JP2007027341A - Printed wiring board and electronic-components mounting structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the structure which improves the reliability of the solder joint between a multilayer wiring board and a BGA. <P>SOLUTION: The printed wiring board is laminated alternately with an insulating layer 10 and a conductive wiring layer 20, in such a way that a conductive wiring layer has a circuit pattern 21 and the through-hole 11 of the insulating layer has a filled via 12 made by a filler which is connected to a via land 13. The wiring layer of the uppermost layer having an electrode pad 22 constitutes a mounting surface for mounting a BGA40. A solder resist layer 30 covers a perimeter 22a of an electrode pad, and has an opening 31 by which a central solder joint 22b is made exposed. On the perimeter edge of the electrode pad, a perimeter notch 22c is formed in the diagonal direction of the BGA, so that bending deformation should not be prevented for heat distortion by making the perimeter notch inscribed to the opening of a solder resist layer. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a multilayer printed wiring board in which filled vias and the like are arranged vertically immediately below an electrode pad for soldering an electronic component, particularly when a bending stress is repeatedly applied to a solder joint of an electrode pad. The present invention relates to a highly reliable printed wiring board and an electronic component mounting structure in which no defects occur.

  Ball grid array package (BGA) type and chip size package (CSP) type semiconductor devices are used in many electronic devices as electronic components that enable connection of multiple terminals in a small area. In the BGA type semiconductor device, solder balls as connection terminals are arranged in a grid pattern on an interposer substrate on the back side of the package, and are soldered onto electrode pads that are also arranged in a grid pattern on the surface of the printed wiring board.

  There are two types of solder joint structures when soldering the BGA type semiconductor device and the electrode pads on the printed wiring board, one is a BGA type semiconductor device 140 as shown in FIG. Is mounted on the electrode pad 122 with an SMD (Solder Masked Defined) structure. This configuration is a multilayer printed wiring board in which insulating wiring layers 120 and conductive wiring layers 120 having wiring patterns 121 are alternately stacked, filled vias 112 are filled in through holes 111 of insulating layers 110, and via lands 113 are provided on the upper layer side. It is. In addition, the opening diameter of the opening 131 of the solder resist layer 130 is smaller than the outer diameter of the electrode pad 122, and the outer peripheral portion of the electrode pad 122 is covered with the solder resist layer 130. Therefore, when subjected to mechanical stress such as a drop impact, the structure is such that peeling at the interface between the electrode pad 122 and the insulating layer 110 does not easily occur.

  On the other hand, FIG. 4 shows a BGA type semiconductor device 140 and an electrode pad 122 mounted with an NSMD (Non Solder Masked Defined) structure. The opening diameter of the opening 131 of the solder resist layer 130 is formed larger than the outer diameter of the electrode pad 122, and the entire structure including the outer peripheral edge of the electrode pad 122 is exposed. For this reason, at the time of soldering such as reflow, the solder 132 is joined not only to the surface of the electrode pad 122 but also to the side surface. Therefore, although the solder joint strength is increased and the temperature cycle life is increased, the outer diameter of the electrode pad 122 is small and is not covered with the solder resist layer 130, so that the electrode pad 122 is easily peeled off due to mechanical stress.

  Currently, a BGA type semiconductor device is required to have a narrow pitch and multiple terminals in order to increase the density. If the pitch between the terminals is narrowed, the electrode pads on the printed wiring board are also narrowed, so it is difficult to pass the wiring between the adjacent electrode pads. It is also difficult to secure a space for arranging a through hole for dropping the wiring in the inner layer. Therefore, the wiring of a narrow-pitch, multi-terminal BGA semiconductor device can be drawn only by arranging a via hole or the like immediately below the electrode pad on which the connection terminal of the BGA semiconductor device is mounted to have a pad-on-via structure.

  Such via holes include those in which the through holes are filled with a filler such as a resin, and those that are filled with a conductive material such as plating or conductive paste to form a filled via. By adopting a stacked via structure in which filled vias are arranged vertically, it becomes possible to lead out wiring deep into the inner layer such as the second, third, and fourth layers.

Conventionally, for example, Patent Document 1 points out a problem that connection reliability of a printed wiring board having a stacked via structure in which filled vias are arranged vertically is lowered.
JP 2004-6576 A

  In a stacked via structure in which filled vias or through-holes are vertically arranged immediately below the electrode pad, when heat is applied to the solder joint between the multilayer printed wiring board and the BGA type semiconductor device, the printed wiring board and the semiconductor device Bending and warping deformation occurs in the solder joint. At this time, in the apparatus of FIG. 5, as shown in FIG. 5B, the stacked via structure arranged immediately below the electrode pad 122 restrains the warpage and bending deformation of the solder joint portion between the printed wiring board and the BGA type semiconductor device 140. . For this reason, bending stress acts in the direction indicated by the arrow with the solder joint as a base point, and the electrode pad 122 prevents the solder 132 from bending deformation, thereby generating a crack from the inside to the outside of the BGA type semiconductor device 140. There is a problem that the reliability of the part is remarkably lowered.

  The present invention has been made in view of the above-mentioned unsolved problems of the prior art, and has improved the reliability of solder bonding between a multilayer printed wiring board having a stacked via structure and the like and an electronic component such as a BGA type semiconductor device. It is to improve. Another object of the present invention is to provide a printed wiring board and an electronic component mounting structure in which cracks due to bending stress hardly occur even when heat is repeatedly applied.

  A printed wiring board according to the present invention includes a multilayer circuit in which insulating layers and conductor wiring layers are alternately laminated, an electrode pad for soldering an electronic component to the uppermost layer of the multilayer circuit, and a solder joint portion of the electrode pad A solder resist layer that covers an outer peripheral portion excluding the uppermost layer of the multilayer circuit, and a part of the outer peripheral edge of the electrode pad exposes the solder joint portion of the electrode pad. It is characterized by inscribed in the opening.

  When heat is applied to a solder joint of an electronic component such as a BGA type semiconductor device, the stacked via structure or the pad-on-via structure arranged immediately below the electrode pad restrains the warp or bending deformation of the solder joint, and as a result, the solder Bending stress based on the joint acts. Therefore, the outer diameter of the electrode pad is reduced in the direction in which the bending stress works, and the outer peripheral notch for inscribed in the opening of the solder resist layer is formed so as not to hinder bending deformation of the solder joint. Configure. As a result, the occurrence of cracks due to the thermal strain of the solder joint is suppressed, and the reliability of electrical joining is improved.

  High-density and highly reliable electronic component mounting structure by enabling high-density wiring by making the electrode pad for mounting electronic components a highly reliable SMD structure and improving the peel strength of the electrode pad Can be realized.

  The best mode for carrying out the present invention will be described with reference to the drawings.

  As shown in FIGS. 1B and 1C, the printed wiring board according to the present embodiment has a multilayer circuit in which insulating layers 10 and conductor wiring layers 20 made of insulating resin are alternately stacked. The conductor wiring layer 20 has a wiring pattern 21, the through hole 11 of the insulating layer 10 has a filled via 12 made of a filler, and each filled via 12 is connected to a via land 13 formed in the upper conductor wiring layer 20. .

  The uppermost conductor wiring layer 20 includes electrode pads 22 and constitutes a mounting surface for mounting a BGA type semiconductor device 40 which is an electronic component. The solder resist layer 30 has an opening 31 that covers the outer peripheral portion 22a of the electrode pad 22 and exposes the central solder joint portion 22b. By joining the solder joint portion 22b to the package of the semiconductor device 40 with the solder 32, a solder joint structure is formed.

  In this printed wiring board, for example, a wiring pattern 21 made of a copper plating film or a copper foil is formed on both surfaces of a plate-like insulating layer 10 formed by impregnating a glass cloth woven with glass fiber with an epoxy resin or the like, and alternately. It has a multilayer structure laminated on. In the uppermost layer of the printed wiring board, the outer peripheral portion 22 a outside the solder joint portion 22 b of the electrode pad 22 to be joined to the semiconductor device 40 is covered with the solder resist layer 30. The through hole 11 of the insulating layer 10 is formed by a laser beam or the like, and the material of the filled via 12 is a conductive material such as a plating such as copper or a conductive paste or a non-conductive material such as a resin. A plurality of filled vias 12 are vertically arranged immediately below each electrode pad 22 to electrically connect the wiring patterns 21 of each conductor wiring layer 20. In the BGA type semiconductor device 40, solder balls are arranged in an array on the bottom interposer.

  A solder paste is applied on the electrode pad 22, and the BGA type semiconductor device 40 is mounted. For example, the BGA type semiconductor device 40 is soldered onto the electrode pad 22 by heating to the melting point of the solder 32 or higher by reflow or the like.

  As shown in FIG. 1A, an outer peripheral notch 22c is formed on the outer peripheral edge of the electrode pad 22 along the line AA in the diagonal direction of the semiconductor device 40. The outer peripheral notch 22c is formed as a solder resist. By being inscribed in the opening 31 of the layer 30, it is configured so as not to prevent bending deformation due to thermal strain.

  As shown in FIG. 1A, the electrode pad 22 has a perfect circle shape, and the outer peripheral portion 22 a is covered with a solder resist layer 30. Further, only the central solder joint portion 22b is exposed from the opening 31 of the solder resist layer 30, and is soldered to the BGA type semiconductor device 40 as shown in FIG. As shown in FIG. 2, the electrode pad 22 includes a pair of outer peripheral notches 22 c on both sides in the diagonal direction of the semiconductor device 40 along the line AA. In other words, in the tangential direction of the opening 31 of the solder resist layer 30, a part of the outer peripheral edge of the electrode pad 22 in the region outside it is locally removed by etching in the printed wiring board manufacturing process, and the outer peripheral notch 22c. Form. The opening 31 of the solder resist layer 30 is formed in a perfect circle.

  As shown in FIG. 2, when the interval between the connection terminals 41 of the semiconductor device 40 is, for example, 0.5 mm pitch, the outer diameter of the electrode pad 22 is 0.4 mm when the solder resist accuracy is ± 0.050 mm in the SMD structure. The opening diameter of the opening 31 of the solder resist layer 30 needs to be 0.3 mm. In the inner layer, a filled via 12 having a via diameter of 0.15 mm is disposed concentrically over each layer in order to make an electrical connection, thereby forming a stacked via structure.

  1B is a cross-sectional view taken along the line AA in FIG. 1A after mounting the semiconductor device 40, and FIG. 1C is a cross-sectional view taken along the line AA in FIG. It is sectional drawing taken along the -B line. In the cross section along the line AA shown in FIG. 1B, since the outer peripheral notch 22c is formed, the opening diameter of the opening 31 of the solder resist layer 30 is equal to the outer diameter of the electrode pad 22 and is inscribed. Therefore, the electrode pad 22 does not exist outside the solder joint portion 22b. On the other hand, as shown in FIG. 1C, the opening diameter of the opening 31 of the solder resist layer 30 is smaller than the outer diameter of the electrode pad 22 in the cross section along the line BB, and the outer peripheral portion of the electrode pad 22. 22 a is covered with the solder resist layer 30.

  When heat is applied, the stacked via structure disposed immediately below the electrode pad 22 restrains warpage or bending deformation of the solder joint area with the semiconductor device 40, and therefore bending stress based on the solder joint area acts. . However, if the outer circumferential notch 22c of the electrode pad 22 is provided in the direction in which the bending stress acts, the bending deformation of the solder joint 22b is not hindered. Therefore, it is possible to suppress the occurrence of cracks occurring from the inner side to the outer side of the BGA type semiconductor device 40, that is, in the direction of the AA line in FIG. As a result, a highly reliable solder joint structure can be realized.

  Further, since the opening diameter of the solder resist layer 30 is the same as that of the conventional structure, the solder resist layer 30 can be mounted with the same bonding area, and by making the electrode pad structure an SMD structure, the electrode pad 22 and the neck portion that is drawn from the electrode pad 22 There will be no problems such as peeling. In addition, since the electrode pad 22 is elongated in a direction substantially perpendicular to the diagonal direction of the BGA type semiconductor device 40, an electrode structure in which wiring is easily drawn out in the direction is obtained. Yes.

  As shown in FIG. 3A, the electrode pad 22 of the present embodiment has an opening 31 of the solder resist layer 30 in the diagonal direction (the direction of the line AA) of the BGA type semiconductor device 40 from the perfect circle shape. The outer peripheral notch 22c is formed in a portion outside the tangent line. Only the region located on the diagonally inner side of the semiconductor device 40 is removed by etching in the printed wiring board manufacturing process. On the other hand, the opening 31 of the solder resist layer 30 is formed in a perfect circle.

  As shown in FIG. 3B, in the cross section taken along line AA in FIG. 3A, the solder resist opening diameter is the same as the electrode pad diameter on the diagonally inner side of the semiconductor device 40, and is inscribed. Therefore, the electrode pad 22 does not exist outside the solder joint portion 22b. On the other hand, on the diagonally outer side of the semiconductor device 40, the solder resist opening diameter is formed smaller than the electrode pad diameter, and the outer peripheral portion 22 a of the electrode pad 22 is covered with the solder resist layer 30. Further, as shown in FIG. 3C, the solder resist opening diameter is formed smaller than the electrode pad diameter in the cross section along the line BB, and the outer peripheral portion 22 a of the electrode pad 22 is formed by the solder resist layer 30. Covered.

  When heat is applied, the stacked via structure disposed immediately below the electrode pad 22 restrains warpage and bending deformation of the solder joint region between the multilayer printed wiring board and the BGA type semiconductor device 40. Therefore, a bending stress with the solder joint region as a base point works, but the electrode pad 22 does not exist in the direction in which the bending stress acts, and thus bending deformation of the solder joint region is not hindered. Therefore, it is possible to suppress the generation of cracks that occur from the inside to the outside of the BGA type semiconductor device 40, and to provide a highly reliable joint structure.

  Also, since the solder resist opening diameter is not changed, it is possible to make the electrode pad structure into the SMD structure with the same mounting area as the conventional mounting method, peeling of the electrode pad and the lead neck portion from the electrode pad, etc. The problem does not occur.

The printed wiring board and electronic component mounting structure by Example 1 are shown, (a) is a top view explaining the shape of an electrode pad and the opening dimension of a soldering resist layer, (b) is the AA line of (a). (C) is sectional drawing taken along the BB line of (a). It is a top view which shows the mounting area | region of a BGA type semiconductor device. The printed wiring board and electronic component mounting structure by Example 2 are shown, (a) is a top view explaining the shape of an electrode pad and the opening dimension of a soldering resist layer, (b) is the AA line of (a). (C) is sectional drawing taken along the BB line of (a). It is a figure explaining the electronic component mounting structure by one prior art example. It is a figure explaining another prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Insulating layer 12 Filled via 13 Via land 20 Conductor wiring layer 21 Wiring pattern 22 Electrode pad 22c Outer periphery notch 30 Solder resist layer 31 Opening 32 Solder 40 Semiconductor device 41 Connection terminal

Claims (6)

  A multilayer circuit in which insulating layers and conductor wiring layers are alternately laminated, an electrode pad for soldering an electronic component to the uppermost layer of the multilayer circuit, an outer peripheral portion of the electrode pad excluding the solder joint, and the multilayer circuit A part of the outer peripheral edge of the electrode pad is inscribed in an opening of the solder resist layer for exposing the solder joint portion of the electrode pad. Printed wiring board characterized by   2. The printed wiring board according to claim 1, wherein the printed wiring board has a stacked via structure in which filled vias are arranged concentrically over the respective layers immediately below the electrode pads.   The printed wiring board according to claim 1, wherein the printed wiring board has a pad-on-via structure in which through holes are arranged concentrically immediately below the electrode pads.   The electronic component is a BGA type semiconductor device, and is provided with a pair of outer peripheral notches disposed symmetrically in a diagonal direction of the semiconductor device at the outer peripheral edge of the electrode pad. Item 4. The printed wiring board according to any one of Items 1 to 3.   2. The electronic component according to claim 1, wherein the electronic component is a BGA type semiconductor device, and an outer peripheral notch portion disposed on an inner side in a diagonal direction of the semiconductor device is provided on the outer peripheral edge of the electrode pad. The printed wiring board according to any one of 3 to 3.   6. An electronic component mounting structure comprising: the printed wiring board according to claim 1; and an electronic component mounted on the printed wiring board.

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