JP3565204B2 - Electronic equipment - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electronic device, and more particularly to a technique for improving the bonding strength of a plurality of substrates constituting an electronic device and improving the electrical reliability.
[0002]
[Prior art]
When mounting components of electronic devices, it is common practice to use solder bumps (solder balls) to join a ceramic substrate for fixing a semiconductor element and the like to an organic printed wiring board on which the ceramic substrate is mounted. . However, in a BGA (Ball Grid Array) substrate using solder bumps, the thermal expansion coefficient of a ceramic substrate is about 3 ppm / ° C., whereas the thermal expansion coefficient of an organic printed wiring board is 20 to 60 ppm / ° C. Therefore, when the temperature rises, a stress is generated due to the difference in the coefficient of thermal expansion between the ceramic substrate and the organic printed wiring board, and this stress may cause cracks in the joined solder bumps and the ceramic substrate, resulting in poor conduction. is there.
[0003]
Various methods have been proposed for the purpose of preventing cracks and poor conduction occurring between such two types of substrates having different coefficients of thermal expansion. For example, as shown in FIG. 5, a method of fixing the ends of two substrates using a fixing rod is disclosed in Japanese Patent Application Laid-Open No. Hei 10-209213.
[0004]
Oite the cross-sectional view showing an end portion of the semiconductor device shown in FIG. 5, the ceramic-made BGA substrate 10, 20 is a printed circuit board, 21 is concave, 30, 60 metallized pads, 40 and 50 eutectic solder , 70 are high-temperature solder balls (bumps), 80 is a fixing rod, 90 and 110 are bonding materials, and 100 is a through hole. Through holes 100 are formed at at least two corners of the ceramic BGA substrate 10, and fixing bars 80 are provided at positions corresponding to the through holes 100 on the printed circuit board 20.
[0005]
The ceramic BGA substrate 10 mounted on the printed circuit board 20 can suppress the deformation of the printed circuit board 20 that expands and contracts due to a temperature change via the fixing rod 80. However, in this method, it is necessary to form the through hole 100 in the ceramic BGA substrate 10 and to form the concave portion 21 in the printed circuit board 20, and further, to join the fixing rod 80 to the concave portion 21, Separately, soldering must be performed. Therefore, since the number of parts and the number of steps are increased, there is a concern that the manufacturing cost may be increased.
[0006]
[Problems to be solved by the invention]
The present invention has been made in order to solve such a problem, and does not significantly increase the number of parts and the number of steps, and in a simple method, such as a ceramic substrate and an organic printed wiring board, has a thermal expansion. It is an object of the present invention to suppress the occurrence of cracks generated when multiple substrates having different rates are laminated.
[0007]
[Means for Solving the Problems]
An electronic device according to the present invention is arranged such that an element mounting substrate on which a first electrode is formed on the back side of an element mounting surface is opposed to the element mounting substrate at a predetermined distance, and furthermore, opposes the first electrode. A wiring substrate having a second electrode formed at a position where the first electrode and the second electrode are to be joined; and a fusible member that joins the first electrode and the second electrode; It is provided with a resin-made reinforcing member for adhering a part of the wiring board facing the end.
[0008]
The resin-made reinforcing member has a shape that expands from the side surface of the element mounting board outward.
[0009]
The resin reinforcing members are formed at appropriate intervals over the entire circumference of the element mounting board.
[0010]
The viscosity of the resin reinforcing member before curing is 5,000 cps or more and 200,000 cps or less.
[0011]
Further, a resin wall member is provided between the fusible member and the resin reinforcing member so as to be spaced from the fusible member and surround the periphery thereof.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
First Embodiment An electronic device according to a first embodiment of the present invention will be described with reference to a cross-sectional view shown in FIG. The ceramic substrate (element mounting substrate) 1 is, for example, an LTCC (Low Temperature Co-fired Ceramic) obtained by laminating and firing several ceramic green sheets, and a wiring pattern is formed between layers. Through this, conduction between the element pads 3 formed on the upper and lower surfaces of the ceramic substrate 1 and the bump pads 4A (first electrodes) is ensured.
[0013]
An element 2 such as a silicon sensor (such as a strain sensor), a thin film magnetic head, or a semiconductor element is mounted on the upper surface of the ceramic substrate 1, and the element 2 is connected to an element pad 3. The element pads 3 and the bump pads 4A are formed by printing or applying an electrode material such as a silver paste on a ceramic green sheet, and then firing.
[0014]
On the upper surface (the surface facing the ceramic substrate 1) of the printed circuit board (wiring substrate) 7, a bump pad 4B (second electrode) is formed at a position facing the bump pad 4A. In order to form the bump pads 4B on the printed board 7, a normal print printing technique can be applied.
[0015]
The bump pad 4A and the bump pad 4B are joined by a bump (fusible member) 8 made of solder, a solder material, or the like. A reinforcing member 6 for bonding the ceramic substrate 1 and the printed board 2 is formed on the outer periphery of the ceramic substrate 1 so as to surround the same.
[0016]
A procedure for joining the ceramic substrate 1 and the printed board 7 will be described with reference to FIGS. 2 (a) to 2 (c). First, the bump 8 is positioned and held using a jig (not shown) so as to overlap the bump pad 4A. While holding the bumps 8 before melting with the ceramic substrate 1, the whole is heated to a temperature equal to or higher than the melting point of the bumps 8, and one side of the bumps 8 is joined to the bump pads 4A (see FIG. 2A).
[0017]
Next, the ceramic substrate 1 with the bump 8 bonded to the bump pad 4A is turned over, and the ceramic substrate 1 and the printed board 3 are positioned so that the bump 8 faces the bump pad 4B. In this state, the entire body is heated again to bond the bump 8 and the bump pad 4B (see FIG. 2B).
[0018]
Next, an adhesive resin having an appropriate viscosity is supplied to the outer periphery of the ceramic substrate 1 using, for example, the needle 9, and when the whole is heated, the resin is cured and the ceramic substrate 1 and the printed substrate 3 are bonded. The reinforcing member 6 is formed (see FIG. 2C). Since the reinforcing member 6 can be formed only by supplying and curing the adhesive resin, the number of steps and the number of components are not significantly increased.
[0019]
In Example 1 described later, an epoxy resin having a viscosity of 23,000 cps is used as the adhesive resin. However, in order to adjust the shape of the reinforcing member 6, the adhesive resin needs to have a certain degree of viscosity. The viscosity of the adhesive resin is desirably 5,000 cps or more. However, it becomes difficult to discharge from a needle or the like as the viscosity increases, so that the viscosity is desirably 200,000 cps or less.
[0020]
It is desirable that the adhesive resin be supplied to the end portion, particularly the side surface of the ceramic substrate 1, that is, such that the reinforcing member 6 protrudes outward from the side surface of the ceramic substrate 1. The reinforcing member 6, which has a flared shape that extends outward from the side surface of the ceramic substrate 1, fixes the substrates much more firmly than when they do not protrude from the ceramic substrate 1.
[0021]
The adhesive resin may be supplied up to the internal gap between the ceramic substrate 1 and the printed circuit board 3, but if the reinforcing member 6 directly touches the bump 8, a crack is easily formed in the reinforcing member 6. As a result, the effect of the reinforcing member 6 decreases. In particular, when a low-viscosity adhesive resin is used, the resin supplied to the outer periphery enters the gap between the ceramic substrate 1 and the printed circuit board 3 toward the bump 8 before the resin hardens, and the bump 8 and the reinforcing member 6 is the most likely to contact, there is a need to pay attention to avoid contact.
[0022]
Therefore, as shown in FIG. 3 (Embodiment 2), a wall member 9 for preventing the adhesive resin from entering may be provided between the reinforcing member 6 and the bump 8 so as to surround the periphery of the bump 8. . The wall member 9 prevents the adhesive resin from entering the gap between the substrates and coming into contact with the bumps 8 even when the viscosity of the adhesive resin is low.
[0023]
If the formation of the wall member 9 is performed when the bump 8 and the bump pad 4B are joined before the formation of the reinforcing member 6, the process is simplified. For this reason, the curing temperature of the resin constituting the wall member 9 is desirably higher than the curing temperature of the reinforcing member 6, and more desirably the same as the joining temperature of the bumps 8.
[0024]
It is not preferable to completely seal the periphery of the ceramic substrate 1 with the reinforcing member 6 because air existing in the gap between the ceramic substrate 1 and the printed board 3 and heat generated in the bumps 8 are confined. In this sense, it is desirable that the reinforcing member 6 and the wall member 9 are separately arranged at several places with an appropriate gap. However, it is necessary that the position where the gap of the wall member 9 is disposed has a positional relationship such that the reinforcing member 6 before solidification cannot enter the bump 8.
[0025]
In the electronic device according to the present invention, the reinforcing member 6 firmly fixes the end of the ceramic substrate 1 to the printed circuit board 7 even if stress is generated so that the ceramic substrate 1 and the printed circuit board 7 are warped by the temperature rise. Therefore, the stress applied to the bump 8 is reduced. For this reason, cracks in the bumps 8 and cracks in the ceramic substrate 1 are suppressed. As a result, the electrical reliability of the electronic device is improved.
[0026]
Further, since the reinforcing member 6 is in a liquid state before it is solidified, there is no inconvenience that the reinforcing member 6 does not reach the printed circuit board 3 and a defective connection occurs.
Next, effects of the present invention will be described based on examples.
[0027]
Embodiment 1 FIG.
A ceramic substrate (30 mm × 30 mm) having a thickness of 1 mm fired at 900 ° C. was used. At the center of the ceramic substrate, 729 (27 columns × 27 rows) bump pads 4A having a diameter of 0.5 mm were formed at a pitch of 1 mm. A printed board (30 mm × 30 mm) having a thickness of 1.6 mm was used, and 729 (27 columns × 27 rows) bump pads 4 B having a diameter of 0.5 mm were formed at a pitch of 1 mm in the center.
[0028]
The bumps 4A and 4B were joined at 230 ° C. by using solder (63Sn-37Pb) having a melting point of 183 ° C. for the bumps 8. An epoxy resin-based sealing resin (EH0548-8, Dexter) was used for the reinforcing member 6 and cured at 150 ° C. for one hour.
[0029]
Next, a heat cycle test (−40 ° C. to + 125 ° C., 15 min./15 min.) Was performed to evaluate the crack resistance of the electronic device prepared as described above. FIG. 4 is a cross-sectional observation photograph of the electronic device after 1000 cycles of the heat cycle test. In the case where the reinforcing member 6 was not provided, cracks extending inside the ceramic substrate 1 were observed after about 30 cycles, but no cracks were found at all even after 1000 cycles as shown in FIG.
[0030]
Embodiment 2. FIG.
In Example 2, the wall member 9 was formed based on Embodiment 2 shown in FIG. For the wall member 9, an epoxy resin-based sealing resin having a viscosity of 50,000 cps (CB011-1R, Dexter) was used.
[0031]
First, the ceramic substrate 1 on which the bump pads 4A and the bumps 8 were bonded was positioned with respect to the printed circuit board. Further, CB011-1R was applied so as to surround the periphery of the bump 8, and the ceramic substrate 1 and the printed substrate 3 were cured at 230 ° C. for one hour. At this time, the bonding of the bump pad 4B and the bump 8 proceeded simultaneously.
[0032]
Next, an epoxy-based sealing resin (EH0548-8, Dexter) was applied to the side surface of the ceramic substrate 1 and cured at 150 ° C. for one hour to form a reinforcing member 6.
Also with the electronic device according to the second embodiment created as described above, sufficient crack resistance was confirmed.
[0033]
In the first and second embodiments, an example is shown in which two types of substrates having different coefficients of thermal expansion are bonded. However, when substrates having the same coefficient of thermal expansion are bonded, for example, a ceramic substrate (small) on which elements are mounted is connected to a small substrate. It is needless to say that the present invention can be applied to the case where the wiring ceramic substrate (large) supporting the ceramic substrate is fixed.
[0034]
【The invention's effect】
An electronic device according to the present invention is arranged such that an element mounting substrate on which a first electrode is formed on the back side of an element mounting surface is opposed to the element mounting substrate at a predetermined distance, and furthermore, opposes the first electrode. A wiring substrate having a second electrode formed at a position where the first electrode and the second electrode are to be joined; and a fusible member that joins the first electrode and the second electrode; The provision of the resin-made reinforcing member for bonding the end portion to the portion of the wiring board facing the end portion can suppress the occurrence of cracks in the fusible member or the like.
[0035]
In addition, since the resin-made reinforcing member has a shape that expands outward from the side surface of the element mounting substrate, cracks can be suppressed in the fusible member and the like.
[0036]
Further, since the resin reinforcing member is formed at appropriate intervals over the entire circumference of the element mounting board, heat generated from the fusible member can be dissipated.
[0037]
In addition, when the viscosity of the resin-made reinforcing member before curing is 5,000 cps or more and 200,000 cps or less, the resin can be discharged and its shape can be adjusted.
[0038]
Further, by providing a resin wall member formed so as to be spaced from and surrounding the fusible member between the fusible member and the resin reinforcing member, the resin reinforcing member and the fusible member Contact can be prevented.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a cross section of an electronic device (first embodiment) according to the invention.
FIG. 2 is a view for explaining a step of forming a reinforcing resin member.
FIG. 3 is a diagram illustrating a cross section of the electronic device according to the second embodiment.
FIG. 4 is a diagram (photograph) illustrating a cross section of the electronic device after the heat cycle test has been performed 1,000 times.
FIG. 5 is a diagram illustrating a cross section of a conventional electronic device (semiconductor device).
[Explanation of symbols]
Reference Signs List 1 ceramic substrate (element mounting substrate), 2 element, 3 element pad, 4A, 4B bump pad (first electrode, second electrode), 6 reinforcing member, 7 printed board (wiring board), 8 bump (meltability) Member), 9 wall members

Claims (3)

An element mounting substrate having a first electrode formed on the back side of the element mounting surface is disposed so as to face the element mounting substrate at a predetermined interval, and a second electrode is provided at a position facing the first electrode. A wiring board on which electrodes are formed, a fusible member for joining the first electrode and the second electrode, and an end disposed on the outer side of the fusible member; A resin reinforcing member that adheres to the portion of the wiring board facing the portion, and a resin resin formed between the fusible member and the resin reinforcing member so as to be separated from the fusible member and surround the periphery thereof. A wall member, and the resin reinforcing members are formed at appropriate intervals over the entire periphery of the element mounting board, and the resin wall members are such that the resin reinforcing members before solidification cannot enter the fusible member. The gap is arranged in a suitable position Electronic devices. An element mounting substrate having a first electrode formed on the back side of the element mounting surface is disposed so as to face the element mounting substrate at a predetermined interval, and a second electrode is provided at a position facing the first electrode. A wiring board on which electrodes are formed, a fusible member for joining the first electrode and the second electrode, and an end disposed on the outer side of the fusible member; A resin reinforcing member that adheres to a portion of the wiring board facing the portion, wherein the resin reinforcing member is formed so as to surround the outer periphery of the element mounting board and at appropriate intervals over the entire circumference thereof, and be that electronic device characterized in that it has the shape of a flared outwardly from the side covers over the entire side surface from the back end of the element mounting surface. 3. The electronic device according to claim 2, wherein the cross-sectional area of the resin reinforcing member increases from the element mounting substrate side to the wiring substrate side.

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