JPH07131145A - Soldering method for electronic component - Google Patents

Abstract

PURPOSE:To suppress the damage in solder bumps by a method wherein a substrate loaded with an electronic component is heated at the temperature exceeding the setting point of a thermo-setting resin and then cooled down at the temperature not exceeding the melting point of solder for the reinforcement of solder bumps. CONSTITUTION:The periphery of a circuit pattern 2 is coated with a mixture 10 of a thermosetting resin and a solder activator. Next, an electronic component 3 is shifted on a substrate 1 so as to position solder bumps 4 on the circuit pattern 2. Next, the substrate 1 is put in a reflowing device to be heated. When the solder reaches the melted down temperature, the solder bumps 4 are melted down in liquid state to be junctioned with the circuit pattern 2 leaving the mixture 10 in the pasty state intact. Next, when the temperature reaches the setting point of thermosetting resin, the mixture 10 is set leaving the solder bumps 4 in the liquid state intact to be firmly reinforced. Finally, after reaching the maximum temperature, the substrate 1 is cooled down leaving the solder bumps 4 in solid state to be cooled down at the ordinary temperature later.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for soldering an electronic component having a solder bump.

[0002]

2. Description of the Related Art In recent years, a plurality of solder bumps have been formed as electrodes of electronic parts such as flip caps and ball grid arrays, and the number of electronic parts for joining these solder bumps to a circuit pattern of a substrate has been increasing. FIG. 2 is an enlarged view showing a portion where such an electronic component is joined to a substrate.
In FIG. 2, 1 is a substrate made of glass epoxy or the like, 2 is a circuit pattern such as copper foil formed on the substrate 1, 3 is an electronic component, 4 is an electrode of the electronic component 3, and is provided on the back surface of the electronic component 3. It is a solder bump.

Generally, the substrate 1 and the electronic component 3 are
The coefficient of thermal expansion differs greatly. Therefore, when heat is applied while the solder bumps 4 are bonded to the circuit pattern 2, the electronic component 3 and the substrate 1 expand and contract at greatly different expansion and contraction rates. Further, the electronic component 3 is bonded to the substrate 1 only with the solder bumps 4, and the solder bumps 4 are attached to the substrate 1 and the electronic components 3
Since a large stress acts on the solder bumps 4, the solder bumps 4 are cracked 5 as shown in FIG. 2, and the reliability of the operation of the electronic component 3 may be deteriorated. Therefore, in order to prevent stress from concentrating only on the solder bumps 4, it is desirable to fill the periphery of the solder bumps 4 with a reinforcing agent such as a resin and seal the solder bumps 4.

[0004]

FIG. 3 shows a solder bump 4
FIG. 7 is a process explanatory view showing a conventional soldering method for reinforcing the solder bumps 4 by sealing the periphery of the with a resin 6. First, as shown in FIG. 3A, the flux 7 is applied around the circuit pattern 2. Next, as shown in FIG. 1B, the surface of the electronic component 3 is sucked by the suction nozzle 8 or the like, and the electronic component 3 is transferred onto the substrate 1 so that the solder bumps 4 are placed on the circuit pattern 2. Then, the substrate 1 is fed into, for example, a reflow apparatus and heated to a temperature equal to or higher than the melting temperature of the solder, and the solder bump 4
By melting and then cooling the solder bumps 4
And the circuit pattern 2 are joined. In addition, 9 of FIG.3 (c) is the heater provided in the reflow apparatus. Next, FIG.
As shown in (d), the flux 7 is cleaned and removed using a cleaning agent. However, since the flux 7 is small and surrounded by a large number of solder bumps 4, it is difficult to completely remove it, and it often remains partially. Next, as shown in FIG. 3E, a resin 6 as a reinforcing agent is poured around the solder bumps 4 to be solidified. However, since the solder bumps 4 are close to each other, a large number of the resin 6
Is often blocked by the solder bumps 4 and does not reach the solder bumps 4 near the center. As described above, the conventional soldering method for electronic components has a problem that the solder bumps cannot be sufficiently reinforced.

Therefore, an object of the present invention is to provide a soldering method for an electronic component, which is capable of sufficiently reinforcing the solder bumps and suppressing damage to the solder bumps.

[0006]

The present invention comprises a step of applying a mixture of a thermosetting resin having a curing temperature higher than the melting temperature of solder and a solder activator to a circuit pattern formed on a substrate, A step of mounting electronic components on the substrate so that the solder bumps are located on the circuit pattern, and heating the substrate on which the electronic components are mounted to a temperature higher than the curing temperature of the thermosetting resin,
Then, there is a step of cooling to below the melting temperature of the solder.

[0007]

With the above structure, the thermosetting resin and the solder activator are applied to the circuit pattern in the state where the solder bump is not yet placed on the circuit pattern. That is, when the thermosetting resin is applied, the solder bumps do not interfere with the application and can be applied uniformly. Next, electronic components are mounted and heated. Here, the curing temperature of the thermosetting resin is the melting temperature of the solder (usually 1
83 ° C.), the solder bumps are activated and melted by the solder activator before the thermosetting resin is hardened in the state of the melting temperature or higher and lower than the hardening temperature to become liquid, and thus the solder bumps and the circuit. The patterns are joined. Further, when the temperature rises to the curing temperature or higher, the thermosetting resin around the liquid solder bump is cured and becomes solid, and the solder bump is reinforced by the cured thermosetting resin. Next, the solder bumps are solidified by cooling to below the melting temperature of the solder.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will now be described with reference to the drawings. FIG. 1 is a process explanatory diagram showing a method for soldering an electronic component according to an embodiment of the present invention. The same components as those shown in FIG. Omit it.

In FIG. 1, 10 is a mixture of a thermosetting resin and a solder activator (0.1 to 20% by weight, preferably 5% by weight or less), which is in a paste form at room temperature. As the thermosetting resin, one having a curing temperature higher than the melting temperature (183 ° C.) of solder is used. For example, a bisphenol A type epoxy resin containing isophthalic acid hydrazide (curing temperature of 210 ° C.) and the same epoxy resin containing 2.4-diamino-6- [2-undecylimidazolyl- (1 )]-Ethyl-S-triazine (curing temperature 1
85 ° C.) is suitable.

As the solder activator, one or more organic acids selected from lactic acid, citric acid, oleic acid, stearic acid, glutamic acid, benzoic acid, oxalic acid and abietic acid are preferable. Then, a mixture 10 is prepared by mixing the thermosetting resin and the solder activator.

Then, as shown in FIG. 1A, the mixture 10 is applied around the circuit pattern 2. At this time, since the circuit pattern 2 is exposed to the outside, the mixture 10 can be applied easily and evenly. Next in FIG.
As shown in (b), solder bumps 4 are formed on the circuit pattern 2.
The electronic component 3 is transferred onto the substrate 1 so that

Next, as shown in FIG. 1C, the substrate 1 is put into a reflow apparatus and heated. The maximum temperature in the reflow device is about 230 to 240 ° C. Therefore,
There is a relation of (normal temperature) <(melting temperature of solder) <(curing temperature) <(maximum temperature). Therefore, when the temperature reaches the melting temperature, the solder bumps 4 melt and become liquid, and the solder bumps 4 are bonded to the circuit pattern 2, but the mixture 10 remains in a paste form. Next, when the curing temperature is reached, the mixture 10 existing around the solder bump 4 is cured and the solder bump 4 is strongly reinforced while the solder bump 4 is in a liquid state and bonded to the circuit pattern 2. Then, after the temperature rises to the maximum temperature, the substrate 1 is cooled, the solder bumps 4 are solidified, and then cooled to room temperature. As a result, the bonding of the solder bumps 4 and the circuit pattern 2 and the curing of the mixture 10 as a reinforcing agent are completed by the process of simply passing the substrate 1 through the reflow apparatus (FIG. 1).
(D)).

Here, as is apparent from comparison of FIG. 1 with FIG. 3, in this embodiment, the step of removing the flux shown in FIG. 3D, the injection of the resin 6 shown in FIG. The process and the process corresponding to the curing process of the resin 6 as the next process of FIG. 3E are not necessary, and the number of steps can be significantly reduced.

[0014]

According to the method for soldering an electronic component of the present invention, a mixture of a thermosetting resin having a curing temperature higher than the melting temperature of solder and a solder activator is applied to a circuit pattern formed on a substrate. Process, the process of mounting electronic components on the board so that the solder bumps are located on the circuit pattern, the substrate on which the electronic components are mounted is heated above the curing temperature of the thermosetting resin, and then the melting temperature of the solder Since it has a step of cooling to the following, the thermosetting resin as a reinforcing agent for the solder bumps can be sufficiently filled around the solder bumps without being hindered by the solder bumps, and damage to the solder bumps can be prevented. It can be effectively prevented.

[Brief description of drawings]

FIG. 1A is a process explanatory diagram showing a soldering method of an electronic component according to an embodiment of the present invention. FIG. 1B is a process explanatory diagram showing a soldering method of an electronic component according to an embodiment of the present invention. Process explanatory drawing which shows the soldering method of the electronic component in the Example of this invention. (D) is a process explanatory drawing which shows the soldering method of the electronic component in the Example of this invention.

[Fig. 2] Enlarged view of the area around a conventional solder bump

3A is a process explanatory view showing a conventional electronic component soldering method. FIG. 3B is a process explanatory view showing a conventional electronic component soldering method. FIG. 3C is a conventional electronic component soldering method. (D) is a process explanatory diagram showing a conventional electronic component soldering method. (E) is a process explanatory diagram showing a conventional electronic component soldering method.

[Explanation of symbols]

 1 substrate 2 circuit pattern 3 electronic component 4 solder bump 10 mixture

Claims (1)

[Claims] 1. A step of applying a mixture of a thermosetting resin having a curing temperature higher than a melting temperature of solder and a solder activator to a circuit pattern formed on a substrate, and solder bumps on the circuit pattern. So as to be positioned, a step of mounting electronic components on the substrate, and a step of heating the substrate on which the electronic components are mounted to a temperature equal to or higher than the curing temperature of the thermosetting resin, and then cooling to a temperature equal to or lower than the melting temperature of the solder. A method for soldering an electronic component, comprising: