JP2001298272A - Printed board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem of a conventional printed board where the exchange of electronic parts is remarkably difficult and that it takes much facility cost for reinforcing resin in a device where a gap between a printed board and a flip chip is filled with reinforcing resin for reducing stress to a solder bump by the thermal expansion coefficient difference of the printed board and the flip chip. SOLUTION: In the printed board, parts connection electrodes 6 connected with electronic parts by solder bumps are formed on a build-up layer 2 where an inner layer conductor pattern 3 is formed. The printed board is provided with a stress relief layer 4 for relieving stress which is formed on the build-up layer 2, and fine conductor poles 5 which are pulled out from the inner layer conductor pattern 3 through the stress relief layer 4 and are connected to the parts connection electrodes 6. When a temperature rises in a state where the electronic parts of the flip chip and the like are connected to the parts connection electrodes 6 by the solder bumps, the fine conductor poles 5 are deformed with the stress relief layer 4, and the expansion difference of the printed board and the electronic parts by the difference of the thermal expansion coefficients of the printed board and the electronic parts is absorbed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed circuit board, and more particularly to a printed circuit board on which fine electronic components such as flip chips are mounted.

[0002]

2. Description of the Related Art In recent years, large-scale semiconductor integrated circuits (LSIs)
The miniaturization of pads has rapidly progressed, and higher-density flip-chip mounting has become widespread. However, when performing flip-chip mounting, in which the semiconductor chip is not directly included in the package but directly on the board, the pads on the printed board and the flip-chip are directly connected by solder bumps. Although the stress due to the generated strain is directly applied to the solder bumps, the distance between the solder bumps has become smaller and the amount of solder to be connected has been reduced, so that the above stress cannot be withstood and the life of the connection is not reduced. Is becoming more difficult.

For example, as shown in FIG. 5A, a component connection electrode 6 of a printed circuit board provided with a build-up layer 2 in which an inner conductor pattern 3 is formed on a core layer 1 is provided.
When the temperature rise occurs while the flip chip 10 is connected with the solder bumps 6, the thermal expansion coefficient of the printed circuit board (about 16 to 20 ppm / ° C.) is reduced to the thermal expansion coefficient of the flip chip 10 (about 3.5 ppm / ° C.). Since the printed circuit board is larger than the flip chip 10, the printed circuit board expands.

The expansion difference at that time is as follows: the thermal expansion coefficient of the printed circuit board is 18 ppm / ° C .; the thermal expansion coefficient of the flip chip 10 is 3.5 ppm / ° C .;
When the temperature is set to 0 ° C., the thickness is about 10 μm in a range of 10 mm □. This difference in thermal expansion coefficient causes the solder bump 9 connecting the printed circuit board and the flip chip 10 to be distorted as shown in FIG. 5 (b), stress is generated, and heat generation and cooling are repeated. Trigger the destruction of.

Therefore, conventionally, in order to reduce the stress on the solder bump due to the difference in the thermal expansion coefficient, the gap between the printed board and the flip chip is filled with a reinforcing resin, and the gap between the solder bump and the printed board and the flip chip is filled with the resin. It is hardened and reinforced. The filling of the reinforcing resin reduces the stress on the soldered portion and increases the connection life.

[0006]

However, in the above-mentioned conventional printed circuit board, a defect of the flip chip is detected in a function test or the like after filling the reinforcing resin, and the flip chip and the reinforcing resin are removed and the flip chip is replaced. In this case, it is extremely difficult to remove the adhered flip chip from the resin, clean the resin remaining on the printed circuit board side, and reproduce the flip chip again. In addition, since it is necessary to purchase a resin and purchase a filling facility and a resin curing facility for filling the reinforcing resin, there is a problem that the cost increases.

[0007] The present invention has been made in view of the above points,
The stress relief layer and the fine conductor pillar absorb the expansion difference caused by the difference in thermal expansion coefficient, and reduce the stress generated in the solder bumps, so the connection life of the printed circuit board and flip chip is reduced without filling with reinforcing resin It is an object of the present invention to provide a printed circuit board capable of preventing the occurrence of a printed circuit board.

Another object of the present invention is to facilitate the regeneration of a printed circuit board even when replacing parts, which was an adverse effect at the time of filling the reinforcing resin. Further, in terms of cost, the resin and equipment for filling the reinforcing resin are required. An object of the present invention is to provide a printed circuit board having a stress relaxation structure that can make purchase unnecessary.

[0009]

According to the present invention, in order to achieve the above object, a component connection electrode connected to an electronic component by a solder bump is formed on a build-up layer on which an inner conductor pattern is formed. In a printed circuit board, a stress relaxation layer formed on the build-up layer for stress relaxation and an inner conductor pattern formed on the build-up layer are drawn through the stress relaxation layer and connected to the component connection electrodes. This is a configuration having fine conductor columns.

According to the present invention, when an electronic component such as a flip chip is connected to a component connecting electrode by a solder bump, when the temperature rises, the fine conductor pillars are deformed together with the stress relieving layer, and the printed circuit board and the electronic component are connected. The difference in expansion between the printed circuit board and the electronic component due to the difference in thermal expansion coefficient can be absorbed.

Here, the stress relaxation layer is smaller than the Young's modulus of the eutectic solder, has heat resistance at the time of soldering the electronic component to the component connection electrode, has solvent resistance, and has insulating properties. It is characterized by being constituted by a heat-resistant low-elastic insulator.

Further, the stress relaxation layer is formed to have a predetermined film thickness that follows a difference in expansion between the printed circuit board and the electronic component caused by a difference in thermal expansion coefficient.

In the present invention, the fine conductor pillar is formed to have a length 5 to 10% longer than the thickness of the stress relaxation layer due to a difference in thermal expansion coefficient between the printed circuit board and the electronic component. When relaxing the stress on the solder bump
It is preferable because disconnection of the fine conductive column can be prevented. In addition, it is preferable that the above-mentioned fine conductor pillar in the present invention is formed in a curved or coiled shape in the stress relaxation layer in order to prevent disconnection of the fine conductor pillar.

[0014]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of a printed circuit board according to an embodiment of the present invention. As shown in the figure,
The printed board includes a core layer 1, a build-up layer 2, an inner conductor pattern 3, a stress relaxation layer 4, fine conductor pillars 5, and component connection electrodes 6.

The core layer 1 includes an inner conductor pattern formed of a heat-resistant glass epoxy substrate as a build-up substrate. The core layer 1 preferably has a thickness of 1.4 mm or more in order to reduce the amount of warpage of the printed circuit board when mounting electronic components. The build-up layer 2 is a layer formed by a build-up method of sequentially building using a photolithography technique. The build-up layer 2 is made of an epoxy resin or the like, which is an insulating material, and is formed by repeatedly applying the resin and the inner conductor pattern 3.

The inner conductor pattern 3 is composed of the build-up layer 2
And is formed by a subtractive or additive method or the like, and is usually made of copper. The stress relaxation layer 4 is made of a heat-resistant and low-elastic insulator such as silicone rubber, and has a Young's modulus of eutectic solder (3.06 ×
10 ¹⁰ Pa), having a heat resistance of 250 ° C. or more to prevent deterioration due to reflow heating during soldering of electronic components, and an insulating property (10 ¹²
Ω · m or more). As for the layer thickness of the stress relaxation layer 4, if the layer thickness is small, the fine conductor pillars 5 for stress relaxation also become short, and the ability to follow the difference in thermal expansion between the printed circuit board and the electronic component is inferior. preferable.

The fine conductor pillar 5 is a conductor pillar for relaxing stress drawn from the inner conductor pattern 3 formed on the build-up layer 2, and is made of copper, for example, and has a diameter of 30 μmφ or less for obtaining flexibility. The height is desirably 100 μm or more. In addition, the length of the fine conductor pillar 5 is extended in an oblique direction when the stress generated due to the difference in thermal expansion coefficient between the printed circuit board and the electronic component is relaxed. It is preferably 5 to 10% longer, and more preferably, it is curved or coiled in the stress relaxation layer 4.

The component connection electrode 6 is an electrode for connecting an electronic component such as a flip chip or the like. The component connection electrode 6 is formed of copper as a material on the conductor pillar 5 and may be plated with nickel and thin gold to prevent oxidation. is there.

Next, the method of assembling (manufacturing) the printed circuit board of the present invention will be described with reference to the sectional views of FIGS. In the figure, the same components as those in FIG. 1 are denoted by the same reference numerals. First, as shown in FIG. 2A, a build-up layer 2 made of epoxy or the like is formed on a core layer 1 made of a heat-resistant glass epoxy substrate or the like including an inner layer conductor pattern by a build-up method. Then, the inner conductor pattern 3 is formed on the build-up layer 2 by a subtractive or additive method.

Subsequently, as shown in FIG. 2B, a stress relaxation layer 4 made of a heat-resistant and low-elastic insulator such as silicone rubber is formed on the build-up layer 2 on which the inner conductor pattern 3 is formed. I do. That is, after forming a heat-resistant and low-elastic insulator on the build-up layer 2 by a method of applying a liquid resin coating or a semi-cured resin on a dry film by pressure bonding, it is cured by heating, ultraviolet rays, infrared rays, or the like. The stress relaxation layer 4 is formed.

Next, as shown in FIG. 2 (c), an opening having the same diameter or a photomask 7 which has been colored is placed on the stress relaxing layer 4 at a portion where the fine conductor pillar 5 is to be formed. Then, as shown in FIG. 3D, the fine conductor pillar generation hole 8 is penetrated to the inner conductor pattern 3 connected to the fine conductor pillar 5 by a laser, an etching method or the like. Thereafter, as shown in FIG. 2E, the photomask 7 is removed to form the fine conductor pillar generation holes 8.

Subsequently, as shown in FIG. 2 (f), the fine conductor columns 5 are formed in the fine conductor column generation holes 8 formed in the stress relaxation layer 4 by an additive method or the like. Thereafter, as shown in FIG. 2G, a component connection electrode 6 for connecting an electronic component such as a flip chip to the fine conductor pillar 5 is formed by a subtractive or additive method. In order to prevent oxidation of the component connection electrode 6, the component connection electrode 6 may be plated with nickel and thin gold. In this way, a printed board having the stress relaxation structure shown in the cross-sectional view of FIG. 1 is produced.

Next, the operation when a flip chip is mounted on the printed circuit board of the present embodiment will be described. FIG. 3 is a cross-sectional view showing an example of a case where a flip chip is mounted on the printed circuit board of the present embodiment shown in FIG. In the figure, the same components as those in FIGS. 1 and 2 are denoted by the same reference numerals. In FIG. 3, the component connection electrode 6 and the flip chip 10 are connected by solder bumps 9.

When the solder bumps 9 connected to the flip chip 10 and the component connection electrode 6 are both eutectic solder, the flip chip 10 side is a high melting point solder having a high lead content and the component connection electrode 6 side is eutectic. In the case of solder, when the flip chip 10 side and the component connection electrode 6 side are both gold,
There are various types.

According to the printed circuit board of this embodiment, as shown in FIG.
FIG. 4 shows a case where a temperature rise occurs while
As shown in (a), the thermal expansion coefficient of the printed circuit board (about 1
6 to 20 ppm / ° C.) is larger than the thermal expansion coefficient of the flip chip 10 (about 3.5 ppm / ° C.), so that the printed circuit board expands from the flip chip 10.

However, in this embodiment, as shown in FIG. 4B, the fine conductive pillars 5 in the low-elasticity stress relaxation layer 4 correspond to the expansion difference between the printed board and the flip chip 10, as shown in FIG. Since the solder bump 9 is deformed together with the stress relaxation layer 4 and absorbs the difference in expansion, the solder bump 9 is not distorted and no stress is applied. Therefore, in the present embodiment, when the flip chip 10 is mounted, destruction of the solder bumps 9 caused by repeated heat generation and cooling during product operation is not induced, and the connection life can be improved.

In this embodiment, the gap between the printed board and the flip chip is filled with a reinforcing resin, and the solder bump and the gap between the printed board and the flip chip are solidified with the resin and reinforced, as in a conventional printed board. Since no resin is used, if a failure of the flip chip is detected in a function test, etc., the flip chip can be easily replaced. Equipment purchases can be eliminated.

In the above embodiment, the flip chip 10 is mounted on the printed circuit board.
The present invention can be similarly applied to a case where other electronic components other than the flip chip 10 are mounted.

[0029]

As described above, according to the present invention,
When the temperature rises when electronic components such as flip chips are connected to component connection electrodes by solder bumps, the fine conductor pillars are deformed together with the stress relaxation layer and printing is performed due to the difference in thermal expansion coefficient between the printed circuit board and the electronic components. Since the difference in expansion between the substrate and the electronic component can be absorbed, it has the following features. (1) It is possible to greatly reduce the stress on the solder bump, which is generated when the heat generation and cooling are repeated during the operation of the product. (2) Since the stress on the solder bumps is reduced, the connection life can be improved as compared with the case where electronic components are mounted on a conventional printed circuit board. (3) Filling of the gap between the printed circuit board and the electronic component for the purpose of reducing the stress on the solder bumps with the filling of the reinforcing resin is not required, so that the purchase of the resin and equipment for filling the reinforcing resin is unnecessary, and the cost is low. It can be configured. (4) When a defect of an electronic component such as a flip chip is detected in a function test or the like as compared with a conventional printed circuit board in which a gap between the printed circuit board and the electronic component is filled with the reinforcing resin, the reinforcing resin is removed from the electronic component. The step and the step of removing the reinforcing resin remaining on the printed circuit board are not required at all, and the electronic components can be easily replaced.

[Brief description of the drawings]

FIG. 1 is a sectional view of an embodiment of the present invention.

FIG. 2 is a cross-sectional view of an element for explaining a manufacturing process according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view illustrating an example in which a flip chip is mounted on a printed circuit board according to an embodiment of the present invention.

FIG. 4 is an explanatory diagram when a temperature rise occurs in a state where a flip chip is mounted in one embodiment of the present invention;

FIG. 5 is an explanatory diagram when a temperature rise occurs in a state where a flip chip is mounted on a printed circuit board of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Core layer 2 Build-up layer 3 Inner layer conductor pattern 4 Stress relaxation layer 5 Fine conductor pillar 6 Component connection electrode 7 Photomask 8 Fine conductor pillar generation hole 9 Solder bump 10 Flip chip

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) H05K 1/11 H01L 23/12 FF Term (Reference) 5E317 AA24 BB02 BB12 CC25 CC31 CC51 CD32 CD34 GG09 GG11 5E338 AA03 AA16 BB25 BB63 BB72 CC01 EE01 EE28 5E346 AA06 AA12 AA15 AA25 AA35 AA38 AA43 BB01 BB16 CC08 CC32 CC37 CC38 DD02 DD03 EE31 FF01 FF35 FF45 GG40 HH07

Claims (6)

[Claims] 1. A printed circuit board having a component connection electrode connected to an electronic component by a solder bump formed on a build-up layer on which an inner conductor pattern is formed, wherein a stress formed on the build-up layer A stress relaxation layer for relaxation, and fine conductor pillars drawn out through the stress relaxation layer from the inner conductor pattern formed in the build-up layer and connected to the component connection electrode, Printed circuit board. 2. The stress relaxation layer is smaller than the Young's modulus of eutectic solder, has heat resistance when soldering the electronic component to the component connection electrode, has solvent resistance, and has insulating properties. 2. The printed circuit board according to claim 1, wherein the printed circuit board is made of a heat-resistant low-elastic insulator. 3. The stress relaxation layer according to claim 1, wherein the stress relaxation layer is formed to have a predetermined thickness to follow a difference in expansion between the printed circuit board and the electronic component caused by a difference in thermal expansion coefficient. Item 3. The printed circuit board according to item 1 or 2. 4. The printed circuit board according to claim 1, wherein the length of the fine conductor pillar is formed to be 5 to 10% longer than the thickness of the stress relaxation layer. 5. The printed circuit board according to claim 1, wherein the fine conductor pillar is formed in a curved or coiled shape in the stress relaxation layer. 6. The printed circuit board according to claim 1, wherein the stress relaxation layer is made of silicone rubber.