Chip mounting structure

Abstract

Highly reliable chip mounting is accomplished by using a substrate having such a shape that a stress exerted on a flip-chip-connected chip can be reduced, so that the stress exerted on the chip is reduced and separation of an interlayer insulating layer having a low dielectric constant (low-k) is minimized. Specifically, in a chip mounting structure, a chip including an interlayer insulating layer having a low dielectric constant (low-k) is flip-chip connected to a substrate via bumps is shown. In the chip mounting structure, the substrate has such a shape that a mechanical stress exerted on the interlayer insulating layer at corner portions of the chip due to a thermal stress is reduced, the thermal stress occurring due to a difference in coefficient of thermal expansion between the chip and the substrate.

Claims

1. A chip mounting structure, comprising: a chip including an interlayer insulating layer having a low dielectric constant; and a substrate to which the chip is flip-chip connected via a bump, the substrate having a shape of a square from which elongated cuts that extend a length e from corners of the square toward the corresponding corners of the chip are cut off, where the length e is expressed as the following expression:
e>({square root over (2)}1)B wherein the elongated cuts reduce a mechanical stress exerted on the interlayer insulating layer at a corner portion of the chip due to a thermal stress, the thermal stress occurring due to a difference in coefficient of thermal expansion between the chip and the substrate, wherein B denotes a distance from each of sides of the chip to a corresponding portion of the edge of the substrate.

2. The chip mounting structure according to claim 1, wherein the substrate has such a shape that satisfies A<B where A denotes a distance from each of corners of the chip to a corresponding position on an edge of the substrate, the corresponding position on the edge being on a line extending from a center of the chip, positioned at a same position as a center of the substrate, through the corner of the chip, the corresponding portion of the edge being parallel to the side of the chip.

3. A chip mounting structure, comprising: a substrate having a shape of a square except for square portions of the substrate that are cut off at corners of the substrate, each square portion having sides of a length c; a chip positioned at a center of the substrate, the chip being flip-chip connected to the substrate via a bump, the chip having a shape of a square, the chip including an interlayer insulating layer having a low dielectric constant; wherein the substrate has a shape that satisfies A<B where A denotes a distance from each corner of the chip to a nearest edge of the substrate and B denotes a distance from a midpoint of each side of the chip to a midpoint of a nearest side of the substrate, and wherein the length c is expressed as the following expression $\begin{array}{cc}c>\left(1-\frac{\sqrt{2}}{2}\right)B& \end{array}$ wherein the square portions that are cut off at corners of the substrate reduce a mechanical stress exerted on the interlayer insulating layer at corners of the chip due to a thermal stress, the thermal stress occurring due to a difference in coefficient of thermal expansion between the chip and the substrate.

4. A chip mounting structure, comprising: a substrate having a shape of a square except for right-angled isosceles triangle portions of the substrate that are cut off at corners of the substrate, each right-angled isosceles triangle having two sides of a length d; a chip positioned at a center of the substrate, the chip being flip-chip connected to the substrate via a bump, the chip having a shape of a square, the chip including an interlayer insulating layer having a low dielectric constant; wherein the substrate has a shape that satisfies A<B where A denotes a distance from each corner of the chip to a nearest edge of the substrate and B denotes a distance from a midpoint of each side of the chip to a midpoint of a nearest side of the substrate, and wherein the length d is expressed as the following expression:
d>(2{square root over (2)})B wherein the right-angled isosceles triangle portions that are cut off at corners of the substrate reduce a mechanical stress exerted on the interlayer insulating layer at corners of the chip due to a thermal stress, the thermal stress occurring due to a difference in coefficient of thermal expansion between the chip and the substrate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying figures wherein reference numerals refer to identical or functionally similar elements throughout the separate views, and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and to explain various principles and advantages all in accordance with the present invention, in which:

(2) FIG. 1 is a cross-sectional view that roughly illustrates the state where an interlayer insulating layer is separated from an adjacent layer.

(3) FIG. 2 is a perspective view schematically illustrating a first chip mounting structure subjected to structure analysis.

(4) FIG. 3 is a perspective view schematically illustrating a second chip mounting structure subjected to structure analysis.

(5) FIG. 4 is a perspective view schematically illustrating a third chip mounting structure subjected to structure analysis.

(6) FIG. 5 is a bar graph illustrating a normalized form of the stress that occurs at the corners of a chip in each of the first to third chip mounting structures subjected to structure analysis.

(7) FIG. 6(A) is a top plan view schematically illustrating a chip mounting structure according to a first embodiment of the present invention.

(8) FIG. 6(B) is a side view of the chip mounting structure according to the first embodiment.

(9) FIG. 7(A) is a top plan view schematically illustrating a chip mounting structure according to a second embodiment of the present invention.

(10) FIG. 7(B) is a side view of the chip mounting structure according to the second embodiment.

(11) FIG. 8(A) is a top plan view schematically illustrating a chip mounting structure according to a third embodiment of the present invention.

(12) FIG. 8(B) is a side view of the chip mounting structure according to the third embodiment.

(13) FIG. 9(A) is a top plan view schematically illustrating a chip mounting structure according to a fourth embodiment of the present invention.

(14) FIG. 9(B) is a side view of the chip mounting structure according to the fourth embodiment.

DETAILED DESCRIPTION

(15) As required, detailed embodiments are disclosed herein; however, it is to be understood that the disclosed embodiments are merely examples and that the systems and methods described below can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present subject matter in virtually any appropriately detailed structure and function. Further, the terms and phrases used herein are not intended to be limiting, but rather, to provide an understandable description of the concepts.

(16) The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.

(17) Best modes for embodying the present invention will be illustrated below in detail with reference to the drawings. However, the present invention within the scope of claims is not limited to the following embodiments. In addition, all the combinations of the characteristics described in the embodiments are not necessarily essential to solution to problems. The present invention may be embodied in various different modes and should not be understood as being limited to the contents described in the embodiments. Throughout the entire description of the embodiments, the same components are denoted by the same reference numerals.

(18) The inventors have studied the relationship between the shape of a substrate and a stress exerted on the chip by performing structure analysis of a chip mounting structure using, for example, a finite element method (FEM). The inventors have thus found that changing the shape of the substrate on the basis of the studied relationship reduces the stress exerted on the interlayer insulating layer through bumps at the corners of the chip.

(19) FIG. 2 is a perspective view schematically illustrating a first chip mounting structure 200 subjected to structure analysis. The chip mounting structure 200 has such a structure in which a chip 205 is mounted on an existing rectangular substrate 210. In a portion 215 in FIG. 2, an arrangement of bumps 220 at a corner portion of the chip 205 is schematically illustrated in an enlarged manner. In the chip mounting structure 200, a distance A from a corner of the chip 205 to the corresponding position on the edge of the substrate 210 is longer than a distance B from a side of the chip 205 to the corresponding side of the substrate 210 that is parallel to the side of the chip 205, that is, A>B.

(20) FIG. 3 is a perspective view schematically illustrating a second chip mounting structure 300 subjected to structure analysis. The chip mounting structure 300 has such a structure in which a chip 205 is mounted on a substrate 305 having such a shape that small rectangular corner portions are cut off. In the chip mounting structure 300, a distance A from a corner of the chip 205 to the corresponding position on the edge of the substrate 305 is equal to a distance B from a side of the chip 205 to the corresponding side of the substrate 305 that is parallel to the side of the chip 205, that is, A=B.

(21) FIG. 4 is a perspective view schematically illustrating a third chip mounting structure 400 subjected to structure analysis. The chip mounting structure 400 has such a structure in which a chip 205 is mounted on a substrate 405 having such a shape that large rectangular corner portions are cut off. In the chip mounting structure 400, a distance A from a corner of the chip 205 to the corresponding position on the edge of the substrate 405 is shorter than a distance B from a side of the chip 205 to the corresponding side of the substrate 405 that is parallel to the side of the chip 205, that is, A<B.

(22) FIG. 5 is a bar graph illustrating a normalized form of the stress that occurs at the corners of a chip in each of the first to third chip mounting structures 200, 300, and 400 subjected to structure analysis. The stress is normalized with reference to the stress that occurs in the first chip mounting structure 200 (where A>B). In the case of the second chip mounting structure 300 (where A=B), the stress is reduced, although to a small degree, compared to the existing rectangular structure where A>B as a result of cutting off small rectangular corner portions so that A=B. In the case of the third chip mounting structure 400 (where A<B), the stress is substantially reduced compared to the existing rectangular structure where A>B as a result of cutting off large rectangular corner portions so that A<B.

(23) On the basis of this finding, the inventor has developed the use of a substrate having a shape in which A<B and in which the mechanical stress exerted on the interlayer insulating layer at corner portions of the chip is reduced. Highly reliable chip mounting is accomplished by using a chip mounting structure in which a chip is mounted on a substrate having such a shape.

(24) FIG. 6 schematically illustrates a chip mounting structure 500 according to a first embodiment of the present invention. FIG. 6(A) is a top plan view of the chip mounting structure 500 and FIG. 6(B) is a side view of the chip mounting structure 500. In the chip mounting structure 500, a substrate 505 has a shape of a square from which squares 510 each having sides of a length c are cut off at corner portions of the square. In order that the substrate 505 has a shape that satisfies the condition A<B, the length c has to satisfy the following condition. Firstly, a distance A is calculated. A distance from a corner of the chip 205 to the corresponding corner of an original square of the substrate 505 from which the squares 510 are not cut off is expressed by the following expression:
{square root over (2)}BExpression 4

(25) The length of the diagonal of the squares 510 is expressed by the following expression:
{square root over (2)}cExpression 5

(26) Thus, the distance A is expressed by the following expression:
A={square root over (2)}B{square root over (2)}c={square root over (2)}(Bc)Expression 6

(27) Since A<B, the following expression is satisfied:
{square root over (2)}(Bc)<BExpression 7

(28) When this expression is changed by changing the subject to the length c, the length c is expressed by the following expression:

(29) $\begin{array}{cc}c>\left(1-\frac{\sqrt{2}}{2}\right)B& \mathrm{Expression}8\end{array}$

(30) In order that the substrate 505 has a shape that satisfies A<B, the length c has to satisfy the above expression. For example, when the chip 205 is a 20 mm square and the original square of the substrate 505 is a 50 mm square, the distance B is 50/220/2, that is, 15 mm. When the distance B is 15 mm, the length c has to be longer than 4.4 mm.

(31) FIG. 7 schematically illustrates a chip mounting structure 600 according to a second embodiment of the present invention. FIG. 7(A) is a top plan view of the chip mounting structure 600 and FIG. 7(B) is a side view of the chip mounting structure 600. In the chip mounting structure 600, a substrate 605 has a shape of a square from which right-angled isosceles triangles 610 each having two sides of a length d are cut off at corner portions of the square. In order that the substrate 605 has a shape that satisfies the condition A<B, the length d has to satisfy the following condition. Firstly, a distance A is calculated. A distance from a corner of the chip 205 to the corresponding corner of an original square of the substrate 605 from which the right-angled isosceles triangles 610 are not cut off is expressed by the following expression:
{square root over (2)}BExpression 9

(32) The length or the height from the base to the vertex of each right-angled isosceles triangle 610 is expressed by the following expression:

(33) $\begin{array}{cc}\sqrt{\frac{d^2}{2}}=\frac{d}{\sqrt{2}}& \mathrm{Expression}10\end{array}$

(34) Thus, the distance A is expressed by the following expression:

(35) $\begin{array}{cc}A=\sqrt{2}B-\frac{d}{\sqrt{2}}& \mathrm{Expression}11\end{array}$

(36) Since A<B, the following expression is satisfied:

(37) $\begin{array}{cc}\sqrt{2}B-\frac{d}{\sqrt{2}}<B& \mathrm{Expression}12\end{array}$

(38) When this expression is changed by changing the subject to the length d, the length d is expressed by the following expression:
d>(2{square root over (2)})BExpression 13

(39) In order that the substrate 605 has a shape that satisfies A<B, the length d has to satisfy the above expression. For example, when the chip 205 is a 20 mm square and the original square of the substrate 605 is a 50 mm square, the distance B is 50/220/2, that is, 15 mm. When the distance B is 15 mm, the length d has to be longer than 8.8 mm.

(40) FIG. 8 schematically illustrates a chip mounting structure 700 according to a third embodiment of the present invention. FIG. 8(A) is a top plan view of the chip mounting structure 700 and FIG. 8(B) is a side view of the chip mounting structure 700. In the chip mounting structure 700, a substrate 705 has a shape of a square from which cuts 610 that extend a length e from the corresponding corners of the square toward the corners of the chip 205 are cut off. In order that the substrate 705 has a shape that satisfies the condition A<B, the length e has to satisfy the following condition. Firstly, a distance A is calculated. A distance from a corner of the chip 205 to the corresponding corner of an original square of the substrate 705 from which the cuts are not cut off is expressed by the following expression:
{square root over (2)}BExpression 14

(41) Since the cuts having a length e are cut off at corner portions of the original square, the distance A is expressed by the following expression:
A={square root over (2)}BeExpression 15

(42) Since A<B, the following expression is satisfied:
{square root over (2)}Be<BExpression 16

(43) When this expression is changed by changing the subject to the length e, the length e is expressed by the following expression:
e>({square root over (2)}1)BExpression 17

(44) In order that the substrate 705 has a shape that satisfies A<B, the length e has to satisfy the above expression. For example, when the chip 205 is a 20 mm square and the original square of the substrate 705 is a 50 mm square, the distance B is 50/220/2, that is, 15 mm. When the distance B is 15 mm, the length e has to be longer than 6.2 mm.

(45) FIG. 9 schematically illustrates a chip mounting structure 800 according to a fourth embodiment of the present invention. FIG. 9(A) is a top plan view of the chip mounting structure 800 and FIG. 9(B) is a side view of the chip mounting structure 800. In the chip mounting structure 800, a substrate 805 has a circular shape that has a center at the same position as the center of the chip 205 and that has a radius longer than a distance from the center of the chip 205 to each corner of the chip 205. When the substrate 805 has such a circular shape, the distance A is calculated by subtracting half the diagonal of the chip 205 from the radius and the distance B is calculated by subtracting half the length of one side of the chip 205 from the radius. Since the diagonal of the chip 205 is longer than the length of one side of the chip 205, the substrate 805 has a shape that satisfies A<B. For example, when the chip 205 is a 20 mm square and the substrate 805 is a circle having a diameter of 50 mm, the distance A is calculated as 10.9 mm by subtracting half the diagonal of the chip 205, which is 14.1 mm, from the radius of 25 mm and the distance B is calculated as 15 mm by subtracting half the length of one side of the chip 205, which is 10 mm, from the radius of 25 mm. Thus, the substrate 805 has a shape that satisfies A<B.

Non-Limiting Examples

(46) Although the present invention has been described thus far using some embodiments, the technical scope of the invention is not limited to the scope described in relation to these embodiments. The embodiments may be modified or improved in various manners and modes to which such modification or improvement has been made are also naturally included in the technical scope of the invention.

(47) The description of the present application has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.