated conductor completely filled within an opening provided in an interlaminar insulative resin layer positioned at the outermost layer, and an uneven amount of the filled-via surface exposed from the interlaminar insulative resin layer surface is about −5 μm to about +5 μm in relation to the thickness of the conductor circuit formed on the interlaminar insulative resin layer.
Further, in the embodiment of the present invention, “conductor pad” is defined as a part of the conductor circuit exposed from the opening provided in the solder resist layer. The conductor circuit can be, for instance, formed in the form (connecting pad) of utilizing a part of the conductor circuit, the form of a viahole (including the filled-via in which plated conductor is completely filled within the opening provided in the resin insulating layer) or the form consisting of the viahole and the conductor circuit, so that in a broad sense, it indicates a part of the conductor circuit including the connecting pads and the viaholes.
Further, in the embodiment of the present invention, “opening diameter (D)” of the opening provided in the solder resist layer means a “diameter” of the opening when the opening side wall is not tapered, and means a diameter (of the opening upper part) of the opening exposed on the solder resist layer surface when the opening side wall is tapered.
Further, in the embodiment of the present invention, “maximum surface roughness” means, as schematically shown in FIG. 8, in the electronic part mounting region, the maximum value in differences X1, X2, X3, X4, X5, . . . between the height of the solder resist layer on the conductor pad or the conductor circuit and that of the solder resist layer on an adjacent conductor pad non-forming portion or a conductor circuit non-forming portion.
Further, “arithmetic mean roughness” means arithmetic mean roughness (Ra) prescribed in JIS B0601, and the content of “arithmetic mean roughness” in JIS B0601 is incorporated herein by reference its entirety.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view of the printed wiring board according to the present invention.
FIG. 2 is a sectional view showing a state of mounting an IC chip on the printed wiring board shown in FIG. 1 and placing on a daughter board.
FIGS. 3A to 3C are views explaining steps of forming solder bumps on the printed wiring board.
FIGS. 4A to 4B are schematic views showing structure of an apparatus for mounting the solder balls on the wiring board.
FIG. 5A is a schematic view explaining positioning of the printed wiring board, and FIG. 5B is a schematic view explaining supply of solder balls to mounting cylinders.
FIG. 6A is a schematic view explaining assembly of solder balls by mounting cylinders, and FIG. 6B is a schematic view explaining assembly and guidance of solder balls by the mounting cylinders.
FIG. 7A is a schematic view explaining dropping solder balls to connecting pads, and FIG. 7B is a schematic view explaining removal of solder balls by adsorbed-ball removing cylinder.
FIG. 8 is a schematic view explaining maximum surface roughness of the solder resist layer surface.
FIG. 9 is a schematic view explaining relation between bump height (H) and solder resist layer opening diameter (D) according to the present invention.
FIGS. 10A to 10B are schematic views explaining unevenness of the filled-via surface as a connecting pad.
FIGS. 11A to 11B are schematic views explaining connecting pad region.



DETAILED DESCRIPTION OF THE EMBODIMENTS
One embodiment of the printed wiring board according to the present invention will be described hereinafter. In the printed wiring board, as shown in FIG. 9, at least one opening is provided in a solder resist layer (SR layer) formed on the outermost layer of a wiring board, a part of the conductor circuit exposed from the at least one opening is formed as connecting pads for mounting electronic parts, the connecting pads are arranged with a pitch of about 200 μm or less, and solder bumps are formed on the respective connecting pads, and a ratio (H/D) of a height H from the solder resist layer surface of the solder bump formed on the connecting pad to the opening diameter D is within a range of about 0.55 to about 1.0.
In the embodiment of the present invention, for forming the respective solder bumps in the corresponding openings provided in the solder resist layer, it is desirable to use a novel method and a device for dropping solder balls having very fine particle diameter on the connecting pads through the corresponding openings of a ball aligning mask as described below, without employing a printing method with the use of a conventional mask.
First, a novel solder ball mounting method and a device thereof are used for manufacturing. As to the printed wiring board of the present invention, the construction of one embodiment is explained by referring to FIG. 1 and FIG. 2.
FIG. 1 shows a sectional view of a printed wiring board 10, and FIG. 2 shows a state in which an IC chip 90 is mounted on the printed wiring board 10 and the printed wiring board 10 is mounted on a daughter board 94. As shown in FIG. 1, the printed wiring board 10 has a conductor circuit 34 formed on both surfaces of a core substrate 30, and the respective conductor circuits are electrically connected through a plated through hole 36.
Further, on the conductor circuit 34 of the core substrate 30 is formed a conductor circuit 58 forming a conductor circuit layer through an interlaminar insulative resin layer 50. The conductor circuit 58 is connected to the conductor circuit 34 through via hole 60. On the conductor circuit 58 is formed a conductor circuit 158 through an interlaminar insulative resin layer 150. The conductor circuit 158 is connected to the conductor circuit 58 through a via hole 160 formed in an interlaminar insulative resin layer 150.
A solder resist layer 70 is formed by covering the conductor circuit 158 and the via hole 160, and a connecting pad 75 is formed by forming a nickel plated layer 72 and a gold plated layer 74 on an opening 71 provided in the solder resist layer 71. On the connecting pad 75 of the top face is formed a solder bump 78U and on the connecting pad 75 of the bottom face is formed a BGA (ball grid array) 78D.
As shown in FIG. 2, the solder bump 78U on the upper side of the printed wiring board 10 is connected to an electrode 92 of the IC chip 90 to form an IC mounted printed wiring board, and the IC mounted printed wiring board is connected to a land 96 of a daughter board 94 through the BGA 78D.
According to the embodiment of the present invention, a height of the solder bump from the solder resist layer surface can be made comparatively large by making a ratio (H/D) of the height H of the solder bump to the opening diameter D of the opening about 0.55 or more, thereby easily deforming the solder bump in itself and enlarging volume (amount) of the solder. As a result, stress which can be absorbed by the solder is increased to improve connection reliability. On the other hand, the solder fused between the adjacent solder bumps is hard to move by making a ratio (H/D) of the height H of the solder bump to the opening diameter D of the opening about 1.0 or less, thereby hardly moving the solder molten between adjacent solder bumps to control irregular solder bump height and to prevent short-circuit of adjacent solder bumps. As a result, connection reliability and insulation reliability are improved.
Further, it is desirable that the surface of the solder resist layer corresponding to at least electronic parts mounting region is flattened. The solder resist layer and the solder bump are different in thermal expansion coefficient, so that there are produced repeatedly contraction and expansion at the boundary vicinity between the solder bump and the solder resist layer. And, when large unevenness is existent on the solder resist layer surface, i.e. flatness is worse, the volume of the solder resist layer in the bump vicinity is small to be easily broken. Therefore, by making flatness of the solder resist layer surface small to some extent, the volume of the solder resist layer where large stress is applied to is increased, bending portion where stress tends to concentrate is lessened, and heat cycle resistance can easily be improved.
The flattened surface of the solder resist layer is desirably about 0.8 to about 3.0 μm in maximum surface roughness. The reason is that when the maximum surface roughness is within a range of about 0.8 to about 3.0 μm, crack is hardly generated in the solder resist in the vicinity of the conductor pad, and air (void) is hard to enter into the under fill resin. As a result, insulation reliability and connection reliability are easily improved.
Further, in the embodiment of the present invention, it is desirable to further apply a roughening treatment to the flattened surface of the solder resist layer.
Wettability of the under fill resin is easily improved by applying the roughening treatment to the surface of the solder resist layer flattened to some extent, so that under fill resin can be filled in a narrow gap portion in the boundary vicinity between the solder resist layer and the solder bump so as to improve connection reliability.
It is desirable that the roughened surface of the solder resist layer is smaller than the maximum surface roughness of the flattened surface and about 0.2 to about 0.5 μm at an arithmetic mean roughness (Ra).
The reason is that when the arithmetic mean roughness Ra is made within a range of about 0.2 to about 0.5 μm, adhesion to the under fill resin can be increased, and flux residue and cleaning residue are hardly remained on the solder resist surface. As a result, insulation reliability and connection reliability are easily improved.
Further, according to this embodiment, thinning and low cost can be estimated without requiring any interposer.
In the embodiment of the present invention, as understood from FIG. 1 and FIG. 2, among the connecting pads 75 provided on the upper surface of the substrate as conductor pads for mounting electronic parts, two connecting pads positioned at the center are formed in the form of a land right above the viahole 160, two connecting pads adjacent thereto are formed in the form of pads adjacent to the land of the viahole 160, and further two connecting pads positioned at both ends are formed in the form of a pad consisting of a part of a wiring pattern of the conductor circuit 158.
Further, among the connecting pads 75 formed on the lower surface of the substrate, two connecting pads positioned at both ends are formed in the form of a land right above the viahole 160, and four connecting pads positioned at the center are formed in the form of a pad adjacent to a land of the viahole 160.
The viahole 160 as a connecting pad formed by the solder bump 78U is preferably a filled-via, and the uneven amount of the filled-via surface exposed from the surface of the interlaminar insulative resin layer 150 is, as shown in FIGS. 10A to 10B, desirably within a range of about −5 μm to about +5 μm in relation to the surface thickness of the conductor circuit 158. The reason why the depressed or protruded amount of the filled-via surface is restricted to a mentioned above is due to the fact that when the depressed amount is about 5 μm (−5 μm) or less, the number of contact point defined by the solder ball and the connecting pad consisting of the filled-via is secured, and wettability in case of forming the solder bump is easily improved, and entanglement of voids within the bump and missing bump can be controlled, while when the protruded amount of the filled-via surface is about 5 μm(+5 μm) or less, the thickness of the conductor circuit 158 is controlled not to become large but easily adaptable for fine patterning.
Further, the “electronic parts mounting region” in the embodiment of the invention substantially corresponds to a region (hereinafter, simply called as “connecting pad region”) where conductor pads such as filled-via and the like for mounting electronic parts are provided.
For example, FIG. 11A shows a state of aligning all of the outermost peripheral connecting pads along each side of a rectangle among grid-like aligned connecting pads, and FIG. 11B shows a state of not aligning a part of the outermost peripheral connecting pads along each side of the rectangle, however, in either case, when the connecting pad region is made rectangle, a rectangle region determined to minimize an area of the region enclosing all connecting pads is called as “connecting pad region”.
FIGS. 3A to 3C are views explaining the steps for forming the solder bumps on the printed wiring board 10 according to the present invention.
First, a flux layer 80 is formed for covering conductor pads formed in the openings 71 provided in the solder resist layer 70 on the top face side of the printed wiring board, i.e. the connecting pads 75 by a printing method (see FIG. 3A).
Next, on the connecting pads 75 on the top face side of the printed wiring board are mounted very small solder balls 78s (for example, made by Hitachi Metals or Tamura) with the use of a solder ball loader described later on (see FIG. 3B). Such solder ball is desirable to be about 40 μm or more and less than about 200 μm in diameter. When the diameter is made within such range, each solder ball easily drops on the corresponding connecting pad because it is not too light in weight, and the solder balls are easily assembled in a cylinder member, thereby to control the presence of connecting pads with no solder balls mounted thereon. In order to match for the fine patterning, the solder ball having a diameter of less than or equal to about 80 μm is desirable.
Thereafter, solder balls 78L of a usual diameter (250 μm) are adsorbed and placed on the connecting pads 75 on the bottom face side of the printed wiring board with the use of an adsorption head as described in Japanese Patent No. 1975429, for instance (see FIG. 3C).
Next, by heating in a reflow furnace to form, 500 pieces to 30,000 pieces of the solder bumps 78U are formed with a pitch of about 60 to about 200 μm on the top face side of the printed wiring board 10 as shown in FIG. 1, and 250 pieces of BGA 78D are formed with a pitch of about 2 mm on the bottom face side, for instance.
The pitch of the solder bumps corresponds to a pitch of the connecting pads, and when the pitch of the connecting pads is about 60 μm or more, manufacture of solder balls suitable for the pitch becomes possible. When the pitch of the connecting pads is about 200 μm or less, it becomes possible to obtain a printed wiring board adaptable for fine patterning or narrow pitching.
Further, as shown in FIG. 2, an IC mounted printed wiring board 10 is formed by mounting the IC chip 90 through the solder bumps 78U by reflowing, and this IC mounted printed wiring board 10 is mounted on the daughter board 94 through BGA 78D.
Next, the solder ball loader for mounting the very small solder balls 78s on the corresponding connecting pads of the above-described printed wiring board is explained by referring to FIGS. 4A to 4B.
FIG. 4A is an illustration showing the structure of the solder ball loader, and FIG. 4B is a view taken from an arrow B of the solder ball loader of FIG. 4A.
The solder ball loader 20 comprises an XYθ suction table 14 for positioning and holding the printed wiring board 10, a shaft 12 for moving the XYθ suction table 14 up and down, a ball aligning mask 16 with an opening corresponding to the connecting pad 75 of the printed wiring board, a mounting cylinder (cylinder member) 24 for guiding the solder balls moving on the ball aligning mask 16, a suction box 26 for giving negative pressure to the mounting cylinder 24, a solder ball removing cylinder 61 for recovering excessive solder balls, a suction box 66 for giving negative pressure to the solder ball removing cylinder 61, an adsorbed ball removing and adsorbing device 68 for holding the collected solder balls, a mask clamp 44 for clamping the ball aligning mask 16, an X-axis direction moving shaft 40 for sending the mounting cylinder 24 and the solder ball removing cylinder 61 to the X-axis direction, a moving shaft supporting guide 42 for supporting the X direction moving shaft 40, an alignment camera 46 for taking an image of the multilayer printed wiring board 10, a residue detecting sensor 18 for detecting residual amount of the solder balls under the mounting cylinder 24 and a solder ball supplier 22 for supplying solder balls to the side of the mounting cylinder 24 based on the residue detected by the residue detecting sensor 18.
A plurality of the mounting cylinders 24 and the solder ball removing cylinder 61 are arranged in the Y-axis direction by corresponding to size of the connecting pad regions. Further, the size may correspond to a plurality of the connecting pad areas. Here, the Y-axis direction is expedient and may be aligned in the X-axis direction. The XYθ suction table 14 functions as positioning, adsorption, maintenance and correction of the solder ball mounted printed wiring board 10. The alignment camera 46 detects an alignment mark of the printed wiring board 10 on the XYθ suction table 14 to regulate a position between the printed wiring board and the ball aligning mask 16 based on the detected position. The residue detecting sensor 18 detects the residue of the solder balls by an optical method.
Next, a process for mounting the solder balls by the solder ball loader 20 will be explained by referring to FIGS. 5 to 7.
(1) Position Recognition and Correction of the Printed Wiring Board
As shown in FIG. 5A, an alignment mark 34M of the printed wiring board 10 is recognized by the alignment camera 46, and the position of the printed wiring board 10 in relation to the ball aligning mask 16 is corrected by the suction table 14. That is, openings 16a of the ball aligning mask 16 are adjusted for corresponding to the connecting pads 75 of the printed wiring board 10 in position, respectively. In addition, here, for illustrating convenience' sake, the printed wiring board 10 for one is only shown, but actually, solder balls are mounted to a printed wiring board of worksheet size for constructing a plurality of wiring boards, and after forming solder bumps, the worksheet size board is cut into respective multilayer printed wiring boards
(2) Solder Balls and Supply Thereof.
As shown in FIG. 5B, the solder balls 78s are quantitatively supplied from a solder ball supplying device 22 to the side of the mounting cylinder 24. Here, as the solder ball, use may be made of any commercial item (for example, made by Hitachi Metals) or, for example, solder balls may be manufactured according to the manufacturing device and method described in Japanese unexamined patent application No. 2001-226705.
After manufactured, such solder balls are placed on a metal plate (e.g. nickel plate of about 25 μm thick) having a square slit (opening) which length and breadth are smaller than a desired diameter of the solder ball by about 1 μm, and the solder balls are rolled thereon and dropped from the slit. Then, small balls having smaller diameters than the desired ones are removed. Thereafter, the solder balls remained on the metal plate are classified by a metal plate having a square slit which length and breadth are larger than the desired diameter of the solder ball by about 1 μm, and solder balls dropped from the slit are collected so as to obtain the solder balls each having a diameter substantially equal to the desired diameter.
The disclosure of Japanese unexamined patent application No. 2001-226705 is incorporated herein by reference in its entirety.
(3) Loading of Solder Balls
As shown in FIG. 6A, on the upper part of the ball aligning mask 16 is positioned the mounting cylinder 24 by keeping predetermined clearance (e.g. about 50% to about 300% of a ball diameter), solder balls 78s are assembled on the ball aligning mask 16 right under the opening 24A of the mounting cylinder 24 by adsorbing air from the suction portion 24B at a running speed of about 5 m/sec to about 35 m/sec in a gap between the mounting cylinder and the printed wiring board.
Thereafter, as shown in FIG. 6B and FIG. 7A, the mounting cylinders 24 aligned along the Y axis of the printed wiring board 10 are sent to the horizontal direction along the X axis by means of the X axis moving shaft 40. Thereby, the solder balls 78s assembled on the ball aligning mask 16 are moved with the movement of the mounting cylinder 24, dropped to the corresponding connecting pads 75 of the printed wiring board 10 through the openings 16a of the ball aligning mask 16 and loaded. Thereby, the solder balls 78s are successively aligned on the whole connecting pads on the side of the printed wiring board 10.
(4) Removal of the Solder Ball
As shown in FIG. 7B, the excessive solder balls 78s are guided to a place where no opening 16a is provided on the ball aligning mask 16, then adsorbed and removed by the solder ball removing cylinder 61.
(5) Removal of Wiring Board
Then, the printed wiring board 10 is removed from the suction table 14.
According to the solder ball loading method and the solder ball loader as explained in the above, the solder balls 78s are assembled by positioning the mounting cylinder 24 on the upper part of the ball aligning mask 16 and adsorbing air from the suction portion 24B on the top of the mounting cylinder 24, the assembled solder balls 78s are moved on the ball aligning mask 16 by moving the mounting cylinder 24 in the horizontal direction, and the solder balls 78s can be dropped to the respective connecting pads 75 of the printed wiring board 10 through the respective openings 16a of the ball aligning mask 16.
Therefore, fine solder balls 78s can certainly be mounted on the whole of the connecting pads 75 of the printed wiring board 10. Further, since the solder balls 78s can be moved with no contact, the solder balls can be mounted on the connecting pads 75 without injury, which is different from a printing method with the use of a conventional squeeze, and the solder bumps 78U can be made having an equal height.
Therefore, according to the above-described method, there are provided excellent mountability of electronic parts such as ICs and the like, heat cycle test after the mounting and environment resistance test such as high temperature-high humidity test and the like.
Further, without depending on flatness of products, even printed wiring board having much undulated surface can place solder balls on the connecting pads.
Further, as the fine solder balls could certainly be placed on the connecting pads, even in the printed wiring board having such pitch alignment that the connecting pad pitch is about 60 to about 200 μm and the solder resist opening diameter is about 40 to about 150 μm, in the whole of bumps, stable bumps having substantially uniform heights can be formed.
Further, the solder balls are guided by suction force so as to prevent aggregation and adhesion of solder balls. Further, works (multilayer printed wiring board of work sheet size) having various sizes can be used by adjusting number of the mounting cylinder 24 so as to be applied to many forms and small production.
In the solder ball loader as described above, the mounting cylinders 24 are aligned in the Y-axis direction by corresponding to width of the work (printed wiring board of work sheet size), so that the solder balls can positively be mounted on the whole of connecting pads 75 of the printed wiring boards by simply sending a plurality of mounting cylinders 24 to the vertical direction (X-axis direction) in relation to the row direction.
Further, the solder balls 78s remained on the ball aligning mask 16 can be collected by the solder ball removing cylinder 61, so that there are no problem such that excessive solder ball are remained to cause any trouble and the like.
With the use of the above-described solder ball loading method and device, the solder balls mounted on the connecting pads of the wiring substrate become solder bumps having predetermined height by means of a reflow treatment, IC chips are mounted on the substrate through such solder bumps, and the printed wiring board according to the present invention is manufactured.
Example 1
(1) Manufacture of Printed Wiring Board
As starting material, a double sided copper-clad laminate (e.g. “MCL-E-67” made by Hitachi Chemical) is used, and on this substrate are formed a through-hole conductor and a conductor circuit by a known method. Thereafter, insulating layers and conductor circuit layers are alternately laminated by a known method (e.g. described in a book entitled “Build-up multilayer printed wiring board” (Kiyoshi Takagi) published by Nikkan Kogyo Shinbunsha on Jun. 20, 2000, and the content of this book is incorporated herein by reference in its entirety), and in the outermost conductor circuit layer, a group of connecting pads for mounting IC chips consisting a grid-like arrangement having thickness: 20 μm, diameter (conductor pad diameter): 150 μm, pitch: 200 μm, number: 50×40 (pieces) is formed within a connecting pad region of 150 mm2.
A dimension of the region for forming these connecting pads was 150 mm2. Such connecting pad are formed by a method similar to that described in Japanese unexamined patent application No. 2000-357762. The disclosure of Japanese unexamined patent application No. 2000-357762 is incorporated herein by reference in its entirety.
Further, in case of changing size, pitch, number and arrangement of connecting pad, the pattern (opening diameter, pitch, arrangement, etc.) of a plated resist is changed.
Formation of a solder resist layer is that screen printing is carried out under the following printing condition with the use of a commercial solder resist to form a solder resist layer having a thickness of about 15 to about 25 μm (on the connecting pad) for covering the connecting pad.
(Printing Condition)
Solder resist ink: “RPZ-1” made by Hitachi Kogyo
Ink viscosity: 45±15 Pa·s
Screen print: polyester fiber (130 to 300 mesh)
Speed of squeeze: 100 to 200 mm/sec
In this embodiment, there is formed a solder resist layer having a thickness of 25 μm.
Thereafter, a photo mask having a pattern (mask pattern) of openings of the solder resist thereon is exposed to ultraviolet ray of 100 to 1000 mJ under the state of adhering to the solder resist layer, and developed with a sodium carbonate solution (Na2CO3) of 10 g/L, thereby forming the openings of about 120 μm in diameter on the corresponding connecting pads.
(2) Mounting of Solder Balls
After applying commercial rosin-based flux to the surface (IC mounting face) of the printed wiring board manufactured in the above (1), solder balls are placed on the suction table of a solder ball loader, alignment marks of the printed wiring board and the ball aligning mask are recognized by using a CCD camera, and alignment of the printed wiring board and the ball aligning mask is carried out.
Here, as the ball aligning mask, use is made of a metal mask made of Ni having openings of about 175 μm in diameter at the position corresponding to the connecting pads of the printed wiring board. Besides, it is possible to use ball aligning masks made of SUS and polyimide.
Further, an opening diameter formed in the ball aligning mask is preferably about 1.1 to about 1.5 times the ball diameter used, and a thickness of the ball aligning mask is preferably about 1⁄2 to about 3⁄4 of the diameter of the solder ball used.
Next, the mounting cylinder of about 200 mm in height with a size (about 1.2 to about 3 times to the connecting pad region) corresponding to the connecting pad region is positioned on the metal mask (ball aligning mask) by keeping clearance of about 2 times the solder ball diameter, and solder balls (made by Hitachi Metals) of about 145 μm in diameter consisting of Sn/Pb solder (Sn/Pb=63:37) are mounted on the peripheral vicinity of the mask.
In this example, Sn/Pb is used for the solder ball, use may be made of Pb free solder consisting of at least one metal and Sn selected from the group of Ag, Co, In, Bi, Zn and the like. And, air is adsorbed from the top of the mounting cylinder, and the air speed in a gap between the mounting cylinder and the printed wiring board is regulated to about 5 to about 35 m/sec for assembling the solder balls within the mounting cylinder.
Thereafter, the mounting cylinder is moved at about 10 to about 40 mm/sec to roll the solder balls, and the solder balls are dropped from the respective openings of the ball aligning mask and mounted on the corresponding connection pads.
(3) Formation of Solder Bump
Further, after removing excessive solder balls on the ball aligning mask, the solder ball aligning mask and the printed wiring board are separately taken out of the solder ball loader, and finally, the printed wiring board is put in the reflow furnace set at 230° C. to form a solder bump.
After forming the solder bump, a height of the solder bump protruded from the solder resist surface is measured by a laser microscope (“VX-8500” made by KEYENCE or “WYKO NT-2000” made by Veeco).
In the above measurement, measurement points are four corners and a center of a rectangle, i.e. four solder bumps located at the four corners of a rectangle defined by the connecting pad group and a solder bump substantially positioned at the center of the rectangle are measured, that is to say, five solder bumps in total are measured at this time. As a result, the minimum value of the solder bump height is 66 μm and the maximum value thereof is 70 μm.
(4) Mounting of IC Chip
After measuring the height of each solder bump, an IC chip is mounted through the solder bumps, and the IC chip mounted printed wiring board is manufactured by filling a commercial under fill resin between the IC chip and the solder resist.
Example 2
Except that the printing condition (mesh of the screen and printing speed) of the solder resist is regulated, film thickness of the solder resist is made 15 μm and the solder ball having a diameter of 140 μm is mounted with the use of the ball aligning mask having an opening diameter of 160 μm, a printed wiring boards is manufactured in the same manner as in Example 1. As a result, the minimum value of the solder bump height becomes 63 μm and the maximum value thereof becomes 68 μm.
Example 3
Except that the printing condition (mesh of screen and printing speed) of the solder resist is regulated, film thickness of the solder resist is made 15 μm and the solder ball having a diameter of 135 μm is mounted with the use of the ball aligning mask having an opening diameter of 155 μm, a printed wiring board is manufactured in the same manner as in Example 1. As a result, the minimum value of the solder bump height becomes 65 μm and the maximum value thereof becomes 70 μm.
Example 4
Except that the printing condition (mesh of screen and printing speed) of the solder resist is regulated, film thickness of the solder resist is made 10 μm and the solder ball having a diameter of 130 μm is mounted with the use of the ball aligning mask having an opening diameter of 150 μm, a printed wiring board is manufactured in the same manner as in Example 1. As a result, the minimum value of the solder bump height becomes 66 μm and the maximum value thereof becomes 68 μm.
Example 5
Except that the pattern of the plating resist is changed to change connecting pad diameter: 120 μm and pitch: 150 μm, the mask pattern of a photo mask in case of forming a solder resist opening is changed to change the solder resist opening diameter to 90 μm, the printing condition (mesh of screen and printing speed) of the solder resist is regulated, film thickness of the solder resist is made 10 μm and the solder ball having a diameter of 90 μm is mounted with the use of the ball aligning mask having an opening diameter of 110 μm, a printed wiring board is manufactured in the same manner as in Example 1. As a result, the minimum value of the solder bump height becomes 46 μm and the maximum value thereof becomes 49 μm.
Example 6
Except that the printing condition (mesh of screen and printing speed) of the solder resist is regulated, film thickness of the solder resist is made 15 μm, and the solder ball having a diameter of 95 μm is mounted with the use of the ball aligning mask having an opening diameter of 115 μm, a printed wiring board is manufactured in the same manner as in Example 5. As a result, the minimum value of the solder bump height becomes 45 μm and the maximum value thereof becomes 49 μm.
Example 7
Except that the printing condition (mesh of screen and printing speed) of the solder resist is regulated, film thickness of the solder resist is made 20 μm and the solder ball having a diameter of 100 μm is mounted with the use of the ball aligning mask having an opening diameter of 120 μm, a printed wiring board is manufactured in the same manner as in Example 5. As a result, the minimum value of the solder bump height becomes 47 μm and the maximum value thereof becomes 49 μm.
Example 8
Except that the printing condition (mesh of screen and printing speed) of the solder resist is regulated, film thickness of the solder resist is made 25 μm and the solder ball having a diameter of 105 μm is mounted with the use of the ball aligning mask having an opening diameter of 130 μm, a printed wiring board is manufactured in the same manner as in Example 5. As a result, the minimum value of the solder bump height becomes 47 μm and the maximum value thereof becomes 48 μm.
Example 9
Except that the pattern of the plating resist is changed to change connecting pad diameter: 80 μm and pitch: 100 μm, the mask pattern of the photo mask in case of forming a solder resist opening is changed to change the solder resist opening diameter to 60 μm, the printing condition (mesh of screen and printing speed) of the solder resist is regulated, film thickness of the solder resist is made 10 μm and the solder ball having a diameter of 50 μm is mounted with the use of the ball aligning mask having an opening diameter of 60 μm, a printed wiring board is manufactured in the same manner as in Example 1. As a result, the minimum value of the solder bump height becomes 31 μm and the maximum value thereof becomes 34 μm.
Example 10
Except that the printing condition (mesh of screen and printing speed) of the solder resist is regulated, film thickness of the solder resist is made 15 μm and the solder ball having a diameter of 55 μm is mounted with the use of the ball aligning mask having an opening diameter of 70 μm, a printed wiring board is manufactured in the same manner as in Example 9. As a result, the minimum value of the solder bump height becomes 33 μm and the maximum value thereof becomes 34 μm.
Example 11
Except that the printing condition (mesh of screen and printing speed) of the solder resist is regulated, film thickness of the solder resist is made 20 μm and the solder ball having a diameter of 60 μm is mounted with the use of the ball aligning mask having an opening diameter of 70 μm, a printed wiring board is manufactured in the same manner as in Example 9. As a result, the minimum value of the solder bump height becomes 33 μm and the maximum value thereof becomes 35 μm.
Example 12
Except that the printing condition (mesh of screen and printing speed) of the solder resist is regulated, film thickness of the solder resist is made 25 μm and the solder ball having a diameter of 65 μm is mounted with the use of the ball aligning mask having an opening diameter of 80 μm, a printed wiring board is manufactured in the same manner as in Example 9. As a result, the minimum value of the solder bump height becomes 32 μm and the maximum value thereof becomes 34 μm.
Example 13
Except that the solder ball having a diameter of 160 μm is mounted with the use of the ball aligning mask having an opening diameter of 190 μm, a printed wiring board is manufactured in the same manner as in Example 1. As a result, the minimum value of the solder bump height becomes 84 μm and the maximum value thereof becomes 87 μm.
Example 14
Except that the solder ball having a diameter of 155 μm is mounted with the use of the ball aligning mask having an opening diameter of 180 μm, a printed wiring board is manufactured in the same manner as in Example 2. As a result, the minimum value of the solder bump height becomes 83 μm and the maximum value thereof becomes 86 μm.
Example 15
Except that the solder ball having a diameter of 150 μm is mounted with the use of the ball aligning mask having an opening diameter of 180 μm, a printed wiring board is manufactured in the same manner as in Example 3. As a result, the minimum value of the solder bump height becomes 83 μm and the minimum value thereof becomes 87 μm.
Example 16
Except that the solder ball having a diameter of 145 μm is mounted with the use of the ball aligning mask having an opening diameter of 170 μm, a printed wiring board is manufactured in the same manner as in Example 4. As a result, the minimum value of the solder bump height becomes 84 μm and the maximum value thereof becomes 86 μm.
Example 17
Except that the solder ball having a diameter of 100 μm is mounted with the use of the ball aligning mask having an opening diameter of 120 μm, a printed wiring board is manufactured in the same manner as in Example 5. As a result, the minimum value of the solder bump height becomes 63 μm and the maximum value thereof becomes 66 μm.
Example 18
Except that the solder ball having a diameter of 105 μm is mounted with the use of the ball aligning mask having an opening diameter of 130 μm, a printed wiring board is manufactured in the same manner as in Example 6. As a result, the minimum value of the solder bump height becomes 63 μm and the maximum value thereof becomes 66 μm.
Example 19
Except that the solder ball having a diameter of 110 μm is mounted with the use of the ball aligning mask having an opening diameter of 140 μm, a printed wiring board is manufactured in the same manner as in Example 7. As a result, the minimum value of the solder bump height becomes 61 μm and the maximum value thereof becomes 67 μm.
Example 20
Except that the solder ball having a diameter of 115 μm is mounted with the use of the ball aligning mask having an opening diameter of 140 μm, a printed wiring board is manufactured in the same manner as in Example 8. As a result, the minimum value of the solder bump height becomes 61 μm and the maximum value thereof becomes 65 μm.
Example 21
Except that the solder ball having a diameter of 60 μm is mounted with the use of the ball aligning mask having an opening diameter of 80 μm, a printed wiring board is manufactured in the same manner as in Example 9. As a result, the minimum value of the solder bump height becomes 40 μm and the maximum value thereof becomes 43 μm.
Example 22
Except that the solder ball having a diameter of 65 μm is mounted with the use of the ball aligning mask having an opening diameter of 85 μm, a printed wiring board is manufactured in the same manner as in Example 10. As a result, the minimum value of the solder bump height becomes 40 μm and the maximum value thereof becomes 43 μm.
Example 23
Except that the solder ball having a diameter of 70 μm is mounted with the use of the ball aligning mask having an opening diameter of 90 μm, a printed wiring board is manufactured in the same manner as in Example 11. As a result, the minimum value of the solder bump height becomes 41 μm and the maximum value thereof becomes 44 μm.
Example 24
Except that the solder ball having a diameter of 75 μm is mounted with the use of the ball aligning mask having an opening diameter of 95 μm, a printed wiring boards is manufactured in the same manner as in Example 12. As a result, the minimum value of the solder bump height becomes 42 μm and the maximum value thereof becomes 42 μm.
Example 25
Except that the solder ball having a diameter of 190 μm is mounted with the use of the ball aligning mask having an opening diameter of 230 μm, a printed wiring board is manufactured in the same manner as in Example 1. As a result, the minimum value of the solder bump height becomes 120 μm and the maximum value thereof becomes 120 μm.
Example 26
Except that the solder ball having a diameter of 185 μm is mounted with the use of the ball aligning mask having an opening diameter of 230 μm, a printed wiring board is manufactured in the same manner as in Example 2. As a result, the minimum value of the solder bump height becomes 121 μm and the maximum value thereof becomes 122 μm.
Example 27
Except that the solder ball having a diameter of 180 μm is mounted with the use of the ball aligning mask having an opening diameter of 220 μm, a printed wiring boards is manufactured in the same manner as in Example 3. As a result, the minimum value of the solder bump height becomes 122 μm and the maximum value thereof becomes 126 μm.
Example 28
Except that the solder ball having a diameter of 175 μm is mounted with the use of the ball aligning mask having an opening diameter of 200 μm, a printed wiring board is manufactured in the same manner as in Example 4. As a result, the minimum value of the solder bump height becomes 122 μm and the maximum value thereof becomes 123 μm.
Example 29
Except that the solder ball having a diameter of 125 μm is mounted with the use of the ball aligning mask having an opening diameter of 150 μm, a printed wiring board is manufactured in the same manner as in Example 5. As a result, the minimum value of the solder bump height becomes 92 μm and the maximum value thereof becomes 94 μm.
Example 30
Except that the solder ball having a diameter of 130 μm is mounted with the use of the ball aligning mask having an opening diameter of 150 μm, a printed wiring board is manufactured in the same manner as in Example 6. As a result, the minimum value of the solder bump height becomes 90 μm and the maximum value thereof becomes 93 μm.
Example 31
Except that the solder ball having a diameter of 135 μm is mounted with the use of the ball aligning mask having an opening diameter of 160 μm, a printed wiring board is manufactured in the same manner as in Example 7. As a result, the minimum value of the solder bump height becomes 91 μm and the maximum value thereof becomes 93 μm.
Example 32
Except that the solder ball having a diameter of 140 μm is mounted with the use of the ball aligning mask having an opening diameter of 170 μm, a printed wiring board is manufactured in the same manner as in Example 8. As a result, the minimum value of the solder bump height becomes 90 μm and the maximum value thereof becomes 91 μm.
Example 33
Except that the solder ball having a diameter of 75 μm is mounted with the use of the ball aligning mask having an opening diameter of 90 μm, a printed wiring board is manufactured in the same manner as in Example 9. As a result, the minimum value of the solder bump height becomes 61 μm and the maximum value thereof becomes 63 μm.
Example 34
Except that the solder ball having a diameter of 80 μm is mounted with the use of the ball aligning mask having an opening diameter of 100 μm, a printed wiring board is manufactured in the same manner as in Example 10. As a result, the minimum value of the solder bump height becomes 60 μm and the maximum value thereof becomes 63 μm.
Example 35
Except that the solder ball having a diameter of 85 μm is mounted with the use of the ball aligning mask having an opening diameter of 110 μm, a printed wiring board is manufactured in the same manner as in Example 11. As a result, the minimum value of the solder bump height becomes 62 μm and the maximum value thereof becomes 63 μm.
Example 36
Except that the solder ball having a diameter of 90 μm is mounted with the use of the ball aligning mask having an opening diameter of 120 μm, a printed wiring board is manufactured in the same manner as in Example 12. As a result, the minimum value of the solder bump height becomes 60 μm and the maximum value thereof becomes 61 μm.
Comparative Example 1
Except that the solder ball having a diameter of 125 μm is mounted with the use of the ball aligning mask having an opening diameter of 150 μm, a printed wiring board is manufactured in the same manner as in Example 1. As a result, the minimum value of the solder bump height becomes 48 μm and the maximum value thereof becomes 50 μm.
Comparative Example 2
Except that the solder ball having a diameter of 120 μm is mounted with the use of the ball aligning mask having an opening diameter of 150 μm, a printed wiring board is manufactured in the same manner as in Example 2. As a result, the minimum value of the solder bump height becomes 46 μm and the maximum value thereof becomes 50 μm.
Comparative Example 3
Except that the solder ball having a diameter of 115 μm is mounted with the use of the ball aligning mask having an opening diameter of 130 μm, a printed wiring board is manufactured in the same manner as in Example 3. As a result, the minimum value of the solder bump height becomes 45 μm and the maximum value thereof becomes 47 μm.
Comparative Example 4
Except that the solder ball having a diameter of 110 μm is mounted with the use of the ball aligning mask having an opening diameter of 130 μm, a printed wiring board is manufactured in the same manner as in Example 4. As a result, the minimum value of the solder bump height becomes 48 μm and the maximum value thereof becomes 50 μm.
Comparative Example 5
Except that the solder ball having a diameter of 80 μm is mounted with the use of the ball aligning mask having an opening diameter of 100 μm, a printed wiring board is manufactured in the same manner as in Example 5. As a result, the minimum value of the solder bump height becomes 35 μm and the maximum value thereof becomes 36 μm.
Comparative Example 6
Except that the solder ball having a diameter of 85 μm is mounted with the use of the ball aligning mask having an opening diameter of 110 μm, a printed wiring board is manufactured in the same manner as in Example 6. As a result, the minimum value of the solder bump height becomes 33 μm and the maximum value thereof becomes 35 μm.
Comparative Example 7
Except that the solder ball having a diameter of 90 μm is mounted with the use of the ball aligning mask having an opening diameter of 115 μm, a printed wiring board is manufactured in the same manner as in Example 7. As a result, the minimum value of the solder bump height becomes 36 μm and the maximum value thereof becomes 38 μm.
Comparative Example 8
Except that the solder ball having a diameter of 95 μm is mounted with the use of the ball aligning mask having an opening diameter of 120 μm, a printed wiring board is manufactured in the same manner as in Example 8. As a result, the minimum value of the solder bump height becomes 36 μm and the maximum value thereof becomes 39 μm.
Comparative Example 9
Except that the solder ball having a diameter of 40 μm is mounted with the use of the ball aligning mask having an opening diameter of 55 μm, a printed wiring board is manufactured in the same manner as in Example 9. As a result, the minimum value of the solder bump height becomes 22 μm and the maximum value thereof becomes 24 μm.
Comparative Example 10
Except that the solder ball having a diameter of 45 μm is mounted with the use of the ball aligning mask having an opening diameter of 60 μm, a printed wiring board is manufactured in the same manner as in Example 10. As a result, the minimum value of the solder bump height becomes 21 μm and the maximum value thereof becomes 23 μm.
Comparative Example 11
Except that the solder ball having a diameter of 50 μm is mounted with the use of the ball aligning mask having an opening diameter of 70 μm, a printed wiring board is manufactured in the same manner as in Example 11. As a result, the minimum value of the solder bump height becomes 20 μm and the maximum value thereof becomes 22 μm.
Comparative Example 12
Except that the solder ball having a diameter of 55 μm is mounted with the use of the ball aligning mask having an opening diameter of 80 μm, a printed wiring board is manufactured in the same manner as in Example 12. As a result, the minimum value of the solder bumper height becomes 24 μm and the maximum value thereof becomes 26 μm.
Comparative Example 13
Except that the solder ball having a diameter of 220 μm is mounted with the use of the ball aligning mask having an opening diameter of 260 μm, a printed wiring board is manufactured in the same manner as in Example 1. As a result, the minimum value of the solder bump height becomes 155 μm and the maximum value thereof becomes 165 μm.
Comparative Example 14
Except that the solder ball having a diameter of 215 μm is mounted with the use of the ball aligning mask having an opening diameter of 260 μm, a printed wiring board is manufactured in the same manner as in Example 2. As a result, the minimum value of the solder bump height becomes 100 μm and the maximum value thereof becomes 180 μm.
Comparative Example 15
Except that the solder ball having a diameter of 210 μm is mounted with the use of the ball aligning mask having an opening diameter of 250 μm, a printed wiring board is manufactured in the same manner as in Example 3. As a result, the minimum value of the solder bump height becomes 150 μm and the maximum value thereof becomes 160 μm.
Comparative Example 16
Except that the solder ball having a diameter of 205 μm is mounted with the use of the ball aligning mask having an opening diameter of 240 μm, a printed wiring board is manufactured in the same manner as in Example 4. As a result, the minimum value of the solder bump height becomes 112 μm and the maximum value thereof becomes 158 μm.
Comparative Example 17
Except that the solder ball having a diameter of 155 μm is mounted with the use of the ball aligning mask having an opening diameter of 180 μm, a printed wiring board is manufactured in the same manner as in Example 5. As a result, the minimum value of the solder bump height becomes 88 μm and the maximum value thereof becomes 120 μm.
Comparative Example 18
Except that the solder ball having a diameter of 160 μm is mounted with the use of the ball aligning mask having an opening diameter of 180 μm, a printed wiring board is manufactured in the same manner as in Example 6. As a result, the minimum value of the solder bump height becomes 120 μm and the maximum value thereof becomes 180 μm.
Comparative Example 19
Except that the solder ball having a diameter of 165 μm is mounted with the use of the ball aligning mask having an opening diameter of 190 μm, a printed wiring board is manufactured in the same manner as in Example 7. As a result, the minimum value of the solder bump height becomes 120 μm and the maximum value thereof becomes 128 μm.
Comparative Example 20
Except that the solder ball having a diameter of 170 μm is mounted with the use of the ball aligning mask having an opening diameter of 200 μm, a printed wiring board is manufactured in the same manner as in Example 8. As a result, the minimum value of the solder bump height becomes 75 μm and the maximum value thereof becomes 160 μm.
Comparative Example 21
Except that the solder ball having a diameter of 105 μm is mounted with the use of the ball aligning mask having an opening diameter of 140 μm, a printed wiring board is manufactured in the same manner as in Example 9. As a result, the minimum value of the solder bump height becomes 80 μm and the maximum value thereof becomes 88 μm.
Comparative Example 22
Except that the solder ball having a diameter of 110 μm is mounted with the use of the ball aligning mask having an opening diameter of 140 μm, a printed wiring board is manufactured in the same manner as in Example 10. As a result, the minimum value of the solder bump height becomes 40 μm and the maximum value thereof becomes 90 μm.
Comparative Example 23
Except that the solder ball having a diameter of 115 μm is mounted with the use of the ball aligning mask having an opening diameter of 140 μm, a printed wiring board is manufactured in the same manner as in Example 11. As a result, the minimum value of the solder bump height becomes 80 μm and the maximum value thereof becomes 85 μm.
Comparative Example 24
Except that the solder ball having a diameter of 120 μm is mounted with the use of the ball aligning mask having an opening diameter of 150 μm, a printed wiring board is manufactured in the same manner as in Example 12. As a result, the minimum value of the solder bump height becomes 75 μm and the maximum value thereof becomes 90 μm.
Here, as to the IC mounted printed wiring boards manufactured according to Examples 1 to 36 and Comparative Examples 1 to 24, a test for evaluating heat cycle resistance is conducted as follows.
(Heat Cycle Resistance)
First, there is measured electric resistance (between a pair of connecting pads exposed to the surface opposite to the IC chip mounted surface of the IC mounted printed wiring board and electrically connected to the IC chip) of a specific circuit through IC chips, and its value is determined as an initial value.
Thereafter, a heat cycle test under the condition of −55° C. (5 minutes) 125° C. (5 minutes) as one cycle is repeated 1000 times to those IC chip mounting printed wiring boards. Electric resistances after 500 cycles and 1000 cycles are measured, respectively, and a rate of change (100×(measured value−initial value)/initial value (%)) with the initial value is obtained. The case within ±10 is evaluated as “good (O)”, and others are evaluated as “no good (x)”. This test result is shown in Table 1 and Table 2.


















TABLE 1









Diameter
Pitch

Opening




Height




of Con-
of Con-
Thickness
Diameter
Diameter
Opening
Height
Height
of Bamp/



necting
necting
of Solder
of Solder
of Solder
Diameter
of Bamp
of Bamp
Opening
Heat Cycle Test



















Pad
Pad
Resist Layer
Resist Layer
Ball
of Mask
(minimum)
(Maximum)
Diameter
500
1000


Examples
(μm)
(μm)
(μm)
(μm)
(μm)
(μm)
(μm)
(μm)
of SR
cycles
cycles





















Example 1
150
200
25
120
145
175
66
70
0.55
◯
◯


Example 2
150
200
20
120
140
160
63
68
0.53
◯
◯


Example 3
150
200
15
120
135
155
65
70
0.54
◯
◯


Example 4
150
200
10
120
130
150
66
68
0.55
◯
◯


Example 5
120
150
10
90
90
110
46
49
0.51
◯
◯


Example 6
120
150
15
90
95
115
45
49
0.50
◯
◯


Example 7
120
150
20
90
100
120
47
49
0.52
◯
◯


Example 8
120
150
25
90
105
130
47
49
0.52
◯
◯


Example 9
80
100
10
60
50
60
31
34
0.52
◯
◯


Example 10
80
100
15
60
55
70
33
34
0.55
◯
◯


Example 11
80
100
20
60
60
70
33
35
0.55
◯
◯


Example 12
80
100
25
60
65
80
32
34
0.53
◯
◯


Example 13
150
200
25
120
160
190
84
87
0.70
◯
◯


Example 14
150
200
20
120
155
180
83
86
0.69
◯
◯


Example 15
150
200
15
120
150
180
83
87
0.69
◯
◯


Example 16
150
200
10
120
145
170
84
86
0.70
◯
◯


Example 17
120
150
10
90
100
120
63
66
0.70
◯
◯


Example 18
120
150
15
90
105
130
63
67
0.70
◯
◯


Example 19
120
150
20
90
110
140
61
67
0.68
◯
◯


Example 20
120
150
25
90
115
140
61
65
0.68
◯
◯


Example 21
80
100
10
60
60
80
40
43
0.67
◯
◯


Example 22
80
100
15
60
65
85
40
43
0.67
◯
◯


Example 23
80
100
20
60
70
90
41
44
0.68
◯
◯


Example 24
80
100
25
60
75
95
42
42
0.70
◯
◯


Example 25
150
200
25
120
190
230
120
120
1.00
◯
◯


Example 26
150
200
20
120
185
230
121
122
1.01
◯
◯


Example 27
150
200
15
120
180
220
122
126
1.02
◯
◯


Example 28
150
200
10
120
175
200
122
123
1.02
◯
◯


Example 29
120
150
10
90
125
150
92
94
1.02
◯
◯


Example 30
120
150
15
90
130
150
90
93
1.00
◯
◯


Example 31
120
150
20
90
135
160
91
93
1.01
◯
◯


Example 32
120
150
25
90
140
170
90
91
1.00
◯
◯


Example 33
80
100
10
60
75
90
61
63
1.02
◯
◯


Example 34
80
100
15
60
80
100
60
63
1.00
◯
◯


Example 35
80
100
20
60
85
110
62
63
1.03
◯
◯


Example 36
80
100
25
60
90
120
60
61
1.00
◯
◯



























TABLE 2









Diameter
Pitch

Opening

Opening


Height




of Con-
of Con-
Thickness
Diameter
Diameter
Diameter
Height
height
of Bamp/



necting
necting
of Solder
of Solder
of Solder
of Solder
of Bamp
of Bamp
Opening
Heat Cycle Test



















Pad
Pad
Resist Layer
Resist Layer
Ball
Resist Layer
(minimum)
(Maximum)
Diameter
500
1000


Examples
(μm)
(μm)
(μm)
(μm)
(μm)
(μm)
(μm)
(μm)
of SR
cycles
cycles





















Example 1
150
200
25
120
125
150
48
50
0.40
◯
X


Example 2
150
200
20
120
120
150
46
50
0.38
◯
X


Example 3
150
200
15
120
115
130
45
47
0.38
◯
X


Example 4
150
200
10
120
110
130
48
50
0.40
◯
X


Example 5
120
150
10
90
80
100
35
36
0.39
◯
X


Example 6
120
150
15
90
85
110
33
35
0.37
◯
X


Example 7
120
150
20
90
90
115
36
38
0.40
◯
X


Example 8
120
150
25
90
95
120
36
39
0.40
◯
X


Example 9
80
100
10
60
40
55
22
24
0.37
◯
X


Example 10
80
100
15
60
45
60
21
23
0.35
◯
X


Example 11
80
100
20
60
50
70
20
22
0.33
◯
X


Example 12
80
100
25
60
55
80
24
26
0.40
◯
X


Example 13
150
200
25
120
220
260
155
165
1.29
X
X


Example 14
150
200
20
120
215
260
100
180
0.83
X
X


Example 15
150
200
15
120
210
250
150
160
1.25
X
X


Example 16
150
200
10
120
205
240
112
158
0.93
X
X


Example 17
120
150
10
90
155
180
88
120
0.98
X
X


Example 18
120
150
15
90
160
180
120
180
1.33
X
X


Example 19
120
150
20
90
165
190
115
120
1.28
X
X


Example 20
120
150
25
90
170
200
76
160
0.84
X
X


Example 21
80
100
10
60
105
140
80
88
1.33
X
X


Example 22
80
100
15
60
110
140
40
90
0.67
X
X


Example 23
80
100
20
60
115
140
80
85
1.33
X
X


Example 24
80
100
25
60
120
150
75
90
1.25
X
X









Next, as to Examples 2, 7, 11, 14, 19, 23, 26, 31 and 35 among Examples 1 to 36, after forming a solder resist layer, printed wiring boards made by applying the following flattening treatment to the solder resist layer surface are manufactured, and these are denoted as Examples 37 to 45.
Example 37
Except that the following flattening treatment id applied to the solder resist layer surface after forming the resist layer, a printed wiring board is manufactured in the same manner as in Example 2.
(Flattening Treatment)
First, on the solder resist layer surface, a connecting pad region for mounting IC chip (region area: 1200 mm2, connecting pad number: 30000) is measured by means of a surface roughness measuring instrument (e.g. “SURFCOM 480A” made by Tokyo Seimitsu or “WYKO N-2500” by Veeco) to examine uneven amount (see FIG. 8) due to the presence or absence of conductor pads. As a result, the uneven amount of the solder resist layer surface becomes 7.2 to 9.8 μm.
Next, a polyethylene terephthalate (PET) film is applied on the surface of the solder resist layer, and the solder resist surface is flattened by applying pressure to the solder resist layer through the polyethylene terephthalate film under the following flattening treatment condition.
(Flattening Treatment Condition)
Press temperature: 60 to 80° C.
Press pressure: 3 to 5 MPa
Press time: 1 to 3 minutes
On the surface of the solder resist layer after flattening treatment, the same region as that already measured is measured by the same surface roughness measuring instrument, a degree of unevenness of the solder resist layer surface after flattening treatment is examined. As a result, an amount of unevenness of the flattened surface of the solder resist layer becomes small to about 0.8 (minimum uneven amount) to 3.2 μm (maximum uneven amount).
In addition, “maximum uneven amount” and “minimum uneven amount” mentioned herein mean, as shown in FIG. 8, maximum value and minimum value of differences X1, X2, X3, X4, X5 . . . between height of the solder resist layer on the conductor pad or conductor circuit and that of the solder resist layer of adjacent conductor pad non-forming part or conductor circuit non-forming part in the electronic part mounting region.
Example 38
Except that after forming a solder resist layer, flattening treatment is applied to the solder resist layer surface with the following condition, a printed wiring board is manufactured in the same manner as in Example 7.
(Flattening Treatment Condition)
Press temperature: 60 to 80° C.
Press pressure: 3 to 5 MPa
Press time: 1 to 3 minutes
An uneven amount of the surface before flattening the solder resist layer obtained in this example is comparatively large such as about 6.6 to 10.2 μm, but the amount of the flattened surface is small such as about 0.7 to 3.0 μm.
Example 39
Except that after forming a solder resist layer, flattening treatment is applied to the solder resist layer surface with the following condition, a printed wiring board is manufactured in the same manner as in Example 11.
(Flattening Treatment Condition)
Press temperature: 60 to 80° C.
Press pressure: 3 to 5 MPa
Press time: 1 to 3 minutes
An uneven amount of the surface before flattening the solder resist layer obtained in this example is comparatively large such as about 8.4 to 9.3 μm, but that of the flattened surface is small such as about 0.8 to 3.1 μm.
Example 40
Except that after forming a solder resist layer, flattening treatment is applied to the solder resist layer surface with the following condition, a printed wiring board is manufactured in the same manner as in Example 14.
(Flattening Treatment Condition)
Press temperature: 60 to 80° C.
Press pressure: 3 to 5 MPa
Press time: 1 to 3 minutes
An uneven amount of the surface before flattening the solder resist layer obtained in this example is large such as about 8.2 to 9.6 μm, but that of the flattened surface is small such as about 0.7 to 3.2 μm.
Example 41
Except that after forming a solder resist layer, flattening treatment is applied to the solder resist layer surface with the following condition, a printed wiring board is manufactured in the same manner as in Example 19.
(Flattening Treatment Condition)
Press temperature: 60 to 80° C.
Press pressure: 3 to 5 MPa
Press time: 1 to 3 minutes
An uneven amount of the surface before flattening the solder resist layer obtained in this example is comparatively large such as about 9.9 to 10.2 μm, but that of the flattened surface is small such as about 0.8 to 3.3 μm.
Example 42
Except that after forming a solder resist layer, flattening treatment is applied to the solder resist layer surface with the following condition, a printed wiring board is manufactured in the same manner as in Example 23.
(Flattening Treatment Condition)
Press temperature: 60 to 80° C.
Press pressure: 3 to 5 MPa
Press time: 1 to 3 minutes
An uneven amount of the surface before flattening the solder resist layer obtained in this example is comparatively large such as about 8.3 to 10.3 μm, but that of the flattened surface is small such as about 0.7 to 3.0 μm.
Example 43
Except that after forming a solder resist layer, flattening treatment is applied to the solder resist layer surface with the following condition, a printed wiring board is manufactured in the same manner as in Example 26.
(Flattening Treatment Condition)
Press temperature: 60 to 80° C.
Press pressure: 3 to 5 MPa
Press time: 1 to 3 minutes
An uneven amount of the surface before flattening the solder resist layer obtained in this example is comparatively large such as about 9.1 to 9.8 μm. but that of the flattened surface is small such as about 0.5 to 3.1 μm.
Example 44
Except that after forming a solder resist layer, flattening treatment is applied to the solder resist layer surface with the following condition, a printed wiring board is manufactured in the same manner as in Example 31.
(Flattening Treatment Condition)
Press temperature: 60 to 80° C.
Press pressure: 3 to 5 MPa
Press time: 1 to 3 minutes
An uneven amount of the surface before flattening the solder resist layer obtained in this example is comparatively large such as about 8.1 to 10.2 μm, but that of the flattened surface is small such as about 0.8 to 3.0 μm.
Example 45
Except that after forming a solder resist layer, flattening treatment is applied to the solder resist layer surface with the following condition, a printed wiring board is manufactured in the same manner as in Example 35.
(Flattening Treatment Condition)
Press temperature: 60 to 80° C.
Press pressure: 3 to 5 MPa
Press time: 1 to 3 minutes
An uneven amount of the surface before flattening the solder resist layer obtained in this example is comparatively large such as about 9.6 to 10.3 μm, but that of the flattened surface is small such as about 0.7 to 3.0 μm.
As to flattened IC mounted printed wiring boards manufactured according to Examples 37 to 45, the same heat cycle test as in Examples 1 to 36 is carried out, electric resistance after 1000 cycles and after 1500 cycles is measured, and a rate of change (100×(measured value−initial value)/initial value (%)) with the initial value is obtained. The case within ±10 is evaluated as “good (O)” and the other cases are evaluated as “no good (x)”. This test result is shown in Table 3.
In addition, as to the IC mounted printed wiring boards manufactured according to Examples 2, 7, 11, 14, 19, 23, 26, 31 and 35 applied no flattening treatment, the same heat cycle test is carried out, a rate of change of electric resistance is obtained and evaluated. These test results are also shown in Table 3 with the test results of Examples 37 to 45.
Then, as to the IC mounted printed wiring boards manufactured according to Examples 37 to 45, in which the solder resist layer surface is flattened, their flattened substrates are further roughened with the following condition, thereby manufacturing IC mounted printed wiring boards formed with fine uneven faces (roughened faces) on the flattened surface of the solder resist layer, and these are made Examples 46 to 54.










TABLE 3









Amount of unevenness of




Flattened Surface of Solder



Resist Layer (μm)
Heat Cycle Test












Minimum
Maximum
500
1000


Examples
Amount
Amount
cycles
cycles





Example 37 (2)
0.8
3.2
◯ (◯)
◯ (X)


Example 38 (7)
0.7
3.0
◯ (◯)
◯ (X)


Example 39 (11)
0.8
3.1
◯ (◯)
◯ (X)


Example 40 (14)
0.7
3.2
◯ (◯)
◯ (X)


Example 41 (19)
0.8
3.3
◯ (◯)
◯ (X)


Example 42 (23)
0.7
3.0
◯ (◯)
◯ (X)


Example 43 (26)
0.5
3.1
◯ (◯)
◯ (X)


Example 44 (31)
0.8
3.0
◯ (◯)
◯ (X)


Example 45 (35)
0.7
3.0
◯ (◯)
◯ (X)









Example 46
Except that roughening treatment is applied to the solder resist layer surface with the following condition after flattening, a printed wiring board is manufactured in the same manner as in Example 37.
(Roughening Condition)
Roughening solution: potassium permanganate solution
Concentration: 60 to 80 g/l
Temperature: 60 to 80° C.
Immersion time: 1 to 5 minutes
After roughening treatment, surface roughness of the solder resist surface is randomly measured at 10 spots by surface roughness measuring instrument (for example, “SURFCOM 480A” made by Tokyo Seimitsu or “WYKO N-2500” made by Veeco). As a result, surface roughness of the surface treated by roughening the solder resist layer becomes small to the extent of about 0.1 to 0.6 μm at Ra.
In addition, “surface roughness (Ra)” mentioned here means “arithmetic mean roughness (Ra)” prescribed by JIS B0601, but Ra within a range of the above measuring result is mentioned that the smallest Ra is Ra(min) and the largest one is Ra(max) in measured 10 spots.
However, surface roughness is measured at random 10 spots in the solder resist layer surface corresponding to the conductor circuit (pad) forming region and the solder resist layer surface corresponding to the conductor circuit non-forming region, but not measured in the boundary vicinity of the conductor circuit forming region and the conductor circuit non-forming region.
Example 47
Except that roughening treatment is further applied to the solder resist layer surface with the following condition after flattening treatment, a printed wiring board is manufactured in the same manner as in Example 38.
(Roughening Condition)
Roughening solution: potassium permanganate solution
Concentration: 60 to 80 g/l
Temperature: 60 to 80° C.
Immersion time: 1 to 5 minutes
Surface roughness of the roughened surface of the solder resist layer becomes small to the extent of about 0.2 to 0.5 μm (Ra(min) to Ra(max)) at Ra.
Example 48
Except that roughening treatment is further applied to the solder resist layer surface with the following condition after flattening treatment, a printed wiring board is manufactured in the same manner as in Example 39.
(Roughening Condition)
Roughening solution: potassium permanganate solution
Concentration: 60 to 80 g/l
Temperature: 60 to 80° C.
Immersion time: 1 to 5 minutes
Surface roughness of the roughened solder resist layer surface becomes small to the extent of about 0.2 to 0.5 μm at Ra.
Example 49
Except that roughening treatment is further applied to the solder resist layer surface with the following condition after flattening treatment, a printed wiring board is manufactured in the same manner as in Example 40.
(Roughening Condition)
Roughening solution; potassium permanganate solution
Concentration: 60 to 80 g/l
Temperature: 60 to 80° C.
Immersion time: 1 to 5 minutes
Surface roughness of the roughened solder resist layer becomes small to the extent of about 0.2 to 0.7 μm at Ra.
Example 50
Except that roughening treatment is further applied to the solder resist layer surface with the following condition after flattening treatment, a printed wiring board is manufactured in the same manner as in Example 41.
(Roughening Condition)
Roughening solution; potassium permanganate solution
Concentration: 60 to 80 g/l
Temperature: 60 to 80° C.
Immersion time: 1 to 5 minutes
Surface roughness of the roughened solder resist layer becomes small to the extent of about 0.1 to 0.5 μm at Ra.
Example 51
Except that roughening treatment is further applied to the solder resist layer surface with the following condition after flattening treatment, a printed wiring board is manufactured in the same manner as in Example 42.
(Roughening Condition)
Roughening solution; potassium permanganate solution
Concentration: 60 to 80 g/l
Temperature: 60 to 80° C.
Immersion time: 1 to 5 minutes
Surface roughness of the roughened solder resist layer becomes small to the extent of about 0.1 to 0.5 μm at Ra.
Example 52
Except that roughening treatment is further applied to the solder resist layer surface with the following condition after flattening treatment, a printed wiring board is manufactured in the same manner as in Example 43.
(Roughening Condition)
Roughening solution; potassium permanganate solution
Concentration: 60 to 80 g/l
Temperature: 60 to 80° C.
Immersion time: 1 to 5 minutes
Surface roughness of the roughened solder resist layer becomes small to the extent of about 0.2 to 0.5 μm at Ra.
Example 53
Except that roughening treatment is further applied to the solder resist layer surface with the following condition after flattening treatment, a printed wiring board is manufactured in the same manner as in Example 44.
(Roughening Condition)
Roughening solution; potassium permanganate solution
Concentration: 60 to 80 g/l
Temperature: 60 to 80° C.
Immersion time: 1 to 5 minutes
Surface roughness of the roughened solder resist layer becomes small to the extent of about 0.2 to 0.6 μm at Ra.
Example 54
Except that roughening treatment is further applied to the solder resist layer surface with the following condition after flattening treatment, a printed wiring board is manufactured in the same manner as in Example 45.
(Roughening Condition)
Roughening solution; potassium permanganate solution
Concentration: 60 to 80 g/l
Temperature: 60 to 80° C.
Immersion time: 1 to 5 minutes
Surface roughness of the roughened solder resist layer becomes small to the extent of about 0.1 to 0.5 μm at Ra.
As to the IC mounted printed wiring boards manufactured according to Examples 46 to 54, the same heat cycle test as in Examples 1 to 36 is carried out, electric resistance after 1500 cycles and after 2000 cycles is measured, and a rate of change (100×(measured value−initial value)/initial value (%)) with the initial value is obtained.
The case within ±10 is evaluated as “good (O)” and the other cases are evaluated as “no good (x)”. This test result is shown in Table 4.
In addition, as to the IC mounted printed wiring boards manufactured according to Examples 37 to 45 applied no flattening treatment, the same heat cycle test is carried out, a rate of change of electric resistance is obtained and evaluated. These test results are also shown in Table 4 with the test results of Examples 46 to 54.










TABLE 4









Roughness of Roughened




Surface (μm)
Heat Cycle Test












Ra
Ra
1500
2000


Examples
(minimum)
(Maximum)
cycles
cycles





Example 46 (37)
0.1
0.6
◯ (◯)
◯ (X)


Example 47 (38)
0.2
0.5
◯ (◯)
◯ (X)


Example 48 (39)
0.2
0.5
◯ (◯)
◯ (X)


Example 49 (40)
0.2
0.7
◯ (◯)
◯ (X)


Example 50 (41)
0.1
0.5
◯ (◯)
◯ (X)


Example 51 (42)
0.1
0.5
◯ (◯)
◯ (X)


Example 52 (43)
0.2
0.5
◯ (◯)
◯ (X)


Example 53 (44)
0.2
0.6
◯ (◯)
◯ (X)


Example 54 (45)
0.1
0.5
◯ (◯)
◯ (X)









It is understood from the above test result that when a ratio (H/D) of the solder bump height H and the solder resist opening diameter D is within a range of about 0.55 to about 1.0, connection reliability is improved. Further, mainly, it is understood that unevenness of the solder resist layer surface due to the presence or absence of the connecting pad positioned beneath the solder resist is flattened, and when roughness of the flattened surface is about 0.8 to about 3 μm of maximum surface roughness (uneven amount), connection reliability is improved. It is assumed that when the height of a solder bump is comparatively large, a space between the IC chip lower face and the solder resist layer surface becomes wider, so that if there is large unevenness (different level), voids are liable to generate within an under fill resin (sealant), but dispersion of the space between the IC chip lower face and the solder resist layer surface becomes small by flattening treatment so as to increase filling ability of the under fill resin.
Further, when fine unevenness formed by roughing treatment is existent on the flattened solder resist layer surface, and roughness of the roughened surface is about 0.2 μm to about 0.5 μm at arithmetic mean roughness Ra, it is understood that connection reliability is further improved. It is assumed that adhesion between the under fill resin and the solder resist layer surface is easily improved, or flux and flux cleaning solvent are hard to remain within a recess of the surface.
(HAST Test)
The printed wiring boards manufactured according to Examples 1 to 54 and Comparative Examples 1 to 24 are left in atmosphere of temperature: 85° C. and humidity: 85% by applying voltage of 3.3V between adjacent and not shorted solder bumps for 50 hours. Thereafter, insulation resistance between the voltage-applied solder bumps is measured.
In addition, when insulation resistance is 107Ω or more, insulation performance is “good (O)” and when insulation resistance is less than 107Ω, insulation performance is “no good (x)” for evaluation.
As the result, it is confirmed that insulation performance of Examples 1 to 54 and Comparative Examples 1 to 12 is good (O) and that of Comparative Examples 13 to 24 is no good (x).
(Observation of Voids in Bump)
As to the printed wiring boards manufactured according to Examples 1 to 54, voids within solder bumps are observed by using an X-ray television system (“SMX-100” made by ShimazuCorporation) and number of voids is measured. 100 solder bumps are randomly selected, but no void is observed.
As to the printed wiring boards manufactured according to Examples 1 to 54, except that number of connection pad is changed from about 2000 (connecting pad region: about 150 mm2) to about 30000 (connecting pad region: about 1200 mm2), an IC mounted printed wiring board is manufactured in the same manner as in Examples 1 to 54, each of these examples is conducted to heat cycle test, HAST test and observation of voids in solder bump in the same manner as in Examples 1 to 54, and the same results as Examples 1 to 54 can be obtained.
That is, in high density mounting such as about 2000 to about 30000 connecting pads (connecting region area: about 150 to about 1200 mm2), shear stress due to thermal expansion coefficient difference between the IC chip and the printed wiring board becomes large, but according to the present invention, it is confirmed that a printed wiring board having easily improved connection reliability and insulation reliability is produced.

## Claims

1. A method for manufacturing a printed wiring board, comprising:
providing a structure comprising a wiring substrate, a build-up multilayer structure formed over the wiring substrate and a solder resist layer formed over the build-up multilayer structure;
forming in the solder resist layer a plurality of openings such that a plurality of conductor pads positioned to mount an electronic element is formed in the plurality of openings of the solder resist layer, respectively; and
forming a plurality of solder bumps on the conductor pads on the plurality of conductor pads, respectively, such that each of the solder bumps has a height H in μm from an outer surface of the solder resist layer prior to mounting the electronic element,
wherein the build-up multilayer structure includes an outermost conductor circuit, the plurality of openings is formed such that each of the openings has an opening diameter D in μm and exposes a portion of the outermost conductor circuit to form each of the conductor pads and that the plurality of conductor pads is formed at a pitch of about 200 μm or less between adjacent conductor pads, and the plurality of solder bumps is formed in the plurality of openings, respectively, such that each of the solder bumps has a ratio H/D of about 0.55 to about 1.0.

2. The method for manufacturing a printed wiring board according to claim 1, wherein the forming of the solder bumps comprises loading a plurality of solder balls on the conductor pads, respectively, and heating the solder balls in a reflow furnace.

3. The method for manufacturing a printed wiring board according to claim 2, wherein the loading of the solder bumps comprises positioning a ball aligning mask having a plurality of openings corresponding to the conductor pads, above the surface of the solder resist layer, positioning a hollow cylinder having an opening toward the ball alignment mask, assembling the solder balls on the ball alignment mask right under the opening of the hollow cylinder by suction therethrough, and moving the hollow cylinder horizontally such that the solder balls assembled are moved and dropped to the corresponding conductor pads through the openings of the ball alignment mask.

4. The method for manufacturing a printed wiring board according to claim 1, wherein the wiring substrate has a conductor circuit.

5. The method for manufacturing a printed wiring board according to claim 1, wherein the structure is formed such that the solder resist layer has an electronic element mounting region on the outer surface and that the electronic element mounting region is flattened to have a maximum surface roughness in a range of about 0.8 μm to about 3.0 μm.

6. The method for manufacturing a printed wiring board according to claim 2, wherein the structure is formed such that the solder resist layer has an electronic element mounting region on the outer surface and that the electronic element mounting region is flattened to have a maximum surface roughness in a range of about 0.8 μm to about 3.0 μm.

7. The method for manufacturing a printed wiring board according to claim 3, wherein the structure is formed such that the solder resist layer has an electronic element mounting region on the outer surface and that the electronic element mounting region is flattened to have a maximum surface roughness in a range of about 0.8 μm to about 3.0 μm.

8. The method for manufacturing a printed wiring board according to claim 4, wherein the structure is formed such that the solder resist layer has an electronic element mounting region on the outer surface and that the electronic element mounting region is flattened to have a maximum surface roughness in a range of about 0.8 μm to about 3.0 μm.

9. The method for manufacturing a printed wiring board according to claim 1, wherein the structure is formed such that the solder resist layer is flattened to have a maximum surface roughness in a range of about 0.8 μm to about 3.0 μm.

10. The method for manufacturing a printed wiring board according to claim 2, wherein the structure is formed such that the solder resist layer is flattened to have a maximum surface roughness in a range of about 0.8 μm to about 3.0 μm.

11. The method for manufacturing a printed wiring board according to claim 3, wherein the structure is formed such that the solder resist layer is flattened to have a maximum surface roughness in a range of about 0.8 μm to about 3.0 μm.

12. The method for manufacturing a printed wiring board according to claim 4, wherein the structure is formed such that the solder resist layer is flattened to have a maximum surface roughness in a range of about 0.8 μm to about 3.0 μm.

13. The method for manufacturing a printed wiring board according to claim 1, wherein the structure is formed such that the solder resist layer has an electronic element mounting region on the outer surface and that the electronic element mounting region has a surface roughness in a range of about 0.2 μm to about 0.5 μm based on an arithmetic mean roughness Ra.

14. The method for manufacturing a printed wiring board according to claim 2, wherein the structure is formed such that the solder resist layer has an electronic element mounting region on the outer surface and that the electronic element mounting region has a surface roughness in a range of about 0.2 μm to about 0.5 μm based on an arithmetic mean roughness Ra.

15. The method for manufacturing a printed wiring board according to claim 3, wherein the structure is formed such that the solder resist layer has an electronic element mounting region on the outer surface and that the electronic element mounting region has a surface roughness in a range of about 0.2 μm to about 0.5 μm based on an arithmetic mean roughness Ra.

16. The method for manufacturing a printed wiring board according to claim 4, wherein the structure is formed such that the solder resist layer has an electronic element mounting region on the outer surface and that the electronic element mounting region has a surface roughness in a range of about 0.2 μm to about 0.5 μm based on an arithmetic mean roughness Ra.

17. The method for manufacturing a printed wiring board according to claim 1, wherein the structure is formed such that the solder resist layer has a surface roughness in a range of about 0.2 μm to about 0.5 μm based on an arithmetic mean roughness Ra.

18. The method for manufacturing a printed wiring board according to claim 2, wherein the structure is formed such that the solder resist layer has a surface roughness in a range of about 0.2 μm to about 0.5 μm based on an arithmetic mean roughness Ra.

19. The method for manufacturing a printed wiring board according to claim 3, wherein the structure is formed such that the solder resist layer has a surface roughness in a range of about 0.2 μm to about 0.5 μm based on an arithmetic mean roughness Ra.

20. The method for manufacturing a printed wiring board according to claim 4, wherein the structure is formed such that the solder resist layer has a surface roughness in a range of about 0.2 μm to about 0.5 μm based on an arithmetic mean roughness Ra.