JP2000138448A - Electronic part mounting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably solder electronic parts on a film substrate. SOLUTION: A step where a cream solder is applied at a specified point on a land formed on the part mounting surface of a film substrate 1, a step where electronic parts 3 is so provided as to contact the cream solder applied on the film substrate 1, a process where the film substrate 1 is fixed to a stage 2, and a step where the film substrate 1 is heated by a heat source 4 so provided as to face the part mounting surface of the film substrate 1 so that the cream solder is melted and solidified to mount the electronic parts 3 on the film substrate 1, are provided. Here, before the substrate 1 is heated, a shield mask 5 comprising an opening 5a at a place corresponding to the place of the film substrate 1 for soldering is provided between the film substrate 1 and the heat source 4, so that a part of the film substrate 1 which is weak to heat is shielded and protected from the heat source using a shield mask 5 while a soldering part is concentrically heated.

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 soldering electronic components to a film substrate.

[0002]

2. Description of the Related Art In recent years, a film substrate made of polyimide or the like has become indispensable as a substrate for an electronic circuit in order to satisfy demands for miniaturization and weight reduction of portable electronic devices such as a portable telephone. . Conventionally, since a film substrate is thin and easily curls (warp), when mounting an electronic component on the film substrate, its peripheral portion is sandwiched by a holder and its plane is kept flat on a stage. So it was fixed.

[0003] As a method of mounting an electronic component on a film substrate, conventionally, a cream solder is applied on a land of a substrate, and the electronic component is arranged so as to be in contact with the land. In general, a method of fixing an electronic component by using a conventional method is used.

However, mounting electronic components on a film substrate has the following problems. If it is attempted to simultaneously heat all of the electronic components by heating the entire film substrate on which a plurality of various electronic components are mixed, it is difficult to uniformly heat the entire substrate because the electronic components have different heat capacities. Therefore, it is necessary to heat the film substrate under conditions that are the most difficult to solder, that is, the portion having the largest heat capacity. As a result, the other portions are excessively heated. Excessive heating causes destruction of electronic components such as ICs having a low heat-resistant temperature. This tendency is particularly remarkable when a film substrate that is thin and easily radiates heat to the outside is used as compared with a ceramic substrate or a copper-clad laminate used for an ordinary circuit board. Another problem is that the film substrate is easily deformed by heat.

In order to solve this problem, there has been proposed a method of locally heating only portions of the film substrate having the same maximum heating temperature to perform soldering. However, even with this method, it is difficult to perform uniform heating because the degree of heat radiation from the film substrate to the stage varies depending on the portion of the film substrate. Heat each part sufficiently,
To ensure that all soldering is successful,
It is necessary to increase the amount of heat to be applied to a portion where the degree of heat radiation is large, but it is also necessary to prevent deformation of the film substrate due to heating.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide a method of mounting an electronic component which can stably solder the electronic component on a film substrate. .

[0007]

According to the electronic component mounting method of the present invention, the other portions are protected by a shielding mask so that only the portion of the film substrate to be soldered is exposed to radiant heat rays. The part is intensively heated to mount the electronic component.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An electronic component mounting method according to the present invention comprises the steps of: applying a cream solder to a predetermined location on a land formed on a component mounting surface of a film substrate; Arranging the electronic component so as to be in contact with the substrate, fixing the film substrate on the stage, and heating the film substrate by a heat source arranged opposite to the component mounting surface of the film substrate to melt the cream solder And then solidifying and mounting the electronic components on the film substrate, prior to heating the film substrate, a film-forming shielding mask having an opening at a location corresponding to the portion to be soldered on the film substrate, It is arranged between the substrate and the heat source. In this manner, by shielding the heat-sensitive portion of the film substrate from the heat source with the shielding mask and protecting it, only the soldered portion can be heated intensively.

[0009] When soldering is repeatedly performed at regular intervals using the same shielding mask by thermal radiation, the heat capacity of the shielding mask affects the soldering. That is, in a shielding mask having a large heat capacity, as the soldering is repeated, the substrate temperature at the time of heating is increased by preheating, so that even if the heating is performed under the same conditions, the temperature of the soldered portion may be increased. Therefore, in a preferred embodiment of the present invention,
A shielding mask made of a material having low specific heat and high thermal conductivity, such as copper, brass, and aluminum, is used. Thereby, even if soldering is repeatedly performed, a rise in the temperature of the shielding mask can be suppressed, so that a rise in the temperature of the soldered portion can be suppressed. Also, by making the shielding mask thinner,
The heat capacity can be reduced. In another preferred embodiment of the present invention, the thickness of the shielding mask is 2 mm or less. Accordingly, it is also possible to suppress the variation in the temperature distribution in the soldering portion caused by the heat ray reflected on the wall surface of the opening of the shielding mask.

[0010] In still another preferred embodiment of the present invention, the shielding mask has a reflective film on its surface for reflecting heat rays from a heat source. When the surface of the shielding mask is covered with a material having a high reflectance in the wavelength region of the light source to be used, a rise in the temperature of the shielding mask can be effectively suppressed, and a rise in the temperature of the soldered portion can be suppressed. The reflection film is made of, for example, gold. The reflection film is formed by, for example, plating that can stably form a film having a uniform thickness. Further, a physical vapor deposition method or a chemical vapor deposition method may be used. In any of these methods, in order to form a reflective film uniformly on the surface without exposing the base material to the surface, the thickness of the reflective film to be formed is set to 0.1.
The thickness is preferably 1 μm or more.

In still another preferred aspect of the present invention, the shielding mask has a substrate pressing portion protruding toward the film substrate at or near the periphery of the opening. By providing a substrate pressing part protruding toward the substrate at or near the periphery of the opening of the shielding mask and pressing around the soldered part of the film substrate when heating the substrate, deformation of the film substrate due to heating can be suppressed Can be. If the substrate holding portion is provided in the form of a wall around the opening of the shielding mask, even if the film substrate is rapidly heated, the scattering of the flux to portions other than the soldering portion can be suppressed. Further, since the adhesion between the film substrate and the stage for fixing the substrate can be improved, it is possible to prevent the flux from penetrating into the substrate from the end of the substrate and contaminating the substrate.

In still another preferred embodiment of the present invention, the film substrate is heated after covering the through hole formed in the film substrate and the land formed in the opening thereof with a shielding mask. When the electronic component is soldered by rapidly heating the film substrate, the flux in the cream solder may scatter and enter the through-hole, thereby contaminating the back surface of the substrate and the stage for fixing the substrate. Therefore, a shielding mask is provided so as to cover the through hole and the land formed in the opening. Thereby, it is possible to prevent the back surface of the substrate and the stage from being contaminated and the substrate from being hardly detached from the stage after soldering. The present invention is not limited to a film substrate, but is also useful for mounting an electronic component on another circuit substrate such as a ceramic substrate or a copper-clad laminate.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in more detail.

Embodiment 1 FIG. 1 shows a state when electronic components are mounted in this embodiment. The shielding mask 5 has a side of 60
It is a stainless steel plate having a square shape of 1 mm and a thickness of 1 mm, and has a frame portion 5b with a height of 2 mm at the periphery. On the surface of the shielding mask 5, a rectangular opening 5a having a length of 25 mm and a width of 10 mm is formed. The film substrate 1
It is made of polyimide having a thickness of 50 μm, and a circuit pattern as shown in FIG. 2A is formed on both surfaces thereof by gold plating and etching. On the upper surface of the film substrate 1, a land 1a for mounting an electronic component is formed. As shown in FIG. 2B, a cream solder 6 is applied to the land 1a.
An electronic component 3 such as a chip resistor is provided.

As shown in FIG. 1, the film substrate 1 is arranged on the upper surface of the substrate fixing stage 2, then sucked by the air inlet 2 b, and fixed to the upper surface of the substrate fixing stage 2. The heat source 4 heats the film substrate 1 arranged on the substrate fixing stage 2. The shielding mask 5 covers the electronic component 3b not to be soldered, and is arranged such that the opening 5a is located above the electronic component 3a to be soldered.

A heat ray was radiated toward the film substrate 1 for 15 seconds from the heat source 4 disposed opposite to the light-shielding mask 5 and the temperature profile of the film substrate 1 at that time was measured. The temperature was measured at a position on the film substrate 1 covered by the shielding mask 5 1 cm outside the periphery of the opening of the shielding mask 5. Further, as a comparative example, the film substrate 1 was heated by directly facing the heat source 4 without using the shielding mask 5. At that time, the temperature profile at the same location was measured in the same manner. The result is shown in FIG. As is clear from FIG. 3, by using the shielding mask, heat applied to a portion of the film substrate that does not require heating can be reduced, and thermal deformation of the film substrate can be suppressed.

<< Embodiment 2 >> When soldering is repeatedly performed using the same shielding mask, the temperature of the shielding mask itself becomes high, and it is difficult to obtain the effect. Therefore, in the present embodiment, the material of the shielding mask will be examined. 1mm thick
The shielding mask 5 was produced using the copper plate of Example 1 in the same manner as in Example 1, and soldering was performed in the same manner as in Example 1. Compared to stainless steel used for the material of the shielding mask of Example 1, copper used for the material of the shielding mask of this example has a higher thermal conductivity,
High heat dissipation at high temperatures.

Using the stainless steel shielding mask of Example 1 and the copper shielding mask of this example, soldering for 15 seconds was repeated at a cycle of 20 seconds. FIG. 4A shows the temperature profile of the copper shielding mask 5 of this embodiment at that time. FIG. 4B shows a temperature profile of the shielding mask when the shielding mask used in Example 1 is used.

At this time, the temperature profile of the soldered portion was measured. FIG. 5A shows the result when the shielding mask of the present embodiment is used, and FIG. 5B shows the result when the shielding mask of the first embodiment is used. As is clear from these results, the use of the shielding mask made of copper, which is excellent in heat dissipation, makes the shielding mask 5 and the soldering when repeated soldering is performed, as compared with the case where the shielding mask made of stainless steel is used. The temperature rise of the part is suppressed. That is, by using a shielding mask made of a material having higher thermal conductivity, even in continuous soldering, stable and reliable mounting of electronic components can be performed without increasing the temperature of the soldered portion.

Embodiment 3 In this embodiment, a method for preventing a rise in the temperature of the shielding mask by forming a heat ray reflective film on the surface of the shielding mask will be described. A 0.5 μm-thick gold film was formed on each surface of a copper shielding mask similar to that used in Example 2 by plating. Using the shielding mask having the gold film, soldering was repeatedly performed in the same manner as in Example 2. FIG. 6A shows a temperature profile of the shielding mask 5 at that time. Example 2 for comparison
The temperature profile of the shielding mask 5 is shown in FIG. Note that a near-infrared light source having a wavelength of 0.8 to 2.5 μm was used as the heat source 4. Further, the temperature profile of the soldered portion at this time was measured. The results are shown in FIGS. 7A and 7B, respectively.

As is clear from FIGS. 6 and 7, the use of a shielding mask having a reflective film made of gold on the surface suppresses a rise in the temperature of the shielding mask and a temperature in the soldered portion. This is because the irradiated near infrared rays can be reflected by the reflection film. As described above, by forming the heat-reflective film on the surface of the shielding mask, even if the same shielding mask is repeatedly used for soldering, the soldering temperature does not increase, and stable and reliable soldering can be performed. The same effect was obtained by plating silver on the surface of the shielding mask 5 with high reflectivity in the near-infrared wavelength region (0.8 to 2.5 μm).

Embodiment 4 When the film substrate is locally heated as in the above embodiment, the heated portion is easily deformed by heat. Therefore, in this embodiment, a method for suppressing deformation of the film substrate due to local heating will be described. In this embodiment, as shown in FIG.
A shielding mask 5 made of copper similar to that used in Example 2 and having a cylindrical portion 5c protruding downward at the periphery of the opening 5a.
Was used. The cylindrical portion 5c presses the upper surface of the film substrate 1 downward when placed on the film substrate 1. Thereby, the deformation is suppressed by pressing down the film substrate 1 at the time of heating. When the soldering was actually performed repeatedly using this shielding mask 5 in the same manner as in Example 2, the thermal deformation of the film substrate was smaller than that of the film substrate of Example 2. Further, the contamination due to the suction of the flux was slight. That is, by making the shape of the substrate holding portion cylindrical as in the present embodiment,
When the substrate is heated, an effect of suppressing the flux contained in the cream solder from being scattered to a portion separated by the substrate pressing portion can also be obtained.

Embodiment 5 Not only a film substrate but also many printed wiring boards have circuits formed on both surfaces thereof.
As shown in FIG. 9, a through hole 8 for electrically connecting both surfaces is provided. Since the through hole 8 is a through hole whose wall surface is plated, when an electronic component is mounted on the land near the through hole 8 using cream solder, the flux in the cream solder is scattered. If the scattered flux reaches the back surface of the substrate through the through hole 8, there is a concern that the back surface of the substrate and the stage that fixes the substrate are contaminated, and that the substrate is less likely to come off the substrate fixing stage after soldering. Therefore, when mounting the electronic component on the film substrate 1, as shown by a broken line in FIG. Then, it is possible to prevent the flux in the cream solder from scattering and entering the through hole 8. In an actual circuit design stage, it is desired that no through-hole is provided on the periphery of the land for mounting electronic components.

[0024]

According to the present invention, it is possible to stably mount an electronic component on a film substrate while preventing deformation of the substrate and contamination by flux contained in the cream solder.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a state where an electronic component is soldered on a film substrate in one embodiment of the present invention.

FIGS. 2A and 2B are diagrams showing a state in which electronic components are arranged on the film substrate, wherein FIG. 2A is a plan view and FIG. 2B is a longitudinal sectional view.

FIG. 3 is a graph showing a temperature profile of a film substrate when the substrate is heated.

4A and 4B are graphs showing a temperature profile of a shielding mask used in an example of the present invention when a substrate is heated, wherein FIG. 4A shows a case where a copper shielding mask is used, and FIG. The case where a shielding mask is used is shown.

5A and 5B are graphs showing a temperature profile of a soldered portion when the substrate is heated, wherein FIG. 5A shows a case where a copper shielding mask is used, and FIG. 5B shows a case where a stainless steel shielding mask is used. Are respectively shown.

FIG. 6 is a graph showing a temperature profile when a substrate is heated by a shielding mask used in another embodiment of the present invention,
(A) shows a case where a shielding mask having a heat ray reflecting film is used, and (b) shows a case where a shielding mask having no heat ray reflecting film is used.

7A and 7B are graphs showing a temperature profile of the soldered portion, in which FIG. 7A shows a case where a shielding mask having a heat ray reflecting film is used, and FIG. 7B shows a case where a shielding mask having no heat ray reflecting film is used. Each time is shown.

FIG. 8 is a longitudinal sectional view showing a state where an electronic component is soldered on a film substrate in still another embodiment of the present invention.

FIG. 9 is a plan view of a main part showing a state where a shielding mask is arranged on a film substrate in still another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Film board 1a Land 2 Substrate fixed stage 2a Intake port 3, 3a, 3b Electronic component 4 Heat source 5 Shielding mask 5a Opening 5b Frame 5c Tubular part 6 Cream solder 8 Through hole

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Yoshifumi Kitayama 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. Terms (reference) 5E319 AA03 AC03 BB05 CC33 CD32

Claims (6)

[Claims] A step of applying cream solder to a predetermined location on a land formed on a component mounting surface of the film substrate; a step of arranging an electronic component so as to be in contact with the cream solder; Fixing the electronic component on the film substrate by heating the film substrate with a heat source disposed opposite to the component mounting surface of the film substrate to melt and solidify the cream solder. Prior to heating the film substrate, disposing a shielding mask having an opening at a location corresponding to a location to be soldered on the film substrate between the film substrate and the heat source. Characteristic electronic component mounting method. 2. The electronic component mounting method according to claim 1, wherein said shielding mask is made of a material selected from the group consisting of copper, brass and aluminum. 3. The electronic component mounting method according to claim 1, wherein the thickness of the shielding mask is 2 mm or less. 4. The electronic component mounting method according to claim 1, wherein the shielding mask has a reflection film on a surface thereof for reflecting heat rays from the heat source. 5. The electronic component mounting method according to claim 1, wherein the shielding mask includes a substrate pressing portion protruding toward the film substrate at or near a peripheral portion of the opening. 6. The electronic component mounting method according to claim 1, wherein the shielding mask covers a through hole formed in the film substrate and a land formed in the opening.