JP3424526B2 - Electronic component mounting method - Google Patents

Description

BACKGROUND OF THE INVENTION [0001] [Technical Field of the Invention The present invention relates to method for mounting electronic components. 2. Description of the Related Art In recent years, as semiconductor products have become smaller and more sophisticated, BGA (Ball Grid Array) CS
2. Description of the Related Art An electronic component of a back surface bonding type having a solder ball formed on a mounting surface, such as P (Chip Size Package), is often mounted on a mounting substrate. Here, the structure of a mounting board on which such a back surface bonding type electronic component is mounted will be described. FIG. 11A is a perspective view showing a conventional mounting board, and FIG. 11B is an enlarged perspective view showing a part of FIG. 11A. FIG. 12 shows the XI in FIG.
It is sectional drawing along the I-XII line. [0005] As shown in FIG.
1 has a base material 102 having an insulating property. Base material 10
2, a solder resist 103 is laminated. The wiring 1 is covered with the solder resist 103.
05 is formed on the base material 102. Then, the land 104 is exposed from the solder resist 103 and the wiring 10
5 are formed integrally. [0006] As shown in FIG.
Are exposed from the through holes formed in the solder resist 103, and the solder resist 103 surrounds the periphery of the land 104 with a predetermined gap. And FIG.
As shown in FIG. 2, the lands 104 are formed integrally with each other.
And the upper surface of the wiring 105 are on the same plane, and the boundary between them is not clear in the cross section. A case in which electronic components are mounted on a conventional mounting board configured as described above will be described. FIG. 13 is a cross-sectional view showing a state in which a back surface bonding type electronic component is mounted on the mounting board of FIG. As shown in FIG. 13, a solder ball 7 for electrically and mechanically connecting the electronic component 6 and the land 104 is formed on the back surface of the electronic component 6 of the back surface bonding type. In general, the diameter of the land 104 is
Is smaller than the diameter of the solder ball 7.
The entire structure is thereby covered. Therefore,
The solder ball 7 and the land 104 at the boundary A between the land 105 and the solder ball 7 in the direction opposite to the wiring 105
Is an obtuse angle. On the other hand, since the upper surface of the land 104 and the upper surface of the wiring 5 are flush with each other, the solder ball 7 tends to wet toward the upper surface of the wiring 5, but the resist 103 hinders. Therefore, the interface angle β between the solder ball 7 and the land 104 at the boundary B between the land 104 and the solder ball 7 in the wiring direction is an acute angle. By the way, when the junction formed by the solder ball 7 and the land 104 becomes high or low temperature during the actual use or reliability test of the semiconductor product, the linear expansion coefficient between the electronic component 6 and the base material 102 becomes lower. The difference causes thermal stress in the joint. Here, the thermal stress will be described. FIG. 14 is an explanatory diagram showing the thermal stress acting on the joint between the solder ball and the mounting board in FIG. As shown in FIG. 14, when a thermal stress is applied, a shearing force F relatively acts on the joint. This shear force F becomes a shear stress τ inside the material, and the shear stress τ acts on the interface between the solder ball 7 and the land 104. In FIG. 14, when the x-axis is taken in a direction along the plane of the mounting substrate 101 and the y-axis is taken in a direction perpendicular to the plane, the shear stress τ _yx is applied to the surface in the x-axis direction, and the y-axis is applied to the surface in the y-axis direction. Shear stress τ _xy acts on each. Here, the interface angle α at the boundary portion A is an obtuse angle, and the interface angle β at the boundary portion B is an acute angle. There is an interface edge at which the angle becomes acute. The stress field at the interface end of the dissimilar material has a higher stress concentration as the interface angle is smaller. Then, in the stress singular field, extreme stress concentration occurs during the action of thermal stress. For this reason, when thermal stress is repeatedly applied during actual use or during a reliability test, or during the cooling process from the solder melting temperature during mounting, an extreme angle β due to the shear stress τ _yx at the interface edge β becomes acute. Stress concentration occurs, and a crack occurs at the boundary portion B. In this case, mounting reliability is significantly impaired. In particular, when the direction of expansion of the electronic component 6 and the base material 102 and the direction of extension of the wiring 105 coincide with each other, the occurrence of cracks becomes remarkable.
In this case, there is a restriction in the wiring direction, and it is impossible to design wiring with a high degree of freedom. SUMMARY OF THE INVENTION It is an object of the present invention to provide a technology for a mounting substrate which can prevent cracks caused by thermal stress generated by joining a solder ball and a land. [0017] In order to solve this problem, the present invention provides a wiring formed on an insulating base material.
And a solder resist covering the base material and the wiring
And continuous from the wiring and from the solder resist
It is formed so as to protrude and is
The side surface is surrounded without gap over a predetermined height,
A land to which a solder ball is fixed;
So that it can cover the entire side of the protruding land.
Prepared mounting board, and penetrated to the position corresponding to the land
When a hole is formed and the mounting board is attached
At least avoiding interference with the land
Prepare a plate formed around the through hole,
Align so that the land is exposed from the through hole
Attach the plate to the mounting board,
After mounting the solder paste on the plate, mount the plate
Remove from the board, and place the solder ball on one side.
Child component to the land where the solder paste is formed
The solder balls are aligned and mounted, and the land is
The solder ball and the solder pace so as to cover the entire side surface.
And the door is what you so that you reflow. As a result, since the interface angle between the solder ball and the land becomes obtuse at all points, no crack occurs even when thermal stress is generated by joining the solder ball and the land. An embodiment of the present invention will be described below with reference to FIGS. 1 to 10. I do. In these drawings, the same members are denoted by the same reference numerals,
In addition, duplicate description is omitted. (Embodiment 1) FIG. 1 is a sectional view showing a mounting board according to an embodiment of the present invention, FIG. 2 is a sectional view showing a state where electronic components are mounted on the mounting board of FIG. 1, and FIG. FIG. 4 is an explanatory view showing the action of thermal stress in FIG. 2, and FIG. As shown in FIG. 1, the mounting board 1 of the present embodiment has a base material 2 having an insulating property, for example, made of a glass cloth base epoxy resin laminate or the like. Substrate 2
A wiring 5 made of, for example, copper and having a predetermined shape is formed thereon. Then, the wiring 5 and the wiring 5
The solder resist 3 is laminated so as to cover the base material 2 at the portion where no is formed. A land 8 is formed which is continuous from the wiring 5 and protrudes from the solder resist 3 and to which solder balls of electronic components to be described later are joined. Therefore, the height of the land 8 is higher than the height of the wiring 5. The land 8 having, for example, a circular shape has its side surface surrounded by the solder resist 3 over a predetermined height without any gap. A case in which a back surface bonding type electronic component is mounted on the mounting board of this embodiment having such a structure will be described. As shown in FIG. 2, for example, BGA / CS
A solder ball 7 for electrically and mechanically connecting the electronic component 6 and the land 8 is formed on the back surface of the electronic component 6 of the back surface joining type such as P. The diameter of the land 8 is adjusted so that the entire land 8 is covered with the solder ball 7 when the land 8 and the solder ball 7 are joined.
Is smaller than the diameter. Here, as described above, the side surface of the land 8 is surrounded by the solder resist 3 without any gap, and the land 8 has a shape protruding from the solder resist 3. Therefore, as shown in the figure, the solder balls 7 bonded to the lands 8
Cover the entire circumference of the side surface from the entire top surface of the. As a result, the boundary between the land 8 and the solder ball 7 is formed on the side surface of the land 8 extending perpendicular to the surface of the base material 2. For this reason, the interface angle between the solder ball 7 and the land 8 becomes obtuse not only at the interface angle α of the boundary portion A other than the wiring direction but also at the interface angle β of the boundary portion B in the wiring direction. That is, the interface angle between the solder ball 7 and the land 8 becomes obtuse at all points. The action of thermal stress in such a joint shape will be described below. At the time of thermal stress during actual use or during a reliability test, as shown in FIG. 3, a shear force F relatively acts on the joint. Then, the shear force F becomes a shear stress τ inside the material, and this shear stress τ acts on the interface between the solder ball 7 and the land 8. Here, as described above, since the interface angle between the solder ball 7 and the land 8 is obtuse at all points, the x-axis is set in the direction along the plane of the mounting When the y-axis is taken in a direction orthogonal to the above, the shear stress τ is only the shear stress τ _xy acting on the surface in the y-axis direction. Therefore, even when a thermal stress is applied, a stress singular field is not formed and an extreme stress concentration does not occur. Even when a thermal stress is generated by joining the solder ball 7 and the land 8, a crack is generated. do not do. Further, since the interface angle between the solder ball 7 and the land 8 becomes obtuse irrespective of the direction of the wiring 5, the wiring 5 can be routed in any direction. Next, the mounting board 1 having such a structure will be described.
Will be described with reference to FIG. First, as shown in FIG. 4A, a substrate 2 and a copper-clad laminate 9 having a copper foil (thin film) 10 as a conductor formed on the substrate 2 are prepared. The thickness of the copper foil 10 is, for example, about two to three times the thickness of the wiring 5 described later. Next, as shown in FIG. 4B, an etching mask 11 made of a dry film photoresist or the like and protecting an unnecessary portion during etching is formed at the land forming position on the upper surface of the copper foil 10. Then, as shown in FIG. 4C, the copper foil 10 is half-etched by a predetermined amount in the depth direction, leaving a land formation position, to obtain a required wiring height. Thereby, the lands 8 are formed. Here, the required wiring height generally ranges from 9 μm to 18 μm.
μm. For the etching, for example, iron chloride or copper chloride is used. Next, as shown in FIG.
Then, an etching mask 11 is formed on the wiring formation position. At this time, the etching mask 11 used in forming the land 8 may or may not have been removed in advance. Next, as shown in FIG.
The copper foil 10 is completely removed by etching except for the wiring formation position. As a result, the wiring 5 continuous to the land 8 is formed. After the lands 8 and the wirings 5 are formed, the etching mask 11 is removed as shown in FIG. Finally, as shown in FIG. 4G, a solder resist 3 is formed on the substrate 2 and the wiring 5 so that the lands 8 protrude. Here, the solder resist 3 is formed without any gap up to the side surface of the land 8, and the land 8 is, for example, 5 μm from the upper surface of the solder resist 3.
So that it protrudes. Thus, the mounting board 1 shown in FIG. 1 is manufactured. (Embodiment 2) FIG. 5 is a cross-sectional view showing successively a manufacturing process of a mounting board according to another embodiment of the present invention. In the present embodiment, the lands 8 are formed of copper, which is the material of the wiring 5, and a metal having good plating properties, such as solder or nickel. A method for manufacturing a mounting board having such a structure will be described. First, in the same manner as in the first embodiment, as shown in FIG. 5A, a copper-clad laminate in which a base material 2 and a copper foil (thin film) 10 as a conductor are formed on the base material 2 9 is prepared. Note that, in the case of the present embodiment in which the thickness of the wiring 5 is directly changed without half-etching the copper foil 10, the thickness of the copper foil 10 is, for example, 9 μm to 18 μm. Next, as shown in FIG.
An etching mask 11 is formed at the land formation position and the wiring formation position on the upper surface of the substrate. At this time, the dimension of the etching mask 11 at the land formation position may be smaller than the dimension of the land 8. Next, as shown in FIG. 5C, the copper foil 10 is completely removed except for the land formation position and the wiring formation position, and thereafter, as shown in FIG. Is removed. Thereby, the wiring 5 is formed. Next, as shown in FIG. 5E, a plating mask 12 is formed at a position other than the land forming part of the wiring. The land formation position is set so as to be exposed from the opening 13 formed in the plating mask 12. And FIG.
As shown in (f), the land 8 is formed so as to fill the inside of the opening 13 with plating. In order to form the lands 8 by plating, a polymer material having plating resistance is used for the plating mask 12. After the lands 8 are thus formed, the plating mask 12 is removed as shown in FIG. Finally, as shown in FIG. 5H, the solder resist 3 is formed on the base material 2 and the wiring 5 so that the lands 8 protrude. Here, also in the present embodiment, the solder resist 3 is formed without any gap up to the side surface of the land 8 and the land 8 is
Projecting from the upper surface of, for example, 5 μm or more. As described above, the land 8 may be formed on the wiring 5. If the land 8 is formed on the wiring 5, the thickness of the copper foil
Therefore, it is not necessary to use a thick copper-clad laminate of special specification. The lands 8 can be formed by using a metal paste instead of plating. In this case, the land forming process by plating described above becomes a land forming process by paste application, and the land 8 is formed by applying a paste material to the opening 13. (Embodiment 3) FIG. 6 is a cross-sectional view showing a manufacturing process of a mounting board according to still another embodiment of the present invention. In this embodiment, both the lands 8 and the wirings 5 are formed of copper. In addition,
In a method of manufacturing a mounting board having such a structure,
The steps shown in FIGS. 6A to 6E and FIGS.
Steps shown in (h) are shown in FIGS.
This is the same as the step shown in (e) and the steps shown in FIGS. 5 (g) and 5 (h). Therefore, only the step shown in FIG. That is, as shown in FIG. 6F, the lands 8 are formed by filling the inside of the opening 13 with the same copper plating as the material of the wiring 5. Note that, also in the present embodiment, the lands 8 can be formed of a paste material. As described above, when the material of the land 8 and the wiring 5 is the same copper, the peel strength between the land 8 and the wiring 5 increases. (Embodiment 4) FIG. 7 is a cross-sectional view showing successively a manufacturing process of a mounting board according to still another embodiment of the present invention. In the present embodiment, a mounting substrate on which a wiring pattern has been formed is prepared in advance, and a protruding land 8 is formed on the mounting substrate. That is, as shown in FIG.
The wiring 5 is covered with the solder resist 3, and a mounting board having a depressed land exposed at the same height as the wiring 5 is prepared with a gap between the wiring 5 and the solder resist 3 covering the base material 2. Next, as shown in FIG. 7B, a plating mask 12 is formed at a position other than the land formation position. An opening 13 is formed at the land formation position. Next, as shown in FIG.
3 is filled with plating to form lands 8. At this time, plating is grown until the land 8 protrudes from the upper surface of the solder resist 3 by, for example, 5 μm or more. The lands 8 are made of copper, which is a material of the wiring 5, and a metal having good plating properties, such as solder or nickel. Then, as shown in FIG. 7D, when the plating mask 12 is finally removed, a mounting board with the lands 8 protruding is obtained. In this way, it is possible to prepare a mounting board in which the protruding crack of the land 8 does not occur using the conventional mounting board. Here, also in this case, the land 8 can be formed by using a metal paste material instead of plating. In this case, the land forming process by plating described above becomes a land forming process by paste application, and the land 8 is formed by applying a paste material to the opening 13. (Embodiment 5) FIG. 8 is a cross-sectional view showing successively a manufacturing process of a mounting board according to still another embodiment of the present invention. In the present embodiment, the lands 8 and the wirings 5 are both formed of copper. In addition,
In the method for manufacturing a mounting board according to the fifth embodiment,
The steps shown in FIGS. 8A, 8B, and 8D are the same as the steps shown in FIGS. 7A, 7B, and 7H in the fourth embodiment. Therefore, only the step shown in FIG. 8C will be described here. That is, as shown in FIG. 8C, the lands 8 are formed by filling the inside of the opening 13 with the same copper plating as the material of the wiring 5. Note that, also in the present embodiment, the lands 8 can be formed of a paste material. As described above, when the material of the land 8 and the wiring 5 is made of the same copper, it becomes possible to prepare a mounting board in which the protruding crack of the land 8 does not occur using a conventional mounting board. In addition, the peel strength between the land 8 and the wiring 5 increases. (Embodiment 6) FIG. 9 is a sectional view showing an electronic component mounting plate according to an embodiment of the present invention.
FIG. 10 is a cross-sectional view continuously showing a process of mounting an electronic component on a mounting board using the plate of FIG. The plate 15 shown in FIG. 9 is formed of, for example, a metal such as stainless steel. A through hole 16 is formed in the plate 15 at a position corresponding to the land 8 of the mounting substrate 1, and the plate 15 is aligned with the mounting substrate 1, and the through hole 16 is filled with a solder paste. The diameter of the through hole 16 is smaller than the diameter of the land 8. Around the through hole 16, an avoiding portion 17 is formed by half-etching the back surface of the plate 15 in order to avoid interference between the land 8 and the plate 15. Note that the half etching depth of the avoidance portion 17 is the same as the protrusion size of the land 8 from the solder resist 3. A procedure for mounting an electronic component on a mounting board using such a plate 15 will be described. First, as shown in FIG. 10A, the plate 15 is mounted on the mounting board by aligning the lands 8 so that the lands 8 are exposed from the through holes 16. Here, plate 1
The half-etching depth of the avoidance portion 17 formed at 5 is:
Since the land 8 has the same size as that protruding from the upper surface of the solder resist 3, the land 8 is
No warping of the plate 15 due to pushing up occurs. Further, since the diameter of the through hole 16 is smaller than the diameter of the land 8 and the half etching depth of the avoidance portion 17 is the same as the protrusion size of the land 8, a gap exists between the through hole 16 and the upper surface of the land 8. do not do. Accordingly, there is no possibility that the solder paste 18 enters the avoidance portion 17 and causes a short circuit between the adjacent land 8. Then, in this state, the through-hole is filled with the solder paste 18 using the squeegee 19). Next, when the plate 15 is removed from the mounting board 1 as shown in FIG. 10B, the solder paste 18 is printed only on the upper surface of the land 8. When the solder paste 18 is formed on the land 8 as described above, the solder ball 7 is positioned on the land 8 on which the solder paste 18 is printed, as shown in FIG. The bonding type electronic component 6 is mounted on the mounting board 1. At this time, the electronic component 6 is pressed toward the mounting board 1 until the solder ball 7 enters into a depth of 50% or more of the thickness of the printed solder paste 18. As a result, the solder paste 18 protrudes from the upper surface of the land 8 and has a shape surrounding the side surface of the land 8. Finally, as shown in FIG. 10D, when the solder ball 7 and the solder paste 18 are melted and cooled by the reflow device, the solder paste 18 is absorbed by the solder ball 7 and the side surface of the land 8 protrudes. Is formed in a shape surrounding the solder ball 7. As a result, the interface angle between the solder ball 7 and the land 8 becomes obtuse at all points, and no crack occurs even when thermal stress is generated by joining the solder ball 7 and the land 8. As described above, according to the present invention, when an electronic component is mounted on a mounting board by a solder ball by forming a land so as to protrude, the side surface of the land from which the solder ball protrudes is completely removed. Because I cover it around the circumference,
The interface angle between the solder ball and the land becomes obtuse at all points. Thus, even when a thermal stress is generated due to the joining between the solder ball and the land, an effective effect that a crack due to the thermal stress does not occur can be obtained. Further, when both the land and the wiring are made of copper, an effective effect that the peel strength between the land and the wiring can be increased can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view showing a mounting board according to Embodiment 1 of the present invention. FIG. 2 is a cross-sectional view showing a state where electronic components are mounted on the mounting board in FIG. FIG. 4A to FIG. 4G are cross-sectional views successively showing a manufacturing process of the mounting substrate of FIG. 1. FIG. 5A to FIG. FIG. 6A to FIG. 6H are cross-sectional views sequentially illustrating a manufacturing process of a mounting substrate according to a second embodiment of the present invention. 7 (a) to 7 (d) are cross-sectional views successively showing a manufacturing process of a mounting board according to Embodiment 4 of the present invention. FIGS. 8 (a) to 8 (d) show an embodiment of the present invention. FIG. 9 is a cross-sectional view showing the manufacturing process of the mounting substrate in Embodiment 5 continuously. FIG. 10A to FIG. 10D are cross-sectional views showing a process of mounting an electronic component on a mounting board using the plate of FIG. 9 continuously. (A) is a perspective view showing a conventional mounting board,
(B) is a perspective view showing a part of (a) in an enlarged scale. [FIG. 12] A cross-sectional view taken along the line XII-XII in FIG. 11 (a). [FIG. 13] FIG. FIG. 14 is a cross-sectional view showing a state in which electronic components are mounted. FIG. 14 is an explanatory view showing thermal stress acting on a joint between a solder ball and a mounting board in FIG. 13. 5 Wiring 6 Electronic component 7 Solder ball 8 Land 15 Plate 16 Through hole 17 Avoidance section 18 Solder paste

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI H01L 21/92 604B (56) References JP-A-7-121722 (JP, A) JP-A 9-275271 (JP, A) JP 52-12575 (JP, A) JP-A-5-29363 (JP, A) JP-A-5-144816 (JP, A) JP-A-5-226502 (JP, A) JP-A-6-204290 (JP, A) A) JP-A-8-111578 (JP, A) JP-A-11-67820 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/60 H05K 3/34 H01L 23 / 12

Claims (1)

(57) Claims 1. A wiring formed on an insulating base material, a solder resist covering the base material and the wiring, and a solder resist continuous from the wiring and from the solder resist. A land that is formed so as to protrude and is surrounded by the solder resist without any gap over a predetermined height, and that has a land to which the solder ball is fixed. Prepare a mounting board as described above, and form a through hole at a position corresponding to the land.
With the land when the mounting board is attached to
An avoidance part for avoiding interference is formed at least around the through hole.
Prepare the formed plate and align it so that the lands are exposed from the through holes
Then, the plate is attached to the mounting substrate, and the solder paste is filled in the through-holes.
The electronic component having a solder ball formed on one surface is removed from the mounting board.
Place the solder ball on the land where the paste is formed.
The solder balls are placed side by side, and the solder balls are
An electronic device characterized by reflowing a solder paste.
Component mounting method.