JPH07235763A - Manufacture of electronic circuit - Google Patents

Abstract

PURPOSE:To realize a production method for an electronic circuit permitting high reliability connection without residue after reflow and without deviation in part position by using no flux thereby providing the connection of high densi ty mounting parts with narrow pitches which is not possible by solder connection using solder paste. CONSTITUTION:This is a production method for an electronic circuit connected with solder by positioning the connecting terminals of an electronic part 5 without using flux on a connecting pattern 2 of a circuit substrate 1; in which solder 3 is supplied in advance at least to one of the connecting pattern 2 and the connecting terminals of the electronic parts 5; an organic matter 4 is supplied to cover the connecting portions before solder heating process; and in the solder heating process, solder is connected while each adjoining connecting portion is independently covered with this organic matter 4 supplied. The organic matter must have a boiling point higher than the melting point of solder to avoid the boiling and evaporation of the organic matter before the solder is melted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an electronic circuit which allows lead components, surface mount components and the like to be soldered to an electronic circuit board without using flux.

[0002]

2. Description of the Related Art In order to solve the problems associated with cleaning residues when flux is used, fluxless solder paste has been developed which can ensure reliability without cleaning. Examples of those related to this conventional technique include JP-A-2-25921 and JP-A-2-290693.

Japanese Unexamined Patent Publication No. 2-25921 discloses a solder paste used in a reducing atmosphere, which has a solder powder and a binder containing alcohol. Since this solder paste does not use solid components such as activators and resins, residues can be eliminated. The boiling point of the alcohol used here is
It exists in the boundary region between the solidus line and the liquidus line in the phase diagram of the solder powder (this is called the paste region). Therefore, when the solder is in a semi-molten state, the alcohol boils and evaporates, which solves the conventional problem of the solder ball scattering in the solder paste containing alcohol having a boiling point of the solidus or lower.

However, when the solder is melted and a connection is made, since there is no liquid and the surface of the solder is exposed, a reducing atmosphere is required to prevent oxidation. In this method, firstly, since the solder paste is supplied to the connection portion by a coating technique such as printing, printing accuracy is limited, and high-density mounting has a problem from the viewpoint of reliability. Secondly, since the connection portion is exposed during solder connection, it is necessary to use a reducing atmosphere such as hydrogen gas in order to prevent the oxidation of the solder, and there is a problem that connection is required in a special atmosphere. .

Further, as an example in which connection is possible in an inert atmosphere, there is JP-A-2-290693. A solder paste composed of alcohols having a boiling point higher than the melting point of solder and solder fine particles, and solder connection is performed with the alcohols covering the surface of the connection portion. Therefore, at the time of connection, since the atmosphere is cut off, the connection can be made even in an inert atmosphere, and there is an advantage that a special atmosphere such as a reducing atmosphere is not required unlike the above-mentioned conventional technique. However, as a solder joining method for electronic components, since a solder paste is used, similar to the above-mentioned conventional technique,
Since the solder is applied and supplied by a printing technique or the like, the supply accuracy is limited, and high-density mounting has a problem in terms of reliability.

[0006]

In the above-mentioned prior art, since the solder paste is used, there is a limit to the accuracy of solder supply to the fine, narrow-pitch connection portions in high-density mounting, and the connection reliability is high. There is a problem from the point. Therefore, an object of the present invention is to solve such a conventional problem, and to provide an improved electronic circuit manufacturing method for realizing a solder joining method for electronic components suitable for high-density mounting. Especially.

More specifically, an object of the present invention is to provide a method of manufacturing an electronic circuit in which soldering is carried out between members to be connected such as an electronic component and a circuit board without using flux. The purpose of is to provide a method for temporarily fixing the members to be connected without using flux, and yet another object is to obtain a highly reliable connection while omitting the cleaning step since there is no residue after the connection. An object is to provide a method of manufacturing an electronic circuit.

[0008]

In order to achieve the above object, in the method of manufacturing an electronic circuit of the present invention, the solder supplying method is not to supply the solder paste in the form of a solder paste but to connect terminals and wirings of the electronic component. Solder is supplied in advance to at least one of the electrodes on the circuit board by a method such as solder plating or solder ball welding, and at the time of connection, an organic material is applied to the board to position electronic components and temporarily fix them. Then, the solder is heated and melted, and the joining is completed with the surface of the connection portion covered with the organic material.

In a more preferable method of manufacturing an electronic circuit of the present invention, when the electronic component is positioned on the substrate,
That is, the organic material is applied independently to each adjacent connecting portion so that the organic material is not continuous. In order to realize such a coating state, the organic layer is formed to have a thickness of 2/3 or less of the height h of the solder previously supplied to at least one of the connection terminal of the electronic component and the electrode on the printed circuit board. Supply materials. Thereby, the coating film of the organic material can be formed independently for each connection terminal and in a non-continuous state. It should be noted that the meaning that the organic material is applied so as to be independent for each adjacent connecting portion and not continuous is not limited to the state in which the organic material is completely applied independently for each connecting portion, and the electrode of the substrate or Even if a thin film is formed at the root of the connection terminal of the electronic component and it is partially continuous, the main part of each adjacent connection does not have a continuous layered structure, but is applied in a state of being separated and independent from each other. The case where it has been included is also included.

The atmosphere in which the solder is heated and melted to connect the solder may be air, but preferably He or A, for example.
An inert gas atmosphere of r, N ₂ or the like is desirable.

Now, practical solder materials and organic materials used in the electronic circuit manufacturing method of the present invention will be described. First, as the solder material, various well-known materials can be used without particular limitation, and practically used solder materials include, for example, Sn and Pb, Sn and Ag, Sn and In, Sn and Bi, Au and Sn, Au and G
Examples thereof include a solder alloy composed of e and a mixture thereof.

The organic material is, for example, a hydrocarbon type, ketones, esters, aldehydes, alcohols, etc., if the boiling point is higher than the melting point (liquidus temperature) of the solder material used. Good. Above all, it is desirable to use alcohols which have an action of reducing and removing the surface oxides of the solder and the member to be connected, and the solder connection can be most preferably performed. Table 1 shows some examples of alcohols as typical examples of these organic materials. The effectiveness of each of these alcohols was confirmed in the examples described below.

[0013]

[Table 1]

As described above, in carrying out the present invention, the combination of the solder material and the organic material is appropriately selected, and the melting point (liquidus line) of the solder material is selected from the organic materials having various boiling points. An organic material having a temperature higher than that may be used.

[0015]

Operation: Solder is supplied in advance to at least one of the connection terminal of the electronic component and the electrode on the printed circuit board, and at the time of connection, the organic material is applied to the substrate to position the electronic component and temporarily fix the solder. By heating and melting and completing the joining in the state where the surface of the connection part is covered with the organic material, the solder supply accuracy is remarkably improved and the pitch of the connection terminals is QFP as compared with the case where the solder paste is used. 0.3 mm or less for such external lead terminals, and 1 m for leadless connection terminals such as flip chips.
Indispensable technology can be provided for high-density mounting of m or less.

In the organic material supplied to the connecting portion, there are bubbles contained due to entrainment during the positioning of the component, and the bubbles become nuclei of evaporation during heating, and bumping occurs at a temperature below the melting point of the solder. May cause misalignment.

Therefore, when a more preferable electronic component is positioned on the substrate, the organic material is applied independently to each adjacent connecting portion so as not to be continuous so that the generation of the air bubbles is reduced. It is possible to secure a diffusion path for the organic material that has evaporated below the melting point of the solder and before the completion of connection, thereby preventing bumping and further suppressing misalignment.

That is, when the organic material is continuously supplied between the connection terminals, the pitch is 0.15 mm for the external lead terminals such as QFP, and the leadless connection terminals such as the flip chip. In this case, joining up to about 0.5 mm can be realized, and even more preferable joining can be realized even if the connection terminals are not independent and continuous with each other at a narrow pitch.

In the method of manufacturing an electronic circuit of the present invention, the role of the organic material at the time of soldering is mainly as follows.
It can be classified into two. (1) Temporary fixing to withstand in-process vibration until reflow connection after components are mounted on the board. (2) Oxidation of solder and connected parts due to heating in the reflow process for ensuring wetness. (3) Oxide removal for shortening self-alignment and increasing process margin (oxygen concentration in reflow atmosphere, solder, oxide film thickness on surface of connecting material, etc.).

The organic material which fulfills the above (1) and (2) is not limited to the alcohol-based material as described above, and the selection range is wide, such as hydrocarbon-based, ketones, ester-based materials, Other types of organic materials such as aldehydes can be used. Further, as the organic material satisfying the role of (3), it is preferable to use an alcoholic organic material having at least one hydroxyl group (OH group). Typical examples thereof are shown in Table 1 above. As shown in.

In the present invention, an appropriate material is selected from the organic materials having various boiling points according to the melting point of the solder and the kind of atmosphere, and one example thereof is a hydroxyl group (OH A reaction state at the time of solder joining in the case of using an alcohol-based organic material having a base) will be described according to the following equations (1) to (3).

First, as shown in the formula (1), an organic material (R-OH) having a hydroxyl group reacts with a metal oxide (denoted as MO) to reduce the oxide to precipitate a metal M. , To an aldehyde (R′-CHO) having a lower boiling point. Furthermore, a part of it is expressed by the equation (2) as follows.
It reacts with the metal oxide (MO) and is reduced, and the metal M is precipitated again, and at the same time, it is converted into an organic acid (R ″ —COOH). Since this organic acid has a higher boiling point than the original organic material, it may remain as a residue as it is. However, this organic acid evaporates so that no residue remains by decarbonating and lowering the boiling point as shown in formula (3).

[0023]

Embedded image R—OH + MO → R′—CHO + M + H ₂ O (1)

[0024]

Embedded image R-CHO + MO → R ″ -COOH + M + H ₂ O (2)

[0025]

Embedded image R ″ -COOH → R ″ -H + CO ₂ (3)

[0026]

EXAMPLES Here, as a specific example, the mounting of electronic components on a ceramic substrate using Sn3Ag solder will be described. The melting point of Sn3Ag solder is 222 ° C,
As the organic material, it is necessary to have a boiling point equal to or higher than this melting point, and it is more preferable to select a material having an appropriate boiling point in consideration of the difference in the evaporation rate of the organic material depending on the heating atmosphere. . Specifically, in He,
As a result of examination that it is necessary to use an organic material having a boiling point of 20 to 30 ° C. higher in order to maintain the same state of the organic material at the same temperature because the evaporation rate is higher than that in Ar and N _2. Revealed.

The example shown here is, C4 (C ontrolled C ollapse C hip C onnection Abbreviation) using a fine solder bumps
In this example, the solder is wet and spread on the metallization on the substrate, and the surface tension of the molten solder causes sphere formation and self-alignment. It is preferable that the series of connection processes be performed in the shortest possible time. This is because it is effective in improving productivity by shortening the takt time and improving the number of repairs by reducing the diffusion amount of solder and metallization.

An embodiment of the present invention will be described in detail below with reference to FIGS. 1 and 2. <Embodiment 1> FIG. 1 is a manufacturing process diagram of an electronic circuit in which a semiconductor integrated circuit (LSI chip) is mounted as an electronic component on a ceramic substrate. FIG. 1A shows an example of the reflow temperature profile. Usually, the peak temperature of reflow is set higher than the melting point (liquidus temperature) of the solder by about 20 to 30 ° C. in order to surely melt the solder. The melting point of Sn3Ag solder is 222 ° C, and in this case, the peak temperature is set to 250 ° C. The time during which the solder is melted, that is, the time during which it is held at the melting point or higher is generally about 1 to 2 minutes. This profile is not limited to the conditions shown here, and may be adjusted so as to be uniformly heated depending on the heat capacity of the sample to be connected.

In the sectional process diagrams shown in FIGS. 1B to 1E, when reflowing in an Ar or N ₂ atmosphere, 2-phenoxyethanol (boiling point 245) is used as an organic material.
(° C.), and when reflowing in a He atmosphere, triethylene glycol (boiling point 285 ° C.) is suitable, and these were carried out.

A detailed description will be given below according to the order of manufacturing steps shown in the drawings. First, as shown in FIG. 1B, the liquid organic material 4 is supplied onto the ceramic substrate 1 having the connection pattern 2 formed on the surface thereof. Next, as shown in FIG. 1C, the electronic component 5 to which the solder material 3 has been previously supplied is mounted on the connection pattern 2 of the ceramic substrate 1 to which the organic material 4 has been supplied. As a result, the electronic component 5 is temporarily fixed on the ceramic substrate 1 due to the viscosity and surface tension of the organic material 4, and it is possible to prevent the displacement of the electronic component 5 due to the vibration during transportation until the reflow connection.

After that, heating is performed with a reflow profile as shown in FIG. Until the solder 3 is melted and the connection is completed, as shown in FIG.
The connection part is covered with. As a result, the oxidation of the solder is prevented, and since the alcohols are used in the present embodiment, the oxide on the solder surface is removed, the solder material 3 wets the connection pattern 2 well, and the self-alignment is short. A good connection can be obtained in time.

After the connection is completed, as shown in FIG. 1E, the organic material 4 is completely evaporated during the cooling process. As a result, it was possible to obtain a clean joint portion without residues, and it was possible to eliminate the need for cleaning in a later step. Although not shown here, the organic material 4 can be more positively evaporated by lowering the atmospheric pressure (vacuum drawing or the like) after the connection is completed.

<Embodiment 2> Next, FIG. 2 is a cross-sectional process diagram showing an example of a method of supplying an organic material to each connection terminal independently and not continuously in the method of manufacturing an electronic circuit of the present invention. is there. In this embodiment, the amount of the organic material 4 supplied to the connecting portion is smaller than that in the case of FIG. 1 shown in the first embodiment. Therefore, in order to surely cover the connecting portion until the solder connection is completed, However, it is necessary to use an organic material having a high boiling point. When reflowing in Ar or N ₂ atmosphere, triethylene glycol (boiling point 285 ° C.) or tetraethylene glycol (boiling point 314 ° C.), when reflowing in He atmosphere, tetraethylene glycol (boiling point 314 ° C.) or penta Ethylene glycol (boiling point 370 ° C.) is preferred.

Hereinafter, detailed description will be given in sequence with reference to the manufacturing process chart shown in FIG. First, as shown in FIG. 2A, the liquid organic material 4 is thinly supplied onto the ceramic substrate 1 as compared with the above embodiment. At this time, the thickness of the organic material 4 is set to 2/3 or less of the height of the solder material 3 previously supplied to the electronic component 5.

As a result, as shown in FIG. 2B, when the electronic component 5 is mounted on the connection pattern 2 of the ceramic substrate 1, the organic material 4 is wetted and the surface tension acts on each connection terminal. Can be independent and not continuous.

As shown in FIG. 2C, thereafter, heating is performed with the same reflow profile as that of the first embodiment shown in FIG. 1A. The connection portion is covered with the organic material 4 until the solder 3 is melted and the connection is completed. As a result, oxidation of the solder 3 is prevented, and since alcohols are used as the organic material 4 in this embodiment, oxides on the solder surface are removed and the solder material 3 wets the connection pattern 2 well. Also, self-alignment occurs in a short time and a good connection can be obtained.

After the connection is completed, as shown in FIG. 2D, the organic material 4 is completely evaporated during the cooling process. As a result, it is possible to obtain a clean joint portion free of residues, and it is possible to eliminate the need for cleaning in a later step. In this case as well, although not shown here, the organic material can be positively evaporated by lowering the atmospheric pressure (vacuum drawing or the like) after the connection is completed.

Example 3 This example describes an example in which an organic material that is solid at room temperature is used. By selecting an organic material that is solid at room temperature, the temporary fixing force of electronic parts to the board is stronger, and the process is more reliable against in-process vibration from the step of positioning the parts on the board to the solder reflow. Is obtained. Among the examples of organic materials shown in Table 1, 3-phenoxy-1,2-propanediol (melting point: 55 ° C.) can be mentioned. Since it is a solid at room temperature, in the organic material supplying step corresponding to the step of FIG. 1B of Example 1 and the step of FIG. 2A of Example 2,
By heating the substrate 1 and the organic material 4 to a temperature equal to or higher than the melting point of the organic material, the organic material that is liquid at room temperature can be supplied in the same manner.

Subsequently, the electronic component 5 is positioned with the substrate 1 heated and the organic material liquefied. After that, when cooled to room temperature, the organic material 4 is solidified and the electronic component 5 is fixed on the substrate 1.

In the solder reflow process, a good connection can be obtained as in the reflow process of each of the above embodiments.
That is, the organic material used here, 3-phenoxy-
Since the boiling point of 1,2-propanediol is 315 ° C, the melting point of Sn3Ag solder is certainly higher than 222 ° C, so that the solder connection is performed in a state where the organic material is liquefied and the connection part is sufficiently covered. .

After completion of the solder connection, the organic material is maintained at a temperature lower than the heating temperature at the time of connection and higher than the melting point of the organic material in the cooling step in the cooling step, so that the organic material is subjected to the cooling step after the connection in the same manner as in each of the above embodiments. In the meantime, it is completely evaporated and removed.

[0042]

As described above in detail, according to the present invention, the intended purpose can be achieved. In other words, for the connection of high-density mounting components with a narrow pitch, which is not possible with solder connection using a solder paste without using flux, there is no misalignment of the parts and there is no residue after reflow for a highly reliable connection. It has been possible to realize a method of manufacturing an electronic circuit that enables it.

[Brief description of drawings]

FIG. 1 is a manufacturing process diagram for mounting an electronic component on a ceramic substrate and soldering it to explain an embodiment of the present invention.

FIG. 2 is a manufacturing process drawing which is also another embodiment.

[Explanation of symbols]

1 ... Ceramic substrate, 2 ... Connection pattern, 3 ... Solder material, 4
… Organic materials, 5… Electronic parts.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Yuko Takehara Inventor Yuko Takehara 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa Inside the Hitachi, Ltd. Institute of Industrial Science (72) Inventor Yasuhiro Iwata 1-Horiyamashita, Hadano, Kanagawa Co., Ltd. (72) Inventor, Mitsunori Tamura, 1 Horiyamashita, Hadano City, Kanagawa Prefecture (72) In-house, General Computer Division, Hiritsu Manufacturing Co., Ltd. (72) Masahito Ijuin, 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa Production Engineering Research Laboratory, Hitachi, Ltd.

Claims (10)

[Claims] 1. A step of supplying solder to at least one of a connection pattern of a circuit board and a connection terminal of an electronic component in advance, and a step of mounting the electronic component on the circuit board without using flux and connecting the both. A method of manufacturing an electronic circuit having a step of solder-connecting a part, wherein the step of solder-connecting a state in which an electronic material having a boiling point higher than the melting point of the solder is applied to the circuit board to position the electronic component A method of manufacturing an electronic circuit, which comprises a step of temporarily fixing the circuit board and a step of heating and soldering while at least the surface of the connecting portion of the positioned circuit board and the electronic component is covered with an organic material. 2. A step of previously supplying solder to at least one of a connection pattern of a circuit board and a connection terminal of an electronic component, and a step of mounting the electronic component on the circuit substrate without using flux to connect the both. A method of manufacturing an electronic circuit having a step of solder-connecting a part, wherein the step of solder-connecting a state in which an electronic material having a boiling point higher than the melting point of the solder is applied to the circuit board to position the electronic component With the step of temporarily fixing with, the organic materials coated on the surface of the connection part of each of the positioned circuit board and electronic parts are
A method of manufacturing an electronic circuit, which comprises a step of heating and soldering in a state in which they are not continuous and are covered independently of each other in a predetermined space. 3. The method of manufacturing an electronic circuit according to claim 1, wherein the organic material is composed of an organic material which is solid at room temperature. 4. The method of manufacturing an electronic circuit according to claim 1, wherein the organic material is composed of an organic material which is liquid at room temperature. 5. The organic material is composed of an organic material having at least one hydroxyl group in the molecule.
Alternatively, the method for manufacturing the electronic circuit according to the item 2. 6. After the connection is completed in the step of heating and connecting the solder, in the heating step, cooling is performed in a temperature range below the melting point of the solder and above the melting point of the organic material, and no residue of the organic material remains. 3. The method for manufacturing an electronic circuit according to claim 1, further comprising the step of evaporating and removing. 7. The method of manufacturing an electronic circuit according to claim 1, wherein an atmosphere of the heating and soldering step is an inert gas atmosphere. 8. The method of manufacturing an electronic circuit according to claim 7, wherein the inert gas atmosphere is a He gas atmosphere. 9. The method of manufacturing an electronic circuit according to claim 7, wherein the inert gas atmosphere is an N ₂ gas atmosphere. 10. The method of manufacturing an electronic circuit according to claim 7, wherein the inert gas atmosphere is an Ar gas atmosphere.