JP2003101210A - Electronic component mounting method and heat generating material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electronic component mounting method which can surely attain the reliability after the mounting and also to provide a heat generating material which is used for solder junction. SOLUTION: In the electronic component mounting method to mount an electronic component 1 to a substrate 5 by joining with solder a connection electrode 2 of the electronic component 1 to an electrode 5 of the substrate 5, a solder bump 3a is previously formed to the electronic component 1, and the electronic component 1 is mounted to the substrate 5 after an epoxy resin 7 which generates reaction heat with heat treatment is supplied to the range of substrate 5 including the electrode 6 corresponding to the solder bump 3a at the internal side of the electronic component 1. Thereafter, in the heat treatment with reflow, the epoxy region 7 generates heat with the thermosetting reaction to heat the part such as periphery of center area which is not easily heated up to the temperature higher than that raised only with the reflow. Accordingly, the solder can surely be fused to assure the reliability after the mounting of the part joined with the solder 3b.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic component mounting method for mounting an electronic component on a substrate by soldering and a heat generating material used for soldering.

[0002]

2. Description of the Related Art A method by soldering is widely used for mounting electronic parts on a substrate. In this method, a connecting electrode of an electronic component is soldered to an electrode of a board.
From the viewpoint of preventing environmental pollution due to lead in recent years, a lead-free solder that does not contain lead as a component has been used for solder joining, instead of the tin-lead solder that has been conventionally used.

[0003]

However, when this lead-free type solder is used for solder joining of electronic parts,
There was a problem as described below. In general, lead-free solder has a higher melting point than conventional tin-lead eutectic solder, and it is difficult to secure a sufficient temperature difference from the heat resistant temperature of electronic components. Further, the lead-free solder has a characteristic that the melting point becomes high when the composition is such that the bonding reliability is secured, and the reliability after the bonding is lowered when the composition where the melting point is low is selected. Therefore, in the conventional electronic component, if soldering is performed with a low melting point type solder for the purpose of preventing the electronic component from being burnt out during reflow, there is a problem in reliability after mounting.

Therefore, an object of the present invention is to provide an electronic component mounting method capable of ensuring reliability after mounting and a heat generating material used for soldering.

[0005]

According to a first aspect of the present invention, there is provided an electronic component mounting method, wherein a connecting electrode of an electronic component is soldered to an electrode of a substrate to electrically connect the connecting electrode and the electrode of the substrate. An electronic component mounting method for mounting an electronic component on a substrate, comprising: a solder supplying step of supplying solder to the electronic component or the substrate in advance; and a reaction heat generated by heating a predetermined portion of the electronic component or the substrate to which the solder is supplied. Heat generating material supplying step of supplying a heat generating material, a mounting step of mounting the electronic component on a substrate, and a heating step of heating the substrate on which the electronic component is mounted by a heating means. Generates heat, the temperature of the predetermined portion is raised to a temperature higher than the temperature raised by only the heating means.

According to a second aspect of the present invention, there is provided an electronic component mounting method, wherein the heat generating material is an epoxy resin mixed with a curing agent containing an acid anhydride and an amine type curing agent. It also serves as a sealing resin that seals between the component and the substrate.

The heat-generating material according to claim 3 is present between the electronic component and the substrate when the connection electrode of the electronic component is soldered to the electrode of the substrate, and generates heat of reaction by heating during the soldering. It is an exothermic material and is made of an epoxy resin mixed with a curing agent containing an acid anhydride and an amine curing agent, and the content of the amine curing agent is 1.5 to 5% by weight.

According to the present invention, an exothermic material that generates reaction heat by heating is supplied to a predetermined portion of the electronic component or the substrate, and the exothermic material is heated in the heating step of heating the substrate on which the electronic component is mounted by the heating means. As a result of the heat generation, the temperature of a predetermined portion such as the central portion of the electronic component, which is difficult to heat up, can be raised to a temperature higher than the temperature raised by only the heating means, and the melting of the solder is ensured and the solder joint It is possible to secure reliability after mounting.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. 1 and 2 are process explanatory diagrams of an electronic component mounting method according to an embodiment of the present invention, and FIG. 3 is a graph showing a heating temperature in a solder joining process of electronic component mounting according to an embodiment of the present invention.

In FIG. 1A, a plurality of connecting electrodes 2 are formed on an electronic component 1, and these connecting electrodes 2 are formed by a transfer tool 4 as shown in FIG. 1B. The solder balls 3 are mounted. Then, the solder ball 3 is melted by heating the electronic component 1 by reflow,
As shown in FIG. 1C, solder bumps 3 are formed on the connecting electrodes 2.
a is formed. This solder bump forming step is a solder supplying step of supplying solder to the electronic component 1 in advance. Here, the material of the solder ball 3 is a lead-free type solder containing almost no or no lead component, and has a higher melting point than tin / lead-based solder that has been generally used in the past.

Next, the electronic component 1 on which the solder bumps 3a are formed in this manner is mounted on the substrate 5 on which the electrodes 6 are provided. Prior to mounting the electronic component 1 on the substrate 5, FIG.
As shown in (a), the epoxy resin 7 is applied by a dispenser 8 to a predetermined portion of the joint surface of the substrate 5 with the electronic component 1.
Is supplied. In the present embodiment, the electronic component 1 of the substrate 5
The epoxy resin 7 is supplied to the central portion of the substrate 5 including the electrodes 6 corresponding to the solder bumps 3 a located inside the electronic component 1 among the bonding surfaces of the epoxy resin 7. The epoxy resin 7 used here is a mixture of an acid anhydride and an amine-based curing agent as a curing agent in the main component of the epoxy resin, and the epoxy resin 7 is heated by the surroundings to cause the curing reaction to proceed.
It is a heat generating material that itself generates heat. In particular, by mixing an amine-based curing agent, the heat of reaction generated during curing is increased to enhance the temperature raising effect. As the amine curing agent, imidazole, amine adduct, aromatic amine, aliphatic amine and the like can be used.

Next, the electronic component 1 is mounted on the substrate 5. As shown in FIG. 2B, the solder bumps 3 a are aligned with the electrodes 6, and the electronic component 1 is mounted on the substrate 5 to which the epoxy resin 7 has been supplied. After that, the substrate 5 is sent to a reflow furnace and heated to a predetermined temperature. As a result, FIG. 2 (c)
As shown in FIG. 3, the solder bump 3a is melted to form a solder joint 3b for joining the connecting electrode 2 and the electrode 6, and the electronic component 1 is mounted on the substrate 5 by solder joining.

The heating temperature in the solder joining process by this reflow will be described with reference to FIG. Figure 3
It shows the temperature distribution in the horizontal direction of the solder joint portion 3b in the solder joint process. The temperature distribution shown by the thick line in FIG. 3A is the temperature distribution of the solder joint portion under the condition that the epoxy resin 7 is not supplied onto the substrate 5, that is, the temperature distribution from the periphery of the electronic component 1 by being heated in the reflow furnace. It shows the heating temperature reached by the solder joint only by the supplied heat.

In the heating by the reflow furnace, the melting point T1 of the material of the solder bump 3a and the heat resistant temperature T2 of the electronic component 1 are set.
The heating temperature is set with the solder joint temperature TS corresponding to the above as a target. At this time, when the electronic component 1 is heated from the surroundings by the high temperature atmosphere in the reflow furnace, there is a time delay in the heat transfer from the outer side to the inner side of the electronic component 1. As shown in FIG. 5, the temperature difference ΔT1 is partially present in the inner portion A of the electronic component 1 from the solder joint temperature TS.
Only low temperature part is generated. In this low temperature portion, the temperature of the solder joint portion does not easily exceed the melting point T1, so that soldering failure is likely to occur. Therefore, if the heating temperature of the reflow furnace is increased to TS ', the temperature of the electronic component 1 itself will exceed the heat resistant temperature T2 (FIG. 3).
(Refer to the temperature distribution indicated by the wavy line in (a)).

FIG. 3 (b) shows the distribution of the temperature rise ΔT due to the epoxy resin 7 supplied on the substrate 5 generating heat by a thermosetting reaction during heating in the reflow furnace. Since the epoxy resin 7 is supplied only to the predetermined portion corresponding to the inner portion of the electronic component 1 on the substrate 5,
The temperature rise range due to the heat generation of the epoxy resin 7 in the reflow furnace is limited to the inner part of the electronic component 1, and the temperature rises by the maximum temperature TA in this range.

FIG. 3 (c) shows the temperature distribution realized in the solder joining process shown in FIG. 2 (c). That is, in the solder joining step of the electronic component mounting method shown in the present embodiment, the temperature rise due to the heating atmosphere in the reflow furnace and the temperature rise due to the epoxy resin 7 being thermoset to generate heat are superposed. The temperature rises in shape.

At this time, by setting the condition that the temperature difference ΔT1 caused by the heat transfer delay is canceled by the maximum temperature TA of the temperature rise due to heat generation, as shown in FIG. A substantially uniform temperature rise is realized over the entire range of. Such condition setting is obtained by experimentally measuring the temperature difference ΔT1 and TA corresponding to this ΔT1 is obtained.
It is possible to experimentally determine the supply amount of the epoxy resin 7 and the mixing ratio of the curing agent of the epoxy resin 7 for realizing the above.

Generally, the lead-free solder has a characteristic that the lower the melting point temperature of the composition, the lower the reliability after bonding. Therefore, in order to secure the required bonding reliability, the high melting point type solder is used. It is necessary to select the composition. However, the melting point temperature of such high melting point type solder is close to the heat resistant temperature of the electronic component, and it is difficult to set the heating temperature in the reflow process so as to secure a sufficient margin on the safe side with respect to the heat resistant temperature.

That is, if the reflow temperature is set so as to surely melt all the solder bumps including the solder bumps of the inner portion where the heat transfer state is poor during reflow, the electronic parts may be damaged by heat. On the other hand, if the temperature is set to a low temperature without heat damage, the solder bumps in the inner portion are not melted well, and as a result, defective bonding is likely to occur.

However, in the present embodiment, since the epoxy resin 7 as the heat generating material is previously supplied to the inner portion where the heat transfer state during reflow is poor, insufficient heating due to the heating atmosphere in the reflow furnace. Can be compensated by the heat generated by the epoxy resin 7. Therefore, even when using a lead-free type solder, which has a narrow width of the proper solder melting point range and is difficult to uniformly solder-bond to all the solder bumps of the electronic component, the solder bumps 3a located in the inner portion are surely melted. As a result, the connecting electrode 2 of the electronic component 1 can be satisfactorily conducted to the substrate 5, and good bonding reliability can be ensured.

In order to confirm the effect of the temperature raising action, the present inventors conducted an experiment using a plurality of exothermic materials having different contents of imidazole which is an amine-based curing agent. The electronic components used in the experiment are BGA (Ball Grid Arr).
ay) 500 bumps (full grid), the reflow condition was 210 ° C., 10 seconds or more, and the electronic component was solder-bonded to the substrate by the procedure described above. A compounding example of the exothermic material and an experimental result are shown in (Table 1).

[0022]

[Table 1]

Since the heat-generating material A had an insufficient temperature raising effect due to heat generation, the proportion of all electronic components which were not bump-bonded was 5%. The heat generating materials B and C have a solder joint ratio of 10
While 0% gave a good result, the heat-generating material C had no bump-bonded electronic components at all. This is because as the content of the amine-based curing agent increases, the heating effect due to heat generation increases, while the curing speed increases and the heat-generating material cures before the molten solder (bumps) spreads over the substrate electrodes. This has hindered solder joining. Therefore, the content of the amine curing agent is preferably 1.5 to 5% by weight.

In the above embodiment, the solder is supplied by forming the solder bump 3a on the electronic component. However, a solder supplying method other than the solder bump formation may be used. Instead of supplying solder,
The solder may be supplied onto the electrodes 6 of the substrate 5 by a printing method or a solder precoating method.

Further, in the above embodiment, the predetermined portion of the substrate 5 for supplying the epoxy resin 7 as the heat generating material is
Although the range corresponding to the inner part of the electronic component 1 is set and the insufficient heating of this part is compensated by the heat generation of the epoxy resin 7, the heat generating material may be supplied to other parts. For example, in the electronic component mounting in which leads protruding outward such as QFP are solder-bonded to the electrodes of the substrate, these leads or electrodes to which the leads are bonded are
You may make it apply the epoxy resin 7 as a heat generating material previously.

[0026]

According to the present invention, in a heating step in which a heat generating material that generates reaction heat by heating is supplied to a predetermined portion of an electronic component or a substrate, and the substrate on which the electronic component is mounted is heated by a heating means. When the heat-generating material generates heat, it is possible to raise the temperature of a predetermined portion, such as the central portion of the electronic component, where it is difficult to raise the temperature, to a temperature higher than the temperature raised by only the heating means, and ensure the melting of the solder. It is possible to secure reliability after mounting the joint portion.

[Brief description of drawings]

FIG. 1 is a process explanatory diagram of an electronic component mounting method according to an embodiment of the present invention.

FIG. 2 is a process explanatory diagram of an electronic component mounting method according to an embodiment of the present invention.

FIG. 3 is a graph showing a heating temperature in a solder joining process for mounting an electronic component according to an embodiment of the present invention.

[Explanation of symbols]

1 electronic components 2 electrodes 3 solder balls 3a Solder bump 5 substrates 6 electrodes 7 Epoxy resin

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Ken Maeda             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Seiichi Yoshinaga             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F-term (reference) 5E319 AA03 AC01 CC33 GG03

Claims (3)

[Claims] 1. An electronic component mounting method for mounting an electronic component on a substrate by connecting the connecting electrode of the electronic component to an electrode on the substrate by soldering to connect the connecting electrode and the electrode on the substrate. A solder supplying step of supplying solder to the electronic component or the substrate in advance; a heat generating material supplying step of supplying a heat generating material that generates reaction heat by heating to a predetermined portion of the electronic component or the substrate to which the solder has been supplied; Is mounted on the substrate, and a heating process for heating the substrate on which the electronic component is mounted is heated by the heating means. In the heating process, the heat generating material generates heat to raise the predetermined portion only by the heating means. An electronic component mounting method, which comprises raising the temperature to a temperature higher than the temperature. 2. The heat generating material is an epoxy resin mixed with a curing agent containing an acid anhydride and an amine type curing agent, and is thermally cured after the heating step to seal between the electronic component and the substrate. An electronic component mounting method characterized in that it also serves as a sealing resin. 3. A heat-generating material which is present between an electronic component and a substrate when soldering an electrode for connecting an electronic component to an electrode of a substrate, and which generates reaction heat by heating during soldering,
A heat generating material comprising an epoxy resin mixed with a curing agent containing an acid anhydride and an amine curing agent, wherein the content of the amine curing agent is 1.5 to 5% by weight.