JPH0936531A - Mounting of lead component - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate a defective bonding of lead components and to make it possible to mount efficiently the lead components on a circuit board by a method wherein a reflow heating treatment is performed on the board in a state that solders have a surface tension smaller than that of the solders at the time of the formation of solder precoatings to mount the lead components on the conductive parts on the board. SOLUTION: Solder precoatings are respectively formed on conductive parts 12 on a board in a state that solders have a prescribed surface tension. At this time, by setting greatly in comparison the surface tension of the solders 13 at the time of the formation of the solder precoatings, the fluidity of the solders 13 can be reduced. Then, a flux having a temporary fixture is fed on the solder precoatings and lead components 11 are respectively mounted on the solder precoatings. After that, a reflow heating treatment is performed on this board to mount the lead components 11 on the parts 12. At this time, the surface tension of the solders at the time of the reflow heating treatment is set smaller than that of the solders at the time of the formation of the solder precoatings, whereby the fluidity of the solders can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mounting method for lead parts using a solder precoat.

[0002]

2. Description of the Related Art Conventionally, as a method of mounting lead parts on a circuit board, after coating a solder paste on a conductive portion (pad) of the circuit board by a printing method,
A method has been adopted in which lead components are mounted on the solder paste, and then the circuit board is subjected to heat treatment to melt the solder paste, thereby mounting the lead components on the pads of the circuit board.

However, as the lead pitch of lead components has become finer in recent years, the pad pitch on the circuit board has also become finer. Especially, when the pad pitch becomes narrower than 0.5 mm, it becomes difficult to print the solder paste. However, there arises a problem that soldering defects such as solder bridges frequently occur.

Therefore, as a method of forming a solder layer on a pad having a narrow pitch on a circuit board, an organic acid salt of a metal having a small ionization tendency (for example, in Sn--Pb type solder) among solder alloy components to be formed. Organic acid lead salt) and a metal powder (for example, Sn) composed of a metal having a greater ionization tendency than the above metals or an alloy containing the metal.
In the -Pb-based solder, a paste-like solder depositing composition containing tin powder or Sn-Pb-based solder powder which is to be formed) is used. A method of depositing solder on a pad by utilizing a substitution reaction with a metal in a metal powder is disclosed in Japanese Patent Laid-Open No.
It is disclosed in Japanese Patent Publication No. 157796. In this method, for example, a paste-like solder deposition composition mainly composed of an organic acid lead salt and tin powder is applied to a region including a pad of a circuit board by solid coating, and a heat treatment is applied to this to form an organic acid lead salt. Is a method of causing a substitution reaction between tin powder and tin powder to selectively deposit a solder alloy on the pad to form a solder precoat. According to this method, even if the pad pitch is less than 0.5 mm, the solder precoat can be formed in a short time without generating a solder bridge.

When the lead component is mounted, the lead component is mounted on the formed solder precoat, and then the solder precoat is melted by heat treatment to mount the lead component on the pad. .

[0006]

However, in the above method, as shown in FIGS. 3 (A) and 3 (B),
The variation in the position of each lead 31 of the lead component in the z-axis direction, that is, the lead coplanarity, is absorbed by increasing the solder precoat, but when the pitch of the pads 32 becomes narrow, the height h ′ of the solder precoat 33 increases. It becomes difficult to do so, and it becomes impossible to absorb the lead coplanarity. For example, when mounting lead parts having a lead coplanarity of 100 μm at a pitch of pads 32 of 0.3 mm or less, the solder precoat 33
It is not easy to increase the thickness to about 100 μm in terms of time, material, and cost, and problems such as the occurrence of solder bridges are very difficult.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a lead component mounting method capable of efficiently mounting lead components on a circuit board without defective joints.

[0008]

According to the present invention, there is provided a step of forming a solder precoat on the conductive part of a substrate having a conductive part in a state of having a predetermined surface tension, and a temporary fixing property on the solder precoat. A step of supplying a flux, a step of mounting a lead component on the solder precoat to which the flux has been supplied, and a surface tension of the substrate on which the lead component is mounted, which is smaller than the surface tension when the solder precoat is formed. And a step of mounting the lead component on the conductive portion of the substrate by performing a reflow heat treatment in the state.

Here, the conductive portion mainly means an electrode pad. The board means a circuit board such as a printed wiring board. Further, the temporary fixing property of the flux means a fixing force that does not cause displacement of components due to vibration of the mounting line or the like. A flux having such temporary fixing property is, for example, Japanese Patent Application No. 6-180712.
And the like disclosed in the publication can be used.

The lead parts used in the method of the present invention include QFP (Quad Flat Package) and SOP.
(Small Outline Package), etc. In the present invention, the following three methods are used to control the surface tension when forming the solder precoat and the surface tension of the solder when performing the reflow heat treatment ( 1) to (3)
Is mentioned. (1) JIS Z of flux during reflow heat treatment
The activity in the copper plate spreadability test according to 3197 is set to 1.05 times or more of the activity of the flux in forming the solder precoat in the test, and the solder leak spread rate in the test in forming the solder precoat is determined. How to set 80-95%. (2) The oxygen concentration in the atmosphere during the reflow heat treatment is
1 / of the oxygen concentration in the atmosphere when forming the solder precoat
A method of setting less than 2 and setting the oxygen concentration in the atmosphere at the time of forming the solder precoat to 1000 ppm or less. (3) The ambient temperature during the reflow heat treatment is set to be 10 ° C. or higher than the ambient temperature during the solder precoat formation, and the ambient temperature during the solder precoat formation is 185 to 185.
Method to set within the range of 220 ℃. In (1), the activity of the flux and the solder wetting spread rate can be adjusted by selecting the flux or adjusting the components. In (2), a method of controlling the oxygen concentration can be performed, for example, by adjusting the flow rate of nitrogen gas flowing in the heating furnace or the reflow furnace when forming the solder precoat.

The methods (1) to (3) may be adopted individually, or in appropriate combination. In the method of the present invention, as shown in FIG. 1, the shape of the conductive portion on the substrate is such that the Laplace effect is exhibited, that is, the wide portion 10a and the narrow portion 10b are provided. The shape is preferably such that the solder height is increased.

In the present invention, the solder precoat is an organic acid salt of a metal having a small ionization tendency among the solder alloy components to be formed (for example, an organic acid lead salt in Sn—Pb type solder) and ionized from the metal. Metal powder consisting of a metal having a large tendency or an alloy containing the metal (for example, tin powder in Sn-Pb solder, or solder powder richer in Sn than Sn-Pb solder to be formed).
Using a paste-like composition for depositing solder, which contains a metal ion in the organic acid salt and a substitution reaction of a metal in the metal powder, a solder may be deposited on a pad to be formed. preferable. Alternatively, it can be formed by a conventional solder paste printing method.

According to the method for mounting lead components of the present invention, a solder precoat is formed on a conductive portion of a substrate with a predetermined surface tension, the lead components are mounted on the solder precoat, and then the solder precoat is applied to the substrate. It is characterized in that the lead component is mounted on the conductive portion by performing the reflow heat treatment in a state having a surface tension smaller than the surface tension at the time of forming.

First, a solder precoat is formed on the conductive portion of the substrate with a predetermined surface tension. At this time,
The fluidity of the solder can be reduced by setting the surface tension of the solder when forming the solder precoat to be relatively large. As a result, the height of the solder precoat can be kept low.

Next, a flux having a temporary fixing property is supplied onto the solder precoat, and a lead component is mounted thereon. Accordingly, the lead component can be mounted on the solder precoat without dropping from the solder precoat.

Then, the substrate is subjected to reflow heat treatment to mount the lead component on the conductive portion. At this time, the fluidity of the solder can be improved by setting the surface tension of the solder during the reflow heat treatment to be smaller than the surface tension when forming the solder precoat. This allows the solder to be collected during the reflow heat treatment,
Can absorb lead coplanarity. In particular, in the conductive portion having the shape shown in FIG. 1, the solder height can be increased in the wide portion 10a, which is very effective. As a result, as shown in FIGS. 2A and 2B, all the leads 11 can be joined to the conductive portion 12 by the solder 13, and the mounting can be performed without an open defect or a solder bridge. it can.

According to the method of the present invention, it is not necessary to increase the height of the solder precoat at the time of forming the solder precoat, which is advantageous in terms of time, material, and cost, and further, a solder bridge is generated. Etc. can also be effectively prevented.

[0018]

Embodiments of the present invention will be specifically described below. (Example 1) Lead coplanarity 100 μm of 0.
3mm pitch 168-pin QFP (Quad Flat Package)
) A circuit board having a pattern having 200 conductive portions (electrode pads) was prepared.

On this electrode pad, organic lead oxide and Sn
/ Pb = 70/30 a paste-like solder deposition composition containing solder powder as a main component in a thickness of about 200 μm, and subjected to heat treatment at 215 ° C. for 2 minutes in an atmosphere with an oxygen concentration of 100 ppm. A solder precoat was formed on the electrode pad. Since this solder precoat utilizes a substitution reaction of organic acid lead, which is an organic acid salt of Pb having a small ionization tendency among Sn-Pb, and Sn having a large ionization tendency in the solder powder, only on the electrode pad. Formed in.

Thereafter, the residue was washed with trichloroethane, and the thickness of the solder precoat on the electrode pad was measured and found to be 60 to 120 μm (average 90 μm). In addition, the flux activation power of this solder precoat is determined by JIS
When examined by a wet spreadability test according to Z 3197, the spread rate was 80%.

Next, each of the fluxes (1 to 5) having a flux activation power (spreading ratio in a wetting spreadability test according to JIS Z 3197) shown in Table 1 below was used to provide an oxygen concentration of 100 ppm on the circuit board. Under an atmosphere of 215 ° C. under an atmosphere of
00 QFPs were mounted on the circuit board. With respect to the circuit board after mounting, the number of lead opens with respect to the total number of QFP pins was checked, and the open failure rate was calculated. The results are also shown in Table 1 below.

[0022]

[Table 1]

As is apparent from Table 1, according to the mounting method of the present invention, that is, when the mounting was performed by selecting the fluxes 3 to 5, the open defect rate was extremely low. On the other hand, when the fluxes 1 and 2 selected outside the range of the present invention were used, the open defect rate was very high. (Example 2) 200 QFPs were mounted on a circuit board in the same manner as in Example 1 except that the oxygen concentration of the solder precoat formation and the reflow heat treatment was set to 20% in the air atmosphere. With respect to the circuit board after mounting, the number of lead opens with respect to the total number of QFP pins was checked, and the open failure rate was calculated. The results are also shown in Table 2 below.

[0024]

[Table 2]

As is apparent from Table 2, according to the mounting method of the present invention, that is, when the mounting was performed by selecting the flux 3 to 5, the open defect rate was very low. On the other hand, when the fluxes 1 and 2 selected outside the range of the present invention were used, the open defect rate was very high. (Example 3) Lead coplanarity 100 .mu.m of 0.
A circuit board on which a pattern having 200 conductive portions (electrode pads) of 168-pin QFP having a 3 mm pitch was formed was prepared.

On this electrode pad, organic lead oxide and Sn
/ Pb = 70/30 solder paste composition containing solder powder as a main component in a thickness of about 200 μm, and heat-treated at 215 ° C. for 2 minutes under oxygen concentration of 1000 ppm to each electrode pad. A solder precoat was formed on top. Since this solder precoat utilizes the substitution reaction of organic acid lead which is an organic acid salt of Pb having a small ionization tendency among Sn-Pb and Sn having a large ionization tendency,
It was formed only on the electrode pad. After that, the residue was washed with trichloroethane, and the thickness of the solder precoat on the electrode pad was measured to find that it was 60 to 120 μm (average 90 μm).
m).

Next, each oxygen concentration shown in Table 3 below (1 to
5) Under ambient temperature of 230 ° C., the circuit board was subjected to reflow heat treatment to mount 200 QFPs on the circuit board. With respect to the circuit board after mounting, the number of lead opens with respect to the total number of QFP pins was checked, and the open failure rate was calculated. The results are also shown in Table 3 below.

[0028]

[Table 3]

As is clear from Table 3, when the mounting method of the present invention is performed, that is, when the mounting is performed under the conditions 3 to 5 in which the oxygen concentration is set within the range of the present invention, the open defect rate is high. Was very low. On the other hand, in the conditions 1 and 2 in which the oxygen concentration was set outside the range of the present invention, the open defect rate was extremely high. (Example 4) Lead coplanarity 100 .mu.m of 0.
A circuit board on which a pattern having 200 conductive portions (electrode pads) of 168-pin QFP having a 3 mm pitch was formed was prepared.

On this electrode pad, organic acid lead and Sn
/ Pb = 70/30 a solder paste composition containing solder powder as a main component in a thickness of about 200 μm, and heat-treated at 210 ° C. for 2 minutes under an oxygen concentration of 100 ppm to each electrode pad. A solder precoat was formed on top.
This solder precoat is formed only on the electrode pad because it utilizes the substitution reaction between the organic acid lead, which is an organic acid salt of Pb having a small ionization tendency among Sn-Pb, and Sn, which has a large ionization tendency. . After that, the residue was washed with trichloroethane, and the thickness of the solder precoat on the electrode pad was measured to be 60 to 120 μm (average 90 μm).
Met.

Next, each atmospheric temperature (1
5), the above circuit board was subjected to reflow heat treatment at an oxygen concentration of 100 ppm to mount 200 QFPs on the circuit board. With respect to the circuit board after mounting, the number of lead opens with respect to the total number of QFP pins was checked, and the open failure rate was calculated. The results are also shown in Table 4 below.

[0032]

[Table 4]

As is clear from Table 4, when the mounting method of the present invention is carried out, that is, when the mounting is carried out under the condition 5 in which the ambient temperature is set within the scope of the present invention, the open defect rate is extremely high. It was very low. On the other hand, under the conditions 1 to 4 in which the ambient temperature was set outside the range of the present invention, the open defect rate was extremely high. (Example 5) 200 QFPs were mounted on a circuit board in the same manner as in Example 4 except that the oxygen concentration in the solder precoat formation and the reflow heat treatment was set to 20% in the air atmosphere. With respect to the circuit board after mounting, the number of lead opens with respect to the total number of QFP pins was checked, and the open failure rate was calculated. The results are also shown in Table 5 below.

[0034]

[Table 5]

As can be seen from Table 5, according to the mounting method of the present invention, that is, when the mounting is carried out under the condition 5 in which the atmospheric temperature is set within the range of the present invention, the open defect rate is extremely high. It was very low. On the other hand, under the conditions 1 to 4 in which the ambient temperature was set outside the range of the present invention, the open defect rate was extremely high. (Example 6) Lead coplanarity 100 .mu.m of 0.
A circuit board on which a pattern having 200 conductive portions (electrode pads) of 168-pin QFP having a 3 mm pitch was formed was prepared.

On this electrode pad, organic lead oxide and Sn
/ Pb = 70/30 a paste-like solder deposition composition containing solder powder as a main component in a thickness of about 200 μm, and heat-treated for 2 minutes at 210 ° C. under an oxygen concentration of 1000 ppm to each electrode pad. A solder precoat was formed on top. Since this solder precoat utilizes the substitution reaction of organic acid lead which is an organic acid salt of Pb having a small ionization tendency among Sn-Pb and Sn having a large ionization tendency,
It was formed only on the electrode pad. After that, the residue was washed with trichloroethane, and the thickness of the solder precoat on the electrode pad was measured to find that it was 60 to 120 μm (average 90 μm).
m). Further, when the flux activation force of this solder precoat was examined by a wetting and spreading property test according to JIS Z 3197, the spreading rate was 80%.

Next, each atmospheric temperature (1
˜3), under the oxygen concentration (1 to 3), the above circuit board is subjected to reflow heat treatment using the flux (1 to 3) having the flux activation power shown in Table 6 below to obtain 200 QFPs. It was mounted on a circuit board. With respect to the circuit board after mounting, the number of lead opens with respect to the total number of QFP pins was checked, and the open failure rate was calculated. The results are also shown in Table 6 below.

[0038]

[Table 6]

As is apparent from Table 6, according to the mounting method of the present invention, that is, the atmospheric temperature and the oxygen concentration are set within the scope of the present invention, and the mounting is performed using the flux specified by the method of the present invention. In the case of carrying out, the open defect rate was extremely low.

[0040]

As described above, according to the lead component mounting method of the present invention, the solder precoat is formed on the conductive portion of the substrate with a predetermined surface tension, and the lead component is mounted on the solder precoat. Later, the reflow heat treatment is applied to the conductive parts with the surface tension smaller than the surface tension when the solder precoat is formed on this board, so that the lead coplanarity is completely absorbed and the bonding failure occurs. In addition, the lead parts can be efficiently mounted on the circuit board without the occurrence of solder bridges.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the shape of a conductive portion of a substrate used in the method of the present invention.

2A and 2B are cross-sectional views for explaining a method for mounting lead components by the method of the present invention.

3A and 3B are cross-sectional views for explaining a method of mounting a lead component by a conventional method.

[Explanation of symbols]

10a ... Wide part, 10b ... Narrow part, 11 ... Lead,
12 ... Conductive part, 13 ... Solder.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hisaeo Irie, 4 671 Mizusui, Noguchi-machi, Kakogawa-shi, Hyogo Prefecture 4 at Harima Kasei Co., Ltd. Harima Kasei Co., Ltd.

Claims (4)

[Claims] 1. A step of forming a solder precoat on the conductive part of a substrate having a conductive part in a state of having a predetermined surface tension, a step of supplying a flux having a temporary fixing property on the solder precoat, The step of mounting the lead component on the solder precoat supplied with the flux, and the substrate on which the lead component is mounted is subjected to a reflow heat treatment with a surface tension smaller than the surface tension at the time of forming the solder precoat. And a step of mounting the lead component on the conductive portion of the substrate. 2. The activity of the flux during the reflow heat treatment in a copper plate spreadability test according to JIS Z 3197 is 1.05 times or more the activity of the flux during the solder precoat formation in the test. The method of mounting a lead component according to claim 1, wherein a solder leakage spread rate in the test when forming the solder precoat is 80 to 95%. 3. The oxygen concentration in the atmosphere during the reflow heat treatment is less than 1/2 of the oxygen concentration in the atmosphere during the solder precoat formation, and the oxygen in the atmosphere during the solder precoat formation is The lead component mounting method according to claim 1, wherein the concentration is 1000 ppm or less. 4. The ambient temperature at the time of the reflow heat treatment is 1 than the ambient temperature at the time of forming the solder precoat.
The lead component mounting method according to claim 1, wherein the temperature is higher than 0 ° C., and the ambient temperature at the time of forming the solder precoat is in the range of 185 to 220 ° C. 3.