JP2004179547A - Wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that it is difficult to effectively enlarge the area of external electrode to withstand a large thermal stress because external size of the insulating base material and size of the external electrode are very small and a metallized conductive layer is formed only on the internal wall surface of the concave part of the external electrode. <P>SOLUTION: In the wiring board 4, a convex portion is provided at the lower surface of an insulating base material 1, including a plurality of wiring conductors 3, on which a plurality of almost square insulating layers are laminated with smaller interval between two sides facing with each other of the insulating layer than that of the insulating layer just above such insulating layer, and a plurality of external electrodes 2 which are electrically connected to a plurality of wiring conductors 3 are formed, via the side surface, on the lower surface of the external insulating base material 1 from the lower surface of the convex portion at the part of two sides facing each other of such convex portion. For connection by soldering with the external circuit substrate, sufficient area can be secured for the external electrode 2 for which a connection terminal can form a large meniscus. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a wiring board in which external electrodes are arranged from a lower surface to a side surface of an insulating base, and the external electrodes are connected to an external circuit board. More specifically, the present invention relates to a connection reliability of the external electrodes to the external circuit board. It relates to a good wiring board.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a wiring board for accommodating a semiconductor element, particularly a semiconductor element such as an LSI or an electronic component such as a piezoelectric vibrator or a capacitor has a semiconductor element mounting portion on an upper surface of an insulating base generally made of ceramics such as alumina ceramics. Further, a plurality of wiring conductors made of a high melting point metal powder such as tungsten and molybdenum are provided from the periphery to the side surface of the semiconductor element mounting portion. The wiring conductor is electrically connected to a plurality of external electrodes formed from the lower surface to the side surface of the insulating base. The external electrode is connected to an external circuit board such as a motherboard via a connection terminal such as tin-lead solder, whereby the wiring board is mechanically and electrically connected to the external circuit board.
[0003]
In recent years, the number of electrodes of electronic components such as semiconductor elements has been increasing along with high integration and miniaturization, and accordingly, high density wiring of wiring conductors and external electrodes on a wiring board is required.
[0004]
In response to such demands, recently, as an external electrode of a wiring board, a concave portion is formed from the lower surface of the insulating base to the middle in the thickness direction of the side surface, and a metallized conductor layer is formed from the lower surface of the insulating base to the inner wall surface of the concave portion. Wiring boards having external electrodes of the formed structure are often used.
[0005]
[Patent Document 1]
JP-A-8-37251
[Problems to be solved by the invention]
However, even when the concave portion is formed from the lower surface of the insulating base to the middle of the side surface in the thickness direction and the external electrode having the metallized conductor layer formed on the inner wall surface thereof, particularly, the borosilicate When a material such as glass-based ceramics or mullite ceramics having a very small thermal expansion coefficient of about 5 × 10 ⁻⁶ / ° C. or less and causing a very large thermal stress with an external circuit board is used, Is extremely small, for example, about 5 mm × 5 mm or less, and when the dimensions of the external electrodes are becoming small, the metallized conductor layer is formed only on the inner wall surface of the concave portion. It is difficult to effectively increase the electrode area to accommodate such a large thermal stress and to accommodate the small external electrode area. There is a problem in that.
[0007]
In addition, since the joint surface between the metallized conductor layer on the inner wall surface of the recess and the connection terminal is mainly parallel to the direction of the shear strain generated in the connection terminal, the connection of the wiring board to the external circuit board is performed. There was a problem that the reliability could not be improved effectively.
[0008]
Therefore, the connection strength between the external electrode and the external circuit board cannot be sufficiently secured, and the reliability of the connection of the wiring board to the external circuit board becomes insufficient.
[0009]
The present invention has been devised to solve the problems in the conventional technology as described above, and its object is to provide an external electrode which is generated by a stress caused by a difference in thermal expansion between a wiring board and an external circuit board. It is an object of the present invention to provide a wiring board which can alleviate the shear strain on the connection terminal connected to the external circuit board and can make the reliability of connection with an external circuit board extremely excellent.
[0010]
[Means for Solving the Problems]
The wiring board according to the present invention is arranged such that, on a lower surface of an insulating base having a plurality of substantially rectangular insulating layers stacked thereon and having a plurality of wiring conductors therein, a distance between two opposing sides of the insulating layer is greater than that of the insulating layer immediately above the insulating layer. The protrusions are also provided by reducing the size of the protrusions, and the plurality of wiring conductors are electrically connected to the lower surface of the insulating base from the lower surface of the protrusions on the two opposite sides of the protrusions to the lower surface of the insulating base outside the side surfaces. A plurality of external electrodes which are electrically connected are formed.
[0011]
According to the wiring board of the present invention, the interval between the two opposing sides of the insulating layer is made smaller than that of the insulating layer immediately above, so that the convex portion is provided. When a plurality of external electrodes electrically connected to the plurality of wiring conductors are formed over the lower surface of the insulating base on the outer side through the side surface, when the external electrodes are to be soldered to an external circuit board. In addition, since the solder forms a large meniscus from the lower surface of the convex portion to the lower surface of the insulating substrate outside through the side surface, a sufficient area can be secured for the external electrodes, and the wiring board and the external circuit board are This can reduce the shear strain on the connection terminals caused by the stress caused by the difference in thermal expansion of the wiring board, and is excellent in long-term reliability of mounting without occurrence of thermal fatigue failure.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, the present invention will be described in detail with reference to the accompanying drawings.
[0013]
FIG. 1 is a bottom view showing an example of an embodiment of a wiring board of the present invention. FIG. 2 is a sectional view showing an example of an embodiment of a wiring board of the present invention. In these figures, 1 is an insulating base formed by laminating a plurality of substantially square insulating layers, 2 is an external electrode, and 3 is a wiring conductor. A wiring board 4 is formed by the insulating base 1, the external electrodes 2 and the wiring conductors 3.
[0014]
The insulating substrate 1 has a mounting portion for a semiconductor element (not shown) on the upper surface, and includes, for example, an aluminum oxide sintered body, a mullite sintered body, a silicon carbide sintered body, an aluminum nitride sintered body, It is formed by vertically laminating a plurality of substantially square insulating layers made of electrically insulating ceramics such as a silicon nitride sintered body and a glass ceramic sintered body.
[0015]
When the insulating substrate 1 is made of, for example, an aluminum oxide sintered body, a sintering aid such as silicon oxide, magnesium oxide, or calcium oxide is added to aluminum oxide powder, and an appropriate organic binder, solvent, or the like is further added. To form a green sheet (green sheet) by employing a doctor blade method or a calender roll method, and then subjecting the green sheet to a suitable punching process to obtain a green sheet. It is manufactured by processing into a square shape, laminating a plurality of them, and firing at a temperature of about 1600 ° C.
[0016]
A plurality of external electrodes 2 are formed from the lower surface to the side surface of the insulating base 1, and wiring including a through conductor such as a via-hole conductor or a through-hole conductor extends from the upper surface on which the semiconductor element is mounted to the external electrode 2 on the side surface. A conductor 3 is formed.
[0017]
In the wiring board 4 of the present invention, the interval between two opposing sides of the insulating layer is directly above the lower surface of the insulating base 1 having the plurality of substantially rectangular insulating layers stacked and having the plurality of wiring conductors 3 therein. Protrusions are provided by making the protrusions smaller than the insulating layer, and a plurality of wiring conductors 3 are formed on two opposing sides of the protrusions from the lower surface of the protrusion to the lower surface of the insulating base 1 outside through the side surface. It is important to form a plurality of external electrodes 2 electrically connected to each other.
[0018]
In this way, the convex portion is provided by making the interval between the two opposing sides of the insulating layer smaller than that of the insulating layer immediately above, and the lower surface of the convex portion of the opposing two sides of the convex portion is interposed through the side surface. By forming a plurality of external electrodes 2 electrically connected to the plurality of wiring conductors 3 over the lower surface of the outer insulating base 1, the external electrodes 2 can be soldered to an external circuit board. The solder as a connection terminal (not shown) is applied to the external electrode 2 formed from the lower surface of the convex portion on the two opposite sides of the convex portion to the lower surface of the insulating base 1 outside through the side surface. Since a sufficiently large area can be secured for the external electrode 2 so that a large meniscus can be formed, the connection terminal generated by the stress caused by the difference in thermal expansion between the wiring board 4 and the external circuit board is obtained. To The shear strain that it is possible to reduce sufficiently, a wiring board 4 having excellent long-term reliability of the occurrence of thermal fatigue fracture is not implemented.
[0019]
These external electrodes 2 and wiring conductors 3 function as conductive paths that conduct the electrodes of the semiconductor element to an external electric circuit.
[0020]
The semiconductor element mounted on the mounting portion of the insulating base 1 is connected to a portion of the wiring conductor 3 exposed through the mounting portion of the wiring conductor 3 via solder, bonding wire, or the like, and connects the external electrode 2 to a connection terminal described later. The semiconductor element and the external electric circuit are electrically connected to each other through the wiring conductor 3, the external electrode 2, and the connection terminal.
[0021]
The external electrode 2 and the wiring conductor 3 are formed of a metallized conductor layer such as a high melting point metal such as tungsten, molybdenum, and manganese, and a low resistance metal such as copper, silver, and aluminum. If simultaneous firing of the external electrodes 2 and the wiring conductors 3 and the insulating base 1 is to be performed, a metal material having a matching firing temperature is appropriately selected according to the ceramic material to be used. A metal paste obtained by adding and mixing an organic binder, a plasticizer, and a solvent is formed into a through-hole in the green sheet before firing the green sheet as the insulating substrate 1 and the metal paste is filled in the through-hole. The green sheet is printed and applied in a predetermined pattern by a screen printing method or the like, and is baked at the same time as the insulating substrate 1, so that the green sheet is adhered to a predetermined position of the insulating substrate 1.
[0022]
Among such external electrodes 2, those that are to be attached to the side surfaces of the projections are formed in advance with groove-shaped portions having a substantially semicircular cross section in the vertical direction on the side surfaces of the projections. It is preferable to form the groove on the side wall surface. When the groove-like portion is formed on the side surface of the convex portion and the external electrode 2 is formed on the side wall surface, the solder enters into the groove-like portion and is joined at a large joint surface. Can be further strengthened.
[0023]
As such an external electrode 2, for example, a semicircular groove having a cross-sectional diameter of 0.3 mm to 0.7 mm is provided on the side surface of the convex portion on the lower surface of the insulating base 1. The external electrode 2 is adhered to the entire inner wall surface of the portion, and a rectangular shape, for example, 0.3 mm to 1 mm in side length is formed on the lower surface of the insulating base through the lower surface of the convex portion and the side surface of the convex portion. What is formed by attaching the external electrode 2 in a rectangular or square shape of a degree can be suitably used in miniaturizing the wiring board 4 and securing sufficient connection strength to the external circuit board.
[0024]
Further, the external electrodes 2 are usually formed with a constant width and an adjacent interval from the lower surface of the projection to the side surface and the lower surface of the insulating base 1 outside the side surface. For example, the length of one side of the convex portion is divided into ten equal parts, and in each of the equal parts, the external electrode 2 having a width of about 1/20 of the length of one side of the convex portion is substantially adjacent to each other. It is formed to be the same.
[0025]
Further, in the case where the external electrodes 2 are formed in the above-described size, for example, if the interval between the adjacent external electrodes 2 is set to 0.5 mm or more, the protrusion of the lower surface of the insulating base 1 may be reduced. It is possible to form a large number of external electrodes 2 at high density without increasing the outer dimensions of the insulating base 1 without reducing the mechanical strength at the outer edge, and at the same time, Good connection reliability to the external circuit board can be ensured.
[0026]
In this case, among the green sheets serving as the respective insulating layers forming the insulating base 1, the green sheet forming the lower surface of the insulating base 1 needs to have a smaller interval between two sides facing each other than the insulating layer immediately above the green sheet. is there. As a result, the two sides facing each other between the green sheet forming the lower surface and the green sheet immediately above it become stepped, and the green sheet forming the lower surface becomes a projection on the lower surface of the insulating base 1. In this case, the projections are not limited to those formed of a single layer of green sheets, and may be formed by laminating a plurality of green sheets having substantially the same dimensions.
[0027]
Further, the length of one side orthogonal to the two opposing sides of the convex portion on the lower surface of the insulating base 1 with respect to the insulating layer located immediately above is reduced to a range of about 80 to 95%. (To be shorter by a length of 0.1 mm to 1.5 mm).
[0028]
The length of one side on the side orthogonal to the two opposite sides (the distance between the two opposite sides) is the length of one side on the same side of the insulating layer located immediately above (between the two opposite sides on the same side). Is less than 95%), it is difficult to increase the area of the external electrode 2 provided on the lower surface of the insulating base 1 outside the side surface of the convex portion, so that the connection reliability of the external electrode 2 is effectively improved. Tend to be difficult to improve.
[0029]
Further, it is preferable that the height of the convex portion on the lower surface of the insulating base 1 be one third to two thirds of the thickness of the insulating base 1.
[0030]
When the height of the protrusion is less than one third of the thickness of the insulating base 1, the bonding surface between the connection terminal and the external electrode 2 formed on the side wall surface of the protrusion is effectively increased to increase the bonding strength. However, if it exceeds two-thirds, the volume of the external electrode 2 formed on the side wall surface of the projection becomes too large, and the amount of solder forming the connection terminal becomes large. Is insufficient, it becomes difficult to form a good meniscus, and there is a tendency that sufficient connection strength cannot be obtained.
[0031]
The external electrode 2 is connected to the external circuit board using solder such as Sn-Pb or Sn-Pb-Bi. The external electrode 2 of the wiring board 4 is connected to the external circuit by using the solder as a connection terminal. Connected to the wiring layer of the substrate.
[0032]
In this case, the external electrode 2 and the wiring conductor 3 have a plating layer made of a metal having good corrosion resistance such as nickel and gold on the exposed surfaces, and excellent in the connectivity of connection terminals formed of solder balls and the like and the bonding property of bonding wires. Is attached, the oxidative corrosion of the external electrode 2 and the wiring conductor 3 can be effectively prevented, and the reliability of connection of the connection terminal to the external electrode 2 and the solder or bonding wire to the wiring conductor 3 Can be further improved, and the reliability of the wiring board 4 can be further improved.
[0033]
Therefore, the external electrode 2 and the wiring conductor 3 are formed by depositing a plating layer of nickel, gold, or the like on the exposed surface in the order of, for example, a nickel layer having a thickness of 2 μm to 10 μm / a gold layer having a thickness of 0.05 to 2 μm. It is preferable to keep it.
[0034]
The external circuit board usually has a larger coefficient of thermal expansion than the insulating substrate 1 of the wiring board 4 and, for example, includes an organic resin such as an epoxy resin or a mixture of an organic resin and an inorganic filler such as glass fiber. The wiring layer is made of a composite material, and the wiring layer is formed of a foil or a plating layer of a metal material such as copper, silver, or aluminum.
[0035]
The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.
[0036]
For example, in the example of the above-described embodiment, the side surface of the convex portion on the lower surface of the insulating base 1 is a single vertical surface. May be further increased by making the shape of the external electrode 2 stepwise along the shape of the convex portion on the lower surface of the insulating base 1.
[0037]
【The invention's effect】
According to the wiring board of the present invention, the interval between the two opposing sides of the insulating layer is made smaller than that of the insulating layer immediately above, so that the convex portion is provided. When a plurality of external electrodes electrically connected to the plurality of wiring conductors are formed over the lower surface of the insulating base on the outer side through the side surface, when the external electrodes are to be soldered to an external circuit board. In addition, since the connection terminal made of solder forms a meniscus from the lower surface of the convex portion of the two opposite sides of the convex portion to the lower surface of the outer insulating base via the side surface, the area of the external electrode is sufficiently large. And can reduce the shear strain on the connection terminals caused by the stress caused by the difference in thermal expansion between the wiring board and the external circuit board. A wiring board which is excellent in the period reliability.
[Brief description of the drawings]
FIG. 1 is a bottom view showing an example of an embodiment of a wiring board of the present invention.
FIG. 2 is a cross-sectional view illustrating an example of an embodiment of a wiring board according to the present invention.
[Explanation of symbols]
1 ... insulating base 2 ... external electrode 3 ... wiring conductor 4 ... wiring board

Claims (1)

A convex portion is formed on the lower surface of an insulating base having a plurality of substantially rectangular insulating layers laminated thereon and having a plurality of wiring conductors therein by making a distance between two opposite sides of the insulating layer smaller than that of the insulating layer immediately above. And a plurality of the plurality of wiring conductors electrically connected to the plurality of wiring conductors, respectively, from a lower surface of the convex portion of the two opposite sides of the convex portion to a lower surface of the insulating base outside the side surface via a side surface. A wiring board having external electrodes formed thereon.

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