JP3360603B2 - Electronic component mounting structure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mounting structure of an electronic component for electrically connecting the electronic component and a mounting board by solder bumps arranged in an array on the back surface of the electronic component, and is particularly used for automobiles. It is suitable to be applied to a mounting structure of a ball grid array semiconductor device (hereinafter, referred to as a BGA package).

[0002]

2. Description of the Related Art FIG. 3 is a schematic cross-sectional view when a BGA package 100 is mounted on a printed wiring board 102.
As shown in this figure, the BGA package 100 is mounted on a printed wiring board 102 via solder bumps 104 arranged in an array on the back surface.

When the mounting structure of the BGA package 100 is used in an automobile or the like, it is necessary to ensure the moisture resistance of the BGA package 100 due to environmental conditions. For this reason,
The connection part by the BGA package 100 and the solder bump 104 is made of a drip-proof material 10 made of a thermoplastic acrylic resin.
6 is used for sealing.

[0004]

However, when a general temperature cycle test (for example, reciprocation of -30 ° C. to 80 ° C.) was performed, the drip-proof material was found to have a compressive stress as shown by an arrow in FIG. This force causes the solder bumps 104 to be gradually crushed, resulting in a problem that the thermal fatigue life is shortened.

The present invention has been made in view of the above problems, and in a mounting structure of an electronic component in which moisture resistance is secured by a drip-proof material, the influence of stress generated by the drip-proof material can be reduced, and the thermal fatigue life can be improved. An object is to provide a mounting structure for electronic components.

[0006]

Means for Solving the Problems In order to solve the above problems, the present inventors have made the following studies. First, FIG. 4 shows the temperature characteristics of the elastic modulus and linear expansion coefficient of a thermoplastic acrylic resin conventionally used for the drip-proof material 106. As shown in this figure, a conventionally used thermoplastic acrylic resin has high elasticity and low linear expansion coefficient characteristics at a low temperature side (for example, -30 ° C.) in a temperature cycle test, and has a high temperature side. (For example, at 80 ° C.), it has characteristics of low elasticity and high linear expansion coefficient. For this reason, as described above, the drip-proof material 106 generates a compressive stress at the low temperature side of the temperature cycle test, and the solder bump 104 is gradually crushed. Specifically, a conventionally used thermoplastic acrylic resin has a linear expansion coefficient of 80 ppm at −30 ° C.
The elastic modulus at 210 ° C. was 210 MPa.

When the relationship between the height of the solder bumps 104 and the thermal fatigue life due to the temperature cycle was calculated by FEM, the calculation result showed that the lower the height of the solder bumps 104, the lower the thermal fatigue life. It can be said that the thermal fatigue life is shortened due to the collapse of the solder bump 104 due to the compressive stress of the material 106. For reference, drip-proof material 10
Failure rate (contact failure occurrence rate) when temperature cycle test is performed when 6 is not applied and when 6 is applied
Is shown in FIG. As is clear from this figure, the failure rate was higher when the protective material 106 was applied than when the protective material 106 was not applied, and the compressive stress of the protective material 106 affected the thermal fatigue life. It can be said that.

Next, the coefficient of linear expansion of the protective material 106 (ppm
/ ° C) and the modulus of elasticity (MPa) were subjected to a temperature cycle test, and FEM analysis was performed to determine whether the solder bumps 104 were crushed. The results shown in FIG. 6 were obtained. Specifically, the coefficient of linear expansion is 26, 56, 86, 26
With the drip-proof material 106 being set to 0, an analysis was performed when the elastic modulus was changed. In the drawing, the solder bump 104
The area in which the solder bump 10
The area where No. 4 was not crushed is defined as a solder uncrushed area.
Further, an epoxy resin, a urethane resin, or the like is used for the drip-proof material 106, and a linear expansion coefficient is changed by mixing a filler or another resin into the drip-proof material 106.

The relationship between the coefficient of linear expansion and the modulus of elasticity in the solder uncrushed region shown in FIG.
And the linear expansion coefficient of the drip-proof material 106 is 26 pp
When m / ° C, the elastic modulus is 1 MPa or more, and when the linear expansion coefficient is 26 to 56 ppm / ° C, the elastic modulus is 1 to 400 M.
Pa, when the linear expansion coefficient is 56 to 86 ppm / ° C., the elastic modulus is 1 to 50 MPa, and the linear expansion coefficient is 86 to 260 pp.
In the case of m / ° C., when the elastic modulus was 1 to 3 MPa, the result that the solder bump was not crushed was obtained.

In the above analysis results, the solder distortion (%) indicates the rate at which the solder bumps 104 are crushed, and the smaller the solder distortion, the less the solder bumps 104 are crushed. Based on this, the elastic modulus at which solder crushing is least likely to occur for each coefficient of linear expansion is found and summarized as shown in FIG. 7 (b). Rate is 3400MPa or more, linear expansion coefficient is 56ppm /
° C, the elastic modulus is about 50 MPa and the linear expansion coefficient is 8
It was found that the elastic modulus was about 7 MPa at 6 ppm / ° C. and about 2 MPa when the linear expansion coefficient was 260 ppm / ° C. The drip-proof material has a linear expansion coefficient of 2
How to make elastic modulus over 3400MPa at 6ppm / ℃
Possible by mixing fillers in epoxy resin.
You. When the linear expansion coefficient of the drip-proof material is 260 ppm / ° C,
In order to obtain a modulus of 2 MPa, a filler is mixed with the urethane resin.
It is possible by entering.

Therefore, the present invention employs the following technical means to achieve the above object. According to the first aspect of the present invention, the drip-proof material (10) has a linear expansion coefficient of 56 p.
It is characterized by being composed of a resin having an elastic modulus of 50 MPa at pm / ° C. In the invention according to claim 2 , the drip-proof material (10) has a coefficient of linear expansion of 56.
It is characterized by being made of a resin having an elastic modulus of 1 to 50 MPa at a pressure of 86 to 86 ppm / ° C. This
In this case, the coefficient of linear expansion is 86 ppm
/ ° C., the elastic modulus is most preferably 7 MPa. Furthermore, in the invention described in claim 4 , the drip-proof material (1
No. 0) is characterized by being composed of a resin having a linear expansion coefficient of 86 to 260 ppm / ° C. and an elastic modulus of 1 to 3 MPa. In this case, as shown in claim 5
When the coefficient of linear expansion is 260 ppm / ° C, the elastic modulus is 2
MPa is most preferred.

Thus, the influence of the compressive stress of the drip-proof material (10) can be suppressed, and the solder bumps (8) can be hardly crushed .

[0013] The Contact, reference numerals in parentheses of each means described above is intended to show the relationship of the specific means described embodiments to be described later.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a BG in which electrodes 2 provided on the back surface of a BGA package 1 and electrodes 4 provided on the front surface of a printed wiring board 3 are connected via solder bumps 8.
1 shows a mounting structure of an A package 1. The mounting structure of the BGA package 1 is mainly used for automobiles that require moisture resistance. FIG. 2 is a schematic view of the mounting structure of the BGA package 1 shown in FIG. In FIG. 2, the portion shown by the dotted line is the BGA
The solder bump 8 joins the package 1 and the electrode 2 to the electrode 4. Hereinafter, the mounting structure of the BGA package 1 will be described with reference to FIGS.

[0015] As shown in FIG.
A semiconductor chip 6 is mounted on an interposer 5 having circuit wiring via an adhesive or the like, and the circuit wiring and the semiconductor chip 6 are electrically connected to each other with an Au wire or the like. The Au wire is sealed. The interposer 5 corresponding to the back surface of the BGA package 1 has holes formed in an array in the same manner as the arrangement pattern of the electrodes 2 shown in FIG. The package 1 is exposed from the back side. The solder balls are melt-bonded to the electrodes 2 through the holes provided in the interposer 5, so that the solder bumps 8 are arranged in an array on the back surface of the BGA package 1.

On one side of the printed wiring board 3, a BGA
There is provided an electrode 4 formed in the same arrangement pattern as the electrode 2 provided on the back surface of the package 1. The arrangement pattern of the electrodes 4 is an array pattern corresponding to the arrangement of the solder bumps 8. At the time of mounting, the solder bumps 8 provided on the BGA package 1 and the electrodes 4 provided on the printed wiring board 3 are combined with each other.

The BGA package 1 is mounted on the printed wiring board 3 such that the solder bumps 8 are opposed to the electrodes 4. Then, the BGA package 1 and the printed wiring board 3 are electrically connected by melting the solder bumps 8. Further, the BGA package 1 bonded by the solder bumps 8 is coated with a drip-proof material 10 by a dipping or the like to form a BGA package.
A joint portion between the package 1 and the solder bump 8 is sealed. As the drip-proof material 10, a material obtained by mixing a filler with an epoxy resin and having a coefficient of linear expansion of 26 ppm / ° C. and an elastic modulus of 3400 MPa or more is employed.

With the above mounting structure, the BGA package 1 is mounted on the printed wiring board 3. At this time,
In the mounting structure of the BGA package 1 in the present embodiment, the drip-proof material 10 has a linear expansion coefficient of 26 ppm / ° C.
Is applied, the solder bump 8 is not crushed even when a temperature cycle test is performed.

That is, in the temperature cycle test,
Since the linear expansion coefficient and the elastic modulus that can suppress the compressive stress applied to the solder bump 8 by the drip-proof material 10 are selected, it is possible to prevent the solder bump 8 from being crushed by the influence of the compressive stress applied by the drip-proof material 10. it can. For this reason, when it is necessary to ensure the moisture resistance of the joint between the BGA package 1 and the solder bumps 8 as in an automobile or the like, even if the drip-proof material 10 for securing the moisture resistance is used, Contact failure between the BGA package 1 and the printed wiring board 3 can be prevented.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing a mounting structure of a BGA package 1 according to an embodiment to which the present invention is applied.

FIG. 2 is a top view of the BGA package 1 in FIG.

FIG. 3 is a schematic diagram showing a mounting structure of a conventional BGA package 100 and a compressive stress generated by a drip-proof material 106.

FIG. 4 is a diagram showing changes in elastic modulus and coefficient of linear expansion with respect to temperature.

FIG. 5 is a comparison diagram showing a difference in temperature cycle life between a case where a drip-proof material 106 is applied and a case where no drip-proof material 106 is applied.

FIG. 6 is a diagram illustrating whether or not the solder bump 104 is crushed when the coefficient of linear expansion and the elastic modulus are changed.

FIG. 7A is a diagram showing a relationship between a linear expansion coefficient and an elastic modulus in which the solder bump 108 is hard to be crushed, and FIG. 7B is a diagram showing the solder bump 108 which is hardest to be crushed among the linear expansion coefficients used in the analysis. It is a figure showing an elastic modulus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... BGA package, 2 ... electrode, 3 ... printed wiring board, 4 ... electrode, 5 ... interposer, 6 ... semiconductor chip, 7 ... sealing resin, 8 ... solder bump, 10 ... drip-proof material.

Continuation of the front page (56) References JP-A-60-63951 (JP, A) JP-A-5-206326 (JP, A) JP-A-7-66326 (JP, A) JP-A-7-94640 (JP) JP-A-8-55867 (JP, A) JP-A-8-55938 (JP, A) JP-A-9-17914 (JP, A) JP-A-10-30050 (JP, A) 9-315057 (JP, A) JP-A-9-315059 (JP, A) Fukuji Kurihara, Fujio Oishi, Utilization Guide Polymer Materials, Japan, Ohm Co., Ltd., January 20, 1980, 1st edition, 10th edition Reprint, pp. 201, 205 (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 23/29 H01L 21/60 311 H01L 23/31

Claims (6)

(57) [Claims] An electronic component (1) provided with a plurality of solder bumps (8) arranged in an array on a back surface, and arranged in an array corresponding to the arrangement of the solder bumps (8). A mounting board (3) having a plurality of electrodes (4), wherein the electronic component (1) and the mounting board (3) are provided.
Are electrically connected to each other via the solder bumps (8), and the connection part by the solder bumps (8) and the electronic component (1) are covered with a drip-proof material (10). Wherein the drip-proof material (10) is made of a resin having a linear expansion coefficient of 56 ppm / ° C. and an elastic modulus of 50 MPa. 2. An electronic component (1) provided with a plurality of solder bumps (8) arranged in an array on the back surface, and arranged in an array corresponding to the arrangement of the solder bumps (8). A mounting board (3) having a plurality of electrodes (4), wherein the electronic component (1) and the mounting board (3) are provided.
Are electrically connected to each other via the solder bumps (8), and the connection part by the solder bumps (8) and the electronic component (1) are covered with a drip-proof material (10). The drip-proof material (10) has a linear expansion coefficient of 56 to 86 pp.
An electronic component mounting structure comprising a resin having m / ° C. and an elastic modulus of 1 to 50 MPa. 3. The drip-proof material (10) has a linear expansion coefficient of 8
The electronic component mounting structure according to claim 2 , wherein the elastic modulus is 6 MPa at 6 ppm / ° C. 4. An electronic component (1) provided with a plurality of solder bumps (8) arranged in an array on the back surface, and arranged in an array so as to correspond to the arrangement of the solder bumps (8). A mounting board (3) having a plurality of electrodes (4), wherein the electronic component (1) and the mounting board (3) are provided.
Are electrically connected to each other via the solder bumps (8), and the connection part by the solder bumps (8) and the electronic component (1) are covered with a drip-proof material (10). The drip-proof material (10) has a linear expansion coefficient of 86 to 260p.
An electronic component mounting structure comprising a resin having a pm / ° C. and an elastic modulus of 1 to 3 MPa. 5. The drip-proof material (10) has a linear expansion coefficient of 2
The electronic component mounting structure according to claim 4 , wherein the elastic modulus is 2 MPa at 60 ppm / ° C. Wherein said drip member (10) is mounted structure of the electronic component according to claim 4 or 5, characterized in that it is composed of those obtained by mixing a filler into the urethane resin.