JPH053197A - Mounting method of semiconductor integrated circuit element on wiring board - Google Patents

Abstract

PURPOSE:To enable semiconductor integrated circuit elements different from each other in weight to be well mounted on the same wiring board. CONSTITUTION:Solder bumps, which are formed on the electrodes of ICs 1a, 1b, and 1c different from each other in weight, are made to change in solder composition corresponding to a load imposed on each of the electrodes, and these ICs are mounted on a common wiring board 3 by soldering through a reflow method. By this setup, a short circuit is prevented from occurring between electrodes or wirings even if they are arranged fine in pitch, so that semiconductor integrated circuit elements can be well mounted by soldering.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mounting method capable of reliably soldering a plurality of semiconductor integrated circuit elements (hereinafter referred to as "IC") to the same wiring board.

[0002]

2. Description of the Related Art A conventional mounting method of this type will be described with reference to FIGS. In FIG. 5, the solder bumps 2 are formed on each of the plurality of electrodes on the surface of the IC 1 (in this case, represented by a flip chip) and the electric circuit wiring 4 formed on the surface of the wiring board 3. The respective solders 5 are welded by reflow to mount the IC 1 on the wiring board 3. However, the heights of the solder bumps 2 are uneven and uneven, and
When the solder 5 on the wiring board 3 is more uneven, the solder bumps 2 are often not connected to the wiring board 3 when both are soldered in such a state. .. Therefore, as shown in FIG.
Place the weight 6 on the entire back surface (upper surface) of C1 and reflow.
It is soldered to prevent such a bad connection.

However, in such a mounting method, an excessive load is applied depending on the type of IC, and the solder bump 2
And the connection portion 7 formed by melting the solder 5 by reflow
When the solder is squeezed out and the IC electrode pitch is a fine pitch such as about 150 μm or less, the wiring between the electrodes or adjacent wiring is short-circuited, and a mounting defect occurs. In addition, the weight 6 is placed on the back surface of the IC 1 each time the IC 1 is mounted on the wiring board 3 as described above.
It makes mounting work complicated and inefficient.

[0004]

Therefore, the present invention is
The above-described weight is not used, but various ICs arranged on the wiring board are mounted surely so that adjacent electrodes or adjacent wirings are not short-circuited.

[0005]

Therefore, according to the present invention, when a plurality of ICs having different weights are mounted on a common wiring board by soldering, each of the ICs is loaded with a load per electrode of the IC. By changing the solder composition of the solder bumps formed on the electrodes of each IC, and
The melting point of the solder of the C solder bump is adjusted to be higher than the melting point of the solder adhered to the wiring board, and the plurality of ICs are soldered and mounted on the wiring board to solve the above-mentioned problems.

[0006]

Therefore, according to the method of mounting an IC on a wiring board of the present invention, even if the ICs have electrodes formed at a fine pitch, or ICs having different sizes and weights, they are mixed and the same wiring is provided. Even if the IC is mounted on the substrate by reflow, an event that short-circuits between adjacent electrodes of the IC or between adjacent wirings does not occur.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for mounting an IC of the present invention on a wiring board will be described below with reference to FIGS. Figure 1 shows multiple ICs
Is a partial plan view showing a common wiring board mounted with,
2 is a cross-sectional view taken along the line AA of FIG. 1, FIG. 3 is a cross-sectional view showing a state where the IC and the electric circuit wiring are connected as a result of reflowing in the state of FIG. 2, and FIG. It is a state diagram of tin solder. The same parts as those in FIGS. 5 to 7 are designated by the same reference numerals.

For example, a common wiring board 3 made of glass epoxy resin shows only a part of these figures, and a plurality of electric circuit wirings 4 are formed on the surface thereof at a pitch of, for example, 150 μm. Has been formed. Solder 5 is attached to these electric circuit wirings 4. On such a wiring board 3, a plurality of ICs 1a, 1b, 1c having different sizes, weights, numbers of electrodes, electrode pitches, etc. are mounted at high density together with electric components constituting other electric circuits. FIG. 1 shows a state where only three ICs are mounted.

In the figure, these ICs 1a, 1b, 1c are represented by flip-chip type semiconductor devices. IC1a is 10
6 electrodes for IC1b, and IC1c for IC1b
Has 16 electrodes, and the solder bumps 2 are formed on the respective electrodes. Also, the solder 5 on the electrical circuit wiring 4
As the solder of the solder bump 2, a solder having a composition of lead and tin as described below was used.

Flux is applied to the electric circuit wirings 4 and / or the solder bumps 2 of the common wiring board 3 as described above, and the ICs 1a, 1b, 1c are mounted so that the solder bumps 2 are accurately mounted on the electric circuit wirings 4. Equipped with, through a heating furnace,
A temperature in the range of 183 ° C to 230 ° C, for example about 21
Heat (reflow) at 6 ° C. Then, the solder 5 is completely melted, and the solder of the solder bump 2 is semi-molten,
Both are welded.

In this mounting method, the most important requirement for preventing the inconvenient short circuit pointed out in FIG. 6 is the load per electrode. The present inventors have confirmed the connection state between the electric circuit wiring 4 and the solder bump 2 by using an IC having a 80 mm electrode on a 6 mm square silicon chip as the IC 1 a. In this case, the solder 5 on the electric circuit wiring 4 is, for example, eutectic solder having a composition of lead and tin in a ratio of 6: 4, and the solder of the solder bump 2 is, for example, lead. Use solder with a composition of the ratio of tin to 1: 9, for example, about 2
Heated at 16 ° C.

As is clear from the phase diagram of lead = tin solder in FIG. 4, the solder having the composition of tin 6 and lead 4 has a constant melting point of approximately 183 ° C., but the composition of tin 9 and lead 1 is The solder is about 18
In the temperature range of 3 ° C to 230 ° C, solid and liquid coexist.

Therefore, when the reflow is performed at the constant temperature of 216 ° C., the solder 5 of the wiring board 3 is melted and the IC 1a
The solder of the solder bump 2 is in a solid solution state. The self-weight of the IC 1a is applied to the place in the solid solution state to absorb the height variation of the solder bump 2 and, as shown in FIG.
It was confirmed that the solder 5 and the solder bump 2 were welded in a good condition, and that no short circuit occurred between the electrodes and between the electric circuit wirings. Then, when the load per electrode of this IC 1a was measured, it was about 0.48 mg.

As the IC 1b, an IC having 40 electrodes on a 3 mm square silicon chip is referred to as the IC 1a.
When the same solder composition was used and heating was performed at the same temperature and the welding state of both was confirmed, it was found that some electrodes were not connected. Therefore, this IC1
When the load per electrode of b was measured, it was about 0.26 m
It was g. Therefore, the inventors of the present invention used a solder having a composition of tin 8 and lead 2 as the solder of the solder bump 2 of this IC, and once again tested the welded state under the same conditions as those described above. As described above, it was confirmed that the solder 5 and the solder bump 2 were welded in a good state.

Further, as the IC 1c, an IC having 120 electrodes on a 9 mm square silicon chip is
When each solder was made to have the same composition as that of C1a and heated at the same temperature to confirm the welding state of both, it was confirmed that a part of the electrodes and the electric circuit wiring were short-circuited. Then, when the load per electrode of this IC1c was measured, it was about 0.65 mg. Therefore, the inventors of the present invention used solder having a composition of tin 9.5 and lead 0.5 as the solder of the solder bump 2 of this IC, and conducted an experiment again under the same conditions as described above, and found that the solder 5 and It was confirmed that the solder bumps 2 were welded in good condition.

Therefore, even in the ICs 1a, 1b, and 1c having different appearances such as size, weight, and number of electrodes, their solder bumps 2 have a composition higher than the melting point of the solder applied to the electric circuit wiring 4. Depending on the load per electrode, that is, depending on the load per electrode, that is, for the IC with a light load, the solder with a relatively low melting point may be used, and for the IC with a heavy load, the solder with a relatively high melting point may be used. For example, it has been confirmed that a good connection state can be obtained even when these ICs are simultaneously mounted on the common wiring board 3.

In the above embodiment, lead / solder
I explained tin solder as an example.
It may be made of tin or the like, and the IC has been described by taking the flip-chip type IC as an example, but the present invention is also applicable to a surface mounting type IC such as a QFJ type.

[0018]

As is apparent from the above description, according to the method of mounting on a wiring board of the present invention, even an IC having electrodes formed at a fine pitch or an IC having a different size, weight, etc. Even if they are mixed and mounted on the same wiring board by reflow, an event that short-circuits between adjacent electrodes of the IC or between adjacent wirings does not occur. Also, since batch reflow can be done at the same temperature,
Work efficiency increases. Further, since all the ICs are reflowed under the optimum conditions, various excellent effects such as improvement in reliability and yield can be obtained.

[Brief description of drawings]

FIG. 1 is a partial plan view showing a common wiring board on which a plurality of ICs are mounted.

FIG. 2 is a cross-sectional view taken along the line AA of FIG.

FIG. 3 is a cross-sectional view showing a state where the semiconductor integrated circuit element and the electric circuit wiring are connected as a result of reflowing in the state of FIG.

FIG. 4 is a state diagram of lead / tin solder.

FIG. 5 is a sectional view for explaining a state of a semiconductor integrated circuit element and a wiring board.

FIG. 6 is a cross-sectional view for explaining a method for mounting a semiconductor integrated circuit device of the related art on a wiring board.

7 is a sectional view showing a state in which a semiconductor integrated circuit element is mounted on a wiring board by the mounting method of FIG.

[Explanation of symbols]

 1 Semiconductor Integrated Circuit Element (IC) 2 Solder Bump 3 Wiring Board 4 Electric Circuit Wiring 5 Solder 6 Weight 7 Connection Part

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H05K 3/34 H 9154-4E

Claims (1)

Claims: 1. When a plurality of semiconductor integrated circuit elements having different weights are mounted on a common wiring board by soldering, one semiconductor integrated circuit element is provided for each semiconductor integrated circuit element.
The solder composition of the solder bumps formed on the electrodes of each semiconductor integrated circuit element is changed according to the load per electrode, and the melting points of the solder bumps of all the semiconductor integrated circuit elements to be mounted are measured on the wiring board. A method for mounting a semiconductor integrated circuit element on a wiring board, which comprises adjusting the melting point of the deposited solder to be higher than the melting point and soldering the plurality of semiconductor integrated circuit elements to the wiring board.